Use of Numerical Modelling to Mitigate Ground Risk · 2017-09-08 · • Numerical Modelling Procedure to Determine Soil-Structure Response • Modern Software Capable of Considering

Use of Numerical Modelling to Mitigate Ground Risk

Gavin & Doherty Geosolutions Ltd.

CECA MEETING – SEPT 2017

Overview

o Introduction to GDG

o Finite Element Modelling & Calibration

o Case Studies

o Flood Defences

o Retaining Walls

o High rise foundations

o Risk Analysis

o Conclusions

Todays Presentation….

GDG Introduction

o Gavin & Doherty Geosolutions (GDG) is a specialist geotechnical & civil engineering consultancy

o Offices in London, Edinburgh, Dublin, and Belfast,

o GDG was formed in 2011 in a challenging market

o Grown throughout the last five years

o Team of 40 highly talented engineers

o Majority of our staff are PhD qualified

o We provide innovative geotechnical solutions & efficient civil engineering designs for challenging projects

About us ….

Engineering Design Services

Structures Infrastructure

Offshore Renewables

R&D

Engineering Design Services

o Concept Design

o Site Investigation Scoping

o Site Investigation Interpretation

o Civil Engineering Design

o Temporary Works Design

o Numerical Modelling (FEA)

o Performance monitoring / instrumentation analysis

o Expert Witness Services

INFRASTRUCTURE

INFRASTRUCTURE

o Geotechnical Interpretation & Ground Modelling for Road, Railway and Flood Defence Schemes

o Geological Assessments & Mapping

o Earthworks Design

o Material Suitability

o Hydrogeological review

o Civil Engineering Design

o Numerical Modelling

o Soil-Structure-Water Interaction Analysis

o Back-analysis of failures & Root Cause Analysis

SERVICES & EXPERTISE

URBAN STRUCTURES

URBAN STRUCTURES


o Basement & Foundation Engineering

o Soil-Structure Interaction

o Ground Movement Assessments

o Retaining Wall Analysis

o Excavation Support and Propping Design

o Construction Sequencing & Temporary Works

o Pile Design & Piled Raft Analysis

o Tunnel and basement impact assessments

o Ground Improvement Engineering

OFFSHORE & MARINE

OFFSHORE & MARINE


o Analysis and Design of Ports & Harbours

o Quay Wall Numerical Modelling

o Offshore Substructure Analysis

o Offshore wind foundation engineering

o Gravity structures, monopiles, jacket piles, etc…

o Pile Installation analysis & Interpretation of offshore driving data

o Site suitability assessments

o Jack-up vessel studies

o Back-analysis of failures & Root Cause Analysis

• NNG Wind Farm

• Rampion Wind Farm

• Zawtika Gas Jacket Pile Analysis

• Hornsea Met Mast

• Firth of Forth Wind Farm Forensics

• Dogger Bank Jackup Analysis

• Shell Conductor Installation Studies North Sea

• Horizont Jacket Pile FEED

RELEVANT PROJECTS RENEWABLES

RENEWABLES


o Site suitability and feasibility studies for onshore wind and onshore solar farms

o Geotechnical risk studies

o Peat stability assessments

o Earthworks engineering for roads, crane bases, hardstands, etc.

o Foundation design for gravity and piled bases

o Interaction analysis for soil-structure-turbine behaviour.

Technical Presentation Sept 2017

www.gdgeo.com

• What is Ground Risk ?

Ground Risk


www.gdgeo.com

• Analytical – Traditional Theoretical Hand (spreadsheet) Calculations

• Empirical – Traditional Approaches based on experience of empirical evidence

• Numerical – Finite Element (or Finite Difference)

• Observational Design Approaches

Pick the most appropriate tool for your project

(consider the limitations of the tool, the complexity of the project and the accuracy required)

Design Tools Available


www.gdgeo.com

• Numerical Modelling Procedure to Determine Soil-Structure Response

• Modern Software Capable of Considering Complex Geometries

• The geometry is discretised into a mesh and the stresses and strains are resolved as loads/actions are applied

• Can accurately determine ground movements and structural stresses, provided the model is well calibrated

• Calibration requires (a) DATA and (b) EXPERTISE

Finite Element Method


www.gdgeo.com

• Soil is highly non-linear

– Pick an appropriate constitutive model

Basics of Geotechnics

Stre

ss

Strain

Real Soil

Elastic-Plastic


www.gdgeo.com

• FEM CALIBRATION

– Simulation of Lab Testing

– Look for repeatability

– Use range of test types



www.gdgeo.com

• FEM CALIBRATION

– Simulation of Field Testing



www.gdgeo.com

• TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS

• Access Shaft for TBM

• Complex Ground Conditions

• Underlying Aquifer

• Base Heave a Serious Concern !

