C746

C746

Old

waterfrontw

allsCIR

IA9 780860 177517

Old waterfront walls

This guide updates and replaces the original CIRIA publication on old waterfront walls firstpublished in 1992 (B13). A significant amount of the material used in the original publication,particularly with respect to the history and types of old waterfront walls, has been incorporated intothis new guide plus new material gleaned from a number of sources.

The history of the subject spans at least 2000 years, with many significant waterfront structuresbeing constructed during the Roman Empire. Over this period the engineering skills and technologywere lost and only found again in the late 17th and early 18th century. Engineering failure at the'sharp end' of technology was frequently accepted as being a necessary evil in the design anddevelopment of this new infrastructure.

Science and engineering has also moved on since the first edition was published. The new guidenow includes information on risk analysis and performance assessment, the use of GIS and BIM inthe design and construction process, and more detail on the loads imposed by waves. It alsocontains an overview of those waterfront walls that proved so troublesome to construct, but whoselongevity is a measure of man's persistence to succeed.

The guide shows how engineers may, by inspection, observation, and investigation and through theapplication of risk management and modern construction techniques, effectively manage andmaintain the substantial national asset which these waterfront walls represent.

Who we areEstablished in 1960, CIRIA is a highly regarded, industry-responsive, not for profit research and information association, which encompasses the construction and built environment industries.

CIRIA operates across a range of market sectors and disciplines, providing a platform for collaborative projects and dissemination by enhancing industry performance, and sharing knowledge and innovation across the built environment.

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Where we areDiscover how your organisation can benefit from CIRIA’s authoritative and practical guidance – contact us by:

Post Griffin Court, 15 Long Lane, London, EC1A 9PN, UKTelephone +44 (0)20 7549 3300Fax +44 (0)20 7549 3349Email enquiries@ciria.orgWebsite www.ciria.org

(for details of membership, networks, events, collaborative projects and to access CIRIA publications through the bookshop)

zz Core membershipAllows your employees to assist with the development of and access to good practice guidance, formal networks, facilitation, conferences, workshops and training.

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zz Project fundingProject funders influence the direction of the research and gain early access to the results.

zz CEEQUALCIRIA co-manages the sustainability assessment, rating and awards scheme for civil engineering, infrastructure, landscaping and works in public spaces.

zz LACL (Local Authority Contaminated Land Network)LACL helps local authorities address responsibilities under Part IIA of the Environmental Protection Act 1990.

zz EMSAGG (European Marine Sand and Gravel Group)CIRIA provides secretariat support to EMSAGG, including management of the Group’s conferences, workshops and website and producing its newsletter.

zz LANDFoRM (Local Authority Network on Drainage and Flood Risk Management)A platform for sharing knowledge and expertise in flood risk management and sustainable drainage.

zz BRMF (Brownfield Risk Management Forum)Promoting sustainable and good practice in brownfield projects in the UK.

CIRIA C746 London, 2015

Old waterfront wallsStephen Cork and Neil Chamberlain HR Wallingford

Griffin Court, 15 Long Lane, London, EC1A 9PNTel: 020 7549 3300 Fax: 020 7549 3349Email: enquiries@ciria.org Website: www.ciria.org

ii CIRIA, C746

Old waterfront walls

Cork, S, Chamberlain, N

CIRIA

C746 RP997 © CIRIA 2015 ISBN: 978-0-86017-751-7

British Library Cataloguing in Publication Data

A catalogue record is available for this book from the British Library

Keywords

Asset and facilities management, inspections, maintenance, coastal and marine quay walls and breakwaters, river walls, inland waterways, groundwater

Reader interest

Civil, maritime and ground engineering, rivers and canals, coastal and marine, infrastructure asset management

Classification

Availability Unrestricted

Content Advice/guidance

Status Committee guided

Users Owners and managers of old waterfront walls, surveyors, engineers and contractors involved in the inspection, assessment, design and execution of repairs, remedial and refurbishment works

Published by CIRIA, Griffin Court, 15 Long Lane, London, EC1A 9PN

This publication is designed to provide accurate and authoritative information on the subject matter covered. It is sold and/or distributed with the understanding that neither the authors nor the publisher is thereby engaged in rendering a specific legal or any other professional service. While every effort has been made to ensure the accuracy and completeness of the publication, no warranty or fitness is provided or implied, and the authors and publisher shall have neither liability nor responsibility to any person or entity with respect to any loss or damage arising from its use.

All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, including photocopying and recording, without the written permission of the copyright holder, application for which should be addressed to the publisher. Such written permission must also be obtained before any part of this publication is stored in a retrieval system of any nature.

If you would like to reproduce any of the figures, text or technical information from this or any other CIRIA publication for use in other documents or publications, please contact the Publishing Department for more details on copyright terms and charges at: publishing@ciria.org/Tel: 020 7549 3300.

iiiOld waterfront walls, second edition

Summary

This guide is the final report of a CIRIA research project (RP) 997 and updates and replaces the original CIRIA publication on old waterfront walls first published in 1992. A significant amount of the material used in the original publication, particularly with respect to the history and types of old waterfront walls, has been incorporated into this publication.

Old waterfront walls are defined as gravity walls of masonry, concrete blockwork, brickwork or mass concrete with vertical or near vertical exposed faces fronting on to the sea, river, canals, lakes or dock. They can be composed of thin masonry facings to rock or cohesive soil, but exclude revetments, sloping sea defences, dams, sheet piled walls and reinforced concrete structures. Many of these structures will have been constructed in the 17th or 18th century – some even earlier.

This guide contains an overview of how such old waterfront walls were constructed. Many proved troublesome to construct, but their longevity is a measure of man’s persistence to succeed. It goes on to guide how to effectively manage and maintain the substantial national asset that these waterfront walls represent by:

ªª inspection, observation, and investigation

ªª understanding the loads and processes acting on the wall

ªª the application of risk management and modern construction techniques.

Numerous case studies and examples of maintenance and repairs are given within the text.

Information for this research project was obtained from the research undertaken for the original publication incorporating new material gleaned from a variety of sources. This includes a literature review, a review of detailed engineering drawings and reports held in the archives of the Institution of Civil Engineers (ICE). Also, responses received from a questionnaire to engineers and organisations responsible for the maintenance of old waterfront walls, discussions with engineers and contractors involved in the assessment and repair of waterfront walls, and a well-informed and encouraging steering group.

iv CIRIA, C746

vOld waterfront walls, second edition

Foreword

For hundreds of years engineers and artisans have been constructing structures including waterfront walls. These gravity masonry and mass concrete structures feature in many of our finest harbours, canals and sea defences. They also form part of river walls, bridge abutments and piers. They contribute to the character of our waterfront infrastructure, many are usually aesthetically pleasing, and are also essential components of vitally important structures.

Old waterfront walls are frequently ignored and neglected, being seen as unnecessary liabilities rather than highly valuable assets. Identification of ownership and responsibility can be problematic. Some are orphan structures, whose ownership has become blurred over the passage of time. Some are maintained or rehabilitated only when showing signs of severe stress or being considered for a new use. A few get the attention they deserve when they fail, often in catastrophic circumstances. However, these walls are nearly always somebody’s responsibility and to neglect them is neither cost-effective, nor likely to reduce the risk or consequences of their failure.

Many of these old structures are difficult to analyse in a structural sense, often being complex in form and problematic to investigate, with little or no historic data on the design and form of construction. They may perform a number of unrelated functions, any one of which might be described as integral to the well-being or safety of the local community. As such, they are often considerably more valuable than might appear at first sight. But past experience has shown that, in spite of this, they can often end up on the “too difficult, not worth bothering about” heap.

Ignore an old waterfront wall at your peril. Regular inspection and maintenance is a minimum that an owner or responsible organisation should do to fulfil its obligations to health and safety, and its liability to specific risks. Even better would be a comprehensive study of the wall’s features, functions and engineering characteristics. It may be surprising how valuable this old structure is, how sensitive it is to changes in loading, and how essential its maintenance is to the local economy and environment.

Just because it has stood for centuries, do not assume that a wall will continue to do so. Deterioration of the structure, changes in direct and environmental loads, effects of undermining and subsidence may all contribute to instability and possible failure. This guide shows how to assess and evaluate such a structure, determine whether it needs attention, identifies possible remedial solutions and how, by engaging with the local community and exploring the right sources, funds may be found for this valuable infrastructure to be maintained in the future for the benefit of all.

When Ben Tatham and I wrote the original old waterfront walls guidance, published in 1992, we were fascinated by the variety of structures involved. We also discovered how little was known about their forms and functions, how to investigate them and how to analyse their behaviour. Asset management of such structures was in its infancy. Over 20 years later, attitudes to management have moved on, risk and responsibility play a greater role in evaluation, and the value of these walls is becoming better understood.

This new guide, which contains much of the information gleaned in the original document, now focuses more on the management of these assets. It emphasises the role that risk plays in this process, the influence of legislation, and the need to ascertain the true value of these old structures to the community as a whole. It also recognises the difficulties in obtaining funding for maintaining these assets.

Science and engineering has also moved on since the first edition was published. The new guide now includes information on risk analysis and performance assessment, the use of GIS and BIM in the design and construction process, and more detail on the loads imposed by waves. Altogether the guide is a worthy successor to the original publication and I recommend its use for the maintenance and rehabilitation of these structures, whether they be mundane or magnificent.

Nick BrayConsulting engineer and co-author CIRIA B13, May 2015

vi CIRIA, C746

Acknowledgements

This guide was prepared by Stephen Cork and Neil Chamberlain of HR Wallingford, under contract to CIRIA, as an update to the original publication CIRIA B13 (Bray and Tatham, 1992). This new guide was prepared with the full support and valuable assistance of the original authors together with supporting contributions from Jim Stirling (formerly of British Waterways), and Professor William Allsop and Michael Wallis, HR Wallingford.

The project was carried out with the guidance and assistance of the CIRIA project steering group (PSG) members.

Authors

Stephen Cork BSc(Eng) ACGI MICE CEngStephen is a technical director at HR Wallingford, UK. Stephen has over 40 years’ experience in the inspection, planning, design and construction of ports and maritime infrastructure projects worldwide. He has been responsible for ports and maritime infrastructure design and development, including the inspection and evaluation of existing infrastructure, design of remedial works and improvements, and the design and construction of new waterfront facilities. He has chaired port and maritime conferences and has authored numerous technical papers on port and maritime infrastructure issues including Construction health and safety in coastal and maritime engineering published by Thomas Telford in 2005.

Neil Chamberlain BEng MSc DIC PhD CEng MICENeil is a principal coastal engineer with Royal HaskoningDHV (formerly with HR Wallingford). Neil has over 20 years’ experience in the planning, inspection, design and construction of maritime and coastal structures worldwide. He has been responsible for the inspection, assessment and design of remedial works and improvements to old waterfront walls. He has also designed and managed the construction of new waterfront wall infrastructure including blockwork quay walls, and concrete seawalls

Project steering groupMr Nick Bray Consulting engineer

Mr Stuart Byrne Atkins Consultants Limited

Mr Robert Dean Network Rail

Mr Brian Doyle Rivers Agency

Mr Nick Ely Environment Agency

Mr Peter Graham* Waterways Ireland

Mr Jim Harvey Waterways Ireland

Dr Daniel Hine Environment Agency

Mr Michael Hodgson BAM Nuttall Ltd

Mr Steve Hold Arup Group Ltd

Dr Owen Jenkins CIRIA

Mr Kerry Keirle* Welsh Assembly Government

Mr Lee Kelly CIRIA

Ms Joanne Larner* Welsh Assembly Government

Mr Peter Radford Institution of Civil Engineers

Mr Steve Roffe Network Rail

Mr Murray Scott* Structural Services Fife Council (representing Scottish Government)

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Mr Andrew Stevenson Scottish Canals

Mr Jim Stirling Independent consultant/HR Wallingford

Mr David Stork Mott MacDonald

Mr Dick Thomas (chair) Independent Consultant

Ms Judith Tracey* Scottish Government

Mr Emyr Williams Pembrokeshire County Council (representing Welsh Assembly Government)* corresponding members

Project funders

Source materialsCIRIA wishes to acknowledge the assistance of the many individuals and organisations who have provided information on design, inspection and repair practices, as well as case studies and photographs.

AECOM

BAM Nuttall

Environment Agency

De partment of Agriculture and Rural Development, Northern Ireland

Network Rail

Scottish Canals

Scottish Government

Waterways Ireland

Welsh Government

viii CIRIA, C746

Glossary

Abutment End support of a bridge that also connects the structure to the ground.

Apron 1 An area of open land adjacent to a berth (immediately behind the quay face).

2 A layer of rubble, stone or a concrete slab, with or without toe piles, to protect the toe of a wall against scour.

Ashlar A square-hewn stone. Masonry consisting of blocks of stone, finely square dressed to given dimensions, and laid in courses with thin joints.

Asset management The systematic and co-ordinated activities and practices through which an organisation optimally and sustainably manages its asset’s condition, performance, risks and expenditures over the life cycle of the asset for the purpose of achieving its organisational strategic plan.

Bag joggle A bag filled with mortar which is inserted in a pre-formed keyway in vertical masonry or concrete block-work joints to provide resistance to sliding.

Bagwork A revetment to protect walls from scour, consisting of dry concrete in bags

Belting Horizontal projection around the hull of a ship at or the above water level to give increased protection from impact when berthing.

Berth A place where a ship can moor and load or unload.

Blockage 1 The ratio of the cross-section area of the immersed portion of a vessel to the cross-section area of the waterway in which it floats.

2 Obstruction to a watercourse such as fallen timber, debris or silt build-up, which may restrict the flow of water.

Bond An interlocking arrangement of stones or blocks within a wall to provide stability. Adhesion between mortar and masonry or concrete block, in a structure composed of these materials.

Close season Seasons when fishing is prohibited for some types of fish on certain types of water.

Cofferdam A dam (usually temporary) to give dry access to an area that is usually submerged or waterlogged.

Cope The top edge of a quay adjacent to a berth.

Counterfort A strengthening buttress at right angles to a retaining wall, generally on the side of the retained material to increase the overturning resistance, but may also be used to increase the bending resistance.

Dead man A large buried concrete or masonry block or timber sleepers to which a tie rod is anchored.

Draw-down Lowering of a water level.

Drystone wall A stone wall constructed without mortar.

Geophysical Of or pertaining to the physics of the earth, as applied to investigation methods.

Geophysics Quantitative physical methods for exploring structures and properties beneath the Earth’s surface. A variety of methods and instruments are available using natural or artificial sources generating, eg electromagnetic/seismic waves or static/dynamic electric/magnetic fields and corresponding sensors at the surface, on/below water or in boreholes to record the response of the subsurface.

ixOld waterfront walls, second edition

Gravity wall A retaining wall of broad cross-section, which depends on its own weight for stability.

Hearting The infilling of broken stone and other granular materials within a wall.

Heel The landward projection of a wall base.

LiDAR Remote sensing technology using laser beams and reflected light to measure distance.

Liquefaction Describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid.

Littoral drift Sedimentary material moved in the littoral zone under the influence of waves and currents.

Littoral transport Movement of material in the littoral zone under the action of waves and currents.

Littoral zone The coastal zone in which material on the seabed is transported by the action of waves and currents.

Natura 2000 site An EU-wide network of nature protection areas established under the 1992 Habitats Directive. The network aims to assure the long-term survival of Europe’s most valuable and threatened species and habitats. It is comprised of Special Areas of Conservation (SAC) designated by Member States under the Habitats Directive, and also incorporates Special Protection Areas (SPAs), which they designate under the 1979 Birds Directive (Europa, 2015).

Overburden drilling A drilling technique for penetrating a mixture of soils and rocks.

Oversails Horizontal projections from the back face of a wall intended to increase stability.

Overtopping Passing of water over the top of a structure as a result of wave action, surge or wind. The water level in front of the structure is lower than the crest level of the structure.

Plumbs Boulders or rocks of large volume placed into mass concrete foundations or backing walls to reduce volumes of mass concrete necessary.

Pointing The filling and finishing of mortar on the outer part of a joint where the bedding mortar has been raked back from the masonry face or left recessed from it in construction.

Pozzolana A cement additive comprising silica in reactive form, which can impart hydraulic set; can be either naturally occurring (eg volcanic ash) or artificially produced (eg brick dust or pulverised fuel ash, PFA).

Puddle clay A plastic mixture of clay and water used to form an impermeable layer.

Quay A berthing structure backing on to the shore or reclaimed land.

Ramsar sites Designated under the Ramsar Convention 1971. The objective of this designation is to prevent the progressive encroachment into, and the loss of, wetlands.

Reno mattress A structure with a large plan area and a small thickness made from wire mesh and filled with stones on site to create a flexible, permeable and monolithic structure, often used for river and canal bank protection works.

Rip-rap Is the term used to describe loose quarry stone with a wide grading (D85/D15 = 1.5 to 2.5 and W85/W15 = 3.4 to 16) that is used for the protection of beds and banks against hydraulic forces.

Rubble Stone of irregular shape and size.

Rubble masonry The term describes many different types of masonry, the main types being random rubble (irregularly shaped stone elements, typically as it comes from the quarry) either coursed or uncoursed, and squared rubble (more regularly shaped stone), either coursed or uncoursed.

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Scour The underwater removal of bed material by waves or currents.

Seawall A shoreline structure primarily designed to prevent flooding, erosion and other damage caused by wave action.

Settlement Settlement occurs from movement of the ground due to some type of external loading, or because of an external action such as mineral mining or water extraction.

Subsidence Movement of the ground (mostly vertical), which is not caused by the application of an external load. Examples of subsidence include karst, internal erosion, the collapse of mine workings, settlement due to animal burrowing and desiccation shrinkage caused by seasonal moisture take by trees and other large vegetation.

Tsunami A large wave induced by the effects of an earthquake or other underwater disturbance.

Translation The lateral movement of a whole structure.

Wedge A thin masonry slice driven into an external joint in a rubble wall to prevent movement of the facing stones.

Wharf See Quay.

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Abbreviations and acronyms

ACOP Approved code of practice

ADCP Acoustic Doppler Current Profilers

AI Annual inspection

ALARP As low as reasonably practical

AMIS Asset management information system

AMS Asset management system

ALWC Accelerated low water corrosion

AONB Areas of Outstanding Natural Beauty

BGS British Geological Survey

BSI British Standards Institution

BW British Waterways

CAD Computer-aided design

CAR The Water Environment (Controlled Activities (Scotland) Regulations 2011

CBA Cost-benefit analysis

CDM Construction (Design and Management)

CEA Cost-effectiveness analysis

CEH Centre for Ecology and Hydrology

CPA Coastal protection authority

CPF Cost to prevent a fatality

CPT Cone penetration test

DAFS Department of Agriculture and Fisheries for Scotland

DARDNI Department of Agriculture and Rural Development (Northern Ireland)

DCC Devon County Council

Defra Department for Environment, Food and Rural Affairs

DfT Department for Transport

DOENI Department of the Environment (Northern Ireland)

DoECLG Department of the Environment, Community and Local Government (RoI)

DRDNI Department for Regional Development (Northern Ireland)

DTTAS Department of Transport Tourism & Sport (Ireland)

EA Environment Agency

EC European Commission

EFNARC Expert for Specialised Construction and Concrete Systems

EIA Environmental Impact Assessment

EPA Environmental Protection Agency (RoI)

EPS European Protected Species

ERT Electrical Resistivity Tomography

ES Environmental Statement

ESPRC Engineering and Physical Sciences Research Council

ETA Event tree analysis

EU European Union

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FCERM Flood and Coastal Erosion Risk Management

FCERM-AG Flood and Coastal Erosion Risk Management – appraisal guidance

FCERM-GiA Flood and coastal erosion risk management – grant-in-aid

FEANI European Federation of National Associations

FEH Flood Estimation Handbook

FEM Finite element model

FEMCA Failure mode, effect and criticality analysis

FMEA Failure modes and effect analysis

FoS Factor of safety

FTA Fault tree analysis

GIS Geographic information system

GPR Ground penetrating radar

GPS Global positioning system

HAZOP Hazard and operability studies

HA Highways Authority

HD High definition

HGV Heavy goods vehicle

HAS Health and Safety Authority (RoI)

HSAW Health and Safety at Work

HSE Health and Safety Executive

HSENI Health and Safety Executive Northern Ireland

IAEA International Atomic Energy Agency

ICE Institution of Civil Engineers

IDB Internal Drainage Board

IMO International Maritime Organisation

ISO International Organisation for Standardization

LA Local authority

LDA Land Drainage Act

LEP Local Enterprise Partnerships

LLFA Lead local flood authority

LLOL Likely loss of life

MBES Multibeam echo sounder

MBSS Multibeam swathe sonar

MCA Maritime and Coastguard Agency

MMO Marine Management Organisation

MPA Cement Mineral Products Association

NE Natural England

NERC Natural Environment Research Council

NPPF National Planning Policy Framework

NI Northern Ireland

NIEA Northern Ireland Environment Agency

NRA National Roads Authority (RoI)

NRC Nuclear Regulatory Commission

NRSWA New Roads and Street Work Act 1991

NRW Natural Resources Wales

xiiiOld waterfront walls, second edition

NSD Nuclear Safety Directorate

O&M Operations and maintenance

OPW Office of Public Works (RoI)

ORR Office of Rail Regulation

PF Proportion factor

PIANC The World Association for Waterborne Transport Infrastructure

POF Probability of failure

PPS Planning Policy Statement

PSCS Project supervisor for the construction stage (RoI)

PSDP Project supervisor for the design process (RoI)

R2P2 Reducing risk protecting people

ROGS Railways and Other Guided Transport Systems (Safety) Regulations 2006

RAIB Rail Accident Investigation Branch (UK)

RAIU Railway Accident Investigation Unit (RoI)

RoI Republic of Ireland

RoRo Roll on/Roll off

ROV Remotely operated vehicle

RSC Railway Safety Commission

SAC Special Areas of Conservation

SBES Single beam echo sounder

SC Scottish Canals

SDD Scottish Development Department

SEPA Scottish Environment Protection Agency

SMP Shoreline Management Plan

SofS Secretary of State

SPA Special Protection Area

SPP Scottish Planning Policy

SPT Standard penetration test

SROI Social return on investment

SRPC Sulphate-resisting Portland cement

SSS Side-scan sonar

SSSI Site of Special Scientific Interest

TAN Technical Advice Note

TOR Tolerability of risk

TS Transport Scotland

UAV Unmanned aerial vehicle

UKHO UK Hydrographic Office

UNEP United Nations Environmental Programme

USACE US Army Corps of Engineers

VPF Value of preventing fatality

WFD Water Framework Directive

WG Welsh Government

xiv CIRIA, C746

Contents

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

Abbreviations and acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

1.1 Background to the guide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Target readership. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Use of old waterfront walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.5 Structure of the guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.6 Relevance to different end users. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.7 Activities involved in the management of walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2 Management – risk, responsibilities and funding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

2.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.2 Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2.2 Performance requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2.3 Functional objectives and change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2.4 Risk-based approach to wall performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.3 Principles of risk management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102.3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102.3.2 Risk, probability and consequence/hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112.3.3 Risk management strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

2.4 Measures and tools for risk management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122.4.1 Asset management systems (AMS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122.4.2 The identification of threats and consequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .132.4.3 Risk analysis – the tiered approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .132.4.4 Risk evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

2.5 Roles and responsibilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142.5.1 Ownership and responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142.5.2 Legal considerations and obligations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162.5.3 Other considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

2.6 Legislative framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .182.6.1 Health and safety law. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .182.6.2 Public safety and emergency planning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .192.6.3 Health and safety at work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .202.6.4 Occupiers liability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .212.6.5 Corporate manslaughter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .212.6.6 Transport law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .212.6.7 Roads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .212.6.8 Railways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222.6.9 Canals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222.6.10 Coastal protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .232.6.11 Land drainage and flood risk management law. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

xvOld waterfront walls, second edition

2.6.12 Environmental law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .252.6.13 Habitats Directive. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .252.6.14 Water Framework Directive (WFD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .262.6.15 Bathing Water Directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .262.6.16 Fisheries Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .262.6.17 Waste Framework Directive. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

2.7 Common law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .272.7.1 Nuisance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

2.8 Consent requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282.8.1 Environmental site survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282.8.2 Planning permission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282.8.3 Consent to work in watercourses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .292.8.4 Marine licence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

2.9 Valuing old waterfront walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .322.10 Funding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

3 Functions, forms and failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .403.2 History of old waterfront walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

3.2.1 Historical context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .413.2.2 Designers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .423.2.3 General wall characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

3.3 Quay, dock and lock walls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .503.3.1 Function and design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .503.3.2 Component characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51

3.4 Breakwaters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .703.4.1 Function and design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .703.4.2 Component characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70

3.5 Seawalls for coastal defence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .813.5.1 Function and design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .813.5.2 Component characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82

3.6 Retaining walls and flood defences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .853.6.1 Function and design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .853.6.2 Component characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

3.7 Skin walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .873.8 Bridge piers and abutments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .883.9 Understanding old waterfront walls and their failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

4 Performance assessment, risk attribution, inspections and data collection . . . . . . . . . . . . . . . . . . . . . 101

4.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1014.2 Framework for analysis and decision making . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102

4.2.1 Performance assessment tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1044.2.2 Role of data in performance assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

4.3 Risk analysis and attribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1064.3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1064.3.2 Knowledge gaps and uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1084.3.3 Components of risk analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1094.3.4 Threat/hazard identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1114.3.5 Event probability estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1124.3.6 Failure probability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1134.3.7 Consequences of failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1144.3.8 Characterisation of potential impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1154.3.9 Estimation of the level of risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1154.3.10 Attributing risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .116

xvi CIRIA, C746

4.3.11 Risk evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1164.3.12 Flood and coastal erosion risk management (FCERM) . . . . . . . . . . . . . . . . . . . . . . . . . 119

4.4 Performance assessment and diagnosis methodology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1204.4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1204.4.2 Diagnosis and performance assessment in the management cycle. . . . . . . . . . . . . . 1204.4.3 Performance assessment methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1214.4.4 Performance assessment process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1214.4.5 Loading conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224.4.6 Data and failure modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224.4.7 Using fault and event trees to examine failure scenarios. . . . . . . . . . . . . . . . . . . . . . . 1234.4.8 Assessment report. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127

4.5 Inspections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1284.5.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1284.5.2 Routine inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1284.5.3 Frequency and purpose of routine inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1304.5.4 Rating and prioritisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

4.6 Investigations, instrumentation and monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1324.6.1 Investigation planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1324.6.2 Instrumentation and monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1334.6.3 Analysis of data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

4.7 Knowledge and data management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1354.7.1 The need for documents, records and archives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1354.7.2 Asset management information systems (AMIS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1364.7.3 Geographical information system (GIS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1364.7.4 Building Information Modelling (BIM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .137

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

Further reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

5 Operations and maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

5.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1405.2 Applying asset management principles to O&M. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141

5.2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1415.2.2 Activities and practices of asset management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1415.2.3 Management life cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1425.2.4 Organisation of O&M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1435.2.5 Importance of an O&M manual. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1445.2.6 General approaches to O&M. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1465.2.7 Further information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149

5.3 Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1495.4 Maintenance issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

5.4.1 Responsibility for maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1505.4.2 Deterioration and failure mechanisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1535.4.3 Encroachments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1555.4.4 Settlement and subsidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1565.4.5 Seepage/drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1575.4.6 Instability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1595.4.7 Cracking and block movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1615.4.8 Burrowing animals and biological attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1635.4.9 Vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1665.4.10 Culverts and discharge pipe systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

5.5 Emergency response actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

6 Site characterisation, data acquisition and management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

6.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173

xviiOld waterfront walls, second edition

6.2 Principles of site characterisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1746.3 Morphological, hydraulic and other natural processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .175

6.3.1 Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1756.3.2 Actions and loads in a fluvial environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1756.3.3 Actions and loads in a coastal environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1776.3.4 Human actions on waterfront walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178

6.4 Assembly of available historic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1786.4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1786.4.2 Sources of archive material. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .179

6.5 Investigation techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1806.5.1 Excavation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1806.5.2 Shape detection problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1816.5.3 Geophysical methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1826.5.4 Unexploded ordnance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

6.6 Investigation techniques for the internal structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1836.6.1 Excavation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1836.6.2 Drilling techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1846.6.3 Remote inspection methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1846.6.4 Geophysical methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1846.6.5 Testing of wall materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

6.7 Investigation techniques for external surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1896.7.1 Acoustic techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1896.7.2 Light Detection and Ranging (LiDAR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1946.7.3 Unmanned aerial vehicles (UAVs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1966.7.4 Investigation by divers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .197

6.8 Ground investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1976.8.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1976.8.2 Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1986.8.3 Type of investigations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

6.9 Geotechnical parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .201References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202

Further reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202

7 Physical processes and assessment tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

7.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2047.2 Key principles and issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205

7.2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2057.2.2 Assembly of available data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2067.2.3 Diagnostic approach to evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2077.2.4 Identification of crack damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2107.2.5 Identification of wave damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .211

7.3 Hydraulic forces acting on waterfront walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2127.3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2127.3.2 Hydrostatic forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2137.3.3 Hydrodynamic forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2137.3.4 Predicting types of wave load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2157.3.5 Pulsating (or non-impulsive) wave loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2157.3.6 Impulsive wave loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2197.3.7 Broken wave conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2207.3.8 Bore wave conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220

7.4 Analysis of stability of walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2217.4.1 Codes of practice (COP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2217.4.2 Loading and strength parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2217.4.3 Modes of failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2227.4.4 Deep slip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222

xviii CIRIA, C746

7.4.5 Overturning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2237.4.6 Sliding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2247.4.7 Bearing pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2247.4.8 Counterforts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2247.4.9 Dewatering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2257.4.10 Overtopping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2257.4.11 Factors of safety (FoS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .226

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

Further reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

8 Maintenance and rehabilitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

8.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2298.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2308.3 Modifying loads on the structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .231

8.3.1 Redefining the standard of service. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2318.3.2 Reduction of soil load on back of wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2358.3.3 Pressure-relieving slabs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236

8.4 Remedial works to the wall toe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2378.4.1 Quay wall toe erosion repairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2378.4.2 Coast protection seawall toe repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2388.4.3 Breakwater toe repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .240

8.5 Increasing wall stability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2408.5.1 Rock placed in front of the wall. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2408.5.2 Ground and rock anchors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2428.5.3 Piling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .244

8.6 Repair of the wall structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2448.6.1 Patching of concrete walls above water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2448.6.2 Patching walls below water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2468.6.3 Repointing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2468.6.4 Heritage issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2468.6.5 Grouting of a wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2478.6.6 Cracks and joint sealers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2518.6.7 Masonry bonding, stitching, dowelling and wedging. . . . . . . . . . . . . . . . . . . . . . . . . . . .2518.6.8 Replacement of brick and stone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2568.6.9 Additional skin of brickwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2568.6.10 Protection of the top surface of wall or backfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2578.6.11 Sprayed concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2588.6.12 Ferrocement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .261

8.7 Replacing the wall with a new structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2618.8 Modification of wall to suit new purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2668.9 Techniques for working underwater. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2678.10 Selection of materials for repairs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268

8.10.1 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2688.10.2 Brickwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2698.10.3 Stone masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2698.10.4 Mortar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2698.10.5 Underwater grout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270

BoxesBox 3.1 Mortar specification for the construction of the Gloucester and Berkeley canal, 1795 . . . . . . . . . . . . . . . 49Box 3.2 Example of timber in a dock wall, Bristol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Box 3.3 Specification for metalwork used in the construction of the Gloucester and Berkeley canal, 1795 . . . . . 60Box 5.1 Guidance on how to assess the deterioration of waterfront walls and how to assess residual life . . . . . 142Box 5.2 Tasks to be included in the O&M manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145Box 5.3 Implementing a risk-based approach to asset inspection in England and Wales . . . . . . . . . . . . . . . . . . . 147

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Box 5.4 Biological attack of timber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165Box 5.5 Safety precautions for visual inspections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170Box 8.1 The reconstruction of the piers, West Bay, Dorset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230Box 8.2 Load restrictions, South Alfred Dock, Liverpool. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232Box 8.3 Repairs to the bullnose, Chatham Dockyard, Kent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232Box 8.4 Use of reinforced earth on river walls, Gateshead, Tyne and Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236Box 8.5 Repairs to St Mary’s Quay, Isles of Scilly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238Box 8.6 Repairs to seawall at Blue Anchor, Somerset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239Box 8.7 Compression piles in use in two repairs at Liverpool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243Box 8.8 Use of rock anchors for deepening a dock in India . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

Case studiesCase study 2.1 Failure of the West Quay, Bridgwater, Somerset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Case study 2.2 Coastal protection project, Lyme Regis, Dorset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Case study 3.1 River wall failure at Bristol Portway, Bristol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97Case study 4.1 Investigations and remediation at Gorey breakwater pierhead, Jersey. . . . . . . . . . . . . . . . . . . . . . . . . . . . 129Case study 5.1 Maintenance and repair of Mullion Harbour, Cornwall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152Case study 5.2 Failure of railway bridge over the River Crane, Feltham, West London . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171Case study 6.1 Restoration of St. Catherine’s breakwater roundhead, Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186Case study 6.2 Breakwater surveys, Dover, Kent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191Case study 8.1 Stitching repairs at Old Quay, Whitehaven, Cumbria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232Case study 8.2 Reconstruction of concrete masonry gravity wall, Tilbury, Essex. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234Case study 8.3 Storm damage repairs, Meadfoot Beach Torquay, Devon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241Case study 8.4 Berwick breakwater refurbishment, Berwick upon Tweed, UK. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245Case study 8.5 Lock chamber leakage at Banavie Locks, Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248Case study 8.6 Grouting of Cullochy Lock, Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249Case study 8.7 East Pier grouting Scarborough, North Yorkshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250Case study 8.8 Innovative dock wall repair works in Milford Docks, Pembrokeshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252Case study 8.9 ‘Stitching up’ the past, St Aubin, Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255Case study 8.10 Seawall investigation and repairs at St Donat’s Castle, Wales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257Case study 8.11 Repairs at Porthcawl Harbour, Wales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259Case study 8.12 Gunite repairs of seawalls at Craigendoran and Scourie Pier, Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . 260Case study 8.13 Seawall concrete repairs, Scarborough, UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260Case study 8.14 Blue Anchor seawall, North Somerset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

FiguresFigure 1.1 Overall structure of the guide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Figure 2.1 Overview of Chapter 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7Figure 2.2 The process of risk identification, assessment and control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Figure 2.3 An example of a tiered approach to risk analysis (UK approach) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Figure 2.4 Failure of the West Quay, Bridgwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Figure 2.5 Flooding behind the river wall before failure on 4 November 2012 (taken from south of the failure) . . . . 33Figure 2.6 Seawall at Lyme Regis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Figure 3.1 Overview of Chapter 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Figure 3.2 Roman Britain settlements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42Figure 3.3 The quayside wall of the Roman waterfront at Chester. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42Figure 3.4 British customs ports in the 18th and early 19th centuries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Figure 3.5 The waterway system in England, 1789 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Figure 3.6 Trig Lane, London, showing back-braced riverfront revetments behind 15th century river wall . . . . . . . . 45Figure 3.7 Baynard’s Castle dock, London, showing timber rubbing posts to protect vessels from damage by

the stone wall. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Figure 3.8 Bearing stress distribution under a waterfront wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46Figure 3.9 Illustrations from a French treatise on civil engineering showing methods of interlocking blocks and

the effects of not doing this . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Figure 3.10 Section of dock wall, Sharpness, circa 1880. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Figure 3.11 Section showing counterfort strengthened by a timber tie in the Cumberland basin, Bristol, 1973 . . . . . 49Figure 3.12 Section showing river and dock wall connected by a timber tie at Sandon half-tide dock, Liverpool, 1901 . . . 49Figure 3.13 The main components of a quay wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Figure 3.14 Sections of the walls in Gloucester Docks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Figure 3.15 King George V Dock London. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52Figure 3.16 Portsmouth Dockyard tidal basin extension, 1864. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52Figure 3.17 The Alexandra Dock, Hull, 1887 to 1888 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52Figure 3.18 The Royal Albert Dock, London, 1880 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52Figure 3.19 Section of the chamber of the entrance lock Blackwall, West India Dock, 1800–1806. . . . . . . . . . . . . . . 53

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Figure 3.20 Quay wall at Tema, Ghana, 1960. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Figure 3.21 The arched wall of the Albert Dock at Hull, 1861 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Figure 3.22 The arched dock walls in the Canada Dock, London. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54Figure 3.23 The arched dock wall at Whitehaven. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54Figure 3.24 Plan and elevations of the arched wall at Great Grimsby (Royal) Docks 1864–1865 . . . . . . . . . . . . . . . . . 54Figure 3.25 Western tidal harbour wall at Greenock, 1878–1886. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Figure 3.26 Increasing the resistance of the wall to overturning with a stepped-back face approach, Spencer Dock,

Belfast, 1872. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Figure 3.27 Retaining walls, showing oversails on the rear face, 1881. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Figure 3.28 Section of wall at the old entrance, sharpness, showing counterfort and serrated base, 1820 . . . . . . . . 56Figure 3.29 Glasson Dock, Morecombe Quay. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Figure 3.30 Edinburgh Dock, Leith. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57Figure 3.31 Cross-section of a wall, Liverpool, 1898. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57Figure 3.32 Curved dock wall with heel, Sheerness, 1813–1927 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57Figure 3.33 Baker’s Quay, Gloucester Docks, 1829 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57Figure 3.34 The tidal basin, Barrow, 1879 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Figure 3.35 Surrey Commercial, Greenland Dock, London, 1898 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Figure 3.36 Fitting out basin, Chatham, circa 1880 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Figure 3.37 The end wall, Winton Pier, 1892 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Figure 3.38 Dock built on running sand, King George V Dock, Hull, 1968 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Figure 3.39 Dock wall later strengthened with land ties, Southampton, 1842 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Figure 3.40 Millwall, London, 1866 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Figure 3.41 Docks and river wall, Sheerness, 1813–1927. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Figure 3.42 Dock wall, cast with internal ashlar blocks, Wallasey Pool, Birkenhead Docks, circa 1856. . . . . . . . . . . . 60Figure 3.43 Wall made of precast blocks, Cork, 1877. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61Figure 3.44 White Star dock, Southampton, 1907 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61Figure 3.45 Dock wall in main basin at Sharpness, Gloucestershire, 1874 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62Figure 3.46 Victoria Docks, London, 1858 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Figure 3.47 New Quay at Blyth Harbour, Northumberland, 1882. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Figure 3.48 Dock wall at Manchester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Figure 3.49 Concrete cylinder wall at Princes Dock, Glasgow, circa 1895 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Figure 3.50 Designed backfill for the Carron Dock, Grangemouth, 1879 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Figure 3.51 Clay and rock seal on rubble: block wall at Nacala, Mozambique, circa 1960. . . . . . . . . . . . . . . . . . . . . . . 64Figure 3.52 Quay wall at Trieste, Italy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65Figure 3.53 Transverse section through King George V Dock, London, 1921. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65Figure 3.54 Section of the tidal harbour wall showing bollard and stay-irons, Hartlepool, 1834 . . . . . . . . . . . . . . . . . . 65Figure 3.55 Cross-section of wall at the entrance to Southwold Harbour, Suffolk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66Figure 3.56 ast iron double-flanged piles being used at the Albert Harbours, Greenock . . . . . . . . . . . . . . . . . . . . . . . . 66Figure 3.57 Section of a wall, Bremerhaven, Germany, 1897. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67Figure 3.58 Section of a wall, Brunsbuttelkoog, Germany, 1914 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67Figure 3.59 ‘Rouen’ type quay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67Figure 3.60 Caisson-type foundations, Rothesay Dock, Glasgow, 1901 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68Figure 3.61 Monolithic foundations, St Andrews Dock, Hull, 1901 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Figure 3.62 Quay wall on cast iron cylinders, Newcastle, 1873 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Figure 3.63 Caisson-type foundations, Broomielaw quay, Glasgow, 1900–1902 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Figure 3.64 Dock wall, Immingham, Lincolnshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Figure 3.65 Concrete quay on south side of basin at Barrow, 1901 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70Figure 3.66 The main components of a breakwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71Figure 3.67 Section of the North Pier, West Hartlepool, 1847–1858 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71Figure 3.68 The pier at Nether Buckie, 1855 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71Figure 3.69 The Old Pier, Wick, 1823 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72Figure 3.70 The pier, Hynish, Argyllshire, 1843 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72Figure 3.71 Breakwater, Donaghadee Harbour, 1821. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73Figure 3.72 Dover breakwater, 1866. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73Figure 3.73 The West Pier, Whitehaven, 1831 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74Figure 3.74 The North Pier, Tyne, 1855–1895. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74Figure 3.75 The breakwater, Anstruther, Scotland. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75Figure 3.76 Piano blockwork used in the breakwater, North Tyne, 1855–1895 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75Figure 3.77 Section showing the method of construction of the Fraserburgh breakwater, 1877. . . . . . . . . . . . . . . . . . .76Figure 3.78 The ancient manner of constructing the Cob, Lyme Regis, 16th century . . . . . . . . . . . . . . . . . . . . . . . . . . . .76Figure 3.79 Typical section of a timber-framed breakwater with rubble hearting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76Figure 3.80 The North Pier, Aberdeen, 1877 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77Figure 3.81 Breakwater, Newhaven, 1880 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

xxiOld waterfront walls, second edition

Figure 3.82 Breakwater formed of concrete blocks with foundation bag work keyed into rock . . . . . . . . . . . . . . . . . . . 77Figure 3.83 The outer portion of the breakwater, Ardrossan, 1892. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77Figure 3.84 Breakwater, Holyhead, 1876 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78Figure 3.85 Breakwater, Alderney, 1851–1864 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78Figure 3.86 Section of breakwater showing disposition of bag joggles, Dover, 1898–1909 . . . . . . . . . . . . . . . . . . . . . .78Figure 3.87 Kilrush Pier, Shannon, Ireland, 1843 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78Figure 3.88 Section through breakwater, Alderney, 1851–1864 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79Figure 3.89 Section of breakwater, St Catherine’s Harbour, Jersey, 1856 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79Figure 3.90 The south breakwater, Aberdeen, 1873 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80Figure 3.91 St Mary’s Quay, Isles of Scilly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80Figure 3.92 Section and elevation of the North Pier, Eyemouth, 1767 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80Figure 3.93 Typical sectional plan showing position of rail cramps, eastern arm pier head, Dover, 1898–1909 . . . . .81Figure 3.94 Sliced blockwork, Lagos Harbour, 1963–1969 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81Figure 3.95 The main components of a seawall for coastal defence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82Figure 3.96 Seawall, Hornsea, 1907 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82Figure 3.97 Typical vertical seawall sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83Figure 3.98 Seawall, Caroline Place, Hastings, circa 1910. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83Figure 3.99 Sea defences, Penzance Harbour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84Figure 3.100 The Royal Prince’s Parade seawall, Bridlington, 1905 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84Figure 3.101 A concrete block seawall, Margate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84Figure 3.102 A section of sea defences, Lyme Regis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84Figure 3.103 Sea defences, Seaford, 1881–1998. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85Figure 3.104 The main components of flood defences and retaining walls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85Figure 3.105 The Thames River wall at Fishmongers Hall, 1837 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86Figure 3.106 River wall between Manchester Dock and Chester Basin entrances, Liverpool. . . . . . . . . . . . . . . . . . . . . . 86Figure 3.107 Section showing the masonry upper portion, designed to reduce scour by the wash from passing

vessels, Grand Union Canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86Figure 3.108 River wall on piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87Figure 3.109 The North River, New York, circa 1883 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87Figure 3.110 Section and plan of the Herculaneum Dock, Liverpool, 1873 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87Figure 3.111 The new dock wall at Seaham, circa 1900. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Figure 3.112 Details of a bridge pier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Figure 3.113 Section and plan of a pier of the old London Bridge as it appeared in 1826 . . . . . . . . . . . . . . . . . . . . . . . . 89Figure 3.114 A design for a new Westminster Bridge, 1739 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89Figure 3.115 Details of a river pier for the Royal Border Bridge, Northumberland, 1850 . . . . . . . . . . . . . . . . . . . . . . . . . 90Figure 3.116 Details of a bridge abutment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91Figure 3.117 Typical detail at a canal bridge abutment, Eastern Canal, France, 1882 . . . . . . . . . . . . . . . . . . . . . . . . . . . .91Figure 3.118 Section of the east wall showing underpinning carried out, Sandon Dock, Liverpool, 1903 . . . . . . . . . . . 92Figure 3.119 Proposed method of strengthening the walls of the Great Float, Birkenhead, 1858 . . . . . . . . . . . . . . . . . 92Figure 3.120 Windmillcrolt Quay, Clyde, constructed in 1838 and strengthened in 1884 . . . . . . . . . . . . . . . . . . . . . . . . 92Figure 3.121 Customs House Quay, Clyde, constructed in 1852 and strengthened in 1887 . . . . . . . . . . . . . . . . . . . . . . 93Figure 3.122 General Terminus Quay, Clyde, original wall constructed in 1849–1850, reconstructed in concrete

in 1932–1934 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93Figure 3.123 Construction work on a dock wall in Sharpness, 1874 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94Figure 3.124 Section of a dock wall showing the addition of a large concrete block above the oversail,

Gloucester, 1852 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94Figure 3.125 Section of a dock wall showing a counterfort that has been added and extended below the original

foundation level, Gloucester, 1908. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95Figure 3.126 Collapse of a section of dock wall, Belfast, 1878 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95Figure 3.127 The design for the reconstruction of the dock wall, Belfast, 1878 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95Figure 3.128 The design for the strengthening of a section of the dock wall, Belfast, 1878 . . . . . . . . . . . . . . . . . . . . . . 96Figure 3.129 Section of the dock wall that collapsed, Limerick, 1887 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96Figure 3.130 The proposed design and reconstruction of the dock wall that collapsed, Limerick, 1887 . . . . . . . . . . . . 96Figure 3.131 The accepted design for the reconstruction of the dock wall, Limerick, 1887. . . . . . . . . . . . . . . . . . . . . . . 96Figure 3.132 Timber quay built on top of a collapsed portion of dock wall, Barrow-in-Furness, 1901. . . . . . . . . . . . . . . .97Figure 3.133 Failure of river wall and collapse of road in 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97Figure 3.134 Failure of river wall in 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97Figure 4.1 Overview of Chapter 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101Figure 4.2 Assessments and decision making for owners/asset managers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105Figure 4.3 Integration of the data handled by each of the activities in this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . 106Figure 4.4 Example of a risk matrix that can be used in qualitative risk analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107Figure 4.5 Graphical evaluation of quantified threats and consequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108Figure 4.6 A framework for the analysis of risk components associated with wall failure. . . . . . . . . . . . . . . . . . . . . . 109

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Figure 4.7 Acceptability of risk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117Figure 4.8 A generic fault tree for a gravity-based wall showing associated failure modes and processes . . . . . . . 124Figure 4.9 An event tree for a gravity-based wall failure showing estimated probabilistic values . . . . . . . . . . . . . . . 125Figure 4.11 General view of Gorey breakwater pierhead and Mount Orguiel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129Figure 4.12 Partial collapse of Gorey breakwater pierhead in 1964 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129Figure 4.13 Superimposed LiDAR models of pierhead, which identified bulges in the masonry wall, a marked loss

of concrete apron base at the end of the pierhead and a loss of beach sand on the outside face of the pierhead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

Figure 4.14 Basic loading conditions on pierhead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129Figure 4.15 Scheme design remedial works – sheet piles, ring beam, deck over slab etc . . . . . . . . . . . . . . . . . . . . . . 129Figure 5.1 Overview of Chapter 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140Figure 5.2 Example of a deterioration curve for a typical riverine waterfront brick and masonry wall. . . . . . . . . . . . 142Figure 5.3 Waterfront wall management life cycle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143Figure 5.4 Cross-section of the western breakwater. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152Figure 5.5 Plan of harbour showing extent if required repairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152Figure 5.6 The results of backfill washout due to a combination of beach lowering beneath the seawall toe,

overtopping of the crest and the structure drainage characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156Figure 5.7 A seawall in the process of overturning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Figure 5.8 Minor cracking in a masonry wall (a) and major movement in a brick waterfront wall (b) . . . . . . . . . . . . . 161Figure 5.9 Impact damage to a bridge abutment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162Figure 5.10 A canal lock wall in a deteriorated condition with broken bricks, missing joint mortar, and suspect

former repair work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163Figure 5.11 Examples of the signs of marine biological attack (gribble) in timber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165Figure 5.12 Vegetation encroachment of an old waterfront wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167Figure 6.1 Overview of Chapter 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173Figure 6.2 Detail gained by excavation of a trial pit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180Figure 6.3 Wall shape detection problems for various types of structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182Figure 6.4 Typical GPR survey from Netherton Tunnel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185Figure 6.5 GPR detail from Netherton Tunnel, the blue contours shows potential leakage paths over tunnel arches. . . 185Figure 6.6 St Catherine’s breakwater, Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186Figure 6.7 Cross section of breakwater (from archives) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186Figure 6.8 Damage and temporary repairs to the roundhead in 2005 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186Figure 6.9 Discovery of a large void beneath concrete slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186Figure 6.10 Resistivity cross-section on a railway embankment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187Figure 6.11 Typical microgravity contour plan showing low gravity and a potential void . . . . . . . . . . . . . . . . . . . . . . . . 187Figure 6.12 Photo survey combined with MBSS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190Figure 6.13 Overview of Dover harbour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191Figure 6.14 Typical section for the second extension of the Admiralty Pier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191Figure 6.15 Sonar survey of Admiralty Pier showing large dislodged blocks on the toe protection . . . . . . . . . . . . . . . 191Figure 6.16 Sonar survey of southern breakwater showing large blocks on the toe protection . . . . . . . . . . . . . . . . . . 191Figure 6.17 ARC-boat capable of undertaking bathymetry, SSS and/or Acoustic Doppler Current Profilers (ADCP)

measurements in shallow water depths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192Figure 6.18 SSS record showing wreck at toe of rubble mound in front of the breakwater at Portland. . . . . . . . . . . . 192Figure 6.19 Deployment of dock wall profiling equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193Figure 6.20 Sector scanning sonar equipment deployed for wall profile measurement . . . . . . . . . . . . . . . . . . . . . . . . 193Figure 6.21 Profile of an arch wall in Gloucester Docks obtained with equipment shown in Figure 6.12 . . . . . . . . . . 194Figure 6.22 Typical harbour wall profile from equipment shown in Figure 6.12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194Figure 6.23 Profile of a river obtained with sector scanning sonar equipment, showing undercutting of bank . . . . . 194Figure 6.24 Above surface laser knitted with digital imagery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195Figure 6.25 Superimposed LiDAR models indicating locations of significant movement . . . . . . . . . . . . . . . . . . . . . . . 195Figure 6.26 Combined MBES and LiDAR survey, Särkisalo Bridge/Meritaito Bridge, Finland . . . . . . . . . . . . . . . . . . . . 195Figure 6.27 Skypower drone used on Caen Hill Locks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196Figure 7.1 Overview of Chapter 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204Figure 7.2 Flow chart showing typical stability evaluation procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206Figure 7.3 Typical crack formations and their causes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210Figure 7.4 Vertical crack clearly indicating forward movement of whole section of wall, Bowling Lock, Forth and

Clyde Canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211Figure 7.5 Storm damage to seawall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211Figure 7.6 Hydrostatic pressures acting on a gravity wall. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213Figure 7.7 Example wave pressure traces on a vertical wall with toe berm: model test results. . . . . . . . . . . . . . . . . 214Figure 7.8 Parameter map to predict occurrence of wave load types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216Figure 7.9 Nomenclature used in Goda’s wave load prediction method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217Figure 7.10 Impulsive breaking wave pressure coefficient α11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

xxiiiOld waterfront walls, second edition

Figure 7.11 Impulsive wave load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219Figure 7.12 Illustration of the active pressure components of forces acting on a retaining wall for consideration

of overturning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223Figure 7.13 Plan and elevation of a counterfort application of earth pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224Figure 7.14 Plan and sections of a counterfort wall showing bearing pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225Figure 8.1 Overview of Chapter 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229Figure 8.2 Following reconstruction, West Bay. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230Figure 8.4 Completed restoration work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230Figure 8.5 Cavities left after removal of decayed timbers, Kytra Lock, Caledonian Canal . . . . . . . . . . . . . . . . . . . . . 231Figure 8.6 Damaged quay wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232Figure 8.7 Completed wall with new stitching, grouting and pointing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232Figure 8.8 Application form for use of a mobile crane on a waterfront . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233Figure 8.9 Failure of the gravity wall at Tilbury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234Figure 8.10 Clearing of debris and positioning of custom made steel shutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234Figure 8.11 Reconstruction of upper section of wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234Figure 8.12 Completion of wall and placing of backfill. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234Figure 8.13 Example of soil being replaced with cemented material, Milford Haven, Wales . . . . . . . . . . . . . . . . . . . . 235Figure 8.14 Grouting of fill behind a quay wall, Appledore, North Devon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235Figure 8.15 Method of using a reinforced earth structure to reduce the pressure on the back of a wall . . . . . . . . . . 236Figure 8.16 Use of a pressure relieving slab for a river wall at Barnstaple, North Devon . . . . . . . . . . . . . . . . . . . . . . . 236Figure 8.17 Pressure grouting into a pre-formed bag at North Deepwater Quay, Port of Cork, Eire. . . . . . . . . . . . . . . 237Figure 8.18 Placing concrete underwater without tremie pipes by means of suitable admixtures. . . . . . . . . . . . . . . . 238Figure 8.19 Seawall at Blue Anchor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239Figure 8.20 Disintegration of the seawall at Blue Anchor, Somerset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239Figure 8.21 Completed refurbishment of seawall at Blue Anchor, Somerset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239Figure 8.22 Proposed repairs to seawall using a double layer of limestone rock, Blue Anchor, Somerset . . . . . . . . . 239Figure 8.23 Typical cross-section of the river wall showing the rock slope placed in front of the wall to stabilise it,

Huskisson Dock, Liverpool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240Figure 8.24 Wall stabilisation, Huskisson Dock, Liverpool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240Figure 8.25 Void on slipway wall. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241Figure 8.26 Damage to beach access steps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241Figure 8.27 Beach level excavated to expose voids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241Figure 8.28 Excavation of toe down to sheet piles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241Figure 8.29 Spray concrete used in voids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241Figure 8.30 Completed repairs of sea wall and beach access steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241Figure 8.31 Strengthening works on a typical section of the Albert River wall, Liverpool . . . . . . . . . . . . . . . . . . . . . . . 242Figure 8.32 Rock anchors being used for a dock-deepening project in India . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242Figure 8.33 Old City Canal, Isle of Dogs, London, showing vertical pile to take compression load from anchorage . 243Figure 8.34 Typical cross-section of the dock wall, Brocklebank Dock, Liverpool, showing rock anchorage and jet-

grouted columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243Figure 8.35 The Canning half-tide dock, Liverpool, showing compression piles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243Figure 8.36 Use of small diameter drilled piles as anchors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244Figure 8.37 Breakwater cross-section. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245Figure 8.38 Damage to southern stone face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245Figure 8.39 Stone face repair detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245Figure 8.40 Shutter design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245Figure 8.41 Final reinforced concrete repair showing match to existing structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246Figure 8.42 Grouting of the Wilson Bridge in Tours, France . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247Figure 8.43 Ramsgate breakwater 1750–1792 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247Figure 8.44 Leaks with contractor’s staff working from pontoon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248Figure 8.45 Target drilling of visible leakage from lock chamber wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248Figure 8.46 Polyurethane injection to visible leakage exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248Figure 8.47 Power washing at Cullochy Lock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249Figure 8.48 Cullochy Lock pressure grouting operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249Figure 8.49 Drilling at the East Pier, Scarborough . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250Figure 8.50 A dock wall showing the curve in plan from movement of the structure, Gloucester, UK . . . . . . . . . . . . . 251Figure 8.51 Section through the north wall showing ties used for strengthening, Lyme Regis, Dorset . . . . . . . . . . . . 252Figure 8.52 Work on the dock entrance walls at Milford Docks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252Figure 8.53 Typical section through wall showing extent of resin grouting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252Figure 8.54 Section through the Cobb showing the use of stainless steel dowels, Lyme Regis, Dorset . . . . . . . . . . . 253Figure 8.55 Section 1 through the reconstructed stone pier at Weymouth, Dorset . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253Figure 8.56 Section 2 through the reconstructed stone pier at Weymouth, Dorset . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254Figure 8.57 Section 3 through the reconstructed stone pier at Weymouth, Dorset . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254

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Figure 8.58 North pier and fort, St Aubin Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255Figure 8.59 Combination of loads in fort breakwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255Figure 8.60 Anchor with plug cap replaced (invisible fix) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255Figure 8.61 Cross-section of north pier with stitching anchors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255Figure 8.62 Area of missing brickwork on the south side of the Alfred Dock, Birkenhead . . . . . . . . . . . . . . . . . . . . . . 256Figure 8.63 Typical section of a wall, showing the face to be of different material from the mass of the structure,

the Great Float, Wallasey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256Figure 8.64 Section showing the new skin of added brickwork, Starcross breakwater, Devon. . . . . . . . . . . . . . . . . . . 257Figure 8.65 Seawall at St Donat’s Castle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257Figure 8.66 Repair to the seawall showing the backfill protected by a revetment, Harrington, Northamptonshire . . 258Figure 8.67 The spraying of concrete onto a seawall. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258Figure 8.68 The seawall at Colwyn Bay after the application of sprayed concrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259Figure 8.69 Filling voids with sprayed concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259Figure 8.70 Emergency repairs and remedial works to Porthcawl Harbour walls following collapse . . . . . . . . . . . . . . 259Figure 8.71 Sea defence showing the application of 100 mm of sprayed concrete incorporating polypropylene

fibres and sulphate resistant cement at Craigendoran, Scotland, 2006 . . . . . . . . . . . . . . . . . . . . . . . . . . 260Figure 8.72 The extent of damage at Sutherland, Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260Figure 8.73 Scourie Pier after refurbishment in 2012. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260Figure 8.74 Application of sprayed concrete to existing mass concrete wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260Figure 8.75 Repointing seawall with sprayed concrete, Dundee, Scotland. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261Figure 8.76 Tied sheet piling being used to strengthen a wall, Portsmouth, Hampshire. . . . . . . . . . . . . . . . . . . . . . . . 261Figure 8.77 Tied steel sheet piling being used to strengthen a wall at Axmouth, Devon. . . . . . . . . . . . . . . . . . . . . . . . 262Figure 8.78 Sheet piling being used to repair a previous sheet piled repair at North Wall Roundhead,

Lyme Regis, Dorset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262Figure 8.79 New, hidden wall behind a reconstructed wall at Crail, Fife, Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262Figure 8.80 The reconstructed wall at Crail, Fife, Scotland. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263Figure 8.81 Remedial works for Anderson’s Quay, Cork, Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263Figure 8.82 Reconstruction of McSwiney Quay, Cork, Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263Figure 8.83 Collapsed portion on Wandesford Quay, Cork, Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263Figure 8.84 Reconstruction of Wandesford Quay, Cork, Ireland. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264Figure 8.85 Phases 1 and 2 reconstruction works at Penrose Quay, Cork, Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264Figure 8.86 Remedial works at Glanmire Road, Cork, Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264Figure 8.87 Remedial works at George’s Quay, Cork, Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265Figure 8.88 Encasement of harbour wall at Saundersfoot, Dyfed, Wales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265Figure 8.89 Cross-section of quay wall and retaining wall at Saundersfoot, Dyfed, Wales . . . . . . . . . . . . . . . . . . . . . . 265Figure 8.90 Design for increasing the height of the wall on the left bank of the Monnow, Monmouth, Wales . . . . . . 266Figure 8.91 Design for increasing the height of the wall on the right bank of the Monnow, Monmouth, Wales . . . . . 266Figure 8.92 Design for increasing the height of Bakers Quay, Barnstaple, North Devon. . . . . . . . . . . . . . . . . . . . . . . . 266Figure 8.93 Original condition of seawall at Blue Anchor in 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267Figure 8.94 Completed scheme comprising a non-standard wall and parapet providing both containment and

seating, while evoking thoughts of ocean liners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267Figure 8.95 Limpet cofferdam used for quay repairs at Harwich, Essex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

TablesTable 1.1 Relevance of chapters for different end users. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5Table 1.2 Relevance of chapters to support different activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6Table 2.1 Changes to functional requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9Table 2.2 Ownership and responsibilities at the Dawlish seawall, Devon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Table 2.3 UK organisations providing guidance on legal obligations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17Table 2.4 Waterfront wall activities and relevant sections of the guide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Table 2.5 Summary of health and safety law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Table 2.6 Summary of transport law and authorities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21Table 2.7 Summary of land drainage and flood risk management law. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Table 2.8 Summary of environmental law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Table 2.9 Statutes and policies for planning permission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Table 2.10 Summary of consent to work in watercourses law. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Table 2.11 Summary of marine licensing law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31Table 2.12 Recommended maintenance costs for quays and river walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35Table 4.1 Useful sources of approaches for the derivation of loading event probabilities. . . . . . . . . . . . . . . . . . . . . 112Table 4.2 Alternative groups of risk criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117Table 4.3 Suggested criteria for TOR to human life in the UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118Table 4.4 Type, purpose and frequency of inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130Table 4.5 Condition assessment rating scale and definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130Table 4.6 Example condition assessment rating table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

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Table 5.1 Further information on topics related to this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149Table 5.2 Programme of maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152Table 5.3 Programme of repairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152Table 5.4 Primary failure modes that may result from deterioration processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154Table 5.5 Adverse effects of encroachments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155Table 5.6 How to prevent common causes of settlement and subsidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157Table 5.7 How to prevent common causes of issues related to seepage/drainage . . . . . . . . . . . . . . . . . . . . . . . . . . 159Table 5.8 Causes of instability in old waterfront walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160Table 5.9 Crack-related issues and management measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162Table 5.10 Overview of methods of mitigating marine borer attack in timber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166Table 5.11 Summary of potential deterioration mechanisms associated with woody vegetation on/near

waterfront walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168Table 5.12 Culvert and discharge pipe components and their maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169Table 7.1 Diagnostic approach to wall failure – simple cause and effect examples . . . . . . . . . . . . . . . . . . . . . . . . . 207Table 7.2 Matrix relating evidence, types of failure and possible causes of problem . . . . . . . . . . . . . . . . . . . . . . . . 208Table 7.3 Detailed possible causes of problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209Table 7.4 Aeration coefficients for broken wave loads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220Table 7.5 FoS against overturning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226

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11 Introduction

1.1 BACKGROUND TO THE GUIDEThe period of the Roman Empire provides many examples around the Mediterranean of waterfront walls and breakwater developments making use of sophisticated underwater construction techniques, the use of driven piles, masonry construction and the incorporation of cement into waterfront structures. In the UK and Europe, it was common through the Middle Ages and later, for traditional wooden sailing ships to ‘take ground’ to load/discharge their cargos. As a result, the start of the construction of any significant waterfront walls in the UK mainly dates from the early 18th century, when royal assent was given for the construction of a ‘wet dock’ at Rotherhithe. This was followed by the Brunswick Dock at Blackwall in 1789 and the West and East India Docks and London Dock in the early part of the 19th century. Cornick (1968) provides an historical overview.

The 18th century was also the ‘golden age’ of canal building. Before 1700, most inland waterways in Britain were built by landowners to carry agricultural produce in southern England. However, in that year the Aire and Calder Navigation river and canal system was opened, connecting Leeds to the Humber ports at Goole. It was built by Yorkshire entrepreneurs, primarily textile merchants and coal owners, and is still a busy waterway today. The early 18th century saw the formation of most of Britain’s important canals and the volume of goods carried increased rapidly. By 1850 approximately 4800 miles of inland waterways had been constructed in Britain. This work continued into the 19th century with the construction of the Forth and Clyde canal, linking the Firth of Forth and Firth of Clyde at the narrowest point in the Scottish lowlands completed in 1790, the Caledonian Canal linking Inverness and Fort William completed in 1822, and the Manchester Ship Canal linking the Mersey with Manchester via the Irwell, which opened in 1894.

An indication of the extent of waterfront walls throughout the UK may be gained from the following:

ªª there are over 300 commercial and historic harbours in the UK with old masonry or blockwork breakwaters or quay walls

ªª there are thousands of miles of canals, which include quays, locks, retaining walls and bridge abutments

ªª many sea defence walls come within the definition of ‘old waterfront walls’

ªª roads and railways have many retaining walls and bridge abutments fronting on to water

ªª rivers and estuaries, particularly in built-up areas, have many miles of walls on their banks for river training, flood protection and building foundations.

There is a great variety in the design of these waterfront walls, with the oldest type being a simple wall of masonry blocks placed on some sort of foundation to form an early type of gravity wall. These early walls were generally curved in cross-section to match the shape of the wooden vessels of the time. A description of a selection of walls is given in Chapter 3. Many of these descriptions and drawings were obtained from the archives of the Institution of Civil Engineers (ICE), while other sources of historic information include, for example, the archives of the Canal and River Trust. However, it should be noted that even where there are drawings available the original design criteria will probably be unknown. Potential sources of archive material and historic data is further discussed in Section 6.4.

Over time the use of a wall may have changed or it may have been neglected. This is particularly true where ownership of the wall is unclear or unknown, resulting in an ‘orphan structure’ with no obvious responsibility for its maintenance and preservation. Often a once-neglected wall may now be seen as an attractive part of a new waterfront development scheme, therefore it may be subjected to a change of service conditions.

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Authorities responsible for waterfront walls include both public and private organisations and vary from those with considerable engineering expertise and resources down to those with little or no in-house engineering knowledge. In many cases those responsible for waterfront walls may be unfamiliar with the problems associated with this kind of structure and in particular the effects that water behind, under, in front and inside the wall may have on the structures. These effects and consequential loads are considered in more detail in Chapter 7.

Inspection and assessment of the structural integrity and stability of the walls can be difficult and costly, particularly where there is no information available on the original design or much of the wall is permanently buried or submerged. If modern design standards are applied when assessing old waterfront walls then theoretically such calculations are likely to indicate that such walls are not stable, even though they are still standing after many years. Other approaches may need to be considered when assessing the condition of walls. Assessment involves consideration of ground conditions in the foundations and behind the wall, as well as the integrity of the wall itself. Investigation requires not only visual inspection, but may require specialist knowledge and equipment, and the application of appropriate inspection techniques. Chapter 6 of this guide identifies and describes some of the techniques available.

The methods of maintenance and rehabilitation need to take into account engineering, environmental and financial factors and methods must be safe, practicable, effective and appropriate for the future use and life expectancy required of the structure. Schemes involving major rehabilitation also require careful consideration of future maintenance costs and the preservation of the appearance for aesthetic reasons. Particular skill is needed to ensure that problem areas are correctly identified and understood, and that the most cost-effective course of inspection, assessment, repair and rehabilitation is undertaken.

Since the original guide was published in 1992, the approach to risk management of vital infrastructure such as waterfront walls, and the techniques for the management of inspections, maintenance and rehabilitation has developed and improved. In addition, new inspection methods and repair techniques have become available to the owners of waterfront walls. The guidance provided here is primarily based on UK data and practice, but will also be applicable to similar structures in other parts of the world.

1.2 TARGET READERSHIPThis guide is addressed primarily at owners or managers of old waterfront walls who have responsibility for their continuing inspection, repair and maintenance. It also provides expert guidance for surveyors, engineers and contractors who may be involved in the inspection, assessment and design of repair, remedial and refurbishment works and in carrying out such works.

The primary objectives of the guide are to assist owners, asset managers, engineers and contractors to:

ªª understand the fundamentals of historic waterfront wall design and construction techniques

ªª provide guidance on risk management, legislation and funding issues

ªª identify and describe techniques for the inspection, management maintenance and repair of these structures.

In Section 1.5, the structure of the guide is outlined along with a table, which highlights the relevance of each chapter for different stakeholders and users.

1.3 USE OF OLD WATERFRONT WALLSWaterfront walls can be found in a wide variety of locations forming all or part of essential infrastructure. Uses include:

ªª elements of dock and harbour complexes

ªª protective breakwaters

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1ªª river and canal locks

ªª entrance locks to impounded docks

ªª river training walls

ªª waterway walls forming the edge of the water channel in canals

ªª coastal protection structures

ªª bridge abutments

ªª piers

ªª foundations for waterfront development.

In this guide old waterfront walls are defined as:

ªª gravity walls of masonry, concrete blockwork, brickwork or mass concrete with vertical or near vertical exposed faces fronting on to the sea, river, canals, lakes or docks

ªª being currently or formerly used as quays, locks, flood defences, coast protection, piers, breakwaters, waterway walls forming the edges of waterway channels, particularly on the towpath side, retaining walls or bridge abutments

ªª being composed of thin masonry facings to rock or cohesive soil, but exclude revetments, sloping sea defences, dams, sheet piled walls and reinforced concrete structures.

Within both commercially active and historic or disused port and harbour complexes and canals, such walls can be found as:

ªª conventional quay walls – where the water level will vary with the tide

ªª wet docks – where the level of water is constantly impounded at a consistent level and vessel access is gained through a locking system

ªª dry docks – where water can be pumped out to allow access to the hull and keel of vessels in the dry.

Each of these structures requires careful consideration, particularly with respect to the loadings imposed by water pressures on the structure. In canals and waterways the rapid increase/draw-down, particularly in locks, can cause its own extreme loading. Similarly breakwaters, river training walls and bridge abutments can be subject to both hydrostatic and dynamic water loads from waves and currents. These issues are discussed further in Chapter 7.

This guide aims to provide an understanding of the historical designs and forms of construction of such walls, and to provide guidance on the tools and techniques available for the inspection, repair and rehabilitation of such structures to maintain and preserve this valuable infrastructure.

1.4 SCOPEThis guide is concerned specifically with the inspection, maintenance and rehabilitation of old waterfront walls.

Inspection is defined as a routine inspection, both visual and intrusive, and structural evaluation leading to recommendations for maintenance or rehabilitation work.

Maintenance is defined as a periodic small-scale works to repair damaged parts of a wall or to prevent further deterioration. Such works are usually classified as ‘revenue works’ and exclude major reconstruction or rehabilitation.

Rehabilitation is defined as major works to fully restore a wall to its original state or to upgrade it to a new standard or function. Such works are usually classified as proactive planned maintenance or ‘capital works’. However, note that this guide does not cover the:

ªª design of new walls

ªª repair of structures behind the wall unless an integral part of the wall rehabilitation. (However, the effect of features behind the wall on wall performance is considered).

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The guide emphasises the importance to the owner or manager of an old waterfront wall of being able to:

ªª understand the basis for the original design of the wall, by providing examples of typical structures used in early construction

ªª understand the current functional requirements of the wall structure and be able to inspect and assess the capabilities of the wall

ªª recognise the responsibilities of ownership and interfaces with third parties who may have an interest or statutory obligations. Assessing these third party interests may also assist owners, particularly private or small organisations, to identify funding sources to help with rebuilding or maintaining their structures.

1.5 STRUCTURE OF THE GUIDE

1.5.1 OverviewThe guide comprises eight chapters. The flow chart (Figure 1.1) identifies the overall structure and key contents. This flow chart is repeated at the start of each chapter, with the key contents of that chapter identified.

Management actionsAdministrative context

Physical context

Severe event(Section 5 .5)

Management of risk(Sections 2 .1 to 2 .3)

Responsibilities (Section 2 .4)

Powers(Section 2 .5)

Beneficiaries(Section 2 .8)

Funding(Section 2 .9)

Framework for decisions (Section 4 .3)

Risk analysis(Section 4 .4)

Operations(Section 5 .2 to 5 .3)

Monitoring and inspection

(Sections 4 .6 to 4 .7)

Regulations and consents

(Sections 2 .6 to 2 .7)

Decision on intervention

Maintenance, repair and rehabilitation (Sections 5 .4 and

Chapter 8)

Physical form and purpose

(Chapter 3)

Physical processes (Section 6 .3)

Loads(Sections 7 .1 to 7 .3)

Wall stability(Section 7 .4)

Historical data(Section 6 .4)

Performance assessment(Section 4 .5)

Data acquisition (Section 4 .7)

Data management (Section 4 .8)

Wall investigation (Sections 6 .5 to 6 .9)

Figure 1.1Overall structure of the guide

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1To further assist Table 1.1 identifies the relevance of each of the chapters for different end users.

Following this introduction, fundamental issues are discussed in Chapter 2, which considers risk management, legislation and funding issues, and Chapter 3, which considers the functions, forms and failures of old waterfront walls. Guidance on the management of waterfront walls is given in Chapters 4 and 5, with Chapter 4 considering performance assessment, risk attribution, inspections and data collection and Chapter 5 providing guidance on operations and maintenance.

Chapters 6 and 7 provide a tool box with methods to enable users to carry out assessments of site characterisation and data management in Chapter 6 and tools required for identification of physical processes and assessments of infrastructure in Chapter 7.

Finally Chapter 8 provides guidance based on the practical maintenance and rehabilitation of actual structures and includes a series of case studies.

1.6 RELEVANCE TO DIFFERENT END USERSTable 1.1 Relevance of chapters for different end users

Stakeholder/user

Chapter

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1 2 3 4 5 6 7

Planner

Developer

Structure owner

Asset manager

Geotechnical engineer

Hydraulic engineer

Risk analyst

Designers

Contractor

Emergency planners and responders

Environmental organisation

Educational institution

Key

= high = medium = low

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1.7 ACTIVITIES INVOLVED IN THE MANAGEMENT OF WALLS

The owner or manager of an old waterfront wall has responsibility for:

ªª ensuring the wall meets its functional objectives

ªª ensuring any planned changes do no compromise the integrity of the wall and its ability to meet its functions

ªª understanding the assets being managed in terms of their structure and maintenance requirements

ªª managing a budget and prioritising expenditure by adopting a risk-based approach

ªª optimising expenditure and investment including in preventative maintenance by following good asset management and operation and maintenance (O&M) practices

ªª understanding legal responsibilities

ªª understanding the potential for obtaining funding via grants and third parties.

Table 1.2 Relevance of chapters to support different activities

Activity

Chapter

Intr

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1 2 3 4 5 6 7 8

Establishing functional objectives

Assessing the effect of changes in use Understanding the structure and maintenance needs

Prioritising work on the wall

Asset management and maintenance Appraising loads and associated ground and water conditions

Appropriate repair and remediation options

Legal responsibilities

Funding via third parties

Key

= high = medium = low

This guide will assist in addressing these responsibilities.

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2 Management – risk, responsibilities and funding

2.1 OVERVIEWChapter 2 sets old waterfront walls within the wider context of risk management, responsibilities and funding. General principles for old waterfront walls management are introduced. This section also presents the legislative issues, duty of care and funding issues associated with their management and maintenance. Figure 2.1 provides an overview of the chapter.

Management actionsAdministrative context

Physical context

Severe event(Section 5 .5)

Management of risk(Sections 2 .1 to 2 .3)

Responsibilities (Section 2 .4)

Powers(Section 2 .5)

Beneficiaries(Section 2 .8)

Funding(Section 2 .9)

Physical form and purpose

(Chapter 3)

Physical processes (Section 6 .3)

Loads(Sections 7 .1 to 7 .3)

Wall stability(Section 7 .4)

Historical data(Section 6 .4)

Framework for decisions (Section 4 .3)

Risk analysis(Section 4 .4)

Performance assessment(Section 4 .5)

Operations(Section 5 .2 to 5 .3)

Monitoring and inspection

(Sections 4 .6 to 4 .7)

Data acquisition (Section 4 .7)

Data management (Section 4 .8)

Wall investigation (Sections 6 .5 to 6 .9)

Decision on intervention

Maintenance, repair and rehabilitation (Sections 5 .4 and

Chapter 8)

Regulations and consents

(Sections 2 .6 to 2 .7)

Figure 2.1Overview of Chapter 2

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2.2 MANAGEMENT

2.2.1 OverviewManagement of any asset should fulfil the requirements laid out in the policies and strategic asset management plans of that owner/organisation. Usually the main objective is to maintain sufficient functionality or performance, quality, and operational safety while minimising the whole-life costs for the remaining serviceable life of the asset. The formal determination of whether or not the functional requirements of an old waterfront wall can continue to be met is generally the responsibility of a qualified and experienced civil or structural engineer. However the regular inspection, assessment of the quality/condition and operational safety of the structure is generally delegated or devolved to a local technical manager who may be an owner, harbourmaster etc.

