QA_QC Foundation Retaining Structures

7/25/2019 QA_QC Foundation Retaining Structures

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QCS 2014 Section 04: Foundations and Retaining Structures Page 1Part 01: General Requirements for Piling Work

1 GENERAL REQUIREMENTS FOR PILING WORK ................................................. 2

1.1 GENERAL ............................................................................................................... 2

1.1.1 Scope 2

1.1.2 References 2

1.1.3 General Contract Requirements 2

1.1.4

Submittals 3

1.1.5

Records 3

1.2 GROUND CONDITIONS ......................................................................................... 3

1.2.1 Ground Investigation Reports 3

1.2.2 Unexpected Ground Conditions 4

1.3 MATERIALS AND WORKMANSHIP ........................................................................ 4

1.3.1 General 4

1.3.2

Sources of Supply 4

1.3.3

Rejected materials 5

1.4 INSTALLATION TOLERANCES .............................................................................. 5

1.4.1 Setting Out 5

1.4.2 Position 6

1.4.3 Verticality 6

1.4.4 Rake 6

1.4.5 Tolerance Variations 6

1.4.6 Forcible Corrections to Pile 6

1.5

NUISANCE AND DAMAGE ..................................................................................... 6

1.5.1 Noise and Disturbance 6

1.5.2

Damage to Adjacent Structures 7

1.5.3 Damage to Piles 7

1.5.4 Temporary Support 7

1.6 SAFETY .................................................................................................................. 7

1.6.1

General 7

1.6.2

Life-Saving Appliances 7

1.6.3

Driving 7


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1 GENERAL REQUIREMENTS FOR PILING WORK

1.1 GENERAL

1.1.1 Scope

1 This Part is concerned with all works associated with installation of piles by any of the

recognised techniques.

1.1.2 References

1 The following standards and codes of practice are referred to in this Part:

BS 5228 ...................... Noise control on construction and open sites

Part I, Code of practice for basic information and procedures for noise

controlPart IV, Code of practice for noise and vibration control applicable to

piling operations

BS 8008 ...................... Safety precautions and procedures for the construction and descent of

machine-bored shafts for piling and other purposes

BS EN 1997 ................ Eurocode 7, Geotechnical Design.

1.1.3 General Contract Requirements

1 The following matters, where appropriate, are described in the contract specificdocumentation for the Works:

(a) general items related to Works

(i) Nature of the Works.

(ii) Classes of loads on piles.

(iii) Contract drawings.

(iv) Other works proceeding at the same time.

(v) Working area.

(vi) Order of the Works.

(vii) Datum.

(viii) Offices for the Engineer's Representative.

(ix) Particular facilities and attendance items where not included in this section.

(x) Details of soil investigation reports.

(b) specific items related to particular type of pile

(i) Soil sampling, laboratory testing and in-situ soil testing.

(ii) Designed concrete or grout mixes, grades of concrete or grout, type of cementand aggregate, grout or concrete admixtures, concreting of piles.


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(iii) Grades and types of reinforcement and prestressing tendons.

(iv) Pile dimensions, length and marking of piles.

(v) Type and quality of pile shoe/splice.

(vi) Type and quality of permanent casing.

(vii) Specified working loads.

(viii) Sections of proprietary types of pile, grades of steel, minimum length to be

supplied, thickness of circumferential weld reinforcement.

(ix) Surface preparation, types and thickness of coatings.

(x) Test piles, driving resistance or dynamic evaluation and penetration.

(xi) Detailed requirements for driving records.

(xii) Acceptance criteria for piles under test.

(xiii) Disposal of cut-off lengths.

(xiv) Preboring.

1.1.4 Submittals

1 The Contractor shall supply for approval all relevant details of the method of piling and the

plant he proposes to use. Any alternative method to that specified shall be subject to

approval.

2 The Contractor shall submit to the Engineer on the first day of each week, or at such longer

periods as the Engineer may from time to time direct, a progress report showing the current

rate of progress and progress during the previous period on all important items of each

section of the Works.

3 The Contractor shall inform the Engineer each day of the intended programme of piling for

the following day and shall give adequate notice of his intention to work outside normal hours

and at weekends.

1.1.5 Records

1 The Contractor shall keep records, as indicated by an asterisk in Table 1.1, of the installation

of each pile and shall submit two signed copies of these records to the Engineer not later

than noon of the next working day after the pile is installed. The signed records will form a

record of the work. Any unexpected driving or boring conditions shall be noted briefly in therecords.

1.2 GROUND CONDITIONS

1.2.1 Ground Investigation Reports

1 Factual information and reports on site investigations for the Works and on the previous

known uses of the Site will be provided by the Engineer where they exist as part of the

specific contract documentation. However, even if a full report is given, including

interpretations, opinions or conclusions, no responsibility is accepted by the Engineer for any

opinions or conclusions which may be given in the reports.


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2 Before the start of work the Contractor shall be given a copy of any subsequent information

which may have been obtained relating to the ground conditions and previous uses of the

Site.

1.2.2 Unexpected Ground Conditions

1 The Contractor shall report immediately to the Engineer any circumstance which indicates

that in the Contractor's opinion the ground conditions differ from those reported in or which

could have been inferred from the site investigation reports or test pile results.

1.3 MATERIALS AND WORKMANSHIP

1.3.1 General

1 All materials and workmanship shall be in accordance with the appropriate British Standards,

codes of practice and other approved standards current at the date of tender except where

the requirements of these standards or codes of practice are in conflict with this Section inwhich case the requirements of this Section shall take precedence.

1.3.2 Sources of Supply

1 The sources of supply of materials shall not be changed without prior approval.

Table 1.1

Records to be Kept (Indicated by an Asterisk)

Data

Drivensteel,precast

concreteandsteel

sheetpiles

Drivensegmen

tal

concretepiles

Drivencast-in-place

concretepiles

Boredcast-in-place

concretepiles

Continuousflig

ht

augerconcrete

or

groutpiles

Contract * * * * *

Pile reference number (location) * * * * *

Pile type * * * * *

Nominal cross-sectional dimensions or diameter * * * * *

Nominal diameter of underream/base - - - * -

Length of preformed pile * * - - -

Standing groundwater level from direct observation or given siteinvestigation data.

- - * * *

Date and time of driving, redriving or boring * * * * *

Date of concreting - - * * *

Ground level/sea bed level at pile position at commencement ofinstallation of pile (commencing surface)

* * * * *

Working elevation of pile driver * * * * *

Depth from ground level at pile position to pile tip * * * * *

Tip elevation * * * * *


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Data

Driven

steel,precast

concreteandsteel

sh

eetpiles

Drivensegmental

concretepiles

Driven

cast-in-place

concretepiles

Bored

cast-in-place

concretepiles

Continuousflight

auger

concreteor

gr

outpiles

Pile head elevation, as constructed * * * * *

Pile cut-off elevation * * * * *

Length of temporary casing - - * * -

Length of permanent casing - - * * -

Type, weight, drop and mechanical condition of hammer andequivalent information for other equipment

* * * - -

Number and type of packings used and type and condition of

dolly used during driving of the pile * * * - -

Set of pile or pile tube in millimetres per 10 blows or number ofblows per 25 mm of penetration

* * * - -

If required, the sets taken at intervals during the last 3 m ofdriving

* * * - -

If required, temporary compression of ground and pile from timeof a marked increase in driving resistance until pile reached itsfinal level

* * * - -

If required, driving resistance taken at regular intervals over thelast 3 m of driving

* * * - -

Soil samples taken and in-situ tests carried out during pileinstallation

* * * * *

Length and details of reinforcements - - * * *

Concrete mix - - * * *

Volume of concrete supplied to pile - - * * *

All information regarding obstructions delays and otherinterruptions to the work

* * * * *

1.3.3 Rejected materials

1 Rejected materials are to be removed promptly from the Site.

1.4 INSTALLATION TOLERANCES

1.4.1 Setting Out

1 Setting out of the main grid lines shall be by the Contractor. The installation of marker pins at

pile positions, as required by the Contract, shall be located by the Contractor from the main

grid lines of the proposed structure. Before installation of the pile, the pile position relative to

the main grid lines shall be verified.


