QCS 2014 Section 04: Foundations and Retaining...

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QCS 2014 Section 04: Foundations and Retaining Structures Part 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

control

Part 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 specific

documentation 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 cement

and 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 the

records.

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 in

which 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

Dri

ve

n s

tee

l, p

reca

st

co

ncre

te a

nd

ste

el

sh

ee

t p

iles

Dri

ve

n s

eg

me

nta

l

co

ncre

te p

iles

Dri

ve

n c

ast-

in-p

lace

co

ncre

te p

iles

Bo

red

ca

st-

in-p

lace

co

ncre

te p

iles

Con

tin

uo

us f

ligh

t

au

ge

r co

ncre

te o

r

gro

ut

pile

s

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 site investigation data.

- - * * *

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

Date of concreting - - * * *

Ground level/sea bed level at pile position at commencement of installation 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

Dri

ve

n s

tee

l, p

reca

st

co

ncre

te a

nd

ste

el

sh

ee

t p

iles

Dri

ve

n s

eg

me

nta

l

co

ncre

te p

iles

Dri

ve

n c

ast-

in-p

lace

co

ncre

te p

iles

Bo

red

ca

st-

in-p

lace

co

ncre

te p

iles

Co

ntin

uo

us f

ligh

t

au

ge

r co

ncre

te o

r

gro

ut

pile

s

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 and equivalent 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 of blows per 25 mm of penetration

* * * - -

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

* * * - -

If required, temporary compression of ground and pile from time of a marked increase in driving resistance until pile reached its final level

* * * - -

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

* * * - -

Soil samples taken and in-situ tests carried out during pile installation

* * * * *

Length and details of reinforcements - - * * *

Concrete mix - - * * *

Volume of concrete supplied to pile - - * * *

All information regarding obstructions delays and other interruptions 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 of

rake 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 environmental

legislation.

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 1 Part 02: Concrete Works for Piling

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 3

2.3.4 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 specified

based 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 750 mm 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 2.1 Standards for Concrete Slump

Piling mix

workability

Slump

Typical conditions of use Minimum Range

mm mm

A 75 75-150

Placed into water-free unlined or permanently lined bore of 600 mm diameter or over, or where concrete is placed below temporary casing, and where reinforcement is widely spaced leaving ample room for free movement of concrete between bars.

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

C 150 150 or more Where concrete is to be placed by tremie under water or drilling 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

2 m 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 1 Part 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 .................................................................... 5

3.3.1 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 13

3.4.7 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 structures

BS 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 support

eccentric 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 extension

about 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 be

taken 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 at

such 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 1 should 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 2 should 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 3 should 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 in

this 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 of

construction, 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 combined

effects 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 workmanship

are 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 ductile performance of the ground/structure system. A lack of ductility, however, will lead to an ultimate limit state characterized by sudden collapse.

12 Numerical methods can be appropriate if compatibility of strains or the interaction between

the 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 temperature

changes, 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 such cases 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 identified

for 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, fissuring, variable permeability and erosion.

NOTE Unfavorable (or destabilizing) and favorable (or stabilizing) permanent actions may in some 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 resist

a 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 mean value 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, as

appropriate. 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 1 Part 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


4.3 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


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

4.5.1 Scope 23

4.5.2 Submittals 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


4.6.11 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

QCS


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

QCS


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.

QCS


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 6 mm. Each face of a pile shall not deviate by

more than 6 mm from any straight line 3 m 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 a pro rata basis 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 the

pile under driving conditions.

QCS


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 than

150 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 10 °C 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 10 °C and the maximum temperature attained shall not exceed 70 °C. The rate

of subsequent cooling shall not exceed the rate of heating.

Table 4.1

Period of Curing at 10 °C

Type of cement Wet 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

QCS


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 otherwise approved. In cases where piles are manufactured off site, the Contractor shall ensure that the Engineer is given adequate notice and every facility for inspecting the manufacturing process.

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

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

(d) Stressing of tendons and transfer of prestress shall be carried out at a gradual and steady rate. The force in the tendons shall be obtained from readings on a recently calibrated 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 3 °C.

(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.

QCS


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 unless an 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 18 C in a covered glass cylinder

approximately 100 mm in diameter with a height of grout of approximately 100 mm, and the water shall be reabsorbed after 24 h.

6 Records

(a) The Contractor shall keep detailed records of times of tensioning, measured

extensions, pressure gauge readings or load cell readings and the amount of pull-in at

each anchorage. Copies of these records shall be supplied to the Engineer within

such reasonable time from completion of each tensioning operation as may be

required, and in any case not later than noon on the following working day.

(b) The Contractor shall keep records of grouting, including the date, the proportions of

the grout and any admixtures used, the pressure, details of interruption and topping up

required. Copies of these records shall be supplied to the Engineer within such

reasonable time after completion of each grouting operation as may be required, and

in any case not later than noon on the following working day.

4.1.6 Driving Piles

1 Strength of Piles

(a) Piles shall not be driven until the concrete has achieved the specified strength.

2 Leaders and Trestles

(a) At all stages during driving and until incorporation into the substructure, the pile shall be adequately supported and restrained by means of leaders, trestles, temporary supports or other guide arrangements to maintain position and alignment and to prevent buckling. These arrangements shall be such that damage to the pile does not occur.

3 Performance of Driving Equipment

(a) The Contractor shall satisfy the Engineer regarding the suitability, efficiency and

energy of the driving equipment. Where designated, dynamic evaluation and analysis

shall be provided.

(b) Where a drop hammer is used, the mass of the hammer shall be at least half that of

the pile unless otherwise approved by the Engineer. For other types of hammer the

energy delivered to the pile per blow shall be at least equivalent to that of a drop

hammer of the stated mass. Drop hammers shall not be used from floating craft in

such a manner as to cause instability of the craft or damage to the pile.

4 Length of Piles

(a) The length of pile to be driven in any location shall be approved prior to the

commencement of driving.

QCS


5 Driving Procedure and Redrive Checks

(a) The driving of each pile shall be continuous until the specified depth or resistance

(set), or both, has been reached. In the event of unavoidable interruption to driving,

the pile will be accepted provided it can subsequently be driven to the specified depth

or resistance (set), or both, without damage. A follower shall not be used unless

approved, in which case the Engineer will require the set where applicable to be

revised in order to take into account reduction in the effectiveness of the hammer blow.

(b) The Contractor shall inform the Engineer without delay if an unexpected change in

driving characteristics is noted. A detailed record of the driving resistance over the full

length of the nearest available pile shall be taken if required.

(c) At the start of the work in a new area or section, a detailed driving record shall be

made over the full length of the first pile and during the last 3 m of subsequent piles

until consistency of behaviour is established. Where required, detailed driving records

shall also be made for 5 % of the piles driven, the locations of such piles being

specified by the Engineer.

(d) The Contractor shall give adequate notice and provide all necessary facilities to enable

the Engineer to check driving resistance. A set or resistance measurement shall be

taken only in the presence of the Engineer unless otherwise approved.

(e) Redrive checks, if required, shall be carried out to an approved procedure.

6 Final Set

(a) When driving to a set criterion, the final set of each pile shall be recorded either as the

penetration in millimetres per 10 blows or as the number of blows required to produce

a penetration of 25 mm.

(b) When a final set is being measured, the following requirements shall be met:

(i) The exposed part of the pile shall be in good condition without damage or

distortion.

(ii) The helmet, dolly and any packing shall be in sound condition.

(iii) The hammer blow shall be in line with the pile axis and the impact surfaces shall

be flat and at right angles to the pile and hammer axis, and the head of the pile

protected against damage from hammer impact.

(iv) The hammer shall be in good condition, delivering adequate energy per blow,

and operating correctly.

(v) The temporary compression of the pile shall be recorded, if required.

7 Preboring

(a) If preboring is specified, the diameter and depth of prebore shall be as designated.

8 Jetting

(a) Jetting shall be carried out only when the Contractor's detailed proposals have been

approved.

QCS


4.1.7 Risen Piles

(a) Piles shall be driven in an approved sequence to minimise the detrimental effects of

heave and lateral displacement of the ground.

(b) When required, levels and measurements shall be taken to determine the movement

of the ground or of any pile resulting from the driving process.

(c) When a pile has risen as a result of adjacent piles being driven, the Engineer may call

for redriving or other testing to demonstrate that the performance of the pile is

unimpaired. If required, the Contractor shall make proposals for correcting

detrimentally affected piles and for avoidance or control of heave effects in subsequent

work.

4.1.8 Repair and lengthening of piles

1 Repair of Damaged Pile Heads

(a) If it is necessary to repair the head of a pile during driving, the Contractor shall carry

out such repair in an approved way which allows the pile-driving to be completed

without further damage. If the driving of a pile has been accepted but sound concrete

of the pile is below the required cut-off level, the pile shall be made good to the cut-off

level, using an approved method so that it will safely withstand the imposed design

load.

2 Lengthening of Reinforced and Prestressed Concrete Piles

(a) Any provision for lengthening piles incorporated at the time of manufacture shall be as designed or approved.

(b) If no provision for lengthening piles was incorporated at the time of manufacture, any method for lengthening shall be such that splices are capable of safely resisting the stresses during driving and under service load and shall be subject to approval.

3 Driving Repaired or Lengthened Piles

(a) Repaired or lengthened piles shall not be driven until the added concrete has reached the specified strength of the concrete of the pile.

4.1.9 Cutting off pile heads

1 Unless otherwise directed by the Engineer, when the driving of a pile has been approved the

concrete of the head of the pile shall be cut off to the designated level. The length of splice

reinforcing bars projecting above this level shall be as designated.

2 Care shall be taken to avoid shattering or otherwise damaging the rest of the pile. Any

cracked or defective concrete shall be cut away and the pile repaired in an approved manner

to provide a full and sound section at the cut-off level.

4.2 PRECAST REINFORCED CONCRETE SEGMENTAL PILES

4.2.1 Scope

1 This Part applies to piles made of elements cast at a precasting works away from the site,

where work cannot normally be closely supervised by the Engineer. The elements are joined

together as necessary on site during driving using special proven steel joints incorporated

into the pile elements when cast.

QCS



This Section

Part 1, .............. General Requirements for Piling Works

Part 2, .............. Concrete Works for Piling

Section 5, Concrete.

4.2.2 References

1 The following Standards are referred to in this Part:

Eurocode 7, EN1997-1, Section 7 Pile foundation

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.

4.2.3 Submittals

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

driving and tests on preliminary piles have been received and evaluated.

4.2.4 Quality Assurance

1 A certificate of quality from the pile manufacturer shall be provided to the Engineer when

required stating that the designated requirements have been fulfilled during manufacture.

2 Each pile element shall be marked in such a manner that it can be identified with the records

of manufacture, which shall state the date of casting, the cement type, concrete grade,

element length and any other relevant data. On delivery, the pile elements shall be

accompanied by records of manufacture.

4.2.5 Tolerances in Pile Dimensions

1 The cross-sectional dimensions of the pile shall be not less than those designated.

2 The head of a pile element or the end of the pile upon which the hammer acts shall be

square to the pile axis within a tolerance of 1 in 50.

3 Each pile joint shall be square to the axis of the pile within a tolerance of 1 in 150. The

centroid of the pile joint shall lie within 5 mm of the true axis of the pile element.

4 Each face of a pile element shall not deviate by more than 6 mm from any straight line 3 m

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 element. Where a pile element is less than 3 m long the

permitted deviation from straightness shall be reduced below 6 mm on a pro rata basis in

accordance with actual length.

QCS


4.2.6 Handling, Transportation, Storage and Acceptance of Piles

1 The method and sequence of lifting, handling, transporting and storing piles shall be such as

to avoid shock loading and to ensure that the piles are not damaged. Only designed 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.

2 All pile elements within a stack shall be in groups of the same length. Packing of uniform

thickness shall be provided between piles at the lifting points.

3 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 less. For this purpose the assessment of the strength of

the concrete and of the stresses produced by the loads shall be subject to the approval of the

Engineer.

4 A pile element shall 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.

4.2.7 Materials and components

1 Fabricated Steel Components

(a) In the manufacture of jointed precast concrete segmental piles, fabricated steel

components shall comply with BS 7613 grades 43A or 50A, cast steel components

with BS 3100 grade A, and ductile iron components with BS 2789.

2 Pile Splices

(a) The splice joints shall be close-fitting face to face and the locking method shall be

such as to hold the faces in intimate contact. The design and manufacture of the

splicing system shall be approved by the Engineer prior to the commencement of the

Contract.

(b) A spliced pile shall be capable of withstanding the same driving stresses or service

axial loads, moments and shear stresses as a single unspliced pile of the same cross-

sectional dimensions and materials.

(c) The welding of a joint to main reinforcement in lieu of a lapped connection with

projecting bars affixed to the joint will not be permitted.

3 Pile Toes

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

during installation. Where fixity is required or socketing into rock, or in other

circumstances, an approved shoe may be required.

4 Pile Head Reinforcement

(a) Where the pile head is not furnished with a joint, it shall be so reinforced or banded as

to prevent bursting of the pile under driving conditions.

5 Main Reinforcement

(a) The main longitudinal reinforcing bars shall be in one continuous length. Splicing of

bars will not be permitted except at element ends.

QCS


(b) Concrete cover to steel reinforcement shall be in accordance with the requirements of

BS 8110.

(c) In very aggressive ground or exposure conditions, cover greater than 25 mm may be

required, but alternative protection methods may be approved.

6 Formwork

(a) If a pile is constructed with a shaped point or shoe, then the end of the pile shall be

symmetrical about the longitudinal axis of the pile.

(b) Holes for handling or pitching, where provided in the pile, shall be lined with steel

tubes; alternatively, approved inserts may be cast in.

(c) 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.

The piles are to be removed from the formwork carefully so as to prevent damage.

4.2.8 Driving piles

1 Strength of Piles

(a) Piles shall not be driven until the concrete has achieved the specified characteristic

strength.


(a) At all stages during driving and until incorporation into the substructure, the pile shall

be adequately supported and restrained by means of leaders, trestles, temporary

supports or other guide arrangements to maintain position and alignment and to

prevent buckling. These arrangements shall be such that damage to the pile does not

occur.



energy of the driving equipment. Where required in the particular specification,

dynamic evaluation and analysis shall be provided.


the pile at the moment of driving unless otherwise approved by the Engineer. For

other types of hammer, the energy delivered to the pile per blow shall be at least

equivalent to that of a drop hammer of the stated mass. Drop hammers shall not be

used from floating craft in such a manner as to cause instability of the craft or damage

to the pile.

4 Length of Piles

(a) The length of pile supplied to be driven in any location and any additional lengths to be

added during driving shall he approved prior to the commencement of pile-driving.

During the execution of the Works, any changes to the supplied lengths shall be

approved.

QCS



(a) Except when making field splices, the driving of each pile shall he continuous until the

specified depth or resistance (set), or both, has been reached. In the event of

unavoidable interruption to driving, the pile will be accepted provided it can

subsequently be driven to the specified depth or resistance (set), or both, without

damage. A follower shall only be used when approved, in which case the Engineer will

require the set where applicable to be revised in order to take into account reduction in

the effectiveness of the hammer blow.


driving characteristics is noted. A detailed record of the driving resistance over the full

length of the nearest available pile shall be taken if required.

(c) At the start of the work in a new area or section a detailed driving record shall be made

over the full length of the first pile and during the last 3 m of subsequent piles until

consistency of behaviour is established. Where required, detailed driving records shall

also be made for 5 % of the piles driven, the positions of such piles being specified by

the Engineer.

(d) The Contractor shall give adequate notice and provide all necessary facilities to enable



(e) Redrive checks, if required, shall be carried out to an approved procedure.