The performance, serviceability and safety objectives must first be formulated into aims, which should then be translated into an operations and maintenance (O&M) plan. Normally these O&M plans would be partially derived during the design phase for a new structure, but with old structures where no such plans exist, new plans may need to be created. Chapter 5 discusses asset management and O&M plans in more detail.

2.2.2 Performance requirementsIn establishing management objectives for waterfront walls, it is important to ensure a clear and common understanding of the desired outcome. However, an asset may have multiple beneficiaries, eg a car park retaining wall to a harbour providing a car park and associated revenue for the car park operator, berthing and associated revenue for the harbour operator and flood defence benefits for the local flood authority and potentially the Environment Agency (EA). This greatly complicates the inspection regime and desired outcome, as all parties may or may not be inspecting the asset, and all may have different minimum criteria they consider for the functional operation of the asset.

In situations not covered by legislation or policy, objectives may be set through socio-economic analysis and expert judgement, taking into account societal concerns. For example, such as ensuring the wall is strong enough to withstand loads imposed by the mooring of modern vessels alongside or the use of the land behind for storage of materials or change of use/loading to park vehicles or stack containers etc.

Each component of the structure and the structure as a whole must perform effectively to the extent that it is necessary to meet the objectives. It should be noted that some elements may fail without detriment to the structure’s effectiveness and so failure of an asset is defined as the inability to achieve a defined performance threshold for a given function/functions. Components of a failure process can include slow deterioration over a long period and/or a large number of loading cycles and rapid damage occurring during a single event. Predicting and avoiding failure requires consideration of structural (including geotechnical) integrity during critical loading stages and hydraulic performance. Also, the structure should ideally have a measure of resilience to failure. The forms and functions of old waterfront walls and their potential failure modes are discussed further in Chapter 3, while Chapter 7 presents tools for the analysis of the stability of waterfront walls.

2.2.3 Functional objectives and changePerformance can be defined as the degree to which an asset is able to fulfil its required functions. However these functional requirements may change over time, based on the needs of new owners and operators who may have modified the original structure to fulfil new or additional functions, or have changed their management approaches. Some examples are shown in Table 2.1.

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Table 2.1 Changes to functional requirements

Original function Nature of functional change

Secure berthing and berth occupation by ships Frequency of berthing, type, size (mooring loads) and power of ships (effects of propeller wash and bow thrusters)

Secure platform for dock/port operations and machinery

Frequency of dock operations, type, size and power of cranes and cargo handling equipment

Secure platform for the storage of goods on or immediately behind a quay wall

Change in the type, size, height and weight of goods and cargo handled, particularly with the advent of containerisation

Wave protection reduction Frequency, intensity and duration of storm events

Flood protection Changing water levels and frequency of flood events

Secure foundation for buildings and bridges Renovation, change in use, type, height, weight or extent of adjacent buildings and/or infrastructure

Secure platform/foundation infrastructure (roads, railways, pipelines, services etc)

Renovation, change in use, type, height, weight or extent of adjacent buildings and/or infrastructure

Erosion protection Increased rate of foreshore down cutting/erosion, commencement or increased depth of channel dredging

Soil retention New or change in adjacent land use – commercial/residential development, amenity, recreation etc

Water retention Change in water level management or dewatering and/or frequency of maintenance

For most well-maintained waterfront walls, a gradual decline in functionality may be experienced through general degradation and deterioration in its condition. In addition, a reduction in function may occur as a result of gradually increasing requirements by the owner or operator (eg more vessel movements, bigger berthing vessels, heavier loads, increasing capacity, larger cranes, or higher crest heights). This is not necessarily the case for bridge abutments, where it has usually been the degradation of these assets, rather than results from the change of function that leads to the wall’s demise. However, the Europe-wide load increase of HGVs has resulted in the quantitative failure of many bridge decks and abutments, which has necessitated a comprehensive bridge strengthening programme in the UK. Sometimes new requirements are less demanding than originally designed for such as when commercial port operations cease and harbour use changes to that of recreational marina – a change evident in many former historic coastal shipping ports around the UK.

As well as the ‘technical’ functional objectives there are other objectives for a waterfront wall that should be considered:

1 The economic viability of the structure is a critical aspect and is often captured during cost-benefit analysis, where the consequences and costs of not maintaining the structure (‘do nothing’) is compared to the costs of maintenance (‘do something’). The appropriate economic appraisal methods should be decided on by the owner, irrespective of the holistic differences between economic models.

2 The environmental status of the area where the structure is situated should also be considered when planning its O&M. Where possible, options should be selected that increase the social acceptability and at the same time improve the environmental and aesthetic features of the structure and its environs.

2.2.4 Risk-based approach to wall performanceHistorically, waterfront walls were designed to remain stable and withstand estimated loads and applied forces, which were often based on engineering judgement and limited experience. To avoid failures and to ensure the structures were capable of performing as required a factor of safety (FoS) was usually incorporated in the design. As a result, many countries now have specific national guidelines for the design of new infrastructure assets such as waterfront walls, which define the appropriate factors of safety to be used against failure. The factors of safety may vary depending on the type of structure and the levels of risk associated with the structure.

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While traditionally, this margin is expressed as a FoS, more recently, the introduction of the Eurocodes in Europe has established the use of limit state calculation methodologies for design. This approach incorporates the application of partial factors to actions (loads) or resistances (strengths) or both as an alternative to the ‘global factor’ approach. As circumstances change and loads and strengths vary over time due to functional changes, the structural performance of waterfront walls should be reviewed periodically. The FoS approach only considers single values for all input variables and yields a single output value. So the focus of this guide is on adopting a risk-based (or risk-informed) approach to the management of waterfront walls. The integrity of the wall and the potential risk of failure should be considered for a range of operational conditions. For example, the extent of overflow, overtopping or scour might be investigated for a range of water levels and durations.

Having stated the general approach, it is important that where prevailing national or even regional standards and approaches exist, these standards should be applied. The UK has specific guidelines for the design of waterfront walls

and the appropriate FoS against failure, but only limited guidance on the assessment of existing walls. Detailed guidance on the tools available for analysis of waterfront wall failure is given in Chapter 7.

In addition to considering performance during the whole life of the structure, temporary conditions, which may exist during any refurbishment or repair works, should also be considered. In the case of waterfront walls this is particularly important because there is a risk of failure of retaining walls due to elevated pore water pressures behind them, and diminished passive resistance at the toe that may potentially be generated by the construction process (see Chapter 6). Also, evaluation of likely structural responses during refurbishment or reconstruction should take account of a range of events that might occur including, where appropriate, conditions above and below the selected nominal water level. Allowing for these conditions, appropriate health and safety protection measures for workers and the public should be maintained both during construction and after completion. Guidelines for safety in the construction of coastal and maritime works, which apply equally to any works on waterfront walls carried out over or adjacent to water, can be found in Cruickshank and Cork (2005).

2.3 PRINCIPLES OF RISK MANAGEMENT

2.3.1 OverviewOver time, all waterfront walls will deteriorate. Throughout their life events occur such as storms, flooding, accidental impacts, change in use, structural modification and adjacent development, all of which can influence the fabric, foundations and surroundings of the structure. These factors can affect a walls ability to perform reliably to a desired standard and can increase the risk of failure.

Risk management is the process of firstly identifying, analysing and assessing these risks, and then making decisions about what to do (if anything) to address the risks (see Figure 2.1). Usually this involves taking some action or creating policies or plans to prevent, mitigate or otherwise control the level of risk by reducing it to an ‘acceptable’ or ‘as low as reasonably practical’ (ALARP) level.

An overview of current good practice for risk management in the context of old waterfront walls can be found in CIRIA; Ministry of Ecology; USACE (2013).

Figure 2.2 The process of risk identification, assessment and control

Calculations for failureThe basic objective of any calculations used to analyse potential failure mechanisms in existing waterfront walls is to check that the sum of the resistances to failure (in terms of forces or moments) exceeds the destabilising forces or moments.

Identifying the risk

Understanding the risk

assessment

Creating policies and

plans

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Risk management is an integral part of any asset management system (AMS). It provides a structured approach for organisations to identify and understand the cause, effect and likelihood of adverse events occurring, and how to manage such risks and reduce costs to an acceptable level. It can range from a simple to a complex series of evaluations according to the size and extent of the walls and the potential liabilities they represent to the organisation owning or managing the walls.

The outcomes of an assessment of risk can also be used to:

ªª programme future works

ªª justify funding for maintenance and expenditure on major repairs or refurbishments

ªª prioritise and justify the urgency of works

ªª ensure effective use of limited funds by identifying early works to prevent major deterioration and minimise future cost

ªª identify where the largest benefits and greatest reductions in risk can be achieved.

In some cases the outcomes of a risk assessment can also be used to show that some proposed works are not justified, because the costs may be disproportionately high compared with the potential reduction in risk.

A logical and auditable process of risk assessment, particularly when conducted or audited by a third party, can be used to build a defensible business or safety case, particularly for major owners/operators with large portfolios of infrastructure assets. It can also serve a similar role for the smaller owner/operator of a single asset who may carry out a simple risk assessment where there are conflicting demands on resources.

Risk assessment provides an opportunity for all owners and managers of waterfront walls to improve their understanding of potential modes of failure including their mechanisms, likelihood and consequences. Where appropriate it may be valuable to communicate these insights, in an appropriate manner, to relevant stakeholders such as the local authority (LA), a port authority or the owner of a nearby property, asset or business.

Owners and managers might also consider including a formal risk assessment within a periodic safety review conducted by an independent engineer, or by undertaking a risk assessment workshop involving responsible personnel from within the organisation, perhaps assisted by an external facilitator.

2.3.2 Risk, probability and consequence/hazardThe overall level of risk is a combination of both the probability and the consequences of an event occurring. To calculate this, the following inputs are required:

ªª The probability of a source or ‘trigger’ event occurring, such as an adverse weather event (eg a storm resulting in high waves or high river flows and flooding) or other events potentially hazardous to the asset (an earthquake, vessel impact etc).

ªª The probability of failure of the asset due to the occurrence of the event under consideration.

ªª The probability of long-term degradation of the asset resulting in a future reduction in performance/capacity.

ªª Quantify and determine the probability of undesirable consequences or hazards occurring if the asset fails.

Risk management is about reducing the probability of events of a particular severity occurring and/or reducing the magnitude of the impacts should the event occur.

Useful guidance on risk management, applied to flood and coastal erosion, can be found in Penning-

Identifying failure modes through risk assessmentOne of the most valuable parts of the risk assessment process is the identification of potential modes of failure – recognised as good practice in the UK and overseas. An understanding of potential modes of failure can be used to target inspection and monitoring of waterfront walls in the short- and long-term. This can also form the basis for a risk assessment to inform decisions on whether or not structural or non-structural risk reduction measures can be justified in the longer term.

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Rowsell et al (2013), which is a standalone step-by-step guide to assessing the relationship between the costs and benefits of investment decisions. This comparison should then allow users to identify those risk management plans that represent ‘best value for money’ by being economically efficient.

2.3.3 Risk management strategyAny risk management strategy should include polices that are understandable, proportionate and acceptable. Risk management policies should be derived from the owner/organisation’s objectives (see Section 2.4) and include the minimum acceptable levels of service, design and maintenance standards and a clear understanding of what assets and risks the owner/organisation is responsible and accountable for. The risk management strategy should govern how asset risks will be managed. The owner/organisation should also be clear about how it integrates these into its operational processes. The extent or detail of this strategy may vary from a very simple statement from a owner/organisation to a formal detailed strategy for an owner/organisation responsible for significant infrastructure assets. The risk management strategy should include statements on:

ªª resources available to conduct the inspections and assessments and prepare and implement the management plans

ªª how the risk assessments, data and management plans will be reported, reviewed, recorded and communicated

ªª procedures for making the business case for resources for selected interventions to reduce risks

ªª procedures for managing environmental, health and safety incidents and ensuring legal compliance (eg environmental permitting, health and safety regulations).

2.4 MEASURES AND TOOLS FOR RISK MANAGEMENT

2.4.1 Asset management systems (AMS)The effective control of assets and their management is essential to realise value through managing risks and opportunities, so that the desired balance of cost, risk and performance can be achieved. Managing assets involves the translation of organisational objectives into asset-related decisions, plans and activities, using a risk-based approach. The management of risk can result in the reduction of financial losses, improvements in health and safety, goodwill and reputation, a reduction in environmental and social impacts, and reduction in financial liabilities such as insurance premiums, fines and penalties.

ISO 55000:2014 provides an overview of asset management, the principles and terminology and the expected benefits to be gained from adopting an AMS. It can be applied to all types of assets and by all types and sizes of organisation. It can provide a structured approach for developing, co-ordinating and controlling asset management activities by an organisation over the stages of an asset’s life cycle and for ensuring that these align with the objectives of the organisation.

This guide has been developed to follow the ISO 55000:2014 guidelines.

The data management required for effective asset management and the use of asset management information systems (AMIS) is discussed further in Section 4.7.2.

AMS can also be applied to the day-to-day O&M requirements for old waterfront walls, discussed further in Chapter 5.

PIANC (the World Association for Waterborne Transport Infrastructure) has produced a number of recommendations and guidelines for the inspection and asset management of waterborne transport infrastructure, which are relevant to old waterfront walls (see PIANC, 1998, 2008 and 2013).

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2.4.2 TheidentificationofthreatsandconsequencesIn asset management, the first stage in the identification of risks is the process of recognising and recording the events that could possibly pose a threat to the asset under consideration. This process should identify the causes and source(s) of the events, situations or circumstances that would have a material impact upon the asset, human lives, the environment and the local economy.

Factors or characteristics that could be included in the identification of events that may pose a threat to old waterfront walls are:

ªª hydro-meteorological and seismic events, eg storms and storm surges, waves, currents, floods, earthquakes

ªª gradual long-term trends in sea level rise

ªª gradual physical deterioration, ie deterioration of structural condition and its probability of failure under normal loads

ªª erosion of structures, particularly those exposed to waves and/or currents such as coastal protection structures or river structures subject to fast flowing water

ªª third party interference, ie vandalism or terrorism, accidental impact/damage, effects of adjacent development including excavations, foundation activity, utility work, increased ground loading and risk of introducing destabilising forces (eg through groundwater build-up)

ªª operational threats, ie those arising from the way the asset is modified, managed, maintained and operated to meet organisational objectives.

To determine these characteristics, knowledge of previous events may be used. However for rare events this may not be sufficient and also the circumstances (eg the threats to the structure) may have changed. It is necessary to use appropriate predictive calculations to assess the probabilities and magnitudes of all possible events.

There are many approaches to the identification of potential threats and subsequent effects (see Section 4.3). The potential impacts or consequences arising from such threats can be identified and might include:

ªª injury or loss of life

ªª financial loss or penalty (business liability)

ªª loss of useful land and/or adjacent infrastructure

ªª effect on navigation (eg loss of water from canals or gradual infill of navigable channels)

ªª flooding

ªª loss of future beneficial use with changing circumstances

ªª collapse of structure into navigable fairway

ªª environmental damage

ªª damage to reputation

ªª legal non-compliance.

2.4.3 Risk analysis – the tiered approachRisk analysis combines the probabilities and consequences of failure. A tiered approach is a risk-based approach in which, following a preliminary risk assessment, the amount of effort put into further investigation, analysis and assessment is adjusted according to the severity of the problem and the magnitude of the consequences of failure. In this way the effort expended may be proportional to the level of perceived risk. Risk analysis can be time-consuming and expensive, so adopting a tiered approach can bring savings. In addition, this approach can be used throughout all aspects of the risk analysis process, with the effort used at each stage being proportionate to its relative importance (see Figure 2.3).

CIRIA, C74614

Figure 2.3 An example of a tiered approach to risk analysis (UK approach) (from CIRIA; Ministry of Ecology; USACE, 2013)

A phased approach can also be used where appropriately detailed or accurate data is not available. For example, where available information about wall materials is limited, a desk study and simple inspection and/or sampling may be used initially. This may then be followed up by detailed surveys, materials testing and other investigation methods if appropriate.

Section 4.3 discusses the components and process of risk analysis in further detail and the analysis of potential failure modes of old waterfront walls is discussed in detail in Chapter 7.

2.4.4 Risk evaluationThe process of examining and judging the significance of estimated risks is termed ‘risk evaluation’.

The Health and Safety Executive (HSE) has a well-established approach to evaluating the significance of risks called the tolerability of risk (TOR) framework described in HSE (2001). It is widely used for regulating the risks to society and the public that are associated with hazardous industries, but it can also be used to evaluate the risks associated with infrastructure assets. Risks to other entities, such as businesses, or to the asset owner/operator, can also be considered in the risk evaluation process. This approach provides an opportunity to manage infrastructure assets using a framework that is common to all major hazards.

Risk management uses the findings of a risk assessment to consider new options, or improvements to existing measures, to prevent, control or mitigate risks. However, risk cannot be entirely eliminated and under the TOR framework, the process of risk evaluation is not complete until it has been demonstrated how the risk can be reduced to be ALARP.

Risk evaluation, and its specific application to waterfront walls, is discussed further in Section 4.3.

2.5 ROLES AND RESPONSIBILITIES

2.5.1 Ownership and responsibilitiesOverall responsibilities as an owner or manager of an old waterfront wall are given in Section 1.6. However, ownership and responsibility, as defined by local by-laws and acts, and the permissive powers of regional authorities, may often be split. Many old waterfront walls provide multiple functions. For example, while very few old waterfront walls are formally designated as flood risk assets, many serve a flood defence function and the key responsibilities and duties of the various bodies, organisations and individuals involved need to be clearly understood. Many organisations may have a responsibility or an influence on a waterfront wall and, in practice, repair or rehabilitation of a structure may entail redefining responsibilities and apportioning the costs of the work between interested parties.

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Table 2.2 identifies the stakeholders with responsibilities for the Dawlish seawall, a structure that protects the main railway to Devon and Cornwall, located within a SSSI and destroyed in the storms of January 2014.

Table 2.2 Ownership and responsibilities at the Dawlish seawall, Devon

Party or organisation General responsibilities SpecificresponsibilityinDawlishseadefences

Network Rail To run and maintain the railway linesTo run the railway lines adjacent to the Dawlish seawall and to maintain the seawall (under the South Devon Railways Act 1844)

Natural EnglandTo protect the countryside of England and is the designated body for Areas of Outstanding Natural Beauty

To award grant-in-aid to LAs for upkeep and improvements to the South West Coastal Path

DfTTo work in tidal waters requires the consent of the Secretary of State (SofS) in relationship to navigational issues

Defra

Issuing licences for offshore dredging and dumpingAlso responsible for coast protection, although this function is delegated to Teignbridge District Council as coast protection authority, and EA in terms of strategic approval and approval of funding

Issue licences if required

Dawlish Town Council

Teignbridge District Council manages all applications for planning permission and are charged with producing the detailed Neighbourhood Plan

Dawlish Town Council is a consultee in the planning process handled by Teignbridge District Council, although repair and maintenance does not require planning consent

Teignbridge District Council Responsible for coastal protection and planning

Responsible for planning issues. Consent to carry out works is required from Teignbridge District Council under the Coast Protection Act 1949

EA

The EA and the relevant lead local flood authority (LLFA) (Devonshire County Council) exercise a supervisory role over all matters relating to flood defence. The EA has a ‘strategic overview’ role for all flood and coastal erosion risk management (FCERM), is responsible for the approval and allocation of all capital funding (FCERM-GiA) on the coast, and is the competent authority for implementing the requirements of the WFD

Is responsible for approving capital works under its overview role and under the WFD

Devonshire County Council (DCC)

Devon County Council are the LLFA and together with the EA have a supervisory role for all matters relating to flood defence

The Crown Estate Ownership of the foreshoreAmbiguous, an agreement with Great Western Railway in 1909 allowed the construction of groynes

Marine Management Organisation (MMO)

The MMO enforces the Marine and Coastal Access Act 2009

MMO are lead for issue of Marine licenses and will consult with other parties, eg DfT for navigation, EA for flood defence consent, to give licences for any work carried out below mean sea level that may affect navigation or other issues

For many waterfront walls, particularly historic seawalls and breakwaters, ownership, and the responsibility for maintenance, is unclear, and the assets can be considered as ‘orphan structures’. In some cases the concept of local community ownership (localism) arises, so although not the legal owners, a community may have an interest in the asset. For example, the community use of LA piers for sea fishing, and promenades used by walkers/tourists. The concept of community ownership and community benefits may help with external funding or justifying expenditure, especially if there is a tourist function that can be given a value.

CIRIA, C74616

2.5.2 Legal considerations and obligationsThe following legal considerations may determine an obligation to maintain an old waterfront wall:

ªª the owner has a ‘duty of care’ that structures should be safe for workers who use them and members of the public who pass or visit them, and complies with any relevant local regulations

ªª the statutory obligation of landowners to maintain rights of way, such as footpaths, towpaths, promenades etc

ªª the requirement for organisations that have been set up by an Act of Parliament to maintain their structures and to fulfil certain functions (flood defences, coast protection, harbours to provide storm protection and specified water depths, canals and waterways to provide minimum navigation widths and depths etc)

ªª obligations written into leases and other legal agreements

ªª the requirement to maintain structures of historical interest in an adequate state of repair, including ‘listing’ of buildings and structures, ancient monuments, and other special local regulations laid down in conservation areas and in local or national planning legislation.

A list of organisations that can provide further guidance on the more important legislative obligations relating to old waterfront walls is given in Table 2.3. See also EA (2010a).

In addition to these legal considerations and obligations there are a number of UK and EC regulations covering environmental and health and safety issues related to the management and execution of repairs and remedial works. These are considered further in Section 2.6.

2.5.3 Other considerationsSustainable development recognises that the three ‘pillars’ of the economy, society and the environment are interconnected:

1 Economy: irrespective of the legal considerations mentioned in Section 2.5.2, most owners and organisations will wish to keep their waterfront walls in a state of good repair for commercial reasons. They will wish to ensure that the walls remain suitable for their intended function and that they do so at the least possible cost. The most cost-effective way of preserving the required standard of services is to have a programme of maintenance and rehabilitation.

2 Society: in many instances, and particularly when existing structures are being incorporated into a new development, it is in the best interests of the owner/developer to maintain the old waterfront walls in a state of good repair. This is most important when the success of the development depends on the aesthetic qualities of the site. Commercial influences are always important, but there is also often pressure from local groups to keep certain heritage and historic areas in good condition.

3 Environment: EC Directive 85/337/EEC (the EIA Directive) implies that all owners, engineers and managers who are directly responsible for the maintenance and rehabilitation of waterfront walls have a moral obligation to be aware of the environmental effects of any works that they are planning, or the effect of allowing a structure to fall into disrepair. There are other EU Directives that may have an influence on the management of waterfront walls (see Section 2.6).

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Tabl

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CIRIA, C74618

2.6 LEGISLATIVE FRAMEWORKSome organisations (under statutory laws) may not know or fully understand their legal responsibilities as owners or managers of old waterfront walls. This section is intended to help those to fully understand the key responsibilities and duties of the bodies, organisations or individuals, and to assist in identifying who to contact in respect of investigation, assessment, maintenance and repairs or refurbishment activities.

If owners/organisations are unsure of their responsibilities over ownership of an old waterfront wall, a useful first source of information may be the engineering department in the relevant LA, which may advise on owners’ responsibilities and obligations.

This section summarises the legislative framework affecting old waterfront walls in navigable canals, watercourses, estuaries, coasts and floodplains in the UK and Ireland at the time of writing. This text is based on guidance by Kirby et al (2015). It is intended to provide information on the legal considerations regarding the design, construction, maintenance of waterfront walls. It is not intended to be comprehensive or definitive and the user is advised to consult a competent legal expert for definitive advice.

The law generally confers rights, powers and duties on the owners of assets and the relevant statutory authorities:

1 Rights: the ability to act or do something, usually conferred as part of land ownership. There is a general right to construct or maintain a structure subject to consent and compliance with other statutory requirements.

2 Powers: a legal entitlement to do something, which comes from legislation. The powers are usually given to a government or other statutory body, eg the powers to carry out and to issue consent for construction of flood defences.

3 Duties: requirement to do something, eg apply for consent, and are derived from statute. Duties can also arise from case law.

The onus to adequately maintain waterfront walls and to ensure they are adequate for their purpose is on the owner, or the highway authority if it is part of the highway, or the operating authority if it is a land drainage, flood management or coastal protection asset. However, it should be noted that many third parties own highway and flood defence structures and the onus to maintain them remains with the owner. The EA regularly serve notice on third parties instructing them to maintain their structures for the wider flood defence benefit.

Table 2.4 summarises the activities involved in waterfront wall management and relevant sections of the guide.

Table 2.4 Waterfront wall activities and relevant sections of the guide

Activity Section of the guide

Anticipation Emergency planning Section 2.6.1

Assessment Survey, inspection and monitoring Section 2.6.1

PreventionMaintenance measures Sections 2.6.1, 2.6.6, 2.6.10,

2.6.11, 2.6.12, 2.8

Debris management Sections 2.7, 2.8

2.6.1 Health and safety lawHealth and safety law applicable to waterfront wall management in the UK and Ireland is summarised in Table 2.5. Advice on health and safety issues can be obtained from the Health and Safety Executives in England, Wales, Scotland, Northern Ireland, the Channel Islands and the Isle of Man, and the Health and Safety Authority (HSA) in Ireland. In addition, the Harbours Act 1964 places duties on municipal

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ports, the Department for Transport (DfT) and Canal and River Trust to maintain ports and their facilities for safe navigation.

Table 2.5 Summary of health and safety law

Issue England Wales Scotland Northern Ireland (NI) Ireland

Public safety and emergency planning Civil Contingencies Act 2004 None

Health and safety at work

Health and Safety at Work etc Act 1974Construction (Design and Management) Regulations 2007

Health and Safety at Work (NI) Order 1978Construction (Design and Management) Regulations 2007

Safety, Health and Welfare at Work Act 2006

Occupiers’ liability Occupiers’ Liability Acts 1957 and 1984 Occupiers’ Liability Act (NI) 1957

Safety, Health and Welfare at Work (Construction) Regulations 2013

Corporate manslaughter Corporate Manslaughter and Corporate Homicide Act 2007 Occupiers’ Liability Act

1995

2.6.2 Public safety and emergency planningIn the UK, emergency planning is guided by the fundamental framework for civil protection, the Civil Contingencies Act 2004. This places a duty to assess, plan and advise on designated bodies including emergency responders and asset owners. Category 1 responders are those at the core of any operational, tactical and strategic level co-ordination of the response to the incident. These include the emergency services, health authorities, LAs and the EA, Natural Resources Wales (NRW) and Scottish Environment Protection Agency (SEPA), and the Rivers Agency within the Department of Agriculture and Rural Development (DARDNI). Note that DARDNI is currently not a Category 1 responder.

The roles and responsibilities of Category 1 responders are set out in the Civil Contingencies Act 2004 and they are required to:

ªª assess the risk of emergencies occurring and use this to inform contingency planning

ªª set up emergency plans

ªª set up business continuity management arrangements

ªª arrange to make information available to the public about civil protection matters and maintain arrangements to warn, inform and advise the public in the event of an emergency

ªª share information with other local responders to enhance co-ordination

ªª co-operate with other local responders to enhance co-ordination and efficiency

ªª provide advice and assistance to businesses and voluntary organisations about business continuity management (LAs only).

The majority of organisations that own, operate and maintain waterfront wall infrastructure are Category 2 responders. These include transport authorities, utility companies, strategic health authorities and the HSE. Category 2 organisations are ‘co-operating bodies’. They are less likely to be involved in the heart of planning work, but will be heavily involved in incidents that affect their own sector. Category 2 responders have less duties – co-operating and sharing relevant information with other Category 1 and 2 responders.

Local resilience forums provide an environment for bringing together representatives from Category 1 and Category 2 responders and to build multi-agency partnerships. These work as a collective body, co-ordinating and collaborating effective emergency management strategies for the local or regional community.

In Ireland, there is no specific legislation with regard to flood emergency management. Emergency planning is guided by government policy and is implicit in the principal response agencies’ existing roles (local authorities, An Garda Síochána and Health and Safety Executive Northern Ireland). Useful references include DoEHLG (2006) and DoEHLG (2013).

CIRIA, C74620

2.6.3 Health and safety at workThe management, maintenance and rehabilitation of old waterfront walls are influenced by the Health and Safety at Work Act (HASAW) 1974 (UK), Health and Safety at Work (NI) Order 1978 and the Safety Health and Welfare at Work Act 2005 (Ireland) and their subordinate regulations. These aim to protect the safety, health and welfare of workers, as well as others affected by the action of those at work.

Council Directive 92/57/EEC (the Health and Safety Directive) sets minimum safety and health requirements at temporary or mobile construction sites and aim to prevent risks by establishing a chain of responsibility linking all the parties involved. The directive is transposed into national law by delegated legislation (see Table 2.5). They apply to all construction projects, including the design and construction of new structures, and the maintenance, repair or demolition of existing structures, although routine maintenance is excluded. The directive also applies to site investigation such as boreholes or coring.

Additional duties apply if the project is notifiable to the health and safety authority, ie work is planned to last more than 30 days or 500 person-days. For notifiable projects, the client must appoint a CDM co-ordinator in the UK or a project supervisor for the design process (PSDP) and project supervisor for the construction stage (PSCS) in Ireland.

Note that the following section is up to date at the time of writing and is based on the draft Construction (design and management) guidance published by the HSE (2015a). However, the content of the draft guidance may be subject to change before Parliamentary approval, which is expected on 6 April 2015 (ie after completion of this guide). Also note that from 6 April 2015, a six month transitional period will be in place between CDM 2007 and CDM 2015 for projects that are already underway (HSE, 2015b).

At the time of writing, there is no approved code of practice (ACOP) to accompany CDM 2015 (as there was for the CDM 2007). Originally the HSE intended that the ACOP be abandoned. However, following consultation this decision has been partially reversed and it is anticipated that an abridged version will be published to accompany the new regulations at a later date.

Guidance on CDM 2015 should be obtained directly from the HSE to ensure the most recent information is considered.

The main duties of the CDM co-ordinator are to:

ªª advise and assist the client with their duties

ªª notify details of the project to HSE

ªª co-ordinate health and safety aspects of design work and co-operate with others involved with the project

ªª facilitate good communication between the client, designers and contractors

ªª liaise with the principal contractor regarding ongoing design work

ªª identify, collect and pass on pre-construction information

ªª prepare/update the health and safety file.

The designer must eliminate hazards by design a so far as is reasonably practicable (SFAIRP), and identify and communicate any residual hazards to other parties involved in the work. This could take the form of notes on drawings, written information or a recommended construction sequence. The designer’s risk assessment should consider the safety of the travelling public as well as those operatives working on the site both day and night, and in varying water levels (river/tidal) and flow conditions. The following issues may be relevant to waterfront wall management works, although this list is not exhaustive:

ªª work near water

ªª work in open excavations

ªª work with contaminated ground

ªª survey, inspection, construction or maintenance access risks

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ªª risks if the structure is blocked with debris or catches debris

ªª safe system of work for removing debris

ªª safe system of work for cleaning and maintenance

ªª any risk to the public and, if so, the best way to reduce or eliminate this risk

ªª access for rescue (if required).

2.6.4 Occupiers liabilityOccupiers owe a duty of care to visitors (and trespassers) under the Occupiers’ Liability Act 1957. An occupier is defined as a person who has control over premises such as a seawall, harbour walls, bridges, locks and canals etc and the duty is owed if the occupier is aware of any danger or has reasonable grounds to believe it exists. This may mean installing warning signs and/or deterrents such as fencing at the structure.

2.6.5 Corporate manslaughterAn organisation involved in managing an asset or design or construction work may be guilty of corporate manslaughter (or corporate homicide in Scotland) if its activities are managed or organised in such a way that causes a person’s death and amounts to a gross breach of a relevant duty of care owed by the organisation to the deceased. The offence is concerned with corporate liability and does not apply to directors or other individuals who have a senior role in the company or organisation. Existing health and safety offences and gross negligence manslaughter continue to apply to individuals and prosecutions against individuals will still be taken where there is sufficient evidence and it is in the public interest to do so.

2.6.6 Transport lawTransport law applicable to waterfront wall management in the UK and Ireland is summarised in Table 2.6.

Table 2.6 Summary of transport law and authorities

England Wales Scotland Northern Ireland (NI) Ireland

Roads Highways Act 1980 Roads (Scotland) Act 1984 Roads (NI) Order 1993 Roads Act 2007

Railways

Railways and Other Guided Transport Systems (Safety) Regulations (ROGS) 2006

Railways (Safety Management) (Amendment) Regulations (NI 2013

Railway Safety Act 2005

Railways Clauses Consolidation Act 1845

Railways Clauses Consolidation (Scotland) Act 1845

Transport Acts (NI) 1967, 2011

Transport (Railway Infrastructure) Act 2001

CanalsTransport Acts 1962 and 1968British Waterways Act 1995Flood and Water Management Act 2010

Water (NI) Order 1999 Canals Act 1986

2.6.7 RoadsHighway authorities in England, Wales and Scotland have powers of entry for the purpose of survey, inspection, maintenance or other actions at roads, structures and works under the Highways Act 1980 and Roads (Scotland) Act 1984. Highway, bridge or transport authorities must bear the cost of measures required in relation to statutory undertaker’s apparatus if these are affected by major bridge works (and by implication, bridge failure due to hydraulic action) under the New Roads and Street Works Act (NRSWA) 1991. Advance notice of street works must be given except for emergency works, in which case notice must be given as soon as reasonably practicable.

CIRIA, C74622

In England and Wales, highway authorities have powers to ‘search for, dig, get and carry away’ gravel, sand, stone and other materials from the bed of any river or brook flowing through common land, provided that it is not within 50 yards of a bridge, dam or weir. This is subject to consent from the drainage authority or EA/NRW. Consideration should be given to the impact of gravel extraction on natural scour and the undermining of a waterfront wall.

In Scotland, highway authorities are permitted to divert or carry out works to inland waters (natural or artificial) or tidal waters, where necessary to construct, improve or protect a public road (or proposed public road), subject to consultation with the owner or occupier of any land affected, any navigation authority concerned with the waters, the LA and any other statutory body that may be affected by the works.

In Northern Ireland, the Department for Regional Development Roads Service (DRDNI) has a duty to maintain roads (including road bridges). DRDNI also has the power to dredge subject to the consent of the harbour authority if the works fall inside the limits within which a harbour authority exercises its functions, and the consent of the Secretary of State (SofS) and The Crown Estate Commissioners for tidal work.

In Ireland, it is an offence to interfere with or carry out any works that affect a bridge, culvert, retaining wall, embankment or other structure providing lateral or other support for a public road. This could include actions (or inactions) that allow scour to take place, such as dredging or failure to maintain a river-bank. The National Roads Authority Ireland (NRA) has overall responsibility for the planning, management and maintenance of national roads, including road bridges, while county or city councils are the highway authority for regional or national roads and LA for local roads.

2.6.8 RailwaysDirective 2004/49/EC (the Railway Safety Directive) and delegated legislation aim to improve safety on the community’s railways by defining responsibilities and developing common safety targets and methods.

The Directive requires the establishment, in every member state, of a safety authority and an accident and incident investigating body to define common principles for the management, regulation, and supervision of railway safety. Safety authorities in the UK and Ireland are the Office of Rail Regulation (ORR) and Railway Safety Commission (RSC) respectively. The Rail Accident Investigation Branch (RAIB) in the UK and the Railway Accident Investigation Unit (RAIU) in Ireland are independent bodies with a duty to investigate the causes of incidents without apportioning blame, with the aim of improving the safety of railways and preventing railway accidents.

Railway undertakings have a duty to report rail incidents involving, among other things, loss of life, serious injury, derailment, suspension of a railway service for more than six hours or accidents that cause (or might have caused, under slightly different conditions) extensive damage to rolling stock, infrastructure or the environment. Railway undertakings also have a duty to implement such systems as are necessary for the effective management of safety and to evidence these in a safety case.

Rail undertakings in the UK and Ireland have the power to alter, repair, or discontinue maintenance works and do what is necessary to make, maintain, alter or repair the railway, subject to doing as little damage as possible. They also have powers of entry for railway works subject to paying landowner compensation.

2.6.9 CanalsThe canal system of the UK and Ireland was generally developed under Acts of Parliament overlaid by other legislation (Table 2.6). The result is a complex area of law where it is difficult to generalise on the powers and responsibilities relating to canals. The advice of the relevant canal or navigable waterway operator should therefore be sought. The Canals and Rivers Trust took over the activities of British

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Waterways in England and Wales in 2012, while Scottish Canals (SC) is responsible for canals in Scotland and Waterways Ireland, established under the Belfast Agreement in 1999 (HM Government, 1999), is responsible for canals and waterways throughout Ireland.

2.6.10 Coastal protectionResponsibility for the coastline is divided between various authorities in accordance with legislation. Coastal protection authorities (normally the district council or unitary authority depending on which is applicable) are empowered under the Coast Protection Act 1949 to carry out works in their area to protect the coast from erosion. The powers given under the Act are permissive, ie they are not obliged to protect eroding coastlines. Instead, responsibility for management and prevention of erosion rests with the landowner of the site concerned. The construction and maintenance of works to resist coastal flooding in England is carried out by the EA and local authorities in accordance with the Land Drainage Act 1991 and Water Resources Act 1991.

2.6.11 LanddrainageandfloodriskmanagementlawLand drainage and flood risk management law applicable to waterfront wall management in the UK, covering England, Wales, Scotland and Northern Ireland and Ireland is summarised in Table 2.7. Useful guidance on the law in England and Wales is given by Howarth (2002) and ICE (2010).

Table 2.7 Summary of land drainage and flood risk management law

England Wales Scotland Northern Ireland (NI) Ireland

Floods Directive Flood and Water Management Act 2010

Flood Risk Management (Scotland) Act 2009

Water Environment (Floods Directive) Regulations (NI) 2009

European Communities (Assessment and Management of Flood Risks) Regulations 2010

Land drainageWater Resources Act 1991Land Drainage Acts 1991, 1994

Drainage (NI) Order 1973Arterial Drainage Act 1945 and (amendment) 1995

Directive 2007/60/EC (the Floods Directive) establishes a framework for the assessment and management of flood risks, aiming to reduce the adverse consequences for human health, the environment, cultural heritage and economic activity associated with floods in the community. The Directive requires each member state to prepare and maintain flood risk assessments and risk management plans, which must include the impact on infrastructure. The Directive is transposed into national law by delegated legislation (see Table 2.7).

England and WalesLand drainage legislation in England and Wales differentiates between main rivers and ordinary watercourses. The extent of designated main rivers can be located by viewing the main river map on the EA website (see Websites) or by contacting the EA or NRW. The term ‘ordinary watercourse’ describes the remaining watercourses.

The EA/NRW have statutory powers in relation to main rivers in England and Wales respectively. Las and Internal Drainage Boards (IDBs) have statutory powers in relation to ordinary watercourses. Details of IDB locations are available from the Association of Drainage Authorities (see Websites).

The Water Resources Act 1991 and Land Drainage Acts 1991 and 1994 cover powers and duties with regard to main rivers and ordinary watercourses respectively. Designated authorities have powers to construct, maintain or improve works required for the purposes of land drainage or flood risk management. Consent is required to construct or modify structures in, over or under a main river, or other obstructions to flow. Neither Act imposes a duty on designated authorities to repair, remove or construct structures or obstructions.

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Under the Land Drainage Act 1991 (Section 21) a lead local f lood authority (LLFA), IDB, the EA or NRW depending on the designation of the watercourse, can serve notice requiring repairs to watercourses or bridges to be undertaken within a reasonable time. Under Section 24 if an obstruction is raised or altered so as to cause a nuisance, the authority can serve notice requiring abatement of the nuisance.

The Flood and Water Management Act 2010 aims to create a simpler and more effective regime for flood and coastal erosion risk management, with an integrated approach to flood management between local flood risk management authorities, water companies and IDBs under the strategic direction of the EA or NRW. The Act amends the Land Drainage Acts and governs work in watercourses (such as taking things out of it or supporting or diverting the banks). The EA, NRW, local authorities and IDBs have powers to designate structures and features (such as scour protection works) that are believed to affect flood risk as flood management assets and require the owners to seek consent for their removal or modification.

ScotlandThe Flood Risk Management (Scotland) Act 2009 imposes a general duty to manage flood risk in a sustainable way and contribute to sustainable development, promoting a move towards restoring river channels to a more natural form and away from new structures unless in exceptional situations. SEPA has a duty to map and assess artificial structures and natural features with the potential to affect flood risk or the transport and deposition of sediment, which could include scour protection works. The Act repeals the Flood Prevention (Scotland) Act 1961 and Flood Prevention and Land Drainage (Scotland) Act 1997.

Northern IrelandThe NI Drainage Council has powers to designate watercourses, and DARDNI has powers to undertake, construct and maintain drainage works, and to carry out emergency works to them and to make by-laws under the Drainage (Northern Ireland) Order 1973 as amended by the Drainage (Environmental Impact Assessment) Regulations (Northern Ireland) 2001 and Drainage (Amendment) (Northern Ireland) Order 2005.

Consent is required from DARDNI to erect or place any structure in, over or under any watercourse, or carry out any work of alteration or repair on any structure in, over or under any watercourse, if the work is likely to:

ªª affect the flow of water in the watercourse

ªª impede any drainage work

ªª prevent or impede the passage of fish

ªª interfere with, or in any way hinder, the maintenance of the watercourse.

DARDNI may serve notice requiring an occupier to carry out maintenance, and carry out the works and recover costs if the occupier does not carry out the work. DARDNI also has powers to maintain or improve existing works, remove or alter dams, weirs or other obstructions to waterways, construct new works that may be required for the purpose of repairing or improving the waterway, repair, strengthen, alter, replace or renew any existing embankment and, for that purpose, use the sediment removed in the carrying out of works and deposit any material so removed on any adjacent land.

IrelandWaterfront wall management, maintenance and rehabilitation are likely to require consent from the Office of Public Works (OPW) under Section 50 of the Arterial Drainage Act 1945, which states that no LA, railway company, canal company, similar body or industrial concern may construct any new bridge or alter, reconstruct, or restore any existing bridge over any watercourse without consent. Consent is also required to erect, enlarge or alter structures in a watercourse where this might cause flooding of any

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land. On all canals and navigable waterways throughout Northern Ireland and Ireland, permission is also required from Waterways Ireland. Further information, including a guide to applying for consent under Section 50, is available from the OPW and Waterways Ireland (see Websites).

2.6.12 Environmental lawEnvironmental law applicable to waterfront wall management in the UK and Ireland is summarised in Table 2.8.

Table 2.8 Summary of environmental law

England Wales Scotland Northern Ireland (NI) Ireland

Habitats: SSSI and protected species

Wildlife and Countryside Act 1981 and (amendment) 1991

Wildlife (NI) Order 1985 Wildlife Act 1976

Habitats: SAC/SPA and European Protected Species

Conservation of Habitats and Species Regulations 2010

Conservation (Natural Habitats &c) Regulations 1994

Conservation (Natural Habitats &c) Regulations 1995

European Communities (Birds and Natural Habitats) Regulations 2011

Water Framework Directive (WFD)

Water Environment (WFD) (England and Wales) Regulations 2003

Water Environment and Water Services (Scotland) Act 2003Water Environment (Controlled Activities) Regulations (CAR) 2005 (as amended)

Water Environment (WFD) Regulations (NI) 2003

European Communities (Water Policy) Regulations 2003European Communities Environmental Objectives (Surface Waters) Regulations 2009

Fisheries

Salmon and Freshwater Fisheries Act 1975Eel (England & Wales) Regulations 2009

Salmon and Freshwater Fisheries (Consolidation) (Scotland) Act 2003Council Regulation (EC) No 1100/2007 (European eel)

Fisheries (Amendment) Act (NI) 2001Eel Fishing Regulations (NI) 2011

Fisheries Consolidation Act 1959European Communities (Quality of Salmonid Waters) Regulations 1988European Communities (Quality of Shellfish Waters) Regulations 2006

Waste

Environmental Permitting Regulations 2010Waste (England and Wales) Regulations 2011

Waste Management Licensing (Scotland) Regulations 2011

Waste Management Licensing Regulations (NI) 2003

Waste Management (Licensing) Regulations 2004

2.6.13 Habitats DirectiveCouncil Directive 92/43/EEC (the Habitats Directive) aims to conserve internationally important natural habitats, flora and fauna, and sets requirements for plans and projects likely to affect designated Special Protection Areas (SPAs) and Special Areas of Conservation (SACs), known as Natura 2000 sites (or European sites in the UK). Under UK policy, proposed and candidate SPAs and SACs, and Ramsar sites are also given the same protection. The directive is transposed into national law by delegated legislation (Table 2.8).

Works that are likely to affect a European site require an appropriate assessment to assess whether there may be adverse effects on the site. This also applies to proposed works outside the site boundary. An appropriate assessment is distinct from Environmental Impact Assessment (EIA) although some areas may overlap. As a rule, the impact of any work on the environment should be minimised.

Works carried out under permitted development rights that are likely to affect a Natura 2000 site may require LA and environmental authority consent.

For works forming part of a larger scheme, the environmental aspects of the works should be addressed as part of the whole scheme. For standalone works, the designer may wish to consult the planning authority for a decision as to whether environmental assessment may be required or voluntarily submit an assessment with the planning application (in this case, the scheme will likely be treated as an EIA project).

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If works are within a SSSI or other designated site, operations that are prohibited in the site notification must not be undertaken unless consent has been obtained from the relevant environmental authority.

Freshwater pearl mussels and its habitat are also protected under the Habitats Directive and delegated legislation, and the Wildlife Act 1976 (RoI). Work in freshwater pearl mussel habitats can only be undertaken under licence and consent is required from the National Parks and Wildlife Service (see Websites).

More details on the Habitats Directive can be obtained from the relevant environmental authorities (NE, NRW, SEPA, NIEA or the Environmental Protection Agency (EPA) in Ireland).

2.6.14 Water Framework Directive (WFD)Directive 2000/60/EC (the Water Framework Directive) aims to maintain or improve the ecological and chemical status of watercourses and to restore surface waters across Europe to a more natural state (where technically feasible). The WFD defines how this should be achieved through environmental objectives and ecological and chemical targets. The WFD is transposed into national law by delegated legislation (see Table 2.8). The so-called ‘competent authorities’ responsible for its implementation are the EA, NRW, SEPA and the DoECLG.

Competent authorities are required to prepare a river basin management plan (RBMP) setting out environmental objectives and the measures required to achieve those objectives. They must also ensure that the objectives are met in water-related protected areas (eg in relation to drinking waters and bathing waters) in relation to water-dependent habitats and species protected under Directive 2009/147/EC (the Birds Directive) and the Habitats Directive.

Where works, including physical modifications, could potentially affect the status of a water body, a WFD compliance assessment may be required as part of the consent application. For example the Marine Management Organisation (MMO) may require a WFD compliance assessment as part of an application for a marine licence. A WFD compliance assessment should establish whether deterioration in the status of the water body might occur, whether the works could prevent the WFD objectives from being achieved, and whether technically feasible and not disproportionately costly improvement measures might be incorporated into the scheme. While maintenance or restoration works are less likely to affect the status of a water body than a capital project, advice on the need for and scope of a WFD compliance assessment should always be sought from the relevant WFD competent authority.

It is an offence to cause or knowingly permit polluting matter or solid waste to enter surface water or groundwater under the Water Resources Act 1991 in England, Wales and Scotland, the Water (Northern Ireland) Order 1999 and the Local Government (Water Pollution) Act, 1977 in Ireland.

2.6.15 Bathing Water DirectiveCouncil Directive 2006/7/EEC (the Bathing Water Directive) complements the WFD and aims to protect the quality of the environment and human health. The Directive imposes a duty to take adequate measures to prevent, reduce or eliminate short-term pollution of bathing waters, defined as surface waters where a large number of people are expected to bathe. Pollution means contamination that affects bathing water quality and presents a risk to bathers’ health. The Directive is transposed into UK law by the Bathing Water Quality Regulations 2008 (England and Wales), Bathing Waters (Scotland) Regulations 2008, Bathing Water Quality Regulations 2008 (as amended 2011) (ROI), and the Quality of Bathing Water Regulations (Northern Ireland) 2008.

2.6.16 Fisheries DirectivesCouncil Directive 2006/44/EC (the Freshwater Fish Directive) aims to protect or improve the quality of freshwaters that support, or would, if pollution was reduced or eliminated, become capable of supporting, fish. Council Directive 2006/113/EC (the Shellfish Waters Directive) aims to protect waters,

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including shellfish waters, against pollution, and safeguard certain shellfish populations from harmful consequences resulting from the discharge of pollutants into the sea. The Eel (England and Wales) Regulations 2009 aims to recover eel stocks by targeting causes of mortality in eels. Measures to achieve this include making rivers passable and improving river habitat. The directives are transposed into national law by delegated legislation (see Table 2.8).

General provisions relating to fisheries and eels are that it is an offence to cause direct mortality to fish, to obstruct the passage of salmon, trout or eels, to cause the degradation of habitats and to allow any deleterious matter to enter a river, lake, watercourse or estuary or the sea (except under licence). The law imposes the following duties with the potential to affect management of waterfront walls:

ªª minimise disruption to fish passage during the construction or maintenance of works such as scour protection

ªª provide a fish pass to facilitate fish passage past obstructions at all times except during any period when, for natural reasons, the flow of the river is so low that salmon would not reasonably be expected to seek passage

ªª maintain those fish passes, sluices, by-washes or screens to ensure the safe passage of fish

ªª meet water quality standards for suspended solids (among other things) in salmonid and shellfish waters.

2.6.17 Waste Framework DirectiveDirective 2008/98/EC (the Waste Framework Directive) aims to “protect the environment and human health by preventing or reducing the adverse impacts of the generation and management of waste and by reducing overall impacts of resource use and improving the efficiency of such use”. The Directive is transposed into national law by delegated legislation (see Table 2.8).

Waste is defined as “any substance or object which the holder discards or intends or is required to discard” (Defra, 2012). This definition excludes non-hazardous sediment relocated within the same (hydraulically connected) water body, and uncontaminated soil and other naturally occurring material excavated during construction and reused for construction in its natural state on the same site. So excavated or dredged material that has been excavated specifically for construction purposes or will be reused on the same site or watercourse are not classed as waste, but excavated or dredged material that requires treatment before reuse are classed as waste.

The Directive defines a waste hierarchy of prevention, reuse, recycle, recovery and disposal. Member States are required to take measures to ensure that waste management does not endanger human health, harm the environment (water, air, soil, plants or animals), cause nuisance through noise or odours, or adversely affect the countryside or places of special interest.

The disposal of contaminated waste to landfill is affected by Council Directive 99/31/EC (the Landfill Directive), and the WFD can be applied to the underwater disposal of waste.

Regulations vary between countries but in most cases a permit or exemption is required for removal and transport. This may necessitate sampling and testing of the excavated material and the soil at the receiving site.

The EA NRW, SEPA, NIEA or EPA should be consulted before planning to remove material from watercourses.

2.7 COMMON LAW

2.7.1 NuisanceStatutory nuisance arises where there has been an unreasonable interference with a landholder’s interest in the enjoyment of land. For example, in terms of waterfront walls, this could arise due to collapse (and subsequent) failure of a structure, through bank erosion.

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2.8 CONSENT REQUIREMENTSThe consent requirements for waterfront wall works may include:

ªª planning permission, which may include a requirement for flood risk assessment and/or EIA (see Section 2.8.2)

ªª watercourses, which may require environmental assessment and WFD compliance assessment (see Section 2.8.3. Programme constraints are also discussed in Section 2.8.3

ªª marine licence (see Section 2.8.4).

2.8.1 Environmental site surveyAn environmental site survey is strongly recommended at an early stage in the planning process. This enables any constraints to be adapted into proposals and allows an appropriate amount of time for the implementation of necessary mitigation measures, not least as ecological constraints can significantly affect the timing of project implementation. An early awareness of environmental constraints will prevent last-minute changes of plan or design.

2.8.2 Planning permissionPlanning permission may be required for the construction, alteration, repair or removal of bridges or other structures over water, although this does not remove the need for consent for work in watercourses (see Section 2.8.3). Emergency repairs can be completed without planning permission but should be notified to the planning authority with justification as soon as possible. Planning requirements differ between countries and a list of statutes and policies is given in Table 2.9.

Permitted developmentPermitted development rights apply to some works that do not need planning permission. These include works by a statutory body to improve or maintain bridges, to improve, maintain or repair a watercourse or drainage works, or to spread dredging material on land from navigable waterways. Relevant statutes are given in Table 2.9. The local planning authority can advise whether proposed works are permitted development or require planning permission.

Environmental Impact Assessment (EIA)The EIA Directive specifies requirements for an EIA with the aim of protecting the environment and quality of life. This has been transposed into UK and Irish law by delegated legislation (see Table 2.9).

In the UK, the local planning authority will make a decision on the need for an EIA based on the criteria set out in the Directive. Small-scale repair or refurbishment works are seldom likely to meet the criteria for full EIA and in many cases may benefit from permitted development rights. It is good practice to obtain a screening opinion from the LA regardless of the size of the development.

In Ireland, the need for an EIA is governed by a list of projects and threshold limits in the Planning and Development Regulations (DOELG, 2015). The LA may require an environmental statement (ES) for developments below the thresholds if they are likely to have a significant effect on the environment.

Flood risk assessmentWorks that require planning permission and are located within the flood plain are likely to require a flood risk assessment to ensure that flood risk is not increased elsewhere and that only appropriate development takes place in areas at risk of flooding. The requirements of a flood risk assessment are defined by the guidance documents in Table 2.9.

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Table 2.9 Statutes and policies for planning permission

England Wales Scotland Northern Ireland (NI) Ireland

Planning authority Local authority DOENI Local authority

Planning permission

Town and Country Planning Act 1990

Town and Country Planning (Scotland) Act 1997

Planning (NI) Order 1991

Planning and Development Act 2000 and (amendment) 2010

Permitted or exempted development

Town and Country Planning (General Permitted Development) Order 1995

Town and Country Planning (General Permitted Development) (Scotland) Order 1992

Planning (General Development) Order (NI) 1993

Planning and Development Regulations 2001 and (amendment) 2013

Environmental Impact Assessment (EIA)

Town and Country Planning (EIA) Regulations 1999EIA (Land Drainage Improvement Works) Regulations 1999 and (amended) 2005

Town and Country Planning (EIA) (Scotland) Regulations 2011

Drainage (EIA) Regulations (NI) 2001

Planning and Development Act 2000 and (amendment) 2010Planning and Development Regulations 2001 and (amendment) 2013European Communities (EIA) Regulations 1989 to (amendments) 2006

Flood risk assessment DCLG (2012) WAG (2004) The Scottish

Government (2010) DOENI (2006) OPW (2009)

2.8.3 Consent to work in watercoursesConstruction or maintenance work in or near watercourses may require consent and separate consent is required for permanent and temporary works. The consenting bodies, statutes and guidance in the UK and Ireland, are summarised in Table 2.10.

Table 2.10 Summary of consent to work in watercourses law

England Wales Scotland Northern Ireland (NI) Ireland

Work in watercourses

Land Drainage Act 1991Water Resources Act 1991Flood and Water Management Act 2010

Water Environment (Controlled Activities) (Scotland) Regulations 2011

Drainage (Northern Ireland) Order 1973

Arterial Drainage Act 1945

Consenting bodies EA or NRW, IDBs, LLFAs SEPA DARDNI OPW

England and WalesA flood defence consent is required for works affecting a statutory main river from the EA or NRW under the Water Resources Act 1991. For work on ordinary watercourses, consent is required under the Land Drainage Act 1991 and the LLFA, EA, NRW or IDB determines applications, depending on which body has jurisdiction. EA (2014a) provides useful guidance.

If the LA is the applicant, the EA or NRW must be consulted unless there is a local flood risk management strategy published for the area the work is within and the works are consistent with it. Conversely the EA or NRW must apply for consent from the LA when they no longer hold powers relating to works on ordinary watercourses.

In addition to the statutory legislation, EA, NRW, IDB or LA by-laws may restrict other activities in or adjacent to all watercourses and on the floodplain and require a by-law consent. The local office of the EA or NRW can advise on any by-laws in the area.

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ScotlandThe Water Environment (Controlled Activities) (Scotland) Regulations (CAR) 2011, which are regulated by SEPA, implements the WFD and covers any activity that directly or indirectly has or is likely to have a significant adverse effect on inland surface waters.

The licensing has a number of escalating steps:

1 General binding rules allowing minor maintenance works such as dredging and erosion control.

2 Registration typically requiring details on scale and nature of activities.

3 Simple licence for works with more impact on the water environment.

4 Complex licence for works likely to have a more significant effect.

Under the general binding rules, the removal of sediment close to a structure requires an authorisation but the maintenance of existing structures and removal or management of debris or trash does not. Operators are permitted to maintain existing engineering works (bridges, bank protection and channel engineering works) if the footprint and materials remain the same and there is minimal effect on the watercourse.

The decision time period can vary and is up to four months for licences, provided that no further information is required by SEPA.

A breach of CAR 2011 can be defended if the contravention was the result of an unforeseeable accident, exceptional or unforeseeable natural causes, or in specified emergency circumstances, provided that all practicable steps were taken to prevent deterioration of the water environment, to restore the water environment to its previous condition, and to notify SEPA promptly.

More information can be found in SEPA (2014) and from SEPA’s website (see Websites).

Northern IrelandConsent is required from DARDNI to erect or place any structure in, over or under any watercourse, or to alter or repair any structure in, over or under any watercourse, if the work is likely to affect the flow of water in the watercourse, impede any drainage work, prevent or impede the passage of fish, or interfere with the maintenance of the watercourse. On all canals and navigable waterways in Northern Ireland consent is also required from Waterways Ireland.

IrelandConsent is required from the OPW to construct a new bridge or alter, reconstruct, or restore any existing bridge over a watercourse, or to erect, enlarge or alter any weir or other like construction in a watercourse where such work might cause flooding of land. Useful guidance is available from OPW (2013). On all canals and navigable waterways consent is also required from Waterways Ireland.

Strategic environmental assessment and sustainability assessmentAn sustainability appraisal may be required as part of an application for flood defence or ordinary watercourse consent in order to protect habitats and species and comply with the Environment Act 1995. Applicants should seek advice from the LLFA before sending an application. The sustainability appraisal should identify all likely effects of the proposed works on the environment and any measures required to mitigate for those effects. The appraisal should consider effects on designated sites, habitats and protected species, such as European Protected Species (EPS) or breeding birds in order to ensure compliance with European law. All areas affected by the works should be considered including access routes and site compounds.

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WFD assessmentA WFD compliance assessment may be required as part of an application for flood defence or ordinary watercourse consent to assess whether a proposal will cause environmental harm or prevent the achievement of objectives set out in the local RBMP (see Section 2.6.17). Applicants should contact the consenting authority before sending an application to check whether an assessment is needed. The authority will give general guidance on the requirements of an assessment.

Failure to complete a WFD assessment will result in consent being refused. Consents for proposals that cause deterioration or prevent the objectives of the WFD from being met could result in financial penalties from the EU.

Scour is a natural process and the installation of scour protection runs counter to the aims of the WFD. SEPA guidance promotes single-span bridges, deeper foundations or scour protection placed below bed level to maintain the natural bed level and material (although these measures may be impractical due to cost and disruption) (SEPA, 2008 and 2010). There is also a move towards soft engineering techniques using bioengineering, geotextile, timber or rock.

Programme constraintsA statutory requirement to avoid in-channel working during fish breeding seasons can present a significant constraint on the programme. Coarse fish have a close season for angling to avoid such impacts, which is generally between mid-March and mid-June. Salmonids (including Brown Trout) have a ‘close’ season between October and the end of February. In watercourses with populations of both, works should be programmed to avoid both close seasons, leaving July, August, September and part of October. In combination with breeding birds this could require a staged approach to site preparation and construction. These dates are all subject to local variations and statutory bodies should be consulted to obtain an accurate period for individual schemes.

2.8.4 Marine licenceA marine licence is required to deposit or remove any object or materials on, under or over any part of the seashore, or to construct, alter or improve any works below mean high water spring. This includes dredging, disposal of dredged materials and construction work, although some small-scale activities are exempt from licensing. Licensable activities are prohibited or restricted in designated conservation zones or protection areas, and the disturbance or removal of foreshore material may be prohibited in some areas to protect flora, fauna, amenities or public rights, or to prevent damage to land or structures. A marine licence may be required in addition to flood and coastal protection consent and is obtained from the consenting bodies in Table 2.11.

Table 2.11 Summary of marine licensing law

Country England Wales Scotland Northern Ireland (NI) Ireland

Marine licence Marine and Coastal Access Act 2009

Marine and Coastal Access Act 2009Marine (Scotland) Act 2010

Marine and Coastal Access Act 2009Marine Licensing (Exempted Activities) (NI) Order 2011

Foreshore (Amendment) Act 2011

Marine Licensing (Exempted Activities) Order 2011

The Marine Licensing (Exempted Activities) (Wales) Order 2011

Consenting bodies MMO Marine Consent Unit Marine Scotland NIEA DOEHLG

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2.9 VALUING OLD WATERFRONT WALLS“Why should I value my old waterfront wall?” Considering the wider benefits to the community in maintaining the wall will allow the owner or asset manager to develop a more robust case for repair and maintenance of their asset.

Many waterfront walls are over 100 years old and in most cases will have a long residual life. With regular inspection and maintenance and in the absence of severe storm, flood or other damage, these walls are likely to retain most of their asset value over time, which is much longer than normal accounting practices consider.

Their value may also result from the benefits generated from the way that they are used. For example, as part of a marina development within a heritage harbour or as part of a residential development alongside a river or canal wall, as well as the wider general amenity and cultural values of historic infrastructure. The ‘value’ of old waterfront walls is therefore closely aligned with the ‘benefits’ arising from their continuing existence. These benefits may include:

ªª protecting valuable infrastructure (roads, railways, services)

ªª protecting properties (coastal protection, flood defence, river training, harbours)

ªª providing amenity and heritage benefits to the public

ªª providing accessibility and availability for users

ªª providing useful land next to the water

ªª as part of a business asset or commercial enterprise (both aesthetic and practical benefits)

ªª retaining heritage or historic assets (sustainability benefits)

ªª providing educational opportunities (educational tourism).

The valuation of a wall based simply on the depreciated total reconstruction costs is generally unrealistic. This is because the depreciation in accounting terms will be substantial since the original construction date. In the event of a catastrophic failure, a detailed cost-benefit analysis

would be required before a decision could be made on whether or not reconstruction was required and justified. Where significant infrastructure (such as roads and railways) is at risk then the intrinsic value of the wall may be high because the consequential costs in the event of failure can be substantial. For example:

ªª West Quay, Bridgwater river wall collapse: on 4 November 2011 a 40 m length of the retaining wall partially collapsed and was displaced outwards by up to five metres after heavy rain and flooding. As well as the adjacent roadway, the area behind the wall contained water, gas electricity and sewers, which complicated both the collapse mechanism and subsequent reconstruction work.

ªª Portway, Bristol river wall collapse: on 5 July 2001 the collapse of a section of around 70 m of the 10 m high river wall and damage to the main highway, following the failure of a 27 inch water main located under the roadway behind the river wall.

ªª Dawlish seawall collapse: on 5 February 2014, following storms that breached the seawall and swept away the rail track. The line remained closed until 4 April 2014 following total refurbishment and reconstruction at an estimated cost (including fines from rail operators for track disruption) of £35m.

Indicative costs for reconstruction of a gravity masonry wall can range from thousands of pounds per linear metre for conventional blockwork and masonry walls to well over £100k per metre for a major wall or breakwater. A good example is the West Quay, Bridgwater river wall collapse (see Case study 2.1).

The value of old waterfront wallsThe valuation of old waterfront walls is a complex issue. It depends more on their potential value in providing services or protecting against the costs of failure than on conventional depreciated values based on historic costs or on replacement costs.

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In November 2011, a length of about 35 m of the West Quay river wall suddenly moved riverwards, forming a shallow V-shaped displacement, with the central part extending some 4.25 m out from its original position, and with four major vertical cracks (see Figure 2 .4). The failure mechanism of the wall was primarily one of the walls sliding along a clay layer at its base into the river due to high groundwater pressure loading at the back of the wall.

At the time of the failure West Quay was flooded and water was able to enter the void behind the wall once it had opened up.

There were a number of potential causes of the failure of the river wall and in all likelihood it was a combination of events that led to the failure, including:ªª the flooding of West Quayªª the probable entrance of water into the ground between

the granite setts in the drainage channel beside the wall raising groundwater pressures on the wall

ªª possible leakage from the surface water drainage pipe raising groundwater levels

ªª possible erosion at the toe of the river wall reducing lateral support for the wall

ªª possible leakage from the sewers locally assisting a further rise in groundwater levels.

It is not feasible to determine the level of contribution of each of these potential causes to the failure of the river wall. No single event is likely to have been the cause and so a combination of two or more of these events, together with the low tide level, caused the wall to fail.

A report prepared following the event concluded that was generally not possible to carry out any modelling or computer analysis to determine the pre-failure stability of a

river wall or to determine the effect of raised groundwater levels or surface flooding on the walls stability. Often, an old structure has too many unknown factors, such as the size, composition and location of buried services or variation in groundwater levels, so that any calculations made will have such large margins of error that the results would be meaningless. It is because of these uncertainties that it is often exceedingly difficult to model old structures such that they can be shown to be capable of standing upright, despite the fact that they can be seen to have been standing for many decades or centuries.

This is reflected in Highways Agency (2006), which states that “an assessment of neither the internal nor external stability is required for existing structures with no signs of distress, as their survival demonstrates that the full-scale model has fulfilled its functional purpose”. However the resistance of the structure to failure is often reduced when further transitory or permanent changes occur over time. This is the case for the West Quay wall where there have been various events that may reasonably have reduced the stability of the structure without any external sign of that change before failure.

Figure 2.4 Failure of the West Quay, BridgwaterFigure 2.5 Flooding behind the river wall before failure on 4

November 2012 (taken from south of the failure)

Case study 2 .1 Failure of the West Quay, Bridgwater, Somerset (courtesy Capita Symonds)

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2.10 FUNDINGThe funding of appropriate levels of inspection, maintenance and refurbishment of old waterfront walls presents one of the most serious challenges to their continuing existence. This is particularly true for ‘orphan structures’ with no clear ownership, individual property owners and private individuals with adjacent waterfronts and heritage trusts responsible for significant heritage or historic sites. In addition heritage conservation is only one of many activities competing for public funds and, to ensure access to suitable funding, risk assessment is an essential tool to justify the case for funding.

If external funding is being sought, any assessment should be as broad ranging as possible. The aim should be to establish the value of the structure to the widest possible range of stakeholders or neighbours. Fully understanding the consequence of failure will be a useful approach as it should identify the effect on the wider community and also potential funding partners. A full understanding of who benefits from the continued existence of the structure will therefore be useful. Benefits can be measured in a number of ways. For example, the United Nations Environmental Programme (UNEP) supports the benefits of an ‘ecosystem’ approach to enhance human well-being. UNEP (2010) states that “many countries still measure development and wealth purely in economic terms without considering the value that ecosystems provide for human well-being”. This approach could be equally applicable to identify and monetise non-financial benefits applicable to the maintenance of old waterfront wall structures. The concept of the social return on investment (SROI) is a method for measuring the environmental and social value of benefits, which are not normally reflected in conventional financial accounting. It can be used by owners and managers of waterfront walls to evaluate the effect on stakeholders, identify ways to improve facilities, and enhance the performance and return on improvements and enhancements to waterfront walls.

It may not be obvious to the owner that the maintenance and continued existence does confer offer benefits, but some examples to help owners when looking at ‘value’ from waterfront walls include:

ªª a long redundant wharf that could be retained for future freight use in accordance with the LAs strategic plan if protected

ªª providing a point of access to the water for emergency services or informal leisure users such as canoeists or anglers

ªª supporting the only access to properties owned by third parties

ªª they are an intrinsic part of a valued landscape or tourist attraction

ªª supporting a footpath, which may be a long distance path or an important local safe route to a school.

If value can be established it may be possible to create stakeholder partnerships to share costs or to access possible funding. External funding may be classified as ‘general’ or ‘specific’.

Lyme Regis is situated on an actively eroding stretch of the Jurassic Coast and the town has faced huge challenges from coastal erosion and land slips. The Lyme Regis Coast Protection Scheme was initiated by West Dorset District Council in the early 1990s. It aimed to provide long-term coast protection for the town and to reduce damage and disruption caused by land slipping, through a long-term programme of engineering works. This major coastal protection project, spanning over 20 years has been carried out, with earlier phases, funded mainly by Defra, comprising the major reconstruction of old seawalls and the construction of new seawalls and promenades. Beaches were also replenished and slope stabilisation works carried out.

The current (2014) Phase IV of this project includes a new 400 m long seawall (Figure 2 .6), 2500 soil nails, bored piling, drainage and landscaping to protect the eastern side of the town. Defra funding of £14.6m was secured

for the latest phase in March 2012 when the Environment Agency approved the scheme. West Dorset District Council has contributed £600 000 to the works and Dorset County Council up to £4.27m.

Figure 2.6 Seawall at Lyme Regis

Case study 2 .2 Coastal protection project, Lyme Regis, Dorset (courtesy ICE South West)

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It may be possible to access general funding from local or national government where the value is derived from the community at large or, for example, where critical infrastructure is at risk. Cost-benefit analysis is normally essential when seeking support from general funding.

Specific funding covers a broad range of possibilities, but in all cases will have specific criteria for support. It is important to understand the criteria and formulate any applications for support carefully. Funding programmes and priorities change over time, so it is not possible to list these as they could quickly become out of date. It is possible to give an indication of current potential specific funding sources, which include:

ªª Coast protection and flood defences – accessed via LAs or the EA and equivalents. Up to 100 per cent of the funds may be available providing the scheme is eligible for funding (EA, 2014b), and applied for in accordance with EA (2010b).

ªª Lottery – possible areas may be the Heritage Lottery Fund (see Websites) accessed via the lottery bodies, but matching funding is normally required

ªª Transport – accessed via local authorities and sometimes national government, potentially up to 100 per cent funding.

ªª Charitable trusts and foundations – such as the National Trust (see Websites), cover a very broad range and are normally accessed directly.

Other sources of funding may be funding in kind, especially if the work involves regeneration projects or is associated in some way with a specific adjacent development of property or infrastructure.

Where there is clear ownership and responsibility for maintenance, for example in the case of the waterways infrastructure managed by the Canals and River Trust, and the EA or LA responsible for flood protection, or a port authority responsible for a harbour, funding for infrastructure inspection and maintenance should normally be provided internally.

In the UK there are also a number of other agencies where external funding for work on waterfront walls may be available. These include:

Guidelines from World Bank (1982) give an indication of the costs of inspection, repair and refurbishment of waterfront walls, which present annual maintenance costs as a percentage of the original capital construction costs. Table 2.12 shows the recommended figures for quays and river walls.

Table 2.12 Recommended maintenance costs for quays and river walls

Type of structure Form of construction Annual average maintenance costs %

Quay walls, river walls

Brickwork 0.2

Masonry 0.1

Mass concrete 0.15

Monoliths 0.05

ªª Department of Transport (DfT)

ªª district and county councils

ªª Local enterprise partnerships(LEPs)

ªª Environment Agency (EA)

ªª English Heritage (and equivalents Welsh Government, Historic Scotland and NIEA)

ªª English Tourist Board

ªª Historic buildings trusts

ªª Welsh Government

ªª Natural Resources Wales (NRW)

ªª Scottish Government

ªª Scottish Enterprise

ªª Highlands and Islands Enterprise

ªª Scottish Regional and Islands Councils

ªª Department of Agriculture and Rural Development Northern Ireland (DARDNI).