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1.4.2 Position

1 For a pile cut off at or above ground level the maximum permitted deviation of the pile centre

from the centre-point shown on the drawings shall be 75 mm in any direction. An additional

tolerance for a pile head cut off below ground level will be permitted in accordance with

Clauses 1.4.3 and 1.4.4.

1.4.3 Verticality

1 At the commencement of installation, the pile, or pile-forming equipment in the case of a

driven pile, or the relevant equipment governing alignment in the case of the bored pile, shall

be made vertical to a tolerance of within 1 in 100. The maximum permitted deviation of the

finished pile from the vertical is 1 in 75.

1.4.4 Rake

1 As in clause 1.4.3, the pile, or driving or other equipment governing the direction and angle ofrake shall be set to give the correct alignment of the pile to within a tolerance of 1 in 50. The

piling rig shall be set and maintained to attain the required rake. The maximum permitted

deviation of the finished pile from the specified rake is 1 in 25 for piles raking up to 1:6 and 1

in 15 for piles raking more than 1:6.

1.4.5 Tolerance Variations

1 In exceptional circumstances where these tolerances are difficult to achieve, the tolerances

of Clauses 1.4.2, 1.4.3 and 1.4.4 may be relaxed by the Engineer, subject to consideration of

the implications of such action.

1.4.6 Forcible Corrections to Pile

1 Forcible corrections to concrete piles to overcome errors of position or alignment shall not be

made. Forcible corrections may be made to other piles only if approved and where the pile

shaft is not fully embedded in the soil.

1.5 NUISANCE AND DAMAGE

1.5.1 Noise and Disturbance

1 The Contractor shall carry out the work in such a manner and at such times as to minimise

noise, vibration and other disturbance in order to comply with current environmentallegislation.

2 The Contractor shall endeavour to ascertain the nature and levels of noise produced by the

mechanical equipment and plant that will be used. He shall than take steps to reduce either

the level or the annoying characteristics, or both, of the noise. Reference should be made to

BS 5228 Part 1 for prediction of noise level due to different types of mechanical equipment

and plant, and to BS 5228 Part 4 for noise and vibration control techniques applicable to

piling operations.


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1.5.2 Damage to Adjacent Structures

1 If in the opinion of the Contractor, damage will be, or is likely to be, caused to mains, services

or adjacent structures, he shall submit to the Engineer his proposals for making

preconstruction surveys, monitoring movements or vibrations, and minimising or avoiding

such damage.

1.5.3 Damage to Piles

1 The Contractor shall ensure that during the course of the work, displacement or damage

which would impair either performance or durability does not occur to completed piles.

2 The Contractor shall submit to the Engineer his proposed sequence and timing for driving or

boring piles, having the intent of avoiding damage to adjacent piles.

1.5.4 Temporary Support

1 The Contractor shall ensure that where required, any permanently free-standing piles are

temporarily braced or stayed immediately after driving to prevent loosening of the piles in the

ground and to ensure that the pile will not be damaged by oscillation, vibration or ground

movement.

1.6 SAFETY

1.6.1 General

1 A competent person, properly qualified and experienced, should be appointed to supervise

the piling operations. This person should be capable of recognising and assessing any

potential dangers as they arise; e.g., unexpected ground conditions that may require a

change in construction technique, or unusual smells which may indicate the presence of

noxious or dangerous gases.

2 Safety precautions throughout the piling operations shall comply with BS 8008 and BS EN

1997. Refer Section 1 for general safety standards to be adopted at a construction site.

1.6.2 Life-Saving Appliances

1 The Contractor shall provide and maintain on the Site sufficient, proper and efficient life-

saving appliances to the approval of the Engineer. The appliances must be conspicuous and

available for use at all times.

2 Site operatives shall be instructed in the use of safety equipment and periodic drills shall be

held to ensure that all necessary procedures can be correctly observed.

1.6.3 Driving

1 Before any pile driving is started, the Contractor shall supply the Engineer with two copies of

the code of signals to be employed, and shall have a copy of the code prominently displayed

adjacent to the driving control station on the craft, structure or site from which the piles will be

driven.

END OF PART


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QCS 2014 Section 04: Foundations and Retaining Structures Page 1Part 02: Concrete Works forPiling

2 CONCRETE WORKS FOR PILING ......................................................................... 2

2.1 GENERAL ............................................................................................................... 2

2.1.1 Scope 2

2.1.2 References 2

2.2

MATERIALS ............................................................................................................ 2

2.2.1 Cementitious 2

2.2.2 Aggregate 2

2.2.3 Water 2

2.2.4 Admixtures 2

2.2.5 Steel Reinforcement and Prestressing Steel 2

2.3

CONCRETE MIXES FOR PILING WORK ............................................................... 3

2.3.1

General 3

2.3.2

Grade Designation 3

2.3.3

Designed Mix 32.3.4

Durability 3

2.3.5

Exposure Classes 3

2.4 PLACING CONCRETE ............................................................................................ 3

2.4.1 General 3

2.4.2 Inspection 4

2.4.3 Cleanliness of Pile Bases 4

2.4.4

Workability of Concrete 4

2.4.5

Compaction 4

2.4.6

Placing Concrete in Dry Borings 5

2.4.7

Placing Concrete under Water or Drilling Fluid 5


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2 CONCRETE WORKS FOR PILING

2.1 GENERAL

2.1.1 Scope

1 This part applies to cast in-situ as well as precast concrete work.

2 Related Sections and Parts are as follows:

This Section

Part 1, General Requirements for Piling Work

Part 3 Shallow Foundations

Part 4 Deep Foundations

Part 5 Retaining Structures

Section 5 Concrete.

2.1.2 References

1 The following Standards are referred to in this Part:

BS 8008 ......................Safety precautions and procedures for the construction and descent of

machine-bored shafts for piling and other purposes

All Standards mentioned in Section 5

2.2 MATERIALS

2.2.1 Cementitious

1 All cementitious materials shall comply with the requirements of Section 5, Part 3.

2 All cementitious materials shall be stored in separate containers according to type in

waterproof stores or silos.

2.2.2 Aggregate

1 Aggregates shall comply with the requirements of Section 5, Part 2.

2.2.3 Water

1 If water for the Works is not available from a public supply, approval shall be obtained

regarding the source of water. For quality of water refer to Section 5, Part 4.

2.2.4 Admixtures

1 Admixtures shall comply with the requirements of Section 5, Part 5

2.2.5 Steel Reinforcement and Prestressing Steel

1 Steel reinforcement shall be stored in clean and dry conditions. It shall be clean, and free

from loose rust and loose mill scale when installed in the Works. For requirements of steel

reinforcement refer to Section 5, Part 11.


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2 The number of joints in longitudinal steel bars shall be kept to a minimum. Joints in

reinforcement shall be such that the full strength of each bar is effective across the joint and

shall be made so that there is no detrimental displacement of the reinforcement during the

construction of the pile.

3 For requirements of prestressing steel refer to Section 5, Part 18.

2.3 CONCRETE MIXES FOR PILING WORK

2.3.1 General

1 For general requirements of concrete mixes, trial mixes, batching, mixing and transportation

of fresh concrete and testing of hardened concrete refer to Section 5.

2.3.2 Grade Designation

1 Grades of concrete shall be as given in Section 5, Part 6.

2.3.3 Designed Mix

1 The Contractor shall be responsible for selecting the mix proportions to achieve the required

strength and workability..

2 Complete information on the mix and sources of aggregate for each grade of concrete and

the water/cementitious ratio and the proposed degree of workability shall be approved before

work commences.

3 Where low-alkali, sulphate-resisting cement to BS EN 197 is specified, the alkali content

(equivalent sodium oxide) of the cement shall not exceed 0.6

% by weight.

4 The Contractor shall submit the slump value for approval before work commences.

2.3.4 Durability

1 For piles exposed to aggressive ground or groundwater, approved measures shall be taken

to ensure durability. Reference shall be made to Section 5, Part 6.

2.3.5 Exposure Classes

1 The minimum cementitious content and type and the concrete grades shall be specifiedbased on the exposure classes as given in Table 6.8, Section 5, Part 6.

2.4 PLACING CONCRETE

2.4.1 General

1 The workability and method of placing and vibrating the concrete shall be such that a

continuous monolithic concrete shaft of the full cross-section is formed.