• Design Solution Needed

CASE STUDY 1


www.gdgeo.com

• Model Calibration

CASE STUDY 1

Non-Plastic Till Fine Sand to Silt Plastic Till Sand to Sand and Gravel

𝑫𝒓𝒂𝒊𝒏𝒂𝒈𝒆 𝑻𝒚𝒑𝒆 - Drained Drained Undrained Drained

𝑷𝒆𝒓𝒎𝒆𝒂𝒃𝒊𝒍𝒊𝒕𝒚 𝑚 𝑠 1 × 10−6 4 × 10−5 8 × 10−8 3 × 10−4

𝜸𝒖𝒏𝒔𝒂𝒕 𝑘𝑁 𝑚3 18 18 24 18

𝜸𝒔𝒂𝒕 𝑘𝑁 𝑚3 20 20 24.3 20

𝒆𝟎 - 0.5 0.5 0.301 0.5

𝑬𝟓𝟎𝒓𝒆𝒇

𝑀𝑃𝑎 30 30 20 30

𝑬𝒐𝒆𝒅𝒓𝒆𝒇

𝑀𝑃𝑎 30 30 20 30

𝑬𝒖𝒓𝒓𝒆𝒇

𝑀𝑃𝑎 90 90 80 90

𝑷𝒐𝒘𝒆𝒓 (𝒎) - 0.5 0.5 0.5 0.5

𝒄𝒓𝒆𝒇 𝑘𝑃𝑎 0 0 0 0

𝝋 ° 35 35 35.9 35

𝝍 ° 5 5 9 5

𝒑𝒓𝒆𝒇 𝑘𝑃𝑎 100 100 100 100

𝑹𝒇 - 0.9 0.9 0.9 0.9

𝒌𝟎,𝒙 - 1 0.8 1.2 0.8


www.gdgeo.com


• Undrained versus Drained

CASE STUDY 1


www.gdgeo.com


CASE STUDY 1


www.gdgeo.com


CASE STUDY 1


www.gdgeo.com


CASE STUDY 1


www.gdgeo.com


• Pore Pressures

(a) End of Excavation

(b) 10 weeks

(c) 20 weeks

(d) 50 weeks

CASE STUDY 1

(a) (b)

(c) (d)


www.gdgeo.com


• Failure Avoided

• Facilitated Economic Construction Sequence

• Observational Method Used to Minimise Risk

CASE STUDY 1


www.gdgeo.com

• NATIONAL GALLERY UNDERPINNING ANALYSIS

CASE STUDY 2

Facilitate basement extension Geotechnical interpretation Geophysical profiling 3D Settlement Analysis of

Construction Stages Recommendation about

underpinning construction Final settlement design for

temporary and permanent works.


www.gdgeo.com


CASE STUDY 2


www.gdgeo.com


CASE STUDY 2


www.gdgeo.com


CASE STUDY 2


www.gdgeo.com


CASE STUDY 2


www.gdgeo.com

• NATIONAL GALLERY UNDERPINNING

• Settlements predicted to be less than 10mm in worst case

• Generally less than 5 mm

• Concrete underpinning shown to be appropriate, however construction quality control critical

• Monitoring system tailored to target critical area of the building and critical point in the construction timeline

• Constant monitoring compared to design predictions with target levels set to stop construction if required.