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ReferencesBRAY, N and TATHAM, P (1992) Old waterfront walls – management, maintenance and rehabilitation, B13, CIRIA, London, UK (ISBN: 978-0-86017-392-2). Go to: www.ciria.org

CIRIA, MINISTRY OF ECOLOGY, USACE (2013) The International Levee Handbook, C731, CIRIA, London, UK (ISBN: 978-0-86017-734-0). Go to: www.ciria.org

DCLG (2012) National Planning Policy Framework, Department for Communities and Local Government, London, UK (ISBN: 978-1-40983-413-7). Go to: http://tinyurl.com/abvfzc2

CRUICKSHANK, I and CORK, S (2005) Construction health and safety in coastal and maritime engineering, SCHO0405BJAS-E-P, Thomas Telford, London, UK (ISBN: 0-72773-345-1). Go to: http://tinyurl.com/k93rfy3

ENVIRONMENT AGENCY (2010a) Coastal handbook, A guide for all those working on the coast, Environment Agency, Bristol, UK. Go to: http://tinyurl.com/pw5pco3

ENVIRONMENT AGENCY (2010b) Flood and coastal erosion risk management appraisal guidance (FCERM-AG), Environment Agency, Bristol, UK. Go to: http://tinyurl.com/o3ajlrm

ENVIRONMENT AGENCY (2014a) Living on the edge – a guide to your rights and responsibilities or riverside ownership, fifth edition, Environment Agency, Bristol, UK. Go to: http://tinyurl.com/qdxb8oc

ENVIRONMENT AGENCY (2014b) Flood and coastal defence funding: for risk management authorities, Environment Agency, Bristol, UK. Go to: http://tinyurl.com/q5zho5v

EUROPA (2015) Natura 2000 network, European Commission, Brussels. Go to: http://tinyurl.com/q3ujsh3

DEFRA (2012) Guidance on the legal definition of waste and its application, PB13813, Department for the Environment, Food and Rural Affairs, London, UK. Go to: http://tinyurl.com/pzmzeu7

DOELG (2006) A framework for major emergency management, Department of the Environment, Community and Local Government, Dublin, Ireland. Go to: http://tinyurl.com/kkvfjar

DOELG (2013) A framework for major emergency management. A guide to flood emergencies, Guidance Document 11, Department of the Environment, Community and Local Government, Dublin, Ireland. Go to: http://tinyurl.com/q8pl55k

DOELG (2015) Planning and Development Regulations, Department of the Environment, Community and Local Government, Dublin, Ireland. Go to: http://tinyurl.com/onkoxqp

DOENI (2006) Planning policy statement (PPS) 15 Planning and flood risk, The Planning Service, Department of the Environment, Belfast, Northern Ireland. Go to: http://tinyurl.com/3cxazw2

HIGHWAYS AGENCY (2006) “The assessment of bridge substructures and foundations, retaining walls and buried structures”, Design manual for roads and bridges, vol 3 Highway structures: inspection and maintenance, Section 4 Assessment, Part 9 BD 55/06, Highways Agency, UK. Go to: http://tinyurl.com/oh7unru

HM GOVERNMENT (1999) The Belfast Agreement, Northern Ireland Office, Belfast, Ireland. Go to: http://tinyurl.com/najmufn

HOWARTH, W (2003) “Private and public roles in flood defence” Non-state actors and international law, vol 3, 1, University of London, London, UK, pp 1–21

HSE (2001) Reducing risks, protecting people. HSE’s decision making process, Health and Safety Executive, London, UK (ISBN: 0-71762-151-0). Go to: http://tinyurl.com/y4kt7b

HSE (2015a) Construction (Design and Management) Regulations 2015, Guidance on Regulations, L153, Health and Safety Executive, London, UK (ISBN: 978-0-71766-626-3)

HSE (2015b) Construction (Design and Management) Regulations 2015 (CDM 2015): Transitional arrangements, Health and Safety Executive, London, UK. Go to: http://tinyurl.com/nvp7juv

KIRBY, A M, ROCA, M, KITCHEN, A, ESCARAMEIA, M and CHESTERTON, O J (2015) Manual on scour at bridges and other hydraulic structures, second edition, C742, CIRIA, London, UK (ISBN: 978-0-86017-747-0). Go to: www.ciria.org

LBBD (2014) Captain John Perry, RN, Local Studies Library Information sheet No 37, Archives and Local Studies Centre, London Borough of Barking and Dagenham, Dagenham, Essex, UK. Go to: http://tinyurl.com/pgn8lyw

OPW (2009) The planning system and flood risk management. Guidance for planning authorities, Office of Public Works, County Meath, Ireland (ISBN: 978-1-40642-466-9). Go to: http://tinyurl.com/p98u6dj

OPW (2013) Construction, replacement or alteration of bridges and culverts. A guide to applying for consent under Section 50 of the EU (Assessment and Management of Flood Risks) Regulations SI 122 of 2010 and Section 50 of the Arterial Drainage Act 1945, Rev 201311-2, Office of Public Works, County Meath, Ireland. Go to: http://tinyurl.com/njkg4ok

PENNING-ROWSELL, E, PRIEST, S, PARKER, D, MORRIS, J, TUNSTALL, S, VIAVATTENE, C, CHATTERTON, J and OWEN, D (2013) Flood and coastal erosion risk management – a manual for economic appraisal (The multi-coloured manual), Routledge, London, UK (ISBN: 978-0-41581-515-4)

PIANC (1998) Life cycle management of port structures. General principals, MarCom Working Group No 31, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: http://tinyurl.com/pr7olpt

PIANC (2008) Life cycle management of port structures. Recommended practice for implementation, MarCom Working Group 103, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/technicalreportsbrowseall.php

PIANC (2013) Waterway infrastructure asset maintenance management, InCom Working Group 129, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: http://tinyurl.com/pr7olpt

SANDERS, R (2012) Bridgewater West Quay advisory report, Capita Symonds, UK (unpublished)

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SEPA (2008) Engineering in the water environment: good practice guide. Bank protection. Rivers and lochs, first edition, WAT-SG-23, Scottish Environment Protection Agency, Stirling, Scotland. Go to: http://tinyurl.com/oy4m6jz

SEPA (2010) Engineering in the water environment: good practice guide. River crossings, second edition, WAT-SG-25, Scottish Environment Protection Agency, Stirling, Scotland. Go to: http://tinyurl.com/oy4m6jz

SEPA (2014) The Water Environment (Controlled Activities) (Scotland) Regulations 2011 (as amended). A practical guide, version 7.1, Scottish Environmental Protection Agency, Stirling, Scotland. Go to: http://tinyurl.com/d5zsqdo

THE SCOTTISH GOVERNMENT (2010) Scottish Planning Policy (SPP) 7 Planning and flooding, The Scottish Government, Edinburgh, Scotland (ISBN: 0-75592-439-8). Go to: http://tinyurl.com/oyv998c

UNEP (2010) Ecosystem management, United Nations Environment Programme, Nairobi, Kenya. Go to: http://tinyurl.com/p9wxt8n

WORLD BANK (1982) Port maintenance referred to civil works and cargo handling equipment. Part 1 Aide memoir, Transportation and Water Department, World Bank (out of print)

WAG (2004) Technical Advice Note (TAN) 15 Development and flood risk, Welsh Assembly Government, Cardiff, Wales (ISBN: 0-75043-501-1). Go to: www.floodrisk.co.uk/downloads/tan_15.pdf

Statutes

DirectivesCouncil Directive 85/337/EEC of 27 June 1985 on the assessment of the effects of certain public and private projects on the environment (the EIA Directive)

Council Directive 92/57/EEC of 24 June 1992 on the implementation of minimum safety and health requirements at temporary or mobile construction sites (eighth individual Directive within the meaning of Article 16 (1) of Directive 89/391/EEC)

Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora (the Habitats Directive)

Council Directive 99/31/EC of 26 April 1999 on the landfill of waste (the Landfill Directive)

Council Regulation (EC) No 1100/2007 of 18 September 2007 establishing measures for the recovery of the stock of European eel

Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy (the Water Framework Directive, WFD)

Directive 2004/49/EC of the European Parliament and of the Council of 29 April 2004 on safety on the Community’s railways and amending Council Directive 95/1 8/EC on the licensing of railway undertakings and Directive 2001/14/EC on the allocation of railway infrastructure capacity and the levying of charges for the use of railway infrastructure and safety certification

Directive 2006/7/EC of the European Parliament and of the Council of 15 February 2006 concerning the management of bathing water quality and repealing Directive 76/160/EEC (the Bathing Water Directive)

Directive 2006/44/EC of the European Parliament and of the Council of 6 September 2006 on the quality of fresh waters needing protection or improvement in order to support fish life (the Freshwater Fish Directive)

Directive 2006/113/EC of the European Parliament and of the Council of 12 December 2006 on the quality required of shellfish waters (the Shellfish Waters Directive)

Directive 2007/60/EC of the European Parliament and of the Council of 23 October 2007 on the assessment and management of flood risks (the Floods Directive)

Directive 2008/98/EC of the European Parliament and of the Council of 19 November 2008 on waste and repealing certain Directives (the Waste Framework Directive)

Directive 2009/147/EC of the European Parliament and of the Council of 30 November 2009 on the conservation of wild birds (the Birds Directive)

ActsArterial Drainage Act 1945 (No 3)

Arterial Drainage (Amendment) Act 1995 (No 14)

British Waterways Act 1995 (ci)

Canals Act 1986 (No 3) (ROI)

Civil Contingencies Act 2004 (c.36)

Coast Protection Act 1949 (c.74)

Environment Act 1995 (c.25)

Fisheries (Amendment) Act (Northern Ireland) 2001 (c.4)

Fisheries (Consolidation) Act 1959 (No 14) (RoI)

Flood and Water Management Act 2010 (c.29)

Flood Prevention (Scotland) Act 1961 (c.41)

Flood Prevention and Land Drainage (Scotland) Act 1997 (c.36)

Flood Risk Management (Scotland) Act 2009 (asp 6)

Foreshore (Amendment) Act 2011 (No 11)

Harbours Act 1964 (c.40)

Health and Safety at Work etc. Act (HASAW) 1974 (c.37)

Highways Act 1980 (c.66)

Land Drainage Act 1991 (c.59)

Land Drainage Act 1994 (c.25)

Local Government (Water Pollution) Acts 1977 (No 1)

Marine (Scotland) Act 2010 (asp 5)

Marine and Coastal Access Act 2009 (c.23)

New Roads and Street Works Act 1991 (c.22)

Occupiers’ Liability Act 1957 (c.31)

Planning and Development Act 2000 (No 30)

Planning and Development (Amendment) Act 2010 (No 30)

Railways Clauses Consolidation Act 1845 (c.20)

Railways Clauses Consolidation (Scotland) Act 1845 (c.33)

Railway Safety Act 2005 (No 31) (RoI)

Roads Act 2007 (No 34) (RoI)

Roads (Scotland) Act 1984 (c.54)

Salmon and Freshwater Fisheries Act 1975 (c.51)

Salmon and Freshwater Fisheries (Consolidation) (Scotland) Act 2003 (asp 15)

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Safety Health and Welfare at Work Act 2005

South Devon Railways Act 1844

Town and Country Planning Act 1990 (c.8)

Town and Country Planning (Scotland) Act 1997 (c.8)

Transport Act 1962 (c.46)

Transport Act 1968 (c.73)

Transport Act (Northern Ireland) 1967 (c.37)

Transport Act (Northern Ireland) 2011 (c.11)

Transport (Railway Infrastructure) Act 2001 (No.55) (ROI)

Water Resources Act 1991 (c.57)

Water Environment and Water Services (Scotland) Act 2003 (asp 3)

Wildlife Act 1976 (RoI) (No 39)

Wildlife and Countryside Act 1981 (c.69)

Wildlife and Countryside (Amendment) Act 1991 (c.39)

OrdersDrainage (Northern Ireland) Order 1973 (No. 69 NI 1)

Drainage (Amendment) (Northern Ireland) Order 2005 (No 1453)

Health and Safety at Work (NI) Order 1978 (No 10.39 NI 9)

Marine Licensing (Exempted Activities) Order 2011 (No 409)

Marine Licensing (Exempted Activities) (Wales) Order 2011 (No 559) (W 81)

Marine Licensing (Exempted Activities) (Northern Ireland) Order 2011 (No 78)

Planning (General Development) Order (Northern Ireland) 1993

Planning (General Development) (Amendment) Order (Northern Ireland) 2013

Planning (Northern Ireland) Order 1991 (No 1220) (NI 11)

Roads (Northern Ireland) Order 1993 (No 3160) (NI 15)

Town and Country Planning (General Permitted Development) Order 1995 (No 418)

Town and Country Planning (General Permitted Development) (Scotland) Order 1992 (No 223) (S 17)

Water (Northern Ireland) Order 1999 (No 662) (NI 6)

Wildlife (Northern Ireland) Order 1985 (No 171) (NI 2)

RegulationsBathing Water Quality Regulations 2008 (SI NO 79)

Conservation of Habitats and Species Regulations 2010 (No 490)

Conservation (Natural Habitats &c) Regulations 1994 (No 2716)

Conservation (Natural Habitats &c) Regulations (Northern Ireland) 1995 (No 380)

Drainage (Environmental Impact Assessment) Regulations (Northern Ireland) 2001 (No 394)

Eel (England & Wales) Regulations 2009 (No 3344)

Eel Fishing (Amendment) Regulations (Northern Ireland) 2011 (No 325)

Environmental Impact Assessment (Land Drainage Improvement Works) Regulations 1999 (No 1783)

Environmental Impact Assessment (Land Drainage Improvement Works) (Amendment) Regulations 2005 (No 1399)

Environmental Permitting (England and Wales) Regulations 2010 (No 675)

European Communities (Assessment and Management of Flood Risks) Regulations 2010 (SI No 122) (RoI)

European Communities (Birds and Natural Habitats) Regulations 2011 (SI No 477/2011) (RoI)

European Communities Environmental Objectives (Surface Waters) Regulations 2009 (SI No 272) (RoI)

European Communities (Environmental Impact Assessment) Regulations 1989 (SI No 349) (RoI)

European Communities (Environmental Impact Assessment) (Amendment) Regulations 1994 (SI No 84) (RoI)

European Communities (Environmental Impact Assessment) (Amendment) Regulations 1998 (SI No 351) (RoI)

European Communities (Environmental Impact Assessment) (Amendment) Regulations 1999 (SI No 93) (RoI)

European Communities (Environmental Impact Assessment) (Amendment) Regulations 2001 (SI No 538) (RoI)

European Communities (Environmental Impact Assessment) (Amendment) Regulations 2006 (SI No 659) (RoI)

European Communities (Environmental Impact Assessment) (Amendment) Regulations 2006 (SI No 659) (RoI)

European Communities (Quality of Salmonid Waters) Regulations 1988 (SI No 293/1988) (RoI)

European Communities (Quality of Shellfish Waters) Regulations 2006 (SI No 268/2006) (RoI)

European Communities (Water Policy) Regulations 2003 (SI No 7222/2003) (RoI)

Planning and Development Regulations 2001 (SI No 600/2001) (RoI)

Planning and Development (Amendment) Regulations 2013 (SI No 219/2013) (RoI)

Railways (Safety Management) Regulations (Northern Ireland) 2006 (No 237)

Railways (Safety Management) (Amendment) Regulations (Northern Ireland) 2013 (No 237)

Railways and Other Guided Transport Systems (Safety) Regulations (ROGS) 2006 (No 599)

Town and Country Planning (Environmental Impact Assessment) (England and Wales) Regulations 1999 (No 293)

Town and Country Planning (Environmental Impact Assessment) (Scotland) Regulations 2011 (No 139)

Waste (England and Wales) Regulations 2011 (No 988)

Waste Management Licensing (Scotland) Regulations 2011 (No 228)

Waste Management Licensing Regulations (Northern Ireland) 2003 (No 493)

Waste Management (Licensing) Regulations 2004 (SI No 395/2004) (RoI)

Water Environment (Controlled Activities) Regulations (CAR) 2005 (No 209)

Water Environment (Controlled Activities) (Scotland) Regulations (CAR) 2011 (No 209)

Water Environment (Floods Directive) Regulations (Northern Ireland) 2009 (No 376)

Water Environment (Water Framework Directive) Regulations (Northern Ireland) 2003 (No 544)

Water Environment (Water Framework Directive) (England and Wales) Regulations 2003 (No 3242)

StandardsISO 55000:2014 Asset management

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WebsitesAssociation of Drainage Authorities: www .ada .org .uk

Canals and Rivers Trust: https://canalrivertrust .org .uk

Department of Agriculture and Rural Development (DARDNI): www .dardni .gov .uk

Environment Agency (main rivers): http://tinyurl .com/czze35

Heritage Lottery Fund: www .hlf .org .uk

Highlands and Islands Enterprise: www .hie .co .uk

MPA Cement: http://cement .mineralproducts .org

National Roads Authority: www .nra .ie

National Parks and Wildlife Service: www .npws .ie

National Trust: www .nationaltrust .org .uk

Office of Public Works: www .opw .ie/en/

Office of Rail Regulation: http://orr .gov .uk

Rail Accident Investigation Branch (RAIB): www .raib .gov .uk/home/index .cfm

Railway Accident Investigation Unit (RAIU): www .raiu .ie/about

Railway Safety Commission: www .rsc .ie

Scottish Canals: www .scottishcanals .co .uk

SEPA Water Regulations: www .sepa .org .uk/water/water_regulation .aspx

Waterways Ireland: www .waterwaysireland .org

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3 Functions, forms and failures

3.1 OVERVIEWThis chapter gives a history and overview of old waterfront walls, a discussion on types of walls and their forms and functions and examples of wall failures. The primary focus of the chapter is related to canals and inland waterways, riverine, estuarine and coastal old waterfront wall structures formed from masonry, brickwork or mass concrete. Steel sheet piled and/or reinforced concrete structures are not discussed here.

Figure 3.1 provides an overview of the chapter.

Management actionsAdministrative context

Physical context

Severe event(Section 5 .5)

Management of risk(Sections 2 .1 to 2 .3)

Responsibilities (Section 2 .4)

Powers(Section 2 .5)

Beneficiaries(Section 2 .8)

Funding(Section 2 .9)

Physical form and purpose

(Chapter 3)

Physical processes (Section 6 .3)

Loads(Sections 7 .1 to 7 .3)

Wall stability(Section 7 .4)

Historical data(Section 6 .4)

Framework for decisions (Section 4 .3)

Risk analysis(Section 4 .4)

Performance assessment(Section 4 .5)

Operations(Section 5 .2 to 5 .3)

Monitoring and inspection

(Sections 4 .6 to 4 .7)

Data acquisition (Section 4 .7)

Data management (Section 4 .8)

Wall investigation (Sections 6 .5 to 6 .9)

Decision on intervention

Maintenance, repair and rehabilitation (Sections 5 .4 and

Chapter 8)

Regulations and consents

(Sections 2 .6 to 2 .7)

Figure 3.1Overview of Chapter 3

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Section 3.2 provides a background to the historical development of old waterfront walls and introduces the designers, materials and design philosophies of those times. Sections 3.3 to 3.8 then present different types and forms of old waterfront walls where each is demonstrated with schematics reflecting their structural components and typical cross-sections. Common weak points within old waterfront wall systems are identified and historic case studies are presented. Types of walls considered in these sections include:

ªª quay, dock and lock walls (Section 3.3)

ªª breakwaters (Section 3.4)

ªª seawalls for coastal defence (Section 3.5)

ªª retaining walls and flood defences, including inland waterways and canal structures (Section 3.6)

ªª skin walls (Section 3.7)

ªª bridge piers and abutments (Section 3.8).

Section 3.9 discusses performance, deterioration and failure modes of old waterfront walls using damage and deterioration categories, including descriptions of the fundamental mechanisms of failure. Various scenarios of the kinetics of failure are described with supporting diagrams. Varying perspectives of old waterfront wall failure analysis are also covered.

3.2 HISTORY OF OLD WATERFRONT WALLS

3.2.1 Historical contextWaterfront walls are well distributed over the whole country, with the exception of hilly or mountainous regions. In those areas they are generally only found as canal or lakeside retaining walls or in the abutments of bridges across rivers or streams.

In the past, in places such as East Anglia with poor or non-existent local sources of rock, timber structures were erected. As these decayed they were replaced with masonry and concrete walls. Other regions, such as south-west England, Wales and the Scottish Highlands, had ample supplies of good quality rock nearby, so construction with masonry was feasible from the start.

The first significant constructors of waterfront walls in the British Isles were the Romans. Figure 3.2 shows the main settlements developed during the Roman occupation (Haverfield, 1924) and Figure 3.3 shows the quayside wall of the Roman waterfront in Chester. Many of these sites are now obscured by later construction but the original Roman foundations are often still in place.

Subsequent development of ports and harbours was dictated by trade patterns and the defence of the country. Figure 3.4 shows the British customs ports in England and Wales in the 18th and early 19th centuries (Jackson, 1983). The figure also shows the principal inland navigation routes in the middle of the 18th century. This was before the major canal building era, which began in 1761. Inland navigation was vastly improved by the development of the canal system up to around 1820. The canal network in 1789 is shown in Figure 3.5 (De Mare, 1987). Details of the canals built after this date may be found in Hadfield (1962). Many of the port and canal structures were built in masonry and brickwork, and a considerable number of waterfront walls from this period still exist today.

In more recent times waterfront walls have been constructed for the railway and road networks, both in coastal locations, and alongside and over rivers and estuaries. They have also been built for coastal and flood defence purposes. Many examples of this work are recorded in various ICE proceedings and other work published at the time.

It is particularly difficult to quantify the different types of wall in existence at the present time, or the number in a specific area, because of the number and variety of types of owner. For example, in the Scottish Highlands alone there are over 100 harbours, piers and ferry terminals of various size and type, many kilometres of coastal walls, and in excess of 1800 bridges.

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Figure 3.3 The quayside wall of the Roman waterfront at Chester (courtesy Chester City Council)

3.2.2 DesignersThe results of the original questionnaire sent to wall owners and other responsible authorities in 1992 showed that there was no relationship between a wall’s location and its designer. In spite of the difficulties in travelling long distances, some of the early engineers designed and supervised works in many different parts of the country and overseas. For instance, Captain John Perry (1670–1733) reputedly worked in Dagenham, King’s Lynn, Dublin, Dover and Russia (LBBD, 2014). Although relationships between designers and their areas of work are unforthcoming, there is considerable benefit

Key

□ large fortresses■ small fortresses○ large town● small towns.

Figure 3.2Roman Britain settlements (from Haverfield, 1924)

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in identifying the designer of a wall because this might lead to additional information about the wall and its construction.

Swann (1959) and Skempton (1987) give a considerable amount of information on the engineers of English port development between 1640 and 1840. After this date it is possible to obtain information that relates engineers to specific developments from the library of the ICE in London.

Figure 3.4 British customs ports in the 18th and early 19th centuries (from Jackson, 1983)

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Figure 3.5 The waterway system in England, 1789 (from de Maré, 1987)

3.2.3 General wall characteristics

HistoricalAlthough the Romans were competent builders of masonry structures and of reliable and durable foundations, the art of constructing masonry waterfront walls seems to have lapsed after the Roman occupation until around the 15th century. A possible exception to this was the construction of moated castles and similar waterfront fortifications by the Normans.

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Before the 15th century riverside retaining walls tended to be of timber construction, braced from the riverside (see Figure 3.6).

This was feasible because the retaining wall was constructed to form additional riverside land, and the shallow-draught vessels of the time used to beach in the shallow creeks to discharge their cargo and did not need to draw up alongside such walls. With the advent of deeper-draught vessels, and the need to provide a

more substantial and durable structure, the riverside walls became both retaining walls and wharves (see Figure 3.7).

The earliest types of masonry quay wall and breakwater were built of irregular blocks. Later, quay walls were formed from rubble masonry faced with ashlar (stones that are finely dressed, cut and worked until squared) or brickwork. As the stones in rubble masonry are irregular, the performance of the structure was dependent on the quality of the work of the stonemason when cutting the blocks and in the mortar, which was much thicker than in an ashlar or brick wall.

Reference can be made to some early British Standards, which have now been replaced by Eurocodes. BSI (1951 and 1952) and BS 5390:1976 (superseded by BS 5628-3:2001) deal with the design and construction of walls faced with stone or cast stone and rubble or rubble faced walls and the general principals described in these publications remain valid.

In addition, BS EN 1996-1-2:2005 is also relevant. BS 5628-1:2005 (superseded by BS EN 1996-1-1:2005+A1:2012) gives recommendations for the structural design of unreinforced masonry units of bricks, blocks, manufactured stone, square dressed natural stone and random rubble masonry. BS 5628-3:2005 (superseded by BS EN 1996-1-2:2005) describes materials, design and workmanship, and provides useful guidance on construction methods that may have been used in original construction of old waterfront walls.

The arrangement of the way brickwork is laid is described as the ‘brick bond’ and is defined by the arrangement of headers (the shorter face of the brick) and stretchers (the longer face of the brick). The most common form on historic structures is the ‘Flemish Bond’. In this arrangement each course of brickwork has alternating headers and stretchers, with the headers aligned with the stretchers in

Figure 3.7Baynard’s Castle dock, London, showing timber rubbing posts to protect vessels from damage by the stone wall (from Marsden, 1981)

Figure 3.6 Trig Lane, London, showing back-braced riverfront revetments behind 15th century river wall (from Milne, 1981)

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adjacent courses. Another common form is ‘English Bond’, where alternate courses of headers and stretchers are laid with the joints in the stretcher courses aligned with the centre of a headers brick. This arrangement is often used where strength is important. Examples of various brick bonds can be found on the Brick Development Associate website (see Websites).

Properties requiredMaterials used in gravity waterfront walls should be durable, dense and have the ability to bind together. High tensile and compressive strengths are generally not important due to the design of such walls. An important exception to this is the design of the counterfort.

A gravity wall is usually designed so that under normal loading there is no tension in the structure and the bearing stress diagram throughout the depth of the wall is triangular (see Figure 3.8). The maximum compressive stress for a uniform width is only twice the average stress arising from the weight of the wall materials above the level considered. For a wall with a height of 10 m the maximum compressive stress would be about 0.50 N/mm2, or less if much of the wall is underwater. A major factor limiting the maximum compressive stress in the wall is often the strength of the soil under the foundations.

Figure 3.8 Bearing stress distribution under a waterfront wall (courtesy Livesey Henderson)

Composite constructionThe principal materials used in gravity wall construction are brick, (natural) stone, mortar, concrete and timber.

Steel and iron were occasionally used as inserts in walls in such places as a projecting toe or for anchoring bollards. There are also a number of examples of chains and tie rods being used to tie back temporary works, and then built into the main body of the wall. Materials are frequently used in combination, a typical example being a wall with a stone facing on the outside and rubble and/or concrete on the inside. The outside appearance of the wall is not therefore necessarily a guide to what is inside (Bray and Tatham, 1992). Indeed one of the main problems in analysing walls is identifying the materials within that cannot be seen. Facing stonework is often of a different type to that inside the wall and the cope is frequently of a different type again.

The designers of some of the old waterfront walls used materials of different densities in an attempt to improve stability and to reduce maximum working stresses in the structure and on the ground. Materials were also varied or voids left to reduce construction costs.

BrickWhere bricks have been used in the construction of waterfront walls their longevity is mostly determined by their resistance to alternate wetting and drying, freeze-thaw cycles and abrasion. It should be noted that old bricks from the same source will vary considerably in their properties due to variations in the quality of the raw materials and the firing of the bricks. This accounts for the enormous variation in the

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degree of degradation found in adjacent bricks in old structures. It is interesting to note that the British Standards Institution (BSI) only started specifying brick durability in the 1970s. A review of the types of brick and stone found in old masonry structures is given in Sowden (1990). The types of brick are also summarised in Section 3.1 of Lawson and Richardson (1986).

Natural stoneNatural stone is one of the most important materials used in waterfront walls and there are few walls that do not have some stone in their composition. Knowledge of the use and behaviour of stone is a key factor in the understanding of wall problems and the evaluation of a wall’s condition.

A number of points are worth noting:

ªª Stone is a natural material so the quality of stone from a particular quarry and also the rate of deterioration of individual stones will vary.

ªª In waterfront structures the types of stone most likely to be durable are those of high density and low porosity. This type of stone is less easy to bond with mortar.

ªª Stone of high density and low porosity has a high compressive strength but is susceptible to crystallisation deterioration and does not necessarily have a high modulus of rupture.

In addition, the following notes regarding the use of stone in waterfront walls may be helpful:

ªª Granite facing was particularly favoured for facing seawalls, which were subjected to abrasion and wave attack.

ªª In good masonry great care was taken to ensure that ashlar facing blocks were keyed into the structure to prevent stones becoming separated from each other and from the core (see Figure 3.9).

ªª Stone from the excavation for the waterfront wall was sometimes used for the core of the wall, and in at least one instance (Kinipple, 1897) was used to form the ashlar facing.

ªª Stone was often used in the core of the wall in place of concrete, which was expensive. There are many examples in which stones were hand-placed in the core of a wall (labour was cheap), with grout inserted into the voids.

ªª Large stones or ‘plumbs’ were used in old mass concrete structures to reduce the volumes of more expensive concrete. They were also used between concrete pours to increase the bond and improve resistance to sliding (see Figure 3.10).

ªª Where large preformed blocks of stone or concrete were used for the facing to a wall, the internal portions of the block were made slightly under-size to ensure that no open joints were left after construction.

MortarAlthough the Romans used lime and pozzolana (pozzolanic ash) to make mortar and concrete, reliable methods of cement manufacture for use in structures were later forgotten. John Smeaton used mortar made with lime and pozzolana in the construction of the Eddystone Lighthouse in 1758 and this mortar was still in good condition in 1882 when the lighthouse was dismantled (Skempton, 1981). An example of a mortar specification used in the construction of the Gloucester and Berkeley canal in 1795 is given in Box 3.1.

Portland cement manufacture began in 1824 but lime mortar continued to be the norm until 1900. Between 1900 and 1930, cement mortar became widely used, although lime is still used with Portland cement today to improve the plasticity of mortar.

The lowest standard of brickwork with lime mortar in the 18th and 19th centuries (Lawson and Richardson, 1986) has a permissible compressive stress of 0.42 N/mm2. Tests carried out in the 1980s (Sutherland, 1988) gave an average strength of 0.96 N/mm2 for a column of bricks and mortar cut from a building where the working load was 0.45 N/mm2. Although this gives a FoS below that recommended in

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BS 5628-1:1978 (now superseded), the building showed no signs of distress. (A working stress of 0.45 N/mm2 is likely to exist in a gravity wall 10 m high.)

ConcreteConcrete was used by the Romans for marine structures and there are reports that they used precast concrete blocks for the construction of breakwaters. However, like many of the other construction skills that the Romans possessed, the knowledge of how to make good concrete was later lost.

Concrete was reintroduced as a material for use in dock works and other maritime structures by the end of the 19th century. It was not considered to be particularly durable, and so in the early walls it was seldom found in the outer faces. By 1850, although Portland cement was being exported from England to France in large quantities for use in harbour construction, it was not being used on a large scale in the UK.

Figure 3.10 Section of dock wall, Sharpness, circa 1880 (courtesy British Waterways Archives)

Figure 3.9 Illustrations from a French treatise on civil engineering showing methods of interlocking blocks and the effects of not doing this (from Sganzin and Reibell, 1839)

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All the Ashlar stone shall be set for six inches in depth from the face inward in tarris mortar composed of one-third part of Aberthaw or Chepstow lime, one-third of good pozzolana earth from Italy or Dutch tarris and one-third of clean fine well washed pure river sand divested of all muddy particles

and gravel. And all other parts of the joints of the said stone work shall be laid in mortar composed of clay stone or Bristol Lime one half lime and the other half of well washed clean and pure river or pit sand screened from all gravel or small stones.

As cements improved, concrete gained in popularity and by the 19th century was in wide use in harbour engineering. Extensive details relating to the development of cement and use of concrete may be obtained from MPA Cement (see Websites).

TimberAlthough this guide defines old waterfront walls as being masonry or concrete structures, it is rare to find a wall that does not include timber. The study of its use in wall construction is an important aspect of waterfront wall technology. Timber is normally found either in the foundations or as an insert in the body of the wall (see Figure 3.11).

In some cases the timber was used as a former around which the wall was built and in others it was used as a tension member, such as might be required to strengthen the upper part of a counterfort (see Box 3.2), or to tie two walls together (see Figure 3.12) (Bray and Tatham, 1992). It is not unusual to find timber in the core of a wall.

Timber can survive for long periods when deprived of oxygen, so timber immersed in water or buried in soft foundations still plays an important role in wall stability. Bray and Tatham (1992) gives a detailed account of the development of piled foundations as would have been used for wall and bridge foundation work.

Figure 3.11Section showing counterfort strengthened by a timber tie in the Cumberland basin, Bristol, 1973 (courtesy Bristol City Council)

Box 3.1 Mortar specification for the construction of the Gloucester and Berkeley canal, 1795 (from Bray and Tatham, 1992)

Figure 3.12Section showing river and dock wall connected by a timber tie at Sandon half-tide dock, Liverpool, 1901 (courtesy Mersey Docks and Harbours Company)

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3.3 QUAY, DOCK AND LOCK WALLS

3.3.1 Function and designThe main components of a quay wall are illustrated in Figure 3.13. The structure is designed to provide a vertical, or near vertical, front face for vessels to lie against.

The top surface is normally flat, allowing unimpeded access to the edge of the structure. Immediately to the landward side there is nearly always an open area, the quay apron, where cargo was handled onto and off the vessels or other activities relating to ship servicing took place. The apron is supported on the backfilling and usually falls slightly towards the top of the wall to facilitate drainage. The back face of the wall is rarely vertical, the wall usually being widened with depth, and often exhibits features to increase the soil friction on the wall.

The base of the wall may be founded on the natural soils or rocks existing at that level, or may rest on other materials, including piles, which have been placed or driven under the base to spread or transfer the load to a lower founding stratum. Some bases contain features to improve their resistance to sliding and many are extended forwards to provide a toe. The toe may also act as an anti-scour device as well as increasing the resistance to overturning.

The whole structure is designed to resist:

ªª the forces imposed by vessels alongside (berthing and mooring)

ªª the pressure exerted by the backfill

ªª hydraulic pressures, which may be continuously changing due to tidal effects

ªª surcharge loads on the top surface

ªª its own self-weight.

In many cases the internal portions of the wall are built using a different material from the outside shell, for reasons of economy, and the backfilling material may be specially chosen for its geotechnical properties. These components are described in more detail in Section 3.3.2.

An example of the use of timber in a wall is shown in Figure 3 .11, which presents the cross-section of a quay wall designed by William Jessop in 1793 for the Cumberland Basin at Bristol. The wall is supported on timber piles. The note about the counterforts says “two half

inch boards in each counterfort at every 5ft in height”. This may have been intended to provide tension reinforcement between the counterfort and the body of the wall. The note at the bottom of the figure “a 3 inch plank in every yard” may refer to the timbers joining the piles.

Box 3 .2 Example of timber in a dock wall, Bristol

Figure 3.13The main components of a quay wall (courtesy Livesey Henderson)

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One point to note is that there may be considerable variety in the designs of dock walls in one location. Places such as London, Leith, Belfast, Liverpool and Gloucester (see Figure 3.14) all contain examples of many radically different wall configurations. So the design of one wall in a port may have little bearing on that of the other walls in an area.

3.3.2 Component characteristicsThe component characteristics for an old waterfront wall in terms of the front face, back face, toe, internal structure, backfilling, and other features, are discussed here.

Front faceThe front face of a wall in this category may be vertical (Figure 3.15), slightly inclined (Figure 3.16), or of curved profile (Figures 3.17 and 3.18). The latter is often accentuated towards the toe, the non-vertical shape being functionally acceptable because of the tendency of old vessels to be similarly shaped in cross-section. In locks and narrow docks this curvature is often extended into the base of the lock or dock to form a structurally efficient inverted arch (Figure 3.19) which transfers the hydrostatic uplift to the walls and acts as a strut between the walls. In later years the upper face of a wall was often built of stone and proud of the lower face, to ensure that the berthing loads, and other damaging forces, were applied to the more durable material (Figure 3.20).

In a number of cases the front face of the wall is discontinuous at the lower level due to the presence of an arched construction similar to a railway viaduct (Figure 3.21). The arches were closed at the back, sometimes arched in plan (Figure 3.22). The arches are usually of short span but occasionally longer spans, such as 12 metres (Figure 3.23), are found, and the depth of the arch may be considerable (Figure 3.24). The use of arches in port construction dates back at least to the Roman era (Cresy, 1847). The front face of a lock wall may also have apertures for sluices, draw shafts etc.

Back faceThe back faces of waterfront walls form the link between the wall and the retained material behind. Being functionally unconstrained with respect to their shape they have been the subject of a variety of methods to improve wall stability.

Figure 3.14 Sections of the walls in Gloucester Docks (courtesy Livesey Henderson)

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Figure 3.15 King George V Dock London (from Binns, 1923)

Figure 3.16 Portsmouth Dockyard tidal basin extension, 1864 (from Harcourt, 1885)

Figure 3.17 The Alexandra Dock, Hull, 1887 to 1888 (from Hurtzig, 1888)

Figure 3.18 The Royal Albert Dock, London, 1880 (courtesy A Stevenson)

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Figure 3.19Section of the chamber of the entrance lock Blackwall, West India Dock, 1800–1806 (from Hadfield and Skempton, 1979)

Figure 3.20Quay wall at Tema, Ghana, 1960 (from Bertlin and Partners, 1969)

Figure 3.21The arched wall of the Albert Dock at Hull, 1861 (from Hawkshaw, 1875)

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Figure 3.22The arched dock walls in the Canada Dock, London (courtesy Museum in Docklands, PLA Collection)

Figure 3.23 The arched dock wall at Whitehaven (from Williams, 1879)

Figure 3.24Plan and elevations of the arched wall at Great Grimsby (Royal) Docks 1864–1865 (from Clark, 1865)

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A simple method of increasing the resistance of the wall to overturning is to widen the structure towards the base by sloping the back face (Figure 3.25). However, a more common and effective way of achieving this is to step the back face (Figure 3.26), which has the added advantage of increasing the friction between the wall and the backfilling material. Another method of increasing this friction on vertical or near-vertical back faces is by means of oversails (Figure 3.27), a method much favoured by Isambard Kingdom Brunel.

A common method of improving the stability of relatively slender walls is through the provision of a counterfort. This is a section of wall that projects perpendicularly backwards into the backfill material. Counterforts are placed at regular intervals along the back of the wall. They may be the same height as the wall (Figure 3.28) or smaller (Figure 3.18) and may be stepped or sloping (Figures 3.29 and 3.30). Some counterforts were also used as piers to support relieving arches.

The counterfort not only acts as a counterweight against the overturning forces of the backfill, but is also intended to harness additional soil resistance through the lateral pressure on the counterfort. The main disadvantage of the counterfort is that it is prone to tension failure at the point where it joins the main wall and its effect on increasing frictional grip within the backfill is uncertain.

Counterfort walls were a popular form of design from the 1700s to about 1860. A few counterfort walls were built in the late 1800s and many of these walls still exist today. Masonry counterfort walls were quite different from modern reinforced concrete counterfort walls – the former have only local piers added to the back of a wall whereas the latter typically have a base slab between the counterforts so that the weight of the backfill on the base increases the resistance to sliding and overturning.

Where a wall is constructed abutting a soil or rock formation that is naturally stable and will form a vertical face, the back face of the wall is often keyed into this material (Figure 3.31 and Section 3.7). If the rock level varied across the site, the section of the wall was often also varied to take advantage of rock where it occurred.

In a number of early cases, such as at Sheerness, the back face of the wall is curved parallel to the front face. For example, in Figure 3.32 notice the ‘stepped heel’. Similar designs have also been found in London, Bristol, Gloucester and Leith. A modern concrete blockwork version of the backward-leaning wall can also be seen in Figure 3.20.

BaseApart from forming the interface between the foundation to the wall and the main structure of the wall, the base must provide sufficient resistance to horizontal sliding to prevent the bottom of the wall from kicking outwards. A number of methods have been used to try to increase this resistance to sliding. These generally involved modifying the shape by means of serrations (Figure 3.28), castellation (Figure 3.33), keying the wall into the ground (Figure 3.34) and sloping or stepping the base up to the front face (Figures 3.18, 3.35 and 3.36). Sometimes close contact with the ground is obtained by casting concrete directly on to the ground or rock. In some cases the method of forming the base of the structure gives added resistance, such as a wall that is founded on bagged concrete (Figure 3.37).

Figure 3.25 Western tidal harbour wall at Greenock, 1878–1886 (from Kinniple, 1897)

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ToeThe toe of the wall can be designed to be extended at the front to increase resistance to overturning (Figures 3.15, 3.18 and 3.44). In some cases scour protection, which is structurally separate from the wall, has been provided (Figure 3.26). It is sometimes difficult to distinguish between structural toe and scour protection. Scour protection is also often provided by metal or timber piles (Figure 3.38). A toe that is expected to carry high loads may be strengthened by addition of a row of toe piles (Figure 3.29) to take vertical loads, or raked piles to take some of the horizontal load (Figure 3.39).

Figure 3.28 Section of wall at the old entrance, sharpness, showing counterfort and serrated base, 1820 (from Simms, 1838)

Figure 3.29 Glasson Dock, Morecombe Quay (courtesy A Stevenson)

Figure 3.26 Increasing the resistance of the wall to overturning with a stepped-back face approach, Spencer Dock, Belfast, 1872 (from Harcourt, 1885)

Figure 3.27 Retaining walls, showing oversails on the rear face, 1881 (from Baker, 1881)

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Figure 3.31Cross-section of a wall, Liverpool, 1898 (from Du Plat Taylor, 1949)

Figure 3.32Curved dock wall with heel, Sheerness, 1813–1927 (from Rennie, 1854)

Figure 3.30Edinburgh Dock, Leith (courtesy A Stevenson)

Figure 3.33Baker’s Quay, Gloucester Docks, 1829 (courtesy British Waterways Archives, Gloucester)

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Figure 3.34The tidal basin, Barrow, 1879 (from Harcourt, 1885)

Figure 3.35Surrey Commercial, Greenland Dock, London, 1898 (from Greeves, 1980)

Figure 3.36Fitting out basin, Chatham, circa 1880 (from Harcourt, 1885)

Figure 3.37The end wall, Winton Pier, 1892 (from Robertson, 1895)

Figure 3.38Dock built on running sand, King George V Dock, Hull, 1968 (from Cornick, 1968)

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3Figure 3.39Dock wall later strengthened with land ties, Southampton, 1842 (from Giles, 1858)

Figure 3.40Millwall, London, 1866 (from Harcourt, 1885)

Figure 3.41 Docks and river wall, Sheerness, 1813–1927 (from Rennie, 1854)

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Figure 3.42 Dock wall, cast with internal ashlar blocks, Wallasey Pool, Birkenhead Docks, circa 1856 (courtesy Mersey Docks and Harbour Company)

Internal structureAlthough the front face of a wall may be of masonry construction the main volume of material forming the core of the wall, and the back face, is often of mass concrete or some other material. In some cases the wall appears to have been built in ‘lifts’ with a masonry band inserted between each lift (Figure 3.40). In other cases the main shell of the wall is built of masonry and filling material is then added (Figure 3.17).

The arch form of construction (see Figures 3.21 and 3.24) avoids having to use a large volume of fill material, and there are other examples of voids being formed for the same reason (Figure 3.41). On occasions large stones (known as ‘plumbs’) are placed within the concrete fill, presumably to save on cement and possibly to reduce the heat of hydration, and there is at least one instance of ashlar blocks being used in this way (Figure 3.42).

The strength of the whole structure may be increased by tying the component parts together by keying (Figure 3.43) or by means of reinforcement. Cast iron bands (Figure 3.16), hoop iron ‘bonds’ (Figure 3.45) etc were used for this purpose. In some cases the ties may have been used as part of the temporary works during construction and were then cast into the permanent works (Figures 3.46 and 3.47).

Evidence that metal work was used in wall construction from an early date is found in the 1795 specification for the Gloucester and Berkeley Canal (see Box 3.3).

“All cramps Chainbars and Landties or other Bars set into the stone work shall be set into the said stones (where necessary and ordered) in Groves so as to be flush with the surface of the course of stones and where it shall be

necessary form parts thereof with lead the same shall be done by the said George Stroud Daniel Spencer and Thomas Cook, the lead being found by the said company.”

Box 3.3 Specification for metalwork used in the construction of the Gloucester and Berkeley canal, 1795 (courtesy Bray and Tatham, 1992)

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BackfillingThe material used to backfill behind the wall is important because it affects the loading on the wall. Materials with low angles of internal friction exert a greater pressure than those with high angles. In some cases the backfilling was not designed and the original excavated material was replaced, but in the majority of cases the backfill is specified on the design drawings.

Generally a granular material is specified such as ballast (Figure 3.46), hand-packed broken rock or rubble (Figure 3.48), quarry refuse (Figure 3.25), or ashes (Figure 3.49). However, when a lock, dock or canal is designed to remain empty or full of water for a period of time it is usual to find that a layer of puddle clay has been placed against the back face of the wall (Figure 3.42), with a granular filling material behind the clay. For example, in Figure 3.51 clay has been mixed with rock and has been used to prevent penetration of fine backfilling into rubble fill at the back of the wall. A particularly good example of designed backfilling is the Carron Dock at Grangemouth (Figure 3.50).

It should be noted that in many cases during excavation for a wall, the original ground has been retained by means of temporary works behind the wall. These temporary works were often left in place and the backfill was placed over them. One effect of this is that when the timber eventually rots, settlement may occur in the apron, which is sometimes mistaken for other types of wall distress.

Figure 3.43 Wall made of precast blocks, Cork, 1877 (from Cornick, 1968)

Figure 3.44 White Star dock, Southampton, 1907 (from Ackerman et al, 1922)

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Figure 3.45 Dock wall in main basin at Sharpness, Gloucestershire, 1874 (courtesy British Waterways Archives, Gloucester)

Other featuresThere are a number of other characteristics of quays, docks and lock walls, including:

ªª Bollards: these are either mounted on their own detached foundation blocks (Figure 3.47) or are integral with the wall structure. They may be built into the counterfort (Figure 3.53) or into the main part of the wall. In the latter case they may be tied back to mooring stones by wrought iron stays (Figure 3.54).

ªª Ties: these have occasionally been used to improve the stability of walls. They are typically of wrought iron rod (Figures 3.49 and 3.55) or chain (Figure 3.47) construction and usually run back to an iron or timber pile driven at a slight rake behind the wall, or to a masonry or concrete block. As can be seen in Figure 3.55, the visible part of the wall may not show any evidence of the existence of a tie rod. Sometimes walls on either side of a narrow strip, separating two basins, are tied together (Figure 3.56).

ªª Piles: these are used extensively in foundations to support walls on soft soils. The older piles are normally of timber, but cast iron was used in many instances and there are numerous examples of composite or semi-composite forms of construction using cast iron circular and sheet piles. The piles are used to support the base (Figure 3.50) of the wall at its normal level, or they may be used to support the entire wall at a point well above seabed level (Figures 3.57 and 3.58), in which case sheet piles are typically used to retain the soil below. However, in a few cases this sheet piling is absent, the wall being suspended above a battered slope (Figure 3.59). Note that bearing piles are not always circular.

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Figure 3.48Dock wall at Manchester (from Cornick, 1968)

Figure 3.47New Quay at Blyth Harbour, Northumberland, 1882 (from Kidd, 1885)

Figure 3.46 Victoria Docks, London, 1858 (courtesy ICE)

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Figure 3.49 Concrete cylinder wall at Princes Dock, Glasgow, circa 1895 (from Cornick, 1968)

Figure 3.50 Designed backfill for the Carron Dock, Grangemouth, 1879 (from Ackerman et al, 1922)

Figure 3.51 Clay and rock seal on rubble: block wall at Nacala, Mozambique, circa 1960 (from Cornick, 1968)

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3Figure 3.52 Quay wall at Trieste, Italy (from Cagli, 1936)

Figure 3.53 Transverse section through King George V Dock, London, 1921 (courtesy ICE)

Figure 3.54 Section of the tidal harbour wall showing bollard and stay-irons, Hartlepool, 1834 (from Rennie, 1854)

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Figure 3.55Cross-section of wall at the entrance to Southwold Harbour, Suffolk (courtesy Waveney District Council)

Figure 3.56 Cast iron double-flanged piles being used at the Albert Harbours, Greenock (from Miller, 1863)

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Examples of joist piles have been found as well as ‘cast iron double flanged’ piles (Figure 3.56).

ªª Caissons: in a few cases walls have been constructed on caissons (Figures 3.60, 3.61, 3.62 and 3.49) and in one example on cast iron cylinders connected by cast iron sheet piles (Figure 3.63). Caissons may be constructed from brick, concrete blocks or in situ concrete.

ªª Drainage: a number of walls have been designed with weep holes to reduce the water pressure behind the wall at periods of low water and to prevent a build-up of surface water (Figures 3.64, 3.38 and 3.48). In some instances these drains are fitted with tide flaps to reduce the flow of water in and out of the soil behind the wall.

ªª Foundation rafts: foundation rafts made in the form of grillages of timber sleepers (Figure 3.16) are often placed immediately below the base of the wall. These may be further supported on timber piles or on tipped rubble.

ªª Fenders and timber rubbing strips: these are often built into the wall at the time of construction (Figure 3.54) or may have been used as permanent shuttering (Figure 3.65).

Figure 3.57Section of a wall, Bremerhaven, Germany, 1897 (from PIANC, 1986)

Figure 3.58Section of a wall, Brunsbuttelkoog, Germany, 1914 (from PIANC, 1986)

Figure 3.59 ‘Rouen’ type quay (courtesy PIANC)

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Figure 3.60Caisson-type foundations, Rothesay Dock, Glasgow, 1901 (from Mason, 1915)

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Figure 3.63 Caisson-type foundations, Broomielaw quay, Glasgow, 1900–1902 (courtesy Clyde Port Authority and Glasgow District Council)

Figure 3.62 Quay wall on cast iron cylinders, Newcastle, 1873 (from Scott, 1895)

Figure 3.64 Dock wall, Immingham, Lincolnshire (from Cornick, 1968)

Figure 3.61Monolithic foundations, St Andrews Dock, Hull, 1901 (from Du Plat Taylor, 1949)

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Figure 3.65 Concrete quay on south side of basin at Barrow, 1901 (from Savile, 1904)

3.4 BREAKWATERS

3.4.1 Function and designThe primary function of a breakwater is to provide an area of calm water between it and the coast behind. There is no constraint on the design of the outer face other than that imposed by the nature of the incident waves, the currents and the seabed at that location. The inner face of the breakwater is similarly unconstrained but as it is commonly used as a berthing face for vessels to moor, it is often nearly vertical.

The wave forces acting on the outer face of the breakwater impose severe localised forces on the individual components of the structure. This can result in degradation and loss of stones and blockwork locally, as well as major overturning and sliding forces on the structure. These issues are discussed further in Chapter 7.

A breakwater is constructed on an exposed site so the method of construction has a considerable effect on the design. For example, the use of large blocks, concrete bags and natural stones are often favoured, even in the internal portions of the structure. By the 1870s, the techniques of forming, transporting and placing large blocks (up to 350t each in Dublin) were quite advanced, as demonstrated in a discussion on this subject at the time (Stoney, 1874). Much of the credit is given to the French, who used the technique in Algiers, circa 1844.

Another popular method of construction was to erect a timber frame along the line of the breakwater and to form the structure around it. Much of the timber was left in situ after the construction was completed (Figure 3.67).

3.4.2 Component characteristicsThe component characteristics for a breakwater are shown in Figure 3.66 and are discussed in terms of the outer face, inner face, base, toe, top, and internal structure.

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Outer face

The outer face of a breakwater may vary from being vertical to sloping outwards at a slope of 1:2 (Figures 3.68 and 3.70), or even flatter (Figure 3.71). The sloping faces usually become steeper towards the top of the wall and are often vertical at the top. Many of the outer faces are extended upwards beyond the main body of the wall to provide a protective wall on the outside edge of the breakwater, which reflects waves and reduces overtopping by broken waves and spray (Figures 3.72 to 3.74). Some outer faces are stepped (Figure 3.75).

The blocks used in the outer face of breakwaters tend to be large, of high quality and securely jointed so that they can withstand the effect of

large waves. Granite and limestone ashlar (Figure 3.74) were popular. Various special arrangements for placing blocks were devised, such as piano blockwork (Figure 3.76) and slicework (Figure 3.94). In particularly severe conditions the blocks were tied back to the mass of the breakwater during construction (Buchan et al, 1985). An alternative method of dissipating wave energy is to cause the waves to break on the outer face of the breakwater as shown in Figures 3.69 and 3.71.

In a number of cases the whole of the breakwater, or a large proportion of it, was formed from mass concrete (Figure 3.77). In others the faces were formed by a timber frame, which contained a rubble hearting (Figures 3.78 and 3.79).

Figure 3.66The main components of a breakwater (courtesy Livesey Henderson)

Figure 3.67Section of the North Pier, West Hartlepool, 1847–1858 (courtesy Dock and Harbour Authority)

Figure 3.68 The pier at Nether Buckie, 1855 (courtesy A Stevenson)

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Inner faceThe inner faces of breakwaters are often vertical or near-vertical. In other respects it is similar in construction to the outer face but may be composed of slightly smaller blocks.

Figure 3.69 The Old Pier, Wick, 1823 (courtesy A Stevenson)

Figure 3.70 The pier, Hynish, Argyllshire, 1843 (courtesy A Stevenson)

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Figure 3.71Breakwater, Donaghadee Harbour, 1821 (from Rennie, 1854)

Figure 3.72 Dover breakwater, 1866 (from Harcourt, 1885).

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Figure 3.73 The West Pier, Whitehaven, 1831 (from Williams, 1879)

Figure 3.74 The North Pier, Tyne, 1855–1895 (courtesy A Stevenson)

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Figure 3.75The breakwater, Anstruther, Scotland (courtesy A Stevenson)

Figure 3.76 Piano blockwork used in the breakwater, North Tyne, 1855–1895 (from Coode et al, 1886)

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Figure 3.77Section showing the method of construction of the Fraserburgh breakwater, 1877 (from Willet, 1886)

Figure 3.78The ancient manner of constructing the Cob, Lyme Regis, 16th century (from Smiles, 1904)

Figure 3.79 Typical section of a timber-framed breakwater with rubble hearting (from Shield, 1895)

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BaseThe base of the breakwater was generally difficult to construct, because of the need to work underwater in exposed sea conditions. A few bases are composed of large bags filled with concrete (Figures 3.77, 3.80 and 3.81). In some examples the bag work has been keyed into the rock beneath to give resistance to horizontal sliding (Figure 3.82). In others the bags are massive and become a major part of the breakwater surmounted by a relatively small masonry structure (Figure 3.83). Where it is possible to remove the overlying material, concrete may be cast directly on to a serrated rock formation. In sandy locations rubble may be used to form a wide platform on which to construct the breakwater (Figure 3.74). This technique has been extended to the point at which the rubble mound is so massive, and reaches such a height, that many of the waves probably break before they reach the masonry construction under normal conditions (Figures 3.84 and 3.85).

Figure 3.81 Breakwater, Newhaven, 1880 (from Carey, 1887)

Figure 3.82 Breakwater formed of concrete blocks with foundation bag work keyed into rock (from Shield, 1895)

Figure 3.83 The outer portion of the breakwater, Ardrossan, 1892 (from Robertson, 1895)

Figure 3.80 The North Pier, Aberdeen, 1877 (from Harcourt, 1885)

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ToeThe toe of a breakwater does not perform the same function as the toe of a retaining wall against overturning. The breakwater toe usually acts primarily as an anti-scour device and a wave spoiler. Toes are usually formed from either rubble (Figure 3.73), concrete or stone blocks (Figures 3.76 and 3.86).

TopThe top surface of a breakwater performs a function that is not so pronounced in other types of waterfront wall. It is used primarily to prevent water entering the internal zones of the structure, thereby avoiding washout of hearting and the imposition of water pressure outwards on the outer skin of the structure. The surface may be constructed to a cross fall to aid the removal of surface water (Figure 3.72) or be sealed with granite pitching (Figures 3.87 and 3.88), or macadam (Figure 3.89).

Figure 3.84 Breakwater, Holyhead, 1876 (from Hayter, 1876)

Figure 3.85 Breakwater, Alderney, 1851–1864 (from Townshend, 1898)

Figure 3.86 Section of breakwater showing disposition of bag joggles, Dover, 1898–1909 (from Cunningham, 1908)

Figure 3.87Kilrush Pier, Shannon, Ireland, 1843 (from Shield, 1895)

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3Internal structureBreakwaters may be constructed from solid masonry or concrete (Figure 3.90) or of masonry/concrete walls with a stone or boulder hearting (Figures 3.91 and 3.92). Some walls may have only thin facings to the loose rubble hearting (Figure 3.89). In some examples the blocks are held more rigidly in place by means of ‘bag joggles’ (Figure 3.86), granite fillets or rail cramps (Figure 3.93), the latter being used to tie in those blocks at the corners that would otherwise be prone to movement.

Figure 3.88 Section through breakwater, Alderney, 1851–1864 (from King and Bishop, 1951)

Figure 3.89 Section of breakwater, St Catherine’s Harbour, Jersey, 1856 (from Harcourt, 1874)

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In some cases the blocks are laid on end at a slight angle to form slicework, which is an easier method of construction when using cranes. An early example of a form of slicework (1767) but restricted to the outer skin of the breakwater, is shown in Figure 3.92. A modern version of this technique is shown in Figure 3.94.

Figure 3.90 The south breakwater, Aberdeen, 1873 (from Cay, 1874)

Figure 3.91 St Mary’s Quay, Isles of Scilly (courtesy Beckett Rankine)

Figure 3.92 Section and elevation of the North Pier, Eyemouth, 1767 (from Skempton, 1981)

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Figure 3.94 Sliced blockwork, Lagos Harbour, 1963–1969 (from Bertlin and Partners, 1969)

3.5 SEAWALLS FOR COASTAL DEFENCE

3.5.1 Function and designVertical seawalls are usually found at the tops of beaches where their main function is to prevent the sea encroaching further inland. Although this type of hard defence is no longer used, due to the erosion caused by turbulence at the toe, there are still many vertical seawalls in existence.

The front face of the wall must resist forces imposed by the attacking waves and is often also designed to reflect the wave crests or breaking waves away from the top of the wall. The back face of the wall is usually hidden because the structure normally acts as a retaining wall or as a protective covering to a cliff face. There is no constraint on the shape of the hidden face.

Where the seawall is a retaining structure, the top surface of the wall and the surface of the backfill need to be able to cope with the considerable volumes of water and spray that are thrown on to them in storm conditions. The toe apron of the wall is subjected to the scouring action of waves breaking against and above it.

The main components of a seawall for coastal defence are shown in Figure 3.95. More details of seawalls are given in Stickland et al (1986).

Figure 3.93Typical sectional plan showing position of rail cramps, eastern arm pier head, Dover, 1898–1909 (from Cunningham, 1908)

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3.5.2 Component characteristicsThe component characteristics for an old waterfront seawall are discussed in terms of the outer face, inner face, base, apron, internal structure, and drainage.

Outer faceThe outer face of the wall may be vertical, battered slightly backwards (Figure 3.96) or curved (Figure 3.97a). Frequently this curve is continued upwards to the cope of the wall, forming a concave cross-section, which has the effect of throwing the wave energy back towards the sea (Figures 3.98 and 3.99). Some walls have a stepped front (Figures 3.100 and 3.101). Front faces are usually constructed from mass concrete, concrete blockwork or granite masonry. Concrete blockwork is sometimes faced with granite or basalt (Figure 3.98). In some cases the walls have been refaced with concrete on top of the original facing.

Back faceThe back face is often vertical. In some cases a stepped effect as in dock walls is used (Figures 3.97b and 3.102). Where the wall backs on to a cliff the back face may be integral with the cliff face (Figure 3.97c and Section 3.7). Even in relatively modern walls counterforts may be used (Figures 3.98 and 3.101).

BaseThe bases of seawalls are usually constructed directly on rock or clay substrata. Where firm material does not exist the base is often extended seawards to form a platform (see Section 3.5.2.4).

ApronSeawall aprons are usually formed from mass concrete and protected at the seaward side by timber or steel piles (Figure 3.99). Frequently the apron has been undercut by the sea and a new apron has been constructed below and in front of the original structure. Sometimes this occurs more than once and a series of new aprons is installed (Figure 3.103).

Figure 3.95The main components of a seawall for coastal defence (courtesy Livesey Henderson)

Figure 3.96Seawall, Hornsea, 1907 (from Matthews, 1918)

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Internal structureThe internal structure of a vertical wall is usually simple, of mass concrete or blockwork throughout. Granular or rubble infilling is infrequent except in cases where the sea defences are widened to allow access to the beach or for a slipway (Figure 3.102).

DrainageWater that falls onto the landward side of the seawall during storms or at very high tides should be conveniently drained off. Surface water is sometimes allowed to escape to the sea through scupper holes running through the wall to the front face at promenade or road level. Water that has percolated through the backfilling material may be drained off through a low-level drain running parallel to the wall immediately behind the back face (Figure 3.97b).

Figure 3.97 Typical vertical seawall sections (from Stickland et al, 1986)

Figure 3.98 Seawall, Caroline Place, Hastings, circa 1910 (from Matthews, 1918)

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Figure 3.99 Sea defences, Penzance Harbour (courtesy Penwith District Council)

Figure 3.100 The Royal Prince’s Parade seawall, Bridlington, 1905 (from Matthews, 1918)

Figure 3.101 A concrete block seawall, Margate (from Matthews, 1918)

Figure 3.102 A section of sea defences, Lyme Regis (from Clark, 1935)

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33.6 RETAINING WALLS AND FLOOD DEFENCES

3.6.1 Function and designRetaining walls and flood defences are generally found inland along the sides of rivers and canals. They retain the river or canal banks and prevent them from being eroded as well as acting as a flood defence at times of high water levels. They do not usually have to be designed to cope with severe wave attack, although lakeside and canal walls may be, and they are not usually subjected to surcharge loadings from above, except when they form the edge of a road or rail track.

Canal walls have to resist the effect of suction caused by the blockage factor of vessels using the canal. Erosion can also be caused by boat wash/wake. The suction effect normally increases as the wall deteriorates and also affects the foundation of the wall in many cases.

These walls often need to be modified because of a change in the hydraulic characteristics of the river, or to improve their flood defence function. It is common to find that they have been raised through the addition of a higher coping, or that a new wall has been built in front of the original one. New walls are often built-in with the old one. On the River Thames, new walls have been added twice in some locations. The main components of a retaining or flood defence wall are shown in Figure 3.104.

Figure 3.103Sea defences, Seaford, 1881–1998 (courtesy Southern Water Authority)

Figure 3.104 The main components of flood defences and retaining walls (courtesy Livesey Henderson)

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3.6.2 Component characteristicsIn many respects these walls are constructed like dock walls, with near-vertical or battered front faces and stepped-back faces. Counterforts are also used to increase friction with the backfilling material (Figure 3.105).

River wall bases are frequently extended forwards to form an apron, which provides scour protection. This apron may be formed of concrete or masonry or often a rubble mattress (Figure 3.106). It is also common to find that extra scour protection has been added to the wall sometime after its original construction date.

Some rivers and canals have small masonry walls at water surface level to provide resistance against wave attack (Figure 3.107). This may consist of large coping stones placed above a timber or sheet-piled wall (Figure 3.108). In other instances there may be timber-relieving platforms (Figure 3.109).

Masonry walls may not be continuous along a stretch of river or canal and may be abutted by other forms of construction, eg an earth embankment or a newer concrete or sheet pile structure.

These interfaces between differing forms of construction are often a potential weak point that may be subject to differential movements, settlement, leakage or other form of discontinuity. They should be carefully assessed when considering the masonry structure section of the wall.

Figure 3.105 The Thames River wall at Fishmongers Hall, 1837 (from Simms, 1838)

Figure 3.106 River wall between Manchester Dock and Chester Basin entrances, Liverpool (courtesy Ronald Leach & Associates)

Figure 3.107 Section showing the masonry upper portion, designed to reduce scour by the wash from passing vessels, Grand Union Canal (courtesy British Waterways)

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3.7 SKIN WALLSSkin walls were used when it was considered that the natural rock or hard clay material behind the wall was capable of standing to a vertical profile. In these circumstances it was only necessary to cover this material with a thin layer of concrete or masonry to protect it from the erosive action of the water, or perhaps to enhance the finish of the front face. Walls of this type have been found in Liverpool (Figure 3.110), where the whole wall is a thin skin and in Seaham, County Durham (Figure 3.111), where the bottom half of the wall is of this type and the top half is more conventional. Kinipple (1897) describes this form of construction that was used at the Garvel Graving Dock in Greenock. Outer skin walls can be found as seawalls on the Isle of Thanet where they cover chalk outcrops, at Glentishen where masonry facing has been placed over shale, and at Robin Hood’s Bay, near Scarborough. An important aspect of a skin wall is the means by which it is attached to the ground behind. In the case of the Herculaneum Dock in Liverpool this was done by the use of keys into the soft rock behind (Figure 3.110).

Figure 3.108 River wall on piles (from PIANC, 1912) Figure 3.109 The North River, New York, circa 1883 (from Harcourt, 1885)

Figure 3.110Section and plan of the Herculaneum Dock, Liverpool, 1873 (from Lyster, 1890)

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3.8 BRIDGE PIERS AND ABUTMENTSEarly bridge piers, like dock walls, were generally founded on piled foundations, unless suitable hard material was discovered in the river bed, but the pier structures were more akin to the early breakwaters, being formed of rubble masonry inside a skin of ashlar (Figure 3.112). One problem with the early piers was that they were prone to degradation from river currents and debris carried by the river, and for this reason ‘starlings’ were built around the bottoms of the piers to provide some protection (Home, 1931) (Figure 3.113). As the starlings increased in size they began to restrict flow through the bridge openings and often made the problem worse.

Designs for solid ashlar piers, which would alleviate this problem, were already in existence. An example by the Swiss engineer Labelye (1739) is shown in Figure 3.114. An elegant combination of ashlar and rubble was used for the piers of the Royal Border Bridge, Northumberland (Figure 3.115).

Bridge abutments were constructed in much the same way (Figure 3.116). However, in the case of canal bridges the abutment was often modified to provide sufficient space to accommodate the towpath (Figure 3.117). Canal bridge abutments are sometimes propped apart at the toe by an inverted arch, similar to those found in some docks.

Figure 3.111 The new dock wall at Seaham, circa 1900 (from Gask, 1906)

Figure 3.112 Details of a bridge pier (from Sganzin and Reibell, 1839)

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Figure 3.114 A design for a new Westminster Bridge, 1739 (from Labelye, 1739)

Figure 3.113 Section and plan of a pier of the old London Bridge as it appeared in 1826 (from Home, 1931)

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Figure 3.115 Details of a river pier for the Royal Border Bridge, Northumberland, 1850 (from Bruce, 1851)

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3.9 UNDERSTANDING OLD WATERFRONT WALLS AND THEIR FAILURES

A number of old waterfront walls failed soon after, or even during, construction. Others were modified to accommodate changes in service conditions. For example, many docks were deepened to accept deeper-draught vessels or in the case of the Forth and Clyde Canal it was deepened by raising the lock walls with vertical masonry. Repairs and modifications are often hidden by the water and backfill, so it is prudent to review the kind of alterations made.

Various methods were used to strengthen walls so the berth in front could be deepened. In Birkenhead, a project was undertaken in 1858 to strengthen the wall of the Great Float by adding a new skin, new toe, and sheet piling (Figure 3.118). On the other side of the River Mersey, the East Wall of the Sandon Dock was underpinned in 1903 (Figure 3.119).

Figure 3.116 Details of a bridge abutment (from Sganzin and Reibell, 1839)

Figure 3.117 Typical detail at a canal bridge abutment, Eastern Canal, France, 1882 (from Dawson, 1879)

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Figure 3.118Section of the east wall showing underpinning carried out, Sandon Dock, Liverpool, 1903 (courtesy Mersey Docks and Harbour Company)

Figure 3.119 Proposed method of strengthening the walls of the Great Float, Birkenhead, 1858 (courtesy Mersey Docks and Harbour Company)

Figure 3.120Windmillcrolt Quay, Clyde, constructed in 1838 and strengthened in 1884 (courtesy Clyde Port Authority and Glasgow District Council)

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In Port Glasgow various types of waterfront wall were strengthened to provide for deeper water. The curved wall shown in Figure 3.120 was strengthened by the addition of a new sheet-piled facing, tied back to the original wall and running through to a mass concrete counterweight. Similar strengthening was carried out on the wall shown in Figure 3.121 but in this case the tie rod was taken back to an anchor block. Another wall in the same location was completely buried by a more recently constructed wall (Figure 3.122).

Figure 3.121 Customs House Quay, Clyde, constructed in 1852 and strengthened in 1887 (courtesy Clyde Port Authority and Glasgow District Council)

Figure 3.122 General Terminus Quay, Clyde, original wall constructed in 1849–1850, reconstructed in concrete in 1932–1934 (courtesy Clyde Port Authority and Glasgow District Council)

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In some instances walls began to fail during construction and designs were adapted to prevent failure. Figure 3.123 shows a dock wall under construction at Sharpness where the design has evidently been modified to stabilise an unstable portion of the structure.

Where the wall had already been constructed, but it was decided to further strengthen the structure, a number of novel solutions were used. In Gloucester, two completely different methods were used:

1 A large weight was added to the back of the wall to bear on an oversail, presumably to act as a counterweight (Figure 3.124).

2 Counterforts were added that extend well below the base of the original wall (Figure 3.125).

In some cases the complete failure of a section of wall has forced the engineer not only to rebuild the fallen section, but also to strengthen the part that did not collapse. For example, in Belfast (Salmond, 1879) a collapsed section (Figure 3.126) was built to a different design (Figure 3.127) and the portion of wall still standing was tied back and encased in a new structure (Figure 3.128). In Limerick (Hall, 1891) the dock wall (Figure 3.129) collapsed due to a toe failure when the timber grillage gave way between pile heads. This failure was caused by a combination of heavy rain and very low water. The engineer’s original proposed reconstruction (Figure 3.130) was considered to be too expensive and he was forced to use the modified design (Figure 3.131).

Figure 3.123Construction work on a dock wall in Sharpness, 1874 (courtesy British Waterways)

Figure 3.124 Section of a dock wall showing the addition of a large concrete block above the oversail, Gloucester, 1852 (courtesy British Waterways Archives)

Note that propped walls indicate that some construction problems may have been encountered

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3Figure 3.125Section of a dock wall showing a counterfort that has been added and extended below the original foundation level, Gloucester, 1908 (courtesy British Waterways Archives)

Figure 3.126 Collapse of a section of dock wall, Belfast, 1878 (from Salmond, 1879)

Figure 3.127The design for the reconstruction of the dock wall, Belfast, 1878 (from Salmond, 1879)

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Figure 3.128 The design for the strengthening of a section of the dock wall, Belfast, 1878 (from Salmond, 1879)

Figure 3.129 Section of the dock wall that collapsed, Limerick, 1887 (from Hall, 1881)

Figure 3.130 The proposed design and reconstruction of the dock wall that collapsed, Limerick, 1887 (from Hall, 1881)

Figure 3.131 The accepted design for the reconstruction of the dock wall, Limerick, 1887 (from Hall, 1891)

Collapsed walls were not always rebuilt. In Barrow (Savile,1904) an open-piled quay was built on top of the collapsed portion of wall (Figure 3.132).

More recent examples of structural failures include the river wall at Bridgewater due to excessive water pressure build-up following a burst water pipe (Case study 2.1), the collapse of the Bristol river wall in similar circumstances (Case study 3.1) and the failure of the Dawlish seawall following storm damage. At Bridgewater and Bristol, these were reconstructed to match the existing adjacent seawalls. At Dawlish extensive emergency repairs were carried out to quickly reinstate the adjacent railway line.

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Figure 3.132 Timber quay built on top of a collapsed portion of dock wall, Barrow-in-Furness, 1901 (from Savile, 1904)

Bristol Portway is a primary highway linking Bristol city to the M5. It runs about 6.5 miles along the bank of the Avon gorge and under the Clifton Suspension Bridge. Construction of the Portway was started in 1919, partly on the line of the original Bristol Port and Pier Railway. In 1924, about 200 yards (180 m) of newly constructed concrete embankment slid into the river, posing a hazard to navigation and adding a further 12 months to the duration of the work.

In 2001, a 27-inch (690 mm) water main burst near the junction with Bridge Valley Road, causing a major collapse and putting the road out of action for several months. One passer-by was swept into the river, but was rescued uninjured. The reconstruction of the road, which took some time, resulted in severe traffic problems on the route. The responsibility for the failure was placed with Bristol Water, because it was their water main that fractured and increased the hydrostatic loading on the rear of the wall causing the collapse.

Figure 3.133 Failure of river wall and collapse of road in 2001 Figure 3.134 Failure of river wall in 2001

Case study 3 .1 River wall failure at Bristol Portway, Bristol (courtesy ICE South West)

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COODE, J, HARCOURT, L F V, MESSENT, P J, DIXON, J, PARKES, W, GILES, A, HAYTER, H, REDMAN, J B, FAIJA, H, BANISTER, F D, MACKINNON, A K, MARTINDALE, B H, STOTHERT, J L, CHALK, W J, DOUGLASS, J N, MACKENZIE, J B, LANGLEY, J, KYLE, J, CAREY, A E, STRYPE, W G (1886) “Discussion on concrete work for harbours” Minutes of the proceedings, vol 87, 1886, Institution of Civil Engineers, London, UK, pp 138–196

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GILES, A (1858) “On the construction of Southampton Docks” Minutes of the proceedings, vol 17, 1858, Institution of Civil Engineers, London, UK, pp 540–550

GREEVES, I S (1980) London Docks 1800–1980. Civil engineering history, Thomas Telford, London, UK (ISBN: 978-0-72770-114-5)

HADFIELD, C (1962) British canals. An illustrated history, Pheonix Publishing, London, UK

HADFIELD, C and SKEMPTON, A W (1979) William Jessop, engineer, first edition, M&M Baldwin Publishers, Kidderminster, UK (ISBN: 978-0-71537-603-4)

HALL, W J (1891) “On the failure of the Limerick (lock walls and the methods adopted for reconstruction and repairs” Minutes of the proceedings, vol 103, 1891, Institution of Civil Engineers, London, UK, pp 257–263

HARCOURT, L F V (1874) “Account of the construction and maintenance of the harbour at Braye Bay, Alderney” Minutes of the proceedings, vol 37, 1874, Institution of Civil Engineers, London, UK, pp 60–83

HARCOURT, L F V (1885) Harbours and docks: their physical features, history, construction, equipment and maintenance with statistics as to their commercial development, Clarendon Press, Oxford, UK

HAVERFIELD, F (1924) The Roman occupation of Britain, Clarendon press, Oxford, UK

HAWKSHAW, J C (1875) “The construction of the Albert Dock at Kingston upon Hull” Minutes of the Proceedings, vol 41, 1875, Institution of Civil Engineers, London, UK, pp 92–113

HAYTER, H (1876) “Holyhead new harbour” Minutes of the Proceedings, vol 44, 1876, Institution of Civil Engineers, London, UK, pp 95–112

HOME, G (1931) Old London Bridge, John Lane the Bodley Head Ltd, London, UK

HURTZIG, A C (1888) “The Alexandra Dock, Hull” Minutes of the Proceedings, vol 92, 1888, Institution of Civil Engineers, London, UK, pp 164–176

JACKSON, G (1983) The history and archaeology of ports, first edition, Littlehampton Book Services Ltd, UK (ISBN: 978-0-43707-539-0)

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KIDD, W (1885) “On the blasting and removal of rock under water and the construction of a deep water quay at Blyth Harbour” Minutes of the proceedings, vol 81, Institution of Civil Engineers, London, UK, pp 302–314

KING, J L and BISHOP, R W (1951) “Maintenance of some rubble breakwaters” ICE Engineering division papers, vol 9, 7, Institution of Civil Engineers, London, UK, pp 1–35

KINIPPLE, W R (1897) “Greenock Harbour” Minutes of the proceedings, vol 130, 1897, Institution of Civil Engineers, London, UK, pp 276–97

LABELYE, C (1739) A short account of the methods made use of in laying the foundations of the piers of Westminster-Bridge with an answer to the chief objections that have been made thereto; drawn up by the order of the Right Hon. &c. the commissioners appointed by act of Parliament for building a bridge at Westminster; to which are annex’d, the plans, elevations and sections belonging to a design of a stone-bridge, adapted to the stone piers which are to support Westminster-Bridge, with an explanation of that design, London, UK

LAWSON, R M and RICHARDSON, B G (1986) Structural renovation of traditional buildings, R111, CIRIA, London, UK (ISBN: 978-0-86017-257-4). Go to: www.ciria.org

LYSTER, G F (1890) “Recent dock extensions at Liverpool with a general description of the Mersey Dock estate, the port of Liverpool and the River Mersey” Minutes of the proceedings, vol 100, 1890 Institution of Civil Engineers, London, UK, pp 2–39

MARSDEN, P (1981) “Early shipping and the waterfronts of London” Waterfront Archaeology in Britain and Northern Europe, Research Report No. 41 Council for British Archaeology, York, UK

MASON, T (1915) “The improvement of the River Clyde and Harbour of Glasgow 1875–1914” Proceedings of the ICE, vol 200, 1915, Institution of Civil Engineers, London, UK, pp 101–135

MATTHEWS, E and CUNNINGHAM, B (2013) Coast erosion and protection, third edition, HardPress Publishing, London, UK (ISBN: 978-131341-630-6)

MILNE, G (1981) “Medieval riverfront reclamation in London” Waterfront Archaeology in Britain and Northern Europe, Research Report No. 41, Council for British Archaeology, York, UK

MILLER, D (1863) “Structures in the sea, without cofferdams; with a description of the works of the new Albert Harbour at Greenock” Minutes of the Proceedings, vol 22, 1863, Institution of Civil Engineers, London, UK, pp 417–438

BERTLIN AND PARTNERS (1969) Port structures, research project, National Ports Council, Kew, UK

PIANC (1912) XII Congress, Philadelphia 1912, second section: ocean navigation: communications, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org

PIANC (1986) Final report of the international commission for the study of locks, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/publications.php

RENNIE, J (1854) The theory, formation and construction of British and foreign harbours, vol 2, J Weale, UK

ROBERTSON, R (1895) “Ardrossan Harbour extension” Minutes of the proceedings, vol 120, 1895, Institution of Civil Engineers, London, UK, pp 289–298

SALMOND, T R (1879) “The River Lagan and Harbour of Belfast” Minutes of the proceedings, vol 55, 1879, Institution of Civil Engineers, London, UK, pp 22–35

SAVILE, L H (1904) “Lowering of the sill of the Ramsden Lock, Barrow in Furness” Institution of Civil Engineers, vol 158, 1904, Institution of Civil Engineers, London, UK, pp 106–119

SCOTT, A (1895) “Deep water quays Newcastle-upon-Tyne” Minutes of the proceedings, vol 119, 1895, Institution of Civil Engineers, London, UK, pp 291–298

SGANZIN, J-M and REIBELL, F (eds) (1839) Programme ou resumé des leçons d’un cours de construction, avec des applications tirées specialement de l’art de l’ingenieur des ponts et chaussées, fourth edition, Carilian-Goeury et V. Dalmont, Paris, France

SHIELD, W (1895) Principles and practice of harbour construction, Green and Co, London, UK

SIMMS, W F (eds) (1838) Public works of Great Britain consisting of railways, bridges, canals, docks and other important engineering works. With descriptions and specifications, J Weale, UK

SKEMPTON, A W (ed) (1981) John Smeaton FRS, first edition, ICE Publishing, London, UK (ISBN: 978-0-72770-088-9)

SKEMPTON, AW (1987) British civil engineering 1640–1840: A bibliography of contemporary printed reports, plans and books, first edition, Contiuum International Publishing, London, UK (ISBN: 978-0-72011-746-2)

SMILES, S (1904) Lives of the engineers: harbours, lighthouses and bridges, John Smeaton and John Rennie (1761–1821), vol 2, John Murray, London, UK

SOWDEN, A M (1990) Maintenance of brick and stone masonry structures, Chapman and Hall, London, UK (ISBN: 978-0-44231-166-7)

STEVENSON, T (2011) Design and construction of harbours, revised edition, Cambridge University Press, Cambridge, UK (ISBN: 978-1-110802-967-4)

STICKLAND, I W, HAKEN, I C and ALLSOP, N W H (1986) Sea walls. Survey of performance and design practice, TN125, CIRIA, London, UK (ISBN: 978-0-86017-266-6). Go to: www.ciria.org

STONEY, B B (1874) “On construction of harbour and marine works with artificial blocks of large size” Minutes of the proceedings, vol 37, 1874, Institution of Civil Engineers, London, UK, pp 332–355

SUTHERLAND, R J M (1988) “How much did workmanship affect the robustness and load bearing capacity of old masonry walls?” In: Proc of conf, Masonry International, March 1989, vol 2, 1, International Masonry Society, London, UK, pp 1–34

SWANN, D (1959) English docks and harbours 1660 to 1830, PhD thesis, Leeds University, Leeds, UK

TOWNSHEND, B O (1898) “Repairs at Alderney breakwater” Minutes of the proceedings, vol 131, 1898, Institution of Civil Engineers, London, UK, pp 307–310

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WILLET, J (1886) “The fishing boat harbours of Fraserburgh, Sandhaven and Portsoy in the north east coast of Scotland” Minutes of the proceedings, vol 87, 1886, Institution of Civil Engineers, London, UK, pp 123–133

WILLIAMS, T E (1879) “Whitehaven harbour and dock works” Minutes of the Proceedings, vol 55, 1879, Institution of Civil Engineers, London, UK, pp 36–48

Statutes

British StandardsBS 5390:1976 Code of practice for stone masonry (superseded)

BS 5628-1:1978 Code of practice for use of masonry. Structural use of unreinforced masonry (superseded)

BS 5628-3:2001 Code of practice for use of masonry. Materials and components, design and workmanship (superseded)

BS 5628-1:2005 Code of practice for the use of masonry. Structural use of unreinforced masonry (superseded)

BS EN 1996-1-1:2005+A1:2012 Eurocode 6. Design of masonry structures General rules for reinforced and unreinforced masonry structures

BS EN 1996-1-2:2005 Eurocode 6. Design of masonry structures. General rules. Structural fire design

WebsitesBrick Development Associate: www .brick .org .uk

MPA-Cement: http://cement .mineralproducts .org/

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4 Performance assessment, risk attribution, inspections and data collection

4.1 OVERVIEWThis chapter discusses the process of assessing and analysing risk in the management of waterfront walls. The approach described allows those responsible for these assets to optimise their management in order to ensure that they perform well, safely and cost effectively. Note that the comprehensive process described in this chapter may not be wholly appropriate for those with a very limited number of walls to manage (perhaps only one), but it is expected that the chapter will be useful in demonstrating the value and principles of risk-based management. Figure 4.1 provides an overview of the chapter.

