WORKSHOP NOTES - E-Geo Consultant Sdn Bhdegeo.com.my/papers/About Pile Foundations/Workshop...

WORKSHOP NOTES

ON

By

Ir. Neoh Cheng Aik E-Geo Consultant Sdn Bhd

[email protected]

www.egeo.com.my 25 Nov 15rev

“Site Supervision of

Bored Pile & Micropile

Installation”

mailto:[email protected]

Workshop Notes on “Site supervision of Bored Pile & Micropile Installation” by Ir. Neoh

Cheng Aik, 25 Nov 15

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TABLE OF CONTENTS

1. Introduction………………………………..….. Pg. 2

1.1 Objective of this course/workshop

1.2 Detail course/workshop contents

1.3 Method statement

1.4 References

2. Role of supervision for piling works…………..Pg. 6

2.1 Parties involved

2.2 Basic role & responsibility

2.3 Duties of supervisors

2.4 Some advice & comments for pile supervisors

2.5 Minimum supervision requirements for piling works

3. Site supervision of bored piles…………………Pg. 14

3.1 BS EN 1536:2000

3.2 Design & construction issues & requirements

3.3 Scope of design validation

3.4 Construction controls

3.5 Common defective design

3.6 Common defective construction

3.7 Construction checklist

4. Site supervision of micropiles……………….....Pg. 48

4.1 BS EN 14199:2005

4.2 Important construction issues & requirements

4.3 Construction checklist

5. Specification for Piling Works………………....Pg. 64

6. Commonly asked Q & A…………………….…Pg. 65

7. Case Histories/case studies…………….……......Pg. 73

8. Attachment: Slide Presentation……………..……………….Pg. 74



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1. Introduction

Pile foundations are very common nowadays especially for high-rise

buildings & heavy structures. Reliability & performance of pile foundations

depend crucially on how they are designed as well as how they are

constructed.

“Construction of piled foundations is a specialist activity, calling for

considerable expertise & reliable workmanship, the more so as the

completed element can rarely be inspected for defects. Remedial work to

piling found to be wanting at a later date can be extremely time

consuming & expensive, if not well-nigh impossible” (Ken Fleming et at,

2009).

To ensure pile design is properly & adequately carried out, independent

check engineer (ICE) or BEM accredited check engineer (Geotechnic)

should be appointed to check/audit the design. Similarly, to ensure piling

works are properly carried out at site, a suitably qualified and

experienced person shall be in charge of the supervision/execution of the

piling works (Cl 9.1 of BS EN 1536).

Proper site supervision to ensure pile foundations are properly constructed

according to good engineering practice, design drawings & specification

is a mandatory requirement by code of practice (BS 8004/EC7). In fact, BS

8004:1986 clearly stipulates that “A competent person, properly qualified

and experienced, should be appointed to supervise the piling operations.

This person should be capable of recognizing 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”.

Eurocode EC7-1 also stipulates that “To ensure the safety & quality of a

structure……… the construction processes and workmanship SHALL be

supervised….” Supervision of the construction process including

workmanship should include the following, as appropriate:

Checking the validity of the design assumptions.

Identifying the differences between the actual ground conditions &

those assumed in the design.

Checking that the construction is carried out according to the

design (drawings & specification).

This workshop/course is designed to provide supervising personnel

(RE/CRE) or inspector of works (IOW) or site technicians/clerk of works with

necessary practical knowledge and information related to how to carry



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out proper site supervision of piling works with particular reference to

bored piles and micropiles.

To carry out proper supervision of piling works means to carry out the

supervision at site to ensure the piling works are carried out by the

Contractor using proper resources, procedures and according to the

approved design & specifications with due care, skill and diligence.

Presentation of the workshop/course through “slides & notes” will be in an

interactive format so that the participants are actively involved in the

learning experience. This course follows typical JKR standard

specifications and good engineering practices for construction of

common bored piles and micropiles.

1.1 Objectives of this Course/workshop

The main objective of this course is to discuss various construction practices

and construction requirements of piling works (bored piles & micropiles) that

should be met to ensure compliance with good engineering practice, design

drawings and specification of piling works. To impart the necessary

information and knowledge to ENABLE site supervisors to carry out proper

supervision of common piling works is the main purpose of this

course/workshop.

1.2 Detail workshop/course Contents

Important workshop/course details/contents covered in this Workshop are as

follows:

Workshop: Site supervision of piling works (bored piles & micropiles)

Objective: To prepare the site supervisor of piling works to inspect, to monitor and document/record

the piling operations (bored piles & micropiles) ensuring safety, serviceability and

durability pile foundation as per requirements of Code of Practice and the Specifications.

Workshop/

Course

Content:

1. Will familiarize the pile supervisor with the relevant bored pile & micropile

terminology, materials, equipment (bore rig & tools) and process details pertaining to

bored pile installation;

2. Will provide the pile supervisor with the necessary knowledge, information and

understanding of bored pile construction drawings/plans, Standard JKR Specifications

(Section 10: Piling), etc.;

3. Will explain & describe the pile supervisor’s role and responsibility for site

supervision of piling works from step one of the pile installation plan to the final step

of pile installation testing & acceptance.

4. The course includes a review of the boring rig & drill tools used for bored pile

installation and the construction requirements;

5. Will explain all the important pile installation processes/sequences & methods of

installation; all necessary scope of inspection & QC tests on materials, workmanship

and acceptance tests/measurements for structural integrity and performance of bored

piles & micropiles, etc.

Duration of

Workshop:

One day



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1.3 Method Statement

A so-called comprehensive method statement for piling work should include

but not limited to the following scopes/contents:

a) Specific, appropriate and adequate 3M (Materials, Manpower &

Machine) should be proposed and deployed to execute & complete

the piling works as specified to suit the specific pile design, specific

project/site conditions and within the time schedule planned/allowed.

For bored pile installation, specific boring rigs & tools (model, type,

capacity/torque & numbers/sets of machines & drill tools to be

deployed), specific drilled shaft stabilization material/method, specific

base cleaning equipment, specific concrete mix design, concreting

method, specific names of operator with CV, etc., shall be clearly

stated), General statement such as suitable machine and tools will be

mobilized/deployed is totally not acceptable.

b) Proper and practical sequence of works and construction

processes/methods with details of proper temporary works for each

activity and sub-activity should be proposed and illustrated with

figures/diagrams. Specific working details including piling layout,

working platform preparation, piling process, etc., should be

elaborated. Design details/drawings with supporting calculations for

temporary works such as staging, bearing capacity of soft ground for

piling platform to support piling frame, etc., should be included with

endorsement by a qualified P Eng. For bored piles, specific

construction method & details for boring (rig & tools), drilled shaft

stabilization, base cleansing, reinforcement cage placement &

concreting should be included. For micropiles, specific construction

method & details for drilling (rig & tools), borehole stabilization &

cleansing, reinforcement placement & grouting should be included.

c) Criteria of piling termination plus details/forms of recording shall be

included. For bored piles, boing termination criteria usually are based

on depth & soil/rock strata description or confirmatory tests, etc. Shall

discuss with the designer if termination criteria are not specified on

drawings or specifications.

d) Rate of production or output of piling works per day/week plus the

completion time required for piling works should be included. For

bored piles, time required to complete boring in soil & rock for a bored

pile should be indicated.

e) Types, frequency and acceptance criteria of the necessary QC

tests/measurements/observations /inspections to check material



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quality and workmanship plus performance or load tests should be

stated/proposed with specific details. These scopes of inspection,

testing and recording should be in line with the requirements

specified/required/instructed subsequently. Proposed remediation if

any quality or workmanship is below par should also be proposed. For

bored piles, procedures/test standards, frequency & acceptance

criteria for QC tests on drilling fluids, sonic logging tests, shock tests,

static load/bidirectional load tests/PDA tests, etc., should be included.

1.4 References

The main references used/referred to prepare this course/workshop note &

slides are as follows:

a) ”Pile Design & Construction Practice”, 4th Edition, by M.J. Tomlinson (1994),

b) “Foundation Design & Construction”, GEO (HK) Publication 1/2006,

c) “Drilled Shafts: Construction Procedures & LRFD Design Methods”,

Publication No. FHWA-IF-99-025.

d) “Drilled Shafts: Construction Procedures & Design Methods”, Publication

No. FHWA-NHI-10-016.

e) “Micropile Design & Construction Guidelines” implementation Manual.

Publication No. FHWA-SA-97-070 (Jun 2000)

f) BS 8004:1986. CP for Foundations

g) BS EN 1997:2004. Part 1:General Rules (EC 7)

h) BS EN 1536:2000. “Execution of special geotechnical work-bored piles.”

i) BS EN 14199:2005. “Execution of special geotechnical works-micropiles.”

j) Code of Practice for Foundations, Hong Kong, 2004.

k) Code of Practice for Foundations,CP4;2003, Singapore Standard

l) “Piling Engineering”, 3rd Edition, by Ken Fleming, et al (2009).

This brief note intends to provide important information and details on how to

carry out site supervision aimed to ensure sound non-displacement piles

(bored piles and micropiles) are formed and installed according to the

design drawings and specifications and also in accordance with the

requirements about safety, serviceability and durability stipulated by code of

practice (BS EN 1536, BS EN14199, BS 8004/EC 7).



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2. Role of Supervision for Piling Works

2.1 Parties involved

Generally and typically, five direct parties involved in a conventional

construction of civil engineering and building project contract

implementation are:

a) The Client/Project owner (specifies the needs of the project,

provides project site & fund).

b) The Project Manager (appointed by the Client to manage and

administer the project on behalf of the project owner & coordinates

all parties involved in the project construction works. Has the

authority to enforce the provisions of the Contract. For small

project, the role of project manager may be played by the

Consultant).

c) The Consultants (appointed by the Client/Project manager to

prepare the design drawings & works specifications (std &

addendum Specs) to meet the requirements of Codes of practice,

BQ & other info for the contract document for the project &

supervise the construction).

d) The Contractor (engaged/entrusted by the Client to carry out the

construction works with necessary resources as designed and

specified by the design Consultants through a contract with the

Client). For design & build contract, the lead contractor engages a

consultant and works together to carry out the works for the project

owner..

e) The Supervisors (IOW, ARE, RE/CRE), appointed/entrusted by the

Client/Project manager to supervise the works. Has the authority to

inspect (to look closely & critically), accept/reject or suspend the

works according to the provisions in the Contract documents..

The construction supervision team including RE & technicians/clerk of

works or inspector of works (IOW) appointed by the Client/project

manager usually is from the design Consultant (as recommended by

BEM) though the Client has the right to appoint any other qualified

person/consultant to supervise the construction works by the

Contractor.

Piling work is usually part of the civil engineering or building project

given to a Contractor, who normally engages a piling specialist to

carry out the piling work.

It is a typical construction contract practice that the Contractor shall

notify the site supervisor of his intention to proceed with each and

every item of works and obtain the supervisor’s approval of his long

term and day to day work program before any works are executed.



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2.2 Basic role & responsibility of pile supervisors

The basic role of pile supervisors (appointed by the project

owner/project manager) is to serve as representative of the

Client/Project manager to take care of the interest of the project

owner and to perform site supervision aimed to ensure piling works are

properly carried out by the Contractor according to the

agreed/signed Contract documents including Conditions of Contract,

BQ, design drawings and works specification.

The supervisor (RE/IOW) should also serve as the eyes and ears of the

designer/Client, and as the recorder (to make accurate & unbiased

observations; document events comprehensively & consistently;

perform duty promptly) and as the reporter (to keep diary up-to-date

& keep the designer/Project manager informed promptly) for the job

entrusted.

The basic role and responsibility of supervision team for the piling work

is primarily to ensure the piling work is carried out by the Contractor

properly according to the approved design drawings & works

specifications and record adequately to establish the as-built

conditions for future analysis and reference. To carry out the piling

work properly means to carry out the piling work using proper

materials, proper procedures and equipment and also with due care,

skill and diligence. Care and diligence are humane attitude factors

while skill means knowledge and experience that requires training

through attending courses/workshops, self-reading, practical/physical

site experience, etc.

Care and diligence are very important human factors or human

attitudes of mind that need to be exercised to fullest when there is

lacking in skill. What is the standard for care? What is the standard for

diligence? What is the standard for skill? What to constitute professional

negligence (lack of care or diligence or skill) in supervision of piling

works? Case histories to illustrate these important issues will be

deliberated during the lecture.

Two (2) basic requirements for properly installed sound piles to be

formed at site are as follows:

Well-perceived pile design, based on adequate info (loads, site

& subsoil conditions/SI) and in compliance with the

requirements about safety, serviceability & durability stipulated

by CP (BS 8004/EC 7) is designed properly by qualified designer.

Properly means with due care, skill & diligence. Performance of

displacement piles is generally more sensitive to design issues

and the site supervisors have to check and discuss with the



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designer to ensure all the issues discussed in Para 3 are

adequately addressed.

Piles are properly installed according to the approved pile

design & specification by qualified Contractor using proper

material, equipment and construction procedure and under

supervision by qualified supervisors (RE/technicians/clerk of

works), whose primary responsibility is to check and ensure

piles are properly installed according to the good engineering

practice, approved design drawings & specification (an audit

function to double check proper construction as required by

CP). Performance of non-displacement piles (bored piles &

micropiles) is more sensitive to construction and the site

supervisors have to check the method statement and discuss

with the Contractor and designer to ensure all the construction

requirements/issues discussed in Para 3 & 4 are adequately

addressed.

As the subsoil conditions are usually highly variable and sometimes

treacherous, the response and effects of piling on the ground are very

complex and difficult to predict mainly due to lack of information and

data available.

Basic knowledge that needs to be learnt and be aware by RE and

supervisors for supervision of various types of piling works will be

discussed in details during the lecture.

In order to discharge the responsibility of supervisor, he/she SHALL be a

suitably qualified and experienced person, who shall be responsible

for:

a) The conformity of piling works with CP, design drawings &

specifications.

This means in compliance with good engineering practice and all

the requirements stipulated by CP (relevant BS EN 1536/BS

8004/EC7), specific design drawings & specifications. To discharge

this responsibility, the supervisor has to be well-versed with the

relevant terminology of piling works, all important

processes/sequence of piling works and their relevant scope of

inspection/QC tests on material, workmanship & performance tests

plus their acceptance criteria. An experienced pile supervisor is

always aware of the common defective piling constructions and

how to mitigate them properly.



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b) Checking the validity of design parameters/assumptions.

c) The inspection & monitoring of all important piling

processes/sequences and keeping of all necessary records to

establish as-built conditions; and to

d) Keep the Clients/representative and/or designer informed of any

variations or deviations from the expected situations or conditions

of the site or any cases of non-conformity.

Properly qualified means adequate basic academic qualification and

training to equip with the necessary skill for the piling supervision. An

understanding of the interaction of piling with the ground is essential for

piling supervisors to understand the principles involved with various

piling behaviours and piling phenomenon such as base boiling,

excessive outflow of drilling fluid, excessive inflow of soil &

groundwater, etc., for installation of bored piles, etc.

As a site supervisor for a piling works, he/she is responsible and

obliged to ensure the above requirements are met. In order to meet

the above requirements, the supervisor has to carry out the supervision

with due care, skill and diligence; otherwise he/she is deemed to have

professional negligence. What is meant by with due care, skill and

diligence in piling supervision?