6 Final Set


penetration in millimetres per ten blows or as the number of blows required to produce



(i) The exposed part of the pile shall be in good condition, without damage or

distortion.

(ii) The helmet, dolly and any packing shall be in sound condition.


be flat and at right angles to the pile and hammer axis.



(v) The temporary compression of the pile shall be recorded if required.

7 Preboring

(a) If preboring is specified, the diameter and depth of prebore shall be as designated.

8 Jetting


approved.

4.2.9 Risen Piles

(a) Piles shall be driven in an approved sequence to minimise the detrimental effects of

heave and lateral displacement of the ground.

QCS


(b) When required, levels and measurements shall be taken to determine the movement

of the ground or of any pile resulting from the driving process.

(c) When a pile has risen as a result of adjacent piles being driven, the Engineer may call

for redriving or other testing to demonstrate that the performance of the pile is

unimpaired. If required, the Contractor shall make proposals for correcting piles

detrimentally affected and for avoidance or control of heave effects in subsequent

work.

4.2.10 Repair and lengthening of piles

1 Repair of Damaged Pile Heads

(a) If it is necessary to repair the head of a pile during driving, the Contractor shall carry

out such repair in an approved way which allows the driving of the pile to be completed

without further damage. If the driving of a pile has been accepted but sound concrete

of the pile is below the required cut-off level, the pile shall be made good to the cut-off

level, using an approved method so that it will safely withstand the imposed design

load.

2 Lengthening of Piles

(a) Where piles are required to be driven to depths exceeding those expected, leaving

insufficient projection for bonding into the following works, the piles shall be extended

or replaced as required by the Engineer using approved materials and methods.


1 Unless otherwise specified, when the driving of a pile has been approved the concrete of the

head of the pile shall be cut off to the designated level. The length of splice reinforcing bars

projecting above this level shall be as designated.

2 Care shall be taken to avoid shattering or otherwise damaging the rest of the pile. Any

cracked or defective concrete shall be cut away and the pile repaired in an approved manner

to provide a full and sound section at the cut-off level.

4.3 BORED CAST IN PLACE PILES

4.3.1 Scope

1 This Part applies to bored piles in which the pile bore is excavated by rotary or percussive

means, or both, using short augers, buckets, grabs or other boring tools to advance the open

bore. Where the open bore is unstable, temporary or permanent casing or bentonite

suspension may be used to support the wall of the bore prior to concreting.


This Section



Section 3, Ground Investigation

Section 5, Concrete

QCS


4.3.2 References

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

BS 5573, ..................... Code of practice for safety precautions in the construction of large

diameter boreholes for piling and other purposes

BS 5930, ..................... Code of practice for site investigation.


1 Inspection

(a) Each pile bore which does not contain standing water or drilling fluid shall be inspected

directly or indirectly prior to concrete being 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 750 mm 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 5573.

2 Cleanliness of pile bases

(a) 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. Large debris and accumulated sediment 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.

3 Samples and Testing

(a) If required in the Contract, soil, rock or groundwater samples shall be taken or soil

tests carried out in-situ while the pile is being bored. The samples shall be taken to an

approved laboratory for testing as specified.

(b) The taking of samples and all subsequent handling, transporting and testing shall be

carried out in accordance with Section 3, Ground Investigation.

4.3.4 Materials

1 Permanent Casings

(a) Permanent casings shall be as specified.

2 Drilling Fluid Supply

(a) A certificate shall be obtained by the Contractor from the manufacturer of the bentonite powder showing the properties of each consignment delivered to the Site. This certificate shall be made available to the Engineer on request. The properties to be given by the manufacturer are the apparent viscosity range (in Pascal seconds) and the gel strength range (in Pascal) for solids in water.

QCS


3 Drilling Fluid Mixing

(a) Bentonite shall be mixed thoroughly with clean fresh water to make a suspension which will maintain the stability of the pile bore for the period necessary to place concrete and complete construction. The temperature of the water used in mixing the bentonite suspension, and of the suspension when supplied to the borehole, shall be

not lower than 5 C.

(b) Where saline or chemically contaminated groundwater occurs, special precautions shall be taken to modify the bentonite suspension or prehydrate the bentonite in fresh water so as to render it suitable in all respects for the construction of piles.

4 Drilling Fluid Tests

(a) The frequency of testing drilling fluid and the method and procedure of sampling shall be proposed by the Contractor for approval prior to the commencement of the work. The frequency may subsequently be varied as required, depending on the consistency of the results obtained, subject to approval.

(b) Control tests shall be carried out on the bentonite suspension, using suitable apparatus. The density of freshly mixed bentonite suspension shall be measured daily as a check on the quality of the suspension being formed. The measuring device shall be calibrated to read to within 0.005 g/ml. Tests to determine density, viscosity, shear strength and pH value shall be applied to bentonite supplied to the pile bore. For average soil conditions the results shall generally be within the ranges in Table 4.2.

Table 4.2.Tests on Bentonite

Property to be measured Range of results at 20 C Test method

Density Less than 1.10 g/ml Mud density balance

Viscosity 30 - 90 s

or less than 0.020 Pa •

s

Marsh cone method

Fann viscometer*

Shear strength (10 minute gel strength)

1.4-10 Pa Or

4-40 Pa

Shear meter

Fann viscometer

pH 9.5 - 12 pH indicator paper strips

or electrical pH meter

* Where the Fann viscometer is specified, the fluid sample should be screened by a

number 52 sieve (300 m) prior to testing.

(c) The tests shall be carried out until a consistent working pattern has been established

account being taken of the mixing process, any blending of freshly mixed bentonite

suspension and previously used bentonite suspension, and any process which may be

used to remove impurities from previously used bentonite suspension. When the

results show consistent behaviour, the tests for shear strength and pH value may be

discontinued, and tests to determine density and viscosity shall be carried out as

agreed with the Engineer. In the event of a change in the established working pattern,

tests for shear strength and pH value shall be reintroduced for a period if required.

4.3.5 Boring

1 Boring Near Recently Cast Piles

(a) Piles shall not be bored so close to other recently completed piles as to damage them.

QCS


2 Temporary Casings

(a) Temporary casing of approved quality or an approved alternative method shall be used

to maintain the stability of a pile bore which might otherwise collapse.

(b) Temporary casings shall be free from significant distortion. They shall be of uniform

cross-section throughout each continuous length. During concreting they shall be free

from internal projections and encrusted concrete which might adversely affect the

proper formation of piles.

(c) The use of a vibrator to insert and withdraw temporary casing may be permitted by the

Engineer subject to compliance with Noise and Disturbance and Damage to Adjacent

Structures of this section and to the method not causing disturbance of the ground

which would adversely affect the construction or the capacity of piles.

(d) Where piles are bored under water or bentonite suspension in an unlined state, the

insertion of a full-length loosely fitting casing to the bottom of the bore prior to placing

concrete will not be permitted.

(e) Where permanent casing is specified to ensure the integrity of a pile, the Contractor

shall submit for approval his proposals regarding the method of installation.

3 Stability of Pile

(a) Where boring takes place through unstable water-bearing strata, the process of

excavation and the depth of temporary casing employed shall be such that soil from

outside the area of the pile is not drawn into the pile section and cavities are not

created outside the temporary casing as it is advanced.

(b) Where the use of drilling fluid is specified or approved for maintaining the stability of a

bore, an adequate temporary casing shall be used in conjunction with the method so

as to ensure stability of the strata near ground level until concrete has been placed.

During construction the level of drilling fluid in the pile excavation shall be maintained

within the cased or stable bore so that it is not less than 1.0 m above the level of

external standing groundwater at all times.

(c) In the event of a rapid loss of drilling fluid from a pile excavation, the bore shall be

backfilled without delay and the instructions of the Engineer shall be obtained before

boring at that location is resumed.

4 Spillage and Disposal of Drilling Fluid

(a) All reasonable steps shall be taken to prevent the spillage of bentonite suspension on

the Site in areas outside the immediate vicinity of boring. Discarded bentonite shall be

removed from the Site without undue delay. Any disposal of bentonite shall comply

with the regulations of the local controlling authority.

5 Pumping from Pile Bores

(a) Pumping from pile bores shall not be permitted unless the bore has been sealed

against further water entry by casing or unless the soil is stable and will allow pumping

to take place without ground disturbance below or around the pile.

6 Continuity of Construction

(a) For a pile constructed in a stable cohesive soil without the use of temporary casing or

other form of support, the pile shall be bored and the concrete shall be placed without

such delay as would lead to significant impairment of the soil strength.

QCS


7 Enlarged Pile Bases

(a) A mechanically formed enlarged base shall be no smaller than the dimensions

specified and shall be concentric with the pile shaft to within a tolerance of 10 % of the

shaft diameter. The sloping surface of the frustum forming the enlargement shall make

an angle to the axis of the pile of not more than 35 .

4.3.6 Extraction of casing

1 Workability of Concrete

(a) Temporary casings shall be extracted while the concrete within them remains

sufficiently workable to ensure that the concrete is not lifted. During extraction the

motion of the casing shall be maintained in an axial direction relative to the pile.

2 Concrete Level

(a) When the casing is being extracted, a sufficient quantity of concrete shall be

maintained within it to ensure that pressure from external water, drilling fluid or soil is

exceeded and that the pile is neither reduced in section nor contaminated.

(b) The concrete level within a temporary casing shall be topped up where necessary

during the course of casing extraction in such a way that the base of the casing is

always below the concrete surface until the casting of the pile has been completed.

(c) Adequate precautions shall be taken in all cases where excess heads of water or

drilling fluid could occur as the casing is withdrawn because of the displacement of

water or fluid by the concrete as it flows into its final position against the walls of the

pile bore. Where two or more discontinuous lengths of casing (double casing) are

used in the construction the proposed method of working shall be approved.

3 Pile Head Casting Level Tolerances

(a) For piles cast in dry bores using temporary casing and without the use of a permanent

lining, pile heads shall be cast to a level above the specified cut-off so that, after

trimming, a sound concrete connection with the pile can be made. The casting level

shall be within the tolerance above the cut-off level shown in Table 4.3, but shall not be

above the original ground level. No pile shall be cast with its head below standing

water level unless approved measures are taken to prevent inflow of water causing

segregation of the concrete as temporary casing is extracted, and, where approved by

the Engineer, the groundwater level for each pile shall be treated as the cut-off level for

the purpose of calculating tolerance.

(b) For piles cast in dry bores within permanent lining tubes or permanent casings, or

where their cut-off levels are in stable ground below the base of any casing used, pile

heads shall be cast to a level above the specified cut-off so that, after trimming, a

sound concrete connection with the pile can be made. The casting level shall be within

the tolerance above the cut-off level shown in Table 4.4, but shall not be above the

original ground level.

QCS


(c) For piles cast under water or drilling fluid, the pile heads shall be cast to a level above

the specified cut-off so that, after trimming to remove all debris and contaminated

concrete, a sound concrete connection with the pile can be made. The casting level

shall be within the tolerance above the cut-off level shown in Table 4.4, but shall not be

above the commencing surface level. Cut-off levels may be specified below the

standing groundwater level, and where this condition applies the borehole fluid level

shall not be reduced below the standing groundwater level until the concrete has set.

(d) Where the cut-off level of piles lies at depths greater than 10 m below the original

ground level, then the tolerances given in Tables 4.3, 4.4 and 4.5 will be varied after

discussion with the Contractor and before the commencement of the piling to take

account of the special conditions which apply.

Table 4.3

Casting Tolerance above Cut-off Level for Piles Cast In Dry Bores Using Temporary Casing

and Without the Use of a Permanent Lining

Cut-off distance below commencing surface,

H, m

Casting tolerance above cut-off level, m

0.15-10.00

0.3 + H/12 + C/8 where C = length of temporary casing

below the commencing surface*

* If H is greater than C, then this tolerance is no longer applicable and the tolerances in Table 4.4 will apply.

Table 4.4

Casting Tolerance above Cut-off Level for Piles Cast in Dry Bores within Permanent Lining

Tubes or Permanent Casings, or Where Their Cut-Off Levels is in Stable Ground below the

Base of Any Casing Used


H, m


0.15-10.00

0.3 + H/10

Table 4.5

Casting Tolerance above Cut-off Level for Piles Cast Under Water or Drilling Fluid**


H, m


0.15-10.00

1.0 + H /12 + C/8

where C = length of temporary casing below the commencing surface

** In cases where a pile is cast so that the cut-off is within a permanent lining tube, the appropriate tolerance is given by deletion of the casing term C/8 in the table.

4 Water levels

(a) During extraction of temporary casings, where circumstances are such that newly placed unset concrete is brought into contact with external groundwater, precautions shall be taken to ensure that the internal concrete pressure at all levels within the pile exceeds the external groundwater pressure.

QCS


5 Temporary backfilling above pile casting level

(a) After each pile has been cast, any empty bore remaining shall be protected and shall be carefully backfilled as soon as possible with approved materials.

6 Disposal of excavated material

(a) Disposal of excavated material shall be carried out by the Contractor as necessary to facilitate the Works and to the satisfaction of the Engineer.

7 Cutting off pile heads

(a) When cutting off and trimming piles to the specified cut-off level, the Contractor shall take care to avoid shattering or otherwise damaging the rest of the pile. Any cracked or defective concrete shall be cut away and the pile repaired in an approved manner to provide a full and sound section at the cut-off level

4.4 BORED PILES CONSTRUCTED USING CONTINUOUS FLIGHT AUGERS

AND CONCRETE OR GROUT INJECTION TROUGH HOLLOW AUGER

STEMS

4.4.1 Scope

1 This Part applies to bored piles which employ a continuous flight auger for both advancing

the bore and maintaining its stability. The spoil-laden auger is not removed from the ground

until concrete or grout is pumped into the pile bore from the base of the hollow-stemmed

auger to replace the excavated soil.


This Section



Section 3, Ground Investigation.

Section 5, Concrete

4.4.2 Materials

1 Concrete Mix Design and Workability

(a) Where not otherwise stated in this Part, the concrete shall comply with Section 5. The

design and workability of concrete to be used in the formation of a pile shall produce a

mix which is suitable for pumping. It shall have a minimum slump of 150 mm unless

otherwise approved and a minimum cement content of 340 kg/m3. The mix shall be

designed so that segregation does not occur during the placing process, and bleeding

of the mix shall be minimised.

2 Grout Mix Design and Workability

(a) Mix design of grout shall be subject to approval. Cement, water and aggregates for

grout shall be according to Section 5. Course aggregate to be used shall be of 6 mm

nominal size and shall be rounded and evenly graded.

QCS


(b) The workability of grout mixes, where used, shall be measured by a suitable and

approved means. The procedure for monitoring the suitability of grout throughout the

Works shall be stated in writing to the Engineer before beginning of the Works and

shall be subject to approval.

(c) Additives to the grout shall require prior approval of the Engineer.

3 Reinforcement

(a) All reinforcement shall be placed with the minimum delay after the completion of the

concreting or grouting operation. It shall be designed and fabricated in cages to permit

it to be placed in the correct position and to the depth specified through the concrete or

grout of the pile. Suitable approved spacers shall be provided to maintain the specified

concrete or grout cover to steel.

(b) The transverse reinforcement of any reinforcing cage shall be approved and may

consist of either spirals, hoops or links.

(c) Longitudinal main steel reinforcement shall be continuous over the specified length.

Where splices are necessary, the number of laps shall be kept to a minimum and bars

shall be welded or joined together in an approved manner.

(d) Reinforcement shall be supported and centred so that it will provide the required

projection above the cut-off level, and the proper concrete cover.