Management actionsAdministrative context

Physical context

Severe event(Section 5 .5)

Management of risk(Sections 2 .1 to 2 .3)

Responsibilities (Section 2 .4)

Powers(Section 2 .5)

Beneficiaries(Section 2 .8)

Funding(Section 2 .9)

Physical form and purpose

(Chapter 3)

Physical processes (Section 6 .3)

Loads(Sections 7 .1 to 7 .3)

Wall stability(Section 7 .4)

Historical data(Section 6 .4)

Framework for decisions (Section 4 .3)

Risk analysis(Section 4 .4)

Performance assessment(Section 4 .5)

Operations(Section 5 .2 to 5 .3)

Monitoring and inspection

(Sections 4 .6 to 4 .7)

Data acquisition (Section 4 .7)

Data management (Section 4 .8)

Wall investigation (Sections 6 .5 to 6 .9)

Decision on intervention

Maintenance, repair and rehabilitation (Sections 5 .4 and

Chapter 8)

Regulations and consents

(Sections 2 .6 to 2 .7)

Figure 4.1Overview of Chapter 4

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The chapter provides an overview of waterfront wall performance assessment and risk analysis, along with a discussion of related data gathering and data management techniques. This section highlights the general concepts for the chapter and the relationship between the different activities detailed within it.

Sections 4.2 and 4.3 explain the framework and principles of methods for conducting old waterfront wall performance assessments, including the diagnosing of main failure mechanisms. The data required for these activities, and the way the data is used and presented, linking them to failure mechanisms.

Section 4.4 discusses how risk analysis can be used to evaluate and show how it can be attributed to various segments of an old waterfront wall system. The elementary components of a risk analysis are detailed, as well as subsequent tasks such as risk attribution and evaluation.

Section 4.5 presents the different types and frequencies of inspections, and details the underlying principles for managing, conducting and reporting inspections. The different types of features to be observed are presented and are linked to possible deterioration and damage mechanisms.

Section 4.6 identifies the importance of conducting investigations and monitoring (including use of instrumentation) to gather data for failure mechanism diagnosis and old waterfront wall performance assessment (see also Chapter 6).

Old waterfront wall performance assessments and risk analysis rely on the analysis of data, which may come from many different sources, and will remain useful throughout the life of the structure. Section 4.7 details the principles of data management related to old waterfront walls, including the need to digitalise all data, the use of electronic data information systems, such as GIS-based systems, and the value in retaining both the historic and the new drawings or surveys of the wall for as long as the structure remains.

4.2 FRAMEWORK FOR ANALYSIS AND DECISION MAKING

Waterfront walls were originally constructed to fulfil a specific function or functions (see Section 2.2.3 and Chapter 3). These functional requirements may change over time as the structure may be required to fulfil new roles. Standards of service are the standards of performance that the wall should conform to in order to fulfil these functions. They may be defined by reference to:

ªª the original or historic use or function of the wall

ªª the current use or function of the wall

ªª the loads to which it may be subjected

ªª the physical environment in which it must survive

ªª acceptable tolerances in its performance

ªª its appearance

ªª or a combination of any of these.

For example, for a quay wall a performance specification could be expected to cover:

ªª the size, type and draught of vessels to be accommodated

ªª maximum vertical and horizontal loads to be applied to the wall, including any equipment on the quay and the stacking of material on the quay apron

ªª the range of water levels to be accommodated both in front of and behind the wall

ªª permissible settlement of the wall and the apron

ªª permissible horizontal movement of the wall.

Breakwaters and sea defence walls might require specifications relating to sea states (waves, currents), areas of protection, acceptable levels of overtopping, design water levels and risk of exceedance.

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Definition of standard of service is essential, ie it forms the basis on which:

ªª the results of performance assessments are compared

ªª the ‘trigger levels’ at which specific actions are initiated are identified

ªª the inspection and monitoring programmes are developed

ªª decisions are made concerning the economics of various options for maintenance and rehabilitation.

In some instances it may be necessary to determine the loads a particular wall is able to take before reviewing or setting appropriate standard of service (especially for old structures where this information may have been lost or may not exist). It is important that the levels of service loading adopted are both suitable and attainable. Sometimes it may be necessary to take account of the changing use of a wall or to define a standard of service required that may relate to a future use.

Changes in the structure can also occur due to factors such as deterioration over time, lack of maintenance, damage (eg from vessel impacts, storm surges, flooding, fire or vandalism) or ground movement. There are many reason, therefore, to periodically undertake a performance analysis, especially on old waterfront walls when either:

ªª there is a requirement for a change in the function of the structure (eg additional loading due to new development or change in use)

ªª there is a need to change the height or geometry of the wall as a result of change of use or to address climate change issues (sea level rises)

ªª when deterioration or a specific event (storm, impact) has led to the need for the capacity of the structure to perform its function to be reassessed (eg damage induced reduction in the FoS).

The level of detail included in a risk assessment of an old waterfront wall should depend on the level of confidence that is required to support various types of safety and asset management decisions. This approach is referred to as a ‘decision-driven’ approach (see Stern and Fineberg, 1996) to determining the level of sophistication required for decision making (see Section 2.2.3). This required level of confidence can be expected to vary with the level of risk posed by a specific waterfront wall, and any requirements of engineers and/or owners (where applicable) for the provision of confidence and defensibility in support of their decisions.

This chapter outlines an approach by which such analysis can be undertaken, and discusses the following:

ªª methods and tools available for performance assessment

ªª analysis of risks

ªª attribution of residual risk

ªª inspections

ªª investigations

ªª instrumentation and monitoring.

This is to provide evidence and information to allow informed decisions to be made on the structure’s ability to either continue to perform its required functions, to perform additional requirements or, in some cases, for its capacity to be de-rated.

Risk assessments should be carried out using the knowledge of those familiar with old waterfront walls, including a professional engineer with suitable experience. A risk assessment workshop is a useful means of initiating and setting the assessment and defining an appropriate scope. When setting out the ‘scope’ of the risk assessment, it is important to establish and understand:

ªª the basis for the original design

ªª the current functional requirements

ªª any third party interfaces (eg structural and operational).

The assessment of such aspects can also help to identify funding sources for refurbishment and/or maintenance of the structure if required.

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4.2.1 Performance assessment toolsAsset managers seek to make good investment decisions that minimise whole-life costs and maximise gains, while ensuring residual risks of failure are reduced to as low as reasonably acceptable now and in the future. Gains may include environmental, improved functionality, reduced liability, improved aesthetics and increased life expectancy. To achieve this it is important to ascertain the:

ªª actual performance (or reliability/safety) of the asset (or asset system)

ªª residual (remaining) risk associated with failure of the asset.

Within this general context, and that of the risk-based approach outlined in Chapter 2, three closely related tools are available for the assessment of old waterfront walls:

1 Structural performance (or ‘reliability’) assessment (see Section 4.4): this is the process of understanding the anticipated structural performance or reliability of an existing waterfront wall given its current state. The most comprehensive assessments should be based on a diagnosis of the actual or possible initiating causes of failure in order to identify means to remediate or prevent these causes. Structural performance/reliability assessments are also inputs into asset system analyses. For owners with a limited number of old waterfront walls and where a screening (qualitative) assessment indicates that risks and consequences are low then comprehensive performance and reliability analyses are not required. Where there is doubt, professional engineering judgement should be sought.

2 Asset system or portfolio risk analysis (see Section 4.3): this is a process that determines the overall level of risk associated with the asset system or portfolio of assets as a whole, given the inputs of the structural performance/reliability assessments and the potential impacts of failure.

3 Risk attribution to assets (see Section 4.3.10): this is an output of the asset system or portfolio analysis and identifies the contribution of each asset to the residual risk posed by failure of any of the assets in the system or the portfolio (ie identifies those assets that contribute most to the risk).

For individual waterfront walls, which do not form part of a system of assets that act together in an area to provide benefits (eg transport links) or reducing risks (eg f lood protection), then an asset system analysis may not be required. However, when assessing the performance of an organisations’ portfolio of assets, both structural performance assessments and risk attribution are activities that may need to be undertaken in order to determine which assets in the portfolio contribute the most to business risk (ie loss of earnings, remediation/rebuilding costs, loss of reputation, exposure to litigation, fines and penalties).

To ensure an appropriate level of long-term safety of a waterfront wall or of a whole asset system, these tools should be used regularly, as well as on specific occasions, such as during or immediately after severe loading events (floods, storms, earthquakes, excessive impacts etc). Use of consistent analysis tools and techniques help to support decision making at all levels by providing:

ªª an improved understanding of the role that an individual asset plays within a larger system or portfolio of assets

ªª a better understanding of the impact of uncertainty within the estimated risk

ªª the ability to progressively refine the analysis.

A risk analysis of the individual asset or asset portfolio, taking into account the structural performance assessment and the consequences of failure, helps asset managers prioritise the actions that need to be taken and to optimise their maintenance strategy. These actions can include, for example:

ªª carrying out an emergency response or procedure

ªª conducting a complete diagnosis of some part of the structure or asset system in order to design and implement remediation of structural or operational problems

ªª undertaking some ‘routine’ maintenance repairs

ªª ‘doing nothing’ except continuing with regular inspection and assessment of the assets.

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Figure 4.2 illustrates a decision making process from system analysis to action (note that the part of the figure enclosed in the dotted box represents the initial system assessment/analysis).

Figure 4.2 Assessments and decision making for owners/asset managers (after CIRIA; Ministry of Ecology; USACE, 2013)

Crucially the level of confidence in these analyses and assessments should be defined in any reporting and will depend on the:

ªª stage within the asset life cycle at which the assessment has been carried out

ªª available data used, including its relevance, reliability and age

ªª treatment/combination method(s) used in the assessment.

The confidence in the performance assessment directly affects the possible measures to be adopted following the assessment. For example, less reliable results are more likely to suggest further data gathering and assessment rather than immediate remedial works and until the confidence level is such that works are readily identified the AMS will need to continue to evolve (see also Section 2.2.1).

Emergency actions can be one of the following:ªª intensify observationsªª waterfront wall reinforcement worksªª appoint expert engineer(s) to better evaluate the situation and propose solution(s)ªª inform authorities in charge of population safety of a possible failure.

Data can be a visual inspection report – all types including routine, periodic, and during and post flood or other, instrumentation and monitoring data, investigation results, and various (any) other types of data

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4.2.2 Role of data in performance assessmentsAll three types of assessments discussed in Section 4.2.1 rely on the processing of data to reach a conclusion. Figure 4.3 shows how the different sections of this chapter are integrated in terms of the data they use, produce and manage.

Some data may already be available at the start of an assessment process, for example from earlier monitoring using installed instrumentation (see Section 4.6). Missing data can be gathered during the performance/reliability assessment process either during a specific inspection (see Section 4.5) or during a more detailed investigation (see Section 4.6). All data has to be recorded and managed and has its place in a suitable information system (see Section 4.7).

The following terminology is used in this guide:

ªª inspections: visually manmade observations (during a field visit), including ‘aided’ methods such as video cameras, registration on laptop/tablet/smart phone

ªª investigations: technical measurements (or sets of measurements) gathered during or for an assessment process

ªª monitoring: regular technical measurements (or sets of measurements) or observations carried out at regular periods over a period of time

ªª instrumentation: the use of measuring devices and equipment used to collect data. These devices may be installed permanently, temporarily or intermittently, and may be operated manually or automatically.

4.3 RISK ANALYSIS AND ATTRIBUTION

4.3.1 OverviewRisk analysis combines the probabilities and consequences of failure (see Section 2.3) and is conducted to:

ªª explicitly evaluate the level of risk assuming no mitigation

Section 4 .5Inspections

Section 4 .6Investigations,

instrumentation and monitoring

Section 4 .4 Performance analysis and diagnosis

Section 4 .3 Risk assessment and attribution

Section 4 .7 Knowledge and data management

Figure 4.3 Integration of the data handled by each of the activities in this chapter

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ªª identify the monetary and non-monetary costs and benefits of mitigation options for reducing risks

ªª account for uncertainty and variability in possible outcomes to better inform decision making.

This section explains how risk analysis may be carried out and the levels of risk associated with an individual wall or wall segment identified.

The analysis of risk should take into account the probability and distribution of all hazards and threat levels and identify the likely consequences of all possible failures modes. However, this is not always practical and an appropriate framework should be selected to undertake an adequate and reasonable analysis of risk or its elements. For example:

1 A tiered approach (see Section 2.4.3) can be adopted in which the outcomes of an initial risk analysis are used to justify further action or inaction. Tiered risk analysis of structures is not necessarily a set of distinct levels, but it is a progression from a simpler approach to one that is more complex – depending on the requirements and level of risk.

2 A phased approach can be used for reduction of uncertainty in the data to be used in the risk analysis. Where appropriately detailed or accurate data is not available, then surveys, studies or measurements may be undertaken to obtain additional data and information of the required quality and coverage. For example, where information about wall materials is required, desk study and simple sampling may be used initially, but may be followed by subsequent use of more detailed surveys, materials testing and other investigation methods.

Depending on the tier or phase used, various approaches to risk analysis can be applied including:

3 A qualitative risk analysis (or semi-quantitative analysis): this may be used as a first step for risk analysis of any waterfront wall and might be a simple report, using descriptive or numeric rating scales to describe the magnitude of potential consequences and the likelihood that those consequences will occur. Its result can typically be represented in a risk evaluation matrix as shown in Figure 4.4. The descriptions of the likelihood of failure (rare, unlikely, possible etc) can also be matched with numeric probability bands (0.01–0.1, 0.1–1 etc) if required. The advantage of the qualitative approach is the short period of time needed to carry out the analysis. A disadvantage is the subjectivity of the assessor(s), so that the outcome might be less stable and satisfactory than that from a more rigorous analysis. In many cases, a qualitative analysis undertaken by one or (preferably) more proficient and experienced engineers familiar with risk assessment will be sufficiently reliable to support a broad-scale screening analysis of risks.

Figure 4.4 Example of a risk matrix that can be used in qualitative risk analysis

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4 A quantitative risk analysis: while qualitative analysis methods may be sufficient where consequences and/or the probability of wall failure are considered to be low, it may be more appropriate to apply a more time-intensive, complex quantitative method. This can help where the initial qualitative risk analysis indicates that either the risk is high or that there is high uncertainty in the likely structural response of the wall to potential threats. This approach is based on numerical values of the potential consequences and likelihood of failure, the intention being that such values are a valid representation of the actual magnitude of the consequences and the probability of the various scenarios that are being examined (Figure 4.5). The advantage of the quantitative approach is that it is objective in nature, while the disadvantages might be the time needed and possible limited availability of suitable data.

In a quantitative risk analysis, the numeric value of risk is intrinsic to a given structure, including all potential hazards, and any of the consequences of failure. Risk is a socially constructed concept and the way that the various aspects of risk are quantified and evaluated depends on the stakeholders’ perception of the potential losses as a result of wall failure. Consequently it is usual practice that such analysis is carried out by a multi-disciplinary team. Damage to human, economic, environmental, social and architectural/heritage aspects can be calculated and evaluated using different methods, indicators or measurements such as people at risk, likely loss of life, numbers of jobs lost, financial costs and/or monetary damages, and local economic consequences in the long-term. Evaluation of the significance of such quantified risks is sometimes categorised (Figure 4.5).

Figure 4.5 Graphical evaluation of quantified threats and consequences

Detailed quantitative risk analysis approaches using fault tree analysis (FTA) and event tree analysis (ETA) (see Section 4.4.7) are valuable for providing insight and understanding failure modes and providing specific estimates of risks (probability and consequences) for stakeholders. However, uncertainties in input values and outcomes need to be taken into account and communicating uncertainties to decision makers is vital. There is no one general universal method of developing fault/event trees or quantitative risk analysis and it is recommended that they should normally only be undertaken by experienced practitioners.

4.3.2 Knowledge gaps and uncertaintyKnowledge gaps and uncertainty are prevalent in all the types of assessment and risk analysis activities, so it is important to recognise and record them where known.

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Risk analysis is often undertaken despite knowledge gaps, which could influence the outcome if filled. The risk analysis process should recognise this and identify where known gaps exist either in the data or in the methods of analysis used for the assessment.

Such gaps could exist in any of the data used in the risk analysis or in the parameters used to derive certain scenarios. For example data on the prevailing hydrodynamic or hydrologic conditions, ground topography and structure geometry, soil typology and strength parameters and structural materials can all vary in completeness, level of accuracy and detail. Such variances can create imprecision in the results from using limited data, which may need to be improved to reduce uncertainty in the outputs of the risk analysis.

Knowledge of the structure and/or its foundations is inevitably incomplete, as is understanding of the impact that interventions will have on the structure. As more aspects of a wall are modelled and multiple models are encapsulated into a single risk assessment (for example, in the case of a flood defence wall, using a hydrodynamic model, defence failure model and impacts assessment model), the need to handle uncertainty in a robust manner becomes ever more important. So it is essential to provide some measure of the uncertainty associated with the overall data, analysis and outputs. This information is invaluable as it provides a level of confidence in the various output risk metrics.

The level of uncertainty that is acceptable will depend upon the application of the risk analysis and on the perceived level of impacts of failure. So the appropriate level of analysis will need to be ascertained through a tiered approach to risk assessment (see Section 2.4.3).

4.3.3 Components of risk analysisAn analysis of the risk of failure requires identification and examination of all component factors that may influence the risk of a wall failing. The process should be able to then evaluate and integrate all these components. Figure 4.6 provides a framework for analysing different components of risks associated with wall failure, including the numbers of subsections containing further information.

Figure 4.6 A framework for the analysis of risk components associated with wall failure (from CIRIA; Ministry of Ecology; USACE, 2013)

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The steps shown in Figure 4.6 comprise:

ªª Risk (threat/hazard) identification: to analyse risk the factors affecting risk must be recognised and recorded, eg f lood pathways and receptors of a f lood risk system where a wall serves a f lood defence function or a vessel collision with a harbour wall resulting in its withdrawal from operative service.

ªª Threat event probability estimation: floods, earthquakes and other natural threats are episodic events. Large floods and seismic events are rarer than medium sized or small ones. The probability of each size of event can be characterised as the chance that it will occur in any one year (ie its annual probability).

ªª Analysis of wall performance: the performance of a waterfront wall can be expressed in terms of whether it meets its present functional requirements. Failure of a wall is when it no longer meets these requirements, whether due to settlement, collapse, or any other change resulting in the inability to withstand applied loads or provide the required degree of protection. The probability of wall failure depends on the performance of the structure and the probability of threat events. How and where a waterfront wall might fail will partly determine the receptors that are affected. This is an important consideration in determining the level of detail required in assessing the level of risk. In a quantitative risk analysis the likelihood of failure needs to be expressed in probabilistic terms.

ªª Impact assessment: to assess potential damage and/or to prepare future mitigation plans. If the wall serves a flood defence function then inundation patterns, including water depths, flow velocities, and timing of inundation are important factors that determine potential consequences. If the wall serves to protect or support valuable infrastructure, then the impact of failure on other parties will need to be identified. If the wall serves to retain water, eg in a canal, then an uncontrolled release of water can pose a flood threat if the adjacent ground is lower than the canal. Whether or not the canal is raised, water leakage can affect navigation depths within the waterway and also users.

ªª Consequence analysis: a ‘consequence’ results when a vulnerable person or property is exposed to a wall failure and suffers actual harm. Consequences may be a direct result of wall failure (eg injury, death, property/vessel damage) or, if a flood defence, of subsequent flooding (eg casualties, damaged buildings and/or contents). There may also be indirect consequences to consider (eg health and social impacts, loss of business earnings due to recovery time). So an analysis and evaluation of the likely consequences of a wall failure needs to be estimated in order to determine the potential magnitude of the impacts.

ªª Estimation of the level of risk: an estimate of the level of risk is calculated by taking into account the probability of a failure occurring and the potential consequences of that event derived from the previous steps. This step produces the results of a risk analysis.

ªª Effectiveness of existing controls: controls are measures, either structural or non-structural, taken to reduce the probability of failure, or reduce its consequences. Controls can apply to the source event (eg storm warning), the structure (eg wall maintenance, monitoring, and emergency management) or to potential consequences (eg danger/flood warning, evacuation, access closure). Existing controls can and should be considered in the estimations of the event probability, probability of the wall failure, and of the consequences of the failure.

Risk attribution and risk evaluation are further optional steps. These can be undertaken at the scale of individual assets, or for portfolio risk assessments, whichever is appropriate to the scale of the organisation, the risk analysis, and to the objectives of the risk assessment:

ªª Risk attribution: waterfront walls and other associated assets all contribute a portion of the risk of failure of a system within which they operate (ie as part of a f lood defence system, a coastal protection system, a port or harbour, a canal or waterway). Risk attribution is a method of attributing the residual risk (the amount of risk remaining after mitigation) in the system to individual assets or segments of assets. This follows the previous risk analysis methods and informs prioritisation of investment between assets and asset segments (ie whole wall structures or sections of wall).

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ªª Risk evaluation: broader society determines the acceptability or tolerability of the levels of residual risk posed by the failure of infrastructure assets as it does for many other risks to society (see Section 4.3.11). Communicating the evaluation to decision makers is important to help them to determine whether or not to proceed further with risk reduction measures given the level of residual risk.

4.3.4 Threat/hazardidentificationIn order to analyse risk of wall failure, the source, pathway and receptor components affecting risk must first be recognised and recorded to identify what might happen and what situations might arise. The actual risk can be analysed by identifying a chain of causes and effects such as:

ªª rainfall or storms causing high water levels that increase the pore water pressure load on walls or induce rapid draw-down failure after high water

ªª partial failure of the structure may result in further damage and loss of material behind the asset or inundation of water

ªª erosion of the land following a structural failure resulting in an uncontrolled release of water, damage to or loss of property, access, other services and/or amenities

ªª failure of a wall retaining or protecting a transport corridor (road and/or rail) resulting in loss/reduced access for vital transport systems

ªª flooding due to a breach of a canal wall (where the canal is elevated above adjacent ground, including on an aqueduct)

ªª failure of a canal wall leading to navigation stoppage because of a loss of water or the waterway is obstructed by the failed wall

ªª failure of waterway or dock walls caused by rapid draw-down due to failure of a lock gate or dock gate elsewhere

ªª formation of a breach through uncontrolled leakage and then discharged into some unknown buried asset (eg storm drainage system).

The risk identification process should consider the following factors:

ªª environmental threats (storm waves and surges, high river levels, extreme rainfall and other hydro-meteorological events, such as earthquakes) and their likelihood/probabilities

ªª accidental or unanticipated loadings from physical impacts, damaged water pipes etc

ªª wall condition, deterioration, and its probability of failure under load (ie reliability)

ªª characteristics of the hinterland (eg geology and friability of soil and vulnerability to flooding)

ªª nature, extent and vulnerability of receptors (human, environmental, economic)

ªª existing risk control mechanisms and measures, and their effectiveness(eg flood warning systems, gate closures, stop log deployment)

ªª uncertainty (in knowledge/data).

To assess these factors, it may be possible to use knowledge from past events, but for rare events this may well not suffice. In any event, the circumstances, for example the condition of the structure(s), and the use of the area and/or vulnerable buildings or infrastructure may have changed.

Through research, it is necessary to investigate the:

ªª probabilities and magnitudes of all possible threat events

ªª probabilities of failure and the effects of any changes to the wall

ªª the consequences of impacts and wall failure.

With this information, the subsequent risk analysis can be carried out using one of the following approaches:

1 Creating specific scenarios by selecting particular combinations of, for example, loading conditions,

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failure probabilities, impact area/zone characteristics and human responses. These scenarios may not be prescribed and can lead to variable analytical outcomes making comparisons between different risk assessments difficult.

2 Assessing all possible combinations of loading, wall failure condition and resulting impacts, using Monte Carlo simulation and impact modelling. Combining the results according to the individual probabilities to generate an overall assessment of risk expressed in economic terms.

4.3.5 Event probability estimationSorting and ranking the threats and adding the frequency component (ie how often such a failure could happen – once a year, once every 10 years, 100 years, 1000 years) generates a risk profile for the structure. The frequency of events can be established using professional advice, judgement or experience and, where appropriate, historical data identified in the first stage of the work. The likelihood or ‘probability’ of such events occurring can be estimated by applying various statistical interpolation/extrapolation techniques to the historic data. However, such historical information may not be available for all types of threat/hazard.

The approaches that exist vary depending on the source event under consideration. Table 4.1 provides a useful list of approaches for wave overtopping and flood events, vessel impacts, and earthquakes.

Table 4.1 Useful sources of approaches for the derivation of loading event probabilities

Loading event Source of probabilistic approach Reference

Water level (floods), wave overtopping and joint probability

The International Levee Handbook (Chapters 5 and 7)

CIRIA; Ministry of Ecology; USACE (2013)

Vessel collision with waterfront walls, bridge piers, quays, breakwaters etc

Models of marine and waterway safety assessment

IMO (2002), PIANC (2014), IAEA (2001), Maritime University of Szczecin (2013)

Earthquake Probabilistic Seismic Hazard Assessment (PSHA) NERC (2014)

Fluvial flows Flood Estimation Handbook (FEH) CEH (1999)

Estimation of loading or ‘threat’ events often requires the assessment of more than one causal factor. For example, two unrelated hazards may occur in conjunction resulting in a worse threat than if only one had occurred. Analysis of the ‘ joint probability’, ie the probability of two or more conditions occurring at the same time, may be required, for example:

ªª total seawater level occurring as a result of storm surge (+ or –ve) and astronomic tide (high or low)

ªª total river water level occurring as a result of storm surge (+ or –ve) and fluvial flows

ªª combinations of wave heights, periods and directions occurring with total water levels.

Joint probability analysis may be required for combined events such as landslides and earthquakes, riverine flood stage and ice loading, or coincidental failure of flood defences on one bank of a river, leading to rapid draw-down and high water pressures on a retaining wall on the opposite bank or elsewhere.

Monte Carlo simulationMonte Carlo simulation is a computerised mathematical technique that relies on repeated random sampling to obtain numerical results, typically running simulations many times over to obtain the distribution of an unknown probabilistic entity. It is a common tool that allows people to account for risk in quantitative analysis and decision making. The technique is used by professionals in a wide variety of fields such as finance, project management, energy, manufacturing, engineering, research and development, insurance, oil and gas, transportation, and the environment.

The technique furnishes the decision maker with a range of possible outcomes and the probabilities they will incur for any choice of action.

Estimating rare eventsEstimating the probability of rare events including their size often requires statistical extrapolation to derive a full magnitude-frequency relationship beyond the available data. This can introduce additional uncertainty on which expert guidance should be sought. For more information see CIRIA; CUR; CETMEF (2011), Rogers et al (2010), CIRIA; Ministry of Ecology; USACE (2013) and CEH (1999).

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While there is no absolute upper limit on the number of variables to consider in a joint probability analysis, the calculations become more complicated for each extra partially dependent variable considered. In practice, most joint probability analyses are reduced to two primary variables, but additional secondary and/or conditional variables can also be incorporated into the analysis in other ways (Hawkes, 2005).

For further information on estimating joint probability of events and combining source events see Chapter 7, or Section 7.4 of CIRIA; Ministry of Ecology; USACE (2013).

4.3.6 Failure probabilityThe subject of the analysis of the failure of a discrete section or length of a waterfront wall is detailed in Section 4.3.3. This section aims to show how the result of a failure analysis can be used as an input into a wider risk analysis of a system or number of discrete lengths of a waterfront wall, particularly as this result then needs to be expressed as a probability.

Probability of wall segment/section failureOld waterfront walls are not always uniform in materials, methods of construction, geometry, reliability etc and this variability can influence the probability of failure. Each section of a wall (or walls within a system) can have an independent and different resistance to loading. These differences can be characterised, for example, by different condition grades, types of structure or construction, structural geometry (foundation level, crest level etc) – especially where there have been historic modifications. So, where such variations are evident, the likelihood/probability of failure for a waterfront wall (or a system of such structures) should be evaluated for each functionally homogenous segment or section. Differences between the probabilities of failure of various lengths of waterfront wall with such different characteristics can then be identified.

Occurrences of extreme loads are defined as continuous random variables (L) associated with each wall. Failure of a section of the wall (structural failure) is defined as a continuous random variable, conditional on load commonly known as ‘fragility curves’ (see Simm et al, 2008). During a loading event each individual wall section can exist in two possible states (ie they are defined as Bernoulli Random Variables, Simm et al, 2008), failed or not failed (di, di), with the likelihood of any particular state obtained with reference to the fragility curves.

A continuous line of wall sections may form a defence or protection system. So, the potential number of wall system states (combinations of failed/not failed segments), for any specified load (l), is 2n. The wall system state, derived from the failed/not failed state of each wall section, is a discrete random variable (D) whose conditional probability mass function (pmf) is:

pD/L(d,l)=P[D=d\L= l] 4.1

where:

D = discrete random variable that represents the wall system state

d = any particular combination of failed and not failed sections that comprise the wall system (d is a vector that comprises the state of all the sections in the wall system)

The performance of consecutive wall lengths are assumed to be independent of one another, so the probability of any particular wall system state, for example, occurring on any given load is through the multiplication rule:

4.2

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4.3.7 Consequences of failureThe type and extent of consequence analysis of wall failure will vary significantly depending on the function(s) of the structure (see Chapter 2). For example, if the wall performs a primary flood defence function or is part of a flood defence (eg surmounting a flood embankment), and is officially designated as such by the regulatory authority, then analysis of the consequence of its failure will require breach and hydraulic modelling of flood inundation and flood spreading. This can be quite extensive and specialised work. Initial contact with the regulatory body (EA, SEPA, NRW, DARDNI) to see what information is already available, may obviate the need for this specialised work. However if no information is available then for details of how to undertake this analysis see CIRIA; Ministry of Ecology; USACE (2013), EA (2010a) and the EA website. Similarly if, for example, the wall protects the toe of a high cliff or unstable coastal slopes then a geotechnical model and recession analysis may be required to determine the likely consequences of wall failure. Again the starting point would be to check national coastal erosion risk maps available from the EA website.

It should be noted that if the local flood and coastal erosion risk management (FCERM) strategy requires that a structure is to be maintained then the owner/manager has an obligation to maintain and retain the structure.

Straightforward analysis would be expected where the waterfront wall serves less spatially extensive purposes such as a wharf, berth, raised canal, or river-bank retaining structure. In such circumstance the consequences of failure are likely to be more localised.

Whatever the circumstance, evaluating the consequences of wall failure requires combining the net result of any failure modelling (where required) and the estimated vulnerability of the different receptors in the affected area.

Failure of an old waterfront wall can potentially affect many different types of receptor including:

ªª people

ªª adjacent (or surmounted) buildings

ªª business activities

ªª critical infrastructure: transport, utility and communications networks

ªª recreational areas

ªª agriculture

ªª nature conservation areas

ªª natural/undeveloped areas

ªª heritage/historic sites.

Once identified, the vulnerability of these receptors also needs to be assessed. Usually the assessment involves consultation with the EA, SEPA, NRW, DARDNI. In such cases there is often sufficient data already available so that recourse to new modelling may not be necessary. Vulnerability relates to the susceptibility of people, infrastructure and assets in the affected area to physical/emotional injury or damage, given their exposure to an event. Some locations will have a higher degree of vulnerability and potential for damage than others, either by their character or by the presence of a large number of people. In a flood event, the vulnerability of people also varies depending on factors such as speed of onset and water level rise, flow speed, duration, ability and time available to evacuate etc. In such cases control measures taken to limit the consequences of a flood inundation, eg flood warnings, organisation of evacuation, shelters, including an estimation of their efficiency, should be taken into account in the analysis.

Where a wall stabilises the toe of a slope, which has buildings or other assets either cut into the slope (eg coastal access roads) or located at the top of the slope, then it would be reasonable to consider their vulnerability to the risk of slope failure if the toe wall failed.

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Many businesses located in ports and harbours depend on waterfront walls for berthing of vessels, delivery, storage and/or transhipment of cargo etc. Failure of a quay wall can severely affect their capacity to operate especially if there is no convenient alternative in the interim until the wall is repaired or rebuilt.

The consequences of failure of a canal waterfront wall will depend on many factors. These include whether the location of the failure is above or below adjacent land level and whether a breach will occur and result in loss of water from the waterway. Response times for deployment of stop logs to prevent total water loss (on narrow canals where these are used) may be an important factor in determining the extent of impacts on canal users and their vessels.

Buildings and other assets that are located on or close to old waterfront walls are particularly vulnerable to damage or collapse if the structure fails. Consideration should also be given to the vulnerability of roads, access routes, and pavements, located close to the crest of the wall and to utility pipes, communication lines or other critical infrastructure in the ground behind the wall.

Waterfront walls that support or form part of bridge abutments may require the assessment of vulnerability of the users to closure of the watercourse over which the bridge passes, as well as the potential damage to the bridge itself, its infrastructure (highway, railway, utility etc) and its users.

The assessment of the piers, including those parts below water, should be part of the major or principal inspection that bridges undergo every six years or less (see Section 4.6).

4.3.8 Characterisation of potential impactsThe potential impacts on people and other receptors or assets can be characterised in terms of:

ªª human health, casualties or life loss (or social consequences)

ªª socio-economic consequences (including business losses)

ªª environmental consequences (including ecological impacts)

ªª cultural and archaeological heritage loss.

The human/social criterion may be the number of detrimentally affected persons, but normally these effects are categorised by loss of life, health effects, stress, safety, equity, community etc.

Economic damage criteria in the simplest case would normally relate to the direct losses arising from the failure of the structure. However, indirect impacts such as business losses or operational interruption may also be considered (eg closure of a vessel berth, road or rail links or a canal).

Environmental criteria can measure, for example, the impact on fauna and faunal habitats, or water quality.

Impacts on cultural and archaeological heritage can include damage to assets such as historic buildings, parks and gardens, ancient monuments etc. In many cases old waterfront walls may be valued aspects of, or contribute to, the cultural heritage of waterfront areas or buildings – and may now be one of the primary reasons for continued management and maintenance. Cultural and archaeological heritage can be included in multi criteria risk analysis in a similar way to environmental receptors through a simple yes/no damage function.

4.3.9 Estimation of the level of riskThe level of risk depends on the chance of a failure event occurring and the potential undesirable consequences should the event occur. Depending on the level of assessment required or undertaken (see Section 4.3.1), this can be represented qualitatively or calculated quantitatively. For example, a qualitative level of risk can be shown by plotting the likelihood of failure and the relative consequences on a risk evaluation matrix as shown in Figure 4.3. However there are various methods for quantifying risk, which involve the integration of:

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ªª a full range of loading conditions (eg extreme water levels for riverine/tidal walls, with extreme wave loading and extreme overtopping rates for breakwaters and coastal walls)

ªª the performance of walls (eg stability, hydraulic response, and probability and nature of failure represented by fragility curves or described by a finite element model, FEM)

ªª simulation models to determine receptor vulnerability and likelihood of impacts

ªª the calculation of potential economic or other types of consequences where sufficient data is available and where category/damage relationships are, or can be, established.

Levels of risk can be calculated for different risk scenarios (see Section 4.3.4). Such scenarios may include those in which potential risk management measures have been introduced to reduce the level of risk. Once a risk analysis has been completed, in order to be able to assess the results, an evaluation of the significance of the identified risks should be conducted before considering measures and instruments to reduce risks further. Risk evaluation is discussed in more detail in Section 4.3.11.

4.3.10 Attributing riskEven though wall sections/segments may work together over a length of wall or system, they are not all equally reliable and so do not contribute the same level of risk to the whole. This is because some may:

ªª be weaker structurally than others, so may fail more readily

ªª have lower crest levels than others, so may overtop more readily

ªª have less efficient maintenance, monitoring, or emergency management.

The attributed risk of failure associated with a particular section/segment is the residual risk arising from the consequences of failure of that section/segment of the wall. So, risk attribution is the process of quantifying the level of this residual risk associated with different section/segments of the wall. Risk attribution is most useful for walls that have a flood defence role, where the failure of one or more system assets and subsequent flood inundation can result in extensive and costly impacts. A detailed example of the methodology used for risk attribution is given and described in CIRIA; Ministry of Ecology; USACE (2013).

4.3.11 Risk evaluationA key outcome of any risk assessment is whether or not the asset is safe, or whether measures are required to reduce the risk (which in principle could, for very high risk assets, comprise complete removal and replacement as a last resort). The subject of what constitutes tolerable risk is a complex subject, with many publications discussing the issues and what is considered tolerable varies between owners, industries and countries. In the UK, guidelines for nuclear power plants (ONR, 2006) and papers discussing criteria for reservoirs include Hughes et al (2000) and Brown and Gosden (2004), which have all presented ideas of ‘tolerable risk’.

Risk cannot be entirely eliminated, so the tolerability of the level of residual risk determined by the risk analysis should be evaluated using societal, regulatory, legal, owner and other values. This can be carried out through two methods:

1 Cost-effectiveness analysis (CEA) – seeks to identify the least costly option that satisfies some performance requirement – primarily risk tolerability, although there are often other constraints in terms of environmental standards and socio-political acceptability of the proposed measures. In practice there can be a range of risk thresholds derived from government guidance, insurance availability and social tolerance levels.

2 Cost-benefit analysis (CBA) – a method that expresses as many costs and benefits of the options as possible in terms of the monetary value placed on them by society, deriving the net benefit, and then assesses whether the expected benefits of a specific risk-reducing option outweigh its expected costs. There are major shortcomings of this approach because all benefits and costs are quantified in monetary terms and aggregated to a single number while some impacts, such as environmental, are more difficult to quantify in monetary terms, and are rarely considered.

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However, it is not normally the responsibility of asset owners or operators to formulate risk tolerability standards. Instead broader society dictates to the technological community the tolerable levels of risk that should be met by assets and asset systems – as it does for many other risks to society.

HSE (2001) defines tolerable risk as “…for the purposes of life or work, everyone who might be impacted is prepared to accept assuming no changes in risk control mechanisms”.

A high level comparison of different criteria to evaluate risk is summarised in Table 4.2.

Table 4.2 Alternative groups of risk criteria (after HSE, 2001)

Risk criteria group Principle

Equity All individuals have unconditional rights to certain levels of protection.

Utility Comparison between the incremental benefits of the measure to prevent the risk of injury or detriment, and the cost* of the measure.

TechnologyThe idea that a satisfactory level of risk prevention is attained when ‘state-of-the-art’ control measures (eg technological, managerial, and organisational) are employed to control risks whatever the circumstances.

AppliedTypically a hybrid of the ‘pure criteria’, ie the generalised framework for TOR (HSE, 2001), which is intended “to capitalise on the advantages of each of the pure criteria while avoiding their disadvantages” and to resemble the decision process that people use in everyday life.

Note

* Where cost is considered in broad terms, which may include time and effort in addition to monetary aspects.

Inevitably, hybrid evaluation criteria for TOR can emerge and are often apparent. HSE (2001) uses an equity-based criterion for risks in the unacceptable region and a utility-based criterion for risk in the other two regions (see Figure 4.7). Technology-based criteria may be used to complement the other criteria in all three regions as described in ICOLD (2005).

Although the general framework for acceptability of risk shown in Figure 4.7 gives a first impression on how risk acceptance can be approached, note that from a social science point of view the realms of tolerability and non-tolerability may vary over time and differ significantly between individuals. Also, a public consensus on risk tolerability may not exist. Defining what constitutes unacceptable harm to

Figure 4.7 Acceptability of risk (from HSE, 2001)

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people and the environment is a difficult task and ultimately depends on what relative values society places on loss of life and damage to buildings, infrastructure, and ecosystems.

There is currently no defined standard for what constitutes a tolerable level for risk posed by an old waterfront wall. Where consequences of failure are particularly linked to flood protection issues this guide is based on what is understood to be current good practice in other industries, as defined in HSE (2001). Where failure primarily has commercial consequences, eg the failure of a quay wall, risk levels should be based on financial criteria, and/or be based on requirements of relevant British Standards such as BS 6349-1-3:2012. This is outside the scope of this guide.

One of the issues in evaluating risk is the relative importance given to individual risk compared to cumulative impact. For example, does a one metre deep flood inundation of 50 houses have a higher impact than the death of two people in an isolated house? Current criteria for both societal and individual risk are summarised in Table 4.3, and it is suggested that these are applied to waterfront walls in the UK.

Table 4.3 Suggested criteria for TOR to human life in the UK (after HSE, 2001)

Type of risk Boundary suggested in R2P2

Tolerable and unacceptable Tolerable and the broadly acceptable

Individual riskFor members of the public who have a risk imposed on them ‘in the wider interest of society’ this limit is judged to be 1 in 10 000

Individual risk of death of one in a million per annum

Societal risk

The risk of an accident causing the death of 50 people or more in a single event should be regarded as intolerable if the frequency is estimated to be more than one in five thousand per annum

No specific advice. Older publications suggest that it may be two orders of magnitude lower than the boundary for broadly acceptable

Levels of tolerability for potential impact on other receptors, such as cultural and environmentally important sites, are less developed. Readers should refer to UK Government and European guidance current at the time of the assessment (HSE, 2001).

ProportionalityIt is common in risk management to refer to safety goals as risks reduced to ALARP, which applies in the tolerable zone of Table 4.3. The EA regularly applies the ALARP principle to the management of all their assets, including waterfront walls, but for a private owner of a small waterfront asset this may not always be feasible and a more simple risk assessment may be required.

To implement the ALARP principle a ‘gross disproportion’ test needs to be applied to determine the balance between individual risks and societal concerns, including societal risks. This is usually done by considering whether the costs of the measures (over a 100-year life) are proportional to the potential reduction in risk to life that could be achieved. The gross disproportion is between the cost of an additional risk reduction measure and the estimated amount of that reduction in risk.

In a qualitative system it is not possible to provide a simple way of comparing costs with benefits, so where this is an important part of the risk assessment, the user should move to a quantitative analysis.

In a quantitative analysis, deciding on whether the costs of the measures to reduce the risk are proportional to the potential reduction in risk gained by those measures is normally achieved by calculating the cost to prevent a fatality (CPF) and comparing this with the value of preventing a fatality (VPF). At its simplest, where the CPF is less than the VPF, then the candidate works would be proportionate risk reduction measures, while where CPF exceeds VPF, then the cost is disproportionate.

Calculating the CPF is summarised as follows:

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CPF = Equivalent annual cost of risk reduction measures – present value (ΔPf x damage)Present value (ΔPf x likely loss of life, LLOL)where ΔPf is the change in annual probability of failure due to the proposed risk reduction works.

Note: only the probability associated with the remediation should be used, ie the probability of failure that it affects, and not the total probability of failure for the wall.

Costs should be estimated realistically. For example, Defra (2003) recommend that, at the pre-feasibility stage, an optimism bias of 60 per cent is added to the best estimate of total cost. This is based on experience of total project out-turn costs against the pre-feasibility estimate.

A suitable discount rate (currently recommended as 3.5 per cent) should be used to calculate the present value. The criteria for economic evaluation should be agreed with the owner/organisation, as some owners may be required to (or wish to) use different discount rates. Financial evaluation criteria in the private sector may well lead to conclusions different from those in economic evaluation in the public sector. As previously noted, such financial analysis is outside the scope of this guide.

The value that should be assigned to VPF is a difficult decision and includes consideration of:

ªª direct costs (measurable) such as the earning potential of the victims, injury and long-term health impairment of other victims, and emergency services costs

ªª indirect costs (business losses)

ªª intangibles (psychological impact on people, environmental damage). It could be argued that a value should be assigned to the intrinsic value of a human life (irrespective of age, health, education etc).

The DfT’s assessed VPF for road and rail in 2010 was £1.7m (DfT, 2012). However, ‘gross’ disproportion is required before ALARP is satisfied and defines a ‘proportion factor’ defined as:

Proportion factor (PF) = CPF VPF

The purpose of a proportion factor grossly greater than unity is to allow for the imprecision of estimated costs and benefits, and also to ensure that the duty holder satisfies the ALARP principle. In HSE (2015) what constitutes a reasonable proportion factor can be defined as “NSD [Nuclear Safety Directorate] takes as its starting point the HSE submission to the1987 Sizewell B Inquiry that a factor of up to 3 (that is, costs three times larger than benefits) would apply for risks to workers; for low risks to members of the public a factor of 2, for high risks a factor of 10”.

Hughes and Gardiner (2004) present a disproportionality factor, which varies with probability of failure (POF), from 3 at POF of 10-6 to 10 at POF of 10-4.

4.3.12 Flood and coastal erosion risk management (FCERM)

Following the heavy floods of 2013, the UK Government (through Defra) provides funding to risk management authorities to manage flood and coastal erosion risk. This includes funding to:

ªª provide flood warnings

ªª build new and improved flood and coastal defences

ªª maintain existing structures

ªª respond to flood incidents.

The majority of funding is given as flood defence grant-in-aid (GiA) to the EA. Other risk management authorities must get technical and financial approval from the EA for their FCERM projects and strategies before they can spend and claim GiA.

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EA (2010) contains guidance on economic analysis, appraisals of positive and negative impacts, scoring and weighting methodology, adaption to climate change and other guidance notes related to flood risk management. See also Defra (2008).

4.4 PERFORMANCE ASSESSMENT AND DIAGNOSIS METHODOLOGY

4.4.1 IntroductionThe performance assessment process involves the use of one or more methods of treating and combining data in order to evaluate the performance of a waterfront wall, according to its main function (eg as a berth for vessels, as a retaining wall for adjacent infrastructure, as a flood prevention barrier) and its reliability (identification of possible failure modes). This can be done in a number of different ways, and assessment method categories are presented in Section 4.4.3.

A good understanding of the wall, its behaviour and its (relative) vulnerability for different failure mechanisms during loading conditions will assist in:

ªª identifying the need to take any immediate emergency measures (and which measures)

ªª directional or bespoke inspections and what specific features to look for and where

ªª the diagnosis or cause of observed discontinuities or features, ie the identification of the cause or nature of a defect or element of deterioration of a wall (this relates to failure modes and deterioration processes)

ªª the prognosis of a wall’s performance during potential future loading events.

A complete assessment should include a diagnosis of the actual or possible causes of failure, in order to remediate or prevent them. This means that all potential failure modes for the wall and their relative importance to the overall structural performance have to be determined. The outcome of the performance assessment should be a prediction of how the wall will perform under a range of loading events. Once assessments have been completed, follow-up actions will be required that may include maintenance and rehabilitation.

4.4.2 Diagnosis and performance assessment in the management cycle

In order to fulfil its duties related to management policy and/or regulations, an owner/organisation with responsibilities for the management and maintenance of waterfront walls should perform both regular inspections and regular assessment related operations.

Regular inspections, however, do not have the same level of accuracy as less frequent detailed assessments (eg diagnosis and risk analyses), which is why O&M instructions and/or regulations include various levels of inspections and assessments.

For risk assessments, a tiered approach (see Section 2.4.3) can be adopted to optimise the assessment resource allocation to the risk level. During the life of the structure, various assessments, including inspections with conclusive reports, as well as complete risk analyses, should be carried out, each with different levels of expertise and detail. The results are not only an assessment score (in whichever form) but should also include a measure of the confidence in the result. The level of confidence can be a clearly expressed result of the assessment, depending on the method used to produce it, but it can also be implicit, and as a function of the type of assessment and its level of expertise and detail.

Risk analyses depend on performance assessments. Risk analyses combine structural performance assessment with the analysis of the consequence of a structural failure (see Section 4.3). During the life

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cycle of an asset, many different assessments may be carried out, and every new assessment should take into account the data and results of the previous assessments. The level of detail for both the data and the methods for combining data used in a performance assessment depends on where this assessment is in the asset management life cycle and on previous results. For further information see Chapter 2 and Section 4.4.3.

Diagnosis is difficult, as observed features do need to be linked to possible failure mechanisms, which will normally require the support of a qualified and experienced engineer.

4.4.3 Performance assessment methodsFor each or all potential failure mechanisms in a waterfront wall, the assessment process should provide an estimation of the potential for failure under one or more different loading events. In an initial desk study, the potential for failure of the wall should be evaluated for the whole structure, but a subsequent more detailed performance assessment may focus effort on the segments of the wall that are of most concern.

In a complete assessment of the performance of a waterfront wall, the failure modes of different wall segments should be identified for each functionally and structurally homogenous part of the wall, as part of a diagnosis. This identification also includes different theoretical wall failure scenarios. The scenarios chosen are then evaluated in terms of probability or likelihood of occurrence according to the performance of the wall’s component functions and of the chosen loading event(s) or identified hazard(s).

There are a number of different methods that can be used when undertaking a performance assessment for an old waterfront wall. All are based on a combination of data and involve:

ªª index-based methods, using a predefined combination of index ratings for different observations or parameters

ªª mathematical models, using both physical or empirical-based equations

ªª expert judgement, direct or using one or more of the previous methods as pre-processed data.

There are several possible types of results arising from performance assessments:

ªª threshold (a limit load)

ªª conditional chance of failure (for a given load)

ªª fragility curve (conditional chance of failure for a range of loads)

ªª safety factor

ªª index (eg on a 0–5 or 0–10 scale)

ªª qualitative (eg very good, good, fair, poor, very poor).

Uncertainties can also be integrated into the assessment process to produce a probabilistic output.

4.4.4 Performance assessment processA generic performance assessment process for an old waterfront wall may include some or all of the following steps:

1 Identifying possible failure modes and mechanisms.

2 Evaluating possible methods that can be applied to analyse each of these failure modes and/or mechanisms.

3 Identifying and reviewing all available data useful for the assessment (see Chapter 6).

4 Defining a specific investigation programme to gather any missing or incomplete data or to complement existing data (see Chapter 6).

5 Combining data for each loading condition and every failure mode.

6 Combining results for all failure modes and all loading conditions.

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This may be followed by a combination of the conclusions for all segments of the wall, and conclusions or recommendations in terms of proposals for subsequent actions.

A combination of the different types of methods outlined in Section 4.4.3 can also be applied in the same assessment.

It is expected that given the variability in materials and parameters in old waterfront walls, some level of expert judgement will be added to the conclusions of any assessment report. This allows for the consideration of any data, even when it is not used as specific input to an analysis, when it is relevant to a given failure mode or deterioration mechanism.

4.4.5 Loading conditionsIn the performance assessment process, the loading conditions should be defined. Different types of results from waterfront wall assessments can include:

ªª a single result for one loading condition

ªª a single result for all loading conditions (eg annual chance of failure)

ªª a result for each load in a list of loading conditions

ªª a fragility curve, which is a curve (or function) linking the chance of failure to a range of loading conditions.

Quantifying the probability of loading events is discussed in Section 4.3.5. The aim of the performance assessment is to quantify the impact of loading events on waterfront walls in terms of probability of failure. The information is then used within the risk analysis (see Section 4.3.6).

System response functions, such as fragility curves, allow an estimation of the relationship between the amount of loading at a given location along the wall and the probability that the structure will fail at a defined location. System response functions are often important components of hydraulic analyses used to assess structure response under various loading conditions (eg rapid draw-down of water level).

4.4.6 Data and failure modesFor a thorough performance assessment, as well as identifying the potential threats and loading conditions on a waterfront wall, it is also necessary to produce a list of possible failure modes related to the structure. This can be simple if the wall is homogeneous and has limited functionality or complex if the structure varies in its composition and has to serve multiple functions and/or may be subject to infrequent/extreme loads. Section 4.3.4 provides examples of possible causes/effects of various failure modes.

It is important to be able to identify the physical or empirical laws governing the failure mechanisms, and design methods to analyse those scenarios. Whatever methods are used to combine data in an assessment process, it is beneficial to list all types of data associated with any failure mode and/or mechanism. Where formal evaluation is difficult, expert judgement based on individual and/or collective experience, will allow failure modes and mechanisms to be identified and evaluated.

Data can be categorised to help clarify the relationship to relevant failure mechanisms of the wall. Categories might include:

ªª topographic (including plan shape and elevation)

ªª structural (including condition assessment and any encroachments)

ªª geotechnical (including geophysics)

ªª hydraulic (including hydrology)

ªª morpho-dynamic (changes in river bed, channel alignment, scour at structures)

ªª environmental-related around the structure (including buried services and pipelines etc)

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Such data may presented in various forms from different sources such as:

ªª borehole geology records

ªª granulometry (morphology)

ªª classification test results

ªª piezometric levels

ªª flow or seepage discharge records

ªª permeability measurements

ªª compressibility tests

ªª shear test results

ªª density measurements

ªª penetrometer tests

ªª cone penetration test (CPT) records.

As well as the type and nature of the data it is also important to consider the different sources of the data for example:

ªª data available from an existing AMS

ªª other historical information

ªª topographic, hydrographic and structural surveys (eg structural survey drawings, LiDAR surveys above water, side-scan sonar (SSS) surveys below water)

ªª visual inspections

ªª records of specific investigations

ªª monitoring records

ªª previous assessment results and initial data records

ªª engineering literature (materials and component data, construction methods, previous failures)

ªª other reliable outside sources (maps, databases, reports, and raw data).

Chapter 6 discusses how and where to look for available data on old waterfront walls.

4.4.7 Using fault and event trees to examine failure scenarios

Deterioration mechanisms can combine in different ways to produce the structural failure of an old waterfront wall. Scenarios of events that lead to a failure can be complex and there are various methods available to assist in the analysis of potential failure modes and/or mechanisms.

In a systematic approach, there are two main techniques for mapping the paths from deterioration to failure, fault tree analysis (FTA) and event tree analysis (ETA).

Post-failure consequences can be combined with these to form a failure modes and effect analysis (FMEA) or ‘Bowtie’ tree scheme. A functional analysis such as this enables not only the identification of causes and consequences of failure but also to identify links between failures of components of the structure and scenarios or chains of events.

FTAFirst proposed by Watson (1961) and subsequently revised by many authors, this is an expert and deductive method to identify every combination of causes (failure scenarios) that can explain the occurrence of a final event (failure of the structure). FTA starts from the final event or state of failure (collapse) and conducts a back analysis, firstly to find the originating causes of the failure, then the causes of those originating causes and so on. The aim of this analysis, conducted step-by-step, is to identify all the conditions, factors and mechanisms that have allowed the final event or failure to occur.

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FTA ends with the identification of the original causes, which are defined as causes external to the studied system.

The analysis and the modelling of these fault trees are usually built from the top to the bottom or from the right to the left, with the final failure event being presented at the top or on the right side, and the original causes at the bottom or at the left side. Each level of the analysis corresponds to a failure of a specific function of a component that can result from numerous causes. These causes may be combined (through ‘and’ gates) or may be independent (through ‘or’ gates).

In the case of waterfront walls, a failure situation can be studied to infer mechanisms and external events (initiators and contributing factors) that have generated the failure (eg through excessive external loading, or extreme hydraulic pressures) (see Figure 4.8).

Figure 4.8 A generic fault tree for a gravity-based wall showing associated failure modes and processes

ETAFirst applied to the dam industry in the context of a risk assessment by Whitman (1984) is used to identify the possible final outcomes starting from an initial unwanted event. The resultant mechanisms are inferred and combined to define and describe the expected consequences. From the initial event, all the resulting scenarios, or chains of events, and contributing factors are identified, described and may be associated with a probability (see Figure 4.9).

The modelling of the event tree is built through a binary (function running/function failed), discrete (events or time punctual evolution) and chronological method. It is presented by a series of linked nodes and branches starting from the left to the right, from the initial unwanted event to the final different consequences. Each node represents an uncertain event or condition. Each branch represents one of the possible binary outcomes of the event or one possible state that a condition may assume. After the identification of the scenarios, the ones that are not physically possible are rejected. In a quantitative approach using this method, a probability value can be associated to each branch resulting from an event (node). Assuming an independence of the different events that comprises a scenario, a scenario consequence probability may be calculated by multiplying the probability values affected to its different branches.

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FMEA or ‘Bowtie’ trees, combines a fault tree and an event tree in one schema, where the final event of the fault tree is the unwanted event of the event tree. This representation is usually built horizontally as shown in Figure 4.10. The studied feared event (state of failure) is in a central position, the possible causes are developed to the left and the possible consequences are then detailed to the right.

Dependence and independence of failure modesFailure modes may be dependent or independent of one another. Probabilities of wall failure are normally modest so this effect is only important where the highest probability of failure is greater than, for example, a 1 in 5 (20 per cent) chance per year.

In the case of full dependence, if one failure mode occurs it can be assumed that all other failure modes will have occurred. So, the associated likelihood of occurrence is simply the maximum value, and can be determined by:

Pf=max [Pfi,Pfj,Pfc] 4.3

where Pf is the overall probability of failure and Pfi is the probability of a single failure mode.

In the case of independence, any chance of any given failure occurring is not influenced by other failure modes. The overall chance of failure can be given through an application of de Morgan’s law to give:

Pf=1–(1–Pfi).(1–Pfj) 4.4

where Pf is the overall probability of failure and Pfi is the probability of a single failure mode.

The two values determined through assumptions of independence and dependence provide bounds on the overall probability of failure (Sayers et al, 2001). These upper and lower bounds can be multiplied with the upper and lower bounds of measures of potential consequences to provide upper and lower bounds of annual expected risk. A mean value can be determined from these.

4.4.8 Assessment reportAs part of conducting any assessment, it is essential to produce a specific report, presenting:

ªª different data used during the assessment, whether already available or produced specifically by conducting investigations or inspections

ªª sources, reliability and confidence in the data

ªª a description of the assessment method

ªª results

ªª conclusions.

The engineer responsible for the assessment should judge the quality and reliability of all data, and present this information in the report. Specific reports about the production of data and pre-processing may be appended to the main assessment report or simply referenced, but the main data used for the assessment should be presented in the main body of the report.

Assessment can be a complex process (and not always standardised), so it is also necessary to present a clear and complete description of the method(s) used for combining the data in order to produce the assessment results.

All results of the assessment, both intermediary and final, should be presented in the report. These results can be presented as text, tables, maps and/or graphics. The intermediary results can include performance assessment for specific events and/or specific failure modes or mechanisms.

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The assessment should reach a conclusion and, after the summary of the results, present clear recommendations such as any follow-up to the assessment, eg proposed repairs of remedial works.

Finally, all assessment reports should be archived and referenced in the AMIS (see Section 4.7) to be available for future reference and to facilitate subsequent assessments. Ideally this information should be digitised, stored electronically and available for immediate access. Information should include a record of the structure in terms of what was done, when it was done, materials used (and sources of materials) time taken and costs.

4.5 INSPECTIONS

4.5.1 IntroductionThis section presents requirements for inspection of old waterfront walls designed to ensure that structures are adequately maintained for the protection of life, environment, property and equipment as well as to maximise longevity of the structure. These requirements include:

ªª type and frequency of inspections

ªª choosing the proper inspection approach

ªª rating and prioritisation.

Stone masonry retaining walls, such as those typically found in old waterfront walls, will normally only require a very simple inspection regime as described in Section 4.6. PIANC (2013) provides an in depth discussion of inspection approaches for a wide range of navigation structures, including masonry walls. The following sub-sections give an overview of these recommendations, but for further information see PIANC (2013). In addition, EA (2006) has some examples of assessments of brick and masonry structures to illustrate condition grading, while guidance by Flikweert et al (2009) explains how to determine the residual life of waterfront assets (Halcrow, 2013).

4.5.2 Routine inspectionsThe routine inspection of masonry and blockwork waterfront walls will typically include a visual inspection only. A ‘visual inspection’ means inspection of structures using some or all of the human senses such as vision, touch and smell and/or any non-specialised inspection equipment. Where access is difficult a visual inspection can be carried out through the use of remote controlled drones to provide images of the structure. The use of drones is discussed further in Section 6.7.3.

Visual inspections, both above and underwater, would typically comprise:

ªª checking for any excessive weathering or abrasive deterioration of the blockwork

ªª assessing general condition of the wall and identification of any loss of mortar from joints

ªª checking for any significant gaps or displacement between stones or blockwork and note of the location, length and depth of any missing stones or blockwork

ªª diving inspection to identify mortar loss and any undermining or scouring at the base of the structure

ªª recording the maximum and minimum depth of water at the base of the structure.

Regular visual inspections can be supplemented with detailed structural inspection surveys as discussed in Chapter 6. This may include using high resolution multibeam echo sounder (MBES) to record profiles underwater and laser scanning (LiDAR) of structures above water to record profiles and identify discontinuities and missing structural elements, and give a full 3D visualisation of the structure. An example of the application of GPS referenced LiDAR surveys is given Case study 4.1 on Gorey Pier.

Bradbury et al (2012) provides useful information on the management of seawalls, and in particular the inspection and monitoring of the seawall toe structures and scour aprons and the impact of change in beach levels.

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The Gorey breakwater has evolved using traditional Jersey marine construction methods of forming outer dressed granite blocks for the main walls with a secondary rock core infill built upon rock-outcrops. The breakwater pierhead suffered a partial collapse in 1964 after a severe storm. The failed sections of the pierhead were rebuilt using a mass concrete backing wall faced with the original masonry from the collapse and founded on sheet piles. A concrete landing jetty structure and a concrete deck slab were also added over the end of the pier in the late 1960s.

In the late 1990s Jersey Harbours observed damage occurring to the building structures supported on the deck slab concrete and it was recommended that a monitoring of crack widths on the breakwater should be regularly measured. In 2000, the estimation was that the major cracks on the deck were opening up some 3 mm each year, year on year. By 2005 the cracks had widened to the extent that a further detailed investigation was required and De-mec studs were placed over the cracks for monitoring movement. In 2007 ground penetrating radar (GPR) was used to identify if voids were present beneath the deck slabs, but the thickness of the slabs

and the amount of reinforcement within them prevented a good reflected signal. In 2009 a study brought together past survey data and inserted the information into a ‘virtual’ model of the pier made possible using LiDAR that enabled a very accurate 3D model of the structure and its surroundings to be constructed. The 400 year old structure has very difficult, irregular geometry and conventional 2D drawings were not easy to produce to scale. A further recent intrusive survey in 2012 together with another LiDAR scan has now enabled the design of a strengthening remedial solution to protect this marine asset for the longer term.

The idealised loads necessary to be resisted by a repaired and strengthened pierhead are indicated in Figure 4 .14.

A design concept was prepared to allow the three abutting structures to be physically ‘tied’ together to make one structural mass on a unified foundation to rock. In this way the combined structure will be better able to resist the overtopping and wave forces for the idealised design life of 50 years. The remedial works are shown in Figure 4 .15.

Figure 4.11 General view of Gorey breakwater pierhead and Mount Orguiel

Figure 4.12 Partial collapse of Gorey breakwater pierhead in 1964

Figure 4.13 Superimposed LiDAR models of pierhead, which identified bulges in the masonry wall, a marked loss of concrete apron base at the end of the pierhead and a loss of beach sand on the outside face of the pierhead

Figure 4.14 Basic loading conditions on pierhead

Figure 4.15 Scheme design remedial works – sheet piles, ring beam, deck over slab etc

Case study 4 .1 Investigations and remediation at Gorey breakwater pierhead, Jersey (courtesy Arup)

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4.5.3 Frequency and purpose of routine inspectionsThe frequency with which routine inspections of waterfront walls should be conducted is a function of many variables. Table 4.4 gives a suggested approach to a supervision and inspection regime for a typical waterfront wall. This is broadly based on the guidelines prepared by British Waterways (BW) now the Canal and River Trust, for asset inspection procedures on their fixed infrastructure.

Table 4.4 Type, purpose and frequency of inspections (after British Waterways, 2008)

Inspection type Purpose Frequency

Continuous supervision (also known as length inspection (LI) by BW)

Supervision by a technical employee, not necessarily a qualified engineer, to notify any obvious major damages in terms of usability of the structure

Monthly to three monthly

Regular supervision (also known as annual inspection (AI) by BW)

Performed and documented annually by qualified technician or engineer who is familiar with the structure to ensure that no major defects affecting capacity and/or usability occur

Annually

Major inspection (also known as principal inspection (PI) by BW)

Detailed visual inspection carried out by a qualified engineer and may include detailed measurements and MBES and LiDAR surveys if appropriate. Each part of the structure should be inspected and the capacity and usability of the structure should be assessed and documented

Performed every three to 20 years based on risk (typically every six years)

Special or post-event inspection

Normally a rapid evaluation by a qualified engineer following damage caused by storm, flood, vessel impact etc. in order to determine if further attention to the structure is required as a result of the event

Not scheduled – performed following a significant potentially damage causing event

4.5.4 Rating and prioritisationThe information gathered from the inspection of relevant structural features can be used to assign a condition rating that can remain associated with the structure until it is re-inspected following a quantitative major or special inspection, repairs or following the next scheduled routine visual inspection.

There are many valid examples of condition rating or grading systems that use various scales. Two such examples are shown in Tables 4.5 and 4.6. An important aspect of such systems is that the condition features or indicators used in the assessment should be related to the performance of the structure.

The EA’s rating system (Table 4.5)makes this explicit in the definitions of the condition grades whereas it is more inferred in the version (Table 4.6) from PIANC (2013).

Table 4.5 Condition assessment rating scale and definitions (from EA, 2006)

Grade Rating Description

1 Very Good Cosmetic defects that will have no effect on performance

2 Good Minor defects that will not reduce the overall performance of the asset

3 Fair Defects that could reduce performance of the asset

4 Poor Defects that would significantly reduce the performance of the asset. Further investigation needed

5 Very Poor Severe defects resulting in complete performance failure

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Table 4.6 Example condition assessment rating table (from PIANC, 2013)

Grade Rating Description

6 Good No visible damage or only minor damage noted. Structural elements may show very minor deterioration, but no overstressing observed. No repairs are required.

5 Satisfactory Limited minor to moderate defects or deterioration observed, but no overstressing observed. No repairs are required.

4 Fair

All primary structural elements are sound, but minor to moderate defects or deterioration observed. Localised areas of moderate to advanced deterioration may be present, but do not significantly reduce the load bearing capacity of the structure. Repairs are recommended, but the priority of the recommended repairs is low.

3 PoorAdvanced deterioration or overstressing observed on widespread portions of the structure, but does not significantly reduce the load bearing capacity of the structure. Repairs may need to be carried out with moderate urgency.

2 SeriousAdvanced deterioration, overstressing or breakage may have significantly affected the load bearing capacity of primary structural components. Local failures are possible and loading restrictions may be necessary. Repairs may need to be carried out on a high priority basis with urgency.

1 Critical

Very advanced deterioration, overstressing or breakage has resulted in localised failure(s) of primary structural components. More widespread failures are possible or likely to occur and load restrictions should be implemented as necessary. Repairs may need to be carried out on a very high priority basis with strong urgency.

Table 4.6 associates a priority repair hierarchy (of low, moderate, high, very high urgency) with the condition rating whereas in Table 4.5 the system does not make such explicit assumptions. However it does recommend the further investigation of assets rated as being in poor condition. The reason for this is that prioritisation of repairs depends on the risks associated with the structure – as well as its condition. The example from PIANC (2013) makes the implicit assumption that a structure must be maintained and repaired to a ‘satisfactory’ (Grade 5) level whatever the risks associated with its deterioration or failure. Visual inspection and condition grading does not normally take into account the consequences associated with a structure deteriorating or failing. However, except in the most simple cases, risk cannot be determined on the basis of condition assessment alone and repairs so cannot be properly prioritised. For example, some old waterfront walls may no longer be required to bear the loads they were once designed for, ie their performance requirements have changed, so the condition to which they were once required to be maintained is no longer as essential (the opposite case is also possible).

An important ‘trigger point’ is the ‘critical point of disrepair’, ie the point at which the onset of progressive failure occurs if the structure is not remediated, generally Grade 4 in Table 4.5, and Grade 2 in Table 4.6. If past repairs and maintenance have not prevented deterioration to this ‘critical’ level then a decision at this point has to be taken as to whether repairs are to be made to the structure to raise its condition back to an acceptable level or whether to rebuild, replace or decommission the asset.

It is therefore important to understand that, as well as the structural concepts of the wall to be inspected, the correct choice of rating system and the actual assignment of ratings requires experience and an understanding of both the original, current and future performance requirements. When inspecting and rating a portfolio of assets judgement should be applied consistently and consider the:

ªª original, current and future performance requirements

ªª scope of any damage (total amount of defects)

ªª severity of the damage (extent, type, size of the defects)

ªª distribution of the damage (localised or general)

ªª types of components affected (and their relative contribution to the integrity of the structure)

ªª location of defects relative to ultimate limit states (eg point of maximum moment/shear).

For further information on condition inspection and rating see EA (2006), which has guidance on the assessment of brick and masonry structures and also PIANC (2013), which contains further practical guidance and useful detail on the topic.

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4.6 INVESTIGATIONS, INSTRUMENTATION AND MONITORING

This section reviews and addresses the use of investigations, instrumentation and monitoring in the context of old waterfront wall performance assessments. It will review existing information, uses of remote sensing technologies and assessment tools, listings of intrusive methods, along with various instrumentation and generalisation of monitoring data analysis. Specific descriptions of these techniques are provided in Chapter 6, however, Chapter 4 offers guidance on how and when to apply investigations techniques for use during old waterfront wall performance assessments.

The discussion of investigations addresses:

ªª what data can be acquired with each investigation method

ªª what failure modes are linked to the available data

ªª when a given investigation should be planned during an assessment process.

The main goal of old waterfront wall investigation is to obtain specific data (topographic, geometric, hydraulic, morphological, geotechnical/geological etc) that can be used in the assessment of condition, performance, or in design of a modification/repair to an existing old waterfront wall. In the framework of this chapter, emphasis is placed on investigating an existing old waterfront wall, mainly for assessment.

In terms of investigations for old waterfront wall performance assessments, there are two main objectives of the assessment depending on whether it is the first assessment of an unknown old waterfront wall system, or a regular assessment for a well-managed system. In the first instance a full investigation program will be required to help retrace the structural composition of the old waterfront wall and its foundation, while in the second some limited investigation will help check that the current condition (including possible evolution) of the old waterfront wall and its foundation is compatible with its required performance (see Section 6.5 for detailed discussions on the various approaches to conducting investigations for existing old waterfront walls).

These different types of information will allow for the assessment of hydraulic structures in terms of relating to the various failure modes or mechanisms (see Chapter 3). This assessment includes the detection of weak points, including their location and quantification that can induce internal and external damage to the waterfront wall (eg internal erosion, non-homogeneous materials, cavity formation, settlement zones, and fractures).

In addition to assessing current waterfront wall condition (see Section 4.5), a critical use of findings from old waterfront wall investigations is in assessing future performance. This is principally informed by the assessment of current condition, performance assessments and the application of likely deterioration or damage processes. Performance and deterioration assessments are approximations of reality based on historical data and scientific approaches. Predictions of future performance require various assumptions to be made (eg asset loading, environmental conditions, third party interference).

Continuous monitoring of old waterfront walls through the installation of electronic and mechanical sensing equipment can also be employed as part of an intrusive investigation. The two main advantages are that the parameters can be continuously monitored and that the requirement for manual inspections by inspector or vehicle can be reduced. Continuous monitoring will produce a more accurate assessment of change over time than inspection records gathered on an irregular (eg six, 12, 24-monthly) basis. It can also record asset parameters at times of both high and low loading conditions, which can be highly significant data in assessing wall performance (see Chapter 7).

4.6.1 Investigation planningAt some point further investigation of the wall is required, which may be because of the results of a regular visual inspection, or because of proposed changes to the way that a wall is to be used. This will

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be more than a visual inspection and is likely to comprise intrusive investigation such as pitting, probing or boreholes, or non-intrusive investigations such as geophysical methods, or a combination of the two. Chapter 6 discusses the range of techniques available for such inspections in more detail.

In order for the maximum information to be obtained from these investigations, it is essential that they are thoroughly planned and follow a logical sequence. Also, the need for changing the scale or type of investigation has to be continually re-assessed during the course of the work as information is gathered. By not constantly appraising the data and re-adjusting the remaining investigation, essential data may not be collected, leading to potentially expensive further investigations being required.

The first step to planning an investigation is the collection of all existing data appertaining to the wall in question. This would include as-built drawings (if available) together with any design reports. These should enable the wall profile and founding depth (toe levels in the case of embedded walls such as sheet pile walls) to be determined. Design reports might also include the results of any ground investigation carried out or a copy of the investigation report itself.

Unfortunately, often these documents are no longer available, so the wall profile will need to be physically determined together with the ground conditions on which the wall relies for stability.

A possible assessment of wall profile might be made if drawings of similar walls in the vicinity are available. Examination of archive information might yield useful information.

Some non-intrusive geophysical techniques offer the possibility of determining the existing wall shape. Advice from specialist geophysical investigation contractors needs to be sought during this planning stage. However, definitive measurement of wall profile will need to be carried out intrusively, ie a programme of vertical and horizontal drilling should be formulated.

In the absence of any previous boreholes, an indication of ground conditions may be obtained from inspection of the geological mapping of the area. In the UK, the British Geological Survey (BGS) maintain a database of historical borehole information (see Websites). Historical boreholes may be available in the vicinity of the wall(s). However, check boreholes should always be made to make sure that there has been no change to the ground conditions, or water table level.

When planning the boreholes, the location, depth and type of boring/drilling all need to be considered to obtain the maximum information from the investigation. The sampling and in situ testing regime (type/frequency) also needs to be determined. These requirements then need to be included in a ground investigation specification for issue to tenderers. ICE (2011a) is a widely used document within the ground investigation industry together with the accompanying conditions of contract (ICE, 2011b).

The contract documents should require daily reporting of the results obtained from the investigation. This will enable any changes to the scope of the investigation to be assessed.

It is often the case that the contractor responsible for the investigation will be asked to provide an interpretative report together with a factual report of the investigation. The information given will depend on the engineering experience of the contractor, the extent of information passed on by the owner (past history and future use) and on the level of responsibility required from the contractor. It is often more effective for interpretation of the data to be carried out by a geotechnical engineer, preferably one that has been involved with the investigation from inception.

4.6.2 Instrumentation and monitoringWhen planning the investigation, consideration needs to be given for installing instrumentation to monitor the behaviour of the wall. It is likely to be more economical if instrumentation is installed during the ground investigation contract before the boreholes are backfilled.