2 The concrete shall be placed without such interruption as would produce a cold joint in the

pile. The method of placing shall be approved.


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3 The Contractor shall take all precautions in the design of the mix and placing of the concrete

to avoid arching of the concrete in a temporary casing. No soil, liquid or other foreign matter

which would adversely affect the performance of the pile shall be permitted to contaminate

the concrete.

2.4.2 Inspection

1 Each pile bore which does not contain standing water or drilling fluid shall be inspected

directly or indirectly before to concrete is placed in it. This inspection shall be carried out from

the ground surface in the case of piles of less than 750 mm diameter. Torches or other

approved means of lighting, measuring tapes, and a means of measuring verticality shall be

provided. For piles of 750mm diameter or larger, equipment shall be provided by the

Contractor to enable his representatives and the Engineer to descend into the bore for the

purpose of inspection. Any method of descent and the equipment used shall comply with the

requirements of BS 8008.

2.4.3 Cleanliness of Pile Bases

1 On completion of boring and where inspection of a dry pile bore indicates the necessity,

loose, disturbed or softened soil shall be removed from the bore. Where pile bores contain

water or drilling fluid, a cleaning process shall be employed before concrete is placed, or the

concrete shall be placed by tremie method. Large debris or accumulated sediment, or both

of them, shall be removed using appropriate approved methods, which shall be designed to

clean while at the same time minimising ground disturbance below the pile bases. Water or

drilling fluid shall be maintained at such levels throughout and following the cleaning

operation that stability of the bore is preserved.

2.4.4 Workability of Concrete

1 Slump measured at the time of discharge into the pile bore shall be in accordance with the

standards shown in Table 2.1.

2.4.5 Compaction

1 Internal vibrators may be used to compact concrete, with the approval of the Engineer

obtained in advance for each specific use.

Table 2.1Standards for Concrete Slump

Piling mix

workability

SlumpTypical conditions of useMinimum Range

mm mm

A 75 75-150

Placed into water-free unlined or permanently lined boreof 600

mm diameter or over, or where concrete is placedbelow temporary casing, and where reinforcement iswidely spaced leaving ample room for free movement ofconcrete between bars.

B 100 100-200Where reinforcement is not spaced widely, whereconcrete is placed within temporary casings, where pilebore is water-free, and the diameter less than 600 mm

C 150 150 or moreWhere concrete is to be placed by tremie under water ordrilling mud, or by pumping


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2.4.6 Placing Concrete in Dry Borings

1 Approved measures shall be taken to ensure that the structural strength of the concrete

placed in all piles is not impaired through grout loss, segregation or bleeding.

2 Concrete shall be placed by elephant trunk, and the free fall shall not exceed 1.2 m.

2.4.7 Placing Concrete under Water or Drilling Fluid

1 Before placing concrete, measures shall be taken in accordance with Clause 2.4.3 to ensure

that there is no accumulation of silt or other material at the base of the boring, and the

Contractor shall ensure that heavily contaminated bentonite suspension, which could impair

the free flow of concrete from the tremie pipe, has not accumulated in the bottom of the hole.

2 Concrete to be placed under water or drilling fluid shall be placed by tremie and shall not be

discharged freely into the water or drilling fluid. Pumping of concrete may be approved where

appropriate.

3 A sample of the bentonite suspension shall be taken from the base of the boring using an

approved sampling device. If the specific gravity of the suspension exceeds 1.20 the placing

of concrete shall not proceed. In this event the Contractor shall modify or replace the

bentonite as approved to meet the specification.

4 The concrete shall be a rich, coherent mix and highly workable, and cement content shall be

in accordance with Clause 2.3.5.

5 The concrete shall be placed in such a manner that segregation does not occur.

6 The hopper and pipe of the tremie shall be clean and watertight throughout. The pipe shall

extend to the base of the bore and a sliding plug or barrier shall be placed in the pipe to

prevent direct contact between the first charge of concrete in the tremie and the water or

drilling fluid. The pipe shall at all times penetrate the concrete which has previously been

placed and shall be withdrawn at a rate such that there shall be a minimum concrete cover of

2m over the end of the tremie pipe, until completion of concreting. A sufficient quantity of

concrete shall be maintained within the pipe to ensure that the pressure from it exceeds that

from the water or drilling fluid. The internal diameter of the tremie pipe shall be not less than

150 mm, and the maximum sized aggregate shall be 20 mm. It shall be so designed that

external projections are minimised, allowing the tremie to pass within reinforcing cages

without causing damage. The internal face of the pipe of the tremie shall be free from

projections.

END OF PART


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QCS 2014 Section 04: Foundations and Retaining Structures Page 1Part 03: Shallow Foundations

3 SHALLOW FOUNDATIONS .................................................................................... 2

3.1 GENERAL ............................................................................................................... 2

3.1.1 Scope 2

3.1.2 Definition 2

3.1.3 References 2

3.1.4

Limit States Considerations 2

3.2 DESIGN CONSIDERATIONS .................................................................................. 3

3.2.1 General 3

3.2.2 Allowable Bearing Pressure 3

3.2.3 Selection of Types of Shallow Foundation 3

3.2.4 Pad foundations 4

3.2.5 Strip foundations 4

3.2.6 Raft foundations 5

3.3

BASIS OF GEOTECHNICAL DESIGN .................................................................... 53.3.1

Design Requirements 5

3.3.2

Design Situations 7

3.3.3 Durability 8

3.4 GEOTECHNICAL DESIGN BY CALCULATION ...................................................... 9

3.4.1 General 9

3.4.2 Actions 10

3.4.3

Ground Properties 12

3.4.4

Geometrical Data 13

3.4.5

Characteristic and Representative Values of Actions 13

3.4.6

Characteristic Values of Geotechnical Parameters 133.4.7

Characteristic Values of Geometrical Data 14

3.4.8 Geotechnical Design Report 14

3.4.9 Actions and Design Situations 15

3.4.10 Design and Construction Considerations 15

3.4.11 Foundations on Rock; Additional Design Considerations 16


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3 SHALLOW FOUNDATIONS

3.1 GENERAL

3.1.1 Scope

1 The provisions of this Section apply to shallow foundations including isolated, pads, strips and

rafts.

3.1.2 Definition

1 Shallow foundations are taken to be those where the depth below finished ground level is

less than 3 m and include isolated, pad, strip and raft foundations. The choice of 3 m is

arbitrary; shallow foundations where the depth/breadth ratio is high may need to be designed

as deep foundations.

3.1.3 References

BS 8004, ..................... Code of practice for foundations.

BS EN 1990 ................ Eurocode 0: Basis of Structural Design

BS EN 1991 ................ Eurocode 1: Actions on structures

BS EN 1992 ................ Eurocode 2: Design of concrete structures -

BS EN 1993 ................ Eurocode 3: Design of steel structures

BS EN 1994 ................ Eurocode 4: Design of composite steel and concrete structures

BS EN 1995 ................ Eurocode 5: Design of timber structures

BS EN 1996 ................ Eurocode 6: Design of masonry structuresBS EN 1997-1 ............ Eurocode 7, Geotechnical design Part 1: General Rules

BS EN 1997-2 ............ Eurocode 7, Geotechnical design Part 2: Ground investigation and

testing

BS EN 1998 ................ Eurocode 8: Design of structures for earthquake resistance

BS 5930 ...................... Code of Practice for Site Investigation

3.1.4 Limit States Considerations

1 The following limit states shall be considered and an appropriate list shall be compiled:

(a) Loss of overall stability;(b) Bearing resistance failure, punching failure, squeezing;

(c) Failure by sliding;

(d) Combined failure in the ground and in the structure;

(e) Structural failure due to foundation movement;

(f) Excessive settlements;

(g) Excessive heave due to swelling, frost and other causes;

(h) Unacceptable vibrations.


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3.2 DESIGN CONSIDERATIONS

3.2.1 General

1 The depth to which foundations should be carried depends on two principal factors:

(a) Reaching an adequate bearing stratum;

(b) Penetration below the zone in which trouble may be expected from seasonal weather

changes.