2.3 Duties of supervisors

Generally important duties for piling supervisors (RE) or IOWs are as follows;

a) To check and approve the method statements prepared & submitted

by the Contractor.

b) To check that all the piling works processes at site are carried out

according to specifications and drawings.

c) To inspect and identify any faulty materials, defective workmanship,

non-conformity work process, etc.

d) To check that the Piling Contractor provides adequate safety

precautionary measures during the course of all the piling works

processes;

e) To check that the Contractor follows the approved works program

and approved method statements;

f) To keep vigilance on any visual signs of pile distress on Site and in

the surrounding buildings/structures and any apparent signs of

abnormal or unforeseen ground conditions.

g) To report to designer/Client or professional staff on faulty materials,

defective workmanship, non-conformity works process, site

problems, site safety, visual signs of distress, possible abnormal or



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unforeseen ground conditions, progress, quality of workmanship and

adequacy of Contractor’s resources for the Works;

h) To make site measurements, sampling and testing of materials for the

piling works;

i) To monitor the piling works of all his subordinates, if any;

j) To record and ensure that all site measurements, site diaries on site

field works, record drawings, in-situ QC testing and other records are

properly maintained and kept up-to-date;

k) To ensure consistent supervision, site safety and measurement

standard across sites under his supervision.

l) To prepare and submit weekly/monthly progress reports and any

other returns as required by his superior;

m) To check and verify bills submitted by the Contractor;

n) To check that the Quality Procedures are followed by all concerned

subordinates;

o) To check & verify the as-built drawings/records prepared by the

Contractor; and

p) To check the overtime duties of all his subordinates, if any.

q) Other specific supervision duty as required or instructed.

2.4 Some advice & comments for pile supervisors

a) Pile supervisors (CRE/RE/IOWs) have to remember that their main job

is to represent the project owner to supervise & to inspect to ensure

that the piling works are properly executed according to the

drawings & specifications. This means the supervisors have to know

the specific requirements of the particular piling work process & be

able to identify defective pile construction & unacceptable materials

that are not in compliance with the specifications and drawings or

not a good engineering practice. Well-versed in BS EN 1536 (bored

piles) & BS EN 14199 (micropiles) is mandatory.

b) Nowadays, in order to achieve more cost & time saving or to be

more competitive, the pile designers and/or pile Contractors are

more inclined to adopt marginal pile design & fast/cheap

construction process (usually are likely to be low quality 3M & poor

workmanship). This means less piles or smaller piles or cheaper piles

or lower FOS or not much contingencies are allowed for unforeseen

eventualities & unexpected/treacherous subsoil conditions. This will

put the responsibility of pile supervisors to be more alert, demanding

and challenging.

c) Inspection is as good as the knowledge, experience & qualification

of the supervisors.

d) For bored piles, the supervisors must learn the importance &

principles of boring operation, drilled shaft stabilization, base

cleaning, reinforcement cage placement, concreting, etc., that will

affect bored pile structural integrity and capacity. For driven RC/spun

piles, the supervisors must learn & understand the operation of



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hammer (plus accessories), pile behaviour, the soil response and

how these 3 components interact. The soil mechanic principles

involved can be quite complex.

e) Most of the piling problems can be mitigated/averted, if a

competent pile supervisor uses systematic inspection procedures

coupled with due cooperation from the pile Contractor.

f) The pile supervisor must be more than just “look see look see at site”

or just a “site recorder” or “blow counter”. The supervisor should be

the “eyes & ears” of the designer/project director/owner. Timely

observations, suggestions & correction advice can ultimately assure

the success of the piling works. The earlier a problem or abnormality

is detected & reported by site supervisor, the earlier a solution or

correction in procedures can be made & hence, a potentially

negative situation can be limited to manageable one. If the same

problem is left unattended, the numbers of piles affected will

increase, as do the cost of remediation & the potential for

claims/disputes or project delays. Thus, prompt detection & reporting

of any problem by site supervisor is very critical to keep the project

on schedule & within budget.

g) Pile supervisors must learn to have the knowledge to identify the

various types/designs of piling/boring rigs & drill tools being used by

the Contractor. Their applications & limitations, etc.

h) Pile supervisor should always REMEMBER that it is NOT his/her

responsibility to direct the Contractor’s works or techniques.

However, pile supervisor must make reliable & accurate records &

notes as to the actual boring rigs & drill tools on site and being used.

If the Contractor only has soil augers on site and rock needs to be

bored & penetrated, it is important to have this info noted, as the

Contractor may say the material cannot be penetrated and was

misrepresented or harder than indicated. May not really be so if the

Contractor had the proper rock auger or rock boring tools.

i) The pile supervisor’s accurate, unbiased observations and

documentation can serve to alleviate a lot of problems or disputes or

claims that might arise.

j) If the Contractor only has soil augers on site and rock needs to be

bored & penetrated, it is important to have this info noted, as the

Contractor may say the material cannot be penetrated and was

misrepresented or harder than indicated. May not really be so if they

had the proper rock auger or rock boring tools.

k) The bored pile designer knows the project by heart as he/she have

lived it for probably a few years or at least several months. The

Contractor knows each detail of construction as he/she has gone

through the Specs & Drgs with fingertip details during the tender

process & site visit. The CRE & RE is most probably sent to site at the

last moment, so it is imperative that CRE/RE should be familiar with

the project (drgs, specs & site conditions) soonest possible so that the

Method Statement can be checked & approved fast.



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l) CRE/RE’s whole purpose of being sent to site is to verify that the bored

piles are constructed in accordance with the specs & drags. Hence,

the specs, in reality, outline the responsibility of CRE/RE.

2.5 Minimum supervision requirements for piling works

The classes of supervision appropriate to a type of building

construction works or civil works are defined by means of the number

and grades of technically competent person (TCPs) and their

frequency level of inspection of the works. The minimum requirements

on the grades of TCPs and frequency level of inspection appropriate to

various types of building works or civil works as practice in Hong Kong

are set out in Table 1 below.

Minimum level of supervision is graded as follows;

Level 1 is inspection as and when required.

Level 2 is inspection monthly

Level 3 is inspection fortnightly

Level 4 is inspection weekly

Level 5 is full-time inspection during site working hours

Technically competent person/TCP or supervisor grade is as follows;

T1 is a certificate or diploma holder with minimum relevant working

experience of 2 years.

T2 is a higher certificate or higher diploma holder with minimum

relevant working experience of 3 years.

T3 is a higher certificate or higher diploma holder with minimum

relevant working experience of 5 years or a degree holder with

minimum 2 years of working experience.

T4 is a degree holder with minimum 4 years of relevant working

experience or a registered professional engineer

T5 is a registered professional engineer with minimum 5years of

relevant working experience.

According to Hong Kong practice, full-time supervision from registered

Contractor/RC and registered geotechnical engineer/RGE’s

representative (at least grade T3) is required for foundation/piling

works.

ABBREVIATIONS in Table 1; RC=registered contractor; AP=authorized

person/SO; RSE=registered structural engineer; RGE=registered

geotechnical engineer.



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Notes to Table 1

1. Level 1 = Inspection as and when required; Level 2 = Monthly inspection; Level 3 = Fortnightly inspection; Level 4 =

Weekly inspection; Level 5 = Full-time inspection during site working hours

2. Higher grade TCP and/or more frequent site inspection up to full time may be required at critical stages. Further

guidance is given in the Code of Practice.

3. For the qualification and experience required for each grade of TCP, refer to para 2.4.

4. The type of building works that are regarded as building works with significant geotechnical content are set out in the

Code of Practice.

5. The type of foundation works, including those in the designated area, that are regarded as building works with

significant geotechnical content are set out in the Code of Practice.



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3. Site Supervision of Bored Pile Installation

Bored piles are the common type of non-displacement/replacement piles,

which are generally more environment-friendly and can be constructed

through any hard obstructions; have much larger range in size (0.5m to 3m

diameter) and capacity (150T to 6500T).

Bored piles up to about 6m diameter & 80m deep have been reported to be

constructed to replace big groups of many driven big steel pipe piles for

bridge over a big river in USA. Non-displacement or replacement piles

generally refer to bored piles, micropiles, augered piles, hand-dug caissons

and barrete piles. Bored piles are also called drilled shafts, drilled piers,

caissons, bored & cast insitu piles.

Bored piles are deep, cylindrical (typically 0.5m to 3m), cast-insitu concrete

piles constructed by boring machine using various types of augers and

buckets, etc., to bore and to take out the cuttings with subsequent filling the

hole with concrete plus necessary reinforcement (typically 0.5% to 1%).

Bored piles are commonly and mainly used to resist lateral loads of deep

excavation and to support large structures with large vertical

compressive/tension loads and/or large lateral loads. It is very important that

bored pile designers should fully understand the design

principles/concept/model/behaviour and scope of design of bored piles in

various site and subsoil conditions with particular reference to estimation of

safe structural & geotechnical capacity (fsu & fbu), in addition to their

limitations & applications.

How drilling and concreting can affect bored pile behavior and performance

is EQUALLY IMPORTANT to how to estimate ultimate unit friction (fsu) and

ultimate end bearing capacity (fbu) of subsoil practically and realistically.

Certainly, bored pile designers should also know/learn what are the site

specific information and substrata properties that will affect bored pile

construction and performance and all these should be learnt & understood

adequately.

3.1 BS EN 1536:2000 “Execution of special geotechnical work-Bored Piles” has

spelt out the details of requirements for good construction practice to

ensure good performance of bored piles covering materials/products

requirements and works execution requirements (boring, shaft

stabilization, base cleaning, placement of reinforcement cage,

concreting & testing). Requirements for quality supervision & records, etc.,

are also included.

The requirements stipulated by BS EN 1536 for bored pile installation are

briefly summarized as follows:



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Technical requirements & QC tests for Materials & Products for

bored Piles (materials for concrete & grout, concrete insitu, grout,

stabilizing fluid & reinforcement bars, couplers, spacers, etc.).

GI report: critical ground information required for proper planning

of bored pile installation works.

Design related considerations (construction tolerance,

excavation/boring, reinforcement, etc.).

Works Execution & construction requirements/controls for

excavation/boring, fixing & placement of reinforcement cage,

concreting, etc.

Requirements for supervisions (pile construction & testing)

Requirements for records

Some of the details about design & construction practice (BS EN 1536) for

bored piles are as follows:

Bored pile is formed by excavation using boring machine and then

fill it up with plain concrete or with some reinforcement (minimum

0.25% to 0.5% if insignificant bending & tension are likely to be

induced by superstructural loading and ground movement) to

provide structural element to support and transfer loads from the

superstructure into the ground through friction and end bearing.

Typical sizes: 0.5m to 3m diameter with maximum structural axial

load of 2000kN to 65000 kN (Qstruct = or < 0.25fcuAc). Can be raked

up to 1:4 (if stiff clay) or 1:3 if cased. Bored piles can be properly

sized to take high range of loads.

Bored piles in groups shall have pile spacing of at least 2 times

diameter or minimum 760mm net clearance. Secant piles have

spacing slightly less than pile diameter while CBP wall have bored

pile spacing slightly larger than pile diameter.

Scope of GI/SI: spacing of investigation points/BH for bored pile

foundation design & construction shall be 10m to 50m grid spacing

and depth shall be until hard layer (at least 5 consecutive SPT>50 or

minimum 3m rock coring) without underlain by weak/soft layer.

SI/GI should be aimed to be sufficient to identify all ground

formations and layers affecting the construction and performance

of bored piles plus the deformation properties of the ground as

specified by Clause 5 of BS EN 1536. For high-rise buildings & heavy

structures, boreholes should only be terminated after at least 12m

into hard material and/or at least one borehole should be bored

until at least 6m into the weathered rock. A comprehensive GI/SI

should contain the following information:



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General site geological description; GL of investigation points;

Presence & characteristics of weak subsoil (loose & soft) or

become unstable during boring; Presence of soil or rock prone to

swelling; Presence of coarse soil of high permeability or cavities

that can cause sudden loss of stabilizing fluid or concrete during

placement; Presence of hard obstruction such as cobles,

boulders/hard metals that are troublesome and time consuming to

break through, etc. (Cl 5, BS EN 1536).

Important scope of monitoring/inspection by site supervisors related to

construction requirements for bored piles are summarized in the Table

below: Construction

activity

Scope of Monitoring/

Inspection/Testing.

Acceptance criteria

1 Pre-construction Site inspection & desk study of

GI/SI report & GDR, etc. Setting

up. Dilapidation survey?

Understand the site, scope &

nature of piling works. Check

permissible limits of ground

movement for nearby structures/

services/utilities that may be

affected by bored pile installation

2 Boring operation Check method statement &

types & details of boring rig &

tools. Monitor boring operation

& effects of boring/ground

movements plus any

abnormalities. Scope & details

of records as required by BS EN

1536 (Cl 10)

Suitability of boring machine

(capacity & power) & tools that

can complete boring as

specified/designed or within 6 hrs?

Consult the designer for criteria of

boring termination & potential

abnormalities, if any.

3 Drilled shaft

stabilization

Check & monitor

types/methods of borehole

stabilization, their applications

& limitations to the specific site

& subsoil conditions. Perform

QC tests on drill fluid & records.

Casing for squeezing very soft

strata & collapsible strata or

subsoil with artesian pressure.

Bentonite for sand strata with

boiling problem &/or artesian

pressures. Polymer for most of the

residual soils especially silty soil.

4 Base cleansing Monitor effectiveness of

cleanout bucket and/or air

lifting/pumping method just

before concreting. Beware of

problems of loose subsoils &

excessive air-lifting.

Base cleansing should be

repeated if concreting is not

carried out within 1 hrs after

cleaning. Cleansing until all loose

& soft materials are removed. Can

be confirmed by CSLogging tests.

5 Placement of

reinforcement

cage

Check conditions of

reinforcement cage (joint/

couplers/spacers) during

pitching & placement into the

hole.

Spacing of rebars should be more

than 100x200mm. Reinf cage

should be rigid, should be stiffened

by temporary steel pipe if

excessive deflection is noted.

Ensure concentric position of the

cage in the hole & within

tolerance limits.

6 Concreting Check & verify concrete mix

design & desired quality/QC

requirements. (BS EN 1536, Cl 6.3)

Check tremie concreting

requirements. QC tests &

Fresh concrete should be cohesive

& no segregation. High slump

(>150mm) till end of concreting,

Add retarder if concreting time

>1.5hrs. Concreting should be



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recoding. Check overbreak by

measuring volume of concrete

consumed per m for each pile.

BS EN 1536 (Cl 10).

continuous & uninterrupted.

Requirement & precautions of

tremie concreting should be

observed.

7 Post installation

Testing

(CSL, Shock tests,

MLT, Bi-directional

test, PDA,

Statnamic test,

etc.)

Evaluate installation records to

identify defective construction.

Select suitable test methods &

test standards for structural

integrity & capacity. Check &

make sure all the requirements

of test standards are complied

with.

Pile selection criteria for tests

should be based on detail records.

Tests shall be planned, conducted,

recorded & interpreted by

qualified Engineer. Acceptance

criteria for structural integrity &

capacity tests? Make sure all

requirements of test standards are

complied with.

Design & construction of large diameter bored piles in Malaysia are only

commonly adopted for high-rise buildings and heavy structures after 70’. One

of the early projects where about 1.2m diameter bored piles were used was

Wisma Persekutuan (2 blocks of 10-storey Office Building) in Johor Bahru in

1974.

3.2 Design & construction issues & requirements for bored piles

Some of the common design & construction requirements & practice for bored

piles in Malaysia are summarized as follows:

a) Bored pile sizes & capacity

Typically, bored piles can be sized from 500mm to 2.5m or up to 3m diameter

to take large ranges of design working loads up to about 65,000kN or higher

for heavy structures and high-rise buildings with deep basements and top-

down constructions. Usually uniform cross section piles are adopted without

base enlargements/under-reams/bells. Depth of bored piles exceeding 80m

is not uncommon. Bored piles can be raked up to 1:4 (in hard/stiff clay) or 1:3

if cased in cases where large load is anticipated.

b) Ultimate limit state

Pile shall be designed to have adequate capacity (structural & geotechnical)

to resist ultimate load combination. Important ultimate limit states that shall

be checked and analyzed (EC7-1) are: EQU (loss equilibrium of the pile or the

ground such as piles near slope, ground subsidence, excessive erosion, etc.).

STRU (internal failure or excessive deformation of the pile due to inadequate

strength to resist loads). GEO (failure or excessive deformation of the ground

in which the strength of soil/rock is insufficient to resist the loads). UPL & HYD.

Design methods by ASD (allowable stress design) are more common though

LRFD or limit state design methods are increasing common nowadays.

c) Serviceability limit state

Settlement and deflection of piles at working load shall be within tolerable

limit in consideration to aesthetic appearance, comfort of users &

functionality. Usually pile settlement at working load should be less than

12.5mm and free from creep for most buildings (JKR/SPJ/2010-S10).