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Instrumentation that can be installed during the investigation includes inclinometers, extensometers, fibre optic strain gauges and piezometers, measuring the displacement, movement, settlement and pore water pressures respectively (see Chapter 6).

Planning the installation of these instruments as part of the investigation allows the contractor to appoint specialist subcontractors for the work.

It may be the case that simple surface mounted survey points will give sufficient information on the movement behaviour of the wall. However, for gravity walls that taper to a narrow crest, there may be insufficient separation between monitoring points to determine any tilt of the structure. If no inclinometer is planned, then it might be necessary to install a deep survey point on the heel of the wall by means of a borehole. Electro-levels across the crest of the wall might offer an alternative solution providing there is sufficient protection from damage.

Instrumentation will need to be readable over a period of time, either to establish movement behaviour for a wall that while not being modified is showing signs of movement or, for a wall that is to be substantially modified, before during and after the alterations. The instruments therefore need to be protected from operational/construction activities carried out in the vicinity, but also need to be positioned such that they can be read without disrupting normal activities. Instruments can be installed with flush surface finished covers, but if these are positioned so that they are semi-permanently covered by cargo, then reading will be intermittent. Similarly, survey points need to be positioned so that they are accessible.

For surveying techniques, it is essential that a stable datum is established. Use of a benchmark situated on a wall that is undergoing deformation will not give reliable measurements of global deformation. The datum should be remote from the structure being monitored and should not be prone to movement.

There are several remote reading instruments available using transducers to record data that can be sent via the internet to a local data-logger for downloading periodically. The cost of such instrumentation is higher, but substantial savings can be made with the reduced man-time in physically reading the instruments, the instruments not needing to be accessible and the ability to directly read the data into an interpretation program.

4.6.3 Analysis of dataHow data from the investigation and instruments is manipulated or interrogated depends on the reasons the investigation was carried out. In most cases, data is reproduced as a series of graphs, as this gives a visual appreciation of changes in the behaviour of the wall – scanning a series of numbers is not usually as informative.

Once data is collected it is important that it is examined by an experienced engineer. There have been projects where instrumentation data indicated development of a failure mechanism that, if appropriate measures had been taken in time, could have been addressed. Unfortunately, the data was not examined and the situation deteriorated until failure occurred. An inspection of all new data should be carried out immediately after it has been collected and manipulated so that any adverse trends can be identified.

Walls with no major changes plannedDepending on the cause for concern, instrumentation of these walls might comprise simple surveying techniques. In this case, the displacement data is often plotted against time.

Survey data can be translated to graphs using a spreadsheet – an xy scatter diagram should be used and not a line diagram where the time series (normally plotted on the x-axis) is plotted at regular intervals. Tilt can be plotted as rotation against time, or preferably the actual levels plotted so that the cause of tilt (settlement of the toe or heel) is apparent. Horizontal displacement can also be plotted against time.

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From these points it should be apparent whether one particular area of the wall is deforming more than others. A longitudinal plot of displacement for several points in time might also be useful.

This data should enable the deformation behaviour of a wall to be determined. It may be that the results show little movement, in which case the frequency of reading can be extended. The data might show a continual movement or even movement that is gradually accelerating. If sufficient data is available, it may be possible to extrapolate the data to predict future movements. Note that while the data can be plotted conventionally against natural time, using logarithmic or square root time functions to plot the data might give more easily interpretable trends.

Installation of additional instrumentation such as inclinometers and extensometer might be necessary in cases where severe deformation of a wall is occurring. Processing the information from these instruments is discussed in the following section.

Walls where major changes are requiredIn this case, it would be advantageous for the wall to be monitored over a period of time before works are carried out so that any background behaviour can be established and, if necessary, accounted for in the deformations observed in the construction and operation phase.

Depending on the nature of the wall and proposed development, similar instrumentation to that previously described might be sufficient. However, it is likely that additional instruments are required, either for their ease of reading (particularly remotely) or because more information of deformation with depth is required. Such instrumentation would comprise inclinometers or extensometers.

Inclinometer data where displacement over the height of the wall is measured can be difficult to present graphically. The total displaced profile (depth or level v displacement) can be presented individually with each date of reading. These types of plots will indicate the zone over which displacement is developing.

The progression of movement can also be seen from such plots but the rate at which that displacement is taking place is not easily discerned. Here, a secondary plot of displacement at a particular point or level (or several points or levels) down the wall should be plotted against time.

If settlement is being monitored (either by survey points or by extensometers) then this data also should be plotted against time.

While the wall will respond to immediate changes during construction, it will be necessary, depending on the ground conditions, to continue to read the instruments after construction. So, it is essential that the initial installation is sufficiently robust to survive the construction process. Monitoring should take place regularly after construction, with intervals increasing if the rate of change is small.

4.7 KNOWLEDGE AND DATA MANAGEMENT

4.7.1 The need for documents, records and archivesAll data collected needs to be collated into an AMS. This should be well documented and be readily available for owners or engineers, at the time recorded and in the future. This applies whether the original drawings and design reports for the wall are available or whether extensive (and expensive) investigation is required to provide the necessary information. To ‘lose’ such data, either by storing paper copies in an obscure place or worse, inadvertently destroying the paper data, may incur additional costs in the future to repeat the exercise. Loss of survey data also loses time series, so that rate of change over time cannot be seen and is not possible to repeat.

There are a number of methods for collating and storing the collected data depending on the number of assets owned. For a major port where there are several quay walls and there have been many separate

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ground investigations, then use of a digital AMS or GIS database with all information such as materials, costs, faults, reports etc kept in layers with an ability to drill down into the data is recommended as a logical approach. For a single or few walls, such systems might not be appropriate and it will then depend on the owner to develop a system whereby data can be retrieved.

It is considered useful for all documents to be available electronically. This includes scanning any original drawings or reports. New data is also likely to have been submitted and manipulated electronically. A clearly identifiable folder on a network should be established to store the data, with the folder divided into logical sub-folders. Such data needs to be backed-up regularly and spare copies stored offsite.

Finally it is worth reminding owners/asset managers that they have a legal responsibility under the Construction (Design and Management) Regulations 2007 (CDM2007) to maintain a health and safety file for all old waterfront walls and failure to do so could lead to prosecution (HSE, 2007). CDM regulations are subject to periodic revisions and updating and it is essential that owners/asset managers check the current regulations.

4.7.2 Asset management information systems (AMIS)An AMIS is a database that contains all available information on a particular wall (or asset) or group of assets. An example of the requirements of such a database is given in

PIANC (1998) provides an example of the requirements for the database, and also suggests that such a database for a typical waterfront wall in a commercial port might contain the following elements:

ªª Main data: facility location, port type, ownership and operators, location of structures, related structures.

ªª Environment: metrological data, hydrographic and hydraulic data, geotechnical conditions, seismic effects, environmental restrictions.

ªª Individual structures: type, design data, as-built and/or modification data, materials, durability.

ªª Operating parameters: type, vessel types, cargo types and systems, loading, utilities, ground transport.

ªª Financial data: capital expenditure (original build plus upgrading), O&M, demolition and removal.

ªª Maintenance data: inspection data including conditions surveys for timber, concrete, steel, fenders, quay wall structures in general, piling, breakwaters.

ªª Demolition data: any planned of actual demolition.

As noted previously, not all of these items will need to be included particularly where the number of assets is small. However, development of such a system limited to suit actual needs, would enable the condition or, more importantly, the continual decline of assets to be monitored.

4.7.3 Geographical information system (GIS)GIS is a different form of database whereby data is presented visually. Data need not be limited solely to walls – services such as pipes for water, fire-fighting bunkering etc can also be indicated on a plan of the area. The whole surrounding infrastructure related to the prime structure can be included in a single database with the various assets or elements represented as layers on a drawing that can be switched on or off as desired. Dialogue boxes can be presented containing details of particular assets. The observations made during various surveys can be obtained from the database.

A GIS can also present a ‘front end’ to the data held in an AMIS and need not be any more complex to set up. A simple link on a map symbol can open up the database relevant to that particular asset. This is only of use where there are a significant number of assets, but it can simplify finding that information. When members of the public report a problem it will be possible to open a GIS, click on the identified asset and gain access to all relevant data, especially photographs. This makes getting an understanding of what is being reported much easier.

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Development of a GIS will initially require a considerable input of data, not only relating to walls. It is likely that development of a GIS will only be economically feasible for major operators, and it is unlikely that owners of a single quay or waterfront wall will wish to go down such a route. Reliance on simple document control is likely to offer a more practical way forward.

4.7.4 Building Information Modelling (BIM)The concept of Building Information Modelling (BIM) was developed in the 1970s by Eastman (1974), however it only started to become regularly used in many engineering offices in the 2000s. A BIM is an enriched 3D computer-based model where each component can be interrogated and modified individually and where any changes to the model are reflected in all views as opposed to traditional computer-aided design (CAD) applications where each view has to be updated individually. This approach avoids errors and is generally faster than conventional 2D CAD. Additional information such as component or construction dating, material properties and costs can be easily added to the model. This facilitates easy generation of project documentation and can be integrated with rendering programs to produce photorealistic renderings. BIM is a compulsory requirement on all new government projects in some European countries and is being similarly considered for the UK (HM Government, 2012). “The Government Construction Strategy (GCS) requires that Government will require fully collaborative 3D BIM (with all project and asset information, documentation and data being electronic) as a minimum by 2016. This refers to all centrally procured government projects as outlined in the GCS including new build and retained estate, vertical and linear.” (BIM Task Group, 2015).

Existing waterfront walls can be modelled using BIM either manually by a CAD technician or automatically with 3D laser scanning technology. Data can be added to the model as it becomes available and the model can interrogated from any perspective. The BIM can easily link with other computational modelling programs to facilitate more advanced simulations and help the engineer develop a better understanding of many of the potential risk scenarios. This may assist with carrying out inspections as well as planning future repairs and upgrades as the engineer can identify which components are affected and plan accordingly with the ability to automatically generate fabrication drawings and link to other project management software packages.

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ReferencesBIM TASK GROUP (2015) What is the extent of the Government Constriction Strategy and it’s BIM requirements, Point 10, FAQs, BIM Task Group, Department for Business, Innovation and Skills, London. Go to: http://www.bimtaskgroup.org/bim-faqs

BRADBURY, A, ROGERS, J and THOMAS, D (2012) Toe structures management manual, SC070056, Environment Agency, Bristol, UK (ISBN: 978-1-84911-290-1). Go to: http://tinyurl.com/p2pdz38

BRITISH WATERWAYS (2008) Asset inspection procedures, AIP2008, British Waterways, UK. Go to: http://tinyurl.com/o83ygbv

BROWN, A J and GOSDEN, J D (2004) Interim guide to quantitative risk assessment for UK reservoirs, Thomas Telford Ltd, London, UK (ISBN: 978-0-72773-267-5)

CEH (1999) Flood Estimation Handbook, Centre for Ecology and Hydrology, UK (ISBN: 978-1-90669-800-3). Go to: www.ceh.ac.uk/feh2/fehintro.html

CIRIA; CUR; CETMEF (2011) The Rock Manual. The use of rock in hydraulic engineering, C683, CIRIA, London, UK (ISBN: 978-0-86017-683-1). Go to: www.ciria.org

CIRIA; MINISTRY OF ECOLOGY; USACE (2013) The International Levee Handbook, C731, CIRIA, London, UK (ISBN: 978-0-86017-734-0). Go to: www.ciria.org

DEFRA (2008) Assessing and valuing the risk to life from flooding for use in appraisal of risk management measures, Project appraisal guidance supplementary note, Department for the Environment, Food and Rural Affairs, London, UK. Go to: http://tinyurl.com/kcky5jp

EASTMAN, C M (1974) An outline of the building description system, Institute of Physical Planning, Carnegie-Mellon University, USA

FLIKWEERT, J, LAWTON, P, ROCA COLLELL, M and SIMM, J (2009) Guidance on determining asset deterioration and the use of condition grade deterioration curves, SCHO0509BQAT-E-P, Joint Defra/Environment Agency Flood and Coastal Erosion Risk Management R&D Programme, Defra and Environment Agency, UK (ISBN: 978-1-84911-056-3). Go to: http://tinyurl.com/q4d7b3u

DfT (2012) The accidents sub-objective. TAG Unit 3.4.1, Department for Transport, London, UK. Go to: http://www.norfolk.gov.uk/view/NCC144252

EA (2006) Condition assessment manual, Document Reference 116_03_SD01, Environment Agency, Bristol, UK

EA (2010) Flood and coastal risk management appraisal guidance (FCERM-AG), Environment Agency, Bristol, UK. Go to: http://tinyurl.com/o3ajlrm

HALCROW (2013) Practical guidance on determining asset deterioration and the use of condition grade deterioration curves: revision 1, SC060078/R1, Environment Agency, Bristol, UK (ISBN: 978-1-84911-304-5). Go to: http://tinyurl.com/m5vh6tw

HAWKES, P J (2005) Use of joint probability methods in flood management. A guide to best practice, R&D Technical Report FD2308/TR2, Flood and Coastal Defence R&D Programme, Department for the Environment, Food and Rural Affairs and Environment Agency, London, UK

HM GOVERNMENT (2012) Industrial strategy: government and industry in partnership. Building Information Modelling, HM Government, London, UK. Go to: http://tinyurl.com/lbrnkew

HSE (2001) Reducing risks, protecting people (R2P2). HSE’s decision-making process, Health and Safety Executive, London, UK (ISBN: 0-71762-151-0). Go to: www.hse.gov.uk/risk/theory/r2p2.pdf

ONR (2006) Safety assessment principles for nuclear facilities, revision 1, Office for Nuclear Regulation, Bootle, UK. Go to: www.onr.org.uk/saps/saps2006.pdf

HSE (2007) Construction (design and management) Regulations 2007 (CDM) Approved Code of Practice, L144 Health and Safety Executive, London (ISBN: 978-0-71766-223-4)

HSE (2015) HSE principles for cost benefit analysis (CBA) in support of ALARP decisions, Health and Safety Executive, London, UK. Go to: http://tinyurl.com/o77fma9

HUGHES, A K and GARDINER, K D (2004) “Portfolio risk assessment in the UK: a perspective”. In: Proc of the thirteenth biennial British Dam Society conference, H Hewlett (ed) Long-term benefits and performances of dams, University of Canterbury, 22–26 June 2004, Thomas Telford, London, UK (ISBN: 978-0-72773-268-2)

HUGHES, A J, HEWLETT, H W M, SAMUELS, P G, MORRIS, M W, SAYERS, P B, MOFFAT, I, HARDING, A and TEDD, P (2000) Risk management for UK reservoirs, C542, CIRIA, London, UK (ISBN: 978-0-86017-542-1). Go to: www.ciria.org

IAEA (2001) Severity, probability and risk of accidents during maritime transport of radioactive material, final report, IAEA-TECDOC-1231, Radiation Safety Section, International Atomic Energy Agency, Vienna, Austria. Go to: http://tinyurl.com/n9qubm5

ICOLD (2005) Risk assessment in dam safety management: a reconnaissance of benefits, methods and current applications. A reconnaissance of benefits, methods and current applications, Bulletin 130, International Commission on Large Dams (ICOLD), Paris, France. Go to: http://tinyurl.com/qcalvk6

ICE (2011a) UK Specification for ground investigation, second edition, Institution of Civil Engineers, London, UK (ISBN: 978-0-7277-3506-5)

ICE (2011b) Infrastructure conditions of contract, Institution of Civil Engineers, London, UK. Go to: http://tinyurl.com/oxjl2j9

IMO (2002) Guidelines for formal safety assessment (FSA) for use in the IMO rule-making process, International Naritine Orgzanization, London, UK. Go to: http://tinyurl.com/psjwgmg

MARITIME UNIVERSITY OF SZCZECIN (2013) BalticMasterII Report, Baltic Sea Region Programme, European Regional Development Fund, Poland. Go to: http://tinyurl.com/nrzfmun

NERC (2014) Increasing resilience to natural hazards in earthquake-prone and volcanic regions, Natural Environment Research Council, London, UK. Go to: www.quakes.bgs.ac.uk/hazard/haz_guide/index.html

PIANC (1998) Life cycle management of port structures – general principles, Report of Working Group 31, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/publications.php

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PIANC (2013) Inventory of inspection and repair techniques of navigation structures (steel, concrete, masonry and timber) both underwater and in-the-dry, Report 119, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/publications.php

PIANC (2014) Harbour approach channel design guidelines, MarCom Working Group 121, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/edits/articleshop.php?id=2014121

ROGERS, J, HAMER, B, BRAMPTON, E, CHALLINOR, S, GLENNERSTER, M, BRENTON, P, BRADBURY and A (2010) Beach management manual (second edition), C685, CIRIA, London, UK (ISBN: 978-0-86017-682-4). Go to: www.ciria.org

SAYERS, P, HALL, J and MEADOWCROFT, I (2001) “Towards risk-based flood hazard management in the UK” Proceedings of the ICE – Civil Engineering, vol 150, 5, Institution of Civil Engineers, London, UK, pp 36-42

SIMM, J, GOULDBY, B, SAYERS, P, FLIKWEERT, J, WERSCHING, S and BRAMLEY, B (2008) “Representing fragility of flood and coastal defences: getting into the detail”. In: Proc of the European conf on flood risk management (FLOODrisk 2008): Research into practice, 30 September to 2 October 2008, Keble College, Oxford, Taylor & Francis, London, UK, pp 621–631

STERN, P C and FINEBERG, H V (eds) (1996) Understanding risk: informing decisions in a democratic society. Committee on risk characterization, National Research Council, Washington DC, USA (ISBN: 0-30957-849-3)

WATSON, H A (1961) Launch control safety study, Bell Telephone Laboratories, Murray Hill, USA

WHITMAN, R V (1984) “Evaluating calculated risk in geotechnical engineering” Journal of Geotechnical Engineering, vol 110, 2, American Society of Civil Engineers, Reston VA, USA, pp 143–188

Statutes

British StandardsBS 6349-1-3:2012 Maritime works. General. Code of practice for geotechnical design

Further readingDE GIJT, J G and BROEKEN, M L (eds) (2013) Handbook of quay walls, second edition, CRC Press, London, UK (ISBN: 978-1-13800-023-0)

HIGHWAYS AGENCY (2007) Inspection manual for highway structures. Volume 1 Reference manual, The Stationery Office, London, UK (ISBN: 978-0-11552-797-5)

HIGHWAYS AGENCY (2007) Inspection manual for highway structures. Volume 2 Inspectors handbook, The Stationery Office, London, UK (ISBN: 978-0-11552-798-2)

KELLY, S W (1999) Underwater inspection criteria, Naval Facilities Engineering Service Centre, California, USA. Go to: www.hmrmarine.com/UWInspection.pdf

LONG, G, SMITH, M, MAWDESLEY, M, TAHA, A (2013) Quantitative assessment methods for the monitoring and inspection of flood defences: New techniques and recent developments, C717, CIRIA, London, UK (ISBN: 978-0-86017-720-3). Go to: www.ciria.org

SAMUELS, P G (1995) “Uncertainty in flood level prediction”. In: A Ervine, A J Grass, M A Leschziner and J Gardiner (eds) HYDRA 2000 XXVIth IAHR Congress: Hydraulics research and its application next century, September 1995, vol 1, Thomas Telford Ltd, London, UK (ISBN: 978-0-72772-061-0)

WebsitesEnvironment Agency: http://tinyurl .com/mnnfp2k

Environment Agency National Costal Erosion Risk Maps: http://maps .environment-agency .gov .uk/wiyby/

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5 Operations and maintenance

5.1 OVERVIEWThis chapter provides an overview of asset management principles as they apply to operational and maintenance (O&M) activities. Figure 5.1 provides an overview of the chapter.

Management actionsAdministrative context

Physical context

Severe event(Section 5 .5)

Management of risk(Sections 2 .1 to 2 .3)

Responsibilities (Section 2 .4)

Powers(Section 2 .5)

Beneficiaries(Section 2 .8)

Funding(Section 2 .9)

Physical form and purpose

(Chapter 3)

Physical processes (Section 6 .3)

Loads(Sections 7 .1 to 7 .3)

Wall stability(Section 7 .4)

Historical data(Section 6 .4)

Framework for decisions (Section 4 .3)

Risk analysis(Section 4 .4)

Performance assessment(Section 4 .5)

Operations(Section 5 .2 to 5 .3)

Monitoring and inspection

(Sections 4 .6 to 4 .7)

Data acquisition (Section 4 .7)

Data management (Section 4 .8)

Wall investigation (Sections 6 .5 to 6 .9)

Decision on intervention

Maintenance, repair and rehabilitation (Sections 5 .4 and

Chapter 8)

Regulations and consents

(Sections 2 .6 to 2 .7)

Figure 5.1Overview of Chapter 5

Following this introduction, Section 5.2 introduces O&M activities in relation to the old waterfront wall management life cycle. It focuses on the organisation of O&M, importance of an O&M manual, and activities and practices of asset management. Section 5.2.6 on general approaches to O&M addresses the use of risk-based and sustainable issues, operating for the long-term, and managing and organising data produced and used during O&M.

Section 5.3 then presents information related to the key functions of an old waterfront wall, which may be operating to maintain a navigation channel, to protect a harbour area, to keep water out of an area, to operate as a wharf or berthing facility or retaining waterfront property.

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Section 5.4 discusses maintenance of old waterfront walls and associated structures. Maintenance of old waterfront walls addresses activities to prevent damage and progression to failure, while maintenance on associated structures highlights key activities to address routine maintenance. Issues covered in Section 5.4 include:

ªª encroachments

ªª settlement and subsidence

ªª seepage/drainage

ªª instability

ªª cracking and block movement

ªª burrowing animals and biological attack

ªª vegetation

ªª culverts and discharge pipe systems.

In Section 5.5 guidance and advice is given on what to do if there is an emergency situation.

5.2 APPLYING ASSET MANAGEMENT PRINCIPLES TO O&M

5.2.1 IntroductionO&M activities can include a range of management techniques that are intended to ensure that old waterfront walls and their associated features meet specific performance objectives. These objectives are normally an inherent part of the original design (eg to act as a berthing facility), but may also be subsequently added or extended (eg for changing port operations). This chapter includes preventive maintenance measures, repairs that can be made within the O&M function, and guidance for determining when repairs are beyond O&M.

5.2.2 Activities and practices of asset managementO&M is a critical part of asset management.

The most critical systematic and co-ordinated activities and practices that apply to O&M are:

1 Define O&M objectives.

ªª identify routine O&M activities

ªª identify any specific O&M requirements

ªª record identified activities and requirements in the O&M manual to ensure that the asset manager understands the considerations and intentions of the use of the structure.

If sufficient structural information is not readily available, it should be collected first to establish the O&M requirements.

2 Define functional objectives, performance objectives, and performance indicators.

ªª functional objectives should include the intended use of the structure, but may also include recreational or environmental objectives. These help asset managers prioritise investments, as they take into account the purpose of the structure and the risks associated with it

ªª functional and performance objectives should inform O&M as part of asset management planning

ªª performance indicators translate objectives into specific structure features. They may be used to define targets that ensure O&M focus on achieving the objectives.

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3 Determine when and how decommissioning may occur.

ªª decommissioning results from an asset management decision that weighs the benefits of continued maintenance and its associated costs (based on a performance/risk assessment) against policy or management objectives. This overview of benefits and costs helps the asset manager decide whether continued O&M is viable and affordable

ªª advice and guidelines on decommissioning of old waterfront walls may be found in new guidance from Defra (in press)

Old waterfront walls are notoriously difficult to assess, both in terms of their stability and in their rate of deterioration. In many cases apparent abnormalities may be relatively harmless while the factors that are crucial to the continuing performance of the wall may go undetected. The reasons for this are that most of the wall is hidden under the soil or water and that a single inspection may well not reveal the rate of deterioration. Box 5.1 provides guidance for asset managers on assessing the deterioration of typical waterfront walls that are part of their stock of flood and coastal defence assets.

5.2.3 Management life cycleThe routine asset management section of the waterfront wall management life cycle (see Figure 5.3) outlines typical O&M functions. These include:

ªª monitoring, inspecting (discussed further in Chapter 4)

ªª maintaining (see Section 5.3)

ªª assessing performance (see Section 4.3)

ªª assessing and prioritising management actions (see Section 4.2)

ªª repairing and adapting (see Chapter 8).

Decommissioning is an important part of O&M to consider how the structure will be dealt with when it is no longer required or is no longer serving its intended purpose. Being clear about which walls need to be operated, maintained, inspected and monitored is important to ensure resources are not spent on those that are no longer needed.

The EA has developed practical guidance to help asset managers assess the deterioration of typical flood and coastal defence assets (including waterfront walls) as well as their residual lives. The guidance helps asset managers assess the residual risk of assets under different conditions and maintenance regimes.

An asset’s rate of deterioration depends on the asset type, its environment and the load it experiences. To continue to provide protection to people and properties from flooding and erosion, asset managers need to understand the likely

deterioration rates across their asset stock. This allows them to gauge when appropriate interventions are most effective for maintenance, repair and replacement.

As deterioration can vary from asset to asset, it is essential to use engineering judgment and practical experience, along with this guidance, to apply and adapt the deterioration curves appropriately. Figure 5 .2 is a sample deterioration curve for a typical riverine waterfront brick and masonry wall.

Figure 5.2Example of a deterioration curve for a typical riverine waterfront brick and masonry wall (from Brommer et al, 2013)

Box 5 .1 Guidance on how to assess the deterioration of waterfront walls and how to assess residual life (from Brommer et al, 2013)

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5Figure 5.3 Waterfront wall management life cycle

Waterfront walls are continuously and/or intermittently challenged by waves, flowing water, wind, precipitation, loading and impacts, encroachments – as well as by changes in the needs of owners, operators and users. So over time, wall materials may degrade or shift, elements or sections may wear out, and new features may be added to the structure. O&M is the function that takes action to observe or monitor, assess, stop, repair and/or accommodate these changes.

5.2.4 Organisation of O&MTo support a waterfront wall’s O&M needs throughout its life cycle, the O&M function is typically divided into three roles, which require different skill sets:

1 Planning, including performance assessment (see also Chapter 4).

2 O&M, including the actual repair work on the ground.

3 Inspection.

How these roles are organised varies depending on the size and nature of the managing organisation and the extent and range of assets to be managed. For example, in small organisations the roles may be combined within one unit. In larger organisations they may be in separate units and in some cases the operational role may even be contracted out to private parties. Whatever the method adopted by organisations, the highest priorities are that:

ªª there is good communication between the roles

ªª the roles and responsibilities are clearly defined and effectively carried out

ªª the planning role specifies the performance standards for the operational role, to ensure that the O&M activities meet specified objectives and the needs of the organisation.

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5.2.5 Importance of an O&M manualThe O&M manual describes the specific tasks a maintainer should perform to ensure the reliability and durability of a waterfront wall and the methods and resources that should be used to perform them successfully. It forms the foundation of the structure’s quality assurance management plan. Ideally, the O&M manual’s guidance and instructions take into account the wider system within which the wall operates (port, river, canal, f lood defence etc) and its environment, the wall’s intended level of reliability, and the resources available to the maintenance program. The manual serves multiple purposes, which include:

ªª functioning as a key document for asset management and organisational strategy

ªª showing third parties that maintenance is being performed in compliance with legal requirements.

Where an existing waterfront wall does not have an O&M manual, as is the case for many old structures, then it is considered good practice to create one. Under some circumstances however, a set of authoritative instructions may perform the same function as an O&M manual.

BenefitsofanO&MmanualIn addition to providing guidance to maintenance staff on how to perform their tasks, the O&M manual may also:

ªª reduce the time lost to ineffective and inefficient practices

ªª provide information for decision makers about the link between resources allocated to maintenance and performance of the structure

ªª allow problems to be identified and resolved in an open manner, thereby encouraging continuous improvement and transparency.

Suggested contents of an O&M manualTo provide these benefits, ideally it should contain:

ªª the precise location of the structure

ªª a written description of the structure

ªª a layout drawing or map showing the alignment and extent of the structure

ªª a set of as-built drawings that have been updated to indicate any on-site modifications or observations noted in the field

ªª references to engineering standards (using references avoids having to make unnecessary changes whenever a standard is updated)

ªª references to relevant regulations, environmental designations and listing status

ªª operational constraints (eg working hours, seasons of the year), interested and affected parties, agreements in place with others

ªª contact details of relevant people, eg if they are urgently needed

ªª roles, contact information and a list of the responsibilities of the stakeholders

ªª legal requirements concerning maintenance

ªª procedures to follow if a detected problem is beyond O&M

ªª where appropriate and possible, include manufacturers’ specifications for any detailing and specialised equipment, and a list of authorised products (eg mooring bollards, fenders, gate mounts, railings) and their specifications (as an addendum to the manual).

Specific tasks to perform to ensure adequate maintenance (see Box 5.2):

ªª appropriate interventions (eg repairing a failure may not be appropriate if the wall is planned for complete refurbishment, rebuild or decommissioning in the near future)

ªª residual risks that continue to need to be managed

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ªª environmental considerations that affect O&M practices and timing, such as restrictions to accommodate bird nesting or animal habitat.

A risk register, where risks associated with operating and maintaining the structure are listed, should also be included in the O&M manual. The register may include:

ªª potential hazards that may pose a threat to the structure

ªª risks associated with working on a platform at height and near water

ªª risks to the wall (risk of failure)

ªª risks to individuals performing construction or O&M tasks (and how to minimise those risks)

ªª risks to the local population

ªª risks to the environment (from the presence of the wall and mitigation measures that may be needed)

ªª risks to the environment if the wall fails.

Those who perform O&M activities should strive to minimise these risks while managing efficiently and in alignment with budgetary and environmental constraints.

If the intended reliability or the maintenance requirements differ from one section of the structure to another, then the nature and frequency of the tasks for each section should be specified. If a task is subcontracted, the manual’s description of the tasks can be used as the contractor’s specification.

The O&M manual and emergency eventsThe O&M manual should include or reference the tasks related to emergency events (eg extreme storms or floods) as well as non-emergency events (eg suggesting that low waters during spring tides are good times to inspect the toe of coastal structures). It is important for the manual to identify who should be contacted in the event of an emergency, for example if it is a coast protection structure then the coast protection authority may insist on doing the repairs and will provide the money. It is also important to stress any proscribed activities, eg working hours or type of activities that are prohibited as a result of its environmental designation. Its description of emergency activities should be in compliance with emergency action plans and should also explain (or reference other documents that explain) the effect emergencies can have on available resources. For example, emergency events can:

ªª occur outside of working hours and last more than a work shift

ªª often require repeated tasks, such as patrols

ªª strain the availability of limited, trained staff.

Coastal and marine guidanceCIRIA has produced a coastal marine environmental site guide and accompanying pocket book, which are due to be published in late 2015. These will supersede C584 and C594 published in 2003. For more information go to: www .ciria .org

The O&M manual should define the tasks associated with:

ªª daily and routine inspections and patrols (see Section 4 .5)ªª what to do in case of an emergencyªª operation of associated structures or mechanisms, eg

fenders, barriers, fences, stairsªª maintenance of auxiliary structures that are needed to

ensure the integrity of the wall (eg closure structures, drainage pipes)

ªª encroachments (see Section 5 .4 .3)ªª vegetation management (see Section 5 .4 .9)ªª all other required maintenance.

It should also include the following information about each task:

ªª where it should be performed (ie the section of the wall or the structures involved, with their location and method of access, if needed)

ªª when and how often it should be done (including conditions if maintenance is condition-based)

ªª applicable engineering standards and as-built drawings

ªª equipment/staff required, and trainingªª design details and plans for the structuresªª risks associated with O&M, such as safety on access

to vertical wallsªª a detailed step-by-step description of the taskªª practices that should be avoidedªª measures to be taken to limit safety risks to workers

and third partiesªª measures to be taken to limit environmental or social

impacts (including historical or recreational if any)ªª efficiency ratio of the taskªª how the task should be tracked and documented.

Box 5 .2 Tasks to be included in the O&M manual

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Owners should make sure that sufficient trained staff are ready to perform emergency tasks and that the O&M manual is readily available at all times even when the office is closed. Also, they should take into account that staff may be mobilised on other tasks or they may not be able to get to the structure because access is not safe.

Emergency measures identified in the manual should be regularly rehearsed and tested to be sure that materials that need to be on hand for emergencies are present and available. Completing trial assemblies of closure structures for example is recommended where possible.

Compiling and updating the O&M manualUsually the ideal time to define a waterfront wall’s O&M procedures and document them in an O&M manual is during the structure’s design phase. However, many waterfront walls were constructed a long time ago and often their original design and as-built drawings have been misplaced or destroyed. If such drawings can be located, or redrawn with the help of a designer, then a new or first version of the O&M manual for an existing structure should be drafted and subsequently updated. Updates are generally made:

ªª after the next maintenance cycle is completed, to take into account unanticipated issues

ªª when there are changes in regulations/legislation, technologies or funding

ªª if a problem unexpectedly requires a waterfront wall designer’s expertise or special techniques.

The manual might be available in hard copy (paper) or soft copy(electronic form) or as part of a password-protected website accessible only by authorised people via a PC or smartphone and users can have this information on a hand held electronic device such as a tablet to take with them site inspection.

O&M manuals should be evaluated regularly for relevance and to determine if updates or new standards are needed in light of changes in legislation or local policies. Updates should be done in accordance with appropriate local and national laws and regulations.

To ensure the O&M manual’s completeness, the authors of the manual should have expertise in the hydraulics of waterfront structures, their design and maintenance, related environmental issues, health and safety, and ideally they should have a familiarity with relevant finance and law.

5.2.6 General approaches to O&MThe following sections explain the benefits of O&M on an old waterfront wall by:

ªª using a risk-based approach (see Chapter 4)

ªª using a sustainable approach

ªª operating for the long-term

ªª managing and organising the data produced and used during O&M.

These are complementary approaches to O&M. It is recommended that all of these approaches be considered for incorporation in a comprehensive O&M plan.

Using a risk-based approach to O&MThe risk-based approach takes into account the risks associated with a wall structure when prioritising levels of O&M. This approach helps to optimise the benefits of O&M (in economic, environmental and social terms) against its costs.

Risk based approaches are discussed earlier in Chapter 4. The challenges associated with the implementation of risk-based approaches include:

ªª the cultural change an organisation may need to go through to overcome O&M practices that are based on habit and tradition;

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ªª the difficulty of quantifying risk and the effect of O&M (ie its benefits) on risk. Methods are only starting to become available (as of 2014) for practical use;

ªª for flood defences – the political controversy associated with protecting rural areas to different condition grades than urban areas.

Using a sustainable approachO&M practices are considered sustainable when they help the present generation meet its needs without compromising the ability of future generations to meet theirs. By ensuring that assets will be maintained well into the future, subsequent generations do not become dependent on assets that are not able to perform. Sustainable practices do this by balancing long-term feasibility and technical, economic, environmental and social considerations with the assets functional and performance requirements.

Long-term feasibilityPlanning O&M practices for the long-term, rather than only for the present, can encourage the development of methods that are appropriate for each phase of the life of a waterfront wall. These methods can help a maintainer take care of the structure now and into the future. They can also ensure maintenance of the structure as designed and the overall performance of the wall (deterioration impacts):

ªª Technical considerations: O&M practices need to be technically sound. Unsound practices may compromise the ability of a waterfront wall to perform as intended.

ªª Economic considerations: O&M practices need to be economically viable (benefit/cost ratio) and affordable. Limited funding usually means compromising in one area to spend money on another. Efforts should be made to ensure that O&M practices make the best use of the money that is available.

ªª Environmental considerations: the O&M of a waterfront wall may have an impact on animals, plants and other forms of life close to the structure. To avoid negative environmental impacts during O&M, the owner should follow all local and national environmental laws, regulations and guidance that apply.

ªª Social considerations: many waterfront walls are important for people (eg they may provide protection). They may also be used and even enjoyed by them (eg seawall promenades or harbour breakwaters). Such multi-functional uses may influence O&M. The health and safety of those maintaining or using these structures should always be kept in mind.

Preventing long-term negative impacts on the waterfront wallThis section elaborates on four aspects of operating a waterfront wall for the long-term:

1 Maintaining the entire structure as designed.

2 Effectively managing encroachments.

3 Understanding the impacts of channels, foreshore and near-shore morphology on the wall (such as activities in the river, in the canal, near to shore, or on the beach).

4 Understanding the impacts of climate change.

Maintenance standards guidanceThe EA has produced a guide (Brommer et al, 2012) on maintenance standards for sustainable asset management for flood and coastal risk management assets. This features guidance for brick walls, concrete walls and sheet piles.

When considering ecological enhancement of an old waterfront wall a useful reference is by Naylor et al (2011)

The EA and NRW use a risk-based approach to determine the frequency of flood defence asset inspections (including waterfront walls) and the minimum condition grade that a defence structure should be maintained to. When determining the standard, the EA balance the risk associated with a failure on that asset against the cost of maintaining the asset to a certain condition grade. When examining the risk, the consequences of a failure are

considered, with factors including the height of the defence, type of land being protected (eg urban, agricultural, rural), the value of the property behind the defence, and the type and frequency of loading (eg by infrequent hurricanes, occasional coastal storms, regular tidal fluxes, riverine high water events). This approach has helped to reduce costs and to focus on funding areas where the consequences of structural failure are the greatest.

Box 5 .3 Implementing a risk-based approach to asset inspection in England and Wales

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Maintaining the entire wall structure as designedIf available, as-built drawings help owners understand what needs to be maintained by showing the form of construction of the entire waterfront wall in plans and cross-sections and whether the structure currently matches with the original design. When construction records or as-built drawings are not available, an experienced engineer may be able to help the owner identify and define the plans and cross-sections of an existing structure.

Effectively managing encroachmentsAn important aspect for many owners is the control over any construction or installation of third party objects on, over, under, through or close to the structure (known as encroachments) that may have an influence of the performance of the wall. However in some redevelopment cases it may provide an opportunity for refurbishment or strengthening of the structure that may not otherwise have arisen.

Understanding the impacts of channels, foreshore and near-shore morphology on the wallMaintaining the entire structure and managing encroachments are important to a long-term operation plan, but owners should also understand the effect that changes in the channels, foreshore topography and near-shore bathymetry can have on their structures. For example, blockages in a river, such as fallen trees or debris, can increase water levels and the risk of overtopping, and changes in sediment transport regimes or dredging practices can increase local scour at the toe of waterfront walls and increase the likelihood of destabilising the structure.

Changes in channels may affect each waterfront wall differently depending on its design (materials, revetments, etc) and conditions, such as the width and depth of the channel, the proximity of the wall to the bank, and whether the waterside toe is supplemented with armour or not. For these reasons, it is difficult to offer specific guidance for any one situation without first evaluating all of the contributing factors. A good approach for the owner is to recognise when there may be a threat to the design or functionality of the structure and correct each threat on a case-by-case basis. O&M staff may need the help of an experienced engineer to make the necessary repairs, especially when the problem or its repair may have environmental implications.

Understanding the impacts of climate changeClimate change in the form of increased frequency of stormy weather, sea level rise and rainfall may affect each waterfront wall differently. In coastal and estuarine environments increase in storminess and sea level rise will not only increase the risk of overtopping of the structure, but it will also potentially lead to increased erosion of the toe due to potentially larger wave energy at the front face. A rise in rainfall will potentially affect all waterfront walls as drainage within the ground behind may struggle to deal with it. This may lead to increases in pore water pressure and subsequent waterfront wall failure because of the additional pressures. However, it is difficult to offer specific guidance, so an owner needs to understand this threat and deal with each individually. O&M staff may need to take guidance from a professional engineer. Natural England (2015) has produced a climate change manual to assist managers and advisors to make informed decisions about adaption. This brings together recent science, experience and case studies and identifies a range of available tools and resources that can support practical adaption.

Managing and organising data produced and used during O&MManaging data and keeping organised records are vital to an effective O&M function. Time series data should be gathered where possible to support the objectives of asset management. Data and records related to the wall and its environment should be gathered and logged by date so that rates of deterioration or other changes can be assessed. The asset manager is typically responsible for assembling maintenance records on the wall and its components. Chapter 6 provides more information on how to manage and access data.

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5.2.7 Further informationThere are many topics discussed briefly in this chapter that are dealt with more comprehensively elsewhere in this manual. Table 5.1 shows where to find additional information about these topics.

Table 5.1 Further information on topics related to this chapter

Topic Why it may be important to an operator or maintainer Further information

Typology/parts of the waterfront wall and related structures

Understanding form, function and materials used in waterfront wall structures may help owners be aware of their waterfront wall design and of the related structures that may affect the performance of the wall

Chapter 3

Failure mechanisms

An asset owner should be committed to ensuring that the waterfront wall they are responsible for does not fail. Understanding the ways in which waterfront walls do fail, in addition to the deterioration mechanisms (see Chapter 3) may be helpfulAs part of the O&M decommissioning of the structure may be seen as a positive way forward as long as there are no legal issues that require the structure to be maintained

Sections 3.9, 4.3

Visual inspectionsAn owner should use the latest visual inspection report to understand the condition of the structure and its components to determine what maintenance activities are needed to meet the specifications in the O&M manual

Section 4.5

Monitoring Monitoring helps owners to spot changes in the structure, particularly any movement and developing issues Section 4.6

Maintenance, repair and rehabilitation Owners should know their limits and recognise when an engineer is needed Chapter 8

Design deficienciesIf the owner has identified design deficiencies then an experienced engineer may be required to resolve the issue. If a condition assessment is needed, Section 4 .3 provides information on how to perform the assessment

Section 4.3

5.3 OPERATIONSThis section discusses the operation of old waterfront walls and those auxiliary structures that may directly affect them, such as gates and closure structures.

The purpose of waterfront wall O&M is to ensure that the structure performs its role safely and according to its design. Waterfront wall systems are used to fulfil various critical roles, including the need to:

ªª channel or retain water and maintain navigation channels

ªª reduce the risk of water inundating a defended area

ªª prevent erosion of the coastline

ªª provide safe haven in estuaries or at the coastline for vessels against dangerous sea conditions

ªª provide secure mooring and/or berthing for vessels

ªª provide secure ground for loading and unloading vessels

ªª provide support to bridge piers and abutments

ªª to support the seafront, eg the promenade

ªª to act as a retaining wall providing useful land to carry transport infrastructure, eg a highway, railway, car park.

Operable features of waterfront walls (eg gates, pipes, flaps, valves) may be part of the original design, or they may have been added either to adapt the wall to new infrastructure (eg riverside development, change of ship or berth operations) or to deal with changes to landside drainage.

This section briefly explores some common operational activities and how and why they are performed.

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Reducing the risk of inundationWhere old waterfront walls serve to reduce the risk of flooding from rivers or the sea several operational activities may be needed to help prevent inundation. Note that in England, the EA are the land drainage agency responsible for flooding issues. If the wall is a designated flood defence, then the EA will decide what to do with regard to operating the defences, not a private owner. Such activities may include:

ªª closing/opening flood gates, stop logs or other closure structures

ªª closing/opening gates and valves in culverts and pipes to prevent back flooding

ªª closing/opening outfalls from interior drainage pumping stations, gravity drainage and wastewater treatment plants

ªª clearing of culverts and outfalls to allow free water passage

ªª erecting/removing demountable flood barriers (eg on top of existing riverside retaining walls).

Operatingtoremovewaterfromafloodedareaortoallowforlandside drainageIf groundwater levels are high on the landside of the wall, several operational activities may help to remove/drain the water such as:

ªª unblocking interior drainage pipes

ªª interior drainage gate control

ªª drainage pumps

ªª outlet gate control.

Operating to keep the wall standingA waterfront wall may be subject to either permanently or periodically increased loading conditions. If so, then there may be some operational activities that could help improve structure resilience and keep the wall from failing due to seepage, instability, uncontrolled overtopping or other issues. Examples include installation or improvement of:

ªª scour protection (eg provision of armourstone) at the toe or exposed waterside of the wall, or on the landside (eg protection from overtopping scour)

ªª seepage/pressure relief holes and toe drains to reduce draw-down issues caused by retained pore water pressures

ªª back-face/landside drainage.

These activities all illustrate things that could be done, address changing requirements, and encourage owners to brainstorm additional options if these are not appropriate to their situation.

Section 8.2 of this guide further discusses changes to loads and defining new standards of service requirements.

5.4 MAINTENANCE ISSUES

5.4.1 Responsibility for maintenanceAs discussed in Section 2.5, there are a number of legal responsibilities and other reasons for maintaining a structure and very few for not maintaining it at all. The reasons for not maintaining it might simply be that a wall may become superf luous in the near future, or because the cost of maintenance outweighs the benefits. There may be other reasons for not maintaining the structure, in particular the SMP or RBMP may stipulate that the wall is not repaired, allowing a river to revert to a more natural state under the provisions of the WFD.

Changes to loading conditionsA proposed permanent change to loading conditions (eg a new landside development) should always be referred to an experienced professional engineer for further consideration of these issues and options for remedial works.

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The reasons for maintaining a structure may be broken down into four main categories.

1 Legal: when the owner/authority has a statutory obligation to preserve, maintain or repair the structure for reasons of aesthetics, function, safety etc.

2 Economic: when it is in the owner/authority’s best interests to maintain the structure to ensure that it functions efficiently.

3 Amenity/heritage: when it is in the best interests of the owner/authority to maintain the structure for amenity and/or heritage purposes.

4 Environmental: the moral obligation of all owners/authorities, and the engineers working for them, to attempt wherever possible to enhance the environmental quality of their structures. In addition the owner/manager must take into account the WFD as this is the most significant piece of environmental legislation and the wall owner must abide by the RBMP.

The importance of maintenance to performanceMaintenance is critical to ensure the long-term performance of a structure. It is also apparent that regular maintenance of a wall to keep up its appearance can prolong its service life and postpone the need for major rehabilitation. But even a perfectly operated and maintained waterfront wall may not provide the intended level of service if there are basic flaws in its design or construction or if the desired Standard of Service (SoS) has increased since the wall was designed. These flaws are frequently the cause of failures. Common design deficiencies include:

ªª inadequate crest heights

ªª discontinuities such as changes in cross-section or alignment

ªª the local application of high loads, eg moorings or guides for pontoons

ªª uncontrolled under or through seepage

ªª unprotected erodible surfaces

ªª unstable or subsiding foundations

ªª poor construction practices

ªª inadequate drainage

ªª inadequate mass or retention.

Though these deficiencies may not be remedied through routine maintenance of the wall, O&M programmes may be reformulated to detect such flaws before failure occurs. By training field staff to routinely inspect their walls for undermining, settlement, drainage problems or evidence of instability and distress, adverse findings may be reported in a timely manner to professional engineers for their assessment and input on recommended repairs and remedial works. Recommendations for inspections are given in Chapter 6.

It is important to adopt a proactive approach to the program of identification and repair given the need for an efficient and effective use of limited repair budgets. Deterioration needs to be monitored closely and addressed in a timely and efficient way. If the owner waits too long and too much deterioration has occurred, it may be challenging to get the necessary equipment into the area to do the repair. But it is also important to be economically efficient about repairs. The money spent on repairs that are made too soon may be looked upon as money that could have been better spent elsewhere.

The consequences of postponing maintenanceA crucial factor in determining appropriate cycles of service, and for justifying the application of maintenance or rehabilitation, is to assess the consequences of lack of maintenance. In some cases the effect will be deterioration in the standard of service provided, reduction in safety standards and, finally, the collapse of the structure. In others there will be no appreciable change in the level of service prior to sudden failure. If this is the case, then the owner may ignore maintenance until it is too late.

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Mullion Harbour is located on the Lizard Peninsula in Cornwall. It was constructed in the 1890s to serve the local Cornish pilchard fishing fleet and since 1945 has been owned by the National Trust. The harbour comprises two stone block breakwaters (the western breakwater and the southern breakwater) and a quay (the northern quay), all of which are now over 100 years old.

The breakwaters have suffered repeated damage from storms ever since their construction and repairs to address these damages have cost the National Trust some £1m. The harbour structures will continue to deteriorate as they age. In addition, sea level has risen since the structures were first built and the projected sea level rise over the next century due to climate change will result in larger waves attacking the structures more frequently.

In 2006, the National Trust published a study (National Trust, 2006) to investigate management strategies for the harbour for the next 100 years. At the same time, a stakeholder group including representatives from the local community, government agencies, local councils and other Cornwall harbours, was established to liaise with the study team. The study has enabled the National Trust to select an appropriate strategy for the future management of Mullion Harbour.

Three fundamental approaches to managing Mullion Harbour over the next century were identified:

1 Undertake major works to protect the existing harbour structures (embellishment).

2 Continue with maintenance and repair until failure.3 Do nothing and allow the existing harbour structures

to be lost (retreat).

The study identified that the ‘maintain and repair until failure’ option was the preferred management strategy for Mullion Harbour. The study recommendations were endorsed by the stakeholder group, which made a significant contribution to this project and its findings, as well as the Mullion Harbour Association, Mullion Parish Council and the National Trust’s projects and acquisitions committee.

For the preferred option, initial repairs will be undertaken comprising concrete repairs and bagwork to the western breakwater and pressure pointing, repointing and grouting on most of the harbour structures (including the corner between the western breakwater and northern quay). A regime of regular maintenance and repair will then be followed (see Tables 5 .2 and 5 .3).

Table 5.2 Programme of maintenance

Programme Maintenance

Annually ªª repointing to the walls, copings, setts and slipway.

5 yearly

ªª local areas of pressure pointing to wallsªª bagwork to seaward face of western

breakwaterªª concrete toe repair to end of western

breakwaterªª handrail, ladder and fender

maintenance/repair.

10 yearly

ªª bagwork to seaward face of southern breakwater

ªª localised grouting, based on observations

ªª local areas of copings, setts and slipway re-laid.

25 yearly ªª widespread grouting.

Table 5.3 Programme of repairs

Programme Repairs

Within 10 years

ªª rebuild 30 m of parapet (the remaining length not done in 1998)

ªª refurbish lamp house.

Within 50 years

ªª re-pile toe at end of western breakwaterªª rebuild western breakwater stepsªª replace southern breakwater tiesªª replace concrete access bridges to

southern breakwater.

Within 100 years ªª replace some western breakwater ties.

The study highlighted many actions and approaches that resulted in a very successful conclusion. In addition Mullion Harbour provides a structured example of how the National Trust is engaging with the complex issues of coastal change and developing adaptive long-term strategies. Particular issues leading to this success included:

ªª A steering group was set up at the start, which encompassed a broad membership of over 30 key stakeholders.

ªª Four steering group meetings were held over 18 months, each having high attendance.

ªª Leadership of stakeholder meetings by external consultants helped maintain a positive atmosphere. All contributions were valued, and the chairmanship was felt to be independent and impartial.

Figure 5.4 Cross-section of the western breakwater

Figure 5.5 Plan of harbour showing extent if required repairs

Case study 5 .1 Maintenance and repair of Mullion Harbour, Cornwall (courtesy Environment Agency)

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ªª Open days were held for broader communication with the local community.

ªª Consultants attended open days and were able to address ‘expert’ level technical questions that local National Trust staff would have otherwise had to follow up.

ªª Weight of evidence helped to convince local ‘experts’ and provided a reasoned response to objections.

ªª A webpage was created on the National Trust website to communicate project progress. This allowed immediate and open access to information. This ‘open’ approach was positively received.

ªª The high profile of climate change reporting in the national media reinforced the importance of the project, supporting the process to find an agreed long-term strategy for Mullion Harbour.

ªª The study was able to draw on the historical data about the harbour. This evidence added to the independent consultants report and helped to inform decision making.

ªª An ability to show the advantages of being ‘wise before the event’ helped to persuade others.

ªª The use of photomontage gave an immediate and accessible visual simulation of the proposed options.

Case study 5 .1 Maintenance and repair of Mullion Harbour, Cornwall (courtesy Environment Agency) (contd)

The consequences of postponing maintenance should be carefully weighed when faced with the decision to do repairs right away or defer them because of costs, environmental regulations, permitting issues or other concerns. Delaying repairs or not doing them may heighten the risk to commercial activities in a port or risk to inhabitants and property or infrastructure in a protected area until the repair is made. The owner will have to determine whether postponing repairs will:

1 Cause the wall or its associated facilities to deteriorate further and result in increased repair costs in the future.

2 Cause the wall’s integrity to be threatened, eventually resulting in substantial and costly design and repair work to restore it to its originally intended level of service.

When a problem is so severe or complex that a civil engineer is required, it is recommended that a condition assessment be performed first. The condition assessment can help to ensure that all issues associated with the problem are known so that a good, workable solution can be designed. Section 4.3 provides guidance on possible ways to assess the wall to determine what action is needed. A civil engineer, who is experienced in designing retaining walls, and has the guidance presented here, should be able to establish the budget cost of a replacement waterfront wall and can then seek a contractor who will design and construct the replacement.

5.4.2 Deterioration and failure mechanismsTable 5.4 elaborates on the relationship between deterioration processes and failure mechanisms. Many of the deterioration processes could cause most of the failure mechanisms. For clarity, only the primary failure mechanism associated with each deterioration process is represented.

Critical point of disrepairOne of the most important factors in evaluating a wall’s performance and establishing a maintenance programme is determining the ‘critical point of disrepair’. This is the point at which the onset of progressive failure occurs. If the wall is repaired before this point is reached, the life of the structure may be extended indefinitely. If repairs are not carried out, major loss of use and reconstruction will be inevitable if the structure is to be returned to its functional level. The ‘critical point of disrepair’ is dependent on the wall type, its environment and its function (see Section 4 .5 .4).

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Table 5.4 Primary failure modes that may result from deterioration processes

Primary failure modes

Foundation failure Dee

p sl

ip/r

otat

ion

Ove

rtur

ning

Burs

ting

Slid

ing

Furt

her e

xpla

natio

n

Det

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ratio

n pr

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s

EncroachmentsSection 5 .4 .3

x x x x x

Adjacent work carried out near an existing wall may have a detrimental effect on the stability and/or can lead to serious settlement of the land behind and reduced longevity of the wall.

Settlement/subsidenceSection 5 .4 .4

x x x

Undermining and overloading can cause settlement/subsidence of a wall. This may reduce the crest height (increasing the risk of overtopping) and can lead to wall instability and/or rotation.

Seepage (through seepage and under-seepage)Section 5 .4 .5

x x x x x

Water passage through the structure can cause seepage that can move fine materials through or under the wall. Washout of soil particles from behind or under the wall can cause instability and/or rotation by removing passive pressure.

Instability due to undermining/scourSection 5 .4 .6

x x x x

Wave scour, current scour and burrowing animals can undermine wall foundations causing instability (wedge failures) and/or rotation by removing passive pressure. Currents and waves can also erode wall materials. Instability can also be manmade, ie dredging or lowering of the bed close to the wall, which results in stability and/or rotational failures. The movement of boats can also cause suction effects leading to scour and erosion of wall joints etc.

Instability due to tie rod failureSection 5 .4 .6

x x

Tie rods can fail because of corrosion. They may be damaged by traffic loading, accidentally or intentionally cut. Excavation in front of the wall can exceed tie rod capacity due to the resultant increased lateral pressure on the walls caused by surcharge in the backfill.

Cracking/block movementSection 5 .4 .7

x xTension cracks and/or block movement in a wall indicate that the wall is unstable. If left unaddressed further movement may cause the whole wall to become unstable.

Erosion/decay of mortar x x

Mortar can deteriorate due to freeze-thaw effects, wave erosion, vessel wash erosion, acid attack (atmosphere and water), seepage water erosion, propeller/bow thruster scour, vegetation root growth. Loss of mortar reduces integral strength and stability between blocks/bricks.

Deterioration of metal clamps, brackets, steel inserts

x xMetallic inserts used to strengthen or repair blockwork walls may deteriorate over time due to rusting and/or ALWC leading to loss of integrity.

Burrowing animals and biological attackSection 5 .4 .8

x x x x

Burrowing animals can undermine wall integrity by eroding the internal structure resulting in changes inflow paths and water pressures behind the front face of the wall.

Decay of timber piles x x xTimber piles can rot due to exposure to the atmosphere and changes in water level. Loss of strength in the foundation or at the wall toe can result in failure.

VegetationSection 5 .4 .9

xVegetation growth can cause damage to blockwork by root penetration breaking down the joints and leading to block failures.

Culverts and discharge pipe systemsSection 5 .4 .10

x x x Lack of maintenance of culverts and discharge pipes may lead to internal and external erosion and wall instability.

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5.4.3 EncroachmentsAn encroachment is any structure that was not considered part of a waterfront wall’s original design that when placed on, over, under, through or near the wall, may have a negative effect on its structural integrity, its ability to perform as desired, or on its access. This includes structures subsequently built directly on or beside the wall on both the land and waterside and any structures that may increase the hydraulic loads on the wall. Examples of encroachments include utility lines, pipes, canal/dock/harbour/port buildings or machinery (eg cranes, winches), jetties, stairs, residential housing, commercial premises, swimming pools, power poles, roads, irrigation or drainage ditches, bridges and railways. Encroachments also include activities performed on or near a wall that are not related to its design function, such as farming and excavations.

Why encroachments occur on and around waterfront wallsWaterfront walls are primarily built to facilitate some other kind of activity or development. Invariably, as these needs change, then so do the requirements placed upon the structure. The older the structure – the more likely situations around it have changed. Competing objectives may also arise. These may include:

ªª meeting the special needs of transportation – a new road link alongside or across a river or harbour may be needed where walls are present (eg requiring a new bridge or railway or upgrading an existing wall)

ªª improving amenity value beside waterways and the sea – creating new paths and promenades

ªª regeneration and new commercial or housing developments

ªª changing port/harbour/dock operations or activities (eg change from commercial to recreational use)

ªª changes in channel dredging practices.

If new or existing encroachments are going to be allowed on a wall, however, then those encroachments should be prevented from threatening the integrity of the wall, inhibiting access, or interfering with regular maintenance and inspection.

Why encroachments need to be controlledControl of potential external sources of encroachments is problematic. In the first instance, careful study of planning applications, which may affect the structure, is important and objections are raised if issues are identified. In some cases it will be necessary to obtain professional advice from engineers and/or lawyers to lodge objections at planning and construction phases.

Table 5.5 provides examples of some of the adverse effects encroachments may have on waterfront walls.

Table 5.5 Adverse effects of encroachments

Type of encroachment Possible adverse effects on waterfront wall

Uncontrolled excavation of soil at toe or foundation

Removal of bearing capacity that may lead to structure instability. Removal or degradation of foundation material can result in collapse of the wall.

New development including buildings and other infrastructure such as roads, railways, bridges etc

Direct effects

ªª new foundations might affect the loading on the wallªª the backfill might be removed to allow a basement to be constructedªª drainage paths and services might be interruptedªª active timber and iron ties might be severed.

Indirect effects

ªª the increased exposure of a wall and its site to currents, in cases where the flow of a river has been modified by new structures

ªª the increased loads and vibration due to increased road traffic levels caused by a new development close to the wall

ªª the alteration of beach levels in front of a wall due to the construction of nearby harbour or sea defence works.

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Type of encroachment Possible adverse effects on waterfront wall

Crest raising for flood defence

Wall raising without raising the level of retained material behind the structure may increase loads due to:ªª the additional water pressure because of higher water levels in front of the wallªª dynamic and impact loading from the water and debris in the water flowªª potential overtopping with associated back pressures on the top part of the wall

and surcharge on the ground behind the wall.

Redevelopment, trenching for sewer and drainage systems behind the wall

Removal of anchors and/or disturbance or severance of wall ties can increases structure instability

Storage of dense bulk materials, installation and operation of heavy equipment for cargo handling

Reduction in FoS against overturning or sliding due to increases in:ªª horizontal force against the back of the wallªª disturbing moment.

5.4.4 Settlement and subsidenceSettlement and subsidence both result in a lowering of the original ground elevation. Settlement occurs from movement of the ground due to some type of external loading, or because of an external action such as mineral mining or water extraction, while subsidence occurs from movement of the ground due to loss of support in the foundation from consolidation of the earth. Consolidation is any process that involves decrease in water content of a saturated soil without replacement of water by air.

Why settlement and subsidence are a concernBoth settlement and subsidence reduce the structure height. This is particularly important with respect to waterfront walls and flood defences as it reduces the design flood mitigation level, but in a port environment it may lead to issues for loading/unloading facilities adjacent to the wall. Also, localised and general movement may reduce the crest elevation, and in the case of seawalls there may be serious consequences such as extreme surge water levels. Localised differential settlements may be easy to identify visually, but gradual reductions in the wall height that occur over long reaches may not be detectable without a survey. In some cases, settlement may induce cracking or tilting, and if left untreated, could result in crack propagation or overturning and ultimately in a collapse. If settlement leads to a sinkhole close to the wall, it can lead to a loss of strength in the wall and a hazard to people.

Figure 5.6The results of backfill washout due to a combination of beach lowering beneath the seawall toe, overtopping of the crest and the structure drainage characteristics (courtesy Aberdeenshire Council and Arun District Council)

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Causes and preventive measuresThe causes of settlement may be related to seepage, soft ground, encroachments, or design. Mining operations beneath the wall could also cause subsidence. Earthquakes, which are rare in the UK but quite common in some areas of the world, can result in both settlement and subsidence of old waterfront walls. Not only do earthquake forces impose additional loads on the structure, but there is often the risk that retained material, or other soil in the vicinity, may suffer from liquefaction due to the vibration of the ground. In such circumstances large ground movements can occur that impose severe loads or even change the position of the whole structure. Table 5.6 suggests some measures in cases where it may be possible to mitigate or prevent settlement or subsidence.

Table 5.6 How to prevent common causes of settlement and subsidence

Observations Preventive measures

Maintenance related

Washout of fine material under or through the wall due to seepage can cause settlement of the backfill (this has been observed particularly at seawalls where the foreshore has been lowered below the toe of the wall).

Monitor the wall and any seepage control features. Ensure maintenance grouting does not interfere with drainage/seepage system (eg use permeable grouting). Seal around pipes to prevent piping of backfill or hearting fines from behind or inside the wall. Keep seepage holes and drains clear of debris.

Encroachment related

Improper compaction of material around culverts, pipes, or other structural features added after wall construction.

When installing pipes through the wall, after remedial work, or when doing any work in the vicinity of the wall that involves excavating and backfilling, use:ªª good design detailingªª proper compaction/sealing around encroachmentªª good quality control and quality assurance.

Leaking or collapsed pipes behind or inside the wall.Periodically inspect pipes that pass over, under or through the wall to identify and address early signs of deterioration or leakage. Monitor seepage and soil migrating from the wall.

Design related

Settlement of compressible foundation soils in small, concentrated areas (possible causes include animal burrowing or drying out of the foundation soils). Changes in moisture content of clay in wall foundations can cause movement and cracking of a wall.Silts and fine sands with a relatively low permeability can be effectively weakened by groundwater movement and changes in pore water pressure. High upward flows of water through sand can cause ‘piping’ so that the bearing capacity is reduced. Silts can suffer from frost heave where the water level is just below the silt.Rock under a wall may weather and soften, particularly if it is exposed to water, alternate wetting and drying, or freeze-thaw cycles when wet. The softening could lead to a reduction of bearing capacity under the toe of the wall.

Monitor the wall for settlement below the design height.If possible, remove the area of compressible material and replace/underpin with suitable material.

For detailed information on the maintenance of mass concrete walls see Dupray et al (2010) and Figure 5.8.

5.4.5 Seepage/drainageDifferential water levels between the face of the wall and backfill can not only cause excessive loading on the back of the wall, but can result in flow of water through a wall, commonly known as seepage. This can wash out mortar in joints, and also result in the loss of backfill and hearting. This seepage can lead to significant degradation of structures over time and loss of backfill will cause cavities to be formed behind the wall, which can result in subsidence of the ground behind the wall.

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When seepage/drainage is a concernChanges in the water levels both behind and in front of a wall can have a considerable effect on its behaviour. Some walls depend on drainage systems behind and through them to limit the maximum difference in level between the water at the back and at the front. If the drainage system is blocked, a large hydrostatic load will be applied to the back of the wall. If the wall has not been designed to accommodate a hydrostatic head difference, sudden changes (such as rapid draw-down) may induce immediate failure.

Waves may overtop a coastal wall and penetrate the surface of the backfill, causing the backfill to be washed out. Sometimes the front face of the wall is then pushed forward by the water pressure acting on the back of the wall. A similar situation can arise in the types of breakwater where a front masonry wall is backed by permeable rubble.

Causes of seepage/drainage issuesªª Uncontrolled/improper grouting can block wall drainage systems.

ªª A sudden draw-down of water level in front of the wall may be necessary for urgent maintenance or it may happen by accident (eg a breach in a canal).

ªª The water level behind a wall may be accidentally increased by draining buildings or paved areas to new soakaways behind the wall.

ªª The conversion of an impounded dock to a tidal basin will have the same effect as a sudden draw-down.

ªª Many impounded docks and canals have been built with puddle clay lining immediately behind the back face of the dock wall. This makes them particularly susceptible to failure when the water level is drawn down.

ªª Walls of canals and impounded docks are vulnerable where they rely on only one or two sets of lock gates to maintain the level of water.

ªª Walls founded on clay are particularly at risk due to the slow rate at which water levels equalise on each side of the wall, and the slow dissipation of excess pore water pressure under the wall, which reduces its effective weight and stability.

ªª Surface water drains, buried foul sewers or water supply pipes can be fractured or broken and leak behind the wall, which raises the water level and the load on the wall. This can also lead to loss of fines in the surrounding ground causing a progressive void that may only be discovered when there is subsidence over a large area.

ªª Contractors’ operations, such as the discharge of construction pumps or the construction of slurry walls, may raise the water level behind a wall.

ªª The groundwater behind a wall can be affected by the installation of a barrier to the flow of water or the piercing of an existing barrier.

ªª If a breakwater is overtopped, and if the rubble backing does not have a durable impermeable surface, the masonry wall can be subjected to high water pressure, leading to eventual deterioration of the wall.

Preventing seepage/drainage related damageIs it important to immediately identify and report any seepage/drainage problems (especially if movement of soil particles is observed) so that the issue can be investigated further and a decision made as to whether further action is needed. Such conditions may progressively worsen over time due to repeated loading conditions (eg tidal cycles), so diligence in observing, documenting and reporting any seepage/drainage condition is important.

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Table 5.7 How to prevent common causes of issues related to seepage/drainage

Observations Preventive measures

Maintenance related

Maintenance of the wall’s seepage/drainage system

Monitor the wall and any seepage control features. Ensure maintenance grouting does not interfere with drainage/seepage system (eg use permeable grouting). Seal around pipes to prevent piping of backfill or hearting fines from behind or inside the wall. Keep seepage holes and drains clear of debris.

Wash out of fine material under or through the wall

Maintain ground levels in front of the wall well above the level of the toe (see Bradbury et al, 2012).Maintain existing impermeable surfaces at the back of the wall and remove any impounded water from the area as soon as possible.Repair separated joints, replace missing blocks, fill cracks that may create a pathway for washout of hearting or backfill materials.Ensure surface water drains, foul sewers or water supply pipes are maintained in good order, free of blockage, and that leaks are quickly repaired.

Encroachment related

Landside development

Consult with planning authority or building control to obtain details of any proposals and/or plans for development in the vicinity of the wall, which could have an impact on the drainage/seepage characteristics of the wall.If there are any proposals and/or new developments consider contacting the utilities companies to make sure there are no plans for any new or revised utility routes close to the wall that may also affect the drainage/seepage characteristics of the wall.

Design related

Draw-down operationsConsult with an experienced engineer or designer before intentionally drawing down water in front of an old waterfront wall.Consider rapid draw-down effects in emergency planning.

5.4.6 InstabilityA waterfront wall is considered unstable when the structure’s ability to react to a disturbing force by maintaining or re-establishing its position has been compromised.

When instability is a concernWall stability is fundamental to the performance of a wall so any instability of the structure is likely to be of concern and should be investigated as soon as it is suspected or has been detected.

Causes of wall instability include:

ªª excavation or excessive scour below the level of the toe

ªª deep slip/foundation shear failure

ªª excessive loading and impacts

ªª decay of timber

ªª detachment, failure or removal of counterforts, ground anchors or ties

ªª settlement and subsidence

ªª excess pore water pressure in foundation

ªª increase in lateral pressures in clayey and silty backfill material behind wall face that can exhibit thixotropic behaviours

ªª backfill washout

ªª rapid draw-down of water level.

Figure 5.7 A seawall in the process of overturning (courtesy Black & Veatch)

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Table 5.8 Causes of instability in old waterfront walls

Cause Explanation

Excavation or excessive scour below the level of the toe*

In rivers and flood channels, canals and locks it is often necessary to deepen a waterway to increase the flow capacity to alleviate flooding in other areas or to maintain navigation. When this is carried out there is a danger of removing material from in front of the toe of old walls, lock gates, piers and abutments of bridges, leading to instability, undermining or outflanking of the structures.Excavation below the level of the toe reduces the bearing capacity under the toe as well as the resistance to sliding and overturning. Often in old masonry wall structures this leads to large wedge failures (see Case study 8 .1) The natural scour of foreshore material and beach lowering in front of the toe of a seawall can lead to both instability of a wall and eventual collapse. Many coast protection walls have anti-scour toe protection of concrete apron slabs, sheet pile cut-offs or rock revetment to control erosion.

Deep slip/foundation shear failure

Shear failure of the earth mass on which a wall is built can result in a ‘deep slip’ and subsequent instability of the wall. Circumstances where waterfront walls are particularly at risk from instability caused by a deep slip include where:ªª the wall is founded on clay or on a soil overlying clay or other weak strataªª the soil behind the wall slopes up from it, as occurs with some coast protection wallsªª where the ground in front of the toe of the wall slopes downwardsªª high pore water pressures can exist below the wall.

Excessive loading and impacts

Horizontal or vertical loads in excess of those originally designed for. Overloading of walls as a cause of problems is believed to be under-reported, particularly where a wall has moved and later stabilised. Examples of excessive loading include:ªª the stacking of dense bulk materials, containers or other heavy cargo on the apron too

close to the coping of quay wallsªª the use of heavy mobile cranes and other cargo handling equipment, particularly large

forklift trucksªª the loading and vibration from modern traffic on top of and behind retaining walls and

bridge abutmentsªª the application of high bollard pulls to quay walls by ships or by bucket and cutter suction

dredgers. Low walls and points that do not have the means to distribute bollard pulls, such as unrestrained ends of walls, are particularly vulnerable.

Wall raising without raising the level of retained material behind the structure may also increase loads due to:ªª the additional water pressure because of higher water levels in front of the wallªª dynamic and impact loading from the water and debris in this flowªª potential overtopping with associated back pressures on the top part of the wall and

surcharge on the ground behind the wall.Internal deterioration behind the front face may lead to overloading, which can cause bulging and collapse of wall.

Decay of timber

Timber used as bearing piles, sheets piles, or foundation grillages, even if it is always submerged, often suffers from abrasion, although some soft woods are prone to marine borer. Local settlement is experienced where block masonry walls constructed in the late 1700s and early 1800s are founded on timber grillages. Where it can dry out, timber may well decay and this can be the cause of unexplained settlements and cracking, particularly where it is not known that timber forms part of the foundation.Timber inserts in the structure of the wall may also decay if exposed. Timber rubbing strips were often used to give some protection to the face of quay walls and invariably are either broken away by ships or eventually rot, exposing the quay wall to direct damage from vessels.

Detachment, failure or removal of counterforts, ground anchors or ties

Removal of horizontal restraints (counterforts, tie rods etc) as a result of encroachments (eg excavation for installation of pipelines or services behind walls) or structural modifications may lead to reduced FoS against sliding and overturning and consequent failure.

Settlement and subsidence See Section 5 .4 .4

Excess pore water pressure in foundation See Section 5 .4 .5

Backfill washout See Section 5 .4 .5

Rapid draw-down See Section 5 .4 .5

For the management of the toe scour of coastal waterfront walls see Bradbury et al (2012).

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Preventing instability issuesExcept in the case of an instantaneous collapse without warning, preventing instability relies on early detection and can be addressed by:

1 Inspecting the structure regularly in accordance with good visual inspection practices (see Chapter 4).

2 Repairing areas promptly when instability issues are found.

3 Identifying historic stability problems, identifying their causes, and preparing a mitigation plan with engineering support.

5.4.7 Cracking and block movementCracking and/or block movement in a waterfront wall may or may not be a concern to the owner. However, it can be a symptom of many issues and should be carefully monitored and investigated (discussed as follows). Crack widths can by cyclical due to thermal stresses, so they need to be monitored during different seasons, ie spring, summer, autumn, winter. It is also important to carry out regular inspections, to record the crack size, appearance etc by photographs and written data, and by date, so that deterioration if any can be assessed.

When cracking and block movement is a concernOnce cracking or movement of blocks has happened, progressive failure may occur such as loss of filling behind the wall, loss of hearting within a breakwater, and break-up of the wall as it becomes increasingly vulnerable to current or wave attack. Cracks and gaps in waterfront structures also provide opportunities for invasive woody vegetation to establish on the structure (Figure 5.8). Subsequent root growth and penetration can cause further damage and facilitate water infiltration.

Figure 5.8 Minor cracking in a masonry wall (a) and major movement in a brick waterfront wall (b)

However, the cracking of walls is not necessarily a cause for concern. Many cracks are formed at an early stage in the life of the structure and, having provided a necessary method of stress relief, do not lead to accelerated deterioration. It is common to find this type of crack in walls adjacent to places where local restraint is provided, such as at the corners of a dock wall.

A few walls were constructed as wedged drystone walls. The wedges were driven into the joints to fix each individual stone into the body of the wall. Waves may loosen and remove the wedges so that stones are no longer fixed and can fall out. Progressive deterioration of the wall then follows.

(a) (b)

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Causes of cracks and/or block movementCracking and/or block movement of concrete, stone masonry and brickwork walls is a symptom of other issues such as:

ªª overstressing of the soil under the foundation

ªª differential settlement/movement

ªª partial failure by overturning or sliding

ªª scour of the toe

ªª mining subsidence

ªª thermal restraint

ªª vessel impact damage

ªª settlement due to decay of timber foundations

ªª shrinkage

ªª breakdown of the bonds of surface renders and facings

ªª loss of structural integrity of internal rubble/heartening

ªª local pull-out of bollards

ªª expansion of corroded steel inserts and cramps

ªª loss/movement of wedges in drystone walls.

Preventing cracks and block movementRegular inspection of the wall is an important step toward catching cracks in their earliest stages. If it is unclear whether the cracks are old and still active then glass plates glued to the wall or proprietary tell-tales can be used to determine if the crack is still moving. Table 5.9 lists several crack-related issues that may arise during inspections and suggests some management measures for them.

Table 5.9 Crack-related issues and management measures

Observation Preventive measure

Maintenance-related

Cracks that continue to grow in length and width

Continued growth of cracks could be a sign that a wall may be under stress and that an initial mode of failure exists:ªª periodically inspect all cracks to document any increase in length or widthªª clearly mark growing cracks and evaluate on a weekly basis for an unloaded condition

and at least daily for a loaded conditionªª seek appropriate expertise to determine what actions may be necessary to stop

further degradation.

Missing blockwork or bricks

Where individual bricks, stones or blocks have decayed, or fallen out of the above water or intertidal face of a waterfront wall, the cavity can be cleaned out by chiselling and high pressure water, and a new stone or brick put back in the wall. Injection pointing may help to complete the repair as it is otherwise difficult to fill all the surrounding space with mortar.

Look for bulging that may be localised or may be large

Encroachment-related

Vegetation growth

Woody vegetation that has established in joints and gaps in the wall should not be allowed to mature. Such plants should be carefully removed because if they are not killed and allowed to wither then they will pull mortar and masonry out of the joints. Once vegetation removed any joints and gaps should be appropriately sealed and damage repaired.

Design-related

Type of wall and foundation materials

Identification of the wall and foundation material will make it easier to assess the severity of the types of cracks that are discovered.

Figure 5.9 Impact damage to a bridge abutment

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Observation Preventive measure

Missing wedges, cramps and mortar joints

Mortar joints close to the exposed face can be repaired, but wedges and cramps used to hold a wall together cannot normally be replaced when they deteriorate or break. If this is the case, then it will be necessary to hold the wall together using a different method, such as injection pointing of the outer skin and grouting of the inside. If these are not feasible, the wall has to be refaced or reconstructed. Another alternative is to tie the wall together with stainless steel rods, either drilled and grouted within the body of the wall or passing right through and anchored at both sides.

For detailed information on the maintenance of mass concrete walls see Dupray et al (2010) and Figure 5.10.