2 Other factors such as ground movements, changes in groundwater conditions, long-term

stability and heat transmitted from structures to the supporting ground may be important.

3 Shallow foundations are particularly vulnerable to certain soil conditions, e.g. loose water-

bearing sands and soils that change structure when loaded. Specialist advice should be

sought where such conditions are indicated by ground investigation.

3.2.2 Allowable Bearing Pressure

1 The center of area of a foundation or group of foundations should be arranged vertically

under the centre of gravity of the imposed loading. If this is not possible, the effects on the

structure of rotation and settlement of the foundation need to be considered.

2 Where foundation support is provided by a number of separate bases these should, as far as

practicable, be proportioned so that differential settlement is minimal.

3.2.3 Selection of Types of Shallow Foundation

1 The selection of the appropriate type of shallow foundation will normally depend on the

magnitude and disposition of the structural loads, the bearing capacity and settlement

characteristics of the ground and the need to found in stable soil.

2 A pad foundation is used for the purpose of distributing concentrated loads. Unless special

conditions control the design, relatively heavy column loads make it advantageous to use pad

foundations.

3 Strip foundations may be more appropriate where column loads are comparatively small and

closely spaced or where walls are heavy or heavily loaded.

4 Adjacent pad foundations can be combined or joined together with ground beams to supporteccentric loads, to resist overturning or to oppose horizontal forces. Walls between columns

may be carried on ground beams spanning between the pad foundations.

5 Where the allowable bearing pressure would result in large isolated foundations occupying

the majority of the available area, it may be logical to join them to form a raft and spread the

loads over the entire area. The combination of isolated foundations to form a raft sometimes

results in a complex design and a large increase in the reinforcement requirement.


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6 In connection with the provision of foundations to an extension of an existing building,

allowance should be made for differential movement of the foundations between the new and

existing structure; such movement affects the structure above foundations. Where a degree

of cracking and subsequent remedial work is not acceptable, provision for a joint between the

extension and existing building should be considered. Where the foundations of an extensionabout the foundations of the existing building, the stability of the existing foundations should

be ensured.

3.2.4 Pad foundations

1 For buildings such as low rise dwellings and lightly framed structures, pad foundations may

be of unreinforced concrete provided that the angle of spread of load from the pier or base

plate to the outer edge of the ground bearing does not exceed one (vertical) in one

(horizontal) and that the stresses in the concrete due to bending and shear do not exceed

tolerable limits. For buildings other than low rise and lightly framed structures, it is customary

to use reinforced concrete foundations.

2 The thickness of the foundation should under no circumstances be less than 150 mm and will

generally be greater than this to maintain cover to reinforcement where provided.

3 Where concrete foundations are used they should be designed in accordance with the design

method appropriate to the loading assumptions.

3.2.5 Strip foundations

1 Similar considerations to those for pad foundations apply to strip foundations. On sloping

sites strip foundations should be on a horizontal bearing, stepped where necessary to

maintain adequate depth.

2 In continuous wall foundations it is recommended that reinforcement be provided wherever

an abrupt change in magnitude of load or variation in ground support occurs. Continuous wall

foundations will normally be constructed in mass concrete provided that the angle of spread

of load from the edge of the wall base to the outer edge of the ground bearing does not

exceed one (vertical) in one (horizontal). Foundations on sloping ground, and where

regarding is likely to take place, may require to be designed as retaining walls to

accommodate steps between adjacent ground floor slabs or finished ground levels. At all

changes of level unreinforced foundations should be lapped at the steps for a distance at

least equal to the thickness of the foundation or a minimum of 300mm. Where the height of

the step exceeds the thickness of the foundation, special precautions should be taken. The

thickness of reinforced strip foundations should be not less than 150mm, and care should betaken with the excavation levels to ensure that this minimum thickness is maintained. For the

longitudinal spread of loads, sufficient reinforcement should be provided to withstand the

tensions induced. It will sometimes be desirable to make strip foundations of inverted tee

beam sections, in order to provide adequate stiffness in the longitudinal direction. At corners

and junctions the longitudinal reinforcement of each wall foundation should be lapped.

3 Where the use of ordinary strip foundations would overstress the bearing strata, wide strip

foundations designed to transmit the foundation loads across the full width of the strip may be

used. The depth below the finished ground level should be the same as for ordinary strip

foundations.


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4 Where the nature of the ground is such that narrow trenches can be neatly cut down to the

bearing stratum, an economical foundation may be achieved by filling the trenches with

concrete. When deciding the trench width, account should be taken of normal building

tolerances in relation to setting out dimensions. Where the thickness of such a foundation is

500mm or more, any step should be not greater than the concrete thickness and the lap atsuch a step should be at least 1 m or twice the step height, whichever is the greater?

5 Where fill or other loose materials occur above the bearing stratum adequate support is

required to any excavation. Consideration may be given to the use of lean mix mass concrete

replacement under ordinary strip footings placed at shallow depth. This mass concrete can

be poured against either permanent or recoverable shuttering. This form of foundation

provides a method of dealing with local areas where deeper foundations are required.

3.2.6 Raft foundations

1 General. Suitably designed raft foundations may be used in the following circumstances.

(a) For lightly loaded structures on soft natural ground where it is necessary to spread the

load, or where there is variable support due to natural variations, made ground or

weaker zones. In this case the function of the raft is to act as a bridge across the

weaker zones. Rafts may form part of compensated foundations.

(b) Where differential settlements are likely to be significant. The raft will require special

design, involving an assessment of the disposition and distribution of loads, contact

pressures and stiffness of the soil and raft.

3.3 BASIS OF GEOTECHNICAL DESIGN

3.3.1 Design Requirements

1 For each geotechnical design situation it shall be verified that no relevant limit state is

exceeded.

2 When defining the design situations and the limit states, the following factors should be

considered:

(a) Site conditions with respect to overall stability and ground movements;

(b) Nature and size of the structure and its elements, including any special requirements

such as the design life;

(c) Conditions with regard to its surroundings (e.g.: neighboring structures, traffic, utilities,vegetation, hazardous chemicals);

(d) Ground conditions;

(e) Ground-water conditions;

(f) Regional seismicity;

(g) Influence of the environment (hydrology, surface water, subsidence, seasonal changes

of temperature and moisture).

3 Limit states can occur either in the ground or in the structure or by combined failure in the

structure and the ground.


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4 Limit states should be verified by any appropriate method such as calculation method as

described in 3.4;

5 In practice, experience will often show which type of limit state will govern the design and the

avoidance of other limit states may be verified by a control check.

6 Buildings should normally be protected against the penetration of ground-water or the

transmission of vapor or gases to their interiors.

7 If practicable, the design results should be checked against comparable experience.

8 In order to establish minimum requirements for the extent and content of geotechnical

investigations, calculations and construction control checks, the complexity of each

geotechnical design shall be identified together with the associated risks. In particular, a

distinction shall be made between:

(a) L ight and simple structures and small earthworks for which it is possible to ensure that

the minimum requirements will be satisfied by experience and qualitative geotechnical

investigations, with negligible risk;

(b) Other geotechnical structures.

9 For structures and earthworks of low geotechnical complexity and risk, such as defined

above, simplified design procedures may be applied.

10 To establish geotechnical design requirements, three Geotechnical Categories, 1, 2 and 3,

may be introduced.

11 A preliminary classification of a structure according to Geotechnical Category should

normally be performed prior to the geotechnical investigations. The category should be

checked and changed, if necessary, at each stage of the design and construction process.

12 The procedures of higher categories may be used to justify more economic designs, or if the

designer considers them to be appropriate.

13 The various design aspects of a project can require treatment in different Geotechnical

Categories. It is not required to treat the whole of the project according to the highest of these

categories.

14 Geotechnical Category 1should only include small and relatively simple structures:

(a) For which it is possible to ensure that the fundamental requirements will be satisfied on

the basis of experience and qualitative geotechnical investigations;

(b) With negligible risk.

15 Geotechnical Category 1 procedures should be used only where there is negligible risk in

terms of overall stability or ground movements and in ground conditions, which are known

from comparable local experience to be sufficiently straightforward. In these cases the

procedures may consist of routine methods for foundation design and construction.

16 Geotechnical Category 1 procedures should be used only if there is no excavation below the

water table or if comparable local experience indicates that a proposed excavation below the

water table will be straightforward.