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d) Durability

Design life for normal buildings & structures (EC 7-1) should be 50 yrs.,

monumental buildings/bridges/special structures 100 yrs, replaceable

structure parts 25 yrs, agricultural structures 30 yrs & temporary structures 10

yrs. For aggressive ground (pH value<5, resistivity<2000 ohm-cm,

Sulphate>0.2%, chloride>0.1%), higher cement content (>380 kg/m3), etc.,

have to be provided. Refer Clause 10 of BS 8004 for durability requirements for

concrete, steel & timber.

e) Nowadays, bored piles for high-rise buildings and heavy structures often

adopt grade 45 concrete with normal 0.5% to 1% reinforcement or more

depending on the lateral load/bending loads on piles. Maximum permissible

average compressive stress (fca) can be as high as fca=0.25fcu, (BS 8004) but

fca is normally discounted by about 20% to account for uncertainties in

submerged tremie concreting as recommended by CP for Foundations (Hong

Kong, 2004). CP 4:2003 of Singapore Standard limits 0.25fcu to 7.5 MPa only,

but for rock socketed reinforced bored piles with full length reinforcement,

the allowable structural capacity is Qstruct =(0.4fcuAc + 0.75fyAs)/FOS, where

fcu=grade of concrete, Ac=concrete area, As=steel area, fy=yield stress &

FOS= or >2.

Typical ranges of working bored pile capacity for the common

sizes based on grade 45 concrete are as follows:

Pile Size (mm) Max Design Working Capacity (kN)

500 (Ac=196,350mm2) 1,750 (2,200)

600 (Ac=384,846mm2) 2,550 (3,200)

700 3,400 (4,300)

800 4, 450 (5,600)

900 5, 750 (7,200)

1000 7,000 (8,800)

1200 10,000 (12,500)

1500 15,500 (19,500)

2000 28,200 (36,000)

2500 44,000 (55,000)

3000 55,500 (65,500)

Maximum structural capacity, Qstruct=0.2fcux As. For grade 45 concrete,

cement content shall be at least 425 kg/m3 with superplasticizer,

W/C<0.5, slump =150mm to collapse. The bracketed values are for

Qstruct=0.25fcuxAc.



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f) Important scope of design verification/analysis/calculations that shall be

carried out to show compliance with the requirements stipulated by CP are

discussed in subsequent Paras.

g) Before discussing the required scope/methods of design/calculations for

bored piles, it is important firstly to know what are the important basic

requirements stipulated by relevant Codes of practice or established design

guides plus what are the important/critical and mandatory requirements that

need to be met.

h) Relevant Codes of practice: EC 7 Part 1 for General Rules for geotechnical

design & design approaches, EC 7 Part 2 & 3 for planning scope of SI &

interpretation. BS 8004 (1986) for scope/details of design for foundations, BS

5930 (1999) & BS 1377 (1990) for planning scope/test methods of GI/I to get

the necessary subsoil parameters for foundation design, BEM 4/2005 for

requirements of adequate & reliable SI. Standard Specification for Bored pile

construction for good construction practice with respect to minimum

acceptable requirements for quality and workmanship for boring,

reinforcement, concreting & testing, etc.

i) Scope of Design Verification/analysis for Bored Pile Design

Bored pile design should be based on site/subsoil conditions derived from SI

plus loads derived from loading analysis. Scope of design verification should

basically include all necessary analysis/calculations to show all the design

requirements about safety, serviceability and durability stipulated by CP (BS

8004/EC7) can be complied with. Common scope of design verification for

bored pile design has been briefly explained in Para 3 above.

Some detail scope of design verification is given in the subsequent Para:

Without SI, geotechnical design has no basis. Without adequate design

verification/calculations, geotechnical design is uncertain and risky.

Adequate & reliable SI (as per BEM 4/2005 requirements) plus proper

selection of parameters & comprehensive analysis to show compliance with

the requirements of Code of practice are fundamental requirements for

design verifications. Adequate QC tests & design validation/ performance

tests are fundamental requirements to validate the design.

In order to plan scope of SI properly geotechnical category (GC) of

investigation, analysis and design shall be determined first. Geotechnical

Category is mainly based on nature and complexities plus the risks of the

project. The following Table provides some guides to determine GC.



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Table 1 : Geotechnical Category (GC) of Design/Investigation

(Clause 2.1, EC 7 Part 1)

Geotechnical

Category

GC I

(Low Risk)

GC 2

(Routine)

GC 3

(Abnormal Risk)

1. Type & nature of

Construction/structure

Small, simple &

conventional

structures with

normal loadings.

Common structures, no

abnormal loadings or

exceptional risks involved.

Large or unusual

structures or structures

with exceptional

loadings

2. Surrounding conditions

No nearby structures

/ utilities or no risk of

damages. No slopes.

Some risk of damages to

nearby structures.

Large ground

movement or high risks

to nearby structures,

utilities, etc.

3.Site & ground conditions

Relative flat ground.

No soft or

compressible

subsoils. Stable

ground.

Can be cut or fill ground

of various types of

formations.

Soft or unstable

ground prone to

deformation,

movement, sinkholes,

subsidence, etc.

4. Groundwater

conditions

No deep excavation

below water table

required.

Excavation below water

table.

Excavation in subsoil

consists of permeable

& collapsible strata.

WT may be lowered

5. Cost of construction

works < RM1 to 3Million RM 1 to RM30 Million > RM 3 Million

6. SI Costs as % of

construction cost 0.2% - 0.5% 0.2% - 1% 0.3% – 2%

7. SI Scope required

Simple SI such as JKR

probe & hand auger

@ 15m to 45m

spacing may be

adequate.

SI to meet Design Code of

Practice requirements.

Spacing of BH/tests should

be 15m to 45m

SI to Code of Practice

and planned by

experienced geo

engineer. Spacing of

BH/tests should be

15m to 45m.

8. Level of

Expertise required

Civil engineer under

supervision by an

experienced

geotechnical

engineer is required.

Experienced geotechnical

engineer under supervision

by very experienced

geotechnical experts.

Experienced

geotechnical

engineers with

independent design

check by BEM

accredited

geotechnical

checker/ experts.

9. Examples

Low-rise buildings of

about 500 kN

column loads or low

retaining wall (<3m)

or roads with cut / fill

<12m over stable

ground, etc.

Commercial/industrial

/high rise buildings, etc.

Roads in rolling terrains

with cuts/fills < 24m or

retaining wall <10m.

Normal bridges with

precast beams.

Dam, tunnel, port,

special /large bridge

projects or special

heavy structures.

Deep excavations

(>8m). Hill roads with

high cuts/ fills (>24m).

Design of ground

anchors, slope

stabilization for

unstable

ground/slopes, etc.



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j) Bored pile construction requirements: Boring operation

Borehole can be advanced or excavated by using many types of

tools/methods depending mainly on subsoil conditions (soil type:

rock/gravel/sand/silt/clay, WT and hardness/density) and design size/depth/

capacity of bored pile. There are many types of boring rigs/capacity (bHP,

torque & weight) & boring tools/equipment plus drilled shaft stabilization

methods to suit various site & subsoil conditions for a particular bored pile

size/depth. Important requirements are boring process shall be as fast as

possible (typically less than 3 hrs. for small piles & <6 hrs. for rock coring or

large size >1.5m diameter). Normally boring machine with high torque

capacity (>300 kN.m) can drill faster, deeper & bigger. Boring machine with

low torque capacity (<200 kN.m) may have difficulty or slow for rock coring

to construct rock socket, especially large diameter (>1.2m) rock socket in

fresh hard rock.

Common borehole advance methods are hydraulic boring using drilling

bucket/auger/chisel, direct circulation boring system, reverse circulation

boring system, etc., up to capacity of 600 kN.m torque or more.

Soil/rock augers and buckets are commonly used. Some bored pile

designers just simply specify that suitable/appropriate boring machine and

tools shall be used to construct the bored piles as shown in drawings (not very

proper or specific). Sometimes, the bored pile designers specify on drawing

that “unless otherwise approved in writing, the Contractor should deploy

suitable boring machine & drilling tools to ensure boring is completed for

each pile as shown in drawing using boring machine with minimum torque of

>250 kNm or equivalent to BG 25 and/or within 6 hours”. If there is rock

coring/chiseling/rock socket construction, longer time (>3hours) to complete

the boring may be required especially when very hard fresh rock is

encountered. Designers also should specify the acceptable method of

construction for rock socket. Common and acceptable methods are by

annular coring with subsequent chiseling & cleaning out by proper cleansing

bucket, by coring with gradual increase in diameter from small diameter to

the required diameter in stages, or total open hole drilling by special rock

augers and/or bucket with a lot of tricone drill bits, etc. Details and specific

types/models of boring machine and drilling tools usually are left to

Contractor to propose through method statement showing how to meet the

requirements specified by the designer. Usually hydraulic boring machine or

reverse circulation machine is used. For small bored piles (<1.2m) without

rock socket or rock coring, boring machine with BHP of 50 to 100 or torque of

50 to 100 kN.m is quite adequate. For rock coring or large bored piles (1.2m

to 2m) boring machine with torque of 200 to 400 kN.m or more is normally

required to complete each bored pile within about 6 hours or so.

Typical specification requires that adequate/appropriate boring rig capacity

(sufficient torque & traction power) and experienced operator shall be



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engaged to ensure boring is completed as soon as possible and concreting

be carried out immediately and completed within the same day (BS EN

1536). Where bored piles are constructed in ground which is likely to

deteriorate with time and it is not possible to finish the pile by the end of the

working day, a depth equivalent to at least twice the shaft diameter but not

less than 1.5m shall be bored the following working day immediately before

concrete placement (BS EN 1536 Clause 8.1.1.8).

During boring, if the ground differs significantly from the design such as

unforeseen impenetrable obstruction prior to reach its designed founding

level, the designer shall be informed of further action required to continue the

work.

The use of explosives for removing obstructions or for socketing piles into

bedrock shall not be allowed as it may result in damage to adjacent piles or

structures.

The construction sequence of piles shall be chosen so as to avoid damage to

neighboring piles.

k) Drilled shaft stabilization

When a bore hole is excavated, there will be some stress relief in subsoil

resulting in some movement of the surrounding ground and drilled shaft

collapse (inflow of water and/or soil into the bore) especially in water bearing

cohesionless subsoil or with artesian pressure. Proper drilled shaft stabilization

is very important:

to reduce zone of stress relief (that will reduce fsu),

to reduce disturbance to or instability of the bearing stratum or the

surrounding ground, especially loose granular and soft cohesive

ground,

to reduce unstable cavities outside the pile

to avoid/reduce overbreak or formation of irregular cavities.

Usual practice is to use temporary casing for the top few meters as guide

length and then use water as drilling fluid if the subsoil is mainly stiff cohesive

soil without very soft layers and absent of collapsible water bearing

sand/gravel layers. Temporary casing shall be cylindrical and without

significant longitudinal or diametrical distortion and also shall be strong

enough to take handling stress and ground pressure. For unstable subsoils

(uniform non-cohesive soils (d60/d10<1.5) below groundwater table or loose

non-cohesive soils with relative density <0.3 or sensitive clays or soft clay with

Cu<15 kPa) especially water bearing sand/gravel with some artesian pressure,

bentonite slurry or casing or both is necessary to suppress “boiling” and

borehole collapse. In built-up areas or more environment sensitive areas or

designed to have high friction, liquid or solid polymer is used instead of

bentonite. At all time during boring and concrete placement the level of

stabilizing fluid (water/bentonite/polymer slurry) shall be maintained (at least



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1m above the groundwater level). For deep very soft substrata, temporary or

permanent casing has to be used to prevent necking problem. Casing

exceeding 12m deep is difficult and/or problematic to install & extract, unless

double/triple casings are used. Nowadays, most bored pile designers specify

polymer to replace bentonite for drilled shaft stabilization because bentonite

slurry has been reported to have about 15% to 40% reduction in fsu, in addition

to environment problems, especially when poor quality bentonite is used and

proper control and tests on sand content, density and pH value of the

bentonite slurry are not carried out. Important QC tests for bentonite slurry (BS

EN 1536) to ensure performance are as follows:

QC Tests Fresh At Time of

ready for re-

use

Before

concreting

Test method

Density <1.10 g/cc - <1.15 g/cc Mud balance

(API 13b-Sec 1)

Viscosity

Marsh value

32 to 50 sec 32 to 60 sec 32 to 50 sec Marsh Funnel

(946cc)

(API 13B-Sec 2)

Fluid loss <30 cm3 <50 cm3 -

pH value 7 to 11 7 to 12 - pH

Paper/meter

Sand

contents

- <4% <4% Sand screen

set (API 13B-

Sec 4)

The successful use of bentonite slurry as a means of excavation support relies on

the tight control of its properties.

The inherent characteristics of bentonite slurry are its ability to swell when wetted,

its capability in keeping small sediments in suspension, and thixotropy, i.e. it gels

when undisturbed but flows when it is agitated.

The slurry penetrates the walls of the bore and gels to form a filter cake that acts

as a sufficiently impervious diaphragm to allow the transmission of hydrostatic

slurry pressure.

To ensure bore stability, the hydrostatic pressure of the bentonite slurry must be

greater than the sum of the water pressure and the net pressure of the soil.

Nowadays, polymer fluids have been used to maintain bore stability during

excavation as an alternative to bentonite slurry. Unlike bentonite slurry, polymer

fluid forms a barrier by blocking the pores within the soil. The polymers consist of

a number of individual molecules joined together and can penetrate deep into

sandy or silty soils. The advantages of polymer fluids include simpler site logistics,

rapid hydration, less requirement for storage, less disposal problems, inertness to

cement and absence of a filter cake. Polymer fluids are biodegradable and



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therefore do not require special disposal measures. However, polymers can be

difficult to mix. The shearing action must be sufficiently high to disperse

the polymers but not so great as to break down the polymers. In addition,

polymer fluid can be susceptible to becoming wet and forming a slime.

Beresford et al (1987) discussed the testing of polymer fluid and suggested

acceptance criteria for the results.

l) Base cleaning

Collapsed materials or debris accumulated at the base of a bored pile is

undesirable as this may lead to intermixing and inclusions in the concrete or a

layer of soft material at the base of the pile. Debris may comprise soft and loose

sediments that settle to the base after completion of excavation.

Alternatively, foreign materials could be deposited accidentally into the pile. It

will be prudent to ensure that a sufficient projection of the temporary casing is

left above ground level and that empty bores are properly covered.

The final cleaning of the pile base may be done with the use of a cleaning

bucket followed by air-lifting. The use of a skirted airlift in which debris

would be drawn in over a larger area may be more effective (Fleming et al,

1985). On some occasions, the reverse-circulation drill has been used for this

purpose. Opinions differ as to the effectiveness and potential disturbance

between the use of an airlift pipe and the reverse circulation

flush, particularly in weathered rocks which may be susceptible to disturbance or

damage of the bonding inherent in the grain structure. Thorough base

cleanliness may be difficult to achieve in practice, particularly with raking piles.

If base cleaning is not done properly, potential problems including plastering of

the filter cake and presence of large pieces of debris at the pile base may

occur.

Even if the base is free from significant debris, the soil below the base may be

disturbed and loosened as a result of digging, stress relief or airlifting

Special techniques may be adopted to consolidate and compact the loosened

soil. These include pressure grouting with the use of a stone fill pack (Tomlinson,

1994) or Tube a-Manchette (Sherwood & Mitchell, 1989). In addition, shaft-

grouting may be carried out to enhance the shaft stiffness and capacity

(Morrison et al, 1987). However, Mojabi & Duffin

(1991) reported that no significant gain in shaft resistance was achieved by shaft-

grouting in sandstone and mudstone. Experience with such construction

expedients is limited in Hong Kong.

Rock-socketed piles are liable to base-cleanliness problems arising from fine

rock materials. If the debris is not removed properly, a 'soft toe' may form at the

base of the pile.