CASE STUDY 2


www.gdgeo.com

• Flood Defences

CASE STUDY 3


www.gdgeo.com

• Flood Wall Analysis

CASE STUDY 3

• Stability Modelling

• Seepage Analysis Deemed Critical


www.gdgeo.com

• Flood Defence Design

CASE STUDY 3


www.gdgeo.com

• Flood Risk Analysis

CASE STUDY 3


www.gdgeo.com


CASE STUDY 3

0.2

0.4

0.6 0.8 1

1

.2

1

.4

1.6 1.8 2 2.2 2.4 2.6

Design Flood Level

Gravel

Gravel

Silt

Peat

0.6

8202

m³/d

ays

2

.85

37 m

³/days

0

.12

612

m³/

days

Distance (m)

0 5 10 15 20 25 30 35

Ele

vatio

n (

m)

-13.5

-12.5

-11.5

-10.5

-9.5

-8.5

-7.5

-6.5

-5.5

-4.5

-3.5

-2.5

-1.5

-0.5

0.5

1.5

2.5

3.5

4.5

5.5


www.gdgeo.com


CASE STUDY 3

0.2

0.4

0.6 0.8 1

1

.2

1

.4

1.6 1.8 2 2.2 2.4 2.6

Design Flood Level

Gravel

Gravel

Silt

Peat

0.6

8202

m³/d

ays

2

.85

37 m

³/days

0

.12

612

m³/

days

Distance (m)

0 5 10 15 20 25 30 35

Ele

vatio

n (

m)

-13.5

-12.5

-11.5

-10.5

-9.5

-8.5

-7.5

-6.5

-5.5

-4.5

-3.5

-2.5

-1.5

-0.5

0.5

1.5

2.5

3.5

4.5

5.5

0.4

0.6

0

.8

1

1.2

1

.4

1

.6

1.8 2 2.2 2.4 2.6 2.8

Gravel

Gravel

Silt

Peat

Distance (m)

0 5 10 15 20 25 30 35

Ele

va

tio

n (

m)

-13.5

-12.5

-11.5

-10.5

-9.5

-8.5

-7.5

-6.5

-5.5

-4.5

-3.5

-2.5

-1.5

-0.5

0.5

1.5

2.5

3.5

4.5

5.5


www.gdgeo.com


CASE STUDY 3


www.gdgeo.com


CASE STUDY 3

• Conceptual hyrogeological model developed

• Model Developed for Current Condition

• Model Calibrated Against Dynamic Borehole Records

Current Ground Level

Current Low River Level 0.75 mOD

Max Expected Tide appox. 1.60 mOD

Distance (m)

0 5 10 15 20 25 30 35 40 45 50 55

Ele

va

tion

(m

)

-9.55

-8.55

-7.55

-6.55

-5.55

-4.55

-3.55

-2.55

-1.55

-0.55

0.45

1.45

2.45

3.45

4.45

5.45


www.gdgeo.com


CASE STUDY 3

• Calibration Process • Consider River Levels

• Tidal Variations


www.gdgeo.com


CASE STUDY 3

• Model Storm Events • Consider River Levels

• Tidal Variations

• Design Options

-1

0

1

2

3

4

5

0 6 12 18 24 30 36

He

ad (

m)

Time (hours)

The change in Head (m) over time (hours)

-0.2 0

0.2

0.4

0.6 1

Low River Level -0.20 mOD

Gravel

Design Flood Level 3.80 mOD

Gravel

Silt

Swale

River Wall

Flood Defence Wall

Golf Course Road Hight Tide 1.54 mOD

0

.32

51

2 m

³/d

ays

0.2

852

9 m

³/days

Distance (m)

0 5 10 15 20 25 30 35 40 45 50 55

Ele

vation (

m)

-9.55

-8.55

-7.55

-6.55

-5.55

-4.55

-3.55

-2.55

-1.55

-0.55

0.45

1.45

2.45

3.45

4.45

5.45


www.gdgeo.com

• Piled-Raft for High Rise Development

CASE STUDY 4

• 32 Storey High Rise Development

• Several Concentrated Column Loads with very high forces

• High wind moment on tower

• Piled-Raft deemed most appropriate solution

• Stratigraphy consisted of London Clay


www.gdgeo.com


CASE STUDY 4


www.gdgeo.com


CASE STUDY 4

• Non-linear soil model used

• Moment applied as an eccentric force on a lever arm above the raft

• Pile Design optimised iteratively


www.gdgeo.com


CASE STUDY 4

• Designed to a settlement criteria rather than to a capacity value

• S<35mm


www.gdgeo.com


CASE STUDY 4

• Examine pile utilisation & optimise design

• Piles shortened by 7m


www.gdgeo.com


CASE STUDY 4

• Analyse the impact of the new raft on existing contiguous wall along site boundary