4.4.3 Boring

1 General

(a) During uncased boring with continuous flight auger, the feed forward and speed

(revolutions per minute) are to be adjusted according to the soil conditions in a way

that the excavation of soil will be limited to a quantity that the lateral support of the

uncased borehole wall will be ensured.

2 Boring Near Recently Cast Piles

(a) Piles shall not be bored so close to other piles which have recently been cast as to

damage them.

3 Removal of Augers from the Ground

(a) Augers shall not be extracted from the ground during the boring or construction of a

pile in such a way that an open unsupported bore or inflow of water into the pile section

would result. While withdrawing the continuous flight auger, the auger shall be rotated

in the same direction as during drilling into the soil or shall be withdrawn without

rotation.

4 Depth of Piles

(a) Any failure of a pile to reach the designated depth shall be reported to the Engineer

without delay and a full statement of the reasons given.

5 Suitability of Boring Equipment

(a) The piles shall be bored using approved and suitable equipment capable of

penetrating the ground without drawing surrounding soils laterally into the pile bore.

QCS


4.4.4 Placing of concrete or grout

1 Equipment for Supply of Concrete or Grout to Piles

(a) Grout or concrete shall be supplied to the pile through suitable tubing and the hollow auger stem. All pipe fitments and connections shall be so constructed that grout does not leak during the injection process.

2 Commencement of Concrete or Grout Supply to Each Pile

(a) The base of the auger stem shall be fitted with a suitable means of sealing it against ingress of water and soil until concrete or grout placing begins.

(b) At the beginning of concrete or grout placement this sealing device shall be removed by the application of concrete or grout pressure. Care shall be taken to ensure that the auger is lifted only sufficiently to initiate the flow of concrete or grout, and that water inflow and soil movement at the base of the auger are minimised. The technique and equipment used to initiate and maintain the concrete or grout flow shall be such that a pile of the full specified cross-section is obtained from the maximum depth of boring to the final pile cut-off level.

3 Rate of Supply of Concrete or Grout

(a) The concrete or grout shall be supplied to the pile at a sufficient rate during auger withdrawal to ensure that a continuous monolithic shaft of the full specified cross-section is formed, free from debris or any segregated concrete or grout.

(b) The rate of withdrawal of the auger, the injection pressures and the rate of supply of concrete or grout shall be measured and recorded throughout the phase of auger withdrawal for each pile.

(c) The Contractor shall submit proposals for his method of monitoring construction for approval before beginning the Works.

4 Completion of Piles

(a) If the concrete or grout placing in any pile cannot be completed in the normal manner, then the pile shall be rebored before concrete has hardened and shall be completely replaced.

5 Casting Level of Pile Head

(a) Concrete or grout shall be cast to the original ground level in all cases, and the reinforcing cage set, as appropriate.


1 When cutting off and trimming piles to the specified cut-off level, the Contractor shall take care to avoid shattering or otherwise damaging the rest of the pile. Any laitance, or contaminated, cracked or defective concrete shall be cut away and the pile repaired in an approved manner to provide a full and sound section up to the cut-off level.

4.5 DRIVEN CAST IN PLACES PILES

4.5.1 Scope

1 This Part applies to piles for which a permanent casing of steel or concrete is driven,

reinforcement placed within it if required, and the casing filled with concrete. It also applies to

piles in which a temporary casing is driven, reinforcement placed within it and the pile formed

in the ground by filling the temporary casing with concrete before and during its extraction.

QCS



This Section



Section 5, Concrete


4.5.2 Submittals

1 Where the Contractor wishes to form a pile with an enlarged base, details of the proposed

method of forming the base and the materials to be used shall be submitted at the time of

tendering.


1 Before placing concrete in a pile casing, the Contractor shall check in an approved manner

that the casing is undamaged, and free from water or other foreign matter. In the event of

water or foreign matter having entered the pile casing, either the casing shall be withdrawn,

repaired if necessary and re-driven, or other action shall be taken as may be approved to

continue the construction of the pile.

4.5.4 Materials

1 Permanent Casings

(a) Permanent casings shall be as specified. Where a permanent casing is to be made

from a series of short sections it shall be designed and placed so as to produce a

continuous water-free shaft. The dimensions and quality of the casing shall be

adequate to withstand the stresses caused by handling and driving without damage or

distortion.

2 Temporary Casings

(a) Temporary casings shall be free from significant distortion. They shall be of uniform

external cross-section throughout each continuous length. During concreting they

shall be free from internal projections and encrusted concrete which might prevent the

proper formation of piles.

3 Pile Shoes

(a) Pile shoes shall be manufactured from durable material capable of withstanding the

stresses caused by driving without damage, and shall be designed to give a watertight

joint during construction.

4 Reinforcement

(a) This type of pile shall normally be reinforced over its full length unless permanently

cased. The use of shorter reinforcement in piles which are not permanently cased

shall be subject to the approval of the Engineer.

(b) The number of splices in longitudinal steel bars shall be kept to a minimum. The full

strength of each bar shall be effective across each splice, which shall be made so that

there is no detrimental displacement of the reinforcement during the construction of

the pile.

QCS


4.5.5 Driving piles

1 Piling Near Recently Cast Piles

(a) Casings shall not be driven or piles formed so close to other piles which have recently

been cast as to damage them.



energy of the driving equipment

(b) Drop hammers shall not be used from floating craft in such a manner as to cause

instability of the craft.

3 Length of Piles

(a) The length of pile to be driven in any location shall be approved.

4 Driving Procedure

(a) Each pile casing shall be driven continuously until the specified or approved depth or

resistance (set), or both, has been reached. In the event of unavoidable interruption to

driving, the pile will be accepted provided on resumption the casing can be driven to

the specified depth or resistance (set), or both, without damage.


driving characteristics is encountered. A detailed record of the driving resistance over

the full length of the nearest available subsequent pile shall be taken if required.

(c) At the start of the work in a new area or section a detailed driving record shall be made

over the full length of the first pile to be installed and over the last 3 m of the driving of

subsequent piles until consistency of behaviour is established. Where required,

detailed driving records shall also be made for 5 % of the piles driven, the positions of

such piles being specified by the Engineer.

(d) The Contractor shall give adequate notice and provide all facilities to enable the

Engineer to check driving resistance. A set shall be taken only in the presence of the

Engineer unless otherwise approved.

5 Final Set

(a) Where piles are driven to a set, the final set of each pile, pile shell or casing shall be

recorded either as the penetration in millimetres per ten blows or as the number of

blows required to produce a penetration of 25 mm.


(i) The exposed part of the pile casing shall be in good condition, without damage

or distortion.

(ii) The dolly, helmet and packing, if any, shall be in sound condition.





(v) Temporary compression of the pile casing shall be recorded if required.

QCS


6 Preboring

(a) If preboring is specified the pile casing shall be pitched after preboring to the

designated depth and diameter.

7 Jetting


approved by the Engineer

8 Internal Drop Hammer

(a) Where a casing for a pile without an enlarged base is to be driven by an internal drop

hammer, a plug consisting of concrete grade 20 with a water/cement ratio not

exceeding 0.25 shall be placed in the pile. This plug shall have a compacted height of

not less than 2.5 times the diameter of the pile. Fresh concrete shall be added to

ensure that this height of driving plug is maintained in the casing throughout the period

of driving, and in any event a plug of fresh concrete shall be added after 1.5 h of

normal driving or after 45 min of hard driving, or, should the driving of a pile be

interrupted for 30 min or longer, fresh concrete shall be added prior to driving being

resumed.

4.5.6 Risen Piles

1 Piles shall be driven in an approved sequence to minimise any detrimental effects of heave

and lateral displacement of the ground.

2 When required, levels and measurements shall be taken to determine the movement of the

ground or any pile resulting from the driving process.

3 When a pile has risen with detrimental effects as a result of adjacent piles being driven the

Contractor shall, if required, submit to the Engineer his proposals for correcting or

compensating for this and for avoidance or control of heave effects in subsequent work.

4.5.7 Extraction of casing

1 Workability of Concrete

(a) Temporary casings shall be extracted while the concrete within them remains

sufficiently workable to ensure that the concrete is not lifted.

2 Concrete Level

(a) When the casing is being extracted, a sufficient quantity of concrete shall be

maintained within it to ensure that pressure from external water or soil is exceeded and

that the pile is neither reduced in section nor contaminated.

(b) Concrete shall be topped up as necessary while the casing is extracted until the

required head of concrete to complete the pile in a sound and proper manner has been

provided. No concrete is to be placed once the bottom of the casing has been lifted

above the top of the concrete.

3 Vibrating Extractors

(a) The use of vibrating casing extractors will be permitted subject to Part 1 (Noise and

Disturbance) and (Damage to Adjacent Structures).

QCS


4 Concrete Casting Tolerances

(a) For piles constructed without the use of a rigid permanent lining, pile concrete shall be

cast to the original ground level.

(b) Where piles are constructed inside rigid permanent lining tubes or permanent casings,

pile heads shall be cast to a level above the specified cut-off so that, after trimming, a

sound concrete connection with the pile can be made. In this case, the tolerance of

casting above the cut-off level shall be determined according to Table 4.6.

Table 4.6

Casting Tolerance above Cut-off Level for Piles Constructed Inside Rigid Permanent Lining

Tubes or Permanent Casings

Cut-off distance below original ground, H, (m)

Casting tolerance above cut-off level (m)

0.15 to any depth 2.2 + H/10

5 Repair of damaged pile heads and making-up of piles to the correct level

(a) When repairing or extending the head of a pile, the head shall be cut off square in

sound concrete, and all loose particles shall be removed by wire brushing, followed by

washing with water.

(b) If the driving of a pile has been accepted but sound concrete of the pile is below the

cut-off level, the pile shall be made good to the cut-off level with concrete of a grade

not inferior to that of the concrete of the pile.

6 Lengthening of cast-in- place piles after driving

(a) When it is required to extend a cast-in-place driven pile above ground, the materials to

be used and procedures to be adopted shall be subject to the approval of the

Engineer.

7 Lengthening of permanent pile casings during construction

(a) The lengthening of permanent steel pile casings by adding an additional length of the

same steel casing during construction shall be carried out in accordance with the

relevant clauses of this Section or by other approved methods. The use of casing

extension materials and methods other than those specified shall be subject to

approval.

8 Temporary backfilling above pile casting level

(a) After each pile has been cast, any hole remaining shall be protected and shall be

carefully backfilled as soon as possible with approved materials.

9 Cutting off pile heads

(a) When cutting off and trimming piles to the specified cut-off level, the Contractor shall

take care to avoid shattering or otherwise damaging the rest of the pile. Any cracked

or defective concrete shall be cut away and the pile repaired in an approved manner to

provide a full and sound section to the cut-off level.

QCS


4.6 STEEL PILES

4.6.1 Scope

1 This Part applies to driven steel piles designed to act as bearing piles.


This Section




Section 5, Concrete

4.6.2 References

1 The following standards and other documents are referred to in this Part:

BS 4, .......................... Structural steel sections

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

BS 5135, .................... Process of arc-welding of carbon and carbon manganese steels

BS 6265, .................... Resistance steam welding of uncoated and coated low carbon steel

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

API 5L, ........................ Interpretation of non-destructive testing.

4.6.3 Submittals

1 Where coatings are specified, the Contractor shall submit for approval full details of the

coating procedure and surface preparation according to relevant British or Swedish

Standards.


1 The Contractor shall provide the Engineer with Works test certificates, analyses, and mill

sheets, together with a tube manufacturer's certificate showing details of the pile number,

cast number of the steel and a record of all tests and inspections carried out. The Engineer

has the right to inspect any stage of the manufacturing processes and shall be given

adequate notice by the Contractor of such processes and production tests, provided that,

once he has been notified, any delay in his attendance does not cause delay to, or disrupt,

the manufacturing process. The Contractor shall provide the Engineer with samples for

independent testing when requested.

2 The Contractor shall submit for approval full details of the welding procedures and

electrodes, with drawings and schedules as may be necessary. Tests shall be undertaken as

may be required by the relevant British Standard or as may be required by the Engineer.

Only welders who are qualified in the approved welding procedure in accordance with the

tests laid down in the relevant British Standard, or who have a proven record over the

previous six months, or who have attained a similar standard, shall be employed on the

Works. Proof of welders' proficiency shall be made available to the Engineer on request.

QCS


4.6.5 Delivery, Storage and Handling

1 The Contractor shall

(a) Order the piles to suit the construction programme.

(b) Obtain the Engineer's approval before placing the order.

2 When preliminary piles are specified, the approval for the piles for the main work will not

necessarily be given until the results of the driving and tests on preliminary piles have been

received and evaluated.

3 Each pile shall be clearly numbered and its length shown near the pile head using white

paint. In addition, before being driven, each pile shall be graduated at appropriate intervals

along its length and at intervals of 250 mm along the top 3 m.

4 All piles within a stack shall be in groups of the same length and on approved supports. All

operations such as handling, transporting and storing of piles shall be carried out in a manner

such that damage to piles and their coatings is minimised.

4.6.6 Materials

1 Pile Shoes

(a) Cast steel shoes shall be of steel to BS 3100, grade Al. Flat plate and welded

fabricated steel shoes shall be grade 43A or 50A, conforming to BS 7613 and related

standards.

2 Strengthening of Piles

(a) The strengthening to the toe of a pile in lieu of a shoe or the strengthening of the head

of a pile shall be made using material of the same grade as the pile unless otherwise

approved.

3 Manufacturing Tolerance

(a) All piles shall be of the type and cross-sectional dimensions specified. For standard

rolled sections the dimensional tolerances and weight shall comply with the relevant

standard. The tolerance on length shall be -0 and +75 mm unless otherwise specified.

For proprietary sections the dimensional tolerances shall comply with the

manufacturer's standards. The rolling or manufacturing tolerances for proprietary

sections shall be such that the actual weight of section does not differ from the

theoretical weight by more than +4 % or -2½ % unless otherwise agreed. The rolling

or manufacturing tolerances for steel tubular piles shall be such that the actual weight

of section does not differ from the theoretical weight by more than ±5 %.

4 Straightness of Piles

(a) For standard rolled sections the deviation from straightness shall be within the

compliance provisions of BS 4, Part 1. When two or more rolled lengths are joined by

butt-jointing, the deviation from straightness shall not exceed 1/600 of the overall

length of the pile.

(b) For proprietary sections made up from rolled sections, and for tubular piles, the

deviation from straightness on any longitudinal face shall not exceed 1/600 of the

length of the pile nor 5 mm in any 3 m length.

QCS


5 Fabrication of Piles

(a) For tubular piles where the load will be carried by the wall of the pile, and if the pile will

be subject to loads that induce reversal of stress during or after construction, the

external diameter at any section as measured by using a steel tape on the

circumference shall not differ from the theoretical diameter by more than ±1.

(b) The ends of all tubular piles as manufactured shall be within a tolerance on ovality of

±1 % as measured by a ring gauge for a distance of 100 mm at each end of the pile

length.

(c) The root edges or root faces of lengths of piles that are to be shop butt-welded shall

not differ by more than 25 % of the thickness of pile walls not exceeding 12 mm thick

or by more than 3 mm for piles where the wall is thicker than 12 mm. When piles of

unequal wall thickness are to be butt-welded, the thickness of the thinner material shall

be the criterion.

6 Matching of Pile Lengths

(a) Longitudinal seam welds and spiral seam welds of two lengths of tubular piles being

joined shall, whenever possible, be evenly staggered at the butt. However, if in order

to obtain a satisfactory match of the ends of piles or to meet specified straightness, the

seams cannot be staggered evenly, then they shall be staggered by at least 100 mm.

7 Welding

(a) Welding of H-piles and piles that will be subjected to stress reversal, during or after

construction, shall be in accordance with BS 5135.