Fresh concrete may also force the base debris up the socket wall thereby

reducing the shaft resistance in the lower region of the socket. A possible



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remedial measure is to use high pressure water jetting to remove the loose

sediments at the base, if the sediments or segregations are not greater than 50

mm in thickness or 100 mm for piles longer than 30 m.

Pressurised grout is then used to fill up any voids. Several holes may be required

to facilitate the flushing of the debris. Further cores should be taken to verify the

effectiveness of remedial grouting in each pile.

The potential problem of trapping debris at the pile base can be minimised by

lifting the tremie pipe with a hydraulically operated equipment. In this system,

the lifting of concrete skip and tremie pipe is carefully controlled to maintain a

constant distance between the tremie pipe and the pile base. Cementitious

materials with a very high cement content or grout are used in the first charge to

prevent direct contact of concrete with water in the first pour.

Before concreting, the base of borehole should be reliably cleansed by suitable

method to avoid accumulation of debris/soft toe at base, especially those

collapsible water bearing silty/sandy subsoils. Normal bucket cleaning before

the end of boring plus air-lifting base cleaning method just before concreting is

usually the reliable base cleaning method that should be specified. Base and

borehole cleaning/stabilization can be a serious problems when the Specialist

bored pile Subcontractor is only involved with boring and placement of

reinforcement cage and concreting are done by the main Contractor himself.

For collapsible subsoil (sandy or silty strata and water bearing), waiting period of

more than 1 hr. for concreting after cleaning can be serious.

Some designers may specify, after normal bucket base cleansing, filling the base

with rock/crusher run and subsequent base grouting to ensure sound base.

m) Concrete mix design & concreting

Usually grade 35 to 45 concrete is specified. Minimum cement content required

is 325 kg/m3 & 450 kg/m3 for dry holes & submerged/tremie concreting

respectively. Other requirements and characteristics of concrete mix for bored

piles that should be designed and specified or indicated on design drawings are

as follows:

1) Excellent Workability

It is essential that the concrete have the ability to flow readily through the

tremie, to flow laterally through the rebar cage, and to impose a high lateral

stress against the sides of the borehole to induce high friction. From a

geotechnical perspective, the objective of placing concrete is to re-establish

the lateral stresses in the ground around the bored pile that existed before

the borehole was excavated. This objective can best be met by using

concrete that is highly fluid with slump of exceeding 150mm to 250mm until

concreting is completed, but with low water cement ratio of less than 0.5. To



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achieve high slump at low water cement ratio (to avoid bleeding and long

term shrinkage), quality superplasticizer shall be added. In case the

concreting takes more than 2 hours, retarder should also be used to ensure.

2) Self-Weight Compaction

Vibration of concrete in a borehole is impractical, except very near the

surface. In some cases this will lead to defects in the completed shaft by

causing ground water, drilling fluid, or soil to mix with the concrete.

3) Resistance to Segregation

The concrete mix should have a high degree of cohesion and should be free

of large-sized aggregate; otherwise, it may segregate during placement,

particularly if free fall is allowed in dry holes, resulting in inferior concrete.

4) Resistance to Leaching

In some instances flowing ground water could cause a weakening of the

concrete after it is placed. A properly designed mix should be resistant to

such flow. However, if the rate of flow is substantial, a permanent casing or

liner will be necessary. Furthermore, when concrete is placed under a drilling

fluid (slurry or water), there is inevitable contact between the concrete and

the fluid, which is a condition that also requires the mix to be resistant to

leaching.

5) Controlled Setting

Bored pile concrete should retain its fluidity throughout the depth of the

borehole during the full time required for complete placement of the

concrete in the borehole to maximize the lateral pressures that are imposed

by the fresh/fluid concrete. Slow setting is also required to allow for inevitable

delays that may occur during concreting, such as: interrupted concrete

supply from ready-mixed trucks, difficulties in extracting casing, etc. At the

same time, it should attain an appropriate strength within a reasonable time

after placement. Normally some retarder is added for the expected delay

especially when concreting time is likely to exceed 2 hours for large and

long bored piles.

6) Good Durability

If the subsoil conditions is potentially corrosive or can become corrosive

during the life of the foundation, the concrete should be designed to have

high density and low permeability so that the concrete is able to resist the

negative effects of the environment. Only concrete with low water cement

ratio (<0.45), high slump (>150mm) and high cement content (>400kg.m3)

can have high density and low permeability. Also, the clear spacing

between rebars should be exceeding 125mm or preferably 200mm.



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7) Appropriate Strength and Stiffness

The size of most bored piles will be controlled by the peripheral area and

base area that are needed to develop the required axial load

resistance/capacity. Therefore, high-performance concrete is usually not

needed. The mechanical properties of the hardened concrete can be

satisfied in such instances without difficulty. However, provision of appropriate

compressive strength where high levels of combined bending and axial

stress occur must be dealt with in some cases, especially soft ground and

sloping sites.

8) Low Heat of Hydration for Large Volumes of Concrete

Careful attention must be given to the design of concrete for large-diameter

bored piles so that excessive heat does not generate excessive heat to

cause thermal tensile cracking.

Detail information requirements for concrete placement techniques and what to be

looking for during inspection of the concreting procedure? Refer elaborations below.

Allowable compressive stress fca=0.25fcu, but fca usually discounted about 20% for

uncertainty in tremie concreting in collapsible subsoil and especially when

bentonite slurry is used. Other concrete properties specified: W/C=0.4 to 0.55

with minimum slump 130mm to 220mm or higher & with superplasticizer.

Concrete shall appear:

To be homogeneous & have a high resistance against segregation;

To be of high plasticity and good cohesiveness;

To have good flowability;

To have the ability to self-compact; and

To be sufficiently workable for the duration of the placement procedure,

including the removal of any temporary casings.

Consistency ranges for fresh concrete in different conditions (BS EN 1536) are as

follows:

Flow diameter range,

mm

Slump range,

mm

Typical conditions of use

(example)

460<D<510 130<H<180 Concrete placed in dry hole

conditions

530<D<600 H>160 Placed by pumping or placed in

submerged conditions under water by

tremie pipe

570<D<630 H>180 Concrete placed by tremie pipe in

submerged conditions under a

stabilizing fluid

Note: The measured slump (H) or flow diameter (D) is to be rounded off to the

nearest 10mm.



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For large & long bored piles or concreting taking more than 2 hours to complete,

retarder admixture should be used to ensure slump of the concrete near the

base remains more than 100mm at the end of concreting. Why? How to check

the concrete is suitable with high quality for tremie concreting?

Concreting should be carried out immediately after the base is cleansed.

Concreting should be continuous and uninterrupted. Records/measurements of

consumption of concrete per unit depth (in 1m to 3m intervals) should be taken

and plotted with depth/location of temporary casing & toe of tremie pipe plus

the theoretical concrete volume to check localized cavities or overbreak.

When the final casting level is well below the working platform, the fresh

concrete should be protected against contamination from above by concreting

above the cut-off level (at least 0.5m), by backfilling the empty bore with

suitable material or by maintaining a stabilizing fluid inside the empty bore until

the concrete has set.

The tremie pipe shall be water tight at all its joints and smooth to allow free flow

of concrete. The internal diameter of tremie pipe should at least 150mm or 6

times the max aggregate size (whichever is the bigger), but not to exceed 0.6

times the inner width of reinforcement cage. The tremie pipe shall extend to the

bottom of the pile at the commencement of the concreting. A bung or plug of

suitable material, to prevent mixing of concrete with any fluid in the tremie pipe,

shall be inserted into the pipe before commencement of concrete placement.

As the first batch, a cement enriched mix or a charge of cement mortar may be

used to lubricate the tremie pipe. To allow the first concrete to leave the tremie

pipe, the pipe shall be lifted slightly, not exceeding a value equal to the inner

diameter of the tremie pipe. Placement shall then proceed quickly to fill the

entire base of the pile so that no concrete which may have segregated at the

beginning of the discharge is trapped. During subsequent placement the tremie

pipe shall be withdrawn progressively as the concrete rises in the bore. The

tremie pipe shall at all times remain immersed in unset and workable concrete

(min 1.5m or >2.5m for pile diameter D>1.2m) which has previously been placed

and shall not be withdrawn from the concrete until the completion of the

concreting process. Tremie pipe shall not be extracted too quickly as the

resulting suction can lead to pile imperfections.

The extraction of temporary casing shall not be started unless the concrete

column has reached a sufficient height inside the casing to generate adequate

excess pressure to protect against inflow of water or soil at the tip of the casing

and to prevent the reinforcement cage from being lifted. The extraction shall be

carried out while concrete is still of the required workability. The supply of

concrete and the rate of extraction of the casing shall be such that no inflow of

soil or water occurs into the freshly placed concrete, even if a sudden drop of

concrete level should occur when a cavity outside the casing is uncovered. This



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is particularly important in loose or soft ground or close to the pile top (BS EN

1536). The depths of casing and of the tremie pipe shall be recorded.

What should be done if the immersion of the tremie pipe is accidently lost during

concreting?

Sampling of concrete on site for compressive strength testing shall be as follows

(BS EN 1536 Clause 6.3.3.4):

One sample (=4 cube specimens) for each of the first 3 piles on a site;

One sample for every subsequent 5 piles (15 piles if the individual

concrete volume is <4 m3);

Two additional samples after interruptions of the works longer than 7 days;

One sample for every 75 m3 of concrete cast on the same day; and

At least one sample for every pile cast where concrete stresses require

concrete classes C35/45 and above.

n) Reinforcement cage placement

Generally, main longitudinal reinforcement, As= 0.5% to 1% or more if designed

as tension pile or large lateral is anticipated. The minimum main reinforcement

shall be 4 bars (ribbed bars) of at least 12mm and the spacing between bars or

bundles shall be 100mm to maximum 400mm and evenly spaced. Actual As

required depends on tension or lateral loads or moment on pile due to ground

movement, etc.

Unless otherwise specified by design to cater for ground movement/tension/

bending, etc., the minimum amount of longitudinal reinforcement as

recommended by BS EN 1536 shall be as follows:

Nominal pile cross section, Ac Minimum area of longitudinal

reinforcement, As

Ac<0.5m2 (or pile diameter, D>0.8m) As>0.5%Ac

0.5m2 <Ac<1.0 m2 As>0.0025 m2

Ac>1.0 m2 (or pile diameter, D>1.2m) As>0.25%Ac

Lateral helical or transverse reinforcement should be at least 6mm or one quarter

of the maximum diameter of the main longitudinal bars at 100mm to maximum

300mm spacing. The transverse reinforcement shall fit closely around the main

reinforcement bars and be bound/fixed by using wire, clips or spot welding.

Additional supports such as stiffening rings/lacing/oblique bars can be

necessary. Net holes to enable tremie concrete to flow out the reinforcement

cage without jams/clogs should be at least 100mm x100mm. Cover to

reinforcement usually is about 75mm in dry holes, non-aggressive subsoil &

grade of concrete >35 is used. For wet holes cover should be 75mm to 125mm or

moderate aggressive subsoil in dry holes. For aggressive subsoil in wet holes,

special treatment by specialist is required. (AASHTO (2007) recommends that



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normally As should be 1% to 2% (mainly for bridges, retaining walls and for slope

stabilization), but may be 3% in high seismic zones or high lateral load sites (soft

ground/unstable slope). BS EN 1536 also recommends that minimum concrete

cover to reinforcement should be minimum 75mm when the bored piles are

constructed without a (full) casing, etc. The concrete cover may be reduced to

40mm to the external face of a permanent casing or lining where used.

Practical minimum As is normally 0.5% for bored piles in stable ground with

negligible bending and tension. Only deformed rebar with fy>410 MPa should be

used if bentonite/clay/polymer slurry is used to stabilize drilled shafts. Rebars

should be bundled if necessary to ensure clear net holes of more than

100mmx200mm to enable concrete to flow out the reinforcement cage or

spacing of rebars (main & transvers) should be10 to 20 times the maximum

aggregate size. Cover for reinforcement recommended by AASHTO for W/C=0.4

to 0.5 concrete for bored piles of 1m, 1m to 1.5m & >1.5m should be respectively

75mm, 100mm and 150mm. If W/C>0.5, the cover should be increased by 20%.

This is because higher W/C will result in higher concrete permeability & more

shrinkage.

Joints /couplers in reinforcement bars shall be such that the full strength of each

bar is effective across the joint. Reinforcing bars shall not be welded at or near

bends, but spot welding is permissible (BS EN 1536).

The reinforcement cages shall be such that the cages can be lifted and installed

without permanent distortion and that all bars remain in the correct position.

To ensure the concentric position of the reinforcement cage and the necessary

concrete cover, proper spacers/centralizers shall be arranged symmetrically

around the cage with at least 3 spacers at each level and level intervals of not

more than 3m. Spacers shall be designed and manufactured using durable

material (plastic or at least grade 35 concrete).

The reinforcement shall be installed and placed in the borehole as soon as

possible after the cleaning of the pile bore. The installation of the reinforcement

has to provide for its alignment with the pile axis and maintain the correct

concrete cover over its full length. During concrete placement, the

reinforcement level shall be maintained to provide the specified projection

above the final cut-off level with 0.15m accuracy.

o) Records

As performance of bored piles is very sensitive to construction, proper and

comprehensive construction records are essential to serve as QC and criteria

for selection of piles for tests. Two types of records as specified & shown in

Annex B1 to B4 of BS EN 1536 shall be made:

The site & general information: Project name, Type of structure, Client,

Name of main Contractor & Piling Specialist Contractor, Pile diameter

or size/depth/design working load, Boring rig type/make, Method of



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shaft stabilization, Casing details, Base cleaning method reinforcement

details (drg) & concrete spec, etc.

Specific site construction procedure: Records for each bored pile

should include Pile reference number; GL & toe level; Boring date &

duration time for boring & rock socketing (if any); Depth of

temporary/permanent casing; Strata description/bore log & details of

encountered obstructions, abnormalities, site constraints, ground

movements & interruptions plus any deviation from the design

drawings/spec (if any); WT; Base cleansing method & duration time;

Material QC test results for stabilizing fluid (fresh, re-use & before

concreting); Time of inserting of reinforcement cage, date & time of

concreting & concrete quality (slump before & after concreting; cube

strength) plus measurements of concrete consumed per m intervals

(or per 2m or 3m intervals for small piles); Base grouting details (if any),

etc. Refer to end of Para 4.7 for the typical to log bored pile

installation.

Supporting/drill fluid general & particular data (Annex B3 & B4 of BS EN

1536)

If site observations or inspection of records reveal uncertainties about the

quality of installed piles, investigations shall be carried out to determine their

condition and if remedial measures are necessary. Records shall be kept for

at least 5 years after completion of works.

p) Pile Testing

Refer Para 3.3 (d) for preliminary pile tests and Para 4.2 (l) below.

Load tests are the most important design validation and are conducted to

determine the load carrying capacity of the piles. Types of load test:

SSLLTT: CRP, MLT (ASTM D1143 for compression, D3689 for tension,

D3966 for lateral). PPDDAA/HSDPT (ASTM D4945-12). BBiiddiirreeccttiioonnaall llooaadd tteessttss (SS CP4:2003 recognizes it as SLT). Refer

www.YJACKpiletest.com SSttaattnnaammiicc llooaadd tteesstt

Applications & limitations of these tests? Test standards? CP requirements: frequency of tests? Interpretation of test results? How to select piles for tests? Basis? Results of testing are not everything unless the results can be representative for the untested ones on safe side. How? Comprehensive inspection & recording for drilling (pressure, rate/timing & observation of

http://www.yjackpiletest.com/



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water return/cuttings, etc.) & grouting (pressure, volume consumed, etc.) are useful guides to select representative piles for tests. PDA shall be conducted & interpreted by Dfi/FQA accredited tester (Advanced or expert Level). Compliance with proper standards is important. Reporting format/presentation & interpretation for pile tests? WCGW in pile tests? Case Histories?

Maximum test load (MTL) for preliminary & working pile tests?

Problems of MTL>4000T? Serious foundation problems for supports of

kentledge. Why? Case history of failure?