• Contig wall predicted to displace by approximately 9 mm

• Existing inclinometer casings used as a cheap/efficient monitoring solution


www.gdgeo.com

• MARINA PILE SETTLEMENT ANALYSIS • Redevelopment of Harbour, involving residential & office buildings on

piled pier

• Focus on estimating settlement of pipe piles

CASE STUDY 5


www.gdgeo.com

• MARINA PILE SETTLEMENT ANALYSIS

CASE STUDY 5


www.gdgeo.com

• MARINA PILE SETTLEMENT ANALYSIS

CASE STUDY 5

• Using state of the art settlement models to assess foundation performance (in-house design tools)

• Excellent prediction

• Confirmed pile acceptability


www.gdgeo.com

• Risk Modelling on a Large Scale (Rail Network)

CASE STUDY 6

2,800Km Track

4,900 Earthworks

5,100 Bridges

900 Level Crossings


www.gdgeo.com

Portarlington Derailment Aug 2008

Manulla Junction Landslide Aug 2007

Wicklow Derailment Nov 2009

Rushbrooke Rock Falls March 2014

• Recent Failures

CASE STUDY 6


www.gdgeo.com

Waterford Rockfall Dec 2013

Kilkenny Waterford Line Landslip Dec 2013

Tullamore Soil Slips and Rock Falls 2011/2012

Cabra Slope Failures 2012

CASE STUDY 6


www.gdgeo.com

PROBABILISTIC MODELLING

• High Level of Uncertainty Across the Asset Characteristics

• Consider COV of input parameters depending on data source

• Develop quantifiable risk profiles

• Hasofer Lind method used to calculate the probability of failure associated with each asset and its coupled limit state

• Outputs: reliability index (β), probability of failure

CASE STUDY 6

g(X) = R-SPf

probability

of failure

0

ßs[g(x)]

E[g(x)]

E[g(x)]

s [g(x)]ß[g(x)] =

Outputs: reliability index (β), probability of failure


www.gdgeo.com

• Risk Modelling on a Large Scale (Rail Network)

• Possible to quantify ground risk

• 4000 Assets

• No excuses for individual sites!

CASE STUDY 6


www.gdgeo.com

• Karst Risk Analysis

• Importance of Desk study research

CASE STUDY 7


www.gdgeo.com

CASE STUDY 7

Soil Profile from Intrusive Investigation

Layer

No.

Depth below

ground level (bgl)

Soil Type Description

1 0.6 to 0.9 m Made

Ground

Grey sandy GRAVEL with cobbles

2 0.9 m to 4 m*

Dynamic Probe No.

T2 encountered

soft soil to 11.1 m

bgl.

Glacial Till The till comprises reddish brown

sandy gravelly, low plasticity CLAY.

The fines content of the soil was

between 35 and 50%.

3 Below 4 m Waulsortian

Limestone

Light Grey, massive reef

LIMESTONE. The rock is strong to

very strong, with strong evidence

of karst solution features


www.gdgeo.com

CASE STUDY 7

Soil Profile from Intrusive Investigation

Layer

No.

Depth below

ground level (bgl)

Soil Type Description

1 0.6 to 0.9 m Made

Ground

Grey sandy GRAVEL with cobbles

2 0.9 m to 4 m*

Dynamic Probe No.

T2 encountered

soft soil to 11.1 m

bgl.

Glacial Till The till comprises reddish brown

sandy gravelly, low plasticity CLAY.

The fines content of the soil was

between 35 and 50%.

3 Below 4 m Waulsortian

Limestone

Light Grey, massive reef

LIMESTONE. The rock is strong to

very strong, with strong evidence

of karst solution features


www.gdgeo.com

CASE STUDY 7

• Geophysics used to map risk


www.gdgeo.com

CASE STUDY 7

• Pragmatic Construction Regime Proposed


www.gdgeo.com

SUMMARY

o Advanced design tools have a place in the right projects

o FEM can allow more efficient design, save money and decrease risk

o Calibration is critical

o Recommend numerical modelling coupled with observational approach

o Monitoring provides the confidence to allow construction to proceed on time and in budget


www.gdgeo.com

• QUESTIONS ???

Contact:

Paul Doherty

[email protected]

Conclusions

mailto:[email protected]

Documents

Use of Numerical Modelling to Mitigate Ground Risk · 2017-09-08 · • Numerical Modelling Procedure to Determine Soil-Structure Response • Modern Software Capable of Considering