(b) For a tubular pile where the load will be compressive and non-reversible and will be

carried by the wall of the pile or by composite action with a concrete core, the welding

shall be to BS 5135 or BS 6265.

8 Coating Piles for Protection against Corrosion

(a) Where coatings are specified they shall be provided in accordance with the Particular

Specification. In general, coatings will not be called for where piles are fully in contact

with undisturbed natural soils or below the standing water table. Cathodic protection

may be called for when there is a possibility of stray electrical current from the

supported structure flowing to earth through the piles.

4.6.7 Acceptance Standards For Welds

1 Acceptance Standards for Shop Welds

(a) Longitudinal or spiral welds made in the manufacture of tubular piles are subject to the

acceptance standard for interpretation of non-destructive testing specified in latest

edition of API 5L. The maximum projecting height of weld reinforcement shall not

exceed 3 mm for wall thicknesses not exceeding 13 mm and 5 mm for wall

thicknesses greater than 13 mm.

(b) Longitudinal welds joining the constituent parts of the box or proprietary section shall

be in accordance with the manufacturer's specification.

(c) The maximum projecting height of weld reinforcement for circumferential welds in

tubular piles shall be the same as specified above for longitudinal welds in tubular

piles.

QCS


2 Acceptance Standards for Site Butt Welds

(a) Welds shall comply with the requirements of the Weld Quality Acceptance Standards

for Site Butt Welds in Steel Bearing Piles published by British Steel Corporation,

General Steels Group.

4.6.8 Acceptability and inspection of coatings

1 The finished coating shall be generally of smooth and uniform texture and free from sharp

protuberances or pin holes. Excessive sags, dimpling or curtaining will not be acceptable.

2 Any coat damaged by subsequent processes, or which has deteriorated to an extent such

that proper adhesion of the coating is in doubt, shall be removed and the surface shall be

cleaned to the original standard and recoated with the specified number and thicknesses of

coats.

3 The completed coating shall be checked for thickness by an approved magnetic thickness

gauge. Areas where the thickness is less than that specified shall receive approved

additional coating.

4 Average measured thickness should be equal to or greater than the specified thickness and

no single reading should be less than 85 % of the specified thickness. The completed

coating shall also be checked for adhesion by the cross-hatching method with lines spaced at

ten times the thickness of the coating. Adhesion tests should not be carried out prior to

seven days after coating.

5 The tests shall be made on 10 % of the piles. Areas where the adhesion is not approved

shall be sand blasted and recoated. The coating shall be approved before pitching and

driving of the piles.

4.6.9 Driving of piles


(a) At all stages during driving and until incorporation in the superstructure, the free length

of the pile shall be adequately supported and restrained by means of leaders, trestles,

temporary supports or other guide arrangements to maintain position and alignment

and to prevent buckling. In marine works, lengths which remain unsupported after

driving shall be adequately restrained until incorporated into the permanent Works.

These constraint arrangements shall be such that damage to piles and their coatings is

minimised.



energy of the driving equipment. Where required in the Contract, dynamic evaluation

and analysis shall be provided.


the pile unless otherwise approved by the Engineer. For other types of hammer the

energy delivered to the pile per blow shall be at least equivalent to that of a drop

hammer of the stated mass. Drop hammers shall not be used from floating craft in

such a manner as to cause instability of the craft.

QCS


3 Length of Piles

(a) The length of pile to be driven and any additional lengths of pile to be added during

driving shall be approved by the Engineer.


(a) The driving of each pile shall be continuous until the specified depth or resistance

(set), or both, has been reached. In the event of unavoidable interruption to driving,

the pile will be accepted provided it can be driven to the specified depth or resistance

(set), or both, without damage.

(b) A follower shall not be used unless approved, in which case the Engineer will require

the set where applicable to be revised in order to take into account reduction in the

effectiveness of the hammer blow.

(c) The Contractor shall inform the Engineer as soon as an unexpected change in driving

characteristics is noted. A detailed record of the driving resistance over the full length

of the nearest subsequent pile shall be taken, if required by the Engineer.

(d) At the start of the work in a new area or section a detailed record shall be made over

the full driving length of the first pile, and during the last 3 m of the driving of

subsequent piles, to establish the driving behaviour. Where required, detailed driving

records shall also be made for 5 % of the piles driven, the locations of such piles being

specified by the Engineer.

(e) The Contractor shall give adequate notice and provide all necessary facilities to enable



(f) Redrive checks, if required, shall be carried out in accordance with an approved

procedure.

5 Final Set or Resistance


penetration in millimetres per ten blows or as the number of blows required to produce


(b) When a final set or resistance is being measured, the following requirements shall be

met:

(i) The exposed part of the pile shall be in good condition, without damage or

distortion.

(ii) The dolly and packing, if any, shall be in sound condition.



(iv) The hammer shall be in good condition, delivering adequate energy per blow


(v) The temporary compression of the pile shall be recorded, if required by the

Engineer.

6 Preboring

(a) If preboring is specified the pile shall be pitched after preboring to the designated

depth and diameter.

QCS


7 Jetting


approved.

4.6.10 Risen Piles

1 Piles shall be driven in an approved sequence to minimise any detrimental effects of heave

and lateral displacement of the ground.

2 When required by the Engineer, levels and measurements shall be taken to determine the

movement of the ground or any pile resulting from the driving of adjacent piles.

3 When a pile has risen as a result of adjacent piles being driven, the Engineer may call for

redriving or other testing to demonstrate that the performance of the pile under load is

unimpaired. If required, the Contractor shall make proposals for correcting detrimentally

affected piles and for avoidance or control of heave in subsequent work.

4.6.11 Preparation of pile heads

1 If a steel superstructure is to be welded to piles, the pile cut-off shall be square and to within

5 mm of the elevations shown on the Drawings. If pile heads are to be encased in concrete

they shall be cut to that same tolerance and protective coatings shall be removed from the

surfaces of the pile heads down to a level 100 mm above the soffit of the concrete.

4.7 MICROPILES (TO BE ADDED LATER)

4.8 REDUCTION OF FRICTION ON PILES

4.8.1 Scope

1 This Part includes preapplied bituminous or other proprietary friction-reducing coating, pre-

applied low-friction sleeving, formed-in-place low-friction surround, and preinstalled low-

friction sleeving.

2 Related Parts are as follows:

This Section




4.8.2 Submittals

1 Where the particular method of reducing friction is not specified, the Contractor shall submit

full details of the method which he proposes.

4.8.3 Friction Reducing Methods

1 General

(a) Where a means of reducing friction on any specified length of pile is required by the

Contract, the Contractor shall provide a suitable interface between pile and soil by one

of the following, or other approved, methods

QCS


(i) Preapplied bituminous or other proprietary friction-reducing coating.

(ii) Preapplied low-friction sleeving.

(iii) Formed-in-place low-friction surrounds.

(iv) Preinstalled low-friction sleeving.

2 Preapplied Bituminous or other Friction-Reducing Coating Materials

(a) Where a proprietary product is specified, the process of cleaning pile surfaces, and the

conditions and methods of application shall conform to the manufacturer's current

instructions. All materials shall conform to the manufacturer's specification, which

shall be given to the Engineer before any coating is applied.

(b) Where a friction-reducing material has been applied to a preformed pile prior to

installation, it shall be protected from damage during handling and transportation. In

the event of inadvertent damage to the coating, it shall be repaired on site, prior to the

pile being driven, to the same specification as the original coating. Where bituminous

materials are involved, precautions shall be taken as necessary in hot weather to

prevent excessive flow or displacement of the coating. The coated piles shall be

adequately protected against direct sunlight and, if stacked, they shall be separated to

prevent their coatings sticking together.

(c) In the case of applied coatings, the piles shall not be driven when the air temperature

is such that the coating will crack, flake or otherwise be damaged prior to entry into the

ground. Where bituminous materials are involved, driving shall be carried out while

the temperature is at or above 5 °C unless otherwise approved or called for in the

manufacturer's instructions.

3 Preapplied Low-Friction Sleeving

(a) Piles may be driven with a preapplied low-friction sleeving subject to the approval of

the detailed design and method by the Engineer.

4 Formed-In-Place Low-Friction Surround

(a) Where a hole is bored in the ground and filled with low-friction material through which a

pile is subsequently driven or placed, the method and the properties of the low-friction

material both above and below standing groundwater level, together with the

dimensions of the prebored hole in relation to the pile, shall be approved by the

Engineer.

5 Preinstalled Low-Friction Sleeving

(a) Where a system is employed involving placing a low-friction sleeve in the ground prior

to pile installation, the detailed materials and method of installation of the sleeving shall

be approved by the Engineer.

4.8.4 Inspection

1 The Engineer may call for piles to be partially exposed or extracted at the commencement of

a contract in order to demonstrate that the method of installation does not impair the

effectiveness of the system in the circumstances of use on the particular site. Where damage

is found to have occurred, or is likely to occur in the opinion of the Engineer, additional

measures or variation of the method may be called for. At the discretion of the Engineer,

further inspections shall be carried out to ascertain the effectiveness of the additional

measures.

QCS


4.8.5 Driving resistance

1 Allowance shall be made in driving piles to a required resistance or set for any differences

between the short-term driving resistance and the long-term static resistance of the coating

or surrounding low-friction material which is in use.

4.9 PILE LOAD TESTING

4.9.1 Static Load Testing of Piles

1 Scope

(a) This Part deals with the testing of a pile by the controlled application of an axial load. It

covers vertical and raking piles tested in compression (i.e. subjected to loads or forces

in a direction such as would cause the piles to penetrate further into the ground) and

vertical or raking piles tested in tension (i.e., subjected to forces in a direction such as

would cause the piles to be extracted from the ground).

2 References

The following standard is referred to in this Part:

BS 1881, .................... Methods of testing concrete.

3 Submittals

(a) When required, the design and full details of the proposed load application system

shall be submitted to the Engineer prior to the commencement of testing. The load

application system shall be satisfactory for the required test.

4 Definitions

(a) Allowable pile capacity: a load which is not less than the specified working load and

which takes into account the pile's ultimate bearing capacity, the materials from which

the pile is made, the required factor of safety, settlement, pile spacing, downdrag, the

overall bearing capacity of the ground beneath the piles and any other relevant factors.

The allowable pile capacity indicates the ability of a pile to meet the specified loading

requirements.

(b) Compression pile: a pile which is designed to resist compressive (downward) axial

load.

(c) Constant rate of penetration (CRP) test: a test in which the pile is made to penetrate

the soil at a constant controlled speed, while the loads applied at the top of the pile in

order to maintain the constant rate of penetration are continuously measured. The

purpose of the test is to derive the ultimate bearing capacity of a pile and not its load

settlement characteristics.

(d) Constant rate of uplift (CRU) test: the same in principle as the CRP test, but the pile is

subject to tension rather than compression. The purpose of the test is to determine

the 'pull-out' capacity of a pile.

(e) Design verification load (DVL): a test load, in lieu of a specified working load, applied

to a single pile at the time of testing to determine that site conditions conform to design

assumptions. This load will be peculiar to each preliminary (test) pile and should equal

the maximum specified working load for a pile of the same dimensions and material,

plus allowances for soil-induced forces and any other particular conditions of the test.

QCS


(f) Kentledge: ballast used in a loading test.

(g) Maintained load test: a loading test in which each increment of load is held constant

either for a defined period of time or until the rate of settlement falls to a specified

value.

(h) Preliminary pile: a test pile installed before the commencement of the main piling

works or a specific part of the Works for the purpose of establishing the suitability of

the chosen type of pile and for confirming its design, dimensions and bearing capacity.

(i) Proof load: a load applied to a selected working pile to confirm that it is suitable for the

load at the settlement specified. A proof load should not normally exceed the design

verification load plus 50 % of the specified working load.

(j) Raking pile: a batter pile, installed at an inclination to the vertical.

(k) Reaction system: the arrangement of kentledge, piles, anchors or rafts that provides a

resistance against which the pile is tested.

(l) Specified working load (SWL): the designated load on the head of a pile.

(m) Tension pile: a pile which is designed to resist a tensile (upward) axial force.

(n) Test pile: any pile, preliminary or part of the works, to which a test is applied.

(o) Ultimate bearing capacity: the load at which the resistance of the soil becomes fully

mobilised through friction, end bearing or a combination thereof.

(p) Working pile: one of the piles forming the foundation of a structure.

5 Construction of a preliminary pile to be tested

(a) Notice of Construction

(i) The Contractor shall give the Engineer at least 48 hours' notice of the

commencement of construction of any preliminary pile which is to be test-

loaded.

(b) Method of Construction

(i) Each preliminary test pile shall be constructed in a manner similar to that to be

used for the construction of the working piles, and by the use of similar

equipment and materials. Any variation will be permitted only with prior approval.

(c) Boring or Driving Record

(i) For each preliminary pile to be tested, a detailed record of the conditions

experienced during boring and of the progress during driving, shall be made and

submitted to the Engineer daily, not later than noon on the next working day.

Where the Engineer requires soil samples to be taken or in-situ tests to be

made, the Contractor shall include that in the daily report, as well as the test

results.

(d) Concrete Test Cubes

(i) In the case of concrete piles, four test cubes shall be made from the concrete

used in the manufacturer of each preliminary test pile and from each 50 m3 of

the concrete used in the manufacture of working piles. If a concrete pile is

extended or capped for the purpose of testing, an additional four cubes shall be

made from the corresponding batch of concrete. The cubes shall be made and

tested in accordance with BS 1881.

QCS


(ii) The pile test shall not be started until the strength of the cubes taken from the

pile exceeds twice the average direct stress in any pile section under the

maximum required test load, and the strength of the cubes taken from the cap

exceeds twice the average stress at any point in the cap under the same load.

Variation of procedure will be permitted only if approved by the Engineer.

(e) Preparation of a Working Pile to be Tested

(i) If a test is required on a working pile the Contractor shall cut off or otherwise

prepare the pile for testing as required by the Engineer.

(f) Cut-off Level

(i) The cut-off level for a preliminary test pile shall be approved by the Engineer.

6 Supervision

(a) The setting-up of pile testing equipment shall be carried out under competent

supervision and the equipment shall be checked to ensure that the set-up is

satisfactory before the commencement of load application.

(b) All tests shall be carried out only under the direction of an experienced and competent

supervisor experienced with the test equipment and test procedure. All personnel

operating the test equipment shall have been trained in its use.

7 Safety precautions

(a) General

(i) Design, erection and dismantling of the pile test reaction system and the

application of load shall be carried out according to the requirements of the

various applicable statutory regulations concerned with lifting and handling

heavy equipment and shall safeguard operators and others who may from time

to time be in the vicinity of a test from all avoidable hazards.

(b) Kentledge

(i) Where kentledge is used, the Contractor shall construct the foundations for the

kentledge and any cribwork, beams or other supporting structure in such a

manner that there will not be differential settlement, bending or deflexion of an

amount that constitutes a hazard to safety or impairs the efficiency of the

operation. The kentledge shall be adequately bonded, tied or otherwise held

together to prevent it becoming unstable because of deflexion of the supports or

for any other reason.

(ii) When kentledge constitutes the principal component of a reaction system, its

weight for each test shall be at least 25% greater than the maximum test load

for that test. The weight may be determined by scale or the density and volume

of the constituent materials. In adding kentledge, care shall be taken to properly

position the centre of gravity of the stack.

QCS


(c) Tension Piles, Reaction Piles and Ground Anchorages

(i) Where tension piles, reaction piles or ground anchorages constitute the principal

components of a reaction system, they shall be so designed that they will resist

the forces applied to them safely and without excessive deformation which could

cause a safety hazard during the work. Such piles (which, unless approved, will

not be working piles) or anchorages shall be driven in the specified locations,

and all bars, tendons or links shall be aligned to provide a stable reaction in the

direction required. Any welding employed to extend or to fix anchorages to a

reaction frame shall be carried out so that the full strength of the system is

adequate and unimpaired.