Can Bidirectional load tests be considered SLT? Advantages of

Bidirectional load tests (T-cells, O-cells & C-cells) for load tests of bored

piles?

The maximum test load of preliminary load test (MLT or bidirectional load

tests) should be until ultimate load or 2.5 to 3 times the design working

load as recommended by Singapore Standard CP 4:2003 (Clause 7.5.4).

Usually 1% to 2% of the working piles should be selected (based on

installation records) for load tests to 2 times the pile design working load

although in certain conditions maximum test load of 1.5 times may be

used. PDA (ASTM D4945-12) can only substitute some of the static load

tests if the numbers of SLT is large (SS CP4:2003).

Other important issues that will be discussed in detail during the lecture

are:

When instrumented test pile should be carried out? Purposes? How?

How to identify/select bored piles that are likely have structural

integrity problems (with particular reference to subsoil conditions,

boring operation, bored shaft stabilization method, placement of

reinforcement cage & concreting)? What are the good construction

practices to mitigate these problems?

What are the applicable/suitable pile load test methods for bored

piles of small capacity (<300 T), medium capacity (300 to 1000T),

large capacity (1000 T to 2000 T) & very large capacity (>2000 T)?

What are the applications & limitations for SLT/MLT (ASTM D1143),

Bidirectional load tests (CP 4, SS), Statnamic load Tests, LSIT/PIT

(ASTM D5882-00) & HSDPT (ASTM D4945-12)? Test standards?

What are the common defects & errors for pile load test methods

such as SLT/MLT, Bidirectional load tests, Statnamic load Tests &

HSDPT? The requirements of test standards commonly ignored or

not fully complied with?



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What are the common tricks & malpractice in pile tests for

conventional contract with quantities remeasureable, direct nego

design & build contract with fixed sum or quantities

remeasureable? Mitigations?

How to determine the ultimate load from load test results?

What is the main uncertainty of load test results?

Refer Para 4.2 (l) for answers.

q) Pile spacing: Usually 2 to 2.5 times the pile size if subsoil mainly cohesive and

pile derive resistance mainly from end bearing or near the base.

3.3 Scope of Design Validation

Basically design validation is aimed to ensure the design requirements about

safety, serviceability and durability stipulated by CP (BS 8004/EC 7) are actually

achieved at site through inspection and tests for quality, workmanship and

performance. In another words, design validation can mean good construction

practice to fulfill the design as shown in drawings and as specified.

BS EN 1536:2000 “Execution of special geotechnical work-Bored Piles” has spelt

out the details of design validation to ensure bored pile performance:

Technical requirements & QC tests for Materials & Products for bored Piles

(materials for concrete & grout, concrete insitu, grout, stabilizing fluid,

reinforcement bars, couplers, spacers, etc.).

Design related considerations (construction tolerance, excavation/boring,

reinforcement, etc.).

Works Execution & construction requirements/controls for excavation/boring,

fixing & placement of reinforcement cage, concreting, etc.

Requirements for supervisions (pile construction & testing)

Requirements for records

Other issues about design validation are discussed as follows:

a) The most important design validation for bored pile construction is to validate

fsu & fbu & overall performance with respect to capacity, settlement &

structural integrity conditions. Types/methods of tests, their frequency (1%-2%)

& acceptance criteria? Basis of selection of piles for tests shall be based on

subsoil conditions, drilling & concreting records? What standards shall be

adopted? How to carry out the design validation in practical ways and in

compliance with CP/established design guides? It is extremely important that

the basis & criteria for selection of method & location of tests shall be based

on sensible/adequate inspection details & records. Results of testing are not

everything until and unless the results can be representative for the untested

ones. How to achieve these? Examples? Case histories?



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QC for boring with respect to proper boring rig equipment/tools, criteria to

terminate boring, time limit of boring (3hrs/6hrs, basis?), alignment control &

acceptance criteria? How to assess & control bored hole collapse? When

bored hole is prone to collapse? What method shall be used to mitigate

against bored hole collapse?

b) What types/methods of QC for installation of reinforcement (typically

As=0.5%-1%)? Basis? What are the problems & how to select suitable type

joint/coupler/spacer for reinforcement? Technical requirements & QC for joint

& spacer? Technical requirements & QC/inspection for reinforcement cage?

Reinforcement cage shall be rigid & without undue deformation during

pitching & handling. How?

c) What types/methods & frequency of QC tests for concreting? Common

methods & problems of concreting? QC test on bentonite or polymer slurry?

Why concreting shall be fast, continuous & uninterrupted? Why slump of

concrete shall be at least 150mm to 220mm? Why high slump of shall be

maintained (>150mm) from the beginning of concreting until concreting is

completed for the first batch of discharge? Maximum fsu that can be

mobilized depends on shear strength of the surrounding soils, later pressure

exerted by the fresh concrete before hardening, conditions of drilled shaft,

etc. Lateral pressure exerted by fresh concrete depends on slump and depth

of fresh concrete column, etc. How slump loss of concrete can happen by

time & its effect on maximum side friction that can be mobilized? When

retarder admixture shall be used? Criteria of terminating concreting? What

are the QC requirements for concrete mix quality (cohesiveness,

homogeneous, high cube strength, high workability/slump, W/C ratio,

admixture, cement content, acceptable bleeding limit)? Acceptance

criteria? Frequency of tests?

d) Methods/types, frequency and acceptance criteria of load tests for bored

pile? Types of static load tests and dynamic high strain tests? Bi-directional

load tests and statnamic load tests? Types/methods of tests to check

structural integrity of bored piles? Criteria of selection of bored piles for tests?

Acceptable test standards & specifications?

Normally 1% to 2% or more of the piles installed should be selected for pile

tests (static and/or high strain dynamic pile test/PDA) to check and verify the

capacity performance & structural integrity & also to assess the suitability of

the construction method for the specific site conditions. For collapsible

subsoil, sonic logging tests and other Pile Integrity Tests should also be

included (3% to 5%). Criteria of selection of piles for tests shall be based on

installation records to ensure the test results are representative for the

untested ones on the safe side. EC7-1 requires that the test locations shall be

representative of the site of the pile foundation and one of the test piles shall

be located where the most adverse ground conditions are believed to occur

(based on installation records).



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The pile load test procedure (ASTM D1143), particularly with respect to

number of loading steps (at least 6 steps) & duration of these steps (until

settlement rate < 0.1mm/20 minutes) and the application of load cycles (2/3

cycles), shall be such that conclusions can be drawn about the deformation

behavior, creep and rebound of a piled foundation from the measurements

on the pile. For trial piles (preliminary test piles or instrumented test piles), the

loading shall be such that conclusions can also be drawn about the ultimate

failure load. The number of trial piles required to verify the design SHALL

depend on the following:

The ground conditions & their variability across the site;

The Geotechnical Category of the structure, if appropriate;

Previous documented evidence of the performance of the same type

of pile in similar ground conditions;

The total number & types of pile in the foundation design

As pile testing to check structural integrity and performance

(capacity/resistance, deformation & creep characteristics) are expensive

and essential design validation, it shall be properly planned, conducted,

recorded and interpreted by qualified engineer and trained personnel to

ensure the results are credible and in compliance with the requirements of

the adopted test standards.

A factual report shall be prepared for all load tests. The report shall include:

A brief description of site conditions with photos;

A brief description of generalized subsoil conditions based on SI

reports;

Pile type/size/length/design working load

Description of pile installation records & any problem encountered

during the works;

A description of the loading & measuring apparatus & the reaction

system;

Test standard adopted & drawing showing layout of load test

arrangement, spacing of Kentledge supports to test pile position &

supports of reference beams, etc.;

Calibration documents/certs for the load cells, the jacks & the gauges;

The installation records of the test pile;

Photographic records of the pile, load test layout & the test site;

Test results including date/time, load applied, displacement of each

gauges/load cells;

Time-displacement plots for each applied load when a step loading

procedure is used;

The measured load-displacement behavior; and

Reasons for any departures from the above requirements.



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e) Durability assessment requirements? Chemical properties (pH value, chloride

& sulphate contents) of the subsoils? Refer Section 10 of BS 8004 for design

guides. How?

3.4 Construction Controls/QA for Bored Piles

QC & requirements for site supervision as per CP/EC 7 requirements shall be

included & provided.

It shall be specified that the installation of all bored piles is closely supervised &

monitored (by qualified personnel) & records are made as the piles are installed

including pile reference number, about the quality of installed piles.

Investigations shall be carried out to determine the conditions and if remediation

are necessary. Equipment used, date & time of installation (plus interruptions, if

any), peculiar observations during drilling/grouting, obstruction encountered,

pile deviations & as-built elevation shall be recorded to facilitate selection of pile

for testing. If observations & inspection of records reveal uncertainties, designer

shall be consulted for necessary design decision.

Important workmanship and quality requirements for materials & their QC tests

plus acceptance criteria shall be indicated on drawing. Design capacity & the

required performance tests & acceptance criteria shall also be indicated.

Piles that shall be selected for static load test shall be at least 1 to 2% or minimum

2 numbers per site. If some of the static load tests are to be replaced by high

strain dynamic pile tests or PDA test, at least 5% to 10% of piles shall be tested.

PDA tests shall be strictly according to ASTM D4945 and shall be planned,

conducted and interpreted by DFI or FQA accredited test engineer with

advanced level certification. Structural integrity assessment by PDA, static load

test (Prof Chin method) and or low strain integrity tests (ASTM D5882) shall be

carried out after detail examination of construction records. Normally about 5%

to 10% piles shall be selected for structural integrity tests.

Important to understand and differentiate what are the “defective design” and

the “defective construction” for displacement piles and how they can lead to

problems related to durability, structural integrity, distress and failure.

3.5 Common defective designs are as follows:

a) Defective design generally means design not in compliance with the

requirements stipulated by local bylaws, codes of practice (BS8004/EC 7) or

not in line with normally locally accepted/established design

standard/practice with particular reference to improper/inadequate SI/GI,

incomplete/inadequate geotechnical & inadequate structural design

verification/calculations, selection of design parameters not

properly/adequately justified, improper method/model of analysis, improper

selection & quality of materials and workmanship, improper method of



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construction, improper/ inadequate scope of design validation,

unclear/ambiguous specification and construction details, etc.

b) Scope of SI/GI shall be adequate to meet the minimum requirements

specified in CP or established local practice/guidelines such as REAM

GL6/2004 or BS 5390 (1999) or EC 7 Part 2 & 3. Inadequate scope of SI to

procure the reasonably accurate subsoil profile with particular reference to

the critical information such as location of suitable/reliable bonding/bearing

strata, site history, WT conditions, localized hard materials/obstructions that

are prone to pile installation problems, bedrock conditions & soil type &

strength properties for each distinct layers, collapsible strata, etc. SI shall be

reliable and adequate as per BEM 4/2005 requirements.

c) Unawareness of site conditions and site history that are prone to have serious

lateral and vertical forces due to ground movements such as creeping

slopes, settling ground, ground prone to subsidence, soft ground,

uncontrolled fill ground, fill ground with underground water flow along the

previous water paths/streams, etc. How these can happen? How to identify

these problems through detail site survey before and after earthworks?

Mitigations? These information and problems can be addressed by proper SI

and site inspection by qualified Engineer/designer. Case histories?

d) Inadequate evaluation of subsoil properties & selection of appropriate fsu &

fbu. If bonding zone/stratum not clearly defined due to inadequate SI, design

variation may be excessive or drastic.

e) Inadequate evaluation of subsoil properties and pile installation process/

drilled shaft stabilization methods that can cause problems during installation

such as drilled shaft collapse, pile deviations/deflection, uncertainty in

bonding zone, etc.

f) Inadequate evaluation of subsoil profile, method of installation requirements

& criteria of termination of boring and method of rock socket construction not

properly specified.

g) Inadequate or unclear specific technical works specification & requirements

for pile installation method (boring/concreting/ reinforcement), pile joint, pile

anchorage and spacer quality. Concrete mix & reinforcement quality

requirements? Lack of provision of adequate QC tests with respect to

frequency, acceptance criteria & need of remediation, etc.

h) Inadequate or unclear/ambiguous works specification & technical

requirements about inspection and recording required, etc.

i) Inadequate or unclear design related to the scope of design validation with

respect to adequacy and relevancy for material quality, workmanship and

pile performance (capacity/bond strength, settlement and structural

integrity).

j) Inadequate evaluation of site construction problems and inadequate

mitigations against WCGW at site.

k) Inadequate provision for requirements for quality supervision as required by

BS 8004/EC 7.



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3.6 Common defective constructions are as follows:

a) Defective construction generally means construction not in compliance

with the works specifications with particular reference to improper

construction method/improper equipment/improper construction

controls/procedure, improper/substandard materials/workmanship,

untrained & inexperienced workers & works operators/supervisors,

incomplete inspection & recording, inadequate/improper QC & design

validation tests, improper/ inadequate supervision by qualified personnel,

etc.

b) Poor construction practice related to improper sequence of works,

improper or inadequate inspection and recording by qualified supervisors.

c) Inadequate or improper construction controls related to piling

workmanship and alignment (verticality, deviation, rotation deflection,

pile heave, pile termination criteria, etc.).

d) Non-compliance with the instruction from the supervisors.

e) Refer to slides presentation for more defective construction for bored pile

construction related to boring, handling reinforcement cage, drilled shaft

stabilization/slurry handling, concreting, etc.

3.7 Construction Checklist for Bored Pile Installation

Construction Checklist and relevant problems and issues related to

supervision of bored pile installation that RE should be aware:

a) Desk study: to collect & study all relevant documents and understand

the scope & nature of piling works involved. Important documents are:

contract document, SI factual report, SI Interpretation report, pile

design report with design drawings, specifications & BQ. In case of

doubt, consult the designer for clarification if necessary.

b) Check and inspect the site conditions and understand how the bored

pile installation works will affect the nearby buildings/structures,

services, etc., (if any). Dilapidation survey & mitigative measures

should be carried out if there are buildings/structures/services likely to

be affected.

c) Check and understand the Method Statement prepared by the

Contractor. Seek explanations & clarifications where necessary.

Method statement should be adequate & comprehensive as explained

in Para 1.5 (page 6). As performance of bored piles is very sensitive to

construction, all the construction requirements as stipulated by BS EN

1536 especially the issues discussed in Para 3.2 items (j) to (n) should

be adhered.

d) Are the proposed drilling rigs, equipment and tools appropriate with

the necessary output to complete within the scheduled time frame

with some contingencies? Consult others if not well-versed in the

subject. Are the Contractor’s operator & site manager well-versed in



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bored pile installation problems and issues plus construction

requirements as discussed in Para 3.2?

e) Are the proposed methods & materials of drilled shaft stabilization

satisfactory and in compliance with the requirements specified by the

designer and BS EN 1536? Refer Para 3.2 item (k) for construction

requirements that should be observed at site.

f) Check and enquire methodology & system for validation of material

quality (stabilizing fluid, tremie concrete mix, reinforcement cage,

spacers/centralizers, couplers, etc.,) product/workmanship tolerance,

QC assurance, etc.

g) Are the proposed method/sequence of reinforcement cage

placement & concreting satisfactory? What are the checks and

inspections plus records for quality and/measurements or dimensional

tolerances before and after placement of reinforcement cage and

concreting? Refer Para 3.2 items (m) & (n) for construction

requirements that should be observed at site.

h) Check bored pile termination criteria & construction controls? If such

criteria are not clearly specified in design drawing or specification,

seek clarification from the designer.

i) Is the noise level and ground movement/deformation or change of

water table acceptable? Potential damages to nearby buildings &

services?

j) What are the typical bored piling problems in limestone formation &

soft ground (if applicable)? Construction controls and mitigations

against the problems?

k) Scope & types of recording and format?

Proper records as discussed in Para 3.2 (o) shall be observed to serve

as QC & criteria for pile selection for tests.

l) Pile tests to check structural integrity & capacity? Types of tests and

test standards? Frequency? Interpretation?

Refer Para 3.2 (p) for requirements that should be observed at site.