5.4.8 Burrowing animals and biological attackBurrowing animals, including mammals, amphibians, reptiles, and invertebrates, dig holes or tunnels into sediments and earth for food, habitation or temporary shelter. Burrows may vary in form from short, single tunnels to lengthy tunnel complexes interspersed with chambers. Burrow gradients may range from horizontal to vertical. Some invertebrates burrow into joint mortar and timber in walls is particularly vulnerable to various forms of biological attack (see Box 5.4).

Animals may burrow in a particular location because:

ªª food sources are available there or nearby

ªª they are occupying and extending abandoned burrows and other voids that have not been backfilled or sealed

ªª some prefer burrowing in ground with a steep gradient

ªª long-term flooding forces them onto dry ground

ªª animal control programs in the area are ineffective.

However, animals that burrow beneath and around walls may cause:

ªª undermining of the wall toe, which may lead to piping (due to shortening of seepage paths)

ªª destabilisation of bricks, masonry blocks, and revetments

ªª collapsed areas/unevenness in backfill (if not capped)

ªª direct seepage paths (through-wall burrows).

Figure 5.10 A canal lock wall in a deteriorated condition with broken bricks, missing joint mortar, and suspect former repair work (courtesy Rebecca Wallis)

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Further information on burrowing animals and their potential impacts is given in CIRIA; Ministry of Ecology; USACE (2013).

Preventing animal burrowingAn effective animal control program should include a plan to regularly remove burrowing animals from the area of influence of the structure and address any voids or damage that they have already created. When designing such programs, remember to take into account:

ªª existing or pending protective legislation

ªª existing or pending environmental legislation

ªª whether there is a way to obtain either exemptions from legislation or special licenses

ªª whether there is a statutory requirement that certain animals be controlled because they are considered pests by the government (eg the wild rabbit in England).

National, and local legislation (eg the Wildlife and Countryside Act 1981 in England), in addition to guidance offered by government or conservation agencies and NGOs, should also be consulted to ensure that the burrowing animal control program is aligned with all applicable laws. Protective legislation tends to be unique to the type of animal. Common provisions of protective legislation include prohibitions against:

ªª harming or killing the animals

ªª treating animals in cruel or inhumane ways

ªª using specific animal control methods, such as trapping or chemical agents (pesticides)

ªª disturbing shelters (tunnels, dens etc) or feeding and mating grounds

ªª interfering with general habitats, including wetlands.

If permissible, given the legislative constraints and available guidance, options for preventing animal burrowing might include:

ªª disturbance

ªª removal of conducive habitat (eg clearance of dense undergrowth)

ªª removal of food sources

ªª installation of impenetrable mesh

ªª removal of animals to an alternative site

ªª eradication.

Further information on the prevention of animal burrowing is given in CIRIA; Ministry of Ecology; USACE (2013).

Why biological attack are a concernTimbers in old waterfront walls can be particularly vulnerable to biological attack and degradation by a variety of organisms including:

ªª fungi (soft rot and wet rot)

ªª insects (may be symptomatic of fungal decay)

ªª crustacean borers, eg gribble (Limnoria spp.)

ªª molluscan borers, eg shipworm (Teredo spp.).

Box 5.4 provides further information on biological attack of timber components.

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Figure 5.11 Examples of the signs of marine biological attack (gribble) in timber

The temperature and degree of salinity, contamination or turbidity of the water in which timber structures are located can affect the durability of the structure and particularly any metal fixtures and fittings. However, this is often less significant than biological attack, which is at least partially correlated to the water conditions and may vary dramatically with time.

Biological attack in freshwaterFungal decay is the most important biological agent that may attack timber in freshwater. Such decay is most prevalent in timber with a moisture content above 20 per cent. This is likely to occur in timber near and above the water-line as well as that embedded in concrete, brick or other porous materials and poorly ventilated, horizontal surfaces. Aggressive fungal decay above the water level may occur, principally by wet rot type fungi. In addition, insects may also attack wet timber above water level, although insect attack may be symptomatic of fungal decay being present in the structure.

Note that timber which is permanently and completely immersed in freshwater will normally only suffer fungal decay of the soft-rot type. Soft rot fungi erode the outer layers of the timber components at a relatively slow rate. The outer surfaces are typically dark, soft and ‘cheesy’ in texture. The depth and rate of penetration of the fungi is largely governed by density. However, the affected timber may also be exposed to fast currents and abrasive conditions. The combined effects of the soft rot fungi and faster erosion of the decayed outer layers of timber may accelerate the deterioration of the component. Pockets of fungal decay detected below the water-line are usually attributable to decay migrating down through the timber component. This observation is also common in marine structures that have been weakened by pockets of wet rot-type decay.

To prevent biodeterioration, timbers in structural positions in which decay might be expected should be naturally durable or preservative treated – legislation permitting.

Biological attack in the marine environmentSalt water can act as a timber preservative and heavy salt deposition in wood may offer some protection against fungal decay for timber out of contact with seawater although it is important to realise that salt deposition may not be permanent. Horizontal faces of timber or joints are at risk of fungal and insect attack if the moisture content of the components rises above the decay threshold of 20 per cent for prolonged periods. Wood that is located below the high tide level may be subject to attack by marine borers, bacteria and fungi.

The principal agents causing biodeterioration of timber in the marine environment are marine borers, which can cause severe damage in relatively short periods of time. In UK and other temperate waters two types of borer are of greatest significance, the mollusc shipworm (Teredo spp.) and the crustacean gribble (Limnoria spp.). The former has commanded particular attention owing to the inherent difficulties in accurately estimating the extent of its attack.

It should be noted that the occurrence of marine borers is sporadic and the severity of attack often varies from site to site and season to season. One factor thought to be of importance is the influence of marine borer infested wrecks and other redundant timber structures as well as driftwood in and around harbours. The risks of introducing borers through wrecks and driftwood may be minimised by good harbour hygiene. This may not prove to be as important a factor where beach/flood defences are erected as driftwood may be carried away by the prevailing tides.

Crossman and Simm (2004) provides further information on the effects of biological attack on timber in the marine and freshwater environment and provides detailed guidance on monitoring, maintenance, repair of timber components.

Box 5 .4 Biological attack of timber (from Crossman and Simm, 2004)

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Mitigating against marine borer attack in timberTable 5.10 outlines the main methods of mitigating marine borer attack in timber.

Table 5.10 Overview of methods of mitigating marine borer attack in timber (after DWW, 1994)

Method Advantages Disadvantages

Preservative treatment

Applying preservatives under pressure

ªª protection against marine borersªª permeable timber species are

easy to treat.

ªª potential leaching of preservatives into environment

ªª timber has to be treated before construction.

External treatment

Applying a protective coating over the timber

ªª protection against marine borer attack.

ªª coating may be damaged (regular maintenance required)

ªª timber has to be treated before constructionªª protective coat may damage the environment.

Sealing

Wrapping the timber in an impermeable covering

ªª protection against marine borersªª kills marine borers already

present in the structureªª can be applied after construction.

ªª expensiveªª covering may be damagedªª does not increase the structural capacity.

Detailing and construction

Reduce number of components exposed and/or use durable timbers

ªª minimal environmental impact.ªª restricted construction possibilitiesªª may require larger section sizes.

Use of alternative materials ªª reduced susceptibility to marine borer attack.

ªª inappropriate use of non-renewable materialsªª often lower ecological value.

5.4.9 VegetationVegetation management is the systematic and continual control of vegetation. The primary purpose of vegetation management on or near an old waterfront wall is to preserve the integrity of the structure, its performance, visibility, and access in the interest of public safety.

Vegetation, both cultivated and naturally occurring, has been present along the banks of rivers and other waterways long before waterfront walls were constructed. Woody vegetation, which consists of plants having hard lignified tissues or woody parts, especially stems, is commonly both inevitable and persistent, and should be managed if the integrity and reliability of a waterfront wall are to be maintained. Vegetation management, on and near waterfront walls, is focused on two performance objectives:

1 Preventing the development of vegetation-induced damage or defects.

2 Maintaining adequate access and visibility.

Vegetation management practices should also seek balance and address sustainability issues by minimising adverse environmental impacts and considering objectives for habitat, aesthetics, and community values.

Why vegetation is a concernªª The growth of bushes, saplings and trees can rapidly disrupt a wall and render it vulnerable to

water penetration and frost action.

ªª It can affect the loading on a wall, by the application of ‘wind rock’, through wind loads transferred via the roots of large trees or other vegetation growth.

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ªª The roots of plants can accelerate the deterioration of mortar. Deterioration of mortar is one of the most important causes of wall degradation and leads to many of the other more obvious signs of wall distress. Vegetation can cause deterioration in mortar by:

ª� attack by chemicals released from growing plants

ª� displacement by the roots of vegetation

ªª It’s effect on the water content of the adjacent soils. Clay will swell and shrink with changes in moisture content caused by, for example, absorption of water by tree roots. Pressure of retained material is also affected. Changes in moisture content of clay in wall foundations can cause movement and cracking of a wall.

ªª Vegetation may also obscure fixed navigation aids on waterways reducing navigational safety.

In many locations, trees and other woody vegetation, together with associated habitats, have become established on old waterfront walls (Figure 5.12). Reasons include:

ªª the age of the wall – over time, vegetation has been allowed to establish and spread, or its prohibition has not been enforced

ªª limitations of resources during times when wall maintenance was a low priority (eg during and post-World War II)

ªª difficulties in accessing walls or slopes with mechanical equipment

ªª in some cases, encouragement of woody vegetation to provide additional erosion protection

ªª encouragement of woody vegetation for habitat

ªª encouragement of woody vegetation for aesthetics and recreation

ªª beliefs that woody vegetation provides more benefits that outweigh the risks

ªª concerns that removing existing woody vegetation may cause harm to wall integrity.

Preventing the development of vegetation-induced damage or defectsA waterfront wall failure can be caused by a vegetation-induced deterioration process or a damage mechanism. Deterioration processes (eg blow-over, overturning of trees) can lead to a damage mechanism (eg external erosion), which can then cause a wall failure. Damage mechanisms can lead directly to a failure. While slow deterioration processes can be managed or mitigated before serious damage occurs, damage to the wall that may result in a failure should be prevented.

Japanese knotweed is a particular concern along waterways and in docks. It is very aggressive and difficult to eradicate. It generally needs specialist treatment to ensure its removal. Recent trials have taken place on the biological treatment of Japanese knotweed introducing a bug that eats the plant (see EA, 2013b).

Untrimmed woody vegetation, in addition to potentially blocking wall visibility and access, may in some cases induce various types of deterioration. This deterioration may contribute to damage modes that significantly affect structural integrity. Although the seriousness of the deterioration may vary significantly for different conditions, two things are clear:

1 It is important to prevent the development of vegetation-induced damage and defects.

Figure 5.12 Vegetation encroachment of an old waterfront wall (courtesy HR Wallingford)

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2 The response to each situation should take into account specific factors such as location, species, damage potential etc.

The potential deterioration processes and damage mechanisms are summarised in Table 5.11.

Table 5.11 Summary of potential deterioration mechanisms associated with woody vegetation on/near waterfront walls

Deterioration process Effect of woody vegetation Potential wall damage mechanisms

Blow-over/overturningThe overturning or blow-over of a large tree may remove a large section of a wall or adjoining ground

Instability, and internal erosion (caused by through seepage, under-seepage, and piping)

Root penetration

Roots can penetrate cracks and gaps, affect mortar joints, and displace wedges, bricks and blocks. They can also concentrate seepage along root pathsAbsorption of water by tree close to a wall can affect the pressure of retained material

Instability, and internal erosion (caused by through seepage, under-seepage, and piping)Changes in moisture content of clay in wall foundations can cause movement and cracking of a wall

Woody vegetation weight and wind loading

Both the weight of woody vegetation and wind loading can be transferred to the wall

‘Wind rock’ can loosen wall materials, bricks and blocks and cause instability

Scour flows Woody vegetation can concentrate scour in waterside or overtopping flows

External erosion of susceptible materials, eg joint mortar

Burrowing Vegetation may attract burrowing animals External erosion of backfill, undermining or of joint mortar

Damage to revetment

If the revetment was not designed for vegetation, the growth of roots and stems may move and loosen the stones, or binding elements such as asphalt and grout

Can cause displacement/uplift of a revetment affecting interlocking characteristics and stability

A clear zone should be established and maintained along a waterfront wall for access, inspection and O&M purposes. A minimum zone width should be kept clear of all vegetation other than maintained turf. New planting in this zone should be prohibited. This clear zone should not be excavated or used for storage or for structures. Walls can be particularly susceptible to severe fire events, so flammable materials should never be stored adjacent to walls.

From an engineering perspective, the preferred or recommended condition for a waterfront wall would be for it to be free of woody vegetation. However, it is recognised that, for a variety of reasons, this condition may be difficult or impractical to achieve where mature woody vegetation is already established. Also, woody vegetation that has matured on old waterfront walls can provide important environmental and landscape aesthetics and there are sometimes concerns about simply clear-cutting existing woody vegetation. Chapter 2 outlined the environmental principles that should be considered in managing the maintenance of old waterfront walls. Among these was the need to consider multiple uses and benefits, and to use balanced and flexible approaches in maintaining the integrity of the wall. Potential impacts on the integrity of a wall will depend upon the species, soil conditions, climate, age and health of the vegetation, and other factors. It may be possible to allow woody vegetation to exist under certain circumstances, and to accept both the risks and the benefits for doing so. In some circumstances removal of woody vegetation may increase the risk of further damage occurring to the wall during the process of removal. Consideration should be given to whether it would be better to leave growth in place if it is not causing an immediate concern until more substantial structural repair/remedial work can be undertaken.

For further information on the management of invasive species see Booy et al (2008).

5.4.10 Culverts and discharge pipe systemsCulverts and discharge pipes are pipe systems that are built under, over or through a waterfront wall to:

ªª provide land drainage or function as part of a flood risk mitigation system (typically from the landside to the waterside)

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ªª function as utility pipes for gas, irrigation, water supply or electrical/communications cabling.

These pipes should not leak or damage the integrity of the wall in any way.

Causes of concernCulverts and discharge pipes are a concern when they are not properly maintained. Lack of proper pipe maintenance increases the risk of the wall deteriorating faster and fail as a result of internal erosion, external erosion or wall instability. Pipe/culvert-related internal erosion may come from water seeping along the exterior of the pipe/culvert due to improper sealing or soil compaction during construction or from leakage caused by deterioration over time. Deterioration in a pipe (eg holes, weakened joints) can shorten the wall’s seepage path, resulting in the piping of hearting/fill materials, internal erosion and the eventual instability and failure of the wall.

Preventing issuesA key to good culvert and pipe maintenance is a program of regular inspections. These inspections identify and report maintenance issues before they become serious concerns such as pipe deformation, leakage or internal obstructions. Table 5.12 lists common maintenance practices for discharge pipes and culverts. Box 5.5 provides information on visual inspections.

Table 5.12 Culvert and discharge pipe components and their maintenance

Component Common maintenance practices

Flap gates, manually operated gates and remotely operated gates (including slide gates, sluice gates and valves)

Examine, grease and trial-operate at least once every 90 days.Wire brush and check the bearing surfaces of the flap gate and seat to ensure there is continuous contact and a proper seal.Examine bushings or hinge pins for excess wear. Replace if flap gate and seat rings do not line up properly.Sandblast and paint (with an appropriate protective coating system) steel parts associated with these components when they show signs of deterioration resulting from corrosion.Inspect and trial-operate sluice gates. Sluice gates are generally furnished with a visible position indicator, so take care when opening and closing the gate so as not to over-run the travel of the gate. Over-running can damage the stem mechanism or the mounting anchor bolts for the gate operator. Carry out with either two people for a complete visual inspection or a remotely operated CCTV camera mounted on an extendable rod.

Flap gates at ends of pumped discharge pipes

All practices listed for flap gates.Consider installing energy-absorbing spring-bumpers to limit the gate’s travel. When the pump begins discharging water, the pressure may cause the flap gate to violently swing open, slamming the gate body up against its discharge headwall. In this scenario the gate body may get damaged.

Trash screensThough not all trash screens are easily visible, they need to be inspected and maintained. So, remove any accumulated debris to allow the water to freely pass into and through the pipe, and repair any corrosion or damage (galvanised steel will corrode heavily if continuously submerged).

Old culverts

There are many old culverts, sometimes built of timber, which require special care. Inspection should be done by experienced people. However, culverts can collapse without much prior warning. If old culverts of uncertain age or construction are present under important waterfront walls consideration should be given to lining the culvert even if there is little indication of problems.

For further guidance on the management and maintenance of culverts see Balkham et al (2010).

Additional guidance can also be found in Sections 3.4.1.2, 3.4.1.8 and 4.17 of CIRIA; Ministry of Ecology; USACE (2013).

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5.5 EMERGENCY RESPONSE ACTIONSIn the event of an inspection identifying an imminent potential failure of a structure, then an emergency response will be required with immediate action to prevent unsafe conditions at the structure. The failure of a water level control structure or wall can lead to considerable hazards due to high water level flows, rapid draw-down of the water, and scour of the adjacent structure leading to undermining. It is critical that plans are in place to manage these situations so that the failure can be managed in a safe way. These immediate action plans may consist of barricading or closing off the structure to block access, posting load restrictions, mobilising a repair crew to quickly restore safe conditions, or performing a structural analysis to prove that the condition may be tolerated by the structure through redundancies.

The inspector must notify the owner/manager of the structure of imminent failure and the immediate actions to be undertaken as soon as they are discovered. The notification must describe the structure condition, potential consequences of failure and recommended actions. Delay in response to potential failures may result in further deterioration occurring, which can result in more extensive damage to the structure in the future.

In some cases identification of potential failure may be made by the general public and the ability of the public to contact owners/managers of such structures to notify them of potential failures is beneficial. For example, in 2009, following the blocking of the watercourse under a railway bridge, the foundations of a Victorian bridge carrying the railway over the River Crane near Feltham in West London failed without warning, causing part of the bridge to subside, requiring closure of the track. Members of the public had noticed the danger of the blockage and photographed the structure, but not notified Network Rail. Following the investigation by the RAIB the following recommendation was made, which has subsequently been implemented on all Network Rail structures: “Network Rail should provide means by which members of the public can report obstructions or other defects, particularly at locations where public access exists. This could include the provision of bridge identification plates giving a telephone number similar to those provided at low headroom highway bridges, together with a location description, map reference and structure number.”

In the event of an actual failure, the owner/manager of the structure may be required to take direct action to secure the safety of the structure and staff, and minimise potential consequential damage, eg flooding or further structural failures, as a result of the incident. However, if the wall is a designated flood defence or coast protection structure then the EA or CPA may well step in and, using emergency powers, provide the funds to carry out the works. Again such actions may include barricading or closing off the structure to limit access, posting load restrictions and mobilising a repair crew to carry out temporary or permanent remedial works and restore safe conditions.

In all cases it will be advantageous to have access to historical data, drawings, inspection records etc to assist the owner/manager to take appropriate actions to mitigate the potential or actual effects of failure.

Detection of these issues will typically require a visual inspection. This can be done either by trained staff physically entering the pipe (if large enough) or by video inspection. If people are to enter the pipes for inspection purposes, it is important that they have the proper training and they take all necessary precautions. For example:

ªª the pipe needs to be large enough and considered

safe for entryªª staff need to have received proper training for working

and performing inspections in confined spacesªª appropriate personal protective equipment (PPE) must

be worn at all timesªª gas monitoring equipment should be used.

Box 5 .5 Safety precautions for visual inspections

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During the evening of 14 November 2009, the foundations of a Victorian bridge carrying the railway over the River Crane near Feltham in West London failed without warning, causing part of the bridge to subside. The bridge was initially constructed as a single six metre span brick arch underbridge with curved wing walls supporting approach embankments on each side. The west abutment was rebuilt in 1858, and extended to incorporate two 3.6 metre wide flood relief arches.

The Rail Accident Investigation Branch (RAIB) carried out an investigation and the cause of the failure was identified as the undermining of the east abutment of the bridge by scour, caused by an obstruction in the watercourse, which channelled the flow towards the east abutment, increasing its velocity.

As a result of this incident RAIB made a number of recommendations:

1 Network Rail should positively identify which structures require checking for obstructions against upstream faces, and how frequently.

2 Such checks should be mandatory and the process for delivering them should be improved.

3 Network Rail should provide means by which members of the public can report obstructions or other defects, particularly at locations where public access exists.

4 Network Rail should reconsider the purpose of the role currently performed by the examining engineer

and then identify the information and resources (including time) that are required to undertake the task effectively, which may include:a confirming that particular requirements for

different types of bridge have been considered during an examination, eg by means of a checklist within the examination report

b requiring submitting elevation photographs of bridges spanning watercourses, which show the surface of the water at each pier and abutment, and direction of flow for the purpose of identifying obstructions

c requiring submitting supplementary photographs in support of a visual examination report to enhance the level of information available to the examining engineer

5 Network Rail should review its underwater examinations to enable a fuller picture of a structure’s condition to be realised.

6 The Environment Agency should, in conjunction with railway infrastructure owners, introduce processes to allow the immediate reporting of obstructions in watercourses where these occur near to railway structures such as bridge piers or abutments.

7 Network Rail should review the guidance provided for non-specialist staff who may be required to assess the failure of track support near a structure, and determine whether it is safe for trains to run over that structure.

Figure 5.13 Upstread face of Bridge 48 following the incident showing the failed arch

Figure 5.14 Obstruction across the upstream face of the bridge before failure in August 2009 (courtesy Environment Agency)

Case study 5 .2 Failure of railway bridge over the River Crane, Feltham, West London (courtesy Network Rail)

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ReferencesBALKHAM, M, FOSBEARY, C, KITCHEN, A and RICKARD, C (2010) Culvert design and operation guide, C689, CIRIA, London, UK (ISBN: 978-0-86017-689-3). Go to: www.ciria.org

BOOY, O, WADE, M and WHITE, V (2008) Invasive species management for infrastructure managers and the construction industry, C679, CIRIA, London, UK (ISBN: 978-0-86017-679-4). Go to: www.ciria.org

BRADBURY, A, ROGERS, J and THOMAS, D (2012) Toe structures for coastal defences – a management guide, SC070056. Environment Agency, Bristol, UK (ISBN: 978-1-84911-290-1). Go to: http://tinyurl.com/mnnfp2k

BROMMER, M FLIKWEERT, J, LAWTON, P, ROCA, M and SIMM, J (2013) Assessment and measurement of asset deterioration including lifetime costs, R&D Project SC060078/SR2, Joint Defra/EA Flood & Coastal Erosion Risk Management R&D programme, Department for Environment, Food and Rural Affairs, London, UK. Go to: http://tinyurl.com/mcxq33c

BUDD, M, JOHN, S, SIMM, J and WILKINSON, M (2003) Coastal and marine environmental site guide, C584, CIRIA, London, UK (ISBN: 978-0-86017-584-1). Go to: www.ciria.org

CIRIA; MINISTRY OF ECOLOGY; USACE (2013) The International Levee Handbook, C731, CIRIA, London, UK (ISBN: 978-0-86017-734-0). Go to: www.ciria.org

CROSSMAN, M and SIMM, J (2004) The manual on the use of timber in coastal and fluvial engineering, ICE Publishing, London, UK (ISBN: 978-0-72773-283-5)

DEFRA (in press) Flood risk and coastal erosion asset no longer maintained: good practice guidance, EA/Defra FCERM R&D Programme Project SC140004, Department for the Envornment, Food and Rural Affairs, London, UK

DUPRAY, S, KNIGHTS, J, ROBERTSHAW, G, WIMPENNY, D and WOODS BALLARD, B (2010) The use of concrete in maritime engineering – a good practice guide, C674, CIRIA, London, UK (ISBN: 978-0-86017-674-9). Go to: www.ciria.org

DWW (1994) Hout in de waterbouw (Timber in waterways) (in Dutch), Wijzer 65, Rijkswaterstaat, Dienst Weg– en Waterbouwkunde, Delft, The Netherlands

ENVIRONMENT AGENCY (2013a) Protocol for the maintenance of flood and coastal risk management assets, version 2, Environment Agency, Bristol, UK. Go to: http://tinyurl.com/nlaklgf

ENVIRONMENT AGENCY (2013b) The knotweed code of practice. Managing knotweed on development sites, version 3.0, Environment Agency, Bristol, UK. Go to: http://tinyurl.com/o6yhagw

NATURAL ENGLAND (2015) Climate change adaptation manual. Evidence to support nature conservation in a changing climate, NE546, Natural England and the RSPB, UK (ISBN: 978-1-84754-106-9). Go to: http://tinyurl.com/o9oulnf

NAYLOR, L A, VENN, O, COOMBES, M A, JACKSON, J and THOMPSON, R C (2011) Including ecological enhancements in the planning, design and construction of hard coastal structures: A process guide, report to the Environment Agency, PID 110461, University of Exeter, UK. Go to: http://tinyurl.com/opk6cat

HOLLIDAY, E, BUDD, M, JOHN, S, SIMM, J and WILKINSON, M (2003) Environmental good practice - working on coastal and marine construction sites, C594, CIRIA, London, UK (ISBN: 978-0-86017-594-0). Go to: www.ciria.org

Statutes

ActsWildlife and Countryside Act 1981 (c.69)

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6 Site characterisation, data acquisition and management

6.1 OVERVIEWThe characterisation of a site is an essential step in the inspection, engineering and design phases of any repair or remedial works. Factors to be considered include historic/geological conditions, any previous use or heritage, geotechnical characteristics, external influences, such as risk of flood or earthquake, and the relationship of the site with surrounding environment. This chapter and Figure 6.1 provide an overview of site characterisation techniques, data acquisition and the management of data obtained.

Management actionsAdministrative context

Physical context

Severe event(Section 5 .5)

Management of risk(Sections 2 .1 to 2 .3)

Responsibilities (Section 2 .4)

Powers(Section 2 .5)

Beneficiaries(Section 2 .8)

Funding(Section 2 .9)

Physical form and purpose

(Chapter 3)

Physical processes (Section 6 .3)

Loads(Sections 7 .1 to 7 .3)

Wall stability(Section 7 .4)

Historical data(Section 6 .4)

Framework for decisions (Section 4 .3)

Risk analysis(Section 4 .4)

Performance assessment(Section 4 .5)

Operations(Section 5 .2 to 5 .3)

Monitoring and inspection

(Sections 4 .6 to 4 .7)

Data acquisition (Section 4 .7)

Data management (Section 4 .8)

Wall investigation (Sections 6 .5 to 6 .9)

Decision on intervention

Maintenance, repair and rehabilitation (Sections 5 .4 and

Chapter 8)

Regulations and consents

(Sections 2 .6 to 2 .7)

Figure 6.1Overview of Chapter 6

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Section 6.2 discusses the principles of site characterisation. It maps at a high level the process by which this can be done through a phased approach to suit the requirements of the project at any given stage of development. The approach is aimed at ensuring that the process is carried out efficiently and economically, minimising expenditure and time input while maximising the information gained.

Section 6.3 considers the actions and loads from natural processes that should be considered for analysis, evaluation or rehabilitation design of an old waterfront wall in a riverine, waterways or marine environment. This includes fluvial morphology, hydraulic actions, stream flow data, river geometry, river flow data, basic energy and flow states, flow velocities, water levels and depths, sediment transport, effects of wind and waves, ship induced currents, ice effects.

Section 6.4 presents archive research and sources of historic records, while Sections 6.5 to 6.7 provide a summary of the techniques available to evaluate the geotechnical parameters required for the analysis of old waterfront walls. These include indicative values, correlations with index properties, and laboratory and field tests. Section 6.8 considers the requirements for ground investigations and the evaluation of a characteristic value from available data. Section 6.9 then discusses the geotechnical parameters relevant to the assessment of old waterfront walls.

6.2 PRINCIPLES OF SITE CHARACTERISATIONIt is not uncommon for a wall to undergo a series of inspections over a period of years with no visible signs of distress. In such circumstances, it could be argued that it is unnecessary to investigate the nature of the wall, its shape, constituents, the nature of the ground on which it is founded and the material that it retains. Many walls that are performing satisfactorily are perceived in this way. However, some have been found at a later date to incorporate features that, with appropriate investigation, might have indicated they represent a higher risk and if action had been taken earlier may have reduced the subsequent costs of maintenance and repairs incurred.

Knowing little about a structure for which an owner or manager is responsible is not recommended and, as a minimum, an appraisal of the site and characterisation of the wall should be carried out.

Characterisation of the wall will aim to determine:

ªª the wall shape (height, breadth, profile)

ªª constituents of the wall (brick, masonry, concrete)

ªª the likely ground conditions on which the wall is founded

ªª the likely range of water levels imposed on either side of the wall

ªª the likely loading that can be imposed to the rear of the wall

ªª clues suggesting non-original modifications and changes that may have adversely affected the wall.

The initial step, which for minor walls in satisfactory condition might also be the last, is a desk study. Depending on the height of the wall, its condition and perceived consequence of failure, such a study will then be used to inform further investigations.

Much of this information might be available from the original drawings, technical papers or design reports, however for old walls these often unavailable. Section 6.4 gives guidance on possible sources of such historic data. Inspection of drawings of other walls of similar age and function might indicate possible dimensions but this will always leave uncertainties.

For walls that are showing signs of distress or where the consequences of failure are high, if such information is not available then it may be considered necessary to carry out an intrusive investigation, or a non-intrusive investigation with some limited intrusive work to provide sufficient data for analysis. The desk study results will inform the scale and type of investigations that may be necessary.

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By carrying out studies in a logical way, beginning with a desk study, it should be possible to undertake investigations in a cost-effective way.

6.3 MORPHOLOGICAL, HYDRAULIC AND OTHER NATURAL PROCESSES

6.3.1 LoadingFunctional loading on a wall will need to be identified to analyse its behaviour. Section 7.4 describes methods for the analysis of stability of walls These loadings may be for past events, current practice or future functional requirements, and may be used as follows:

1 To identify reasons for past behaviour. For example, when a wall has partially failed, or shows signs of distress, and the loading condition at the time of failure is known.

2 To establish current safety factors, or possible partial factors if using BS EN 1997-1:2004+A1:2013, see DfT (2006).

3 Current wall loadings may also be used to show the FoS for different types of failure mode. This may then be correlated with the results of a past failure (see point 1).

4 To establish FoS under proposed future loading conditions.

Loads may be categorised into horizontal and vertical applied loads and those resulting from the water regime. For example:

ªª Horizontal: vessels berthing, bollard pull, fender forces.

ªª Vertical: surface loads, surcharges, vehicle and crane loads, stacked materials etc (though these are subsequently resolved during calculation to an equivalent horizontal component).

ªª Water regime: hydrostatic forces, waves and currents, extreme surges, rapid draw-down applying additional horizontal forces to the wall.

6.3.2 Actionsandloadsinafluvialenvironment

Cross-wallflowSimple water level measurement behind and in front of a wall should provide the magnitude of water level lag contributing to disturbing horizontal forces. There may be occasions when it is necessary to make a more comprehensive study of the flow of water through a wall and this may be achieved with a series of boreholes forming a cross-section of the wall and the backfilling. Measurement of water levels in the boreholes, and in front of the wall throughout a tidal cycle will also enable a picture to be obtained of the varying water pressures acting on the back, front and ideally the base of the wall.

Cyclic water level changesThe water level in front of the wall will often vary in a cyclical fashion according to the function of the wall and the hydraulic regime in which it is situated. So, the water in an impounded dock or enclosed canal system will normally only vary by small amounts, but walls forming breakwaters, piers, locks and river-banks may be subjected to regular large changes in water level.

In a fluvial, estuarine and/or coastal environment, information on extreme rainfall events and extreme water levels can be obtained from the EA, SEPA, NRW, NIEA and DARDNI, and the UK Met Office. Information on predicted tide levels in the UK can be obtained from Admiralty Tide Tables produced by the UK Hydrographic Office (UKHO) (see Websites).

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Rapid water level changesAn important aspect of the assessment of old waterfront walls is their risk of failure. This may in turn depend on the risk of a rapid draw-down of water in front of the wall, while water levels behind remain substantially unchanged, as will the behaviour of the wall in these circumstances. It is important to investigate the possible causes of any rapid changes in levels of this nature and their chances of occurring. For example:

ªª canal locks including lock gates failing causing rapid draw-down of water

ªª any need to lower water levels at a fast rate (eg to flush out a pollutant)

ªª rapid draw-down or increase in level due to storm surge, hurricane, typhoon etc.

Review of local sedimentary regimeOne of the primary causes of wall failure is the removal or loss of the ground in front of the wall reducing passive resistance. So the measurement of the ground level at the toe of a wall is an important investigation. Where the wall is in a relatively benign environment, where natural fluctuations of the ground in front of a wall are unlikely, it is important to establish whether the ground is still at its original or design level or has been altered by dredging or other works. It will also be important to discover whether there have been any changes in level during the wall’s history.

Some walls are in an environment where the ground level is frequently altering. In these cases it may be necessary to monitor the ground level in front of a wall over a period of time to establish maximum and minimum levels. It will also be beneficial to determine the cause of the fluctuations in ground levels.

Measurement of ground level may be carried out by various means. For impounded docks and other locations, where the wall toe is permanently obscured, it may be possible to determine the measurement from acoustic surveys of the wall face, or from measurements made directly with a hand-line. In docks, rivers and canals, air lifting of any soft overburden by diver may be needed to reveal the profile of firm ground. In some tidal locations it may be possible to obtain access to the toe of the wall in the dry and measurements may then be made to a fixed point on the wall such as the cope level.

Historical scour followed by sedimentary deposition may have resulted in a weak material existing in front of the wall. This may not accord with the design intent. Although ground level in front of a wall may appear from measurement to offer passive resistance to the wall, some investigation as to the strength of this material is necessary to assess the actual resistance available. Depending on the shape of the wall, this might be possible by simple probing, for example a probe sinking under its own weight or with few blows, would be indicative of weak material.

Water velocitiesHigh water velocities close to a wall may cause erosion of ground level in front of the wall leading to reduction of passive resistance and wall stability. In many cases a quay wall will have been designed for the berthing of sailing vessels and the water velocities arising from these manoeuvres have been insufficient to cause any problems.

However, modern powered vessels particularly those with bow and/or stern thrusters or water jet propulsion, create a flow of water at appreciable velocities that can cause significant scour at the wall toe. Roll on/Roll off (RoRo) vessels are often introduced to port areas that contain old waterfront walls. It is desirable to estimate the velocity of water at the wall toe to check whether the ground in front of the wall will remain in place. The effect of propeller wash in shallow and confined area has been studied by several authors (see Further reading). These provide guidance on methods of estimating water velocities caused by propeller wash, water jets and bow/stern thrusters.

Natural water velocities may also scour the ground in front of a wall. Most walls subjected to scour will have been designed to resist such forces. However, when the hydraulic regime is altered in any way these

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velocities may increase and it may be necessary to measure or predict the new velocities. In England, the EA should be consulted on flood data and river flow records, in Wales this information is managed by NRW, in Scotland, similar information can be obtained from SEPA, and in Northern Ireland from DARDNI.

Currents may be measured by direct reading or self-recording current meters. Measurements should be taken over a sufficient period to assess the effects of spring tides and high flows associated with floods and seasonal variations etc.

Assessment of river regimeRiver regimes will affect bridge piers and abutments, river walls and waterfront walls in estuaries. Although the analysis of a river regime is complex, the relationship between sediment types and scour/deposition velocities may be determined by examination of a site. These may then be used to predict the effects of extreme flows arising at times of flood. The important aspects to be investigated are the effect of scouring currents on bed levels in front of a wall and the possible increase of currents due to changes in the river regime, obstructions or construction activity in the river etc.

Scour protectionMany walls situated in hostile environments are designed with some form of scour protection. Others have scour protection added when it is discovered that problems are occurring due to the removal of toe ground. It is important to investigate the state of the toe of these walls and to detect any signs that would indicate loss of protection. HR Wallingford (1992) may assist owners with their scour assessment (to be replaced by Kirby et al, 2015). A further source is Bradbury et al (2012).

6.3.3 Actions and loads in a coastal environment

Wave measurementsWave attack is of particular importance when assessing the stability of breakwaters and other exposed quays or seawalls. Wave measurement is difficult to carry out in the nearshore zone and in consequence it is normal for measurements to be taken in deep water further off-shore. The effect of the shallowing water and any obstruction to the waves can be estimated by the use of refraction and diffraction computational models and methods. The effect of bottom friction will also need to be estimated.

In an assessment of wave climate for the purposes of an old waterfront wall investigation, it is normally necessary to identify any changes in regime that have occurred. So, the absolute values of wave height and period in the offshore zone may be less significant to the investigator than changes in seabed bathymetry in the nearshore zone, which will affect the waves reaching the wall. However, actual wave heights may be needed for checking the rock sizes and slopes used in any foundation mounds under breakwaters and for designing any new rock mounds to protect seawalls. Such information may be available from the local coastal observatory, which are usually run in partnership with maritime LAs.

Assessment of coastal processesFor walls in the coastal zone, wave attack and the level of ground at the wall toe will be controlled to a great extent by the coastal processes in the area. These processes are usually:

ªª wave induced littoral drift

ªª onshore/offshore sediment movements

ªª sediment movement due to tidal currents.

Coastal processes are complex and considerable amounts of data collection and analysis are required to determine the processes active in an area and quantify their effects. Generally, it would not be feasible

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to investigate these processes solely for the purpose of assessing their effects on an old waterfront wall. However, if the coastal zone has been studied for other reasons such as design of coastal defences, beach or shoreline management etc, then the results of these studies are of great value in the prediction of old waterfront wall behaviour.

Data may well already be available and it is worthwhile to research the local SMP, consult with the EA (in England) or equivalent bodies elsewhere on local strategy studies and contact the local coastal observatory. In particular, it should be noted that the construction of new sea defence works, piers, groynes etc may be well documented and may have a considerable effect on the beach levels in front of an existing wall.

6.3.4 Human actions on waterfront walls

Dredging recordsThe fact that the current bed level at the toe of the wall is similar to that envisaged at design, may be insufficient to assure its stability. It may be possible that the material is different from the original, eg if the initial granular material has been removed by scour or dredging and replaced by structurally weaker material as a result of subsequent siltation or other infill.

To detect the occurrence of such a situation, or to prevent it happening in the future, it is advisable to obtain records of past dredging activities and present dredging practices and to measure the level of the top of firm material below the silt.

Effect on the local environmentWhenever rehabilitation or upgrading work is carried out there is an effect on the locality. If the structure is enhanced aesthetically this will affect local amenity values. Local property will become more desirable and more valuable.

If there are a number of developments being carried out at the same time it is necessary to look at the whole development area to ascertain where benefits are accruing. An analysis of this type may assist in providing the economic justification for carrying out maintenance work on a wall or strengthen the case for obtaining third party contributions to the cost that, if viewed in isolation, might not warrant the expenditure.

Neighbouring developments may also bring some problems. Modern construction methods and the insertion of new services along or near the rear of the wall may interfere with parts of the wall’s original construction. Also, the adjacent development may bring increase loadings to the wall by virtue of increased traffic levels and changed drainage patterns and may interfere with access to the wall. When a new development is being permitted close to a wall, there should be a requirement for the provision of suitable access to it. If possible, a working apron should be left beside the top of the wall suitable for the use of light plant.

6.4 ASSEMBLY OF AVAILABLE HISTORIC DATA

6.4.1 OverviewMoney spent on detailed archival research of data may be more beneficial than spending the equivalent on conventional site investigation. This is particularly true if the historical search is carried out early on in the investigation. Information obtained from archival research may help to address typical questions such as:

1 How old is the structure?

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2 Who designed it and how was it designed?

3 Who built it, how was it built and were there any construction difficulties or issues that were addressed?

4 Is there any history of problems of a similar or related nature?

5 What type of construction is it?

6 What loads was it designed for?

7 What were the original ground conditions like?

8 What kind of foundations does it have?

9 Has it always looked like this or has its use altered over time?

10 Is it listed or otherwise protected?

The search for archive data needs to be intelligently planned. For example, source data from those who are interested, may have funded the previous wall (eg Defra or the coast protection authority) or had approved the wall (eg the planning authority).

Data resources include textbooks, journals, newspapers, trade literature and maps. They may also include films and videos. Unpublished resources may also include maps and plans, manuscripts, typed reports, photographs, and private records, files etc.

6.4.2 Sources of archive materialTo find collections of papers either by name or by work, the National Archives provides a useful reference tool (see Websites).

In addition, the ICE (see Websites) holds historic records and archives from historical engineering projects, which include photographic and documentary evidence for owners and engineers to understand and conserve the built environment. The ICE proceedings, containing useful technical papers and reports on the design and construction of structures, are indexed from 1836.

Other relevant data sources include:

ªª Local libraries, councils and universities: these often hold archives with a large amount of historical records for their area.

ªª Royal Institute of British Architects (RIBA): the national collection of papers of architects, the archives and drawings collections are housed at the Victoria and Albert Museum.

ªª Comisiwn Brenhinol Henebion Cymru (Royal Commission on Ancient and Historical Monuments of Wales): holds the National Monuments Record for Wales.

ªª English Heritage: looks after over 400 historic buildings, monuments and sites. Its Swindon office houses the National Monuments Record.

ªª Historic Scotland: an Agency within the Scottish Government directly responsible to Scottish Ministers for safeguarding the nation’s historic environment.

ªª Network Rail: the regional plan offices contain original drawings, microfilm and digital images of the railway infrastructure. Access is very restricted for non-Network Rail staff.

ªª Canal and River Trust: archives are currently held in a number of their sites, and in museums at Gloucester Docks and Ellesmere Port.

ªª Scottish Canals: archives are stored at the Grangemouth Archive facility.

ªª Port Authorities: these often hold archives with historical records of construction/development for their particular port.

ªª Local heritage societies: documents local historical information, for example Societe Jersaise provided information for the Gorey Breakwater Pierhead in Jersey.

Guidance by Cooper et al (2013) provides information on sources of historical and other data.

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6.5 INVESTIGATION TECHNIQUES

6.5.1 ExcavationExcavation can be carried out in the apron area behind a dock, retaining wall or seawall, or in between the back and front face of a pier or breakwater. This excavation would normally be in the form of a number of trial pits and trenches up to five metres deep. Such excavations should be limited so as not to affect the integrity of the structure.

Excavations are limited by the groundwater level, because below that level the ground is liable to be unstable. Where the water in front of the wall is tidal, the excavation should be started at high tide so that it can be completed at low tide. Trenching along the back of the wall is needed to explore for counterforts with maximum spacing, usually five metres, and tie rods.

An excavation of this type will typically give the following information:

1 Whether the wall has counterforts and, if so, how deep they are and what their spacing is.

2 Whether there are any ties or old timbers linking the wall to the ground behind.

3 Whether any bollard blocks are built into the wall or are separate.

4 The form of construction and composition of the top of the wall below the coping stones.

5 The nature of the backfilling material.

6 The nature, in the case of a breakwater or pier, of the top surface and hearting.

The disadvantages of an excavation are that it is depth-limited by expense, safety considerations and by the high groundwater levels typically found behind walls of this type. It may also cut off a large area of working space, which may be a significant factor in a busy port or highly used riverside location.

However, an excavation gives a clear picture of the wall at the excavation site and allows large representative samples of wall and backfilling to be collected for testing. An example of the extent of detail exposed by excavation is given in Figure 6.2.

Figure 6.2 Detail gained by excavation of a trial pit (courtesy Sir Bruce White, Wolfe Barry and Partners)

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Beyond the limits of economic excavation, a system of probing can be used to assist in the identification of the back profile of a wall. The use of probes is by no means fool proof. It is difficult to differentiate between large pieces of debris and the structural components of the wall, and the probe may well glance off sloping or angled steps in the rear of the wall, giving a false impression of the shape of the structure. Backfilling is frequently carried out using coarse and granular material, often with rubble and debris used, and this makes penetration by any rotary drilling method particularly difficult.

Various types of probe are available, from a manual percussive probe, to an electrically powered percussive drill with a flow-through sampler. The latter not only defines the levels of hard strata encountered, but also obtains a continuous 30 mm or 50 mm diameter core of material above.

Probes are only suitable for investigation in homogenous and relatively soft materials such as clays or fine sands. Obstructions such as rocks or debris can cause refusal and give misleading information. Probes are also depth-limited, dependent on soil conditions.

In materials that are predominantly soft but contain occasional obstructions the use of a shell and auger (cable percussion) rig may be considered. This allows soft material to be continuously sampled as it is removed and the obstructions can be broken up by chiselling. Once the back of the wall is reached a short core can be taken by a rotary coring rig to prove the material.

The relative costs of probes, shell and auger, and rotary coring methods are also relevant. To mobilise a rotary coring rig is roughly two or three times more expensive than a shell and auger, or probing, rig. The cost per metre run for investigation is about three or four times as high.

6.5.2 Shape detection problemsThere are a number of special problems associated with the investigation of the base of a wall, and the toe and heel of the wall, if they exist:

1 Some walls have a curved back profile that is almost parallel to the front of the wall and a borehole placed in the middle of the top of the structure would give a false indication of the nature of the base (see Figure 6.3a). To overcome this problem it is necessary to put down a number of boreholes and to be vigilant when comparing the break-out levels with that of the toe level of the wall. An absence of designed backfilling might indicate this type of wall.

2 Some walls have a small heel at the rear of the base (see Figure 6.3c). This heel is difficult to detect but significantly increases the stability of the structure, due to the additional weight of the soil above the heel acting at a large lever arm about the centre of rotation at the toe of the wall.

3 The toe of many walls may be obscured by sediment and, in some cases, covered by debris and/or anti-scour armouring (see Figure 6.3b). To determine the extent of the toe it may be necessary to remove the material covering the toe or to probe with a steel rod. Removal of material can be achieved by using an air-lift, or by mechanical means from a barge or the shore. In the latter case it is important not to excavate to too low a level, which may endanger the stability of the wall by undermining.

Probing for the toe tends to be unreliable because it is not possible to be certain that refusal of the probe is caused by the toe or an obstruction. Some toes are extended forwards, at some time after the original construction, in a stepped fashion, and a probe may not detect this modification to the original design.

The front face of the wall should be carefully examined where accessible, for signs of what the remainder of the wall might be like. The following should be looked for:

ªª tie rod anchorages

ªª type and materials of the face of the wall including differences between the top and bottom of the wall

ªª drainage holes

ªª changes in foundation levels

ªª structural features, such as arches

ªª timber piling.

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6.5.3 Geophysical methods

Identifying the rear face of an old water-front wall by geophysical methods may be possible but may be complicated by the lack of:

ªª information regarding the shape of the interface, due to the loss of historical records

ªª contrast between the geophysical properties of the structure, the backfilling material and the original ground

ªª working space for the deployment of geophysical equipment on the ground due to the presence of buildings or dock facilities.

Close attention should be given to the internal construction features of a range of typical walls (see Chapter 2). The use of geophysical methods on many of these complex structures is likely to be impractical with the range of equipment and methods currently available.

Choice of the best site-investigation method depends on close collaboration between the geophysical specialist and engineer/client. Where it exists, historical information should be used to establish how the wall was designed and constructed, so that the most appropriate geophysical method can be selected and an assessment made of its likely degree of success.

One possible approach at present is the use of ground penetrating radar (GPR) deployed on the front face of a wall. This would require the operation of the radar equipment in a vertical mode, and this has been shown to be a practical proposition. The main limitations of this method are:

ªª attenuation of the electromagnetic energy by the internal fabric of the structure

ªª insufficient contrast in the electromagnetic properties of the materials on either side of the rear face

ªª lack of knowledge of the internal fabric of the wall leading to difficulty in calibration.

A further major problem associated with the use of GPR is that the electromagnetic signals are severely attenuated by seawater, either inside or outside the structure. This is a considerable disadvantage when the wall being investigated is partly submerged.

The seismic reflection method, with the seismic source and geophone array deployed on the front face of the wall, should also be considered. Like electromagnetic energy, seismic energy is attenuated during propagation. An additional problem is the lack of resolution when normal low-frequency seismic sources are used. Further improvement of this method for wall investigation will require the development of a high-frequency seismic source, used in conjunction with suitable geophones, or accelerometers, and combined with modern data-processing techniques.

Figure 6.3 Wall shape detection problems for various types of structure (courtesy Livesey Henderson)

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Ultrasonic reflection techniques have also been investigated but the results were not conclusive and no experimental work has been carried out.

Where boreholes have been used to investigate the internal fabric of a wall they may also be employed for cross-hole seismic or electromagnetic measurements. Of particular value would be boreholes on opposite sides of the anticipated position of the rear face of the structure. It may then be possible to predict the shape of the face between the boreholes by recording the variation of the compressional or shear wave velocity with depth.

Alternatively, it might be possible to position seismic sources in one of the boreholes with a geophone or hydrophone array and reflect seismic energy off the rear face. Horizontal probe holes could also be used in this application. These would also be extremely useful for cross-hole seismic or electromagnetic surveys and the deployment of standard geophysical borehole logging tools.

In locations where the ground surface is clear, standard surface geophysical methods can be used if there is a contrast in physical properties between the internal fabric of the wall and the geological material that it abuts. The simplest method is a ground-conductivity survey, which can be carried out rapidly. Data can be plotted and contoured so that changes in ground conductivity, related to changes on either side of the rear face of the wall, should be readily apparent.

Other surface geophysical techniques, such as seismic and electrical resistivity methods, may also be applicable. Using a magnetic survey, to locate tie rods or vertical sheet steel anchors, should also be considered.

6.5.4 Unexploded ordnanceThere is always a risk of discovering unexploded ordnance (UXO), particularly in coastal locations and around commercial ports, and its absence should never be assumed. Guidelines on dealing with UXO can be found in Cruickshank and Cork (2005), Cooper and Cooke (2015) and in Section 4.2.6.

6.6 INVESTIGATION TECHNIQUES FOR THE INTERNAL STRUCTURE

Many walls, both retaining and free-standing, are composed of masonry or brick skins infilled with a hearting of a different material such as rubble or rubble concrete. Loss or deterioration of this hearting will have a serious effect on the strength and stability of the wall.

Investigation of the internal portions of the wall is sometimes required to identify the nature of the hearting and its state, and to detect any cavities that may have been formed by loss of hearting through cracks in the outer skin of the wall. Investigation can be by means of:

ªª excavation from the top of the wall

ªª drilling techniques

ªª remote inspection methods

ªª geophysical methods

or a combination of these.

6.6.1 ExcavationExcavation (see Section 6.5.1) gives a reliable picture of the composition of the upper layers of a wall and enables the investigator to determine whether there are any ties, cross walls, timbers etc within the wall. It may also detect whether there are any large voids in the core caused by leaching out of the hearting at lower levels. Excavation of this type has been carried out at numerous old waterfront walls.

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6.6.2 Drilling techniquesDrilling may be used to investigate the core of the wall if it is composed of sand, concrete, brickwork or stone. In these cases coring techniques may be used to sample the material and at the same time to determine changes in composition, voids and the level of the wall base. Core sampling will allow the densities of the materials to be measured and their strengths to be tested.

If the wall has been filled with coarse rubble, stone or debris, it is most likely that drilling methods will prove to be unsuitable because the hole will need to be cased and the drill string may become trapped in the loose material. Rotary percussive drilling with a proprietary ‘overburden drilling’ system (designed for the simultaneous drilling and casing of holes through unstable ground conditions using an eccentric drill bit to avoid trapping the drill) might overcome this problem, but has the disadvantage that it is generally unsuitable for taking samples.

6.6.3 Remote inspection methodsWhere the structure is delicate, listed, or the top is inaccessible, it may be difficult to obtain access to the core of the wall to inspect and measure voids. In such cases remote inspection methods can be used.

If a large enough hole can be made in the skin of the structure it may be possible to insert remotely controlled CCTV cameras. Where the entry hole is small, such as through a borehole or a hole cored through the side of the structure, a borescope or inspection camera can be used. A borescope, which uses fibre optics to link an objective lens on one end of a flexible tube/cable and an eyepiece on the other, can be inserted down a narrow hole and can give an all-round view of any cavity found. Photographs or videos can be taken internally using a miniature camera or video at the end of the flexible tube in the case of a ‘video borescope’, or externally with a digital camera or video attached to the eyepiece end of the fibre optic borescope. Measurements can be made using this method, but lighting is often a problem in large voids.

6.6.4 Geophysical methodsThe use of geophysical methods to investigate the internal structure of a wall has been very limited. The most common technique used has been GPR to investigate voids behind waterfront structures, tunnel linings and in bridge abutments. However, other techniques have been used to measure differences in material or ground properties to give an indication of developing problems and temperature differences to try and spot leaks.

These include the use of electrical resistivity tomography (ERT) to measure ground properties and detect leaks, and microgravity measurements to investigate voids behind waterfront walls.

The internal construction of many old waterfront walls is highly complex (see Chapter 3). Some information concerning this construction may be obtained from historical records and any previous borehole investigations carried out. It is essential that this information is made available to the geophysical specialist to enable the most suitable method to be selected for investigating the internal fabric of the structure.

GPRGPR is typically used from above to investigate ground properties in a similar manner to airborne radar. It can be used to give an indication of developing problems. GPR has also been used horizontally to investigate the construction of walls, tunnels and locks by the Canal and River Trust. The Trust has been able to establish thickness, material types, presence of voids, hidden timbers, counterfort walls, tunnel construction shafts etc. They have also used GPR to investigate voids under reservoir spillways and used the results to target subsequent investigation and/or strengthening works. Examples of the results of GPR surveys are shown in Figures 6.4 and 6.5.

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Figure 6.4 Typical GPR survey from Netherton Tunnel (courtesy Canal and River Trust)

Figure 6.5 GPR detail from Netherton Tunnel, the blue contours shows potential leakage paths over tunnel arches (courtesy Canal and River Trust)

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St Catherine’s breakwater at the eastern end of the island of Jersey in the Channel Islands was constructed in the 1850s as part of a series of naval harbours. The harbour was never completed but the 600 m long arm of the St Catherine’s breakwater forms a major landmark and tourist attraction on Jersey.

The breakwater is an open jointed mass gravity structure with dressed stone outer facings and a secondary core material built upon a substantial rock bund projecting out from the shore.

A particularly strong storm in December 2005, with an adverse combination of large waves and high tide, resulted in a significant loss of facing stones at the roundhead. A concrete pump and ready-mix concrete trucks were immediately sent to the end of the roundhead to fill the void that was exposed on the face of the wall and to then fill the breach in the missing roundhead stones with cement bags.

Immediately before the severe storm, archive searches had been made to obtain information and data relative to the original construction and maintenance history of the breakwater. Another significant part of the data gathering and analysis was to assess the information produced by HR Wallingford who had mapped the island with predicted wave, current and tide movements. This information was

used to understand the conditions being experienced at the roundhead at the time of failure and to predict maximum wave heights and impacts.

A series of investigations were then designed so that the cause of the accelerating level of distress at the roundhead could be identified. Initially an impulse radar survey was carried out on the whole length of the breakwater. Following this, a further targeted radar survey upon the breakwater roundhead deck and walls was undertaken. Several areas of potential voiding beneath the concrete deck slabs and behind the walls at the roundhead were detected, whereas no substantial voids were discovered along the length of the main breakwater.

The strategy presented to the States of Jersey was that a rock armour revetment should be constructed capable of protecting the foundation of the rebuilt structure and safeguarding the repair investment. In addition to filling the voids behind the breakwater roundhead, replacing missing facing blocks and replacing the concrete deck surface with flexible protection to deal with overtopping.

Some lessons learnt include:

ªª It is often difficult to obtain funds to undertake the repair and/or restoration of heritage structures that generate no income. However, the States of Jersey Treasury made funds available to carry out the project.

ªª Owners of maritime structures of this type, ie with concrete decks over old free draining masonry quays or piers, should survey them regularly and check that hidden voids have not been forming beneath the concrete slab.

ªª A measure of the success of the project is that with the exception of the armour rock revealed at low tide, the St Catherine’s breakwater roundhead retains the same appearance as it has done for 150 years.

Figure 6.6 St Catherine’s breakwater, Jersey

Figure 6.7 Cross-section of breakwater (from archives)

Figure 6.8 Damage and temporary repairs to the roundhead in 2005

Figure 6.9 Discovery of a large void beneath concrete slabs

Case study 6 .1 Restoration of St . Catherine’s breakwater roundhead, Jersey (courtesy Arup)

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Electrical resistivity tomography (ERT)ERT is a geophysical imaging technology that measures electrical resistivity in the ground. It involves inducing a small DC current in the ground and measuring the electrical resistance between that point and the detector – similar to modern medical imaging such as ultrasound, MRI or CT scans. The technology can be used to obtain a ‘snapshot’ of subsurface conditions, groundwater detection and locate voids or buried infrastructure.

The Canal and River Trust are currently working with the BGS to develop a way of continually measuring the electrical properties of the ground and a way of using these measurements to develop a model of where problems such as leaks or voids may be.

The science has been around for some years, but now cheap disposable detectors can be buried in the ground and, with the addition of mobile phone technology, they can be instructed to scan at will and to send back real time information in 3D as things change. Measurements can then show how leaks are developing, how water is moving through the ground, how contaminants move or even how solid strengths change over time.

Figure 6.10 is a resistivity cross-section on a railway embankment, showing the penetration of water (red) around and beneath a clay seal (blue). Subsidence of the clay seal has allowed water to pond above.

The technology is still new and more work is needed to simplify the technology and reduce the costs, but it does have the potential to predict where problems may emerge in canal embankments, reservoir dams or behind waterfront walls.

Microgravity surveysMicrogravity surveys are typically used to detect subsurface voids and/or changes in subsurface density. The theory is that changes in gravity measured at the earth’s surface reflect the underlying geological structure. By accurately determining gravity at a specific point the ground beneath can be better understood.

Very high resolution gravity mapping is known as ‘microgravity surveying’. Using modern equipment and careful field procedures it is recognised as an accurate and reliable method for detecting underground voids, both natural and manmade. Microgravity mapping is currently being used by the Canal and River Trust to find voids behind the waterfront walls at West India Docks in London (Figure 6.11).

Figure 6.10 Resistivity cross-section on a railway embankment (from BGS, 2013)

Figure 6.11 Typical microgravity contour plan showing low gravity and a potential void (blue) (courtesy Canal and River Trust)

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Summary of remote sensing technology applicationsThere are considerable benefits to be gained by using remote sensing technology to investigate old waterfront walls. While the costs are relatively high at present, the environmental benefits are significant. The applications give owners the ability to collect information where manual collection is difficult or impractical – a health and safety benefit. Although the equipment required is generally considered expensive, as technology and applications increase the costs will come down.

Remote sensing geophysical investigation can be used to identify and evaluate:

ªª abandoned wells

ªª buried obstructions

ªª buried trenches, pits or voids

ªª confining different layers

ªª identifying contamination plumes (inorganic)

ªª localised bedrock, landfill or slag

ªª permeable pathways

ªª underground piping

ªª munitions/explosives etc.

The surveys are repeatable and can be easily geo-referenced allowing baseline and subsequent monitoring of conditions or any identified problems.

Equipment is often specialist and expensive. However, the coverage, resolution and non-intrusive nature of the surveys, especially when working around historic structures, is extremely useful in identifying problem areas and any potential major interventions or remedial work required on a structure.

The limitations of the systems are that typically remote sensing is a specialist field and requires a high amount of processing and interpretation. The final survey is only as good as the surveyor who is acquiring and processing the data, and there is the danger that a lay person will read into the results what they want to see.

Remote sensing can be time-consuming and repeat visits with specialist equipment are often required, which may not always be possible.

With all these techniques it is difficult, almost impossible, to investigate the foundations of mass gravity walls. The Canal and River Trust have also had difficulties in applying remote sensing techniques to locks and docks where there is a high water table, which often produce erroneous reflections. Meaningful results require an experienced operator and careful processing.

Geophysics and microgravity investigations do not necessarily replace the need for investigations using conventional drilling but can assist drilling and other further investigations by maximising the information obtained from them.

Typically these techniques cannot give owners a continuous view of what is happening, but by using ERT with autonomous remote detectors, this is changing.

At the time of writing there is an ongoing 10-year research study funded by the Engineering and Physical Sciences Research Council (ESPRC) looking into the technologies available to map subsurface infrastructure and ground conditions. The University of Birmingham’s Mapping the Underworld project (see Websites) seeks to develop the means to locate, map in 3D and record, using a single shared multi-sensor platform, the position of all buried utility assets without excavation. Although this research project is primarily looking into utilities, the outcomes of the study may well have benefits to the technologies and methods used to investigate old waterfront walls.

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6.6.5 Testing of wall materialsWall materials may need to be tested for a number of reasons, such as to determine the:

ªª density of the material for stability calculations

ªª strength of materials for calculations relating to crushing and cracking

ªª type, extent and depth of degradation

ªª physical and chemical composition of wall materials

ªª porosity of material for assessments of the hydrostatic head due to differential water levels.

Materials may be tested either in situ or by removal of samples. In situ testing would normally consist of a visual examination of the different materials to detect signs of degradation. The use of non-destructive testing equipment, such as low-frequency sonic sources, appears to be at the early stages of development.

Samples for testing at a laboratory would usually be obtained during excavation of a trial pit in the top or back of a wall, or from cores or bulk samples taken from a borehole.

6.7 INVESTIGATION TECHNIQUES FOR EXTERNAL SURFACES

The condition of the external surfaces of old waterfront walls may be determined above water level by visual inspection (see Section 4.5), LiDAR, and by use of unmanned aerial vehicles (UAVs), also known as drone surveys. Underwater inspections were often undertaken by divers and/or remotely operated underwater vehicles (ROVs), but with the development of acoustic methods (SSS, MBES), the use of divers has been minimised to reduce the health and safety risk. Acoustic methods, LiDAR and UAVs are discussed in Sections 6.7.1 to 6.7.4.

6.7.1 Acoustic techniquesThe front face of a waterfront wall, and in particular the area at the toe of the wall where a build-up of sediment is likely, may be investigated using acoustic techniques. The same methods will identify areas where scour may be occurring and where large cavities or recesses exist in the wall face. Techniques that may be used are:

ªª echo sounding

ªª side-scan sonar

ªª sector scanning sonar.

Echo soundingEcho sounding technology has progressed since 1992, when single beam echo sounders (SBES) were normally used. Today these are rarely employed. Instead multibeam echo sounders (MBES) or, as they are now more commonly referred to, multibeam swathe sonar (MBSS) are the norm.

Single beam echo sounders are sonar systems that gather 3D data when connected to a GPS or other geographical co-ordinate collection system. The primary disadvantage of the echo sounder or SBES is its inability to collect data outside the path of the vessel transporting the transducer. The data density is low in comparison to multibeam swathe sonar (MBSS), so they are not able to detect channel bottom irregularities and/or scour holes unless the vessel passes directly over the top of the area in question. The data also needs interpolation, which can lead to inaccurate representation of actual conditions.

MBSS was first developed in the 1960s and has replaced single beam echo sounders due to their limitations. Most modern systems work by transmitting a series of broad acoustic fan-shaped pulses from a specially designed transducer. The sonar transducer emits acoustic pulses propagated inside a wide

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across-track and narrow along-track angular sector. The receive array directed perpendicularly to the transmit array forms a large number of receiving beams that are narrow across track and steered simultaneously at different across-track directions by a beam forming process. So the system performs spatial filtration of acoustic signals backscattered from different portions of the seafloor along the swathe. Modern shallow-water MBSSs, operate at hundreds of

kHz, transmit short pulses of several tens of microseconds, and form hundreds of beams of about one degree width. Because they employ short pulse lengths, narrow-beam MBSSs are capable of resolving small features a few decimetres wide in the seafloor relief in the horizontal plane along with finer bathymetry details.

The main advantage of MBSS is the ability to quickly obtain large quantities of 3D data. They produce a 3D image often referred to as a ‘point cloud’. The primary limitation of the MBSS is that the vast quantities of data produced can be cumbersome and time-consuming to post process. The complexity of the system means it is more time-consuming to set up the system when compared to single beam system. The data post processing also requires the operator to be skilled to obtain satisfactory results. Finally MBSS systems can have difficulty to smoothly transition from acquiring data from the seabed to the vertical face of a structural member when looking in a downward direction.

A recent modification of MBSS is real time multibeam sonar. Instead of using a single line of narrow beams, real time multi-beam sonar uses many rows and columns of narrow beams, allowing for more dense data coverage. For example, thousands of data points are created with a single ‘ping’ using real time multi-beam sonar, as opposed to hundreds with traditional MBSS. These systems create 3D images that are updated in real time, similar to watching a video, and they can be mounted on a vessel, ROV or fixed installation.

There are many advantages when using real time MBSS. For example, they provides the benefits of 3D data, but unlike traditional multi-beam systems, some can be rapidly deployed and require less special operator skills, training and post processing. Due to the large number of beams and high data density, large complex structures can be covered quickly without the need for multiple passes resulting in greater productivity.

The downside is that they have the same limitations as MBSS and if used as a standalone unit they still need to be fully geo-referenced using GPS and motion compensation for the best results. Unfortunately these systems typically take significant time to install on a vessel, so often a fully pre-equipped survey vessel with swathe or real time MBSS installed will need to be mobilised.

Side-scan sonarSide-scan sonar (SSS) works by emitting a fan-shaped acoustic pulse through the water column. The beam is narrow in one plan (around one degree depending on the system) and wide in the other direction (typically between 35 to 60 degrees). The transducer is either towed behind a boat or mounted on the transom or hull of the vessel. To obtain an image from a SSS it is necessary for the vessel to move forward, so that each successive sonar ping will be positioned in front of the previous ping. In this way a series of images can be spliced together along the direction of travel to form a continuous image of the seabed identifying any objects on the bottom or in the water column.

Figure 6.12 Photo survey combined with MBSS (courtesy Port of London Authority)

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The foundation stone of the Admiralty Pier was laid on 2 April 1848 as the first stage in the proposed harbour of refuge at Dover for the Royal Navy (Figure 6 .13). Since then, the harbour has been developed with various modifications. In 1899 work started on extending the Admiralty Pier again as part of the new Admiralty Harbour, and in 1900 the extension of 2000 feet was completed bringing the total length to over 4000 feet.

Figure 6 .14 is a cross-section of Admiralty Pier.

As part of an asset evaluation exercise, the Dover Harbour Board (DHB) appointed the Port of London (PLA) survey unit to carry out a multi-beam sonar survey of all of the harbour breakwater structures (sub-sea) in 2006.

The results of the sonar survey of the Admiralty Pier, clearly showing the toe protection and dislodged blocks are shown in Figure 6 .15.

The survey of the southern breakwater also showed similar dislodged blocks on the toe protection (Figure 6 .16).

Figure 6.13 Overview of Dover harbour (courtesy Google Earth)

Figure 6.14 Typical section for the second extension of the Admiralty Pier (courtesy DHB)

Case study 6 .2 Breakwater surveys, Dover, Kent (courtesy HR Wallingford)

Figure 6.15 Sonar survey of Admiralty Pier showing large dislodged blocks on the toe protection (courtesy DHB)

Figure 6.16 Sonar survey of southern breakwater showing large blocks on the toe protection (courtesy DHB)

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In narrow rivers, canals or where the water depth would make it difficult to allow access for a full size boat, HR Wallingford (with the EA) have developed a radio controlled boat capable of undertaking bathymetry and SSS surveys, which can be used in locations that would otherwise be inaccessible (Figure 6.17) (see Websites).

The main advantage of SSS is the ability to quickly and efficiently generate images of large areas of the channel bottom. For this reason SSS is considered the tool of choice for large-scale survey operations. The primary limitation of SSS is the inability to easily generate full images of the vertical components of submerged structures. However, it is possible to obtain images of portions of vertical components of marine infrastructure with SSS. To achieve this, the transducer needs to be pole mounted and the transducer head needs to be rotated by 90 degrees. The quality of the image obtained is dependent on the operators’ ability to maintain a close and consistent distance to the structure and a constant speed while

manoeuvring the vessel along the structure. As a result sector scanning or MBES are generally considered better solutions for generating images of vertical components on submerged structures.

An example of a SSS record using a modern system is shown in Figure 6.18 for the sea floor immediately in front of the breakwater in Portland. The clarity of the rubble base of the breakwater should be noted, together with the fine detail of the sunken tender.

This example demonstrates the improvements made to SSS over

the past decade. The use of high frequencies (675 kHz) and colour graphics gives the best final product and a good visual presentation to the civil engineer. However, even simple low frequency systems may yield sufficient information, because their sonar frequencies of around 65 kHz will still give a reasonably clear picture of the sea floor.

Sector scanning sonarSector scanning sonar was used to investigate submerged structures many years ago. However, it was not until recently, with the development of alternative higher resolution imagery devices at much reduced costs, that sector scanning sonar has almost become obsolete.

Figure 6.17 ARC-boat capable of undertaking bathymetry, SSS and/or Acoustic Doppler Current Profilers (ADCP) measurements in shallow water depths (courtesy HR Wallingford)

Figure 6.18 SSS record showing wreck at toe of rubble mound in front of the breakwater at Portland (courtesy BGS)

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Sector scanning sonar works in a similar way to SSS in that a transducer emits a fan-shaped acoustic pulse through the water column. Unlike SSS, which requires vessel movement to develop an image, sector scanning sonar works best if the transducer remains stationary while the head is mechanically rotated. For this reason sector scanning sonar is usually deployed from a winch mounted on a trailer that is towed along the top of the wall. The transducer is lowered into the water at the chosen location and a trace is produced showing the profile of the wall below the water and the nearby sea or river bed. Voids under the toe can be measured, provided the transducer is positioned at a low enough level. The transducer can also be turned through 90 degrees to record horizontal profiles of the wall.

Figures 6.19 and 6.20 show a typical sector scanning sonar deployment for recording wall profiles. The detailed results shown in Figures 6.21 and 6.22 were obtained in Gloucester Docks. Another good example of the use of this type of equipment is shown in Figure 6.23, where the profile of a river has been obtained and the presence of undercutting on one bank is clearly demonstrated.

The main advantage of sector scanning sonar is the ability to produce detailed images of the sea bed and vertical components of submerged structures that extend from the seabed to the water surface. Sector scanning sonar can also be used before and during diving operations to direct the underwater team to potential anomalies. The main disadvantage is the limited range and the need to maintain the sonar head in a stable mounting position.

Figure 6.19 Deployment of dock wall profiling equipment (courtesy ABP Research and Consultancy)

Figure 6.20 Sector scanning sonar equipment deployed for wall profile measurement (courtesy SIMRAD Albatross Ltd)

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6.7.2 Light Detection and Ranging (LiDAR)LiDAR is used to make a high resolution 3D map. The system is usually mounted on a fixed platform or tripod while the LiDAR sensor rotates 360 degrees emitting a pulsed laser beam. It is a remote sensing technology that measures distance by illuminating a target with a laser and analyses the reflected light. The pulsed beam is reflected from objects such as building fronts, lamp posts, vegetation, cars and even people. The returned pulses are recorded and the distance between the sensor and the object is calculated. The data produced is in a ‘point cloud’ format, which is a 3D array of points, each having x, y and z positions relative to a chosen co-ordinate system.

LiDAR has been around for some time now and the technology has improved significantly since the early days. There are many case studies around that have used a range of vehicles (ie boats, quad bikes) to mount a LiDAR scanner to record the x, y, z data. The results are sometimes combined by stitching LiDAR data with digital imagery or to MBES data to produce a 3D image of an old waterfront all above and below the water surface. Figure 6.24 and 6.26 shows LiDAR data knitted with digital imagery.

For Gorey breakwater pierhead in Jersey, LiDAR surveys in 2009 and 2012 were compared to determine the actual structural movements that have occurred between the two survey dates (see Case study 4.1). Figure 6.25 shows the superimposed LiDAR models indicating locations of significant movement.

Figure 6.21 Profile of an arch wall in Gloucester Docks obtained with equipment shown in Figure 6.20 (courtesy Livesey and Henderson)

Figure 6.22 Typical harbour wall profile from equipment shown in Figure 6.20 (courtesy SIMRAD Albatross ltd)

Figure 6.23 Profile of a river obtained with sector scanning sonar equipment, showing undercutting of bank (courtesy Livesey and Henderson)

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Figure 6.24 Above surface laser knitted with digital imagery (courtesy Canal and River Trust)

Figure 6.25 Superimposed LiDAR models indicating locations of significant movement (courtesy Arup)

Figure 6.26 Combined LiDAR survey with digital imagery (courtesy Canal and River Trust)

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6.7.3 Unmanned aerial vehicles (UAVs)Inaccessible areas are difficult and expensive to survey, however, with access to innovations such as UAVs it is now possible to survey many inaccessible areas without the need for scaffolding, mobile platforms or cranes. This makes it a far more convenient and cost-effective way to complete initial condition surveys.

It has become commonplace to replace the name ‘unmanned aerial vehicle’ or UAV with the name ‘drone’ and historically these have been military vehicles. A UAV, which is a remotely operated aircraft, can vary widely in shape, size, configuration, and characteristics. Typically they are a lightweight, fixed wing or helicopter type aircraft (Figure 6.27).

Beyond the military applications, drones are now establishing themselves as platforms for civilian remote sensing activities. They have been used to aerial survey crops, in filmmaking, in search and rescue operations, to inspect power lines, survey pipelines, count wildlife and deliver medical supplies to remote or otherwise inaccessible regions.

Applications are diverse and vary depending on range and complexity of the drones. A basic UAV can be purchased for a couple of hundred pounds and operated via a smartphone or tablet, whereas a more ‘professional’ grade UAV is a registered aircraft and as such must be operated by a trained pilot.

The Canal and River Trust has used UAVs fitted with high definition cameras to get close-up visual surveys of structures, for example bridge soffits, aqueducts and river weir crest inspections, which are dangerous and inaccessible in most cases.

The benefits of UAVs are mainly in the ease, rapid deployment and relatively inexpensive cost relative to traditional techniques. For visual survey work the key benefits include:

ªª ability to gain access to inaccessible areas

ªª large areas can be covered in a single day of surveying

ªª health and safety implications of working over water and at height are reduced

ªª live images can be streamed to a monitor to make sure shots and viewing angles are correct

ªª camera can pan and tilt remotely to cover points of interest

ªª sophisticated GPS systems can be used to hover and maintain position

ªª relatively inexpensive to hire a professional drone with high definition (HD) imagery.

The limitations are:

ªª typically limited to wind speeds below 15 mph

ªª they do not generally operate in the rain because they are predominately battery operated

ªª have to kept in the line of sight

ªª maximum operating range/radius typically 500 m

ªª maximum height normally limited to 400ft, however sometimes possible to fly higher with special permission.

Use of UAVs is still in its infancy within the industry, but it is currently possible to use helicopter UAVs to undertake the following:

ªª create a 3D survey by using integrated GPS to knit the imagery to a CAD or similar point cloud overlay

Figure 6.27 Skypower drone used on Caen Hill Locks (courtesy Canal and River Trust)

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ªª attach instrumentation to measure crack widths and go back to tangible reference points

ªª carry our environmental surveys including bat surveys and/or evidence of badgers on inaccessible embankments

ªª include thermal imaging to map leakage paths within locks or embankments.

UAVs extend the use of digital technologies to capture data at height and in inaccessible areas, and they allow quick and easy investigation, interpretation and dissemination of information. The processed data they provide can be integrated into the latest technical survey and interpretation techniques. Their practical application in heritage interpretation, education and conservation is still in the early stages of being realised, but as the technology is used more applications will be realised.

6.7.4 Investigation by diversUnderwater investigation by divers was once the norm but with the development of acoustic techniques such as SSS and MBES, the need for diver inspection has significantly reduced. Today diver surveys are only usually undertaken to examine and verify particular defects or anomalies found in SSS/MBES surveys.

Diving work tends to be very expensive, because of the number of diving personnel required to satisfy health and safety regulations. The operations are frequently hampered by poor visibility, waves or currents, so it is more usual to limit the use of divers to the detailed investigation of specific problem areas of a wall.

Where a large area of wall is to be examined it is important that the divers have a reliable location system. This should consist of a method of obtaining longitudinal distances along the cope of the wall together with a method of measuring the vertical distance down from the cope level to the area of interest. There are two ways of achieving the latter:

ªª vertical, marked lines hung at one metre centres down the face of the wall

ªª a light metal frame suspended over the side of the wall.

In the UK all diving work is covered by the Diving at Work Regulations 1997 and the approved code of practice (ACOP) for commercial diving work inland/inshore (HSE, 2014) specifies exactly what is required to meet these regulations.