(d) Testing Equipment

(i) In all cases the Contractor shall ensure that when the hydraulic jack and load-

measuring device are mounted on the pile head the whole system will be stable

up to the maximum load to be applied.

(ii) If in the course of carrying out a test any unforeseen occurrence should take

place, further loading shall not be applied until a proper engineering assessment

of the condition has been made and steps have been taken to rectify any fault.

Reading of gauges should, however, be continued where possible and if it is

safe to do so.

(iii) Where an inadequacy in any part of the system might constitute a hazard,

means shall be provided to enable the test to he controlled from a position

remote from of the kentledge stack or test frame.

(iv) The hydraulic jack, pump, hoses, pipes, couplings and other apparatus to be

operated under hydraulic pressure shall be capable of withstanding a pressure

of 1.5 times the maximum pressure used in the test without leaking. The

maximum test load expressed as a reading on the gauge in use shall be

displayed and all operators shall be made aware of this limit.

(e) Pile Head for Compression Test

(i) For a pile that is tested in compression, the pile head or cap shall be formed to

give a plane surface which is normal to the axis of the pile, sufficiently large to

accommodate the loading and settlement measuring equipment and adequately

reinforced or protected to prevent damage from the concentrated load applied

by the loading equipment.

(ii) Any test pile cap shall be concentric with the test pile; the joint between the cap

and the pile shall have a strength equivalent to that of the pile.

(iii) Sufficient clear space shall be made under any part of the cap projecting beyond

the section of the pile so that, at the maximum expected settlement, load is not

transmitted to the ground by the cap.

(f) Pile Connection for Tension Test

(i) For a pile that is tested in tension, means shall be provided for transmitting the

test load axially without inducing moment in the pile. The connection between

the pile and the loading equipment shall be constructed in such a manner as to

provide strength equal to 1.5 times the maximum load which is to be applied to

the pile during the test.

QCS


8 Reaction systems

(a) Compression Tests

(i) The reaction for compression tests shall be provided by kentledge, tension piles

or specially constructed anchorages. Kentledge shall not be used for tests on

raking piles except where the test set-up has been specifically designed to

conform to Item 7(g). and has been approved by the Engineer.

(ii) Where kentledge is to be used, it shall be supported on cribwork and positioned

so that the centre of gravity of the load is as close as possible to the axis of the

pile. The bearing pressure under supporting cribs shall be such as to ensure

stability of the kentledge stack.

(b) Tension Tests

(i) The reaction for tension tests shall be provided by compression piles, rafts or

grillages constructed on the ground. In all cases the resultant force of the

reaction system shall be coaxial with the test pile.

(ii) Where inclined piles or reactions are proposed, full details shall be submitted for

approval prior to the commencement of testing.

(c) Working Piles

(i) Working piles shall not be used as reaction piles without approval from the

Engineer.

(ii) Where working piles are used as reaction piles their movement shall be

measured and recorded to with an accuracy of 0.5 mm, and recorded.

(d) Spacing

(i) Where kentledge is used for loading vertical piles in compression, the distance

from the edge of the test pile to the nearest part of the crib supporting the

kentledge stack in contact with the ground shall be not less than 1.3 m.

(ii) The centre-to-centre spacing of vertical reaction piles from a test pile shall

conform to Paragraph 1 above, but shall be not less than three times the

diameter of the test pile or the reaction piles or 2 m, whichever is the greatest,

except in the case of piles of 300 mm diameter (or equivalent) or less, where the

distance may be reduced to 1.5 m. Where a pile to be tested has an enlarged

pile cap, the same criterion shall apply with regard to the pile shaft, with the

additional requirement that no surface of a reaction pile shall be closer to the

pile cap of the test pile than one half of the pile cap plan dimension.

(iii) Where ground anchorages are used to provide a test reaction for loading in

compression, no section of fixed anchor length transferring load to the ground

shall be closer to the test pile than three times the diameter of the test pile.

Where the pile to be tested has an enlarged pile cap, the same criterion shall

apply with regard to the pile shaft, with the additional requirement that no section

of the fixed anchor transferring load to the ground shall be closer to the pile cap

than a distance equal to one half the pile cap plan dimension.

(e) Adequate Reaction

(i) The reaction frame support system shall be adequate to transmit the maximum

test load in a safe manner without excessive movement or influence on the test

pile. Calculations shall be provided to the Engineer when required to justify the

design of the reaction system.

QCS


(f) Care of Piles

(i) The method employed in the installation of the reaction system shall be such as

to prevent damage to any test pile or working pile.

9 Equipment for applying load

(a) The equipment used for applying load shall consist of a hydraulic ram or jack. The

jack shall be arranged in conjunction with the reaction system to deliver an axial load

to the test pile. Proposals to use more than one ram or jack will be subject to approval

by the Engineer of the detailed arrangement. The complete system shall be capable of

safely transferring the maximum load required for the test. The length of stroke of a

ram shall be sufficient to account for deflexion of the reaction system under load plus a

deflection of the pile head by up to 15 % of the pile shaft diameter unless otherwise

specified or agreed prior to commencement of test loading.

10 Measurement of load

(a) A load measuring device shall be used and in addition a calibrated pressure gauge

included in the hydraulic system. Readings of both the load measuring device and the

pressure gauge shall be recorded. In interpreting the test data the values given by the

load measuring device shall normally be used; the pressure gauge readings are

required as a check for gross error.

(b) The load measuring device may consist of a load measuring column, pressure cell or

other appropriate system. A spherical seating of appropriate size shall he used to

avoid eccentric loading. Care shall be taken to avoid any risk of buckling of the load

application and measuring system. Load measuring and application devices shall be

short in axial length in order to secure stability. The Contractor shall ensure that axial

loading is maintained.

(c) The load measuring device shall be calibrated before and after each series of tests,

whenever adjustments are made to the device or at intervals appropriate to the type of

equipment. The pressure gauge and hydraulic jack shall be calibrated together.

Certificates of calibration shall be supplied to the Engineer.

11 Control of loading

(a) The loading equipment shall enable the load to be increased or decreased smoothly or

to be held constant at any required value.

12 Measuring pile head movement

(a) Maintained Load Test

(i) In a maintained load test, movement of the pile head shall he measured by one

of the methods in Items 11 (d), (e), (f), (g) in the case of vertical piles, or by one

of the methods in 11 (d), (f), (g) in the case of the raking piles, as required.

(b) CRP and CRU Tests

(i) In a CRP or a CRU test, the method in Item 11 (d) shall be used. Check-

levelling of the reference frame or the pile head shall not be required. The dial

gauge shall be graduated in divisions of 0.02 mm or less.

QCS


(c) Reference Beams and Dial Gauges

(i) An independent reference beam or beams shall be set up to enable

measurement of the movement of the pile to be made to the required accuracy.

The supports for a beam shall be founded in such a manner and at such a

distance from the test pile and reaction system that movements of the ground

do not cause movement of the reference beam or beams which will affect the

accuracy of the test. The supports of the beam or beams shall be at least three

test pile diameters or 2 m from the centre of the test pile, whichever distance is

the greater.

(ii) Check observations of any movements of the reference beam or beams shall be

made and a check shall be made of the movement of the pile head relative to a

remote reference datum at suitable intervals during the progress of the test.

(iii) The measurement of pile movement shall be made by four dial gauges rigidly

mounted on the reference beam or beams, bearing on prepared flat surfaces

fixed to the pile cap or head and normal to the pile axis. Alternatively, the

gauges may be fixed to the pile and bear on prepared surfaces on the reference

beam or beams. The dial gauges shall be placed equidistant from the pile axis

and from each other. The dial gauges shall enable readings to be made to an

accuracy of at least 0.1 mm and have a stem travel of at least 25 mm.

Machined spacer blocks may be used to extend the range of reading. Equivalent

electrical displacement-measuring devices may be substituted.

(d) Optical Levelling Method

(i) An optical levelling method by reference to a remote datum may be used.

(ii) Where a level and staff are used, the level and scale of the staff shall be chosen

to enable readings to be made to within an accuracy of 0.5 mm. A scale

attached to the pile or pile cap may be used instead of a levelling staff. At least

two reliable independent datum points shall be established. Each datum point

shall be so situated as to permit a single setting-up position of the level for all

readings.

(iii) No datum point shall be located where it can be affected by the test loading or

other operations on the Site.

(e) Reference Wires and Scales

(i) Two parallel reference wires, one on either side of the pile, shall be held under

constant tension at right angles to the test pile axis between supports formed as

in the method in Item 11 (d). The wires shall be positioned against scales fixed

to the test pile head in an axial direction and the movements of the scales

relative to the wires shall be determined.

(ii) Check observations of any movements of the supports of the wires shall be

made and a check shall be made on the movement of the pile head at approved

time intervals. Readings shall be taken to within an accuracy of 0.5 mm.

(f) Other Methods

(i) The Contractor may submit for approval any other method of measuring the

movement of the test pile head.

QCS


13 Protection of testing equipment

(a) Protection from Weather

(i) Throughout the test period all equipment for measuring load and movement

shall be protected from exposure to adverse effect of weather.

(b) Prevention of Disturbance

(i) Construction activity and persons who are not involved in the testing process

shall be kept at a sufficient distance from the test to avoid disturbance to the

measuring apparatus. Full records shall be kept of any intermittent unavoidable

activity that might affect the test set-up.

14 Notice of test

(i) The Contractor shall give the Engineer at least 24 hours' notice of the

commencement of the test. No load shall be applied to the test pile before the

commencement of the specified test procedure.

15 Test procedure

(a) Proof Load Test Procedure (working compression piles)

(i) The maximum load which shall be applied in a proof test shall normally be the

sum of the design verification load (DVL) plus 50 % of the specified working load

(SWL). The loading and unloading shall be carried out in stages as shown in

Table 4.7. Any particular requirements given in the particular contract

documentation shall be complied with.

(ii) Following each application of an increment of load, the load shall be maintained

at the specified value for not less than the period shown in Table 4.7 and until

the rate of settlement is less than 0.25 mm/h and decreasing. The rate of

settlement shall be calculated from the slope of the line obtained by plotting

values of settlement versus time and drawing a smooth curve through the

points.

(iii) Each decrement of unloading shall proceed after the expiry of the period shown

in Table 4.7.

(iv) For any period when the load is constant, time and settlement shall be recorded

immediately on reaching the load, at not more than 5 min intervals up to 15 min;

at approximately 15 min intervals up to 1 h; at 30 min intervals between 1 h and

4 h; and 1 h intervals between 4 h and 12 h after the application of the increment

of load.

(v) Where the methods of measuring pile head movement given in Item 11 is used,

the periods of time for which loads must be held constant to achieve the

specified rates of settlement shall be extended as necessary to take into

account the lower levels of accuracy available from these methods and to allow

correct assessment of the settlement rate.

QCS


Table 4.7

Load * Minimum time of holding load

25% DVL 1 h

50% DVL 1 h

75% DVL 1 h

100% DVL 1 h

75% DVL 10 min

50% DVL 10 min

25% DVL 10 min

0 1 h

100% DVL 6 h

100% DVL + 25% SWL 1 h

100% DVL + 50% SWL 6 h

100% DVL + 25% SWL 10 min

100% DVL 10 min

75% DVL 10 min

50% DVL 10 min

25% DVL 10 min

0 1 h

100% DVL 6 h

100% DVL + 50% SWL 6 h

100% DVL + 75% SWL 1 h

100% DVL + 100% SWL 6 h

100% DVL + 75% SWL 10 min Applicable

100% DVL + 50% SW 10 min to tests on

100% DVL + 25% SW 10 min Preliminary

100% DVL 10 min Pile only

75% DVL 10 min

50% DVL 10 min

25% DVL 10 min

0 1 h

* SWL denotes specified working load; DVL denotes design verification load.

(b) Test Procedure for Preliminary Compression Piles

(i) The procedure to be adopted for carrying out load tests on preliminary

compression piles shall be either the extended proof load test procedure or the

constant rate of penetration testing procedure given below. A normal proof load

test will constitute the first stage of such a test unless otherwise specified.

(ii) Extended proof load test procedure. Where test pile is to be loaded up to the

sum of design verification load (DVL) plus 100 % of the specified working load,

the loading procedure may be carried out as a continuation of the proof load

testing procedure given in Item 14 (a).

(iii) Following the completion of the proof load test, the load shall be restored in two

stages (DVL, DVL +50 % SWL), and shall subsequently be increased by stages

of 25 % of the specified working load. Following each application of an

increment of load, the load shall be maintained at the specified value for the

period shown in Table 4.7 and until the rate of settlement is decreasing and is

less than 0.25 mm/h.

QCS


(iv) Where verification of required minimum factor of safety is called for or the pile is

to be tested to failure, the loading procedure shall be continued after reaching

DVL +100 % SWL stage by increasing the load in increments of 25 % of the

specified working load or other specified amount until the maximum specified

load of the test is reached. Following each application of increment of load, the

load shall be maintained at the specified value for not less than 1 h and until the

rate of settlement is decreasing and is less than 0.25 mm/h, or other approved

rate appropriate to the stage of loading and its proximity to a failure condition.

Permissible settlement at the load corresponding to the required minimum factor

of safety called for in the design will not normally be specified.

(v) The rate of settlement shall be calculated from the slope of the line obtained by

plotting values of settlement versus time and drawing a smooth curve through

the points. Reduction of load at the end of the test shall be gradual as required

by Item 14 (a).and the final rebound of the pile head shall be recorded.

(vi) Constant rate of penetration (CRP) testing procedure. Where it is required to

determine the ultimate load of a preliminary compression pile, and particularly

where piles are largely embedded in and bearing on clay soils, the CRP testing

procedure will normally be specified.

(vii) The rate of movement of the pile head shall be maintained constant in so far as

is practicable and shall be approximately 0.01 mm/s.

(viii) Readings of loads, penetration and time shall be made simultaneously at regular

intervals; the interval chosen shall be such that a curve of load versus

penetration can be plotted without ambiguity.

(ix) Loading shall be continued until one of the following results is obtained

1. The maximum required test load.

2. A constant or reducing load has been recorded for an interval of

penetration of 10 mm.

3. A total movement of the pile base equal to 10 % of the base diameter, or

any other greater value of movement specified, has been reached.

(x) The load shall then be reduced in five approximately equal stages to zero load,

penetration and load being recorded at each stage.

(c) Testing of Piles Designed to Carry Load in Tension

(i) The testing of piles designed to carry load in tension shall follow the same

procedure as specified in 4.9.1

(ii) In testing by the constant rate of uplift method, overall movements of the pile

head will normally be less than those expected in a constant rate of penetration

test. The rate of movement of the pile head shall be maintained at approximately

0.005 mm/s in so far as is practicable.

16 Completion of a test

(a) Removal of Test Equipment

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(i) On completion of a test and subject to the approval of the Engineer, all

measuring equipment and load application devices shall be dismantled and

checked. All other test equipment, including kentledge, beams and supporting

structures shall be removed from the test pile location. Measuring and other

demountable equipment shall be stored in a safe manner so that it is available

for further tests, or removed from the Site as approved by the Engineer.

(ii) Temporary tension piles and ground anchorages shall be cut off below ground

level, and off-cut materials removed from the Site. The ground shall be restored

to the original contours.

(b) Preliminary Test Pile Cap

(i) Unless otherwise specified, the head of each preliminary test pile shall be cut off

below ground level, off-cut material shall be removed from the Site and the

ground restored to the original contours.