Detail checklist for bored pile installation is given as follows:

The following is a detail checklist to follow when constructing a bored pile or drilled shaft. The answer to each of these questions should be "YES" or "NO" or "NA" unless drawings, specifications or specific approval has been given otherwise. CONSULT WITH CRE/RE or RESPONSIBLE ENGINEER FOR YOUR SPECIFIC PROJECT RESPONSIBILITIES/DUTIES. This checklist is modified from FHWA



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Contractor & Equipment Arrive on Site YES NO NA

1. Has the contractor submitted bored pile Installation Method Statement including specific 3M, sequence of works & QC, etc., to show compliance with the specification and design drawings?

1A. Can the proposed drill rig & tools in the method statement complete the boring operation for each bored pile as designed within 6 hrs or as specified?

2. Has the Bored Pile Installation Method Statement been checked & approved?

3. Does the Contractor have an approved concrete mix design that can meet the requirements specified?

4. Has the contractor run the required Trial Mix and slump loss test for the concrete mix design up to 4 hrs or up to maximum estimated concreting time for each bored pile?

5. If concreting is estimated to take more than 1.5 hours, has the Contractor performed a satisfactory slump loss test for the extended time period till completion of concreting?

6. If the Contractor proposed a blended bentonite or polymer slurry, do they have an approved Slurry Management Plan/method statement to meet all the QC requirements (pH value=7 to 11, density <1.1 g/cc, sand content <4% & viscosity/Marsh value=30 to 50) specified?

7. Is the Contractor’s technician qualified to log, to describe subsoil strata & to take soil/rock samples of the bored hole (shaft excavation) in accordance with BS 5930:2015?

8. Has the Contractor carried out dilapidation survey to meet the safety & protection requirements for the nearby structures/utilities as specified?

9. Has the site clearing & platform preparation been completed and ready for Bored pile installation?

10. Does the Contractor has all the equipment and tools proposed in the method statement and mobilized to the site for inspection?

11. If casing is to be used, is it the right size & stiffness in accordance with the specification or method statement?

12. Does the Contractor have the proper equipment & facilities to mix & test the quality for the proposed & approved slurry?

13. Is a desander required for the recycled slurry?

14. If a desander is required, does the Contractor have it on site and operational?

15. Does the Contractor's tremie pipe meet the requirements specified with respect to size, surface conditions, water-tightness, etc.?

16. Do you have all the required bored pile/drilled shaft forms (for logging the subsoil strata, rock socket construction, base cleanliness, concreting log & volume consumption/depth, etc.) that need to be filled out during the bored pile installation?

16A. Are all the forms include all the important details to be filled as per requirements of BS EN 1536:2000?



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17. Do you understand & familiarize with all of the necessary forms to record bored pile installation (if not contact the CRE/designer for assistance)?

Trial/test Shaft

18. Is the trial/test shaft positioned away from the production shafts or as suggested by CRE/RE or as specified in the contract documents?

19. Has the Contractor performed a successful test hole/trial shaft in accordance with the approved method statement?

20. Can the Contractor complete a bored pile including boring, base cleaning, placement of reinforcement cage & concreting within the same working day?

21. Is the proposed construction method of rock socket suitable (using proper rock auger/bucket/special tools)?

22. Has the Contractor revised the technique and equipment to (and the revision approved) to successfully construct a bored pile within the same day unless otherwise approved?

Shaft Excavation & Cleaning

23. Is the shaft being constructed in the correct location and within the tolerances specified?

24. Does the Contractor have a benchmark so the shaft can be constructed and inspected to the proper elevations?

25. If core holes are required, has the Contractor taken them in accordance with the specification?

26. If a core hole was performed, was the Rock Core form completed and did the Contractor maintain a log as specified?

27. If the Contractor is using slurry, can they perform tests and report results in accordance with the practice/specification?

28. Is the slurry level being properly maintained in accordance with the practice /specification?

29. Are the proper number and types of tests being performed on the slurry in accordance with the practice/specification?

30. Are you logging the Soil and Rock Excavation forms?

31. If permanent casing is being used, does it meet the specification?

32. If temporary casing is being used, does it meet the specification?

33. Is the Contractor maintaining an excavation log in accordance with the specification?

34. Is the shaft within the allowable vertical alignment tolerances as specified?

35 Is the shaft of proper depth after checking?

36. Does the shaft excavation time meet the specified time limit (< 6hrs)?

37. Does the shaft bottom (cleanliness conditions) meet the requirements in accordance with the practice/specification?

39. Did you complete the Shaft Inspection form?



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Reinforcement Cage Placement

40. Is the rebar the correct sizes and configured in accordance with the project design drawings?

41. Is the rebar properly tied to ensure rigidity and stiffness as required without excessive deformation during handling?

42 Does the Contractor have fixed the proper and adequate spacers for the reinforcement cage to ensure the reinforcement cage is centralized in the hole?

42A. Does the Contractor have an approved method for centering & supporting the reinforcement cage configuration?

43. If the reinforcement cage was spliced/coupled, was it done in accordance with the specification?

44. Is the reinforcement cage secured from settling and from floating (during concrete placement the cage sometimes rises with the placement of the concrete)?

45. Is the top of the steel cage at the proper elevation in accordance with the specification?

Concreting Operations

46. Prior to concrete placement, has the slurry been tested in accordance with the specification to check quality?

47. If required, was the temporary casing removed in accordance with the specification?

48. Was the discharge end of the tremie pipe maintained in the concrete mass with proper concrete head above it?

49. If free-fall placement (dry shaft construction only), was concrete place in accordance with the specification?

50. Did concrete placement complete within the specified time limit as approved in the method statement/specification?

51. Are you filling out the Concrete Placement and Depth/Volume forms?

52. When placing concrete, did the Contractor overflow the shaft until good concrete flowed out?

53. Were concrete acceptance tests performed as required?

Post Installation

54. If shaft is constructed in open water, is the shaft protected for seven days or until the concrete reaches a minimum compressive strength of 20 MPa in accordance with the specification/method statement?

55. Is all casing removed to the proper elevation in accordance with the specification/method statement?

56. If required, has the Contractor complied with the specification related to Non-destructive Evaluation?

57. Is the shaft constructed within the acceptable construction tolerances?

58. Has the bored pile installation recorded with details as specified in Annex B1 to B4 of BS EN 1536?



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Notes/Comments

Construction details that shall be recorded are explained and detailed in Cl.10 of BS EN 1536

Forms to record bored pile installation are suggested as follows:

a) Form 1: Bored pile installation log (usually logged by Contractor’s

technician & checked & verified by Consultants’ site

supervisor/RE).

b) Form 2: Bored pile inspection record (usually checked & logged

by Consultants’ site supervisor/RE).

c) Form 3: Bored pile Concrete placement log (usually logged by

Contractor’s technician & checked & verified by Consultants’ site

supervisor/RE).

d) Form 4: Bored pile Concrete Volume record (usually logged by

Contractor’s technician & checked & verified by Consultants’ site

supervisor/RE)



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Form 1: BORED PILE INSTALLATION LOG

1. Project: ………:……………………………………………………………………………. Page………of………….. 2. Contractor:………………………………………………………………………………….. Pile Ref No: ………… 3. Logged by:…………………………………………. Date:.…………………………… Pile Diam: ………….. 4. Inspected by………………………………………... Date:…………………………….

5. Construction Drg No.:

Casing information ID:………Top Elev: …… OD:……..Bot:…….. Elev:……... Length:…………… Type: ……………….

Elevation/RL GL: …….. WL: ……. Cut off L: ……

Dimensions Soil auger dia: ………………. Rock Auger dia: …….......... Drill bucket dia: ……………. Cleanout bucket dia: …….

Drill Fluid Type: …………………….. Test results: …………. ……………………….. Meet spec:

Concrete & Reinf Theoretical vol: …m3 Actual vol: ………… m3 Overbreak: …………%

Reinf Cage: …………

Depth (m)

Date/time Elevation/ RL (m)

Drill Tool

Soil/rock strata description (BS 5930:2015) & observations/abnormalities

In out

Rock socket construction details: Tools used & time start & end

Base cleaning method:

Signatures & date from Contractor & Client/consultant representative



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Form 2: BORED PILE INSPECTION RECORDS

1. Project: ………:……………………………………………………………………………. Page………of………….. 2. Contractor:………………………………………………………………………………….. Pile Ref No: ………….. 3. Logged by:…………………………………………. Date:.…………………………… Pile Diam: ………….. 4. Inspected by………………………………………... Date:…………………………….

Type of drill fluid: ………………………………………….. .. Reinforcement cage information Drill QC test results: ………………………………………….. Proper # main bars & size: ………… Base cleanout method: …………………………………….. Size of lateral bar & spacing: ……………. Date/time of final cleanout: ……………………………… Side standoffs: ………………………. Base elevation: …………………. External diam of cage: ………….. Estimated base diam: ……….. Type of coupler: ……………………. Shaft plumbness: ………………. Ties & connections: ……………….. Pile position deviation:……………. Type of spacer:…………………………

Results: Satisfactory/unsatisfactory Signatures& date from Contractor & Client/consultant representative Measured by: ……………………………… Date & time: …………………………………



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Form 3: BORED PILE CONCRETE PLACEMENT LOG

1. Project: ………:……………………………………………………………………………. Page………of………….. 2. Contractor:………………………………………………………………………………….. Pile Ref No: …………… 3. Logged by:…………………………………………. Date:.…………………………… Pile Diam:………………. 4. Inspected by………………………………………... Date:……………………………. 5. Method of concreting:…………………….. Concrete mix supplier:………………………..

Placement method: Freefall/tremie/pumped

Deairing method: Relief valve/tremie plug/tremie cap Shaft top Elev: …………………… Shaft bottom Elev: …………….. Top of rock Elev: ……………….. Cut-off level: ……………………….

Tremie pipe size: ………… Depth to water inside: ……. m. OD casing at start: ……. Rebar Cage top Elev at start: ………. At finish: …………..

Truck No.

Concrete Volume

Arrival time

Start time

Finish time

Tremie depth

Depth to concrete

Notes/observations (depth of casing & tremie pipe, etc).

Concrete Volume delivered: ……… Placement time: start: …………. Finish: ………… (Casing removal)

OD Top Elev. Bot Elev. Start Finish Reinf cage centred: …. Concrete finished: …..

Casing

Casing removal

Notes

Signatures& date from Contractor & Client/consultant representatives.



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Form 4: BORED PILE CONCRETE VOLUME

1. Project: ……….…………………………………………………………………………….. Page………of………….. 2. Contractor:………………………………………………………………………………….. Pile Ref No: ……….. 3. Logged by:…………………………………………. Date:.…………………………… Pile Diam: …………. 4. Inspected by………………………………………... Date:…………………………….

Concrete Volume-depth Graph (indicate Elev of toe of tremie pipe & toe of casing)

Concrete Volume (m3)

Total Vol delivered: VD= ………….. Vol in lines: VL= ……………………….. Wastage: VW= …………………………. Vol placed: VP=VD-VL-VW= ……… Theoretical Vol: VT= ………………… Over pour: OP=VP-VT= ……………..

Cross-sect area of rebars & access pipe, AR= ………. m2

Rock socket length, RSL= ……...m2 Est. rock socket vol from graph, VRS= …….. m2 Actual rock socket vol, VRS



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4. Site Supervision of Micropile Installation

4.1 Execution standard & Installation processes

BS EN 14199:2005. “Execution of special geotechnical works-

Micropiles” elaborates the scope of installation and the important

micropile construction requirements that site supervisors shall know to

ensure compliance at site.

Important scope of inspection/monitoring by the site supervisors for

various construction stages and requirements of micropile installation

are summarized in the following Table and elaborated in Para 5.2

below: Construction activity Scope of Inspection/ monitoring/testing. Acceptance criteria

1 Pre-construction Site inspection & desk study of SI report

& GDR, etc. Setting up. Dilapidation

survey?

Understand the site, scope & nature of

works. Check nearby structures/

services/utilities that may be affected by

micropile installation.

Understand the subsoil conditions. Any

collapsible starta?

2 Drilling operation Check & study method statement &

types/methods & details of drilling

(machine & drill tools). Monitor drilled

hole conditions & logging. Scope &

details of records. Monitor boring

operation & observe any abnormalities.

Effects of boring & ground movements.

Suitability of drilling method & machine

(capacity & power) & tools that can

complete the drilling as specified/designed

or within 3 hrs. & without hole collapse.

Criteria of termination of boring. Record &

report for any abnormalities.

Pneumatic rotary percussion/duplex method

or wash boring method with proper

stabilizing fluid is suitable for collapsible

holes.

3 Drilled hole

stabilization

Check types/methods of drilled hole

stabilization plus their applications &

limitations to the specific site & subsoil

conditions. Required QC tests & records.

Casing is commonly used for squeezing soft

& collapsible strata or subsoil with artesian

pressure. Bentonite for sand strata with

boiling problems. Water or Polymer for

most residual soil, etc.

4 Drilled hole

cleansing

Monitor suitability & procedure of

flushing fluid until clean before grouting.

Refer spec.

Base & borehole cleansing should be

repeated if grouting is not carried out

within ½ hrs.

4 Placement of

reinforcement pipe or

rebar bundle/cage

Check conditions of joints, couplers,

centralizers & conditions of

reinforcement (tolerances) during

placement into the hole. Strength of

joint/coupler should be tested especially

for tension pile.

Ensure the requirements of joint, couplers

& centralizers are observed & concentric

position of reinforcement in the hole.

5 Grouting operation Check grout mix and the QC

requirements. Monitor grouting

operation & records. Observe any

abnormalities, ground movements, etc.

Ensure the grout requirements for W/C

ratio, bleeding, flow & cube strength have

met what are specified. Grouting should be

continuous & uninterrupted.

Grout should be mixed by high speed mixer

(>1000 rpm).

6 Pile testing Evaluate installation records & identify

piles that may have defective

construction. Select suitable pile test

methods & test standards

Derive criteria of selection of piles for tests.

Types of pile defects & the most adverse

conditions shall be tested to ensure

representative. Make sure all requirements

of test standards are complied with.



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4.2 Important Construction Issues & Requirements for Micropiles are as follows:

a) Classification of Micropiles

Micropiles, also called minipiles, pinpiles or root piles, are small diameter

(100mm to 300mm) piles, drilled, flushed by compressed air or water with

or without bentonite/polymer, reinforced by rebars (single or bundle) or

steel pipe & grouted cast insitu replacement piles.

It is very important that micropile site supervisors shall understand the

design principle/concept of micropiles with particular reference to the

characteristics & behavior in various soil/rock conditions under various

applied loading conditions, applications & limitations, etc. How drilling,

drilled hole stabilization, placement of reinforcement and grouting can

affect micropile performance IS EQUALLY IMPORTANT to how to estimate

unit bond/friction and end bearing capacity accurately. Certainly

micropile designers and supervisors shall also know what are the

information and substrata properties that will affect micropile construction

and performance and what the construction requirements that will ensure

long term performance of micropiles. Driven small piles (<150mm) can

also be called micropiles (Cl 3.1 BS EN 14199).

Classification of micropiles is mainly and usually based on:

Applications: underpinning, foundation piles in special situations &

slope stabilization, etc.

Drilling methods: pneumatic rotary percussion, wash boring,

augering, etc.

Grouting techniques: gravity grouting, pressure grouting, multiple

post grouting, etc. Usually pure cement grout (grade fcu=30 MPa,

W/C=0.4 to 0.5, bleeding <3% (after 2hrs), efflux flow time <15 sec)

is used. Sand (up to max 25% by weight) can only be used if

micropile is more than 200mm diameter.

Reinforcement types: Single steel bar, bundle (3 to 6 bars in cage),

steel pipe, etc.

One of the common classifications cited by FHWA (based on grouting

techniques) is given below.



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b) Important differences between bored piles and micropiles are discussed

as follows :-

Basically and usually micropiles refer to small diameter piles (100mm to

300mm diameter) constructed by drilling & cement grouting with

reinforcement while bored piles refer to large diameter piles (typically

500mm to 3m) formed with or without pile casing by boring a hole in the

ground and filling with plain or reinforced concrete.