6.8 GROUND INVESTIGATIONS

6.8.1 GeneralIt is often the case that where a wall has been performing satisfactorily over a long period and there are no plans to develop the area that may affect the wall or its environs, then little attention is given to it. However, it may be a requirement to quantify the current state and potential longevity of a wall and this will require investigation. More often, investigation is triggered because some form of development is proposed, which may result in increased loading at the rear or providing deeper water at the front, or the asset is showing signs of distress.

These investigations need to determine the physical dimensions of the wall, either from original drawings and/or from field measurements, groundwater levels, and both the nature of the ground upon which the wall is founded and the ground in front of and behind the wall. For example:

ªª ground conditions below the wall will dictate sliding resistance, together with roughness of the base of the wall in contact with the ground

ªª ground in front of the wall will determine the restoring earth pressure (passive pressure)

ªª ground behind the wall will determine the disturbing earth pressure (active pressure)

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ªª water level variations in front of and behind the wall will determine hydrostatic loadings on and under the wall.

The ground conditions will also determine, via the coefficient of active or at-rest earth pressure, the proportion of horizontal force to be applied resulting from any surface applied vertical loading. Such loads are often positioned behind the wall and hence are normally applied as disturbing forces. Externally applied forces direct to the wall such as mooring loads are not determined by the ground conditions.

The first recourse is to the original reports and drawings, as discussed in Section 6.4. For old structures, any description of ground conditions may be vague, but might include an indication of strength, for example medium dense or dense for sands, soft, firm or stiff for clays. These descriptors can be assigned to approximate strengths to give an indication of wall stability.

Some old walls may have been constructed on timber grillages with timber piles beneath and this may not be revealed by discrete boreholes. The bearing capacity/sliding resistance might be greater than calculated using the soil strength revealed at the base of the wall. Determining whether such sub-foundations have been provided is difficult without original drawings but might provide an explanation for calculated ground bearing capacity being substantially below the applied loading of the wall.

6.8.2 IssuesOld waterfront structures have, by definition, been standing for many years, so it may seem unlikely that geotechnical problems would be a major concern. However, soil behaviour can be affected by a number of factors that change over time. Many of these are discussed in BS EN 1997-1:2004+A1:2013. The main geotechnical issues are summarised as follows:

ClaysThe following characteristics of clay are important in relation to the performance of walls:

ªª The strength of over-consolidated clays diminishes with progressive strain. It is possible for a slip surface to develop many years after construction.

ªª Some (medium to high plasticity) clays will exhibit volume change (swell/shrink) with changes in moisture content. There is a ready supply of water to waterfront walls and equilibrium moisture contents should soon develop. However, with cohesive backfills with little recharge from water at the front of the wall, effects such as planting of high water demand trees for environmental purposes can reduce moisture content and cause shrinkage.

ªª Clays under load may continue to consolidate over a long period causing wall settlement. This is particularly apparent with soils having a high organic content where secondary consolidation or creep occurs. High stress areas such as under the toe of the wall are likely to consolidate more than low stress areas such as at the heel, resulting in tilt.

ªª With low permeability soils such as silts and clays, any rapid reduction in water level (reduction in impounding level for instance) may lead to a reduction in the restoring force acting at the front of the wall while the disturbing force on the back remains essentially unchanged.

Sands and siltsWhere sand has been used as backfilling and has not been compacted adequately, the active pressure applied to a wall will be increased if the sand is subjected to vibration, such as an increase in traffic/vehicle loading or by re-routing of a road over a previously un-trafficked backfill.

Sands and silts, when in a loose condition and saturated, may also be susceptible to liquefaction when subjected to an appropriate shock or other input of energy such as an earthquake.

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Silts and fine sands with a relatively low permeability can be effectively weakened by groundwater movement and changes in pore water pressure. High upward flows of water through sand can cause ‘piping’ so that the bearing capacity is reduced. Silts can suffer frost heave where the water level is just below the silt, although this mainly affects surface paving rather than stability of the wall.

Softening of rocksIt is often necessary to reduce rock levels to form an adequate berthing pocket or to found the retaining wall. Such excavation will cause stress relief on the exposed rock surface and with sedimentary rocks can cause softening, a reduction in bearing capacity and also a marked reduction in sliding resistance. Such cases can be mitigated if load is to be reapplied by construction of the wall and its backfill, but passive resistance in front of the wall will remain reduced.

Inadequate FoS in original designAlthough Coulomb published his theory of earth pressure on retaining walls in 1773, for over 100 years after many wall designs were based on rules of thumb. Despite Rankine publishing his theory of earth pressures in 1857, in 1881 Sir Benjamin Baker derided theoretical calculation and stated that in his experience “the width of the base should be one-third of the height for a wall built in ground of average character” (Baker, 1881).

Even where Coulomb’s (or Rankine’s) theory was used, there were many problems in its application such as:

ªª The properties and strengths of the soils were not understood.

ªª Properties of the soil were not adequately investigated and measured.

ªª Inadequate FoS against overturning were used. For instance, Allen (1876) recommended that the resultant should be within the middle half as opposed to the middle third of the base. It was French practice to keep the resultant within the middle three quarters of the base.

ªª Methods taking account of ‘designed’ backfilling and of the effects of counterforts were not available. Some difficulties in analysis of these types of wall continue today, although the developing use of 3D finite element techniques is advancing analysis.

ªª Methods of assessing the FoS against a deep slip were not developed so there were several wall failures during or shortly after construction. Many others have been left with a low FoS.

The result of such problems is that when old waterfront walls are investigated and analysed by conventional modern techniques, it is not unusual to find they have FoS below those recommended in modern ACOPs or standards, and sometimes below unity.

6.8.3 Type of investigationsInvestigations would normally comprise boreholes together with trial pits. These might be augmented by cone penetration, geophysical or pressuremeter testing. Boreholes and particularly the use of trial pits, can also give information on wall shape.

BoreholesBoreholes enable direct observation of the soils/rocks encountered, enable in situ testing to be carried out (most commonly standard penetration testing (SPT), and the recovery of samples for subsequent examination and testing in a laboratory.

Normal practice is to carry out a SPT (followed by an undisturbed sample in clays) at each change of stratum and at 1.5 m intervals thereafter. The interval can be varied for particular locations – for shallow holes the frequency is increased to obtain more data.

Boring in front of the wall can be achieved using a cantilever frame from the wall cope, provided the toe of the wall does not project far beyond the wall. Boreholes can be undertaken at the rear, which will reveal both the backfill materials and the in situ natural ground beneath. If ground conditions are

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uniform, it may be possible to infer the original ground conditions below the wall from the information obtained from the back and front of the wall.

Information on ground conditions beneath the wall may be obtained from a borehole starting from the top of the wall and may also provide some data on the shape of the wall. For high mass gravity walls, this might require a considerable amount of drilling, though use of a rock roller bit can speed up the process if continuous core samples of the concrete/masonry are not required. For ‘L’ shaped reinforced concrete cantilever walls, the initial bore through the backfill will need to be continued by rotary drilling through the heel and then revert to boring in original ground. Selection of a rig that can carry out these operations is desirable.

Embedded walls, relying on sufficient penetration and their flexural strength for stability such as sheet pile and piled walls, require the ground conditions at the front and back of the wall to be determined. Such walls might still be retaining backfill placed to achieve the required cope level, but much of the existing original ground at the back might have been kept.

Trial pitsTrial pits will provide information on the backfill behind a wall, though the depth achieved might be limited unless shoring is used. Pits might also be terminated by water entry. The use of trial pits allows direct examination of the ground over the depth of the pit, and also allows disturbed samples to be recovered for classification testing in the laboratory. Trial pits have the benefit of not being expensive, so more can be carried out. A drawback is the reinstatement required to any pavement because the pit will disturb the existing surface area.

In situ strength testing carried out in pits is normally limited to probing, which then need to be correlated with strength. Samples can be compacted in the laboratory to a field density recorded in the pit and then tested in a shear box to give an indication of strength parameters.

Features such as puddle clay behind the wall and the presence of buried temporary works and debris all tend to complicate investigation of the backfilling, but these are better overcome by use of trial pits rather than by boreholes. Depending on the backfill material and water level it may, for lower height walls, be possible to extend pits to the base of the wall (shoring the excavation as necessary) in order to reveal the presence of any timber grillage/piled foundations and their condition.

These investigations, particularly pitting behind the wall, can form part of the investigation of the wall shape and condition as well as enabling samples to be collected of the wall material. The holes can also be used as part of any geophysical investigation and their positioning may need adjustment to get the maximum gain in data.

GroundwaterGroundwater levels, particularly behind the wall, affect the disturbing pressures on the wall. Unlike soil, which although of greater density frequently has active earth pressure coefficients less than unity, water pressures are hydrostatic. So they have a significant influence on wall stability. Uplift water pressures on the base of a wall reduce its sliding resistance.

In low permeability soils, a rapid drop in water level in front of the wall can leave elevated water levels behind the wall, increasing disturbing forces at the same time that restoring water level in front of the wall decrease.

Investigation gives the opportunity to install piezometers within the backfill and ideally below the base of the wall. Depending on ground conditions, these would ideally be piezometers with fast response transducers, such as vibrating wire or pneumatic instruments. These should give the maximum water pressures under tidal conditions. These data are required to assess wall stability.

Use of transducers allows data to be collected over tidal cycles (spring and neap tides) to measure groundwater response to such variations.

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InstrumentationFor mass gravity walls, deformation within the rigid wall should be minimal and only shear deformation at the base and tilt is likely to be recorded. Data might be obtained by surveying points along the cope of the wall for x y z co-ordinates – points also measured along the rear of the wall would also indicate any tilt.

Boreholes put down for investigation may also be used for the installation of inclinometers to enable measurement of any ongoing lateral deformation of a wall or development of any global overall slip failure.

For flexible walls, such as sheet pile or tubular walls, an inclinometer installed juxtaposed to the wall would provide any lateral deformations along the vertical length of the wall and may assist in determining its present condition.

Inclinometers should extend to a depth where no lateral movement is anticipated. Otherwise, it will be necessary for the top of the instrument to be surveyed each time of reading so as to determine total lateral movements.

Recent development in inclinometer technology has allowed instruments to be installed and monitored remotely. Earlier instruments required an operator each time the instrument was recorded. Remote monitoring can reduce overall costs of retrieving data.

Geophysical investigationsFurther information on substrata may be gained from geophysical methods and this may be an economic way of augmenting the information obtained from other investigation methods, particularly if geophysics is being used to define the shape of the wall or to identify voids or other features. Techniques for use of geophysical methods to investigate waterfront walls are described in Sections 6.5 to 6.7.

Further information on geophysical investigation techniques is also given in McDowell et al (2002), presenting a logical sequence through the process of using geophysical investigation methods in site characterisation.

6.9 GEOTECHNICAL PARAMETERSParameters for strength and compressibility should be derived from the in situ and laboratory testing carried out during the ground investigation. The parameters determined will be used in the stability analysis of waterfront wall as outlined in Section 7.4.

SPTs can be used in granular materials to assess relative density and strength (angle of friction). Disturbed samples can be re-compacted in a shear box in a laboratory to give a direct value of angle of friction. Several tests at varying density might be necessary to establish an appropriate value for use in design or back-analysis. The SPT can also be carried out in cohesive soils to estimate undrained shear strength via established correlations.

Strength of cohesive soils is normally determined by triaxial tests in either undrained or drained shear. It is essential that the appropriate strength is used in design or back-analysis and a geotechnical engineer should be consulted over choice of parameters.

Compressibility of cohesive soils is carried out in the laboratory using an oedometer. Again, for interpretation of parameters, a geotechnical engineer should be consulted.

Parameter values of several different types of soils are given in various text books and these could be used for assessing strength or compressibility when only a visual description of a material is available. Unfortunately, descriptions of strength based solely on a visual assessment are highly subjective and should be used with great care.

A number of general reference books and guidelines are available to give the reader guidance on current good practice for the design of maritime infrastructure (see Further reading).

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ReferencesALLEN, J (1876) Design and construction of dock walls, E & F N Spon, London, UK

BAKER, B (1881) “The actual lateral pressure of earthwork” Minutes of the proceedings, vol 65, 1881, Institution of Civil Engineers, London, pp 140–186

BRADBURY, A, ROGERS, J and THOMAS, D (2012) Toe structures for coastal defences – a management guide, SC070056. Environment Agency, Bristol (ISBN 978-1-84911-290-1). Go to: http://tinyurl.com/mnnfp2k

BRAY, N and TATHAM, P F B (1992) Old waterfront walls – management, maintenance and rehabilitation, B13, CIRIA, London, UK (ISBN: 978-0-86017-392-2). Go to: www.ciria.org

COOPER, N and COOKE, S (2015) Assessment and management of UXO risk in nearshore and offshore environments, C754, CIRIA, London, UK (ISBN: 978-0-86017-760-9). Go to: www.ciria.org

COOPER, N J, BOWER, G, TYSON, R, FLIKWEERT, J J, RAYNER, S, HALLAS, A (2013) Guidance on the management of landfill sites and land contamination on eroding or low-lying coastlines, C718, CIRIA, London, UK (ISBN: 978-0-86017-721-0). Go to: www.ciria.org

CRUICKSHANK, I and CORK, S (2005) Construction health and safety in coastal and maritime engineering, SCHO0405BJAS-E-P, Thomas Telford, London, UK (ISBN: 0-72773-345-1). Go to: http://tinyurl.com/k93rfy3

DfT (2006) Design manual for roads and bridges, volume 3 Highway structures; inspection and maintenance. Section 4 Assessment Part 9 BA 55/06 The assessment of bridge substructures and foundations, retaining walls and buried structures, Department for Transport, London, UK. Go to: http://tinyurl.com/pu86jdp

HR WALLINGFORD (1992) Hydraulic aspects of bridges: Assessment of the risk of scour, Report EX2502, HR Wallingford, Oxon, UK

HSE (2014) Commercial diving project inland/inshore. Diving at Work Regulations 1997. Approved Code of Practice and guidance, L104, Health and Safety Executive, London (ISBN: 978-0-71766-593-8). Go to: www.hse.gov.uk/pubns/priced/l104.pdf

KIRBY, A M, ROCA, M, KITCHEN, A, ESCARAMEIA, M and CHESTERTON, O J (2015) Manual on scour at bridges and other hydraulic structures, second edition, C742, CIRIA, London, UK (ISBN: 978-0-86017-747-0). Go to: www.ciria.org

MCDOWELL, P W, BARKER, R D, BUTCHER, A P, CULSHAW, M G, JACKSON, P D, MCCANN, D M, SKIPP, B O, MATTHEWS, S L, ARTHUR, J C R (2002) Geophysics in engineering investigations, C562, CIRIA, London, UK (ISBN: 978-01-86017-562-9). Go to: www.ciria.org

PIANC (1997) Guidelines for the design of armoured slopes under open piled quay walls, Report of Working Group 22, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/publications.php

PIANC (2008) Considerations to reduce environmental impacts of vessels, Report of Working Group 27, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/publications.php

Statutes

British StandardsBS EN 1997-1:2004+A1:2013 Eurocode 7 Geotechnical design. General rules

Further readingARBEITSAUSSCHUSS (eds) (2012) Recommendations of the Committee for Waterfront Structures: harbours and waterways (EAU 2004), eighth edition, Wiley, London, UK (ISBN: 978-3-433-60144-0)

BAW (2005) Principles for the design of bank and bottom protection for inland waterways, Mitteilungen 88, Federal Waterways Engineering and Research Institute, Karlsruhe. Go to: http://tinyurl.com/qdhnv5b

CIRIA; CUR; CETMEF (2011) The Rock Manual. The use of rock in hydraulic engineering, C683, CIRIA, London, UK (ISBN: 978-0-86017-683-1). Go to: www.ciria.org

CUR (2005) A handbook quay walls, CUR 211E, Taylor and Francis Group, The Netherlands (ISBN: 978-0-41536-439-3). Go to: http://tinyurl.com/ouprk5r

PANNELL, J P M (1964) An illustrated history of civil engineering, Thames & Hudson, London, UK

PIANC (1998) Life cycle management of port structures – general principles, Report of Marcom Working Group 31, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/publications.php

PIANC (2001) Seismic design guidelines for port structures, Report of Working Group 34, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/publications.php

PIANC (2003) Guidelines for managing wake wash from high-speed vessels, Report of Marcom Working Group 41, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/publications.php

PIANC (2003) Considerations to reduce environmental impacts of vessels, Report of Working Group 27, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/publications.php

PIANC (2014) Harbour approach channels design guidelines, Report of Marcom Working Group 121, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/publications.php

PIANC (2015) Guidelines for vessel induced scour at berthing structures, Report of Marcom Working Group 48, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/publications.php

REVILLA, J A, JUANES, J A, ONDIVIELA, B, GÓMEZ, A G, GARCÍA, A, PUENTE, A, CARRANZA, I, GUINDA, X, ROJO, J, LÓPEZ, M (2007) Recommendations for Maritime Works. ROM 5.1-05. Quality of coastal waters in port areas, Ministry of Development. Spanish National Port Administration, Madrid, Spain. Go to: http://tinyurl.com/prdh9xj

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STRAUB, H (1952) History of civil engineering, Leonard Hill, London, UK (ISBN: 978-0-26269-005-8)

SUTHERLAND, R J M, HUMM, D and CHRIMES, M (2001) Historic concrete: background to appraisal, Thomas Telford Ltd, London, UK (ISBN: 978-0-72772-875-3)

USACE (2003) Coastal engineering manual, EM 1110-2-1100 (2003), US Army Corps of Engineers, Reston VA, USA. Go to: http://chl.erdc.usace.army.mil/cem

WebsitesCanal & River Trust: https://canalrivertrust .org .uk/history

Comisiwn Brenhinol Henebion Cymru: www .rcahmw .gov .uk

English Heritage: www .english-heritage .org .uk

Historic Scotland: www .historic-scotland .gov .uk/index .htm

HR Wallingford ARC boat: www .hrwallingford .com/expertise/arc-boat

Institution of Civil Engineers: www .ice .org .uk/topics/historicalengineering

Local heritage societies: www .local-history .co .uk/Groups

The Archon Directory: www .archon .nationalarchives .gov .uk/archon

The National Archives: http://discovery .nationalarchives .gov .uk

National Register of Archives: http://tinyurl .com/pxcs88d

Network Rail: www .networkrail .co .uk

Royal Institute of British Architects (RIBA): www .architecture .com/Explore/Home .aspx

UK Hydrographic Office Admiralty Tide Tables: http://tinyurl .com/p27l87o

University of Birmingham Mapping the Underworld: www .mappingtheunderworld .ac .uk

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7 Physical processes and assessment tools

7.1 OVERVIEWThis chapter discusses the physical processes and assessment tools available to carry out the structural appraisal of old waterfront walls, with particular emphasis on the hydrostatic and hydrodynamic loadings that may be experienced.

Figure 7.1 provides an overview of the chapter.

Management actionsAdministrative context

Physical context

Severe event(Section 5 .5)

Management of risk(Sections 2 .1 to 2 .3)

Responsibilities (Section 2 .4)

Powers(Section 2 .5)

Beneficiaries(Section 2 .8)

Funding(Section 2 .9)

Physical form and purpose

(Chapter 3)

Physical processes (Section 6 .3)

Loads(Sections 7 .1 to 7 .3)

Wall stability(Section 7 .4)

Historical data(Section 6 .4)

Framework for decisions (Section 4 .3)

Risk analysis(Section 4 .4)

Performance assessment(Section 4 .5)

Operations(Section 5 .2 to 5 .3)

Monitoring and inspection

(Sections 4 .6 to 4 .7)

Data acquisition (Section 4 .7)

Data management (Section 4 .8)

Wall investigation (Sections 6 .5 to 6 .9)

Decision on intervention

Maintenance, repair and rehabilitation (Sections 5 .4 and

Chapter 8)

Regulations and consents

(Sections 2 .6 to 2 .7)

Figure 7.1Overview of Chapter 7

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Section 7.2 introduces the key principles and issues discussed in this chapter, including the assembly of available data, a diagnostic approach to evaluation, identification of non-critical defects and issues relating to old waterfront wall analysis. It also provides links to other chapters.

Section 7.3 discusses the multiple hydraulic processes, both hydrostatic and hydrodynamic, that impose loading on an old waterfront wall. These processes include static water pressures in front and behind walls, wave run-up and overtopping, overflow, wave forces, including the prediction of types of wave loads, including pulsating (or non-impulsive) wave loads, impulsive wave loads, broken wave and bore wave conditions scour in rivers, canals and waterway channels, scour in front of shoreline and coastal structures.

Section 7.4 considers the methods that can be applied to undertake the stability analysis of waterfront walls, taking into account all the loads, including hydrostatic and hydrodynamic loads, which can be applied. The section refers to appropriate COP, loading and strength parameters and modes of failure, including deep slips, overturning and sliding and considers bearing pressures, the influence of counterforts and dewatering and appropriate FoS.

7.2 KEY PRINCIPLES AND ISSUES

7.2.1 IntroductionAt the start of a structural appraisal, it is necessary to establish whether the information at hand is sufficiently comprehensive to determine which modes of failure or deterioration are likely, and those that are unlikely. A clear picture of the condition of the wall and any adjacent relevant infrastructure and services should be available to act as a baseline against which further deterioration can be assessed. This is particularly relevant where, for example, buried water or sewage pipelines behind the wall may be fractured or leaking, causing unknown or unidentified hydrostatic pressures behind the wall, or where significant undermining of a wall as a result of scour, cannot be easily observed. Such ‘hidden’ effects can lead to sudden and serious failures.

A recommended procedure for carrying out an evaluation of the stability of a waterfront wall is shown in Figure 7.2 and comprises the following steps:

1 Assemble all the available data.

2 List all the apparent symptoms of degradation and changes in the condition of the wall.

3 Identify possible failure modes.

4 Use the diagnostic approach (see Section 7.2.3) to identify those causes that may be resulting in the effects (symptoms) listed.

5 If necessary, carry out stability evaluation for the various possible modes of failure.

6 Divide the wall defects into critical and non-critical.

7 On the basis of the function of the wall and its environment establish which risks to its stability and deterioration are foreseeable and determine the probability of these risks occurring.

8 Determine whether the identified risks may be controlled or mitigated.

9 Forecast the effects of continuing deterioration on the wall’s future performance.

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7.2.2 Assembly of available dataBefore attempting to carry out an evaluation of the stability of a waterfront wall, it is essential that the maximum amount of data has been assembled relating to the wall and its surroundings. In particular, detailed information concerning the history of the wall, its original design, construction, and subsequent performance is of great benefit in the evaluation process.

Information may be classified as follows:

ªª Historical information, records and drawings relating to the design, construction, repair, maintenance and performance of the wall.

ªª Current and recent information on the behaviour of the wall as presently used, such as might be revealed by any routine inspection or monitoring.

ªª Information relating to the environment in which the wall is situated, including hydraulic regime, soils data, existing services etc.

ªª Information relating to the present level of service, including a definition in terms of the size and frequency of occurrence of loads imposed on the wall.

ªª Detailed investigation results including an assessment of their reliability and an estimate of how representative they are of the length of wall to which they apply.

ªª Information relating to the apparent degradation of the wall such as deterioration or loss of materials, temporary and permanent movement of the structure, movement of the surrounding ground, scour or undermining etc.

It is common to find conflicting information at this stage. For this reason it is important that the reliability of the data should be carefully assessed before the main stability evaluation.

A Assembly of data

c Identificationofpossiblemodes of failure

E Stablity evaluation of possiblemodeoffailure

B Identificationofsymptomsof any distress

D Diagnosticapproachtoestablishcausesofanydistress

F Identificationofnon-critical wall defects

I) Forecast effects of continuing deterioration on wall’sfutureperformance

G Assessmentofprobabilityof failure due to foreseeable risks

H Can risks be minimised?

Figure 7.2 Flow chart showing typical stability evaluation procedure

Consider archived researchMoney spent on detailed archival research may be of considerably greater use in the evaluation process than the equivalent sum spent on conventional site investigation. This is particularly true if the historical search is carried out early on in the investigation.

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7.2.3 Diagnostic approach to evaluationThe evaluation of a wall’s condition calls for a process of deduction, which is partly intuitive and partly logical. Where distress is apparent, and the cause is similarly obvious, the evaluation process may be straightforward; although the stability evaluation may be complicated by the existence of non-standard forms of construction.

However, in many cases while there may be a number of distinct signs of distress, the cause and the mode of failure that has been initiated may be unclear. Often the most obvious signs of distress prove to be localised degradations of the wall or adjustments to wall shape that occurred in the past but do not necessarily signify a decline in the wall’s overall integrity or stability.

It is suggested that a diagnostic approach should be used to identify the causes of any wall distress. This approach will not only help to identify the underlying causes of the real distress but, almost as importantly, will also allow the ‘non-critical defects’ to be logged for future reference. Non-critical defects are those that do not affect the serviceability of the wall and will not lead to progressive degradation.

In simple cases the diagnostic approach is based on a list of identified defects set against possible causes, as given in Table 7.1.

Table 7.1 Diagnostic approach to wall failure – simple cause and effect examples

Cause Effect

Freeze-thaw cycles Decay of wall material

Alternate wetting and drying Decay of wall material

Wave erosion Deterioration of wall

Wave impact Deterioration of wall

Vessel wash erosion Undermining of wall

Acid water attack Decay of wall material

Erosion by water passing through the wall Deterioration of wall

Vegetation/plant root damage Deterioration of wall

Poor quality of original stone, brick, concrete or mortar Decay of wall material

Alkali/aggregate reaction in concrete Decay of wall material

Abrasion by wave driven gravel Loss of wall thickness

Ship impact damage Cracking and break-up of cope

Low level impact from bulbous bows Cracking and impact damage just above and below water-line due to vessel belting or other projections

Propeller or bow thruster scour Damage to face material and undermining of toe

Wave/current action Undermining of toe

For more complex cases a matrix is suggested in Table 7.2 relating to the:

ªª evidence of failure

ªª type of failure

ªª possible causes of problem.

The matrix is used by marking the items of ‘evidence’ and identifying which type of failure corresponds to the combination of items of evidence. At first not all items of evidence may have been identified and the wall may need to be rechecked. At the bottom of the matrix is a list of ‘possible causes of problem’ – usually only one of which could have been the actual cause. Occasionally a wall may have more than one cause of distress, eg the cutting of a tie rod may only reduce a FoS, with the wall suffering distress later when excessive loads are placed on the backfilling. Another possible joint cause of failure is the loss of

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integrity of internal material/heartening leading to bulging and cracking, which is common in rubble heartening where lime mortar has been washed out due to water flows through the structure. The possible causes of problem are further expanded and explained in Table 7.3.

Table 7.2 Matrix relating evidence, types of failure and possible causes of problem

Evidence of failure

Bulging in cope line X X X X X

Horizontal movement X X

Vertical cracks X X

Bulging in face of wall X X X X

Settlement of backfill X X X X X

Forward rotation of wall X

Vertical or sloping crack with greater displacement at top X X

Settlement of cope X X X

Backward rotation of wall X X

Cracks in backfill parallel to wall X X

Fences/lamp posts out of line or out of vertical X

Forward rotation of top of wall X X

Vertical or sloping crack in top part of wall X X

Type of failure

Hor

izon

tal

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ing

Ove

rtur

ning

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Possible cause of problem

Loss of strut to toe of wall X X

Erosion or decay of mortar X

Crack in wall X

Failure of tie rod X X X X

Decay of timber pile or grillage X X

Softening of soil/rock under foundation X X

Scour X X X X

Excessive vertical loading on wall X X

Excessive bollard pull X X X X X

Drawdown of water in front of wall X X X X X X X

Raising of water level behind wall X X X X X X X

High superimposed load on backfill X X X X X X X X

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Table 7.3 Detailed possible causes of problem

Effect Possible cause

Erosion or decay of mortar

ªª freeze-thawªª wave erosionªª vessel wash erosionªª acid water attackªª erosion by water passing through wallªª propeller or bow thruster scourªª vegetation/plant root damageªª mortar washed out due to water flows through structureªª poor initial quality.

Crack in wallªª caused by other type of failureªª loss of integrity of internal material/heartening.

Failure of tie rod(s)

ªª corrosionªª damage by trafficªª accidental or deliberate cuttingªª accidental excavation in front of anchorageªª increase in lateral pressure on wall due to surcharge on backfill.

Decay of timber pilesªª exposure to atmosphereªª changes in water level.

Softening of soil/rocks under foundationªª long-term weatheringªª effects of exposure.

Scour

ªª wavesªª currentsªª littoral driftªª over-dredgingªª deliberate removal of beach materialªª bow thruster scourªª propeller scourªª movements of vessels with small underkeel clearanceªª loss of scour protection.

Excess vertical load on wall

ªª mobile cranesªª RoRo rampsªª heavy unit loadªª overtopping waves.

Excess horizontal load on wall

ªª dredging wiresªª construction activitiesªª high winds on moored vesselªª misuseªª wave impact loads.

Drawdown of water in front of wallªª failure of dock or lock gateªª conversion from impounded to tidal or semi tidal dockªª leakage from canal.

Raising of water level behind wall

ªª broken water mainªª new soakawaysªª broken surface water drainªª discharge from contractors pumpsªª connection to other body of waterªª effect of cut-off wallsªª wave overtopping and failure of waterproofing on top of fill.

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Effect Possible cause

High superimposed load on backfill

ªª stacking bulk materialsªª stacking of containersªª high density materialsªª heavy mobile cranesªª road traffic and vibrationªª large unit loadªª large volumes of water from wave overtopping.

7.2.4 IdentificationofcrackdamageWhere there are cracks in the wall, they should be examined for evidence of their cause. Particular points to note include:

ªª the crack widths

ªª whether a crack is wider at one end

ªª the pattern of cracks

ªª the depth of the cracks

ªª the position of cracks in relation to restraints in movement such as exterior or interior corners or changes in wall section

ªª the displacement forward of one side in relation to the other and whether the displacement is uniform along the crack

ªª seasonal or tidal variations.

Some interpretations of cracks, although not exhaustive, are given in Figure 7.3. A typical example of where a crack can be used to determine how a wall has behaved is shown in Figure 7.4. The crack is of uniform width from top to bottom, and one side of the crack stands proud of the other side (as evidenced by the sunlight striking the inner face), so it is possible to deduce that the whole of the wall to the left of the crack has moved forward.

The diagnostic procedure may need to be carried out more than once for a particular length of wall if there are different types of defect to be considered. It may also have to be done in conjunction with a stability analysis as described in Section 7.4.

Figure 7.3 Typical crack formations and their causes

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7.2.5 IdentificationofwavedamageWave loading is a key component governing the stability of exposed blockwork breakwaters and seawalls, which is discussed further in Section 7.3. Wave forces (whether slowly acting of pulsating nature, or short-duration high-intensity impulsive) are particularly relevant when assessing the overall stability of breakwaters and sea defences where there may not be retained fill behind the structures and are more susceptible to sliding or overturning. Methods for analysing the stability of walls are given in Section 7.4.

However, as well as the direct influence of wave loading on the stability of seawalls and breakwaters, other hydrodynamic effects can be identified that may affect the long-term stability of the structure. Some examples are:

ªª Scouring of the toe: wave action, particularly during storms, can cause erosion and accretion of the seabed around the toe of a coastal structure. The highly reflective nature of a vertical or near vertical wall can exaggerate this process leading to walls being undermined, where scour has removed material from under the seawalls base, allowing the stone work to shear under self-weight or wave action. It is important to note that the scour depth during a storm will always be lower, perhaps by some metres, than when the storm abates and/or the water level falls.

ªª Degradation to wall surfaces and upstands: it is worth considering that the waves can entrain objects, effectively increasing the wave’s ability to cause damage to the structure. An example of the prolonged effect of waves smashing pebbles and rocks against a seawall is shown in Figure 7.5.

ªª Composite structures: the influence of placing structure elements within the path of up rushing water on the face of a vertical or near vertical wall, needs careful consideration. Water running up the front of a vertical wall can carry considerable momentum, particularly when the wave breaking can be categorised as impulsive.

Figure 7.4 Vertical crack clearly indicating forward movement of whole section of wall, Bowling Lock, Forth and Clyde Canal (courtesy British Waterways)

Figure 7.5 Storm damage to seawall (courtesy HR Wallingford)

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ªª Block removal: individual block removal is often an important cause of problems on old blockwork walls. The processes for the loss of individual blocks are not always fully understood, but two mechanisms may contribute:

ª� ‘pulsating’ negative forces (relative to the ‘no waves’ condition) will apply a net outward force to the lower part of the wall during wave draw-down, so that hydrostatic pressure from water retained inside the wall act on the back of the block. These forces vary over the same time and spatial scales as the waves themselves, so will often be relatively wide-spread over the wall. Under oblique attack, these forces will travel along the wall

ª� short-duration impact pressures of waves being transmitted back into the wall through joints, then acting on the rear face of the block, causing a block to pop out. The potential loss of individual blocks can often be mitigated by ensuring that the blocks are well keyed in with sound mortar, there are no open joints or cracks visible that would allow wave pressures to act on the rear faces of the blocks, and that the internal fill is compact and relatively impermeable. It is worth noting all areas of outward block movement from the plane of the wall because this can often indicate where a ‘disguised void’ has been created by washout of fine material from the core fill behind the wall, ie as at St Catherine’s breakwater (see Case study 6.1)

ªª Other wave impact effects: wave impacts may also result in sudden increases in internal water pressures in the backfill or drainage systems at the back of a wall, leading to paving slabs or drain covers behind the wave wall being thrown some metres into the air. These problems pose a serious safety risk and, if unchecked, a threat to the overall integrity of the structure. These threats can again be mitigated by ensuring there are no open joints or cracks, which would allow water to enter under pressure, and that any open drainage or weep holes are not directly leading to vulnerable spots behind the wall. If the drainage is for surface water runoff via man-holes, then consideration should be given to provision of flap valves on the surface of the wall.

ªª Identification of non-critical defects: one method of identifying non-critical defects is given in Section 7.2.3. However, there are many other ways in which similar information becomes apparent. It is particularly important to list all the non-critical defects that are discovered because this may well save a considerable amount of time and money at a later date when another evaluation is being carried out.

In the past, maintenance work was given low priority and staff engaged in this work changed over a period of time, so it is quite common to find that non-critical defects are the cause of much timewasting and alarm. This in itself is more than enough justification for the small amount of effort and cost required for the proper logging of these defects.

In many cases a regular and consistent inspection programme will be all that is required to establish whether defects are critical or not, because it will be possible to show whether (and how) the defects have deteriorated between one inspection and the next. For particular defects, for example cracks, specific monitoring can be carried out using Tell-Tales fixed across the crack to monitor any movement. Detailed recommendations on relevant inspection regimes and frequencies to monitor defects are given in Chapter 6.

7.3 HYDRAULIC FORCES ACTING ON WATERFRONT WALLS

7.3.1 IntroductionHydraulic loads acting on a waterfront wall can be split up into two primary categories:

ªª Hydrostatic forces typically consist of difference in static head of water across the walls’ cross-section, for example,e tidal lag or local groundwater behind a sea or quay wall. Difference in head across lock walls as the lock water level is lowered during operation is also a possible load case. Differences in head of water can also occur across breakwaters if harbour layouts or hydrodynamic

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processes allow for differing water levels on each side of the structure (see Section 7.3.2).

ªª Hydrodynamic forces can be separated into a number of different categories depending on the nature of the loading (waves, currents), and wall interaction (see Sections 7.3.3).

7.3.2 Hydrostatic forcesThe hydrostatic forces are the horizontal forces produced by water acting perpendicular to the surface of the object containing it (eg a blockwork wall). The pressure that water exerts on a vertical surface can be calculated by multiplying the density of water, γ = ρg, × the depth of water at the point of interest, y (see Equation 7.1). The pressure varies linearly with depth increase as shown in Figure 7.6. The water density may be assumed constant for depths associated with landward side of the waterfront wall, but will be determined by whether the water body is composed of fresh, brackish, or seawater in the case of rivers, estuaries, and oceans, respectively.

7.1

The horizontal forces act at the centroid of the pressure distribution, which is 2/3 × h below the water surface (for a vertical wall). In general, the force at any point on a vertical wall is a function of the depth of water to the point of interest.

There is always a level of uncertainty associated with estimating the differential head, as the level of the groundwater and ability for water to pass through or around the structure can be difficult to estimate.

7.3.3 Hydrodynamic forcesWave loading is considered a key component governing the stability of exposed blockwork breakwaters and seawalls, and for some quay walls subject to action of swell waves. This section describes some of the more widely used methods to predict wave forcing acting on such vertical breakwaters and seawalls. A description of the various categorisations of wave loads is given along with associated prediction methods. The majority of prediction methods have been developed for vertical caisson breakwaters using small-scale Froude similarity tests, but are equally applicable to any solid vertical waterfront wall or breakwater structure.

The main component of the hydrodynamic force is formed by the bulk of the wave, which is the non-breaking or pulsating wave form, causing a change in water elevation over a cycle of a wave length. In addition to this component, wave dynamics can change, with additional processes going on or changing the underlying pulsating wave characteristic. These components are typically:

ªª impulsive breaking or impact

ªª broken waves

ªª post breaking or bore waves.

Impacting wave loads are typically of high intensity, 10 times or more greater than the pulsating load, and normally have a duration that is a fraction of the pulsating wave load duration. They are generally considered to be relatively limited in extent, not acting over larger areas, and mainly focused around the still water level.

The hydrodynamic forces acting on exposed waterfront walls generally fall into one or more of the following cases:

Figure 7.6 Hydrostatic pressures acting on a gravity wall

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ªª landward acting horizontal pulsating force Fh max

ªª seaward acting horizontal pulsating force Fh min

ªª pulsating uplift force Fu acting on the base of the wall if placed on a rubble mound

ªª landward acting horizontal impulsive/impact force Fh imp

ªª seaward acting short-duration impulsive negative pressures (seldom formally predicted).

It has been appreciated for many years that apparently similar wave conditions may give rise to dramatically different wave pressures or forces depending on the form of wave breaking at, onto, or close to the wall. Under wind waves, there will inevitably be a wide range of wave breaking, but it is generally convenient to use three or four categories of wave load/breaking conditions:

ªª non-breaking or pulsating

ªª impulsive breaking or impact

ªª broken waves

ªª post-breaking or bore waves.

Wave pressures on a vertical wall for two of these breaking types, non-breaking (ie pulsating) and breaking (ie impulsive) are given in Figure 7.7. The simplest case (type a) is generally when the wave is non-breaking, also termed reflecting or pulsating. For this condition, the wave motion is relatively smooth, and the main processes can be predicted by simple wave theories. Simple prediction methods for pulsating wave loads by Goda (2010) generally predict average pressures up to about pav = 2ρgHs where Hs is the incident (local) significant wave height.

Figure 7.7 Example wave pressure traces on a vertical wall with toe berm: model test results (after Allsop et al, 1996)

The most intense wave forces/pressures arise if the wave can break directly against the wall, termed plunging, breaking, impulsive or impact (type b). This may particularly occur where a steep slope (natural or artificial) approaches the toe of the wall. Research studies in Europe have measured local wave impact pressures up to or greater than pimpact =40ρgHs, much higher than would be predicted by simple design methods (see Allsop et al, 1996b, 1996c, and Allsop and Vicinanza, 1996). In extremis, tests by Kirkgoz (1995) suggest impact pressures up to pimpact =100ρgH, although these are highly unlikely in practice. Such high pressures will not act statically, so identifying their potential influence will generally require some form of dynamic analysis.

Impulsive breaking is strongly influenced by any mound, berm, or steep bed slope in front of the wall with conditions difficult to predict, and producing significant variability/uncertainty. In the past, these variations have led to significant lack of clarity in advice on wave forces.

Rather lower forces arise if waves have already broken before reaching the wall (type c). The wave motion is turbulent, but often highly aerated. Predictions of broken wave loads are uncertain, with relatively few laboratory or field data.

 

0

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The last class is the post-breaking or bore wave (type d) usually applied to a wall where the toe is above the static water level, but where the run-up bore can still reach the wall. Broken waves occur when the local water depth is insufficient to support unbroken waves. For simple vertical walls with no significant mound, waves may start to break when the local wave height to depth exceeds (say) Hsi/d>0.35. As local wave conditions approach the breaking limit, so the proportion of broken waves increases, and the probability of a large but unbroken wave reduces.

7.3.4 Predicting types of wave loadA method to identify occurrence of some types of breaking, and wave load, was developed in the PROVERBS project (Oumeraci et al, 2001) and is shown in Figure 7.8.

The version shown in Figure 7.8 was derived for seabed approach slopes no steeper than 1:50. The parameter map indicates that wave impacts are most likely to occur for three categories of conditions:

1 Vertical walls with large waves (Hsi/d>0.35).

2 Walls on low mounds with large waves (0.65<Hsi/d<1.3).

3 High mounds with moderate berm widths (0.14<Beq/Lpi <0.4) and large waves (0.65<Hsi/d<1.3).

Using this general approach, methods to predict wave forces on vertical wall, and where applicable on composite walls, are:

ªª for non-breaking waves (Goda, 2010)

ªª when a berm may cause impulsive breaking of waves, Takahashi’s modification to Goda (Takahashi et al, 1994)

ªª to estimate impulsive force of breaking waves (Allsop and Vicinanza, 1996, and Cuomo et al (2010a)

ªª to estimate force when wave action is broken before reaching the wall (Blackmore and Hewson, 1984)

ªª to estimate force when a breaking or broken bore travels over a slope or beach (Camfield, 1991).

7.3.5 Pulsating (or non-impulsive) wave loadsThe main default method to calculate quasi-static wave loads should be Goda’s method, or Takahashi’s modified version.

The most robust (and most widely accepted) prediction method for wave loads on vertical and composite walls is that developed by Goda (1974 and 2010). This method assumes that wave pressures on the front face can be represented by a trapezoidal distribution, reducing from p1 at the still water level (SWL) to p3 at the caisson base (Figure 7.9). At points above SWL, wave pressures reduce to zero at the notional run-up point given by a height η* above SWL.

Note that with wave load or overtopping predictions, the response calculations may be made over a range of different water levels as it is often not obvious which combination of wave and water level will give the worst response. So SWL is not necessarily at a single fixed level.

If wave pressures can penetrate under the wall, uplift pressures at the waterward edge might be determined by a separate expression, and may be less than pressures calculated for the toe of the waterward face. In Goda’s method, uplift pressures are distributed triangularly from the waterward edge to zero at the rear heel. The method was developed from hydraulic model tests where wave pressures were measured, and from a larger set of tests of sliding of model breakwater caissons. The resulting prediction formulae were then calibrated by comparison with field experience. The main response parameters given in Goda’s method are:

7.2

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p1=0.5(1+cosβ)(a1+a2cosβ)γH

p2=p1

p3=a3pp4=0.5(1+cosβ)a1a3γH

η*–hc

η*

H=H1/250

Figure 7.9 Nomenclature used in Goda’s wave load prediction method (from Goda, 1985)

7.4

are the coefficients a1, a2, and a3 are determined from:

7.5

7.6

7.7

where η* is the maximum elevation above SWL (m) to which pressure could be exerted (taken by Goda as η* = 1.5Hmax for normal wave incidence) β is the angle of wave obliquity in plan (°). The design wave height, Hmax, is taken as 1.8Hs for all positions waterward of the surf zone. In conditions of broken waves, Hmax should be taken as Hmax,b. The water depth h is taken at the toe of the mound, and d over the mound at the front face of the wall, but hb is taken as 5Hs waterward of the wall.

The total horizontal force, Fh, is calculated by integrating pressure p1 over the height hf of the front face. Similarly, where appropriate, the total uplift force is calculated by integrating from p = pu at the front edge to p = 0 at the rearward edge, giving a total uplift force of Fu = 0.5 pu B. All force and pressures calculated by Goda’s method represent a 1/250 exceedance level, F1/250.

For mounds with a relatively large height, the water depth over the mound, d, may be sufficiently smaller than the depth in front of the mound, h, to cause impulsive breaking. Takahashi et al (1994) have devised an adaptation of α1 in Goda’s method:

7.8

where α10 is given by α10 = H/d for H/d ≤ 2, or α10 = 2 for H/d > 2 and α11 is given by the diagram in

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Figure 7.10. Coefficient α11 takes a maximum value of 1 when d/h = 0.4 and BM/L = 0.12. The impulsive breaking coefficient α1 takes values between 0 and 2, with larger values giving larger wave forces.

When calculating wave forces using Takahashi et al (1994) modifcations, α1 is used in place of α2 when α1 > α2.

Over the years modifications extending Goda’s original formula have been seen with the most notable being:

ªª inclusion of incident wave direction Tanimoto et al (1976)

ªª inclusion of impulsive pressure coefficient Takahashi et al (1994)

ªª various modification factors to allow for application to other types of vertical walls (inclined walls, cylindrical, perforated etc).

Note that the Goda formula deals with wave action only. The hydrostatic action of water on both sides of the floodwall has to be added in order to calculate the resultant action of water.

Most design methods for caisson and other vertical breakwaters concentrate on the forces that act landward (Fh max) usually termed positive or positive forces. It has however been shown that some breakwaters have failed by sliding or rotation seaward, indicating that net seaward or negative forces may indeed be greater than positive forces. Previous prediction methods for ‘negative’ forces by Sainflou and Goda were extended by McConnell et al (1999). Both of these methods were based on relatively deep water, and pulsating waves.

Values of Fhmin(1/250)/Fhmax(1/250) from Oumeraci et al (2001) showed that there is some risk that negative forces exceed positive forces for small relative wave heights, Hsi/hs <0.2, most test data give measured Fmin forces that are greater than the conventional landward forces. The work resulted in the following expression to be adopted for desk study and initial design:

Using a probabilistic approach:

7.9

Using a deterministic approach:

7.10

a2 = max {a2Goda,at}at = a10+a11

H/d≤H2d 2 H>2d

cosd2/coshd1 d2≤0 1/(coshd1 (coshd2)

0.5) d2>0

{{

a10 =

a11 =

20d11 d11≤0 15d11 d11>0

4.9d22 d22≤0 3d22 d22>0

{{

d1=

d2=

d11 = 0.93(Bm/L-0.12)+0.36{(h-d)/h-0.6}

d22 = -0.36(Bm/L-0.12)+0.93{(h-d)/h-0.6}

Figure 7.10Impulsive breaking wave pressure coefficient α11 (after Takahashi et al, 1994)

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where:

P1’ = ρg(Hmax – h0)

P2’ = ρgHmax/cosh(2πh/L)

H0 = (πHmax2/L)coth(2πh/L)

d = water depth

7.3.6 Impulsive wave loadsA simple and robust method to predict wave impact pressures was derived by Allsop and Vicinanza (1996) based on testing by Allsop et al (1996b). They noted that for waves close to breaking given by 0.35 < Hsi/d < 0.6, other prediction methods underestimate measured forces. Differences are greatest where the incident wave conditions approach the breaking limit, approximated for shallow bed slopes by Hsi/hs≈0.55. A simple prediction curve was fitted to test results for composite walls (vertical wall with a toe berm/mound) for 0.35 < Hsi/d < 0.6 (see Figure 7.11).

7.11

This equation seems also to give a good description of wave impact forces for walls on low mounds given by 0.3 < hb/hs < 0.6, and higher relative wave heights given by 0.6 < Hsi/d ≤ 1.3.

Figure 7.11 Impulsive wave load (after Allsop and Vicinanza, 1996)

Recently Cuomo et al (2010a, 2010b, 2011) improved the prediction of impulsive loads using results from the Big-VOWS (Violent Overtopping of Waves at Seawalls) large-flume experiments (Cuomo et al, 2010a, 2010b and 2011) resulting in:

7.12

where Lhs is the wave length at the toe of the structure, and the water depth at breaking, hb, is evaluated using:

7.13

where k = 2π/Lhs

0

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Hsi/hs

Fh1/

250/ρ

ghs2

HR94 1:50 bed slopeHR97 1:50 bed slopeAllsop & Vicinanza (1996) - over region of validityAllsop & Vicinanza (1996) - extrapolatedNew prediction curve for 1:50 bed slope, Hsi/hs > 0.35 (Equation2)

Fh1/250/ρghs2 = 15(Hsi/hs)3.134

Fh1/250/ρghs2 = 20.2(Hsi/hs)3.5

Fh1/250/(ρgd2)=15•(Hs/d)3.134

Allsop and Vicinanza 0.4<Hs/d<0.6

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7.3.7 Broken wave conditionsFor many coastal seawalls, and for some breakwaters, the design wave condition may be limited by depth in front of the structure. In these cases, the larger waves at the structure will be broken and it is unlikely that significant wave impact loads will be caused. A method to estimate an average wave pressure from broken wave loads was developed by Blackmore and Hewson (1984).

7.14

where λ is an aeration coefficient for which values are suggested in Table 7.4, ρ is the water density, Tp is the peak wave period, Cb is the velocity of the breaker, and d is the depth at the wall. The simplest formula for breaker celerity may be given by shallow water wave theory:

7.15

Table 7.4 Aeration coefficients for broken wave loads (from Blackmore and Hewson, 1984)

Approach slope 1:5 to 1:10 1:30 to 1:50 1:100

Foreshore conditions

Smooth bed, sand 1.5 0.9 0.7

Rough, rocky 0.5 0.3 0.24

These methods may be used to make an initial estimate of the horizontal wave force under broken waves, FhBroken, to be applied only if FhBroken < FhGoda:

7.16

7.3.8 Bore wave conditionsWhere the wall (toe) is above the static water level, there is a single method cited by USACE (2002) developed by Camfield (1991) based on earlier work by Cross (1967) for wave loads on back-beach seawalls. The method requires a wave run-up limit on the beach to be calculated, from which a wave surge height (Hw) at the wall is deduced. Wave run-up levels are subject to significant measurement uncertainties, and also to some debate. The classic method for estimating wave run-up on beaches or shallow slopes is that from Hunt (1959), as re-stated by Battjes (1974). The surge force, Fsurge, is calculated from a surge height, Hsurge, by:

7.17

where

7.18

where x1 is the horizontal distance from shoreline to toe of the wall, and x2 from the shoreline to the notional run-up point without the wall.

In its original application, on shallow beaches, the breaking wave height was approximated as Hb = 0.78hs, but this would not be a safe estimate of Hb on slopes steeper than 1:50. Camfield (1991) recommends the method for slopes between 1:100 and 1:10, but notes that waves “on composite slopes should be investigated on a case-by-case basis”.

This method gives no indication of the height over which the load applies, nor of the average pressure, so a simple rectangular distribution over the full wall height is generally assumed. The calculation of bore wave load is rather subjective, and it is not known whether it has been validated by any measurements, either field or laboratory, so its reliability is unknown.

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7.4 ANALYSIS OF STABILITY OF WALLS

7.4.1 Codes of practice (COP)Where the stability of a wall is in doubt or where a change in the loading on a wall is proposed, then the wall should be analysed to assess its stability. Depending on location, there are several codes that could be used to make such an assessment (for example BS 6349-1:2000, BS 6349-1-1:2013, BS 6349-1-2, BS 6349-1-3:2012, BS 6349-1-4:2013, BS 6031:2009, CP2 (1951), BS 8002:1994, BS EN 1997-1:2004+A1:2013, AS 4997-2005 and ROM 0.5-05:2005).

The code or standard to be adopted depends on the extent of changes proposed to a wall. Where analysis is being undertaken as a check on the stability of a wall and there are no proposed changes to its retained height, loading or structure, then it would seem appropriate to check the wall in accordance with the appropriate standard if one exists at the time of design. Checking against the requirements of CP2 (1951) or BS 8002:1994 would seem appropriate, even though these are superseded by the newer Eurocode (EC7).

Where substantial changes are to be made to the wall’s regime, then it might be more appropriate to consider it as an entirely new wall, and the requirements of EC7 would need to be followed.

The main difference between the earlier codes/standards and EC7 lies in the former adopting global FoS whereas the later adopts a partial factor. Depending on the design approach adopted, a condition where the forces are factored is also considered and the worst case adopted.

In these instances it is often necessary to re-examine the input data to the calculations to see if any of the values adopted are too pessimistic. Where any of the input data is based on assumptions or estimates, further efforts should be made to verify the information before contemplating wall-strengthening works. Various aspects of stability analysis are considered in Sections 7.4.2.

7.4.2 Loading and strength parametersThe minimum uniformly distributed live load that should be considered on backfilling behind a wall or on the hearting of a breakwater is 5 kN/m2. This corresponds to the crowd loading of pedestrians. Other vertical live loads should be based what the area is to be used for. For example BS 8002:1994 recommends a minimum of 10 kN/m2 or more for commercial port and highway loadings. Advice on such loading is given in Clauses 44, 45 and 46 of BS 6349-1:2000 and EC7.

Bollard pulls may be assessed in accordance with Clause 42 of BS 6349-1:2000 or based on a more detailed investigation of the type of vessel and the local wind speeds. Where dredgers are to be used the loads imposed by the side and head wires should be investigated.

Dead loads should, whenever possible, be based on actual measurements of the densities of the various parts of the structures. Brick, stone and concrete have dry densities that may vary from 16 kN/m3 to 26 kN/m3 (ie effective submerged densities of 6 kN/m3 to 16 kN/m3) and all three materials may be used in a single structure. Some designers varied the densities deliberately to maximise the stability or minimise the bearing pressure under the foundations (see Figure 3.62).

Soil properties should be based on recent investigations (see Section 6.9) and an assessment by a geotechnical engineer. Separate parameters should be identified for the backfilling, the various layers in the original ground behind the backfill and the soil below and in front of the foundation. Effective stress parameters should be measured or assessed for cohesive materials.

Use experience and engineering judgementIn some cases, the analysis of wall stability carried out in accordance with the current codes can result in a low FoS, and occasionally less than one for walls that have been standing satisfactorily for many years. Care should be taken when basing decisions on the results of such analysis and it is essential that experience and engineering judgement are used in their interpretation.

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Water levels behind the wall should be based on measurements in boreholes to show how the water levels vary in relation to the water level in front of the wall, and on a review of likely changes that may affect the water level in the future. The full range of factors that may affect the water levels behind and in front of the wall need to be evaluated. These include:

ªª Behind the wall (including inside):

ª� groundwater levels (including potential for failure of buried water and sewage pipes)

ª� effect of rivers and flooding

ª� canal operating levels

ª� connections now and in the future to other sources of water

ª� surface water drainage arrangements

ª� drain connections through the wall and effect of drainage layers behind the wall

ª� risk and effect of overtopping by waves.

ªª In front of the wall:

ª� normal and river-in-flood levels

ª� range of levels in impounded docks system

ª� extreme tide levels (eg surge) including meteorological effects

ª� canal operating levels

ª� lowest water levels used in maintenance.

Wave loadings are discussed in Section 7.3.

It may occasionally be necessary to assess the strength of the wall materials, particularly where new loads are to be applied to the wall. Ideally, a composite block should be cut out of the wall for testing. Alternatively, cores may be tested.

7.4.3 Modes of failureThe principal modes of possible failure of a gravity wall:

ªª deep slip

ªª overturning

ªª sliding (which may need to be checked at various levels).

ªª foundation failure.

Overturning and sliding can also affect individual parts of the wall, as opposed to the whole cross-section. Each of these four modes is considered in Sections 7.4.4 to 7.4.7.

7.4.4 Deep slipDeep slip refers to instability involving shear failure of the earth mass on which a wall is built. Circumstances in which waterfront walls are particularly at risk from a deep slip include:

ªª where the wall is founded on clay or on a soil overlying clay or other weak strata

ªª where the soil behind the wall slopes up from it, as occurs with some coast protection walls

ªª where the ground in front of the toe of the wall slopes downwards

ªª where high pore water pressures can exist below the wall.

The stability of the slope should be analysed using an appropriate computer program to find the most critical slip surface and the lowest FoS, which is expressed as:

= Sum of restoring moments/sum of disturbing moments

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While computer programmes can be used for slip circle analysis, there are other methods for simple structures, such as those described in BS 6031:2009, or Hoek tables, or back-analysis of local failure. It should also be noted that rock outcrops revetted by waterfront walls will result in different loading and different slope failure mechanisms to retained soils.

7.4.5 OverturningOverturning means failure of the wall by rotation about the toe of the wall. The FoS against overturning is expressed as:

= Moment of restoring forces about toe/moment of disturbing forces about toe

Computer programs can be used for the analysis of overturning and also for sliding and bearing pressure failures on the same program. They are particularly useful for situations where it is necessary to carry out a sensitivity analysis or to consider various loading cases. The following points should be noted with regard to overturning calculations for old waterfront walls:

1 The soil pressure acting against the back of the wall should usually be calculated as the ‘active’ pressure because even sizeable walls move sufficiently for soil pressure to reduce to the active value. However, tied walls or other post-tensioned or bending structures mobilise restoring forces to counteract the applied loadings. Higher pressures should be allowed for walls with ties, for swelling of over-consolidated clays and where soil is to be compacted behind the wall.

2 Account should be taken of the shape of any excavation out of the original ground before backfilling was placed and the high internal angle of friction for designed rubble backfills.

3 Effective stress parameters should be used for backfilling.

4 The angle of wall friction should be carefully assessed allowing for the effect of a ‘virtual back’ for a wall with a stepped rear face and for the effect of projecting wall bases, oversails (artificial projections to increase wall friction), counterforts and the roughness of unfaced rubble masonry. Variations in the angle of wall friction have a significant effect on wall stability.

5 Where the resulting active pressure is resolved into vertical and horizontal components, both components should be treated as ‘disturbing’ forces with the vertical component shown as negative (see Figure 7.12).

6 Dry densities of the various materials in the wall should be used for calculations of the restoring moment of the wall. The effects of horizontal water pressure and of uplift should be calculated separately. This procedure makes it easier to allow for a non-uniform water pressure under the base of the wall and to carry out a succession of calculations with different water level assumptions.

7 Horizontal concentrated loads such as bollard pulls should be distributed at 45 degrees down through and along the wall unless the wall is constructed in separate sections of a smaller length than this dispersion.

8 The effect of passive pressure in front of the toe is usually insignificant due to the small lever arm and the low pressure that can be overcome with the slightest of movement of the wall.

9 It may be necessary to check the overturning at different levels above the base of the wall, particularly where it is proposed to apply heavy concentrated loads on filling behind the wall.

Figure 7.12 Illustration of the active pressure components of forces acting on a retaining wall for consideration of overturning (courtesy Livesy and Henderson)

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7.4.6 SlidingThe FoS against sliding is expressed as:

= Horizontal disturbing forces/horizontal resisting forces

The same points should be taken into account as mentioned in relation to overturning except for:

ªª the base friction arising from the vertical component of the active pressure should be considered as a restoring force

ªª the angle of friction between the base and the ground should be evaluated based on the detail of the base and foundation including any serrations, upward slopes and concrete cast directly on to the ground, which may modify the angle of friction to be taken

ªª a designed ‘shear key’, eg a downstand nib on the wall base or piles may provide resistance to sliding over and above soil types and roughness as previous mentioned

ªª the amount of passive resistance available from any soil in front of the wall is likely to be small. Where passive pressure is included in the resisting forces, it should be restricted to a value at which movement of the wall will be small

ªª the resistance to sliding may need to be checked at various levels in walls of varying thicknesses, particularly if some new localised horizontal loading is proposed.

7.4.7 Bearing pressureFoundation failure may occur as a result of excessive bearing pressures. The maximum bearing pressure under the wall should be calculated from the position, magnitude and direction of the resultant force derived from soil pressures, water pressures, imposed loads, and structure weight acting on the base of the wall. These figures can be derived from the data used in the overturning calculations. Bearing pressures under the heel of the wall due to wave or berthing loads are unlikely to be critical as such forces are usually resisted by the passive resistance of the backfilling or hearting.

7.4.8 CounterfortsFor walls with counterforts (see Figure 7.13) the following assumptions can be made for calculating the resistance to overturning:

ªª Active pressure (Ka) acts on the back of the wall between the counterforts and on the back of the counterforts and can be resolved into horizontal and vertical components.

ªª As the wall tends to rotate about the toe of the wall, the counterforts rise and mobilise friction on their sides.

ªª The soil pressure on the side of a counterfort is earth pressure at rest (Ko) because the soil is constrained by the counterforts.

ªª Vertical friction (Ko tan Δ) on the whole of each face of a counterfort assists in resisting overturning provided that the counterforts are not too close together. In the latter case the weight of the soil between the counterforts would limit the amount of side friction that can be mobilised.

ªª To allow for the varying section of the wall, a length equal to the spacing of the counterforts should be considered at one time, instead of the more usual one metre length.

Figure 7.13 Plan and elevation of a counterfort application of earth pressure (courtesy Livesy and Henderson)

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In considering the effect of counterforts on the resistance of a wall to sliding the following can be assumed:

ªª Active pressure (Ka) acts on the backs of the wall and the counterforts, and can be resolved into horizontal and vertical components.

ªª The lower part of the side of the counterfort, which is outside the active wedge for the wall without counterforts (area A in Figure 7.13), resists horizontal sliding directly by friction based on Ko and tan Δ.

ªª As the wall tends to move forwards, the active wedge behind the wall moves downwards and transfers a vertical friction load to the part of the side of the counterfort within the wall active wedge (the whole side except area A in Figure 7.13).

ªª The vertical friction is a function of Ko and tan Δ, and is transferred as an additional vertical load to the base of the counterfort where it increases the base frictional resistance.

The bearing pressure under a counterfort wall with a base slab of non-uniform width can be estimated from the width of the wall foundation in compression, and calculating bearing stresses using the Z value for the T shape of the area in compression (see Figure 7.14). A better estimate of the width in compression can then be made and the calculation repeated until the centroid of the pressure diagram coincides with the resultant of the disturbing and restoring forces. The tension at the top of the counterfort where it joins the main wall should be checked as failure at this point has been noted in some cases.

7.4.9 DewateringProjects that involve dewatering of dock basins or locks, require particular care to ensure that the likely water pressures behind and under the walls and under any floor are correctly estimated. Although most such structures were originally constructed in a dewatered site, the water pressures will be more onerous when the water is pumped out again many years later. This is because the water level in the soil may take a long time to respond to changes, particularly where clay exists under or behind a wall.

7.4.10 OvertoppingOld waterfront walls that are exposed to wave action are potentially vulnerable to overtopping by water, even when still water levels are below the crest level of the structure. Wave action on the wall can exceed the wall crest level. Under those conditions, wave overtopping flows, and accompanying spray can result in significant amounts of water reaching the back of the wall, leading to increased groundwater levels and loading on the back of the wall. Wave overtopping can also cause damage to the surface behind the wall. If this is sealed or paved then the surfacing may be damaged and allow water to seep into the fill behind the wall. If it is unprotected, then this fill may be eroded.

The hydrodynamics of overtopping are complex. The amount of water overtopping will vary in time, and the unsteady discharge will be a function of wave height, wave period, and water elevation relative to the wall. There are a number of methods available to calculate wave overtopping on a wall or slope and these can be found in Die Küste (2007), and also provides information for required data input and allows users to calculate:

Figure 7.14 Plan and sections of a counterfort wall showing bearing pressures (courtesy Livesy and Henderson)

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ªª mean overtopping discharge, overtopping volumes and the number of overtopping waves

ªª flow velocity and flow depths of waves overtopping sloping structures.

Further background on overtopping of seawalls, can also be found in CIRIA; Ministry of Ecology; USACE (2013).

7.4.11 Factors of safety (FoS)Ideally, the following FoS against each failure mode should be achieved:

Table 7.5 FoS against overturning

Failure mode Normal loading* Extreme loading**

Deep slip 1.40 1.20

Overturning 2.00 1.50

Sliding 1.75 1.50

Foundation failure Calculated allowable Allowable+ 25%

Notes

* Normal loading refers to any combination of loads that may be reasonably expected to occur during the design life of the structure, associated with normal operating conditions. This should include foreseeable modification to the structure, adjacent earthworks, paving, storage patterns, handling equipment or dredge depth.

** Extreme loading refers to any combination of loads that may be expected to occur during the design life of the structure, associated with the most severe credible load that could physically be applied, excluding accidental loads such as that due to an uncontrolled berthing. The likelihood of more than one extreme load occurring at any time should also be assessed.

Frequently these FoS are not achieved and it is then necessary to review the input data to the calculations. The following points should be examined:

1 Are the soil parameters realistic? Would it be more realistic to adopt mean strengths rather than a lower bound? Were laboratory tests based on the complete range of particle sizes present or only on the finer fraction? Would further investigation and testing produce a more reliable (and possibly more favourable) answer?

2 Is the loading on the backfilling realistic?

3 With the water levels at the back of the wall, would further field measurements, including checking how they respond to changes of water level at the front, be useful?

4 For wall and base friction, sensitivity analyses should be carried out to check the effect of different assumptions.

5 Are all the assumptions about the shape of the wall (ie its geometry) justified by the evidence?

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ReferencesALLSOP, N W H and VICINANZA, D (1996) “Wave impact loadings on vertical breakwaters: development of new prediction formulae”. In: Proc 11th int harbour congress, Antwerp, Belgium, 17–21 June 1996, Koninklijke Vlaamse Ingenieursvereniging (KVIV), Antwerpen (ISBN: 9-05204-030-3), pp 275–284

ALLSOP, N W H, VICINANZA, D and MCKENNA, J E (1996a) Wave forces on vertical and composite breakwaters, Research Report SR 443, HR Wallingford, Oxford, UK. Go to: http://tinyurl.com/obwe6kj

ALLSOP, N W H, MCKENNA, J E, VICINANZA, D and WHITTAKER, T J T (1996b) “New design formulae for wave loadings on vertical breakwaters and seawalls”. In: Proc 25th int conf on coastal engineering, 2–6 September, Orlando, Florida, USA. B L Edge (ed) Coastal engineering, American Society of Civil Engineers, New York, USA (ISBN: 978-0-78440-242-9), pp 2508–2521

BATTJES, J A (1974) “Surf similarity”. In: Proc 14th int conf on coastal engineering, 24–28 June 1974, Copenhagen, Denmark, American Society of Civil Engineers, New York (ISBN: 978-0-87262-113-8), pp 466–479

BLACKMORE, P A and HEWSON, P (1984) “Experiments on full scale impact pressures” Coastal Engineering, vol 8, 4, Elsevier BV, UK pp 331–346

CAMFIELD, F E (1991) “Wave forces on wall” Journal of waterway, port, coastal and ocean engineering, vol 117, 1, American Society of Civil Engineers, New York, USA, pp 76–79

CIRIA; MINISTRY OF ECOLOGY; USACE (2013) The International Levee Handbook, C731, CIRIA, London, UK (ISBN: 978-0-86017-734-0). Go to: www.ciria.org

CROSS, R H (1967) “Tsunami Surge Forces”, Journal of waterways and harbour division, vol 93, 4, American Society of Civil Engineers, New York, USA, pp 201–231 (out of print)

CUOMO, G, ALLSOP, N W H and TAKAHASHI, S (2010a) “Scaling wave impact pressures on vertical walls” Coastal Engineering, vol 57, 6, Elsevier BV, UK, pp 604–609

CUOMO, G, ALLSOP, N W H, BRUCE, T and PEARSON, J (2010b) “Breaking wave loads at vertical sea walls and breakwaters” Coastal Engineering, vol 57, 4, Elservier BV, UK, pp 424–439

CUOMO, G, PISCOPIA, R and ALLSOP, N W H (2011) “Evaluation of wave impact loads on caisson breakwaters based on joint probability of impact maxima and rise times” Coastal Engineering, vol 58, 1, Elsevier BV, UK, pp 9–27

DIE KÜSTE (2007) EurOtop – Wave overtopping of sea defences and related structure assessment manual, HR Wallingford, Oxford, UK. Go to: www.overtopping-manual.com/eurotop.pdf

GODA, Y (1974) “New wave pressure formulae for composite breakwaters”. In: Proc 14th int conf on coastal engineering, 24–28 June 1974, Copenhagen, Denmark, American Society of Civil Engineers, New York (ISBN: 978-0-87262-113-8), pp 1702–1720

GODA, Y (2010) Random seas and maritime structures, third edition, Advanced series on engineering, vol 33, World Scientific Press, Tokyo, Japan (ISBN: 978-9-81428-240-6)

HUNT, J A (1959) Design of seawall and breakwaters, University of California Libraries, California, USA (ISBN: 978-1-12541-290-9)

KIRKGÖZ, M S (1995) “Breaking wave impact on vertical and sloping coastal structures” Ocean Engineering, vol 22, 1, Elsevier Science, UK, pp 35–48

MCCONNELL, K J, ALLSOP, N W H and FLOHR, H (1999) Seaward wave loading on vertical coastal structures”. In: Proc int conf, Coastal Structures ’99, 7–10 June 1999, Santander, Spain. I J Losada (ed) CRC Press, UK (ISBN: 978-9-05809-092-8), pp 447–454

OUMERACI, H, KORTENHAUS, A, ALLSOP, N W H, DE GROOT, M B, CROUCH, R S, VRIJLING, J K and VOORTMAN, H G (2001) Proverbs: Probabilistic design tools for vertical breakwaters, Balkema, Rotterdam (ISBN: 9-0580-248-8)

TAKAHASHI, S, TANIMOTO, K and SHIMOSAKO, K (1994) “A proposal of impulsive pressure coefficient for the design of composite breakwaters”. In: Proc int conf on hydro-technical engineering for port and harbour construction, Hydro-Port’94, 19–21 October 1994, Yokusuka, Japan (ISBN: 978-4-90030-204-4), pp 489–504

TANIMOTO, K, MOTO, K, ISHIZUKA, S and GODA, Y (1976) “An investigation on design wave force formulae of composite-type breakwaters”. In: Proc of 23rd Japanese conf on coastal engineering (in Japanese), pp 11–16

USACE (2002) Coastal engineering manual, EM 1110-2-1100, US Army Corps of Engineers, Reston VA, USA. Go to: http://chl.erdc.usace.army.mil/cem

Statutes

British StandardsBS 6349-1-1:2013 Maritime works. General. Code of practice for planning and design for operations

BS 6349-1:2000 Code of practice for maritime structures

BS 6349-1-2 Maritime works. General. Code of practice for assessment of actions (in press)

BS 6349-1-3:2012 Maritime works. General. Code of practice for geotechnical design

BS 6349-1-4:2013 Maritime works. General. Code of practice for materials

BS 6031:2009 Code of practice for earthworks

BS 6031:2009 Code of practice for earthworks

BS 8002:1994 Code of practice for earth retaining structures (superseded by EC7)

CP2 (1951) Code of practice for earth retaining structure (superseded by EN 1997)

European StandardsBS EN 1997-1:2004+A1:2013 Eurocode 7 Geotechnical design. General rules (EC7)

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International standardsAS 4997-2005 Guidelines for the design of marine structures (Australia)

ROM 0.5-05:2005 Recomendación Geotécnica para las Obras Marítima y/o Portuaria (Spain)

Further readingPIANC (2003) Breakwaters with vertical and inclined concrete walls, Report of Working Group 28, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium. Go to: www.pianc.org/publications.php

BS 8004:1986 Code of practice for foundations

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8 Maintenance and rehabilitation

8.1 OVERVIEWThis chapter discusses repair and rehabilitation techniques suitable for old waterfront walls. It includes discussion on modifying the loads on the structure, remedial works to the toe, increasing wall stability, repairing, and replacing the wall with a new structure. A selection of suitable repair materials is also discussed and case studies are included.

Figure 8.1 provides an overview of the chapter.

Management actionsAdministrative context

Physical context

Severe event(Section 5 .5)

Management of risk(Sections 2 .1 to 2 .3)

Responsibilities (Section 2 .4)

Powers(Section 2 .5)

Beneficiaries(Section 2 .8)

Funding(Section 2 .9)

Physical form and purpose

(Chapter 3)

Physical processes (Section 6 .3)

Loads(Sections 7 .1 to 7 .3)

Wall stability(Section 7 .4)

Historical data(Section 6 .4)

Framework for decisions (Section 4 .3)

Risk analysis(Section 4 .4)

Performance assessment(Section 4 .5)

Operations(Section 5 .2 to 5 .3)

Monitoring and inspection

(Sections 4 .6 to 4 .7)

Data acquisition (Section 4 .7)

Data management (Section 4 .8)

Wall investigation (Sections 6 .5 to 6 .9)

Decision on intervention

Maintenance, repair and rehabilitation (Sections 5 .4 and

Chapter 8)

Regulations and consents

(Sections 2 .6 to 2 .7)

Figure 8.1Overview of Chapter 8

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8.2 INTRODUCTIONThe replies to the original questionnaires (see Section 3.2.2) for development of the original manual (Bray and Tatham, 1992) and the more recent responses to the updated questionnaire confirmed that the commonest faults found in old waterfront walls are undermining of the wall and degradation of the wall materials. As a result, many of the repairs are in principle fairly simple, except for the complications introduced by working over or underwater, in the tidal zone or in locations exposed to waves or currents. However, as discussed in Chapter 3, there are a wide variety of faults that have to be remedied and this section examines some of the most commonly used methods for the repair and refurbishment of walls.

Many walls standing today were constructed over 100 years ago and would be considered under-designed by modern standards. When faced with the task of repairing one of these walls the engineer is in a dilemma. Should they upgrade the design to modern standards, which may lead to the expenditure of unnecessary funds, because of having to rely on the ‘belt and braces’ principle due to potential uncertainties in the wall structure and ground conditions? Or should they reinstate the wall to its original condition, and by doing so leaving it open to criticism and possible legal action if the wall should subsequently fail. There is a need for the engineer to draw the attention of those responsible for the wall to this conflict and to agree on the approach to be adopted.

Irrespective of the agreed type of overall design philosophy, there is still an onus on the engineer to produce cost-effective designs. It is surprising how a small mistake can have dramatic consequences (see Box 8.1).

West Bay, also known as Bridport harbour, is located at the heart of Dorset’s Jurassic Coast and is England’s first natural World Heritage Site. West Bay relies heavily on both tourism and its working harbour. However, West Bay’s piers and sea defences have regularly suffered major and sustained storm damage since their construction (Figure 8 .2).

In the early 1970s the piers at the entrance to West Bay, which were designed as stone faced rubble filled structures by John Coode in the 1860s, were rehabilitated by driving sheet piles around the structures and filling the space between the piers and the piling with shingle and concrete. Figure 8 .3 shows a cross-section of the works as designed.

In a relatively short space of time the beach shingle had abraded away the bottom of the piles, allowing the shingle fill to escape from below the concrete. In 1978 exceptional storms caused further damage to the seawalls and freak denudation of East Beach, causing great damage to the piers. In the 1980s extensive emergency repair works were carried out. This work may not have been necessary if the concrete filling had been taken down well below any anticipated beach level.

In 2001 a decision was taken to undertake a £17m programme to rebuild West Pier on a new alignment, construct a new slipway with outer harbour and strengthen East Pier.

Figure 8.2 Following reconstruction, West Bay

Figure 8.3 Cross-section of the design for the reconstruction of the east pier

Figure 8.4 Completed restoration work

Box 8 .1 The reconstruction of the piers, West Bay, Dorset (courtesy Dobbie and Partners/West Dorset County Council

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It is also surprising how much material can be removed from a masonry structure, for the purpose of repair or reconstruction, without the structure showing any apparent sign of distress. Figure 8.5 shows the cavities formed under a lock wall when the sill timbers are replaced. Similar work of a more comprehensive nature was carried out on the five-lock staircase of the Caledonian Canal at Fort Augustus and monitoring of the movement of the structure, using one metre long vibrating wire strain gauges, showed no signs of distress during repairs.

8.3 MODIFYING LOADS ON THE STRUCTURE

8.3.1 RedefiningthestandardofserviceWhere a wall has been overloaded or is at risk from some type of overloading, it may be possible to reduce loads by regulating the use of areas affecting the wall. Typical possibilities include:

ªª Restricting stacking loads on the backfilled area behind the wall (see Box 8.2). Particular attention should be paid to the densities of stacked materials. Tables A1 and A2 of BS6349-1-1:2013 give typical densities of bulk and stacked materials.

ªª Imposing partial restrictions on loading so that the loaded area is kept a certain distance from the face of the wall.

ªª Controlling the weight and position of equipment. It may be preferable to use heavier equipment further from the wall or to use lifting equipment on the ship or on rails on independent foundations. In some places operators of heavy mobile equipment have to obtain the port engineer’s approval before using the equipment near waterfront walls. An example of a request form, as used at Hull, is shown in Figure 8.8.

ªª Controlling the use of mooring bollards by dredgers or other vessels.