(c) Proof Test Pile Cap

(i) On completion of a test on a proof pile, the test pile cap shall be prepared as

specified and left in a state ready for incorporation into the Permanent Works.

Any resulting off-cut materials shall be removed from the Site.

4.9.2 Presentation of results

1 Results to be submitted

(a) During the progress of a test, all records taken shall be available for inspection by the

Engineer.

(b) Results shall be submitted as

(i) Preliminary report of the test results to the Engineer, unless otherwise directed,

within 24 hours of the completion of the test, which shall show.

1. For a test by maintained load: for each stage of loading, the period for

which the load was held, the load and the maximum pile movement at the

end of the stage.

2. For a CRP or CRU test: the maximum load reached and a graph of load

against penetration or load against uplift.

(ii) The final report of recorded data as prescribed in Item 15 (b).within ten days of

the completion of the test.

2 Schedule of Recorded Data

(a) The Contractor shall provide information about the test pile in accordance with the

following schedule where applicable.

(i) General.

1. site location contract identification

2. proposed structure

3. main contractor

4. piling contractor

5. engineer client/employer

6. date and time of test

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(ii) Pile details.

1. all types of pile

2. identification (number and location)

3. specified working load (SWL)

4. design verification load (DVL)

5. original ground level at pile location

6. head level at which test load was applied

7. type of pile

8. vertical or raking, compression or tension

9. shape and size of cross-section of pile, and position of any change in

cross-section

10. shoe or base details

11. head details

12. length in ground

13. tip Elevation

14. dimensions of any permanent casing

15. concrete piles

concrete mix/grade

aggregate type and source

cement type and cement replacement and type where used

admixtures

slump

cube test results for pile and cap

date of casting of precast pile

reinforcement

16. steel piles

steel quality

coating

filling or core materials type and quality, if applicable

(iii) Installation details.

1. all piles

dates and times of boring, driving and concreting of test pile

difficulties and delays encountered

date and time of casting concrete pile cap

2. bored piles

type of equipment used and method of boring

temporary casing - diameter, type and length

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full log of pile borehole

method of placing concrete

Volume of concrete placed

driven preformed and driven cast-in-place piles

Method of support of hammer and pile driven length of pile or temporary casing at final set

Hammer type, and size or weight

Dolly and packing, type and condition

Driving log (depth, hammer drop, blows per 250 mm, interruptions or breaks in driving)

Final set in number of blows to produce penetration of 25 mm

Redrive check, time interval and set in number of blows to produce penetration of 25 mm or other agreed amount at final set and at redrive set, for a drop hammer or for a single acting hammer the length of the drop or stroke, for a diesel hammer the length of the stroke and the blows per minute, for a double acting hammer the operating pressure and the number of blows per minute

condition of pile head or temporary casing after driving

use of a follower

use of preboring

use of jetting

lengthening

method of placing concrete

(iv) Test procedure.

1. mass of kentledge

2. tension pile, ground anchorage or compression pile details

3. plan of test arrangement showing position and distances of kentledge

supports, rafts, tension or compression piles or ground anchorages, and

supports to pile movement reference system

4. jack capacity

5. method of load measurement

6. method(s) of penetration or uplift measurement

(v) Test results.

1. in tabular form

2. in graphical form: load plotted against pile head movement

3. ambient temperature records during test.

4.9.3 Low strain Integrity test

1 This test shall be carried out in accordance with ASTM D5882 in a frequency as mentioned in

Section 2

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4.9.4 Grosshole Sonic Logging Test

1 This test shall be carried out in accordance with ASTM D4428, D6760 in a frequency as

mentioned in Section 2

4.9.5 Calliper Logging Test


Section 2

4.9.6 Axial Tensile Load Test


Section 2

4.9.7 Lateral Load Test


Section 2

4.9.8 Alternative Methods for Testing Piles

1 Scope

(a) This Part outlines the alternative methods for testing piles. A significant advance in

identifying the existence of defects in construction of piles has been the development

and adoption of modern integrity testing systems which may be employed to check the

quality of construction when required by the Engineer.

(b) Dynamic pile-testing is normally used to evaluate the pile capacity, soil resistance

distribution, and immediate settlement characteristics, hammer transfer energy

(efficiency), and pile stresses during driving. The results obtained relate directly to

dynamic loading conditions.

(c) Related Sections and Parts are as follows:

This Section

Section 2

2 Quality Assurance

(a) The testing shall be carried out by an approved firm.

(b) The interpretation of tests shall be carried out by persons competent in the test

procedure, and the full test results and findings shall normally be given to the Engineer

within 10 d of the completion of each phase of testing. Full details of the ground

conditions, pile dimensions and construction method shall be made available to the

specialist firm when required in order to facilitate interpretation of the tests.

3 Integrity-testing of piles

(a) General

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(i) Integrity-testing of piles is designed to give information about the physical

dimensions, continuity and consistency of materials used in piles, and not to

give direct information about the performance of piles under the conditions of

loading. The methods available are normally applied to preformed concrete piles

made in a single length, to steel piles and to cast-in-place concrete piles.

(ii) This type of testing will not be regarded as a replacement for static load testing,

but as a source of supplementary information.

(iii) There is normally a limit to the length: diameter ratio of pile which can be

successfully and fully investigated in this way, depending on the ground

conditions.

(iv) In the event that any anomaly is found in the results of such testing, the

Engineer may call for further testing to be carried out in order to investigate the

cause, nature and extent of the anomaly and whether the pile is satisfactory for

its intended use.

(b) Method of Testing

(i) Where integrity-testing is called for but the method is not specified, the method

to be adopted shall be approved by the Engineer and shall be one of the

following

1. The sonic method.

2. The vibration method.

3. The sonic logging method.

(ii) Other methods may be adopted subject to the approval of the Engineer and

subject to satisfactory evidence of performance.

(c) Age of Piles at Time of Testing

(i) In the case of cast-in-place concrete piles, integrity tests shall not be carried out

until 7 d or more have elapsed after pile-casting, unless otherwise approved by

the Engineer.

(d) Preparation of Pile Heads

(i) Where the method of testing requires the positioning of sensing equipment on

the pile head, the head shall be clean, free from water, laitance and loose

concrete and readily accessible for the purpose of testing.

4 Dynamic pile-testing

(a) General

(i) Dynamic pile-testing involves monitoring the response of a pile to a heavy

impact applied at the pile head. The impact is often provided by the pile-driving

hammer and response is normally measured in terms of force and acceleration

or displacement close to the pile head.

(ii) The results directly obtained refer to dynamic loading conditions. Interpretation

in terms of static loading requires soil- and pile-dependent adjustments, and

corroboration from experience may be required to correlate dynamic testing with

normal static load tests as specified in clause 4.9.1 of this Section.

(iii) Details of the equipment to be used and of the method of analysis of test results

shall be provided to the Engineer before the commencement of testing.

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(b) Measuring Instruments

(i) All instruments affixed to the pile for the purpose of measuring stress and

movement, and all equipment for receiving and processing data shall be suitable

for the purpose. The equipment required to be attached to the pile shall be

appropriately positioned and fixed to the approval of the Engineer.

(c) Hammer

(i) The hammer and all other equipment used shall be capable of delivering an

impact force sufficient to mobilise the equivalent specified test load without

damaging the pile.

(d) Preparation of the Pile Head

(i) The preparation of the pile head for the application of the dynamic test load shall

involve, where appropriate, trimming the head, cleaning and building up the pile

using materials which will at the time of testing safely withstand the impact

stresses. The impact surface shall be flat and normal to the axis of the pile.

(e) Time of Testing

(i) Dynamic load tests shall be carried out at appropriate and approved times after

pile installation. The time between the completion of installation and testing for

a preformed pile shall normally be more than 12 h, and in the case of a cast-in-

place concrete piles shall be after the concrete has reached 75 % of its specified

28 day strength so that the pile is not damaged under the impact stresses.

(f) Set Measurements

(i) Where required and appropriate, the permanent penetration per blow and

temporary compression of the pile and soil system shall be measured

independently of the instruments being used to record the dynamic test data.

(g) Results

(i) Initial the results shall be provided to the Engineer within 24 hours of the

completion of a test. These shall include

1. The maximum force applied to the pile head.

2. The maximum pile head velocity.

3. The maximum energy imparted to the pile.

(ii) Normally within 10 d of the completion of testing final report shall be given to the

Engineer which includes:

1. Date of pile installation.

2. Date of test.

3. Pile identification number and location.

4. Length of pile below ground surface.

5. Total pile length, including projection above commencing surface at time

of test.

6. Length of pile from instrumentation position to tip.

7. Hammer type, drop and other relevant details.

8. Blow selected for analysis.

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9. Test load achieved (i.e. total mobilised deduced static load).

10. Pile head movement at equivalent design verification load.

11. Pile head movement at equivalent design verification load plus 50 % of

specified working load.

12. Pile head movement at maximum applied test load.

13. Permanent residual movement of pile head after each blow.

14. Temporary compression.

4.10 DESIGN METHODS AND DESIGN CONSIDERATIONS

4.10.1 Design method

1 The design shall be based on one of the following approaches:

(a) The results of static load tests, which have been demonstrated, by means of

calculations or otherwise, to be consistent with other relevant experience;

(b) Empirical or analytical calculation methods whose validity has been demonstrated by

static load tests in comparable situations;

(c) The results of dynamic load tests whose validity has been demonstrated by static load

tests in comparable situations;

(d) The observed performance of a comparable piles foundation, provided that this

approach is supported by the results of site investigation and ground testing.

2 Design values for parameters used in the calculations should be in general accordance with

design parameters from geotechnical investigations report, but the results of load tests may

also be taken into account in selecting parameter values.

3 Static load tests may be carried out on trial piles, installed for test purposes only, before the

design is finalized, or on working piles, which form part of the foundation.

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

Transient Situations

1 When considering a limit state of rupture or excessive deformation of a structural element or

section of the ground (Structural and Geotechnical), it shall be verified in accordance with

(Eurocode1997-1) or equivalent.

4.10.3 Design Considerations

1 The behavior of individual piles and pile groups and the stiffness and strength of the structure

connecting the piles shall be considered.

2 In selecting calculation methods and parameter values and in using load test results, the

duration and variation in time of the loading shall be considered.

3 Planned future placement or removal of overburden or potential changes in the ground-water

regime shall be considered, both in calculations and in the interpretation of load test results.

4 The choice of type of pile, including the quality of the pile material and the method of

installation, shall take into account:

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(a) the ground and ground-water conditions on the site, including the presence or

possibility of obstructions in the ground;

(b) the stresses generated in the pile during installation;

(c) the possibility of preserving and checking the integrity of the pile being installed;

(d) the effect of the method and sequence of pile installation on piles, which have already

been installed and on adjacent structures or services;

(e) the tolerances within, which the pile can be installed reliably;

(f) the deleterious effects of chemicals in the ground;

(g) the possibility of connecting different ground-water regimes;

(h) the handling and transportation of piles;

(i) the effects of pile construction on neighboring buildings.

5 In considering the aspects listed above, the following items should receive attention:

(a) the spacing of the piles in pile groups;

(b) displacement or vibration of adjacent structures due to pile installation;

(c) the type of hammer or vibrator used;

(d) the dynamic stresses in the pile during driving;

(e) for those types of bored pile where a fluid is used inside the borehole, the need to

keep the pressure of the fluid at a level to ensure that the borehole will not collapse

and that hydraulic failure of the base will not occur;

(f) cleaning of the base and sometimes the shaft of the borehole, especially under

bentonite, to remove remolded materials;

(g) local instability of a shaft during concreting, which may cause a soil inclusion within

the pile;

(h) ingress of soil or water into the section of a cast-in-situ pile and possible disturbance

of wet concrete by the flow of water through it;

(i) the effect of unsaturated sand layers around a pile extracting water from the

concrete;

(j) the retarding influence of chemicals in the soil;

(k) soil compaction due to the driving of displacement piles;

(l) soil disturbance due to the boring of a pile shaft.

4.11 AXIALLY LOADED PILES

4.11.1 Limit state design

1 The design shall demonstrate that exceeding the following limit states is sufficiently

improbable:

(a) ultimate limit states of compressive or tensile resistance failure of a single pile;

(b) ultimate limit states of compressive or tensile resistance failure of the pile foundation

as a whole;

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(c) ultimate limit states of collapse or severe damage to a supported structure caused by

excessive displacement or differential displacements of the pile foundation;

(d) serviceability limit states in the supported structure caused by displacement of the piles.

2 Normally the design should consider the margin of safety with respect to compressive or

tensile resistance failure, which is the state in which the pile foundation displaces significantly

downwards or upwards with negligible increase or decrease of resistance.

3 For piles in compression it is often difficult to define an ultimate limit state from a load

settlement plot showing a continuous curvature. In these cases, settlement of the pile top

equal to 10% of the pile base diameter should be adopted as the "failure" criterion.

4 For piles that undergo significant settlements, ultimate limit states may occur in supported

structures before the resistance of the piles is fully mobilized. In these cases a cautious

estimate of the possible range of the settlements shall be adopted in design.

4.11.2 Compressive Ground Resistance

1 To demonstrate that the pile foundation will support the design load with adequate safety

against compressive failure, the following inequality shall be satisfied for all ultimate limit

state load cases and load combinations:

Fc ≤ Rc

Where

Fc: design axial compression load on a pile or a group of piles

Rc: design value

2 In principle Fc should include the weight of the pile itself and Rc should include the

overburden pressure of the soil at the foundation base. However these two items may be

disregarded if they cancel approximately. They need not cancel if:

(a) downdrag is significant;

(b) the soil is very light,

(c) the pile extends above the surface of the ground.

3 For piles in groups, two failure mechanisms shall be taken into account:

(a) compressive resistance failure of the piles individually;

(b) compressive resistance failure of the piles and the soil contained between them acting

as a block.

NOTE: The design resistance shall be taken as the lower value caused by these two

mechanisms.

4 The compressive resistance of the pile group acting as a block may be calculated by

treating the block as a single pile of large diameter.

5 The stiffness and strength of the structure connecting the piles in the group shall be

considered when deriving the design resistance of the foundation.

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6 If the piles support a stiff structure, advantage may be taken of the ability of the structure

to redistribute load between the piles. A limit state will occur only if a significant number of

piles fail together; therefore a failure mode involving only one pile need not be considered.

7 If the piles support a flexible structure, it should be assumed that the compressive

resistance of the weakest pile governs the occurrence of a limit state.

8 Special attention should be given to possible failure of edge piles caused by inclined or

eccentric loads from the supported structure.

9 If the layer in which the piles bear overlies a layer of weak soil, the effect of the weak layer

on the compressive resistance of the foundation shall be considered.

10 The strength of a zone of ground above and below the pile base shall be taken into

account when calculating the pile base resistance.

NOTE: This zone may extend several diameters above and below the pile base. Any weak

ground in this zone has a relatively large influence on the base resistance.

11 Punching failure should be considered if weak ground is present at a depth of less than 4

times the base diameter below the base of the pile.

12 Where the pile base diameter exceeds the shaft diameter, the possible adverse effect

shall be considered.

13 For open-ended driven tube or box-section piles with openings of more than 500 mm in

any direction, and without special devices inside the pile to induce plugging, the base

resistance should be limited to the smaller of:

(a) the shearing resistance between the soil plug and the inside face of the pile;

(b) the base resistance derived using the cross-sectional area of the base.

4.11.3 Ultimate compressive resistance from static load tests

1 The manner in which load tests are carried out shall be in accordance with 4.11.2 and shall be

specified in the Geotechnical Design Report.

2 Trial piles to be tested in advance shall be installed in the same manner as the piles that will

form the foundation and shall be founded in the same stratum.