Cuttings of small holes of micropiles can be flushed out from the ground

by compressed air or pressured drilling fluid. Cuttings of bored piles are

usually & efficiently removed from the holes by soil/rock augers or

buckets though sometimes the cuttings/rocks of bored piles can be grind



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to small particles and flushed out by drilling fluid in reverse circulation

boring.

Micropiles Bored Piles

Common sizes &

capacity

100mm to 300mm diameters

with slenderness ratio up to 220.

Axial capacity = 200 to 3500 kN.

(Qstru = 0.4fcu Ac + 0.47 f y As )

500mm to 3m diameters with

slenderness ratio < 80. Usual

axial capacity = 2000 kN to

65500 kN. (Qstru = ¼ fcu Ac )

Reinforcement Steel pipe or rebar (single or

bundle), ƒy = 250 to 550 MPa.

About 2-8% steel.

Rebar cage. Usually 0.5 – 1%

steel

Drilling/boring Small drilling machine to flush

out cuttings or debris by

compressed air or water with

polymer or bentonite. Casing

may be required in collapsible

strata. Classification of drilling:

Single tube advancement by

wash boring or rotary

percussion, rotary duplex,

rotary percussion concentric

/eccentric duplex & double head

duplex.

Large boring machine (torque =

50 – 600 kN.m) using soil/rock

auger or bucket to take out the

cuttings/debris. Casing may be

required in collapsible strata or

use bentonite or polymer slurry

to stabilize drilled shaft. Boring

machine capacity is classified

according to BHP/ torque &

weight/crowd, etc.

Grout/concrete Cement grouting method:

normal tremie gravity, injection

with grouting pressure of about 1

to 10MPa with packers or tube-a-

Manchette/ secondary/post

grouting. Grout mixture: w/c <

0.45 with admixture to ensure

efflux flow (< 15 sec) & bleeding

< 3% after 2hrs) & fcu > 30Mpa.

Sand may be added if pile

size>200mm.

Fresh cohesive & homogeneous

concrete with w/c < 0.5 with

superplasticizer & slump = 150 –

250 mm, cement content > 400

kg/m3 for submerged tremie

concreting. Concreting shall be

uninterrupted & high slump

property shall be maintained

(>100mm) before concreting is

completed. Retarder shall be used

if concreting time

.>1.5 hrs.

Applications For underpinning works to

increase foundation capacity &

to arrest settlement of existing

structures. As structural

support for new structures in

difficult site constraint sites &

erratic/adverse subsoil

conditions. As dowels for

creeping slopes/grounds), etc.

Small machine, very mobile &

portable machine for very

difficult sites also possible.

As structural foundation for

large, heavily loaded structures

or structures with large lateral

loads. As foundations for site

where vibration and/or high

noise level are not allowed.

Bored piles can be sized in large

range to take large range of

loads.

Large machine with a lot of

accessories & required large

space for installation.

Limitations Low lateral load resistance

unless the ground is treated.

Expensive generally, but can be

cost-effective & competitive in

certain peculiar situations.

Required large machine & big

space to operate. Difficult at site

constraints & soft ground.



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c) Method statement

Method statement (MS) for micropiling shall be prepared by the

Contractor & checked & approved by the CRE/RE before commencement

of works. MS shall include 3M (materials, machine & manpower with

specific details), sequence of works, output of works & QC including

types, frequency & acceptance criteria of tests/ measurements or

observations, etc. Specific details about drilling, drill hole stabilization,

placement of reinforcement and grouting shall be included. Refer Para 1.3

for guide and detail requirements. Refer Para 1.3 for guides.

Criteria of terminating the micropile shall be clearly specified on

construction drawings. Critical Installation requirements shall also be

stated on drgs. The site supervisors shall seek the designers’ clarification in

case of doubts.

Duplex drilling system or equivalent shall be specified & used through

collapsible strata such as water bearing granular strata, soft & loose soils

to prevent collapse of drilled hole. Collapsible drilled hole can also be

partly stabilized by casing or duplex method in case of pneumatic rotary

percussion drilling method or by mud water, polymer/bentonite slurry in

case of wash boring drilling method.

Strict control on the density & quality of drilling fluid shall be observed, if

used. Requirements for bentonite slurry: density=1.03 to 1.15; pH value=7 to

11; Marsh Funnel flow time=32 to 60 seconds. Frequency of QC tests: at

least once daily or one set of tests per 5 piles.

Construction methods of rock socket or bond length shall be clearly

specified. Risk or uncertainty in irregular & erratic bedrock and karstic

limestone formation shall be adequately considered with necessary

mitigations. Refer to specification/drawings/designer.

Adequate scope of design validation & QC/QA scheme shall be specified

to check & verify the important critical design assumptions & performance

criteria (capacity, settlement & structural integrity).

d) Performance of micropiles is very sensitive to construction. The installation

of all micropiles shall be closely supervised & monitored (by qualified

personnel) & records are made as the piles are installed including pile

reference number, about the quality of installed piles. Investigations shall

be carried out to determine the conditions and if remediations are

necessary when there is uncertainty or deviation of installation of

micropiles from the design. Equipment used, date & time of installation

(plus interruptions, if any), peculiar observations during drilling/grouting,



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obstruction encountered, pile deviations & as-built elevation shall be

recorded to facilitate selection of pile for testing. If observations &

inspection of records reveal uncertainties, designer shall be consulted for

necessary design decision.

Important workmanship and quality requirements for materials & their QC

tests plus acceptance criteria shall be indicated on drawing. Design

capacity & the required performance tests & acceptance criteria shall

also be indicated.

Piles that shall be selected for static load test shall be at least 1 to 2% or

minimum 2 numbers per site. If some of the static load tests are to be

replaced by high strain dynamic pile tests or PDA test, at least 5% of piles

shall be tested. PDA tests shall be strictly according to ASTM D4945-12 and

shall be planned, conducted, recorded and interpreted by DFI or FQA

accredited test engineer with expert or advanced level certification.

Structural integrity assessment by PDA, static load test (Prof Chin method)

and or low strain integrity tests (ASTM D5882) shall be carried out after

detail examination of construction records. Normally about 5% to 10%

piles shall be selected for structural integrity tests.

e) Geometrical construction tolerances required by Bs EN 14199:2005 are as

follows:

Plan position at working level < 50mm

Deviation from theoretical axis: For vertical pile maximum 2% of the

length.

f) Minimum reinforcement cover with cement gout shall 20mm for

compression piles & 30mm for tension piles. Proper & durable centralizers

at about 2m intervals along the reinforcement should be properly fixed to

ensure concentric position in the drilled hole. For aggressive ground (see

Table below) larger cover and sulphate resisting cement may be needed

subject to structural design evaluation by the designer.



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Table: Criteria for Assessing Ground Corrosion Potential

Test Units

Strong

Corrosion

Potential /

Aggressive

Mild to no

Corrosion

Potential / Non-

Aggressive

ASTM

Standard

AASHTO

Test

Method

BS 1377.3

(1990)

PH - < 4.5, >10 5.5 < pH < 10 G51 T 289 - 91 Clause 9

Resistivity ohm -

cm < 2,000

Greater than

5,000 G57 T 290 – 91 Clause 10

Sulfates ppm(1) > 200 Less than 200 D516 T 290 – 91 Clause 5

Chlorides ppm > 100 Less than 100 D512 T 291 – 91 Clause 3

Stray

current - Present - - - -

g) QC for cement grout.

Unless otherwise specified by the designer, typical cement grout shall

have water cement ratio, W/C=0.4 to 0.5, characteristic strength, fcu=25 to

30 MPa; bleeding <3% after 2hrs, viscosity flow time through efflux flow

funnel should be less than 15 seconds. Cement grout mix shall be mixed

by high speed colloid mixer (>1000 rpm). The quality control test should

be carried out at least daily or one set of test per 5 piles.

h) There are many drilling techniques and methods for micropiles. Each

method has its applications and limitations or its suitability depending

mainly on subsoil conditions and size/depth of the micropiles.

Table: Drilling Methods and Procedures

Modified from Elias and Juran, (1991)

Drill Rig Type

Drilling Method Open Hole?

Cased or Auger-Cast?

Drillhole Diameters

(mm) Drill Bit Types

Cuttings Removal

Comments

Auger

Lead Flight Kelly-Best Driven

Yes No

100 – 300 Rock, Soil, Drag, etc.

Mechanical

Hydraulic rotary auger methods for drilling competent soils or

weathered rock

Sectional Solid-Stem Yes No

Sectional Hollow-Stem Yes Yes Mechanical (air support)

Continuous Flight Solid-Stem

Yes No Mechanical



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Continuous Flight Hollow-Stem

Yes Yes Mechanical (air support)

Rotary

Single-Stem Air Rotary Yes No

100 – 200 Button, Roller,

Drag, etc. Compressed

Air

Hydraulic rotary methods for drilling

competent soils, rock, or mixed ground

conditions (pneumatic hammers available)

Duplex Air Rotary Yes Yes

Wash Boring Yes Yes 100 – 300 Roller, Drag,

etc. Water / mud

Sectional Solid-Stem Augers

Yes No

100 – 300 Rock, Soil, Drag, etc.

Mechanical Hydraulic rotary auger methods for drilling competent soils or

weathered rock Sectional Hollow-Stem Augers

Yes Yes Mechanical (air support)

Air Track Single-Stem Air Rotary Yes No 100 – 300 Button, Roller,

Drag, etc. Compressed

Air

Pneumatic rotary methods for drilling

non-caving competent soils or rock

i) Methods of drilling (<300mm diameter):

Contractor shall propose specific and appropriate drilling method and

specific type of machine & tools for the project in the method statement

after taking into account of the subsoil conditions, design and

specification requirements. Unless otherwise specified and approved,

duplex drilling technique or equivalent shall be deployed.

Drilling can be cased or uncased wash rotary drilling with water (with or

without bentonite/polymer), rotary pneumatic percussive drilling with or

without casing, augering, percussion, etc., depending on subsoil

conditions and drilling tools, etc. Rotary action can be by power-driven

rotary table turning Kelly bar or tophead drive pneumatic/hydraulic motor

turning drill rod/casing or chuck drive rig or special rig /machine.

Requirements for rotary (rpm) /torque & pull-down capacity for hard rock,

soft rock, soils? Drilled hole stabilization methods? Flushing medium

(water, air, mud, foam & combinations with additives to meet specific

ground & flow rates, etc.) & circulation methods? Applications & limitation

of each method to the specific site and design conditions for the project

shall be assessed.

Factors governing the selection of drilling methods /equipment/tools &

detail procedure? Subsoil conditions (soil/rock/hardness, obstruction,



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collapsible strata, groundwater, etc.), site constraints and pile size/length

/capacity, etc.

Subsoil & geological conditions: WT, collapsible strata (cased or uncased,

risk of being jammed by gravels/boulders/loose fractured rocks), very

hard strata/obstructions, saturated or unsaturated strata & permeability,

prone to ground subsidence, problems of drilling in very soft/loose strata?

Limestone formation problems?

Site conditions: Access, headroom & space constraints, suitable size of

machine, portable machine. Machine for rotary percussive methods are

usually smaller.

Environmental factors (noise, dust, ground subsidence, etc.): Pneumatic

rotary percussive methods have more noise & some ground vibration.

Lowering of WT in permeable strata may lead to ground subsidence, etc.

Wash boring is messy & has problem of siltation of drains & waterways, etc.

Economy, pile size & capacity: Machine & tool cost are high for drillholes

exceeding 250mm for rotary percussive methods, especially for deep

holes that have localized collapsible strata

Drilling tools/bits: proper selection is the key to successful drilling.

Special tools for difficult site & subsoil conditions such as water bearing

sandy strata, collapsible strata, subsoil with excess pore water pressure, fill

ground with hard construction debris/boulders, etc. What are the

problems and how to address the problems?

j) Reinforcement

Purposes of reinforcement: to transfer load to deeper strata & then through

grout to bonded soil/rock.

Reinforcement Types: API standard, BS, EC. Reinforcement can be single

high yield steel bar, bundle of 3 or more bars or MS or API pipe. Usual yield

stress, fy=250 MPa (MS steel), fy=500/550 MPa for GEWI bars or fy=550 MPa

for API N80 pipes, etc.

Functions & Technical Requirements: material strength. Coupler/joint shall

have the same compression/tension strength. Centralizers & Spacers at

about 3m intervals along the reinforcement to ensure concentric position

in the drilled hole with cover of minimum 20mm (non-aggressive ground &

compression) or minimum 30mm (non-aggressive ground & tension) shall

be of durable material (plastic or galvanised bars, etc.). Pile head

anchorage construction as designed. Straightness/alignment tolerance (<



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3mm per 3m). Joint for compression/tension, strength fy. Protection vs

corrosion of aggressive ground? Refer design drawings and BS 8004

(Clause 10).

Common QC tests for reinforcement: Reinforcement bars or pipe

laboratory test certificates by accredited lab shall be checked to ensure

compliance with specification. Test certificates for joint, coupler & spacer

to ensure performance shall also be checked and documented. Coaxial

requirements single and bundle of bars check shall also be carried out.

Functions & significance of centralizer/spacer, coupler & anchorage?

Design verification? Design model & load transfer? Types & technical

requirements? Corrosion protection?

k) Grouting

Specific functions/purposes & technical requirements of grout mixture &

grouting operation shall be observed as specified.

Grout Properties: Desired/required properties? Why? Unless otherwise

specified, pure cement gout with W/C<0.4 to 0.5 shall be adopted. Sand

(<25% by weight) may be added if the drilled hole is >200mm and

specified/approved by designer. Addition of sand in cement grout is not

recommended as it will significantly reduce the flowability of the grout.

Admixtures/superplasticisers/retarder should/may be used to achieve the

required QC/workability properties specified below. Grout mix shall be

mixed by high speed (>1000 rpm) colloid mixer.

QC tests: strength (unless otherwise specified, fcu>30 MPa),

workability/flow>250mm, bleeding<3% (after 2hrs), efflux cone flow

time<15 seconds. Test frequency: at least once daily or one test per 5

piles. These properties are critical to performance or load transfer of

micropiles.

Grouting operation: Refer spec for requirements of machine/mixer (>1000

rpm), paddle mixer, time limit for mixing, transfer & grouting, grouting

method (Type A/B/C/D or single step or multiple steps grouting with

packers or Tubes-a-Manchettes) & pressure level, etc. Site supervisor shall

refer specification/design and to ensure the grouting requirements are

complied with at site.

Common shortfalls or WCGW at site for grouting? Mitigations?

Inadequate/unclear works spec for scope of inspection, recording & QC

to check bleeding, strength & flow properties, etc. Lack of quality and

competent supervision.



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Performance and capacity of micropiles for a given pile geometry &

ground conditions are substantially dictated by grouting pressure, less

influence by drilling & flushing. Type A (normal tremie gravity

displacement grouting, suitable for hard soil or rock. Type B

grouting/injection pressure is about 1MPa, grout permeates through pores

& fractures & increases effective grouted diameter, also can increase end

bearing. Type C, pressure>2MPa, by insitu packers or tube-a-Manchette,

hydrofracturing, secondary grouting. Type D includes post grouting. (BS

8081).

For weathered & fractured rocks, it is important to know locations & size of

fractures & permeability plus its reaction to grouting. This can be

determined by Packer/Lugeon tests using double packer. Lu>3L/m/MPa

implies that pregrouting is necessary & useful. What are the factors &

information required in proper design of rock socket strength (fub) for

micropiles?

Pressure and post grouting are expensive & difficult to do at site though it

can get very high bond stress fub in fractured rock socket with low RQD

(only if properly done). What should be the design approach to address

these issues? Understand how the bond fub that can be mobilized?

Factors? How to ensure rock socket is clean or not filled with debris or

disturbed by drilling? How the grout properties & pressure can fill the rock

discontinuities/fractures? Rock properties & grout shrinkage problems?

l) Pile Testing

Pile testing is the main part of QC/QA for piling works (bored piles &

micropiles). The performance of piles with respect to structural integrity

and capacity (ultimate friction fsu & end bearing fbu) is very sensitive to

how they are constructed, especially bored piles & micropiles.