ªª Controlling the water level in front of the wall either by restricting the times at which gates are opened in relation to the tide or by deciding to avoid dewatering of the area in front of the wall for repairs, by using other repair methods.

ªª Controlling the water level at the back of the wall. An example of this is shown in the repairs carried out at Chatham (see Box 8.3).

ªª Reducing the depth of water available in front of the wall.

ªª Reducing the level of the ground behind the wall.

ªª Reducing the exposure of the wall to waves by other works such as beach raising.

In many instances such solutions will not be possible, but in others it may be feasible to save considerable expenditure on civil engineering works that would otherwise be needed to strengthen the wall.

Figure 8.5 Cavities left after removal of decayed timbers, Kytra Lock, Caledonian Canal (courtesy British Waterways)

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The Albert dock in Liverpool was officially opened in 1846 by the Prince Consort HRH Prince Albert and stopped commercial operations in 1971.The top half of the south wall in the Alfred Dock in Liverpool started to overturn due to excessive imposed loads. The wall had been weakened

by the loss of face material and mortar over a period of time, coupled with rapid draw-down of water (as the dock is used as a half-tide dock). Movement of the wall appears to have been curtailed as a result of the enforcement of loading restrictions.

Box 8 .2 Load restrictions, South Alfred Dock, Liverpool

Chatham Dockyard in Kent was one of the Royal Navy’s main facilities for several hundred years until it was closed in 1984. After closure the dockyard was divided into three sections. The eastern most basin was handed over to Medway Ports and is now a commercial port. Another slice was converted into a mixed commercial, residential and leisure development. The final 80 acres (324 000 m²), comprising the 18th century core of the site, was transferred to the Chatham Historic Dockyard Trust and is now open as a visitor attraction.

The dock has a bullnose separating the entrances of the north and south locks. This is a mass concrete structure with granite cope and quoins, backfilled by

miscellaneous material and founded on gravel overlying chalk. Investigation showed that the structure had a low FoS against sliding, due to the partial loss or absence of its toe, and that propeller wash and bollard pull from modern vessels were likely to induce collapse of an already highly cracked structure.

Repairs included the grouting of a granite-filled trench around the toe of the wall, the installation of tie bars in the back face of the wall (tensioned back to a steel frame in the centre of the bullnose) and improvements to the drainage paths. The last of these was achieved by drilling drain holes through the wall, installing a filter membrane and the placing of free-draining granular backfill.

Box 8 .3 Repairs to the bullnose, Chatham Dockyard, Kent

During the winter of 1999–2000 a north-westerly storm caused huge waves to break directly over the Old Quay at Whitehaven. These exceptional conditions resulted in a vertical crack forming in part of the pier (Figure 8 .6). Several options for repairing the quay were considered, and the agreed solution was a combined scheme of stitching, grouting, waterproofing and drainage.

Once finances had been secured and relevant permissions from English Heritage had been obtained, the work was undertaken during spring 2002. Initially all voids in the quay were grouted using an OPC/PFA grout, working from holes drilled from the top of the quay. The surface stones at the stitching nail positions were cored. Using a light quarry crawler rig mounted on a pontoon floating in the harbour, 104 holes were drilled and glass reinforced resin nails grouted in (Figure 8 .7). The drilling method used a

down-the-hole hammer and air flush, and the grout was retained in the holes by the use of geotextile socks.

The Whitehaven Harbour Master assisted the work by controlling the harbour water level so that the four rows of holes could be drilled at their correct levels. Towards the bottom of the pattern of nails, a series of drainage holes were drilled and lined with geotextile wrapped plastic tubes. Particular attention was given to environmental controls during the work with biodegradable oils used and pollution control booms being readily available in the event of oil or fuel spillages.

Finally, to reduce water ingress into the quay, the surface was sealed by new pointing done sympathetically with the original pointing. The cores from the surface stones were replaced to cover the heads of the nails.

Figure 8.6 Damaged quay wall Figure 8.7 Completed wall with new stitching, grouting and pointing

Case study 8 .1 Stitching repairs at Old Quay, Whitehaven, Cumbria (courtesy BAM Ritchies)

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8Figure 8.8 Application form for use of a mobile crane on a waterfront (courtesy Associated British Ports Hull)

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The existing Victorian gravity blockwork gravity wall at Tilbury in Essex failed through overloading on the quayside over a 120 m length (Figure 8 .9). Blocks were displaced and the retained fill slipped into the berth.

The initial work included clearing up the debris and preparing the site for repair by cleaning the existing foundation and base of the wall to allow reconstruction of the upper section of wall (Figure 8 .10). A custom made formwork of 12 m in length was then prepared and moved into position over the remaining base of the wall. A landing platform was prepared on the outer face of the existing wall to land the shutter. This platform was anchored to the existing base of the wall with steel rock anchors. The formwork comprised a hydraulically operated steel shutter, which enabled the seal to be made underwater by the hydraulic arm operating at the top of the shutter.

Concrete was then tremied into place, with the concrete mix varied throughout the 12-hour, 200 m3 pour to suit varying serviceability requirement. The concrete used a high proportion of ground granulated blast-furnace slag (GGBFS). Concrete made with GGBFS sets more slowly than concrete made with ordinary Portland cement (PC), depending on the amount of GGBFS in the mix, and gains strength over a longer period, with lower heat of hydration and lower temperature rises that reduces the potential for cold joints on large pours. A total of 10 pours were required to complete 120 m of quay repair (Figure 8 .11).

The final pour used higher strength concrete (C40) with fibre reinforcement. Finally fill was place behind the new wall and the area re-paved to allow operations to continue (Figure 8 .12).

Figure 8.10 Clearing of debris and positioning of custom made steel shutter

Figure 8.12 Completion of wall and placing of backfill

Case study 8 .2 Reconstruction of concrete masonry gravity wall, Tilbury, Essex (courtesy BAM Ritchies)

Figure 8.9 Failure of the gravity wall at Tilbury

Figure 8.11 Reconstruction of upper section of wall

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8.3.2 Reduction of soil load on back of wallWhere a wall has an inadequate FoS against overturning, sliding etc, one solution is to reduce the loading on the back of the wall by modifying the backfill. Such works include:

ªª Excavating the fill behind the wall and replacing it by a reinforced earth structure (see Box 8.4).

ªª Replacing part or all of the backfill by material with a high internal angle of friction or with cement (Figure 8.13).

ªª Removing part of the filling behind the wall where the use of the area will permit this. For example, at Gateshead a quay wall had been damaged by a deep slip (Box 8.4). It was no longer required to function as a quay but could continue as a retaining wall with a lower ground level behind it.

ªª Replacing part of the backfill with lightweight material, such as expanded polystyrene slabs, which have been used on road embankment construction. Expanded polystyrene can only be used above the level of the groundwater because it is buoyant. Sufficient fill should be placed above the polystyrene to spread heavy point loads.

ªª Grouting up the backfill to reduce the active pressure on the wall (see Figure 8.14). In a design drawing, it is very easy to show a neatly grouted zone of filling behind a wall. In practice it can be difficult to achieve and this method should only be used if it can be ensured that:

ª� the material will be effectively grouted

ª� the grout will not spread to other areas

ª� drains will not be blocked by grout

ª� the groundwater level will not be adversely affected

ª� the liquid grout will not apply high pressures to the back of the wall

ª� the additional weight of grout in the soil will not excessively increase pressure on the wall below the grouted zone.

There have been a number of cases where grouted backfills have been subsequently excavated and little evidence of the grout has been found. One reason for this is that the material of some backfills is non-uniform and the grout takes the path of least resistance through any coarse material and leaves the fine material un-grouted. Trial pits should be excavated to check the suitability of the material for grouting. It is also prudent to carry out trial grouting and to check the result by excavation. Snowden (1990) gives further details of the grout treatment of fills.

Figure 8.13 Example of soil being replaced with cemented material, Milford Haven, Wales (courtesy Wallace Evans and Partners)

Figure 8.14 Grouting of fill behind a quay wall, Appledore, North Devon (courtesy Wallace Evans and Partners)

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The Metropolitan Borough Council of Gateshead needed to improve the stability of a river wall on the south bank of the Tyne, as part of the preparations for the Gatesehead Garden Festival held between May and October 1990. Cracking of the wall indicated forward movement and monitoring of the cracks showed that movement occurred throughout the tidal cycle. It was decided to construct a thrust-relief structure behind the existing wall to reduce the imposed loads and to improve the stability.

The thrust-relief structure was formed of earth reinforced by geogrids, manufactured from high-density polyethylene, and tied to a bagwork-facing unit (see Figure 8 .15). The gap between the wall and the thrust-relief structure was filled with a coarse drainage medium.

In 2011 and again in 2013, sections of the old and unrefurbished river wall failed and a spokesman Gateshead Council, said “The complicated and long history of the banks of the River Tyne means that we are left with retaining walls of a myriad of different techniques and dates of construction.”

8.3.3 Pressure-relieving slabsWhere the main cause of wall distress is the surcharge applied to the backfilling, one solution is to carry the loads on a slab, which is not supported on the filling. Possible methods include:

ªª A concrete surface slab supported on piles behind the wall. The slab should extend sufficiently far back from the wall to remove any loading from the active wedge behind the wall or any part of a potentially unstable soil mass. Bored piles should normally be used because the installation of driven piles would apply additional horizontal pressure to the wall.

ªª Where the wall had adequate bearing capacity, it may be possible to support one end of the relieving slab on the wall (see Figure 8.16), where the new wall facing work has also been matched to the original wall).

ªª Further relief can be given to the back of the wall by removing part of the backfill and constructing a piled relieving slab at a lower level.

Figure 8.15 Method of using a reinforced earth structure to reduce the pressure on the back of a wall (courtesy Netlon)

Figure 8.16 Use of a pressure relieving slab for a river wall at Barnstaple, North Devon (courtesy MAFF)

Box 8 .4 Use of reinforced earth on river walls, Gateshead, Tyne and Wear

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8.4 REMEDIAL WORKS TO THE WALL TOE

8.4.1 Quay wall toe erosion repairsRepairs to the toes of quay and similar walls usually have to be carried out underwater. In some cases the use of cofferdams or limpet dams may be appropriate (see Section 8.7). Where the toe of a wall has been partially undermined or eroded the following methods of repair can be considered:

ªª Grout-filled bags: the void should be cleaned out and then measured so that grout bags of the correct size can be made. Figure 8.17 shows a cross-section of the North Deepwater Quay at Cork, Ireland, where the wall has been partially undermined. Pressure grouting into a purpose-made bag was used to fill the void.

ªª Tremie concrete: where the concrete is placed using gravity through a pipe, typically around 250 mm in diameter with a hopper on the top and suspended vertically in the water, with the delivery end embedded about 0.5 m to 1.0 m under the surface of placed concrete to minimise washout. Tremie is considered the most reliable way of placing high quality concrete underwater. The void should be cleaned out and appropriate permanent formwork devised to suit the particular situation. Examples of such formwork are precast concrete blocks and concrete bagwork. The shape of the void for this method has to be accessible for the placing of tremie concrete and capable of being entirely filled without leaving voids (see Box 8.5).

ªª Grouted aggregate: in this method large size aggregate is placed in the void and grout pipes are inserted so that grout can be placed from the bottom upwards. The space to be filled may be constrained by temporary or permanent formwork or by purpose-built grout filled bags.

ªª Non-tremie underwater concrete: recently developed admixtures allow concrete to be placed underwater without the use of tremie pipes (see Figure 8.18).

ªª Use of buckets or skips to place concrete directly at the point required.

The use of underwater concrete is vulnerable to cement washout, which needs to be controlled carefully, not only to achieve good strength, but also to avoid environmental damage, segregation, cold joints and entrapment of water during placing. In particular:

ªª Underwater concrete should be able to flow easily and completely fill the area to be filled without entrapping water.

ªª The concrete should be able to consolidate by itself, because conventional mechanical vibration is not possible underwater.

ªª The concrete should remain cohesive too ensure no washout and to maintain strength.

ªª Underwater concrete typically has a cement content of 400 to 500 kg/m3, which is generally higher than concrete used in the dry.

Figure 8.17 Pressure grouting into a pre-formed bag at North Deepwater Quay, Port of Cork, Eire (courtesy Cork Harbour Commissioners)

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ªª Anti-washout admixtures can be used. These are water soluble organic polymers that increase the cohesion of the concrete and reduce washout of the finer particles when the cement is placed. These admixtures are often used in conjunction with superplasticisers to aid placing and compaction underwater (see BS 8443:2005).

Where the bed has been eroded in front of the toe of the wall, and the erosion is likely to continue, a layer of rip-rap or a grouted mattress may also be used as anti-scour protection. This can, however, reduce the available depth of water alongside the wall if this is critical for berthing of vessels.

Figure 8.18 Placing concrete underwater without tremie pipes by means of suitable admixtures (courtesy Sorensen, 1986)

The outer half of St Mary’s Quay, in the Isles of Scilly, suffered a number of problems including settlement, leaching of fines from the core, local bulging of the quay face, erosion of the face and undermining of the foundations – the last being exacerbated by the scour from the bow thrust of a new ferry.

Repairs have included grouting of the hearting from the deck, stabilising bulging areas by grouting reinforcing bars into vertical holes drilled down the face, and the filling of erosion pockets and undermining by using bagwork and tremied concrete.

Box 8 .5 Repairs to St Mary’s Quay, Isles of Scilly

8.4.2 Coast protection seawall toe repairBefore considering how repairs should be carried out to the toe of a seawall, the possibility of changing or mitigating the conditions that caused the erosion should first be examined.

Such changes could include:

1 Improvement to the littoral drift regime such as halting the removal of beach material updrift of the site of the seawall.

2 The installation of groynes to minimise littoral drift.

3 The protection of the beach from wave attack (eg by the use of an offshore breakwater) (Barber and Davis, 1985).

4 Provision of artificial beach nourishment.

Guidance on management and repair of toe structures can be found in Bradbury et al (2012) Kirby et al (2015).

If the erosion is caused by wave reflection from the wall, changes to the shape of the wall or the placing of a rubble mound in front of it should be considered (see Box 8.6). Examples of this technique may also be found at Aberystwyth, Lancaster and Holderness.

Repairs to the toe of a seawall can usually be carried out in dry conditions, as for the majority of such walls the toe is exposed at low tide. In situ concrete stepped aprons of various shapes with some type of cut-off wall, sometimes formed by steel sheet piling, are often used to protect the toe. Where the cause of the toe erosion is not controlled, further trouble can be expected in the future and there are many instances of successive repairs and extensions to the aprons of seawalls (see Figure 3.103). Repairs to the toe itself can also be made with concrete using an accelerator so that the repair can resist the effect of the rising tide.

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The seawall at Blue Anchor, Somerset, which protects the B3191 coast road, was built around the turn of the century (Figure 8 .19). Since its construction a number of schemes have been introduced to try to reduce scour and reduction of beach level at the toe of the wall. These included shingle traps and the present stone-pitched bitumen grouted apron in front of the wall. Considerable erosion has taken place at the toe of this apron resulting in the removal of beach material.

The original rehabilitation works proposed, which were tested in a deep random wave flume (Figure 8 .25), and include a double layer of three to six tonne local limestone rock. A trial section has been placed on-site and has already validated the proposed construction method.

More recently, Somerset County Council carried out a major improvement exercise on the seawall, which was a 1.4 km

long structure up to five metres high in places, protecting the main coastal road through Blue Anchor (Figures 8 .20 and 8 .21). Below road level the wall came in a variety of forms from the original Victorian ashlar stonework to mid-20th century concrete, but with a largely consistent and disintegrating concrete/rubble filled parapet (Figure 8 .22).

The work was carried out in phases over a four year period with the replacement of the disintegrating wall parapet designed to improve the wall’s strength, durability and appearance. It also provided full vehicle containment for the coastal road, which was completely absent in the weak old wall. The scheme’s final phase also included some scour repairs and won an environmental award.

Figure 8.19 Seawall at Blue Anchor

Figure 8.20 Disintegration of the seawall at Blue Anchor, Somerset

Figure 8.21 Completed refurbishment of seawall at Blue Anchor, Somerset

Figure 8.22 Proposed repairs to seawall using a double layer of limestone rock, Blue Anchor, Somerset (from Allsop et al, 1986)

Box 8 .6 Repairs to seawall at Blue Anchor, Somerset

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8.4.3 Breakwater toe repairFor breakwater walls there is usually no opportunity to modify the sea conditions that cause damage to the toe of the wall, because the breakwater is, by its nature, exposed to wave attack. Where the breakwater consists of a vertical wall on top of a rubble mound, repairs to the rubble mound should be preceded by a check that the size, density, shape, slope, profile and thickness of the armouring are all designed to resist the wave attack.

In some cases the toes of gravity wall breakwaters are permanently underwater and can be repaired by methods similar to those used for quay walls (see Section 8.4.1) although the causes of the damage are not the same as for seawalls. In other cases the lower part of the breakwater wall is exposed at low tide, even if only for a short period on favourable tides. In these cases, repairs to the toe and to the lower part of the breakwater wall, can be made conventionally with concrete as for seawalls. For example, Holyhead breakwater wall has been successfully repaired using pneumatically sprayed concrete or ‘shotcrete’ (see Section 8.6.11) with an accelerator added at the nozzle so that a setting time of 20 minutes is achieved. This technique allowed the maximum use to be made of the available four-hour tidal window.

8.5 INCREASING WALL STABILITY

8.5.1 Rock placed in front of the wallWhere the soil mass under, behind and in front of the wall has an inadequate FoS against a deep slip failure, it may be possible to improve its FoS by placing rock on the toe to act as a counterweight, but this is only feasible where the water depth in front of the wall can be reduced. This solution has been proposed for stabilising a dock wall in the Cumberland Basin in Bristol.

A rock slope placed in front of the wall is also effective in stabilising a wall that is failing by sliding horizontally. The Huskisson Dock in Liverpool was originally opened in 1852. Following severe storms the river wall sections of the dock were observed to be moving and were stabilised by placing rockfill on the seaward side (see Figures 8.23 and 8.24). See also CIRIA; CUR; CETMEF (2013).

Figure 8.23 Typical cross-section of the river wall showing the rock slope placed in front of the wall to stabilise it, Huskisson Dock, Liverpool (courtesy Mersey Docks and Harbour Company)

Figure 8.24Wall stabilisation, Huskisson Dock, Liverpool (courtesy Mersey Docks and Harbour Company/Land and Marine Contractors Ltd)

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In 2014, winter storms attacked the south west of England and caused severe damage to the Victorian Sea wall at Meadfoot Beach, Torquay, where thousands of tonnes of sand were washed out exposing the base and foundations of the seawall. The wall acts as a main defence of the base of the cliffs at the beach, and also forms one of the main road accesses to the beach area, with slipway access to the beach.

Initial work involved excavation of the beach to expose both voids and the sheet piled foundations to assess the extent of repairs required. Spray concrete (gunite) was used to fill the exposed voids with mass concrete and then galvanised mesh was fixed to the wall by means of galvanised tie bars which were chemical anchored into place, before further spray concrete was applied to the exposed surface.

Figure 8.25 Void on slipway wall

Case study 8 .3 Storm damage repairs, Meadfoot Beach Torquay, Devon (courtesy Environment Agency)

Figure 8.26 Damage to beach access steps

Figure 8.27 Beach level excavated to expose voids

Figure 8.28 Excavation of toe down to sheet piles

Figure 8.29 Spray concrete used in voids

Figure 8.30 Completed repairs of sea wall and beach access steps

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8.5.2 Ground and rock anchorsGround and rock anchors can be used to increase the resistance of the wall to sliding and overturning. The anchors have to be designed so that no part of the wall is put into tension. To achieve this, the centroid of the anchor forces has to pass through the wall at a relatively small angle to the vertical, ensuring that the resultant of all forces acting on the wall remains within the middle third of the width, at all levels of the wall. An example of this at the Albert River wall in Liverpool, is shown in Figure 8.31. Such anchors increase the vertical loading on the foundation and, where the soil is insufficiently strong, compression piles under the wall may be required (see Box 8.7).

An example of a different solution devised to preserve a Grade 2 listed lock wall at the Old City Canal in the Isle of Dogs in London is shown in Figure 8.32. The foundation of the wall was deemed unable to take any increase in load and the vertical component of the anchor force has been transferred to a vertical pile.

Rock anchors have also been used in the deepening of a dock in India (see Box 8.8). In this case the sequence of the work was particularly important.

Ground anchors can also be installed horizontally and post-tensioned to ensure the middle third rule. It should be noted that there may be significant management implications for ground anchors installed behind walls, where long-term development may result in the construction over, or cutting through such ties resulting in loss of effectiveness.

Guidance on the design and installation of ground anchors can be found in BS 8081:1989 and BS EN 1537:2013. Figure 8.32 Rock anchors being used for a dock-deepening project in

India (courtesy Consulting Engineering Services (India) Ltd)

Figure 8.31 Strengthening works on a typical section of the Albert River wall, Liverpool (from Allsop et al, 1986)

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There are two examples of the use of compression piles for wall repair work in Liverpool (Figure 8 .33). These are in the east wall of the Brocklebank Dock and the south wall of the Canning Half-tide Dock.

In the Brocklebank Dock a row of columns was installed under the rear of the wall (see Figure 8 .34) using a jet-grouting method. After installation of this row each column was redrilled to take a rock anchor of 20 m length which was stressed to 1.25 times its working load and then de-stressed to the working load. Subsequently the row of

columns under the front face was installed. These columns formed a contiguous interlocking impermeable support underneath the wall adjacent to the dock.

In the case of the Canning Dock partial collapse of the wall had occurred which necessitated the installation of a temporary rubble embankment for support (see Figure 8 .35). Two rows of near-vertical compression piles were then installed by using the mini-pile system and drilling through the wall. Finally a row of tension piles was placed at an angle of 35° to the horizontal.

Figure 8.33 Old City Canal, Isle of Dogs, London, showing vertical pile to take compression load from anchorage (courtesy DHV Burrow-Crocker Consulting)

Figure 8.34 Typical cross-section of the dock wall, Brocklebank Dock, Liverpool, showing rock anchorage and jet-grouted columns (from Allsop et al, 1986)

Figure 8.35 The Canning half-tide dock, Liverpool, showing compression piles (from Bray and Tatham, 1992)

Box 8 .7 Compression piles in use in two repairs at Liverpool

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8.5.3 PilingPiling through the wall to improve the bearing strength of the wall can be done by jet grouting (see Figure 8.34) or small-diameter drilled piles (as small as 90 mm diameter and reinforced with a single bar) (see Figure 8.36).

In the Mazagon Dock in Bombay, the foundation of a wall was strengthened using underpinning within a dewatered cofferdam by excavating one metre ‘hit and miss’ sections and replacing clay and weathered rock with concrete bag work and in situ concrete. In most cases in the UK dewatering within a cofferdam is not now a financially viable option.

8.6 REPAIR OF THE WALL STRUCTURE

8.6.1 Patching of concrete walls above waterWhere a concrete wall has been damaged above water, the damaged area should be cleaned and all loose material removed by high-pressure water jets. Pumps with delivery pressures of over 1000 bar are available but the pressure has to be limited to avoid removing sound material. Where the shape of the hole is likely to lead to a poor bond between the new and the old concrete, it may be necessary to consider using stainless steel dowel bars drilled and grouted into the wall.

Formwork should be fixed over the damaged area with space left to place and vibrate the concrete from the top. In the intertidal zone, the use of accelerators will assist in preventing damage from the rising tide.

An example of the use of patching on waterfront walls at Berwick is given in Case study 8.4.

Figure 8.36 Use of small diameter drilled piles as anchors (courtesy Fondepile Foundations Ltd)

A wet dock in India is being deepened and converted into a dry dock. Part of the dock wall consists of an old masonry wall founded on weak rock overlying stronger rock. Figure 8.21 shows how rock anchors and diaphragm walling are being used to convert the wall to its new function. The following sequence of construction illustrates the importance of correct phasing of this type of work:

ªª install top anchorsªª dewater dock to existing level of bottom of dockªª construct diaphragm wall panels (excavation by

mechanical rock cutters)ªª install bottom anchorsªª construct RC facing to existing wallªª install middle anchorsªª excavate dock floor to new levelªª construct new dock floor and facing to diaphragm.

The effect of any horizontal restraints, such as wall corners, to movement of the wall caused by inclined anchors should be assessed. The diameter of holes through the wall for anchors should be kept as small as possible to avoid weakening the wall. Anchors should be designed and installed in accordance with BS EN 1537:2013.

Box 8 .8 Use of rock anchors for deepening a dock in India

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The present breakwater at Berwick, which is classified as a coastal protection structure, was constructed following parliamentary approval in 1808, with the lighthouse erected at the end of the pier in 1826.

The breakwater consists of stone masonry walls and block infill within the core. A parapet wall is located along the seaward length of the structure on its crest to reduce wave overtopping. Figure 8 .37 shows the typical cross-section through the breakwater.

A roundhead, strengthened by a buttress wall, has been formed at the distal end. Much of the breakwater dries out on an ordinary spring tide on its northern face, but is usually submerged at its toe on its southern face where it abuts the river channel.

The principal defects seen in the structure (Figure 8 .38) and identified through a regular programme of inspections were:

ªª significant cracking, spalling and abrasion of mass concrete

ªª plucking of facing stonesªª washout of mortarªª developments of voids within the core with air and

seawater being compressed and forced through cracks in concrete and masonry

ªª undercutting of the base along about 70 per cent of the length of its estuary-facing side, in places by up to one metre, but more typically by around 0.5 m to 0.7 m

ªª break-up of some previous repairs and strengthening works

ªª vegetation growth in joints.

The approach to repair of the stone face was to reuse as much of the existing stone blocks from the structure as possible or use original displaced stone salvaged from adjacent to the foreshore. The voids left behind the face were then filled with concrete, which was tied to the face blocks using anchors (see Figure 8 .39). This aided in minimising the quantities of new stone required for the scheme.

In addition, reinforced concrete repairs were required over two areas totalling about 130 m3. This required specialist formwork on the face of the structure (Figure 8 .39). Concrete with a red/pink pigmentation was selected to blend in with the existing Northumbrian sandstone and a formwork liner with blockwork pattern was chosen to provide the appearance of sandstone blocks, although

Figure 8.38 Damage to southern stone face

Figure 8.40 Shutter design

Figure 8.39 Stone face repair detail

Figure 8.37 Breakwater cross-section

Case study 8 .4 Berwick breakwater refurbishment, Berwick upon Tweed, UK (courtesy Royal Haskoning DHV/BAM Ritchies)

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it was difficult to achieve an exact match to the existing random pattern of the stonework (Figure 8 .41). Alternative methods of repairing concrete are also given in Section 8 .6 .11, and in Allen et al (1992) and Perkins (1997).In addition, reinforced concrete repairs were required over two areas totalling about 130 m3.

8.6.2 Patching walls below waterDamaged parts of a wall that are always below water should be cleaned with a high-pressure water jet and repaired with concrete, irrespective of the original material of construction, because the repair will never be seen. However, care should be taken because the effect of concrete on the original surrounding stone or masonry, which may have different moduli and different behaviours, will need to be considered. The jets for use underwater should have a balancing jet to avoid putting a high reactive force on the diver. Formwork should be used as described in Section 8.6.1. Concrete with an additive to prevent segregation underwater should be pumped in at one end until it emerges at the other or, in the case of larger holes, concrete without an additive can be placed by tremie (see also Sections 8.9 and 8.10).

8.6.3 RepointingWhere the mortar in a brick or masonry wall is missing or crumbling away, the joints should be cleaned out with a jet of water that has sufficient pressure to remove loose or defective material but without damaging sound mortar. Care should be taken not to displace individual bricks or stones. Where all the original mortar is weak, hand raking or mechanical removal of loose material may be preferable to avoid unnecessary damage to the wall. Where the resulting voids are shallow, the joints should be filled with pressure pointing.

In some types of pressure pointing, OPC, fly-ash, sand, and a non-ionic wetting agent are mixed, and then passed via a pressure pot to a nozzle. Mortar is forced out of the nozzle by compressed air. Narrow joints up to 100 mm deep can be filled, as can wider joints up to 300 mm deep in rubble masonry.

Where the joints are deeper than 300 mm, injection pointing should be used with nozzle sizes appropriate to the width of the joint. Where the voids in the joint are wide and of moderate depth, but the appearance of the wall is not important, spray concrete (see Section 8.6.10) may be more economic.

In the intertidal zone, accelerators should be used in the mortar to achieve sets of between 20 seconds and 30 minutes according to the particular situation. The accelerator is added at the nozzle. Even shorter setting times can be achieved with use of specialist additives where the mortar is being placed on a wall in running water.

When extensive repointing is contemplated, consideration should be given to the possibility that the reduction in permeability of the wall may cause problems by preventing free drainage of water from the back of the wall. If this is likely to be the case, weep pipes should be inserted before repointing.

8.6.4 Heritage issuesIn some cases due to the heritage value of the wall, it may be necessary to obtain approval from the Heritage body (English Heritage, Historic Scotland etc) for the repair method. If the structure is listed then approval from the relevant planning authority is also required. It is possible that the

Figure 8.41 Final reinforced concrete repair showing match to existing structure

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heritage bodies will seek a repair method involving materials matching the existing wall. It should not be assumed that in all cases concrete can be used because the repair cannot be seen. Case study 8.1 demonstrates how this particular issue was addressed in Jersey for three heritage masonry structures.

8.6.5 Grouting of a wallGrouting of a wall is usually carried out to improve its integrity, ie to bond together all the individual stones or bricks of the wall so that it acts as one coherent mass. Grouting may also be done to reduce the permeability of the wall and to fill voids in the foundation. The technique is not new, and has been in use for over 150 years. For example, there are records of the Wilson bridge in Tours being grouted in 1835 (see Figure 8.42).

Figure 8.42 Grouting of the Wilson Bridge in Tours, France (from Bray and Tatham, 1992)

One of the more common applications of grouting is to solidify the loose filling in breakwaters such as the one shown in Figure 8.43. In this type of structure, the outer coursed skin walls of the Ramsgate breakwater were originally designed to retain the chalk and lime filling and resist the wave forces. The outside walls can have a low height/width ratio because of the high internal angle of friction of the rubble filling. Although some examples of this type of breakwater wall have survived for over 100 years with only minor maintenance, the structures are vulnerable to progressive failure once the outer wall is breached, as the internal filling has no resistance to wave action.

Grouting has the attraction of solidifying the loose filling and, in theory, bonding the whole structure together. A higher-risk solution is to repair the outer wall by replacing missing stones, repairing the pointing, sealing the top surface of the breakwater to prevent internal water pressures caused by overtopping waves, and protecting the toe of the wall. The decision on whether to grout the filling or not depends on the history of the severity and frequency of the damage. Another factor to consider is whether making the structure rigid, or less porous, is desirable. A reduction in porosity may affect the breakwater’s ability to dissipate wave energy.

Figure 8.43 Ramsgate breakwater 1750–1792 (courtesy W S Atkins & Partners)

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Banavie Locks are located near Fort William on the Caledonian Canal. The lock flight consists of eight locks in total and was subject to major investment (£20m) as part of a 10 year rolling programme between 1995 and 2005 to ensure operational efficiency and structural integrity of all locks on the canal.

The lock chamber walls are constructed in mass, random sandstone and have double skinned walls, approximately one metre thick, with rubble infill. The copestones are granite. The lock chambers are inverted arch in profile with additional support from counterfort walls at right angles to the main chamber walls.

As part of the project, secondary grouting of locks was carried out to arrest lock chamber leakage missed as part of the major works. Historically cementitious grouting has been used for secondary grouting operations. However, in this case, an alternative material, ie polyurethane, to seal lock leakage was offered by the contractor. Trials were undertaken to assess the proposed materials efficiency in leak sealing, targeting the leakage exit points from the lock chamber walls by directly drilling and injecting into the visible leakage exit point.

Following the successful trial the full repair work was instructed, incorporating methodology improvements. The polyurethane injection system worked well and a visible reduction and arrest of lock chamber leakage was achieved. This work, carried out at a total cost of around £100K, started on the 8 March 2011 and was completed on the 17 March 2011.Figure 8.44 Leaks with contractor’s staff working from pontoon

Figure 8.45 Target drilling of visible leakage from lock chamber wall

Case study 8 .5 Lock chamber leakage at Banavie Locks, Scotland (courtesy Scottish Canals)

Figure 8.46 Polyurethane injection to visible leakage exit

If grouting is to be used, trial pits should be excavated in the filling to estimate the volume of voids to be filled and to provide information for determining the details of the grouting process. The outer walls will have to be made grout proof.

It is most important that the specification for the work should require that the grouting be carried out in defined stages so that the pressure of grout against the back of the skin wall is limited to a safe value. The applied grout pressure should also be limited to a safe value. Arrangements should be made to check how far the grout has spread. It is advantageous to carry out grouting trials in advance of a contract to grout the whole wall. Its effectiveness can then be checked as well as the amount used and the cost.

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Cullochy Lock had undergone grouting works in the late 1990s following substantial refurbishment. However, no secondary grouting or pointing was carried out as part of this work and over time deterioration of pointing began to be noted, resulting in an increase in the number and severity of leaks from the lock wall. Further work was subsequently required to grout and repoint the walls.

A floating platform in the lock chamber allowed the contractor to build access cradles from the water so that cradles up to 12 m in length could be suspended from the lock side. During site set up the leaks were located and marked on the top of the lock wall to help during the grouting phase.

The lock walls were initially prepared by power washing with a 3000psi pressure washer fitted with a turbo nozzle (rotating nozzle) attachment. The turbo nozzle created an even cleaning pattern but more importantly the centrifugal force of the jet removed any loose mortar in the masonry joints. Further defective mortar, not removed by the power washer, was removed using hand tools, because Historic Scotland would not permit the use of power tools (eg angle grinders) for removal of mortar.

Deep areas of joints were repointed using a mortar mix, which was applied using a mortar screw pump powered by a 6Kva generator. Shallow areas were repointed using hand tools. When hand applying mortar the mix has to be in a workable consistency and the surface should be dampened beforehand (a paintbrush and bucket of water is ideal for the task).

Two methods can be used to apply the grout:

1 Create a uniform grid of grout hoses along the entire lock wall and pressure grout each hose until refusal.

2 Locate specific voids, by assessing severity of leaks or carrying out a radar survey of the lock wall and then targeting these areas with grout hoses.

The second method will save time, minimise disruption and, if applied correctly, should give good results. Grouting operations should begin once the pointing mortar has set. Typically a five man grouting team is employed consisting of:

ªª two men controlling the material into the grout pump

ªª one man acting as top man and conveying information from nozzle to grout pump

ªª two men on cradle controlling the grout gun.

The following method was used for the work:

ªª The grout pump was located lock side and the hose lowered into the access cradle.

ªª Mortar was mixed in isolated mixing area away from the watercourse.

ªª On predetermined areas 20 mm dia. holes were drilled through the masonry joints, avoiding the actual masonry blocks, to a depth suitable to carry grout behind masonry.

ªª Injection nozzles were inserted and selected grout was injected into the holes with a low pressure grout machine.

ªª Starting at the bottom of the lock and working upwards grout was applied at a rate of around seven litres per minute until refusal. Note if over pressurised, grout will shoot out when the nozzle is removed. Normally a suction noise can be heard when pumping stops and the nozzle is retracted.

ªª Once grout had set sufficiently the chamber was flooded. Time was then allowed for the water to settle and find any potential weaknesses before draining the lock. While the chamber was draining, any leaks from the lock wall were noted and made good with further grouting. Note that even pinhole leaks should be made good – if left they can develop into major leaks. The process was then repeated until no further leaks were detected from the masonry.

ªª On completion of the grouting works the locks were repeatedly filled and emptied and any areas still showing signs of water ingress were repointed.

Figure 8.47 Power washing at Cullochy Lock

Figure 8.48 Cullochy Lock pressure grouting operation

Case study 8 .6 Grouting of Cullochy Lock, Scotland (courtesy Scottish Canals)

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Grouting is also carried out on masonry and concrete coast protection and quay walls, bridge abutments and piers to fill cracks and voids within the coursed masonry structure. Where the face of the wall is accessible it has been reported that grouting into horizontal holes is more effective than using vertical holes. As it is usually impossible to seal the rear face of quay and coast protection walls, the possibility and any effects of leakage of grout from the rear of the wall should be considered. In some cases grouting of masonry has been found to be ineffective. This may be due to a low void content or to an inappropriate type of grout.

Before grouting of a structure is carried out the following should be considered:

ªª spacing and penetration of grout holes

ªª need to use staged grouting

ªª sizes of fissure to be filled

ªª specification of the grout

ªª means of escape for the air or water within the voids to be filled by grout

ªª grout pressure to be used

ªª need for intermediate grout holes if grout fails to appear at the next grout hole down the wall

ªª action to be taken if the wall continues to accept grout without any reduction in flow (eg use of special grouts)

ªª whether vacuum grouting should be used to increase penetration

ªª whether water leakage needs to be controlled by water-reactive grouts

ªª methods of monitoring the grouting operation, ie grout take up at each place, location and depth of grout holes, observation of grout spread.

Note that grouting can have implications on the hydrostatic pressures that can develop within the core of the wall. This is because of delays to tidal lag due to a reduction in permeability of groundwater from behind the wall, which can instigate failure if not assessed thoroughly beforehand.

As there is no CoP for remedial grouting, advice should be sought from specialist contractors or consultants, who will be able to assist in the selection of suitable techniques and types of grout. For instance, grout for structural void filling will have a much higher 28-day compressive strength (typically 14 N/mm2) than one designed for ground stabilisation (around 2.2 N/mm2). See Snowden (1990) for grouting techniques.

As part of the Scarborough Coastal Protection Scheme, Ritchies undertook the drilling and grouting of the East Pier. The purpose of this work was to strengthen the pier by filling and sealing voids in the historic structure caused by the sea and washout. As the structure is listed, care was needed both with the methods and the grout materials used, including the use of a lime based grout and avoiding the use of air flush for drilling.

Drilling was undertaken using Boart Deltabase DB100 rigs with hydraulic top hammer and both simultaneous casing systems and open hole drill steels. Grout was mixed at a central batching plant with tight environmental controls to avoid nuisance from dust and noise to the businesses and public located immediately near to the work area.

Figure 8.49 Drilling at the East Pier, Scarborough

Case study 8 .7 East Pier grouting Scarborough, North Yorkshire (courtesy BAM Ritchies)

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8.6.6 Cracks and joint sealersWhere walls are to be grouted, it is first necessary to seal cracks and joints in the face of the wall. Above water or in the intertidal zone the normal method would be to use pressure or injection pointing. Below water an alternative method is to caulk the cracks, eg with hemp, although underwater pressure pointing is also possible. In areas below water, where joints between blocks of concrete or masonry require sealing, and proprietary joint sealers that swell when immersed in water, such as hydrophobic polyurethane resin, may be considered.

Where isolated large cracks have occurred due to differential movement of two parts of a wall, rigid sealing of the crack may be ineffective. Such cracks sometimes occur near corners in dock walls. Away from a corner walls can rotate slightly to allow the backfill pressure to reduce to the ‘active’ level, but near a corner each wall is prevented from moving by the restraint provided by the other.

Where the FoS against overturning is high, the relative movement will be small and may be accommodated by the normal flexibility of a masonry wall. In such a case a curve in plan in the wall may be observed (see Figure 8.50). Where the FoS is lower, the movement will be larger and will exceed the capacity of the masonry wall to flex so that a crack forms. If the crack is large enough, filling will be washed out from behind the wall and settlement of the surface behind the wall will occur.

Repair of such cracks is difficult. Where the wall movement has ceased, it may be possible to seal the front face of the crack and then drill and grout it. Alternatively, it may be possible to excavate the fill from behind the wall and replace it with coarse rubble, which is too large to pass through the crack.

8.6.7 Masonry bonding, stitching, dowelling and wedgingConventional methods of calculating sliding, overturning and the distribution of concentrated loads such as wave forces, bollard pulls and ship impacts assume that a wall acts as one homogeneous structure. A number of different methods have been used in the construction of masonry walls in the past to ensure that the individual stones in the wall act together as one coherent mass. Some of the methods used such as mortar jointing, wedging, timber and iron cramps, may deteriorate and fail over time.

Mortar joints close to the exposed face can be repaired, but wedges and cramps used to hold a wall together cannot be replaced when they deteriorate. It is then necessary to hold the wall together using a different method, such as injection pointing of the outer skin and grouting of the inside. If these are not feasible, the wall has to be refaced or reconstructed. A further alternative is to tie the wall together with stainless steel rods, either drilled and grouted within the body of the wall or passing right through and anchored at both sides. Figures 8.51 and 8.54 shows the repair of the north wall on the Cobb at Lyme Regis, and Figures 8.55 to 8.57 show the breakwater at Weymouth, where dowelling techniques were used.

In Jersey three heritage structure all had masonry integrity issues and working closely with the local authorities, heritage bodies, a series of grouted anchors were used to stitch the structures back together. This approach is subtly different to the approaches at Lyme Regis and Weymouth because the grouted anchors are hidden and consist of a metal bar surround by a fabric sock. The anchor, including sock, is

Figure 8.50 A dock wall showing the curve in plan from movement of the structure, Gloucester, UK (courtesy P F B Tatham)

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placed within a small diameter pre-drilled hole within the structure. Once in position, grout is pumped under low pressure through the anchor, which seeps into the sock. Only a small amount leaks out into the surrounding masonry, stitching the structure together. The pre-drilled hole is then filled with a replace cap to hide the anchor from view. See Case study 8.9.

The dock walls at Milford Docks were built over 120 years ago and are now in need of upgrading, with works concentrated on rectifying settlement of the lock entrance wall and strengthening concrete walls in the dry dock (Figure 8 .52). The walls are constructed on bedrock consisting of sandstone and siltstone/mudstone. This bedrock has become weathered leading to a reduction in bearing and subsequently settlement and distress of the walls.

Investigation holes were drilled over 40 feet deep into the bedrock underneath the lock entrance wall, which confirmed that the bedrock is highly fractured. The wall was strengthened by pumping over 100 tonnes of liquid cement into the body of the wall. The fine fractures in the rock were first sealed by injecting an expanding polyurethane resin under pressure that can flow into the fractures and set very quickly. This hydro-reactive polyurethane resin was used as this material only reacts in contact with water or moisture and is low in viscosity.

The injection process was undertaken in stages and in a ‘bottom up’ fashion. An 85 mm diameter, 1000 mm length packer was lowered down the borehole and inflated to isolate the grouting zone and to reduce hydro fracturing of

resin up above the packer position. The resin was brought to the correct working temperature and an air operated low pressure diaphragm pump was used to pump the resin (Figure 8 .53). The diaphragm pump was connected to the injection lance and the grout pumped under low pressure into the grout zone until either a significant pressure increase was noted at the pump or until grout refusal.

The grouting operation was then stopped, the grout packer deflated, raised 700 mm and re-inflated. The grouting operation resumed and continued in this fashion until the full depth of the weathered rock was injected.

Following injection of the resin 25 mm diameter stainless steel bars were installed in the boreholes and fixed with a neat cement grout.

Figure 8.53 Typical section through wall showing extent of resin grouting

Case study 8 .8 Innovative dock wall repair works in Milford Docks, Pembrokeshire (courtesy Atkins)

Figure 8.52 Work on the dock entrance walls at Milford Docks

Figure 8.51 Section through the north wall showing ties used for strengthening, Lyme Regis, Dorset (courtesy Dobbie and Partners)

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Figure 8.55 Section 1 through the reconstructed stone pier at Weymouth, Dorset (courtesy DHV Burrow-Crocker Consulting)

Figure 8.54 Section through the Cobb showing the use of stainless steel dowels, Lyme Regis, Dorset (courtesy Dobbie and Partners)

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Figure 8.57 Section 3 through the reconstructed stone pier at Weymouth, Dorset (courtesy DHV Burrow-Crocker Consulting)

Figure 8.56 Section 2 through the reconstructed stone pier at Weymouth, Dorset (courtesy DHV Burrow-Crocker Consulting)

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The pier and breakwater at St Aubin on the south coast of Jersey in the Channel Islands were originally constructed from two outer walls of dressed granite masonry blocks with secondary rock core fill material (Figure 8 .58). The structures are founded upon the beach sands and have distorted vertical and horizontal geometry, which is difficult to conventionally survey accurately. LiDAR was used to record and model both the structures and their surroundings.

The valuable heritage of these two structures and the limited funding available has resulted in a secret fix ‘stitching’ solution being applied to the masonry piers both horizontally and vertically in their vulnerable inner walls (Figure 8 .59). The ‘virtual’ models generated by LiDAR survey enabled an ‘engineered’ number to be determined for the reinforced cementitious grout mini stitching anchors, which both support the inner walls as well as and tie them back to the main body of the structures.

The engineering problems that needed resolution included:

ªª cracks and fissures across the grouted core, which were providing paths for impulsive wave pressure propagation

ªª settlement of the harbour wall, which was causing the loosening of blockwork in the deteriorated areas

ªª hydrostatic pressures that were building up in the core of the breakwater.

The chosen stitching solution used anchors consisting of a number of solid stainless bars contained within a fabric sleeve injected with cementitous grout after positioning. The bond of the grout that seeps through the fabric sock used in the anchor between the masonry and the reinforced anchor is very high, tying areas of loose masonry blocks together. In the granite sections plugs in the masonry were reinserted to ensure an ‘invisible fix’ once the anchor had been installed (Figure 8 .60).

This stitching methodology also provided a foundation solution, with the numerous small diameter vertical anchors becoming mini piles when drilled down through the granite wall stones, through the beach deposits and into the Jersey rock shale beneath (Figure 8 .61). There is a certainty with respect to the capacity of each anchor or mini pile as the drilling technique means that every element’s bearing capacity is known and recorded.

The stitching method used to stabilise and strengthen these two marine heritage structures has proved to be effective. It also showed that by combining methods of historical research, intrusive site investigations and virtual modelling through LiDAR surveys, even these unique and geometrically difficult structures can be secretly and effectively strengthened and preserved for future generations.

Figure 8.58 North pier and fort, St Aubin Jersey

Figure 8.59 Combination of loads in fort breakwater

Figure 8.60 Anchor with plug cap replaced (invisible fix)

Figure 8.61 Cross-section of north pier with stitching anchors

Case study 8 .9 ‘Stitching up’ the past, St Aubin, Jersey (courtesy Arup)

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8.6.8 Replacement of brick and stoneWhere individual bricks or stones have decayed, or fallen out of the above water or intertidal face of a waterfront wall, the cavity can be cleaned out by chiselling and high-pressure water, and a replacement

stone or brick put back in the wall. Injection pointing may help to complete the repair as it is otherwise difficult to fill all the surrounding space with mortar.

An example of the use of the replacement technique may be found in Swansea, where maintenance work has been carried out on the sea defences (Bray and Tatham, 1992). Loosened stone blocks, 1 m × 0.65 m ×0.65 m, were bonded back into the wall with rapid-curing epoxy adhesives, and then back-grouted and repointed.

Where substantial areas of facing brickwork or stonework have fallen out, for example at the Alfred Dock, Birkenhead (see Figure 8.62), the situation is more difficult. In many walls the facing is of different construction from the body of the wall. Figure 8.63 shows the cross-section of such a wall at Wallasey. The body of the wall may first require repair by grouting or injection pointing. If the new facing has no adequate key, stainless steel anchorage bars can be drilled and grouted into the wall. The face of the wall can then be concreted or, if the original appearance of the wall is important, the brickwork or stonework can be reconstructed – possibly with a concrete backing.

8.6.9 Additional skin of brickworkWhere a wall or a breakwater has suffered considerable degradation to its facing, and where the appearance of the wall is important, a complete new skin of brickwork may be an appropriate solution. Figure 8.64 shows a section through the Network Rail (formerly British Rail) breakwater at Starcross, Devon, which has been refaced with a new skin of brickwork tied to the existing core by steel anchors.

Figure 8.62 Area of missing brickwork on the south side of the Alfred Dock, Birkenhead (courtesy Mersey Docks and Harbour Company)

Figure 8.63 Typical section of a wall, showing the face to be of different material from the mass of the structure, the Great Float, Wallasey (courtesy Mersey Docks and Harbour Company)

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St Donat’s Castle is a medieval castle in the Vale of Glamorgan, Wales, overlooking the Bristol Channel. A breach in this important seawall protection to the castle wall following a major storm required careful investigation (Figure 8 .65). The damage included the collapse of the pavement into the washed out voids, washout and loss of facing stones. The extent of the voids created by the washout behind the wall was initially disguised by the concrete apron slab spanning over the void

The project was to design a replacement of the core fill, provide a flexible topping and re-fencing with the approval of Cadw, the Welsh Government’s historical environment service.

The wave energy impact reduction was achieved with a reinforced concrete re-curve to replace the damaged cope beam of the wall. The rock armour, originally proposed as an option to reduce wave loading on the wall, was classified as ‘betterment’ by the insurers who funded the project. Figure 8.65 Seawall at St Donat’s Castle

Case study 8 .10 Seawall investigation and repairs at St Donat’s Castle, Wales (courtesy Arup)

8.6.10 ProtectionofthetopsurfaceofwallorbackfillProtection of the top surface of a wall is a particular requirement for breakwaters, exposed piers and other structures subject to overtopping by waves. The surface of the backfill to coastal defences also needs to be protected to prevent erosion of the backfill. Protective surfaces should be designed to resist overtopping by the maximum forecast wave and to be sufficiently waterproof to prevent the build-up of water pressure within any permeable hearting or filling, which then increases the outward load on the wall forming the seaward surface of the structure.

The amount of overtopping will be affected by the profile of the wall and of the seabed slope on the beach seaward of the wall. In the past the surfaces behind the wall subjected to wave overtopping have typically been protected by stone pitching. This may still be appropriate in cases of listed structures and where the appearance is important. In other cases concrete, asphalt or a designed revetment should be considered.

Figure 8.66 shows an example of a seawall where the backfill has been protected by a revetment formed from a Reno mattress after failure of the top of the wall due to overtopping. Figure 8.64 Section showing the new skin of added brickwork,

Starcross breakwater, Devon (courtesy Network Rail)

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Figure 8.66 Repair to the seawall showing the backfill protected by a revetment, Harrington, Northamptonshire (courtesy Allerdale District Council)

8.6.11 Sprayed concreteSprayed concrete, also known as ‘gunite’ or ‘shotcrete’, is the process whereby a cementitious mix is propelled into place by a high-pressure air stream. In the maintenance and rehabilitation of old waterfront walls sprayed concrete is used for complete re-facing, the filling of voids and the repointing of wide mortar joints. The finished material is a high-strength concrete, which will form an integral part of the wall. Lime can be added to the mixture to give masonry walls some ability to accommodate movement.

Figures 8.67 to 8.69 illustrate the relatively simple access arrangements that can be used for repairing a wall with sprayed concrete. Figure 8.67 also shows the extent of marine growth that often has to be removed by high-pressure water jetting before repair can begin. It is important that the access arrangements used should be approved by the HSE or other similar regulatory body.

The term ‘gunite’ is used for sprayed concrete where the aggregate is smaller than 10 mm and ‘shotcrete’ where the aggregate is 10 mm or larger. There are also dry arid wet processes requiring different techniques and equipment. In the dry process the dry mix is conveyed by air to the nozzle where water is added. In the wet process, wet concrete is pumped to the nozzle where high-velocity air is used to propel the mix into position. The dry process is more suitable where small volumes of concrete are to be replaced or where access is difficult, as the plant may be positioned up to 400 m from the point of application. The wet process is more suitable where large volumes of concrete are to be placed. A specialist contractor should be consulted on the most suitable process for any particular situation.

The quality of sprayed concrete depends on the following:

1 Correct specification: advice is given in BS EN 14487 part 1 (2005) and part 2 (2006).

Figure 8.67 The spraying of concrete onto a seawall (courtesy Duracrete Limited)

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A partial collapse of a stone block harbour wall within the tidal range resulted in the necessity for emergency repairs at Porthcawl Harbour in Wales (Figure 8 .70). Bridgend County Borough Council arranged for access to be made available by means of a mobile crane operating from the top of the harbour wall, supporting a man-riding basket and the contractor provided a sprayed concrete crew to undertake the works.

Temporary ‘Acrow’ props were placed in the void to support upper stonework and an initial 50 mm layer of accelerated sprayed concrete was applied to seal the exposed face from inundation and secure the wall fill. Dowels and reinforcing mesh were then fixed to this layer and sprayed concrete applied to the original profile, with a finishing coat of pigmented concrete to replicate the appearance of the original stonework.

Figure 8.70 Emergency repairs and remedial works to Porthcawl Harbour walls following collapse

Case study 8 .11 Repairs at Porthcawl Harbour, Wales (courtesy BAM Ritchies)

2 Correct preparation: thorough preparation and cleaning of the surface to which the sprayed concrete is to be applied.

3 Correct application: select only reputable contractors, eg those who are either members of the Sprayed Concrete Association, or other firms who can demonstrate their competence. There is also a move to test and certify ‘nozzle men’ in the same way as welders, in view of their importance in achieving quality in the finished product.

Sprayed concrete can be reinforced with stainless steel or polypropylene fibres added to the mix, or steel mesh can be fixed to the wall before spraying the concrete. The latter should be used where the thickness of the sprayed concrete is greater than 25 mm. Sprayed concrete can be used for intertidal work if an accelerator is added to the mix.

BS EN 14487 part 1 (2005) and part 2 (2006) cover the use of sprayed concrete and BS EN 14488 parts 1 to 7 cover methods of testing.

Further information can also be obtained from the Sprayed Concrete Association (see Websites) who publish a number of booklets on the use of the material including the European Federation of National Associations (FEANI) representing producers and applicators of specialist building products for concrete, the Expert for Specialised Construction and Concrete Systems (EFNARC) specifications and guidelines.

Figure 8.68 The seawall at Colwyn Bay after the application of sprayed concrete (courtesy Tarmac Structural Repairs Ltd)

Figure 8.69 Filling voids with sprayed concrete (courtesy Duracrete Limited)

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As part of a £25m Defra-funded seawall refurbishment contract, BAM Ritchies carried out extensive repairs to the face of the concrete seawall at Scarborough for Scarborough Borough Council in 2002. Along the 2.1 km seawall over 300 m2 was identified for remedial works including:

ªª infilling of open joints using sprayed concreteªª refacing of the concrete wall by grit blast cleaning the

surface, fixing a stainless steel mesh and application of Cemrok 40 accelerated sprayed concrete to resist wave action

ªª stitching of cracks using stainless steel ‘U’ pins and sprayed (Figure 8 .74).

The project illustrates a range of simple repair techniques for waterfront wall refurbishment.

Figure 8.74 Application of sprayed concrete to existing mass concrete wall

Case study 8 .13 Seawall concrete repairs, Scarborough, UK (courtesy BAM Ritchies)

The application of Gunite to repair damaged seawalls is a cost efficient and common method used for remedial works. The first task normally is to clean the entire wall using high pressure water jetting to remove all the deposits, including marine growth and algae, which has built up over the years. Steel dowels (typically 16 mm dia.) are then drilled and resin fixed into the wall to hold the weld mesh (typically A353), which forms the reinforced part of the concrete overlay. Once the weld mesh is fixed, the whole of the structure is then overlaid with around 100 mm to 250 mm thickness of 40 kn/m2 sprayed concrete. The sprayed concrete may also use sulphate-resistant cement and include polypropylene fibres to increase its durability. In addition, sprayed concrete can also incorporate an accelerator to provide an early initial set to resist water and wave action during subsequent high tide.

While sprayed concrete is a quick and cost-effective repair technique for infill of exposed voids and reinstatement of structural faces, it is not normally suitable for historic or heritage structures where the original form of construction needs to be maintained. However, in some cases it may be

possible to modify the final colour of the sprayed concrete through the addition of pigments to match, for example, existing sandstone blocks.

Figure 8.71 Sea defence showing the application of 100 mm of sprayed concrete incorporating polypropylene fibres and sulphate resistant cement at Craigendoran, Scotland, 2006

Note that the pier was closed to the public due to its unsafe condition .

Figure 8.72 The extent of damage at Sutherland, Scotland

Case study 8 .12 Gunite repairs of seawalls at Craigendoran and Scourie Pier, Scotland (courtesy BAM Ritchies)

Note that refurbishment included the application of sprayed concrete to stabilise the large voids at the pier head to provide additional load bearing capacity to enable safe working on the pier .

Figure 8.73 Scourie Pier after refurbishment in 2012

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8.6.12 FerrocementFerrocement is a cement-rich mortar reinforced with layers of small-diameter steel mesh. It has been used for many years for making the hulls of boats and other thin structural sections by a process of plastering and building the material up in thin layers. More recently it has been employed as a thin liner to rehabilitate sewers and other structures, including seawalls. In the form used for seawalls, the material is typically placed by a gunite process (see Section 6.2.11) with the mesh fixed to the wall.

8.7 REPLACING THE WALL WITH A NEW STRUCTURE

Where the existing wall is beyond practical or economic repair, the structure can be replaced, completely refaced or reconstructed. If ground conditions are suitable and the appearance of the wall is not particularly important, one solution is to drive steel sheet piles in front of the wall and use ground or rock anchors to secure the top of the sheet piling, such as has been carried out in Portsmouth and Axmouth (see Figures 8.76 and 8.77). The space between the sheet piles and the original wall is then usually filled with concrete to reduce corrosion of the sheet piles and transmit the anchor force from the sheet pile to the original wall. One disadvantage is that the life of the sheet piles will usually be far less than the life of the original wall due to corrosion of the steel, and the particular effects of accelerated low water corrosion (ALWC) in tidal waters. ALWC is associated with a rapid pitting form of microbial induced corrosion. Further information on ALWC can be found in PIANC (2005), BS 6349-1-3:2012, and Breakell et al (2005).

Figure 8.78 shows additional repair that is needed when the sheet pile corrodes. One particular advantage of sheet piles is that they can be installed from the surface even when most of the wall to be protected or replaced is permanently below water level.

Where the wall is exposed for at least part of the tide, there are many possible alternatives for wall reconstruction. Figures 8.55 to 8.57 show three different sections along the length of the reconstructed Stone Pier at Weymouth, with variations to suit the height and type of the original structure.

Figure 8.75 Repointing seawall with sprayed concrete, Dundee, Scotland (courtesy Tarmac Structural Repairs Ltd)

Figure 8.76 Tied sheet piling being used to strengthen a wall, Portsmouth, Hampshire (courtesy T F Burns and Partners)

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Where the appearance of the wall is important, but its structure is beyond repair, the outside face of the wall can be retained or simulated by a replica, but with the soil loads being carried by a new wall behind, as shown in Figures 8.79 and 8.80 of wall reconstruction at Crail in Fife. There are many different ways of constructing a hidden new wall. Figures 8.81 to 8.87 show the variety of solutions adopted for the quay and river walls at Cork, Ireland, and Figures 8.88 and 8.89 illustrate two of the designs adopted for the harbour wall at Saundersfoot, Wales.

Figure 8.77 Tied steel sheet piling being used to strengthen a wall at Axmouth, Devon (courtesy East Devon County Council/Lewis & Duvivier)

Figure 8.78 Sheet piling being used to repair a previous sheet piled repair at North Wall Roundhead, Lyme Regis, Dorset (courtesy Dobbie and Partners)

Figure 8.79 New, hidden wall behind a reconstructed wall at Crail, Fife, Scotland (courtesy Wallace Evans and Partners)

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Figure 8.80The reconstructed wall at Crail, Fife, Scotland (courtesy Trekearth.com)

Figure 8.81 Remedial works for Anderson’s Quay, Cork, Ireland (from Langford and Mulhern, 1982)

Figure 8.82 Reconstruction of McSwiney Quay, Cork, Ireland (from Langford and Mulhern, 1982)

Figure 8.83 Collapsed portion on Wandesford Quay, Cork, Ireland (from Langford and Mulhern, 1982)

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Figure 8.84 Reconstruction of Wandesford Quay, Cork, Ireland (from Langford and Mulhern, 1982)

Figure 8.85 Phases 1 and 2 reconstruction works at Penrose Quay, Cork, Ireland (from Langford and Mulhern, 1982)

Figure 8.86 Remedial works at Glanmire Road, Cork, Ireland (from Langford and Mulhern, 1982)

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Figure 8.87 Remedial works at George’s Quay, Cork, Ireland (from Langford and Mulhern, 1982)

Figure 8.88 Encasement of harbour wall at Saundersfoot, Dyfed, Wales (courtesy Saundersfoot Harbour Commissioners)

Figure 8.89 Cross-section of quay wall and retaining wall at Saundersfoot, Dyfed, Wales (courtesy Saundersfoot Harbour Commissioners)

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8.8 MODIFICATION OF WALL TO SUIT NEW PURPOSE

One of the commonest modifications required is to increase the height of the wall for flood defence purposes. Three examples of this are shown in Figures 8.90 to 8.92. A more difficult modification is lowering of the ground in front of the wall – typically to provide a greater depth of water for a ship berth at a quay. Anchored sheet piling is also a suitable solution. Where sheet piling is not possible or aesthetically desirable, some type of underpinning is required, which will involve drilling piles through the wall and anchoring to resist the increased overturning moment.

Figure 8.90 Design for increasing the height of the wall on the left bank of the Monnow, Monmouth, Wales (courtesy Welsh Water/Halcrow)

Figure 8.92 Design for increasing the height of Bakers Quay, Barnstaple, North Devon (courtesy MAFF)

Figure 8.91 Design for increasing the height of the wall on the right bank of the Monnow, Monmouth, Wales (courtesy Welsh Water/Halcrow)

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8.9 TECHNIQUES FOR WORKING UNDERWATERAll work carried out underwater is slower, more risky and more costly than that above water and is also usually of lower quality. So every opportunity to make repairs in the dry should be taken, even though the available working periods may be quite short. Such opportunities may arise from tidal working, making use of low river levels, lowering the level in an impounded dock, constructing a cofferdam and dewatering the area of repair or by using a limpet dam.

Any method involving dewatering the area in front of a wall should be preceded by a check that the stability of the wall is not endangered, as the water pressure in front of the wall may be providing a vital component of the forces supporting the wall.

One method, which allows dewatering of small areas of wall for repair work to be carried out, is the use of a limpet cofferdam: This is a small open-topped caisson, which is shaped to fit closely against the front face of a wall with rubber seals, and gives contractors access to inspect and repair quayside walls and other underwater structures. The limpet dam is lowered into the water, placed against the wall and pumped out using a high-capacity pump to affect an initial seal. The outside water pressure then forces the dam and its rubber seals against the wall and holds it in place (Figure 8.95).

Figure 8.95 Limpet cofferdam used for quay repairs at Harwich, Essex (courtesy Livesey and Henderson)

In the mid 1990s, Somerset County Council carried out a major improvement exercise on the Blue Anchor seawall, which was a 1.4 km long structure up to five metres high in places, protecting the main coastal road through Blue Anchor. Below road level the wall came in a variety of forms from the original Victorian ashlar stonework to mid-20th century concrete, but with a largely consistent and disintegrating concrete/rubble filled parapet (Figure 8 .93).

The work was carried out in phases over a four year period with the replacement of the disintegrating wall parapet. It was designed to improve the wall’s strength, durability and appearance while also providing full vehicle containment for the coastal road, which was completely absent in the weak old wall. The scheme’s final phase also included some scour repairs and won an environmental award, proving that value can be added by thoughtful/aesthetic design (Figure 8 .94).

Figure 8.93 Original condition of seawall at Blue Anchor in 2001

Case study 8 .14 Blue Anchor seawall, North Somerset (courtesy ICE South West)

Figure 8.94 Completed scheme comprising a non-standard wall and parapet providing both containment and seating, while evoking thoughts of ocean liners

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Unlike a normal cofferdam, a limpet cofferdam does not affect the forces acting on the wall, apart from a redistribution of the hydrostatic forces locally to the perimeter and a local outward pressure on the wall within the limpet dam. The latter may make the use of a limpet dam inappropriate where the wall is of composite construction with a thin facing, which could be blown off by water pressure behind the face. Access to a limpet dam for workers, materials and equipment is via the open top. All work on the wall can then be done in the dry, even though the access and working conditions will be somewhat restricted. No staff should be allowed within the limpet while shipping is moving in the vicinity as accidental breaking of the seal to the wall will lead to immediate flooding. Different limpet dams will be required for each different wall profile and will not be effective if there are appreciable leakage paths through cracks in the wall.

Other methods for dewatering small areas such as open-topped caissons, diving bells (with or without airlocks) and underwater habitats are for work on the seabed and are not normally suitable for work on the vertical face of a wall.

Most repair work on parts of walls that are always below water will have to be done by qualified divers. This should be planned because of the difficulties that divers have to contend with, including:

ªª poor visibility (in some docks visibility is virtually nil)

ªª the inability to apply great force to the work because of a diver’s low negative buoyancy

ªª the problems caused by boats and other craft

ªª effects of waves or currents in some locations.

Legislation covering diving at work is provided in HSE (2014), which also gives advice on meeting the requirements of the regulations for commercial diving projects inland/inshore. It applies to all diving projects conducted in support of civil engineering or marine-related projects and fish farming:

ªª inshore within UK territorial waters adjacent to Great Britain (generally 12 nautical miles from the low water-line)

ªª inland in the UK including in docks, harbours, rivers, culverts, canals, lakes, ponds and reservoirs

ªª in tanks or swimming pools.

Full details can be found on the HSE website (see Websites). For general information on diving, see HSE (2014) and HSE (2015).

The details of any underwater work required should be kept simple. A design that is suitable for use underwater may be quite different from one appropriate for use above water, such as the technique for filling a hole under the toe of a wall. Above water, a suitable technique might be making and fixing formwork and filling directly with concrete. Below water one of the techniques discussed in Section 8.4.1 is probably more appropriate.

8.10 SELECTION OF MATERIALS FOR REPAIRS

8.10.1 ConcreteBS 6349 is now split into four smaller parts on the general requirements for materials to be used in maritime construction.

In addition the common cements are classified in accordance with BS EN 197-1:2000, which specifies the cement composition, requirements and conformity criteria. Further information can be found in Dupray et al (2010).

BS 6349 covers the requirements for underwater and other types of concrete used in marine works except for where concrete is made with an admixture, which allows it to be placed without the use of a tremie or similar device. A range of materials is now available for use underwater so that mortar

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patching, grouting, concreting and pressure pointing can all be done using appropriate proprietary materials. These materials are polymer modified cement-based systems. It is important to use the appropriate material for the particular situation.

The requirements in BS 6349 for concrete placed in the intertidal zone and for concrete to resist abrasion should also be noted.

Sulphate-resisting Portland cement (SRPC) is necessary where leachates and sulphates are present in the bricks, blocks or stone, or in the groundwater.

8.10.2 BrickworkBricks should be frost resistant, and the mortar in intertidal work should be protected by a quick-setting water-proofing compound to prevent damage from the rising tide as described in BS 6349.

8.10.3 Stone masonryWhere stone masonry has to be reconstructed rather than replaced by concrete, it is usually desirable to clean off and reuse the stone from the existing wall. If replacement stone is needed, it should be obtained from the original quarries where possible. The design, selection of materials and construction of new stone masonry should be based on reference to PD 6697:2010, BS EN 1996 parts 2 and 3 (2006), and BS EN 1996-1-1:2005+A1:2002.

8.10.4 MortarOld waterfront walls of stone masonry, brickwork and block were usually constructed without movement joints. Mortar that can creep and yield should be specified as described in Chapter 5 of Snowden (1990), which deals comprehensively with mortar as it was used in the past and how it should be specified now for repairs made to existing structures. It should be noted that there is an increased risk of catastrophic en bloc failure when unyielding (eg hard cement) mortar is deployed meaning stress cannot be relieved locally and larger sections of the wall may fail as a consequence.

8.10.5 Underwater groutSpecialist underwater grout is available from a number of suppliers and is typically a single component, high early strength repair mortar designed for use in marine environments. Underwater grout provides a very fast setting repair mortar that will not segregate when placed in underwater and can be used on vertical, horizontal or overhead surfaces. The advantages of this grout are that it:

ªª is very fast setting – typically less than 10 minutes

ªª will not segregate when placed underwater

ªª can be applied to vertical, horizontal or overhead surfaces

ªª is fully cured in less than two hours.

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ReferencesALLEN, R T L, EDWARDS, S C, SHAW, D N (1992) Repair of concrete structures, CRC Press, UK (ISBN: 978-0-75140-086-1)

ALLSOP, N W H, POWELL, K A and BRADBURY, A (1986) The use of rock in coastal structures, Hydraulics Research Limited, HR Wallingford, Oxford, UK

BARBER, P C and DAVIS, C D (1985) “Offshore breakwaters – Leasowe Bay” ICE Proceedings, vol 78, 1, Institution of Civil Engineers, London, UK, pp 85–109

BRADBURY, A, ROGERS, J and THOMAS, D (2012) Toe structures for coastal defences – a management guide, SC070056. Environment Agency, Bristol, UK (ISBN 978-1-84911-290-1). Go to: http://tinyurl.com/mnnfp2k

BREAKELL, J E, SIEGWART, M, FOSTER, K, MARSHALL, D, HODGSON, M, COTTIS, R and LYON, S (2005) Management of accelerated low water corrosion in steel maritime structures, C634, CIRIA, London, UK (ISBN: 978-0-86017-634-3). Go to: www.ciria.org

CIRIA; CUR; CETMEF (2011) The Rock Manual. The use of rock in hydraulic engineering, C683, CIRIA, London (ISBN: 978-0-86017-683-1). Go to: www.ciria.org

DUPRAY, S, KNIGHTS, J, ROBERTSHAW, G, WIMPENNY, D and WOODS BALLARD, B (2010) The use of concrete in maritime engineering – a good practice guide, C674, CIRIA, London, UK (ISBN: 978-0-86017-674-9). Go to: www.ciria.org

GROGAN, C, DIXON, T, SELLERS, K and COOPER, N (2013) “Berwick Breakwater Refurbishment, Berwick Upon Tweed, UK”. In: Proc ICE conf on coastsm marine structures and breakwaters, 18–20 September 2013, Edinburgh. Go to: www.ice-conferences.com/ice-breakwaters

HOLD, S and ULANOVSKY, A (2012) “‘Stitching the past’ the strengthening of three heritage marine structures in Jersey with needling technology”. In: M Grantham, V Mechtcherine, Schneck, U (eds) Concrete solutions, CRC Press/Balkema, The Netherlands (ISBN: 978-0-41561-622-5), pp 69–78

LANGFORD, P and MULHERN, S (1982) Cork City quay walls, Institution of Engineers of Ireland, Dublin, Ireland

HSE (2014) Commercial diving project inland/inshore. Diving at Work Regulations 1997. Approved Code of Practice and guidance, L104, Health and Safety Executive, London, UK (ISBN: 978-0-71766-593-8). Go to: www.hse.gov.uk/pubns/priced/l104.pdf

HSE (2015) Diving at Work Regulations 1997. List of approved diving qualifications, Health and Safety Executive, London, UK. Go to: http://tinyurl.com/q65zbvt

KIRBY, A M, ROCA, M, KITCHEN, A, ESCARAMEIA, M and CHESTERTON, O J (2015) Manual on scour at bridges and other hydraulic structures, second edition, C742, CIRIA, London, UK (ISBN: 978-0-86017-747-0). Go to: www.ciria.org

PERKINS, P H (1997) Repair, protection and waterproofing of concrete structures, third edition, E&F Spon, London, UK (ISBN: 0-41920-280-3)

PIANC (2005) Accelerated low water corrosion, Report of Working Group 44, PIANC – The World Association for Waterborne Transport Infrastructure, Brussels, Belgium (ISBN: 2-87223-153-6). Go to: http://tinyurl.com/oe5o3z6

SNOWDEN, A M (1990) The maintenance of brick and stone masonry structures, Chapman and Hall, London, UK (ISBN: 978-0-44231-166-7)

SORENSEN, P (ed) (1986) Ports’86, American Society of Civil Engineers, Reston VA, USA (ISBN: 978-0-87262-538-9). Go to: http://tinyurl.com/qbg249q

StatutesBS 8081:1989 Code of practice for ground anchorages

BS 8443:2005 Specification for establishing the suitability of special purpose concrete admixtures

BS 6349-1-1:2013 Maritime works. General. Code of practice for planning and design for operations

BS 6349-1-2 Maritime works. General. Code of practice for assessment of actions

BS 6349-1-3:2012 Maritime works. General. Code of practice for geotechnical design

BS 6349-4:2014 Maritime works. General. Code of practice for design of fendering and mooring systems

BS EN 197-1:2000 Cement. Composition, specifications and conformity criteria for common cements

BS EN 1537:2013 Execution of special geotechnical work. Ground anchors

BS EN 1996-2:2006 Eurocode 6. Design of masonry structures Design considerations, selection of materials and execution of masonry

BS EN 1996-3:2006 Eurocode 6. Design of masonry structures Simplified calculation methods for unreinforced masonry structures

BS EN 1996-1-1:2005+A1:2012 Eurocode 6. Design of masonry structures General rules for reinforced and unreinforced masonry structures

BS EN 14487-1:2005 Sprayed concrete. Definitions, specifications and conformity

BS EN 14487-2:2006 Sprayed concrete. Execution

BS EN 14488-1:2005 Testing sprayed concrete - sampling fresh and hardened concrete

BS EN 14488-2:2006 Testing sprayed concrete Compressive strength of young sprayed concrete

BS EN 14488-3:2006 Testing sprayed concrete Flexural strengths (first peak, ultimate and residual) of fibre reinforced beam specimens

BS EN 14488-4:2005+A1:2008 Testing sprayed concrete Bond strength of cores by direct tension

BS EN 14488-5:2006 Testing sprayed concrete Determination of energy absorption capacity of fibre reinforced slab specimens

BS EN 14488-6:2006 Testing sprayed concrete Thickness of concrete on a substrate

BS EN 14488-7:2006 Testing sprayed concrete Fibre content of fibre reinforced concrete

PD 6697:2010 Recommendations for the design of masonry structures to BS EN 1996-1-1 and BS EN 1996-2

WebsitesSprayed Concrete Association: www .sca .org .uk

EFNARC: www .efnarc .org

AECOM

Arup Group Ltd

Atkins Consultants Limited

Balfour Beatty Civil Engineering Ltd

BAM Nuttall Ltd

Black & Veatch Ltd

Buro Happold Engineers Limited

BWB Consulting Ltd

Cardiff University

Environment Agency

Galliford Try plc

Gatwick Airport Ltd

Geotechnical Consulting Group

Golder Associates (Europe) Ltd

Halcrow Group Limited

Health & Safety Executive

Heathrow Airport Holdings Ltd

High Speed Two (HS2)

Highways Agency

HR Wallingford Ltd

Imperial College London

Institution of Civil Engineers

Lafarge Tarmac

Laing O’Rourke

London Underground Ltd

Loughborough University

Maccaferri Ltd

Ministry of Justice

Morgan Sindall (Infrastructure) Plc

Mott MacDonald Group Ltd

Mouchel

MWH

Network Rail

Northumbrian Water Limited

Rail Safety and Standards Board

Royal HaskoningDHV

RSK Group Ltd

RWE Npower plc

Scottish Water

Sellafield Ltd

Sir Robert McAlpine Ltd

SKM Enviros Consulting Ltd

SLR Consulting Ltd

Temple Group Ltd

Thames Water Utilities Ltd

Tube Lines

United Utilities Plc

University College London

University of Reading

University of Sheffield

University of Southampton

WYG Group (Nottingham Office)

April 2015

Core and Associate members

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Old waterfront walls

This guide updates and replaces the original CIRIA publication on old waterfront walls firstpublished in 1992 (B13). A significant amount of the material used in the original publication,particularly with respect to the history and types of old waterfront walls, has been incorporated intothis new guide plus new material gleaned from a number of sources.

The history of the subject spans at least 2000 years, with many significant waterfront structuresbeing constructed during the Roman Empire. Over this period the engineering skills and technologywere lost and only found again in the late 17th and early 18th century. Engineering failure at the'sharp end' of technology was frequently accepted as being a necessary evil in the design anddevelopment of this new infrastructure.

Science and engineering has also moved on since the first edition was published. The new guidenow includes information on risk analysis and performance assessment, the use of GIS and BIM inthe design and construction process, and more detail on the loads imposed by waves. It alsocontains an overview of those waterfront walls that proved so troublesome to construct, but whoselongevity is a measure of man's persistence to succeed.

The guide shows how engineers may, by inspection, observation, and investigation and through theapplication of risk management and modern construction techniques, effectively manage andmaintain the substantial national asset which these waterfront walls represent.