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17 Geotechnical Category 2should include conventional types of structure and foundation with

no exceptional risk or difficult soil or loading conditions

18 Designs for structures in Geotechnical Category 2 should normally include quantitative

geotechnical data and analysis to ensure that the fundamental requirements are satisfied.

19 Routine procedures for field and laboratory testing and for design and execution may be used

for Geotechnical Category 2 designs.

(a) the following are examples of conventional structures or parts of structures complying

with Geotechnical Category 2:

(i) Shallow foundations;

(ii) Pile foundations;

(iii) Walls and other structures retaining or supporting soil or water;

(iv) Excavations;(v) Bridge piers and abutments;

(vi) Embankments and earthworks;

(vii) Ground anchors and other tie-back systems;

(viii) Tunnels in hard, non-fractured rock and not subjected to special water tightness

or other requirements.

20 Geotechnical Category 3should include structures or parts of structures, which fall outside

the limits of Geotechnical Categories 1 and 2.

21 Geotechnical Category 3 should normally include alternative provisions and rules to those inthis standard.

(a) Geotechnical Category 3 includes the following examples:

(i) Very large or unusual structures;

(ii) Structures involving abnormal risks, or unusual or exceptionally difficult ground

or loading conditions;

(iii) Structures in highly seismic areas;

(iv) Structures in areas of probable site instability or persistent ground movements

that require separate investigation or special measures.

3.3.2 Design Situations

1 Both short-term and long-term design situations shall be considered.

2 In geotechnical design, the detailed specifications of design situations should include, as

appropriate:

(a) The actions, their combinations and load cases;

(b) The general suitability of the ground on which the structure is located with respect to

overall stability and ground movements;

(c) The disposition and classification of the various zones of soil, rock and elements ofconstruction, which are involved in any calculation model;


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(d) Dipping bedding planes;

(e) Mine workings, caves or other underground structures;

(f) In the case of structures resting on or near rock:

(i) inter bedded hard and soft strata;

(ii) faults, joints and fissures;

(iii) possible instability of rock blocks;

(iv) solution cavities, such as swallow holes or fissures filled with soft material, and

continuing solution processes;

(g) The environment within which the design is set, including the following:

(i) effects of scour, erosion and excavation, leading to changes in the geometry of

the ground surface;

(ii) effects of chemical corrosion;

(iii) effects of weathering;

(iv) effects of long duration droughts;

(v) variations in ground-water levels, including, e.g. the effects of dewatering,

possible flooding, failure of drainage systems, water exploitation;

(vi) the presence of gases emerging from the ground;

(h) Earthquakes;

(i) Ground movements caused by subsidence due to mining or other activities;

(j) The sensitivity of the structure to deformations;

(k) The effect of the new structure on existing structures, services and the local

environment.

3.3.3 Durability

1 At the geotechnical design stage, the significance of environmental conditions shall be

assessed in relation to durability and to enable provisions to be made for the protection or

adequate resistance of the materials.

2 In designing for durability of materials used in the ground, the following should be considered:

(a) For concrete:

(i) Aggressive agents in the ground-water or in the ground or fill material, such as

acids or sulfate salts;

(b) For steel:

(i) Chemical attack where foundation elements are buried in ground that is

sufficiently permeable to allow the percolation of ground-water and oxygen;

(ii) Corrosion on the faces of sheet pile walls exposed to free water, particularly in

the mean water level zone;

(iii) The pitting type of corrosive attack on steel embedded in fissured or porous

concrete, particularly for rolled steel where the mill scale, acting as a cathode,

promotes electrolytic action with the scale-free surface acting as an anode;


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(c) For timber:

(i) Fungi and aerobic bacteria in the presence of oxygen;

(d) For synthetic fabrics:

(i) The ageing effects of UV exposure or ozone degradation or the combinedeffects of temperature and stress, and secondary effects due to chemical

degradation.

3 Reference should be made to durability provisions in construction materials standards.

3.4 GEOTECHNICAL DESIGN BY CALCULATION

3.4.1 General

1 Design by calculation shall be in accordance with the fundamental requirements of EN 1990

and with the particular rules of this specification. Design by calculation involves:

(a) Actions, which may be either imposed loads or imposed displacements, e.g. from

ground movements;

(b) Properties of soils, rocks and other materials;

(c) Geometrical data;

(d) Limiting values of deformations, crack widths, vibrations etc;

(e) Calculation models.

2 It should be considered that knowledge of the ground conditions depends on the extent and

quality of the geotechnical investigations. Such knowledge and the control of workmanshipare usually more significant to fulfilling the fundamental requirements than is precision in the

calculation models and partial factors.

3 The calculation model shall describe the assumed behavior of the ground for the limit state

under consideration.

4 If no reliable calculation model is available for a specific limit state, analysis of another limit

state shall be carried out using factors to ensure that exceeding the specific limit state

considered is sufficiently improbable. Alternatively, design by prescriptive measures,

experimental models and load tests, or the observational method, shall be performed.

5 The calculation model may consist of any of the following:

(a) An analytical model;

(b) A semi-empirical model;

(c) A numerical model.

6 Any calculation model shall be either accurate or err on the side of safety.

7 A calculation model may include simplifications.

8 If needed, a modification of the results from the model may be used to ensure that the design

calculation is either accurate or errs on the side of safety.


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9 If the modification of the results makes use of a model factor, it should take account of the

following:

(a) The range of uncertainty in the results of the method of analysis;

(b) Any systematic errors known to be associated with the method of analysis.

10 If an empirical relationship is used in the analysis, it shall be clearly established that it is

relevant for the prevailing ground conditions.

11 Limit states involving the formation of a mechanism in the ground should be readily checked

using a calculation model. For limit states defined by deformation considerations, the

deformations should be evaluated by calculation or otherwise assessed.

NOTE: many calculation models are based on the assumption of a sufficiently ductileperformance of the ground/structure system. A lack of ductility, however, will lead to anultimate limit state characterized by sudden collapse.

12 Numerical methods can be appropriate if compatibility of strains or the interaction betweenthe structure and the soil at a limit state are considered.

13 Compatibility of strains at a limit state should be considered. Detailed analysis, allowing for

the relative stiffness of structure and ground, may be needed in cases where a combined

failure of structural members and the ground could occur. Examples include raft foundations,

laterally loaded piles and flexible retaining walls. Particular attention should be paid to strain

compatibility for materials that are brittle or that have strain-softening properties.

14 In some problems, such as excavations supported by anchored or strutted flexible walls, the

magnitude and distribution of earth pressures, internal structural forces and bending

moments depend to a great extent on the stiffness of the structure, the stiffness and strength

of the ground and the state of stress in the ground.

15 In these problems of ground-structure interaction, analyses should use stress-strain

relationships for ground and structural materials and stress states in the ground that are

sufficiently representative, for the limit state considered, to give a safe result.

3.4.2 Actions

1 The definition of actions shall be taken as:

(a) Set of forces (loads) applied to the structure (direct action);

(b) Set of imposed deformations or accelerations caused for example, by temperaturechanges, moisture variation, uneven settlement or earthquakes (indirect action).

The values of actions shall be taken from EN 1991 or equivalent international standard,where relevant.

2 The values of geotechnical actions to be used shall be selected, since they are known before

a calculation is performed; they may change during that calculation.

NOTE: Values of geotechnical actions may change during the course of calculation. In suchcases they will be introduced as a first estimate to start the calculation with a preliminary,known value.

3 Any interaction between the structure and the ground shall be taken into account when

determining the actions to be adopted in the design.


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4 In geotechnical design, the following should be considered for inclusion as actions:

(a) the weight of soil, rock and water;

(b) stresses in the ground;

(c) earth pressures and ground-water pressure;

(d) free water pressures, including wave pressures;

(e) ground-water pressures;

(f) seepage forces;

(g) dead and imposed loads from structures;

(h) surcharges;

(i) mooring forces;

(j) removal of load or excavation of ground;

(k) traffic loads;

(l) movements caused by mining or other caving or tunneling activities;

(m) swelling and shrinkage caused by vegetation, climate or moisture changes;

(n) movements due to creeping or sliding or settling ground masses;

(o) movements due to degradation, dispersion, decomposition, self-compaction and

solution;

(p) movements and accelerations caused by earthquakes, explosions, vibrations and

dynamic loads;

(q) temperature effects, including frost action;

(r) imposed pre-stress in ground anchors or struts;

(s) down drag.