3 If the diameter of the trial pile differs from that of the working piles, the possible difference in

performance of piles of different diameters should be considered in assessing the

compressive resistance to be adopted.

4 In the case of a very large diameter pile, it is often impractical to carry out a load test on a full

size trial pile. Load tests on smaller diameter trial piles may be considered provided that:

(a) the ratio of the trial pile diameter/working pile diameter is not less than 0,5;

(b) the smaller diameter trial pile is fabricated and installed in the same way as the piles

used for the foundation;

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(c) the trial pile is instrumented in such a manner that the base and shaft resistance can be

derived separately from the measurements.

NOTE: This approach should be used with caution for open-ended driven piles because of

the influence of the diameter on the mobilisation of the compressive resistance of a soil plug

in the pile.

5 In the case of a pile foundation subjected to downdrag, the pile resistance at failure, or at a

displacement that equals the criterion for the verification of the ultimate limit state determined

from the load test results, shall be corrected. The correction shall be achieved by subtracting

the measured, or the most unfavorable, positive shaft resistance in the compressible stratum

and in the strata above, where negative skin friction develops, from the loads measured at

the pile head.

6 During the load test of a pile subject to downdrag, positive shaft friction will develop along the

total length of the pile. The maximum test load applied to the working pile should be in excess

of the sum of the design external load plus twice the downdrag force.

7 When deriving the ultimate characteristic compressive resistance from values measured in

one or several pile load tests, an allowance shall be made for the variability of the ground and

the variability of the effect of pile installation.

8 The systematic and random components of the variations in the ground shall be recognized

in the interpretation of pile load tests.

9 The records of the installation of the test pile(s) shall be checked and any deviation from the

normal execution conditions shall be accounted for.

10 The characteristic compressive resistance of the ground may be derived from the

characteristic values of the base resistance and of the shaft resistance in accordance with

Eurocode1997-1.

4.11.4 Ultimate compressive resistance from ground test results

1 Methods for assessing the compressive resistance of a pile foundation from ground test

results shall have been established from pile load tests and from comparable experience.

2 A model factor may be introduced as described as following to ensure that the predicted

compressive resistance is sufficiently safe :

(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

3 In assessing the validity of a model based on ground test results, the following items should

be considered:

(a) soil type, including grading, mineralogy, angularity, density, pre-consolidation,

compressibility and permeability;

(b) method of installation of the pile, including method of boring or driving;

(c) length, diameter, material and shape of the shaft and of the base of the pile (e.g.

enlarged base);

(d) method of ground testing.

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4.11.5 Ultimate compressive resistance from dynamic impact tests

1 Where a dynamic impact (hammer blow) pile test [measurement of strain and acceleration

versus time during the impact event is used to assess the resistance of individual

compression piles, the validity of the result shall have been demonstrated by previous

evidence of acceptable performance in static load tests on the same pile type of similar

length and cross-section and in similar ground conditions.

2 When using a dynamic impact load test, the driving resistance of the pile should be

measured directly on the site in question.

NOTE A load test of this type can also include a process of signal matching to

measured stress wave figures. Signal matching enables an approximate evaluation of shaft

and base resistance of the pile as well as a simulation of its load-settlement behaviour.

3 The impact energy shall be high enough to allow for an appropriate interpretation of

the pile capacity at a correspondingly high enough strain level.

4 The design value of the compressive resistance of the pile could be calculated and

verified according to Eurocode1997-1.

4.11.6 Ultimate compressive resistance by applying pile driving formulae

1 Pile driving formulae shall only be used if the stratification of the ground has been

determined.

2 If pile driving formulae are used to assess the ultimate compressive resistance of individual

piles in a foundation, the validity of the formulae shall have been demonstrated by previous

experimental evidence of acceptable performance in static load tests on the same type of

pile, of similar length and cross-section, and in similar ground conditions.

3 For end-bearing piles driven into non-cohesive soil, the design value of the compressive

resistance shall be assessed by the same procedure as in 4.11.5.

4 When a pile driving formula is applied to verify the compression resistance of a pile, the pile

driving test should have been carried out on at least 5 piles distributed at sufficient spacing in

the piling area in order to check a suitable blow count for the final series of blows.

5 The penetration of the pile point for the final series of blows should be recorded for each pile.

4.11.7 Ultimate compressive resistance from wave equation analysis

1 Wave equation analysis shall only be used where stratification of the ground has been determined

by borings and field tests.

2 Where wave equation analysis is used to assess the resistance of individual compression piles,

the validity of the analysis shall have been demonstrated by previous evidence of acceptable

performance in static load tests on the same pile type, of similar length and cross- section, and in

similar ground conditions.

3 The design value of the compressive resistance derived from the results of wave equation analysis

of a number of representative piles, shall be assessed by the same procedure as in 4.11.3.

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NOTE Wave equation analysis is based on a mathematical model of soil, pile and driving

equipment without stress wave measurements on site. The method is usually applied to

study hammer performance, dynamic soil parameters and stresses in the pile during driving.

It is also, on the basis of the models, possible to determine the required driving resistance

(blow count) that is usually related to the expected compressive resistance of the pile.

4.11.8 Ground tensile resistance

1 The design of piles in tension shall be consistent with the design rules given in 4.11.2, where

applicable. Design rules that are specific for foundations involving piles in tension are presented

below.

2 To verify that the foundation will support the design load with adequate safety against a failure in

tension, the following inequality shall be satisfied for all ultimate limit state load cases and load

combinations in accordance with Eurocode1997-1.

3 For isolated tensile piles or a group of tensile piles, the failure mechanism may be governed by the

pull-out resistance of a cone of ground, especially for piles with an enlarged base or rock socket.

4 When considering the uplift of the block of ground containing the piles the shear resistance along

the sides of the block may be added to the resisting forces.

5 Normally the block effect will govern the design tensile resistance if the distance between the piles

is equal to or less than the square root of the product of the pile diameter and the pile penetration

into the main resisting stratum.

6 The group effect, which may reduce the effective vertical stresses in the soil and hence the shaft

resistances of individual piles in the group, shall be considered when assessing the tensile

resistance of a group of piles.

7 The severe adverse effect of cyclic loading and reversals of load on the tensile resistance shall be

considered.

8 Comparable experience based on pile load tests should be applied to appraise this effect.

4.11.9 Ultimate tensile resistance from pile load tests

1 Pile load tests to determine the ultimate tensile resistance of an isolated pile shall be carried out in

accordance with 4.9.1 and with regard to 4.11.3.

2 The design tensile resistance could be calculated and verified according to Eurocode1997-1.

4.11.10 Ultimate tensile resistance from ground test results

1 Methods for assessing the tensile resistance of a pile foundation from ground test results shall

have been established from pile load tests and from comparable experience.

2 A model factor may be introduced as following to ensure that the predicted tensile resistance is

sufficiently safe.

(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

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3 The design value of tensile resistance of a pile could be calculated and verified according to

Eurocode1997-1.

4.11.11 Vertical displacements of pile foundations

1 Vertical displacements under serviceability limit state conditions shall be assessed and checked.

2 When calculating the vertical displacements of a pile foundation, the uncertainties involved in the

calculation model and in determining the relevant ground properties should be taken into account.

Hence it should not be overlooked that in most cases calculations will provide only an approximate

estimate of the displacements of the pile foundation.

NOTE For piles bearing in medium-to-dense soils and for tension piles, the safety

requirements for the ultimate limit state design are normally sufficient to prevent a

serviceability limit state in the supported structure.

4.11.12 Pile foundations in compression

1 The occurrence of a serviceability limit state in the supported structure due to pile settlements shall

be checked, taking into account downdrag, where probable.

NOTE When the pile toe is placed in a medium-dense or firm layer overlying rock or very

hard soil, the partial safety factors for ultimate limit state conditions are normally sufficient to

satisfy serviceability limit state conditions.

2 Assessment of settlements shall include both the settlement of individual piles and the settlement

due to group action.

3 The settlement analysis should include an estimate of the differential settlements that may occur.

4 When no load test results are available for an analysis of the interaction of the piled foundation with

the superstructure, the load-settlement performance of individual piles should be assessed on

empirically established safe assumptions.

4.11.13 Pile foundations in tension

1 The assessment of upward displacements shall be done and Particular attention should be paid to

the elongation of the pile material.

2 When very severe criteria are set for the serviceability limit state, a separate check of the upward

displacements shall be carried out.

4.12 TRANSVERSELY LOADED PILES

4.12.1 Design method

1 The design of piles subjected to transverse loading shall be consistent with the design rules given

in 4.10, where applicable. Design rules specifically for foundations involving piles subjected to

transverse loading are presented below.

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2 To demonstrate that a pile will support the design transverse load with adequate safety against

failure, the following inequality shall be satisfied for all ultimate limit state load cases and load

combinations:

Ftr ≤ Rtr

Where;

Ftr: design value of the transverse load on a pile or a pile foundation

Rtr : design resistance of transversally loaded pile

3 One of the following failure mechanisms should be considered:

(a) for short piles, rotation or translation as a rigid body;

(b) for long slender piles, bending failure of the pile, accompanied by local yielding and

displacement of the soil near the top of the pile.

4 The group effect shall be considered when assessing the resistance of transversely loaded piles.

5 It should be considered that a transverse load applied to a group of piles may result in a

combination of compression, tension and transverse forces in the individual piles.

4.12.2 Transverse load resistance from pile load tests

1 Transverse pile load tests shall be carried out in accordance with 4.9.6.

2 Contrary to the load test procedure described in 4.9 tests on transversely loaded piles need not

normally be continued to a state of failure. The magnitude and line of action of the test load should

simulate the design loading of the pile.

3 An allowance shall be made for the variability of the ground, particularly over the top few meters of

the pile, when choosing the number of piles for testing and when deriving the design transverse

resistance from load test results.

4 Records of the installation of the test pile(s) should be checked, and any deviation from the normal

construction conditions should be accounted for in the interpretation of the pile load test results.

For pile groups, the effects of interaction and head fixity should be accounted for when deriving the

transverse resistance from the results of load tests on individual test piles.

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

1 The transverse resistance of a pile or pile group shall be calculated using a compatible set of

structural effects of actions, ground reactions and displacements.

2 The analysis of a transversely loaded pile shall include the possibility of structural failure of the pile

in the ground.

3 The calculation of the transverse resistance of a long slender pile may be carried out using the

theory of a beam loaded at the top and supported by a deformable medium characterized by a

horizontal modulus of subgrade reaction.

4 The degree of freedom of rotation of the piles at the connection with the structure shall be taken

into account when assessing the foundation’s transverse resistance.

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4.12.4 Transverse displacement

1 The assessment of the transverse displacement of a pile foundation shall take into account:

(a) the stiffness of the ground and its variation with strain level;

(b) the flexural stiffness of the individual piles;

(c) the moment fixity of the piles at the connection with the structure;

(d) the group effect;

(e) the effect of load reversals or of cyclic loading

2 A general analysis of the displacement of a pile foundation should be based on expected degrees

of kinematic freedom of movement.

END OF PART

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QCS 2014 Section 04: Foundations & Retaining Structures Page 2 Part 05: Retaining Structures

5 RETAINING STRUCTURES ---------------------------------------------------------------------------------- 2

5.1 GENERAL ---------------------------------------------------------------------------------------------------------- 2

5.2 LIMIT STATES ---------------------------------------------------------------------------------------------------- 2

5.2.2 Ultimate Limit State ---------------------------------------------------------------------------------------------- 2 5.2.3 Serviceability Limit State ---------------------------------------------------------------------------------------- 3

5.3 ACTIONS AND GEOMETRICAL DATA -------------------------------------------------------------------- 3

5.3.1 Actions -------------------------------------------------------------------------------------------------------------- 3 5.3.2 Geometrical data ------------------------------------------------------------------------------------------------- 4 5.3.3 Design Situations ------------------------------------------------------------------------------------------------- 4

5.4 DESIGN AND CONSTRUCTION CONSIDERATIONS ------------------------------------------------- 5

5.5 DETERMINATION OF EARTH PRESSURES ------------------------------------------------------------ 6

5.5.1 General ------------------------------------------------------------------------------------------------------------- 6 5.5.2 At rest values of earth pressure------------------------------------------------------------------------------- 7 5.5.3 Limiting values of earth pressure ----------------------------------------------------------------------------- 7 5.5.4 Intermediate values of earth pressure ----------------------------------------------------------------------- 7 5.5.5 Compaction effects ---------------------------------------------------------------------------------------------- 7

5.6 WATER PRESSURES ------------------------------------------------------------------------------------------ 8

5.7 ULTIMATE LIMIT STATE DESIGN -------------------------------------------------------------------------- 8

5.7.1 General ------------------------------------------------------------------------------------------------------------- 8 5.7.2 Overall stability ---------------------------------------------------------------------------------------------------- 8 5.7.3 Foundation failure of gravity walls ---------------------------------------------------------------------------- 8 5.7.4 Rotational failure of embedded walls ------------------------------------------------------------------------ 8 5.7.5 Vertical failure of embedded walls --------------------------------------------------------------------------- 9 5.7.6 Structural design of retaining structures -------------------------------------------------------------------- 9 5.7.7 Failure by pull-out of anchorages ----------------------------------------------------------------------------- 9

5.8 SERVICEABILITY LIMIT STATE DESIGN ----------------------------------------------------------------- 9

5.8.1 General ------------------------------------------------------------------------------------------------------------- 9 5.8.2 Displacements ---------------------------------------------------------------------------------------------------- 9

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5 RETAINING STRUCTURES

5.1 GENERAL

1 The provisions of this Part 5 apply to retaining structures in general. These are structures

used to retain ground comprising soil, rock or backfill and water and this at an angle steeper

than the angle they would normally adopt without the presence of those structures. Common

retaining structures used within the state of Qatar taking into account the prevailing geologic

conditions are:

(a) Sheet Piles

(b) Bored and Cast in Place Concrete Piles

(i) Contiguous Piles

(ii) Secant Piles

(c) Diaphragm Walls

(d) Composite Shoring Systems

(e) Concrete Retaining Walls

(i) Cantilever Retaining Wall

(ii) Counter Fort Retaining Wall

(iii) Gravity Retaining Wall

(iv) Buttressed Retaining Wall

(f) Reinforced Soil Retaining Structures

(i) Geogrid and Geotextile Reinforced Earth Systems

(ii) Galvanized Strips Reinforced Earth System

(g) Soil and Rock Nailing Systems

2 This revision of Section 4 – Part 5 is considered preliminary and shall be reviewed and

amended as needed in the next revision to elaborate on various subjects not covered herein.

3 This revision of Section 4 – Part 5 is based generally on “EN1997-1:2004+A1:2013”

Eurocode 7.

4 Section 4 – Part 5 will cover at this stage the general design aspects knowing that the

construction procedures shall be added in future revisions of this Section. Hence, at this

stage, the construction related subjects of the retaining structures will follow relevant Parts of

the QCS.

5.2 LIMIT STATES

1 During the design of retaining structures the following typical limit states should be

considered:

5.2.2 Ultimate Limit State

1 Loss of overall stability: it should be demonstrated that an overall stability failure is unlikely.

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2 Foundation failure of retaining structures with footings: it should be demonstrated that the

foundation pressures (lateral and vertical) do not exceed neither the ground allowable

bearing capacity nor the sliding resistance. Uplift pressures under the foundation due to

water seepage should also be included in the analysis.

3 Foundation failure of gravity walls, which is the loss of equilibrium of the wall considered as a

rigid body.

4 Failure of embedded walls by rotation or horizontal translation or by lack of vertical

equilibrium.

5 Failure of a structural element such as a wall, anchorage, wale or strut, including failure of

the connection between those elements.