5 Consideration shall be given to the possibility of variable actions occurring both jointly and

separately.

6 The duration of actions shall be considered with reference to time effects in the material

properties of the soil, especially the drainage properties and compressibility of fine-grained

soils.

7 Actions, which are applied repeatedly, and actions with variable intensity shall be identifiedfor special consideration with regard to, e.g. continuing movements, liquefaction of soils,

change of ground stiffness and strength.

8 Actions that produce a dynamic response in the structure and the ground shall be identified

for special consideration.

9 Actions in which ground- and free-water forces predominate shall be identified for special

consideration with regard to deformations, f issuring, variable permeability and erosion.

NOTE Unfavorable (or destabilizing) and favorable (or stabilizing) permanent actions may insome situations be considered as coming from a single source. If they are considered so, a

single partial factor may be applied to the sum of these actions or to the sum of their effects.


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3.4.3 Ground Properties

1 Properties of soil and rock masses, as quantified for design calculations by geotechnical

parameters, shall be obtained from test results, either directly or through correlation, theory

or empiricism, and from other relevant data.

2 Values obtained from test results and other data shall be interpreted appropriately for the limit

state considered.

3 Account shall be taken of the possible differences between the ground properties and

geotechnical parameters obtained from test results and those governing the behavior of the

geotechnical structure.

4 The above differences can be due to the following factors:

(a) many geotechnical parameters are not true constants but depend on stress level and

mode of deformation;(b) soil and rock structure (e.g. fissures, laminations, or large particles) that may play a

different role in the test and in the geotechnical structure;

(c) time effects;

(d) the softening effect of percolating water on soil or rock strength;

(e) the softening effect of dynamic actions;

(f) the brittleness or ductility of the soil and rock tested;

(g) the method of installation of the geotechnical structure;

(h) the influence of workmanship on artificially placed or improved ground;

(i) the effect of construction activities on the properties of the ground.

5 When establishing values of geotechnical parameters, the following should be considered:

(a) published and well recognized information relevant to the use of each type of test in

the appropriate ground conditions;

(b) the value of each geotechnical parameter compared with relevant published data and

local and general experience;

(c) the variation of the geotechnical parameters that are relevant to the design;

(d) the results of any large scale field trials and measurements from neighboring

constructions;

(e) any correlations between the results from more than one type of test;

(f) any significant deterioration in ground material properties that may occur during the

lifetime of the structure.

6 Calibration factors shall be applied where necessary to convert laboratory or field test results

according to EN 1997-2 into values that represent the behavior of the soil and rock in the

ground, for the actual limit state, or to take account of correlations used to obtain derived

values from the test results.


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3.4.4 Geometrical Data

1 The level and slope of the ground surface, water levels, levels of interfaces between strata,

excavation levels and the dimensions of the geotechnical structure shall be treated as

geometrical data.

3.4.5 Characteristic and Representative Values of Actions

1 Characteristic and representative values of actions shall be derived in accordance with EN

1990:2002 and the various parts of EN 1991.

3.4.6 Characteristic Values of Geotechnical Parameters

1 The selection of characteristic values for geotechnical parameters shall be based on results

and derived values from laboratory and field tests, complemented by well-established

experience.

2 The characteristic value of a geotechnical parameter shall be selected as a cautious estimate

of the value affecting the occurrence of the limit state.

3 The selection of characteristic values for geotechnical parameters shall take account of the

following:

(a) geological and other background information, such as data from previous projects;

(b) the variability of the measured property values and other relevant information, e.g.

from existing knowledge;

(c) the extent of the field and laboratory investigation;

(d) the type and number of samples;

(e) the extent of the zone of ground governing the behavior of the geotechnical structure

at the limit state being considered;

(f) the ability of the geotechnical structure to transfer loads from weak to strong zones in

the ground.

4 Characteristic values can be lower values, which are less than the most probable values, or

upper values, which are greater.

5 For each calculation, the most unfavorable combination of lower and upper values of

independent parameters shall be used.

6 The zone of ground governing the behavior of a geotechnical structure at a limit state is

usually much larger than a test sample or the zone of ground affected in an in situ test.

Consequently the value of the governing parameter is often the mean of a range of values

covering a large surface or volume of the ground. The characteristic value should be a

cautious estimate of this mean value.

7 If the behavior of the geotechnical structure at the limit state considered is governed by the

lowest or highest value of the ground property, the characteristic value should be a cautious

estimate of the lowest or highest value occurring in the zone governing the behavior.


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8 When selecting the zone of ground governing the behavior of a geotechnical structure at a

limit state, it should be considered that this limit state may depend on the behavior of the

supported structure. For instance, when considering a bearing resistance ultimate limit state

for a building resting on several footings, the governing parameter should be the mean

strength over each individual zone of ground under a footing, if the building is unable to resista local failure. If, however, the building is stiff and strong enough, the governing parameter

should be the mean of these mean values over the entire zone or part of the zone of ground

under the building.

9 If statistical methods are employed in the selection of characteristic values for ground

properties, such methods should differentiate between local and regional sampling and

should allow the use of a prior knowledge of comparable ground properties.

10 If statistical methods are used, the characteristic value should be derived such that the

calculated probability of a worse value governing the occurrence of the limit state under

consideration is not greater than 5%.

NOTE : In this respect, a cautious estimate of the mean value is a selection of the meanvalue of the limited set of geotechnical parameter values, with a confidence level of 95%;where local failure is concerned, a cautious estimate of the low value is a 5% fractal.

11 When using standard tables of characteristic values related to soil investigation parameters,

the characteristic value shall be selected as a very cautious value.

3.4.7 Characteristic Values of Geometrical Data

1 Characteristic values of the levels of ground and ground-water or free water shall be

measured, nominal or estimated upper or lower levels.

2 Characteristic values of levels of ground and dimensions of geotechnical structures or

elements should usually be nominal values.

3.4.8 Geotechnical Design Report

1 The assumptions, data, methods of calculation and results of the verification of safety and

serviceability shall be recorded in the Geotechnical Design Report.

2 The level of detail of the Geotechnical Design Reports will vary greatly, depending on the

type of design. For simple designs, a single sheet may be sufficient.

3 The Geotechnical Design Report should normally include the following items, with cross-reference to the Ground Investigation Report :

(a) a description of the site and surroundings;

(b) a description of the ground conditions;

(c) a description of the proposed construction, including actions;

(d) design values of soil and rock properties, including justification, as appropriate;

(e) statements on the codes and standards applied;

(f) statements on the suitability of the site with respect to the proposed construction and

the level of acceptable risks;

(g) geotechnical design calculations and drawings;


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(h) foundation design recommendations;

(i) a note of items to be checked during construction or requiring maintenance or

monitoring.

4 The Geotechnical Design Report shall include a plan of supervision and monitoring, asappropriate. Items, which require checking during construction or, which require maintenance

after construction shall be clearly identified. When the required checks have been carried out

during construction, they shall be recorded in an addendum to the Report.

5 In relation to supervision and monitoring the Geotechnical Design Report should state:

(a) the purpose of each set of observations or measurements;

(b) the parts of the structure, which are to be monitored and the locations at which

observations are to be made;

(c) the frequency with which readings is to be taken;

(d) the ways in which the results are to be evaluated;

(e) the range of values within which the results are to be expected;

(f) the period of time for which monitoring is to continue after construction is complete;

(g) the parties responsible for making measurements and observations, for interpreting

the results obtained and for maintaining the instruments.

6 An extract from the Geotechnical Design Report, containing the supervision, monitoring and

maintenance requirements for the completed structure, shall be provided to the owner/client.

3.4.9 Actions and Design Situations

1 Design situations shall be selected in accordance with 3.3.2.

2 The actions listed in 3.4.2(4) should be considered when selecting the limit states for

calculation.

3 If structural stiffness is significant, an analysis of the interaction between the structure and

the ground should be performed in order to determine the distribution of actions.

3.4.10 Design and Construction Considerations

1 When choosing the depth of a shallow foundation the following shall be considered:

(a) reaching an adequate bearing stratum;

(b) the depth above which shrinkage and swelling of clay soils, due to seasonal weather

changes, or to trees and shrubs, may cause appreciable movements;

(c) the level of the water table in the ground and the problems, which may occur if

excavation for the foundation is required below this level;

(d) possible ground movements and reductions in the strength of the bearing stratum by

seepage or climatic effects or by construction procedures;

(e) the effects of excavations on nearby foundations and structures;

(f) anticipated excavations for services close to the foundation;

(g) high or low temperatures transmitted from the building;


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(h) the possibility of scour;

(i) the effects of variation of water content due to long periods of drought, and subsequent

periods of rain, on the properties of volume-unstable soils in arid climatic areas;

(j) the presence of soluble materials, e.g. limestone, clay stone, gypsum, salt rocks;

2 In addition to fulfilling the performance requirements, the design foundation width shall take

account of practical considerations such as economic excavation, setting out tolerances,

working space requirements and the dimensions of the wall or column supported by the

foundation.

3 One of the following design methods shall be used for shallow foundations:

(a) a direct method, in which separate analyses are carried out for each limit state. When

checking against an ultimate limit state, the calculation shall model as closely as

possible the failure mechanism, which is envisaged. When checking against a

serviceability limit state, a settlement calculation shall be used;

(b) an indirect method using comparable experience and the results of field or laboratory

measurements or observations, and chosen in relation to serviceability limit state loads

so as to satisfy the requirements of all relevant limit states;

(c) a prescriptive method in which a presumed bearing resistance is used.

3.4.11 Foundations on Rock; Additional Design Considerations

1 The design of shallow foundations on rock shall take account of the following features:

(a) the deformability and strength of the rock mass and the permissible settlement of the

supported structure;

(b) the presence of any weak layers, for example solution features or fault zones, beneath

the foundation;

(c) the presence of bedding joints and other discontinuities and their characteristics (for

example filling, continuity, width, spacing);

(d) the state of weathering, decomposition and fracturing of the rock;

(e) disturbance of the natural state of the rock caused by construction activities, such as,

for example, underground works or slope excavation, being near to the foundation.

2 Shallow foundations on rock may normally be designed using the method of presumed

bearing pressures. For strong intact igneous rocks, gneissic rocks, limestone and

sandstones, the presumed bearing pressure are limited by the compressive strength of the

concrete foundation.

3 The settlement of a foundation may be assessed on the basis of comparable experience

related to rock mass classification.

END OF PART


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QCS 2014 Section 04: Foundations and Retaining Structures Page 1Part 04: Deep Foundations

4 DEEP FOUNDATIONS ............................................................................................ 4

4.1 PRECAST REINFORCED AND PRESTRESSED CONCRETE PILES .................... 4

4.1.1 General 4

4.1.2

Limit States Considerations 4

4.1.3 Precast Reinforced and Prestressed Concrete Piles 4

4.1.4 Materials and components 5

4.1.5 Prestressing 7

4.1.6 Driving Piles 8

4.1.7 Risen Piles 10

4.1.8 Repair and lengthening of piles 10

4.1.9 Cutting off pile heads 10

4.2

PRECAST REINFORCED CONCRETE SEGMENTAL PILES ............................... 10

4.2.1 Scope 10

4.2.2

References 11

4.2.3 Submittals 11

4.2.4 Quality Assurance 11

4.2.5 Tolerances in Pile Dimensions 11

4.2.6 Handling, Transportation, Storage and Acceptance of Piles 12

4.2.7 Materials and components 12

4.2.8 Driving piles 13


4.2.10

Repair and lengthening of piles 15

4.2.11

Cutting off pile heads 15

4.3

BORED CAST IN PLACE PILES ........................................................................... 15

4.3.1 Scope 15

4.3.2 References 16


4.3.4 Materials 16

4.3.5 Boring 17

4.3.6 Extraction of casing 19

4.4

BORED PILES CONSTRUCTED USING CONTINUOUS FLIGHT AUGERS AND

CONCRETE OR GROUT INJECTION TROUGH HOLLOW AUGER STEMS ....... 21

4.4.1 Scope 21

4.4.2

Materials 21

4.4.3 Boring 22

4.4.4 Placing of concrete or grout 23

4.4.5 Cutting off pile heads 23

4.5

DRIVEN CAST IN PLACES PILES ........................................................................ 23

4.5.1

Scope 23

4.5.2

Submittals 24

4.5.3

Quality Assurance 24

4.5.4

Materials 24

4.5.5 Driving piles 25



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4.5.7

Extraction of casing 26

4.6 STEEL PILES ........................................................................................................ 28

4.6.1 Scope 28

4.6.2 References 28

4.6.3

Submittals 28


4.6.5 Delivery, Storage and Handling 29

4.6.6 Materials 29

4.6.7

Acceptance Standards For Welds 30

4.6.8

Acceptability and inspection of coatings 31

4.6.9

Driving of piles 31

4.6.10

Risen Piles 33

4.6.11

Preparation of pile heads 33

4.7 MICROPILES (TO BE ADDED LATER) ................................................................. 33

4.8 REDUCTION OF FRICTION ON PILES ................................................................ 33

4.8.1

Scope 33

4.8.2

Submittals 33

4.8.3

Friction Reducing Methods 33

4.8.4

Inspection 34

4.8.5 Driving resistance 35

4.9 PILE LOAD TESTING ........................................................................................... 35

4.9.1 Static Load Testing of Piles 35

4.9.2 Presentation of results 45

4.9.3

Low strain Integrity test 47

4.9.4 Grosshole Sonic Logging Test 48

4.9.5

Calliper Logging Test 48

4.9.6

Axial Tensile Load Test 48

4.9.7

Lateral Load Test 48

4.9.8 Alternative Methods for Testing Piles 48

4.10 DESIGN METHODS AND DESIGN CONSIDERATIONS ...................................... 51

4.10.1 Design method 51

4.10.2 Verification of Resistance for Structural and Ground Limit States in Persistent and

Transient Situations 51

4.10.3

Design Considerations 51

4.11

AXIALLY LOADED PILES ..................................................................................... 52

4.11.1

Limit state design 52

4.11.2 Compressive Ground Resistance 53

4.11.3 Ultimate compressive resistance from static load tests 54

4.11.4 Ultimate compressive resistance from ground test results 55

4.11.5 Ultimate compressive resistance from dynamic impact tests 56

4.11.6 Ultimate compressive resistance by applying pile driving formulae 56

4.11.7 Ultimate compressive resistance from wave equation analysis 56

4.11.8 Ground tensile resistance 57

4.11.9

Ultimate tensile resistance from pile load tests 57

4.11.10 Ultimate tensile resistance from ground test results 57


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4.11.11

Vertical displacements of pile foundations 58

4.11.12

Pile foundations in compression 58

4.11.13

Pile foundations in tension 58

4.12 TRANSVERSELY LOADED PILES ....................................................................... 58

4.12.1

Design method 58

4.12.2 Transverse load resistance from pile load tests 59

4.12.3 Transverse load resistance from ground test results and pile strength parameters 59

4.12.4 Transverse displacement 60


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4 DEEP FOUNDATIONS

4.1 PRECAST REINFORCED AND PRESTRESSED CONCRETE PILES

4.1.1 General

1 The provisions of this Part apply to end-bearing piles, friction piles, tension piles and

transversely loaded piles installed by driving, by jacking, and by screwing or boring with or

without grouting.

4.1.2 Limit States Considerations

1 The following limit states shall be considered and an appropriate list shall be compiled:

(a) Loss of overall stability;

(b) bearing resistance failure of the pile foundation;

(c) Uplift or insufficient tensile resistance of the pile foundation;

(d) Failure in the ground due to transverse loading of the pile foundation;

(e) Structural failure of the pile in compression, tension, bending, buckling or shear;

(f) combined failure in the ground and in the pile foundation;

(g) combined failure in the ground and in the structure;

(h) Excessive settlement;

(i) Excessive heave;

(j) Excessive lateral movement;

(k) Unacceptable vibrations.