6 Failure of a retaining structure by hydraulic heave, internal erosion or piping, unacceptable

leakage of water, or transport of soil particles through or under the wall caused by excessive

hydraulic gradients.

5.2.3 Serviceability Limit State

1 Unacceptable movement of the retaining structure, which may affect the appearance or

functionality of the structure itself, or other neighbouring structures or utilities influenced by

the movement.

2 Unacceptable change in the groundwater regime.

5.3 ACTIONS AND GEOMETRICAL DATA

5.3.1 Actions

1 Generally, the forces exerted on retaining structure with values assumed known at the

beginning of the calculation are considered as 'actions', while forces with initially unknown

values, to be determined by the interaction of the retaining structure with support elements

(ground springs, anchorages, struts, etc.), are considered as 'reactions'. The following

actions are to be taken into account:

(a) Weight of backfill material

(b) Surcharges

(c) Weight of water

(d) Wave forces for marine projects

(e) Seepage forces

(f) Collision forces

(g) Temperature effects

(h) Forces from propping elements (i.e. post-tensioned anchors)

(i) Siesmic related effects

2 The above actions should result in the determination of various earth pressures acting on the

retaining structure.

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5.3.2 Geometrical data

1 This paragraph covers the uncertainties in the geometrical data namely excavation and water

levels. In general, small variations in geometrical data are considered to be covered by the

safety factors included in the calculations. However, since the design of retaining structures

is sensitive to ground and water levels, special requirements are included in this paragraph,

mainly for unforeseen over-dig in front of the wall and groundwater levels change on both

sides of the wall.

2 Unforeseen over-dig in front of the wall

In Ultimate Limit State design calculations, where the wall stability depends on the earth resistance in front of the wall, the level of the resisting soil should be lowered below the nominally expected level by an amount which depends on the degree of control on the excavation level. With a normal degree of control the expected difference in resisting soil level should be:

(a) Equal to 10% of the wall height above excavation level (up to a maximum of 0.5 m), for

cantilever walls;

(b) Equal to 10% of the distance between the lowest support and the excavation level (up

to a maximum of 0.5 m), for supported walls.

3 Groundwater levels in front of and behind the wall

The selection of the levels of the phreatic surfaces in front of and behind the wall must consider long-term variations of the groundwater regime and/or the ground permeability, the presence of perched or artesian aquifers and the possibility that drainage behind the wall may cease to function with time.

5.3.3 Design Situations

1 The following conditions shall be considered during the design of retaining structures:

(a) Anticipated variations in soil properties

(b) Variations in actions and the ways they are combined

(c) Excavation, scour or erosion in front of the retaining structure

(d) The effect of compaction of the backfill behind the retaining structure

(e) The effect of anticipated future structures and surcharge loads/unloads

(f) Anticipated ground movements

(g) Inclination of the wall to the vertical

(h) Variations in groundwater table and the seepage forces in the ground

(i) Horizontal as well as vertical equilibrium for the entire retaining structure

(j) The shear strength and weight density of the ground

(k) The rigidity of the wall and the supporting system

(l) The wall roughness

(m) Seismic effect on the various forces

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5.4 DESIGN AND CONSTRUCTION CONSIDERATIONS

1 The design of retaining structures requires consideration of all relevant Ultimate Service

States and Service Limit States.

2 For retaining structures without strict serviceability requirements, the geometry is usually

determined by Ultimate Limit State design calculations and checked by Service Limit State

calculations (if relevant). For the retaining structures with strict serviceability requirements,

the Service Limit State requirements often govern the design.

3 The design and construction considerations should cover the following:

(a) Demonstrate that vertical equilibrium can be achieved for the assumed pressure

distributions and actions on the wall.

(b) Verification of vertical equilibrium may be achieved by reducing the wall friction

parameters.

(c) Retaining walls should be designed in such a way that there are visible signs of the

approach of an ultimate limit state. The design should prevent brittle failure of the

structure, e.g. sudden collapse without conspicuous preliminary deformations.

(d) A critical limit state should be considered to occur if the wall has displaced enough to

cause damage to nearby structures or services. Although collapse of the wall may not

be imminent, the degree of damage may considerably exceed a serviceability limit

state in the supported structure.

(e) The design methods and partial factor values recommended by “EN1997-

1:2004+A1:2013” are usually sufficient to prevent the occurrence of ultimate limit

states in nearby structures, provided that the soils involved are of at least medium

density or firm consistency and adequate construction methods and sequences are

adopted. Special care should be taken, however, with some highly over-consolidated

clay deposits in which large at rest horizontal stresses may induce substantial

movements in a wide area around excavations.

(f) The complexity of the interaction between the ground and the retaining structure

sometimes makes it difficult to design a retaining structure in detail before the actual

execution starts. In this case, use of the observational method for the design should be

considered. The observational method consists of setting criteria enabling monitoring

during construction, allowing necessary corrective actions to be taken to rectify the

design. Hence, the following requirements shall be set before construction:

(i) Acceptable limits of behaviour

(ii) The range of potential behaviour shall be analysed showing acceptable

probability that the actual behaviour will be within the acceptable limits

(iii) A plan of monitoring shall be established (including necessary instruments and

procedures) enabling the comparison of the actual behaviour to the acceptable

limits. The monitoring shall allow early detection of nonconformities, allowing

enough time for corrective actions to be taken successfully.

(iv) A list of contingency actions shall be established which could be used if the

actual observed behaviour is outside of the acceptable limits.

(g) The effects of constructing the wall, including:

(i) The provision of temporary support to the sides of excavations;

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(ii) The changes of in situ stresses and resulting ground movements caused both

by the wall excavation and its construction;

(iii) Disturbance of the ground due to driving or boring operations;

(iv) Provision of access for construction;

(h) The required degree of water tightness of the finished wall;

(i) The practicability of constructing the wall to reach a stratum of low permeability, so

forming a water cut-off. The resulting equilibrium ground-water flow problem shall be

assessed;

(j) The practicability of forming ground anchorages in adjacent ground;

(k) The practicability of excavating between any propping of retaining walls;

(l) The ability of the wall to carry vertical load;

(m) The ductility of structural components;

(n) Access for maintenance of the wall and any associated drainage measures;

(o) The appearance and durability of the wall and any anchorages;

(p) For sheet piling, the need for a section stiff enough to be driven to the design

penetration without loss of interlock;

(q) The stability of borings or slurry trench panels while they are open;

(r) For fill, the nature of materials available and the means used to compact them

adjacent to the wall.

(s) Drainage systems

If the safety and serviceability of the designed structure depend on the successful

performance of a drainage system, the consequences of its failure shall be

considered, taking into account both safety and cost of repair. One of the following

conditions (or a combination of them) shall apply:

(i) A maintenance program for the drainage system shall be specified and the

design shall allow access for this purpose;

(ii) It shall be demonstrated both by comparable experience and by assessment of

any water discharge that the drainage system will operate adequately without

maintenance.

The quantities, pressures and eventual chemical content of any water discharge

should be taken into account.

5.5 DETERMINATION OF EARTH PRESSURES

5.5.1 General

1 The Determination of the earth pressures shall take into account the acceptable mode and

amount of any movement and strain, which may occur at the limit state under consideration.

2 In the following context the words "earth pressure" should also be used for the total earth

pressure from soft and weathered rocks and should include the pressure of ground-water.

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3 Calculations of the magnitudes of earth pressures and directions of forces resulting from

them shall take account of the issues highlighted under paragraph “5.3.3”.

4 The amount of mobilized wall friction and adhesion should be considered as a function of:

(a) The strength parameters of the ground

(b) The friction properties of the wall-ground interface

(c) The direction and amount of movement of the wall relative to the ground

(d) The ability of the wall to support any vertical forces resulting from wall friction and

adhesion

5 A concrete wall or steel sheet pile wall supporting sand or gravel may be assumed to have a

design wall ground interface parameter dcvd k ;. . k should not exceed 2/3 for precast

concrete or steel sheet piling. For concrete cast against soil, a value of k = 1.0 may be

assumed. For a steel sheet pile in clay under undrained conditions immediately after driving,

no adhesive or frictional resistance should be assumed. Increases in these values may take

place over a period of time.

6 In the case of structures retaining rock masses, calculations of the ground pressures shall

take into account the effects of discontinuities, with particular attention to their orientation,

spacing, aperture, roughness and the mechanical characteristics of any joint filling material.

7 Account shall be taken of any swelling potential of the ground when calculating the pressures

on the retaining structure.

5.5.2 At rest values of earth pressure

1 When no movement of the wall relative to the ground takes place, the earth pressure shall be

calculated from the at rest state of stress. The determination of the at-rest state shall take

into account the stress history of the ground.

5.5.3 Limiting values of earth pressure

1 Limiting values of earth pressures shall be determined taking into account the relative

movement of the soil and the wall at failure and the corresponding shape of the failure

surface.

5.5.4 Intermediate values of earth pressure

1 Intermediate values of earth pressure occur if the wall movements are insufficient to mobilize

the limiting values. The determination of the intermediate values of earth pressure shall take

into account the amount of wall movement and its direction relative to the ground.

2 The intermediate values of earth pressures may be calculated using, for example, various

empirical rules, spring constant methods or finite element methods.

5.5.5 Compaction effects

1 The determination of earth pressures acting behind the wall shall take into account the

additional pressures generated by any placing of backfill and the procedures adopted for its

compaction.

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5.6 WATER PRESSURES

1 Determination of characteristic and design water pressures shall take account of water levels

both above and in the ground.

2 When checking the ultimate and serviceability limit water pressures shall be accounted for in

the combinations of actions considering the possible risks of flooding or change in

groundwater levels from either sides of the retaining structure.

3 For structures retaining earth of medium or low permeability (silts and clays), water pressures

should normally be assumed to act behind the wall. Unless a reliable drainage system is

installed, or infiltration is prevented, the values of water pressures should normally

correspond to a water table at the surface of the retained material.

4 Where sudden changes in a free water level may occur, both the non-steady condition

occurring immediately after the change and the steady condition shall be examined.

5 Where no special drainage or flow prevention measures are taken, the possible effects of

water-filled tension or shrinkage cracks shall be considered.

5.7 ULTIMATE LIMIT STATE DESIGN

5.7.1 General

1 The design of retaining structures shall be checked at the ultimate limit state for the design

situations appropriate to that state, as specified in 5.3.3, using the design actions or action

effects and design resistances.

2 All relevant limit modes shall be considered. These will include, as a minimum, limit modes of

the types illustrated in Figures 5.1 to 5.6 for the most commonly used retaining structures.

3 Calculations for ultimate limit states shall establish that equilibrium can be achieved using the

design actions or effects of actions and the design strengths or resistances. Compatibility of

deformations shall be considered in assessing design strengths or resistances.

5.7.2 Overall stability

1 Principles and calculations should be used as appropriate to demonstrate that an overall

stability failure will not occur and that the corresponding deformations are sufficiently small

taking into account progressive failure and liquefaction into account as relevant.

5.7.3 Foundation failure of gravity walls

1 The principles of foundation design shall be used as appropriate to demonstrate that a

foundation failure is sufficiently remote and that deformations will be acceptable. Both

bearing resistance and sliding shall be considered. Failure modes shown in Figure 5.2 should

be verified as a minimum.

5.7.4 Rotational failure of embedded walls

1 It shall be demonstrated by equilibrium calculations that embedded walls have sufficient

penetration into the ground to prevent rotational failure. As a minimum, limit modes of the

types illustrated in Figure 5.3 should be considered.

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2 The design magnitude and direction of shear stress between the soil and the wall shall be

consistent with the relative vertical displacement, which would occur in the design situation.

5.7.5 Vertical failure of embedded walls

1 It shall be demonstrated that vertical equilibrium can be achieved using the design soil

strengths or resistances and design vertical forces on the wall. As a minimum, the limit mode

of the type illustrated in Figure 5.4 should be considered.

2 Where downward movement of the wall is considered, upper design values shall be used in

the calculation of pre-stressing forces, such as those from ground anchorages, which have a

vertical downward component. The design magnitude and direction of shear stress between

the soil and the wall shall be consistent with the check for vertical and rotational equilibrium.

If the wall acts as the foundation for a structure, vertical equilibrium shall be checked using

the principles of Pile Foundations Design.

5.7.6 Structural design of retaining structures

1 Retaining structures, including their supporting structural elements such as anchorages and

props, shall be verified against structural failure in accordance with EN1997-1:2004+A1:2013

“2.4 Geotechnical Design by Calculation” and EN1992, EN1993, EN1995 and EN1996. As a

minimum, limit modes of the types illustrated in Figure 5.5 should be considered.

5.7.7 Failure by pull-out of anchorages

1 It shall be demonstrated that equilibrium can be achieved without pull-out failure of ground

anchorages. Anchors shall be designed in accordance with Anchorage Design procedures

with minimum the limit modes of the types illustrated in Figure 5.6 (a, b) should be

considered. For dead-man anchors, the failure mode illustrated in Figure 5.6 (c) should also

be considered.

5.8 SERVICEABILITY LIMIT STATE DESIGN

5.8.1 General

1 The design of retaining structures shall be checked at the serviceability limit state using the

appropriate design situations as specified in 5.3.3. The assessment of design values of earth

pressures should take account of the initial stress, stiffness and strength of the ground and

the stiffness of the structural elements.

2 The design values of earth pressures should be derived taking account of the allowable

deformation of the structure at its serviceability limit state. These pressures need not

necessarily be limiting values.

5.8.2 Displacements

1 Limiting values for the allowable displacements of walls and the ground adjacent to them

shall be established for a particular deformation is the value at which a serviceability limit

state, such as unacceptable cracking or displacement of adjacent structures or utilities, is

deemed to occur. This limiting value shall be agreed during the design, taking into account

the tolerance to displacements of supported structures and services.

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2 If the initial cautious estimate of displacement exceeds the limiting values, the design shall be

justified by a more detailed investigation including displacement calculations.

3 It shall be considered to what extent variable actions, such as vibrations caused by traffic

loads behind the retaining wall, contribute to the wall displacement.

4 Displacement calculations should also be considered in the following cases:

(a) where the wall retains more than 6m of cohesive soil of low plasticity,

(b) where the wall retains more than 3m of soils of high plasticity;

(c) where the wall is supported by soft clay within its height or beneath its base.

5 Displacement calculations shall take into account the stiffness of the ground and structural

elements and the sequence of construction.

6 The effect of vibrations on displacements shall be considered with regard to the following:

(a) Foundations for structures subjected to vibrations or to vibrating loads shall be

designed to ensure that vibrations will not cause excessive settlements.

(b) Precautions should be taken to ensure that resonance will not occur between the

frequency of the dynamic load and a critical frequency in the foundation-ground

system, and to ensure that liquefaction will not occur in the ground.

(c) Vibrations caused by earthquakes shall be considered using the guidelines of the

designated section of the QCS.

Figure 5.1 – Examples of Limit Modes for Overall Stability of Retaining Structures

(EN 1997-1:2004+A1:2013)

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Figure 5.2 – Examples of Limit Modes for Foundation Failures of Gravity Walls

(EN 1997-1:2004+A1:2013)

Figure 5.3 – Examples of Limit Modes for Rotational Failures of Embedded Walls

(EN 1997-1:2004+A1:2013)

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Figure 5.4 – Example of a Limit Mode for Vertical Failure of Embedded Walls

(EN 1997-1:2004+A1:2013)

Figure 5.5 – Examples of Limit Modes for Structural Failure of Retaining Structures

(EN 1997-1:2004+A1:2013)

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Figure 5.6 – Examples of Limit Modes for Failure by Pull-out of Anchoes

(EN 1997-1:2004+A1:2013)

END OF PART

QCS 2014 Section 04: Foundations and Retaining...

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