4.1.3 Precast Reinforced and Prestressed Concrete Piles

1 Scope

(a) This Part applies to precast concrete driven piles usually supplied for use in a single

length without facility for joining lengths together.

(b) Related Sections and Parts are as follows:

2 References

(a) The following Standards are referred to in this Part:

BS 7613, ..................... Hot rolled quenched and tempered weldable structural steel plates

BS 3100, ..................... Steel castings for general engineering purposes

BS 2789, ..................... Spheroidal graphite or nodular graphite cast iron

BS 8110, ..................... Structural use of concrete.

3 Submittals

(a) The Contractor shall order the piles to suit the construction programme and seek the

Engineer's approval before placing the order. When preliminary piles are specified,

the approval of the piles for the main work will not necessarily be given until the results

of the driving and loading tests on preliminary piles have been received and evaluated.


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4 Quality Assurance

(a) After a pile has been cast, the date of casting, reference number, length and, where

appropriate, the prestressing force shall be clearly inscribed on the top surface of the

pile and also clearly and indelibly marked on the head of the pile. Lifting positions shall

be marked at the proper locations on each pile.

5 Tolerances in Pile Dimensions

(a) The cross-sectional dimensions of the pile shall be not less than those specified and

shall not exceed them by more than 6mm. Each face of a pile shall not deviate by

more than 6mm from any straight line 3m long joining two points on that face, nor

shall the centre of area of the pile at any cross

section along its length deviate by more

than 1/500 of the pile length from a line joining the centres of area at the ends of the

pile. Where a pile is less than 3

m long, the permitted deviation from straightness shall

be reduced below 6 mm on apro ratabasis in accordance with actual length.

6 Handling, Transportation and Storage of Piles

(a) The method and sequence of lifting, handling, and storage of piles transporting and

storing piles shall be such as to avoid shock loading and to ensure that the piles are

not damaged. Only the designated lifting and support points shall be used. During

transport and storage, piles shall be appropriately supported under the marked lifting

points or fully supported along their length.

(b) All piles within a stack shall be in groups of the same length. Packing of uniform

thickness shall be provided between piles at the lifting points.

(c) Concrete shall at no time be subjected to loading, including its own weight, which will

induce a compressive stress in it exceeding 0.33 of its strength at the time of loading

or of the specified strength, whichever is the lesser. For this purpose the assessment

of the strength of the concrete and of the stresses produced by the loads shall be

subject to the agreement of the Engineer.

(d) Pile may be rejected when the width of any transverse crack exceeds 0.3

mm. The

measurement shall be made with the pile in its working attitude.

4.1.4 Materials and components

1 Fabricated Steel Components

(a) In the manufacture of precast concrete piles, fabricated steel components shall comply

with BS 7613 grades 43A or 50B, cast steel components with BS 3100 grade A, and

ductile iron components with BS 2789.

2 Pile Toes

(a) Pile toes shall be constructed so as to ensure that damage is not caused to the pile

during installation. Where positional fixity is required on an inclined rock surface or in

other circumstances, an approved shoe may be required.

3 Pile Head Reinforcement

(a) The head of each pile shall be so reinforced or banded as to prevent bursting of thepile under driving conditions.


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4 Main Reinforcement

(a) The main longitudinal reinforcing bars in piles not exceeding 12

m in length shall be in

one continuous length unless otherwise specified. In piles more than 12

m long, lap

splicing will be permitted in main longitudinal bars at 12

m nominal intervals, with no

more than 25

% of the bars lapped at one location, and laps staggered by a minimum

of 1.2

m. Laps in reinforcement shall be such that the full strength of the bar is

effective across the joint.

(b) Lap or splice joints shall be provided with sufficient link bars to resist eccentric forces.

(c) Sufficient reinforcement shall be provided for lifting and handling purposes.

5 Concrete

(a) Unless otherwise agreed by the Engineer, concrete shall be compacted with the

assistance of vibrators. Internal vibrators shall be capable of producing not less than150

Hz and external vibrators not less than 50

Hz. Internal vibrators shall operate not

closer than 75

mm to shuttering.

(b) Vibrators shall be operated in such a manner that neither segregation of the concrete

mix constituents nor displacement of reinforcement occurs.

(c) Immediately after compaction, concrete shall he adequately protected from the harmful

effects of the weather, including wind, rain, rapid temperature changes and frost. It

shall be protected from drying out by an approved method of curing.

(d) Piles shall not be removed from formwork until a sufficient pile concrete strength has

been achieved to allow the pile to be handled without damage.

(e) The period of curing at an ambient temperature of 10C shall not be less than that

shown in Table 4.1. If the temperature is greater or less than 10 C, the periods given

shall be adjusted accordingly and shall be approved.

(f) When steam or accelerated curing is used the curing procedure shall be approved.

Four hours must elapse from the completion of placing concrete before the

temperature is raised. The rise in temperature within any period of 30 min shall not

exceed 10C and the maximum temperature attained shall not exceed 70 C. The rate

of subsequent cooling shall not exceed the rate of heating.

Table 4.1Period of Curing at 10 C

Type of cementWet curing time after

completion of placing concrete, d

Ordinary Portland 4

Sulphate-resisting Portland 4

Portland blast-furnace 4

Super-sulphated 4

Rapid-hardening Portland 3


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6 Formwork

(a) shaped point or shoe, then the end of the pile shall be symmetrical about the

longitudinal axis of the pile. Holes for handling or pitching, where provided in the pile,

shall be lined with steel tubes; alternatively, approved inserts may be cast in.

(b) Formwork shall be robust, clean and so constructed as to prevent loss of grout or

aggregate from the wet concrete and ensure the production of uniform pile sections,

free from defects. The piles are to be removed from the formwork carefully so as to

prevent damage.

4.1.5 Prestressing

1 General

(a) Tensioning shall be carried out only when the Engineer is present, unless otherwiseapproved. In cases where piles are manufactured off site, the Contractor shall ensurethat the Engineer is given adequate notice and every facility for inspecting themanufacturing process.

(b) Prestressing operations shall be carried out only under the direction of an experiencedand competent supervisor. All personnel operating the stressing equipment shall havebeen trained in its use.

(c) The calculated extensions and total forces, including allowance for losses, shall beagreed with the Engineer before stressing is commenced.

(d) Stressing of tendons and transfer of prestress shall be carried out at a gradual andsteady rate. The force in the tendons shall be obtained from readings on a recentlycalibrated load cell or pressure gauge incorporated in the equipment. The extension of

the tendons under the agreed total forces shall be within 5

% of the agreed calculated

extension.

2 Concrete Strength

(a) The Contractor shall cast sufficient cubes, cured in the same manner as the piles, to

be able to demonstrate by testing two cubes at a time, with approved intervals between

pairs of cubes, that the specified transfer strength of the concrete has been reached.

(b) Unless otherwise permitted, concrete shall not be stressed until two test cubes attain

the specified transfer strength.

3 Post-Tensioned Piles

(a) Ducts and vents in post-tensioned piles shall be grouted after the transfer of prestress.

4 Grouting Procedure

(a) Grout shall be mixed for a minimum of 2 min and until a uniform consistency is

obtained.

(b) Ducts shall not be grouted when the air temperature in the shade is lower than 3C.

(c) Before grouting is started all ducts shall be thoroughly cleaned by means of

compressed air.

(d) Grout shall be injected near the lowest point in the duct in one continuous operation

and allowed to flow from the outlet until the consistency is equivalent to that of the

grout being injected.

(e) Vents in ducts shall be provided in accordance with Clause 8.9.2 of BS 8110.


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5 Grout

(a) Unless otherwise directed or agreed by the Engineer

(i) the grout shall consist only of ordinary Portland cement, water and approved

admixtures; admixtures containing chlorides or nitrates shall not be used(ii) the grout shall have a water/cement ratio as low as possible consistent with the

necessary workability, and the water/cement ratio shall not exceed 0.45 unlessan approved mix containing an expanding agent is used

(iii) the grout shall not be subject to bleeding in excess of 2 % after 3 h, or in excess

of 4% maximum, when measured at 18C in a covered glass cylinder

approximately 100 mm in diameter with a height of grout of approximate

Documents

QA_QC Foundation Retaining Structures