There are two types of post installation pile tests namely IINNTTEEGGRRIITTYY tteessttss or

non-destructive tests to evaluate the soundness or integrity of the

constructed bored piles & LLOOAADD tteessttss to determine the load capacity of

the bored piles.

What are the important issues about pile testing?

• How many piles should be selected for integrity tests? Types of

integrity tests & test standards? Selection criteria?

• How many piles should be selected for load tests? Types of load

tests & test standards? Purpose of instrumented, preliminary &

working load tests? Selection criteria? Test result interpretation &

acceptance?



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Types of pile tests can be classified as shown in the figure as follows:

Structural Integrity Tests

Usually about 3% to 5% of piles installed should be selected for integrity tests to check and evaluate the pile soundness conditions. Selection of piles for integrity tests should be based on installation records/concrete volume-depth graphs especially those have been suspected of structural integrity problems such as major faults, necking, discontinuity, etc. All integrity tests shall be planned, conducted and interpreted by approved DFI accredited tester of specialist agency with advance level certification.

Common integrity tests are cross-hole sonic logging test (ASTM D6760) and sonic echo/hammer test (ASTM D5822). Some pile load test methods such as PDA and MLT also can be used to check pile integrity conditions. Excavation (for shallow depths <3m) and coring are also can be used to check structural conditions of bored piles.

Cross-hole sonic logging (CSL) Test (ASTM D6760)

Cross-hole Sonic Logging Method to check their integrity should be

carried out strictly in accordance to ASTM D 6760.

The Sonic Logging Method is a method of investigation using the lateral

transmission of waves consisting of emission of an ultrasonic vibration

in an access tube filled with water and capturing this vibration at the

same level in another tube within the pile shaft. This operation is repeated

at a high frequency and at a level sufficiently close to each other in order

to get a continuous recording over the entire length of the pile shaft.

The tubes for integrity tests by sonic logging shall have an internal

diameter of not less than 50 mm with no internal projections or



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couplings. They can be of mild steel pipe or galvanised iron (G.I.) pipe.

Four (4) nos. of tubes are required for each selected pile of diameter less

than 1.3 m while six (6) nos. are required for each selected pile of

diameter greater than 1.3 m.

The tubes shall be cleaned with a non‐greasy product before use in order

to prevent oil films from causing adherence problems between the tube

and the concrete. This could cause a variation that might be incorrectly

interpreted as a significant defect in the pile.

The tubes shall be fixed to the vertical bars with equal spacing on the

inside perimeter of the links. The tubes shall be watertight with the

bottom of the tube sealed and suitably weighed to prevent floating. The

upper ends of the tubes must be closed and extended to at least

500 mm above the concrete surface to prevent debris or concrete from

falling into the tube. The tubes shall be secured to the internal face of

the reinforcement cage at equal distance from each other on the

circumference.

In all cases, the steel tubes shall rest on the founding level of the pile so

that the full length of the pile can be tested. The type of tube and

condition of sealing shall be checked and approved by the RE before

installation.

The tube shall be filled with water to provide the necessary acoustic

coupling, and then plugged or capped before concreting. After

conducting the tests, all tubes shall be grouted and the water in the tubes

displaced. The grout shall be dense cement grout with an approved

expanding agent.

The acceptance criteria according to FHWA-NHI-10-016 are as follows:



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Shock Test/Hammer test

The shock/hammer test should be carried out strictly in accordance to

ASTM D5882. In this test, the shock which is to be imparted on to the

properly prepared pile head shall be carried out using a suitable size

hand held hammer or any approved method which is capable of

transmitting vibration to the base of the pile shaft. The electronic pick‐ups

located on the pile head shall be approved velocity transducers or

accelerometers. Preliminary tests shall be carried out to establish the

appropriate scales and to check the electronic circuit.

Load Tests

Usually about 1% to 2% of piles installed should be selected for load tests.

Selection of piles for load tests should be based on installation records

where weak piles should be chosen. Result of testing is not everything until

and unless the result can be representative of the untested ones.

Preliminary test piles or instrumented test piles aimed to confirm and verify

the pile design should be tested to ultimate load, usually 2.5 or 3 times the

pile design working load whenever possible (SS CP 4:2003). Working piles

should be tested to proof loads, usually to 2 times the design working load

although in certain conditions proof load of 1.5 times may be used.

For large projects, some of the load tests (MLT/SLT) may be substituted by

PDA tests.

Common types load tests are as follows:

o SSttaattiicc LLooaadd TTeessttss:: CRP, MLT (ASTM D1143 for compression, D3689 for

tension, D3966 for lateral). Static maintained load test (MLT) should

be carried out according to JKR/SPJ/2010-S10 and acceptance

criteria:

Pile load test is deemed to have failed if

Settlement >12.5mm @ design working load; or

Settlement > 10% pile size or 38mm @ 2 x design load: or

Residual settlement after removal of test load > (4 + D/120)

or 12.5mm, whichever is the lower value (JKR Standard Spec:

JKR/SPJ/2010-S10).

Ultimate loads & structural integrity conditions can be evaluated by

Prof. Chin FK’s method or Davison's Method, etc.



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• High-strain Dynamic Testing of Piles-PDDAA/HSDTP (ASTM D4945-12).

PDA shall be planned, conducted, recorded & interpreted by

Dfi/FQA accredited test engineer (expert or advanced Level).

Compliance with the requirements of the test standards and

specifications is important.

For piles to be selected for PDA tests, full length reinforcement is

required. Force measured on pile head by hammer >2Qd by

hammer impact with hammer weight as heavy as possible (1% to

2% of 2Qd) & drop height as low as possible (<2m). The induced

dynamic compressive stress (fc) & tensile stress (ft) should be

checked by WEAP or Broms method to ensure they are within the

permissible limits. How?

• BBiiddiirreeccttiioonnaall llooaadd tteessttss ((SS CP4:2003 recognizes it as SLT). Refer www.YJACKpiletest.com

• SSttaattnnaammiicc llooaadd tteesstt;; nnoo AASSTTMM ssttaannddaarrdd aavvaaiillaabbllee..

Can Bidirectional load tests be considered SLT? Advantages of

Bidirectional load tests (T-cells, O-cells & C-cells) for load tests of

bored piles?

Refer Para 4.2 (o) for record requirements for micropile installation.

MLT or SLT is the most reliable test. A must to verify the estimated capacity

& settlement

Ultimate objective of load tests: to ensure all untested piles are

represented statistically by the results of test piles on the safe side. How?

Criteria of selection of piles for tests shall be based on installation records.

Purpose of preliminary or trial pile tests & working pile tests

Interpretation of load test results

Common errors/problems

o Non-compliance with test stds, inadequacies in method statement

o Interaction of test pile & supports for kentledge/ reaction piles/

anchors

o Soft ground problems & piling in limestone formation (group

analysis)

o Selected case histories of load tests

http://www.yjackpiletest.com/



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4.3 Construction Checklist and relevant problems and issues related to

supervision of micropile installation that site supervisor (RE/IOWS) should be

well-versed:

a) Desk study: to collect all relevant documents and be aware and

understand the scope of piling works involved. Important relevant

documents are: contract document, GI/SI factual report, GI/SI

Interpretation report, GDR/pile design report with design drawings,

specification & BQ. Consult the designer for clarification if necessary.

b) Check and inspect the site conditions and understand how the

micropile installation works will affect the nearby buildings/structures,

services, etc. (if any). Carry out dilapidation survey & monitoring

instruments (surface markers/piezometers, etc.), if necessary.

c) Check and understand the Method Statement prepared and submitted

by the Contractor. Seek explanations & clarifications where necessary.

Method statement should be adequate & comprehensive as explained

in Para 1.3 above. Make sure all the construction requirements

stipulated by BS EN 14199:2005 are complied with.

d) Are the proposed drilling rigs, equipment and tools appropriate to the

site/subsoil conditions with necessary output to complete within the

scheduled time frame with some contingencies? Consult others if not

well-versed in the subject. Are the Contractor’s operator & site

manager well-versed in micropile installation problems?

e) Are the proposed methods & materials of drilled shaft stabilization

satisfactory with anticipated subsoil conditions and in compliance with

the requirements specified by the designer?

f) Check and enquire methodology & system for validation of material

quality (tremie grout mixture, reinforcement elements, centralizers,

couplers, etc.,) product/workmanship tolerance, QC assurance, etc.

g) Are the proposed method/sequence of reinforcement elements

placement & grouting satisfactory? What are the checks and

inspections/measurements plus records for quality and/

measurements or dimensional tolerances before and after placement

of reinforcement cage and grouting?

h) Check micropile termination criteria & construction controls?

i) Check & mitigations vs. drilled shaft structural integrity?

j) Are the noise level and ground vibration/deformation or subsidence

level acceptable? How to estimate and control the noise and ground

vibration/deformation or subsidence level for the proposed pile

installation method? Potential damages to nearby buildings &

services?

k) What are the typical micropile installation problems in limestone

formation & soft ground? Construction controls and mitigations against

the problems?

l) Scope & types of recording and format?

m) Pile tests to check structural integrity & capacity? Types of tests and

test standards? Frequency? Interpretation?



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5. Specification for Piling Works

Specification for piling woks as given by Section 10 of JKR Standard

Specification for Road Works (JKR/SPJ/2010-S10) deals with piling works

with particular reference to requirements for materials/products,

installation, workmanship and testing/performance for precast RC piles,

prestressed spun piles, bored cast-in-place piles, steel H piles, steel pipe

piles and micropiles. All site supervisors of piling works should be well-

versed with all the requirements specified.

For bored pile installation, all site supervisors of piling works should be

familiar and well-versed with all the construction requirements specified.

The bored pile supervisors should be well-versed and understand the

following terminology, information and requirements in particular:

o General requirements & Construction Tolerances

The specification contains general requirements of materials,

records and all the allowable pile tolerances, such as location,

verticality (plumbness), cut-off elevation, rebar stick up, and

diameter. Failing to meet these tolerances will result in a

rejected pile.

o Boring and Excavation Methods

The specification contains the allowable procedures for the

different shaft drilling methods. They also provide the

requirements of each procedure. The requirements for base

cleansing & drilled shaft stabilization. The contractor must

adhere to these requirements or once again the shaft could be

rejected.

o Reinforcement cage placement

Requirements for proper fabrication & handling of reinforcement

cage.

o Concrete Placement, and Temporary Casing Removal

The specification contains the requirements of concrete mix and

the allowable procedures and requirements for the above

operations. Again, the contractor must adhere to these

requirements or risk rejection of the shaft.

The specification also contains additional miscellaneous information

on drilled shaft requirements that the supervisor should become

familiar with. A good working knowledge of the specification is

essential in proper bored pile or drilled shaft construction monitoring.



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For micropile installation, JKR Specification does not specified much

construction requirements for drilling, drilled hole stabilization & grouting.

Maximum permissible bleed up to 5% in JKR specification is too

excessive. Normally the permissible limit for bleed after 2 hrs is 1 to 3%.

Refer slide presentation. Some of the lackings and shortfalls in JKR

Specifications will be discussed during the lecture.

6. Commonly asked Q & A

We have compiled these Q & A from the problems we were asked about

most frequently, so that you can find the answers you are looking for.

Answers to the questions will be discussed during the end of the

presentation.

a) What is meant by “supervision of pile foundation installation”? Purpose

of site supervision? Role and responsibility of supervisors? Basic

required qualification/training & knowledge/experience of qualified

supervisors for piling works?

Ans: Site supervisors including RE & technician/IOWS/COW are appointed by the

Client/project owner or project manager to take care of their interest. The role pile

supervisors is to take care the Client’s interest to ensure the piling works are properly

carried out according to the CP, design drawings and specifications. The required

fundamental responsibility of site supervisor is to inspect and to make sure the piling

work is properly carried out with due care, diligence & skill, i.e. the piling works are

completed smoothly without much problems (within the time frame & budget or not

much costs/time overruns through proper project management & Contract administration)

and according to the approved pile design & specification (to ensure quality &

performance & also meet the requirements stipulated by CP through proper technical

supervision).

In order to discharge the required fundamental responsibility of supervision of piling

works to ensure quality & performance, the site supervisor must have the basic academic

training plus some site training and experience to acquire the practical aspects of piling

works process and the required QC to ensure workmanship & performance.

Basically, if you cannot read & understand the technical basis of pile design drawings,

specifications & SI report, you are basically and actually not qualified to supervise the

piling works concerned. A competent qualified piling supervisor not only can read and

understand the basis of important aspects of pile design drawings and specifications, but

also has the capability to distinguish and to recognize the proper construction

method/procedure plus mitigations against various risks and uncertainties of subsoil

conditions encountered. This means the site supervisors should be capable of distinguish,

identify and recognize what are the defective constructions/piling works, which are

defined as piling works that are not carried out according to good engineering practice or

not according to specifications and design drawings.



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How to learn to read and understand the pile design drawings?

To learn to read pile design drawings certainly is much easy and faster than to learn how

to design pile foundation & express the design on drawings and specification.

Basic design details shown in pile design drawings: Piling layout, pile cap details,

structural details of pile body, pile joint. pile shoe, etc. (illustrations) and construction

controls, method/sequence/procedure, QC requirements, etc. (usually expressed in notes).

To understand these details and their engineering purposes and basis requires structural &

geotechnical engineering knowledge and training. What are the relevant subjects of

structural & geotechnical engineering involved? Availability of resources (experienced

contractors, materials and machine) and practical aspects of cost-effectiveness

(economics) are equally vital to be learned.

How to read and understand pile specification?

What is meant by good engineering practice? What is meant by defective construction for

piling works? To be discussed more detail during the Q & A session.

b) What is meant by defective design for piling works? What are the

common causes and typical cost-effective mitigations vs. defective

design?

Ans: Basically, defective design means the design has not met the requirements stipulated by CP or

local authority. Common causes for defective design are:

Inadequate and/or unreliable GI/SI. Inadequate GI/SI means the scope of GI/SI does

not meet the minimum requirements stipulated by CP or local authority. Unreliable

GI/SI means the GI/SI works are not properly carried by accredited SI Contractor or

using improper equipment or improper test procedure or not supervised by qualified

personnel.

Inadequacy in scope of design verification, where safety, serviceability and

durability aspects are not adequately carried out in accordance with the requirements

stipulated by CP and local authority, etc.

Inadequacy in scope of design validation to ensure the requirements with respect to

performance, serviceability and durability stipulated by CP and local authority, etc.

Cost-effective mitigations vs. defective design are:

The designer should adequately and properly qualified

Properly qualified independent check engineer or auditor preferably BEM accredited

Check Engineer is engaged to audit the design

c) What is meant by defective construction for piling works? What are the

common causes and typical cost-effective mitigations vs. defective

construction?

d) How to conduct redriving test & false set in granular & cohesive

subsoil? How to check & conduct pile heave/uplift for big pile group in

saturated subsoil? How to measure ground vibration & movement for

large displacement pile in saturated cohesive subsoils? How to check

pile position/deviation, pile verticality & rake to ensure compliance

with specifications?



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e) What are the usual permissible limits/tolerances for pile position,

verticality and rake? How to inspect and check/verify/test these limits

at site? In case some of the piles are found to be out of alignment or

position exceeding the tolerable limits, what are the acceptable

methods of remediation or rectification? Who should bear the

additional costs involved according to JKR Specification for Piling

Works (JKR/SPJ/2010-S10)?

f) What are the general construction requirements and scope of

inspection checks for following aspects of piling works and the

underlying principles involved?

Permissible/tolerable pile deviations: positions, rake & verticality

Pile shoe: dimensional tolerance, basic structural requirements,

purpose & functions of various types of pile shoe for precast

concrete piles

Pile joint: dimensional tolerance, basic structural requirements,

purpose & functions of various types of pile joint (welded or

mechanical joints) for precast concrete piles.

g) What are the important scopes of inspection and QC for precast

concrete piles before installation (MS 1314 Part 1)?

h) What are the common defective constructions and problems in (a) soft

ground, (b) boulder abundant residual subsoils, (c) ex-mining areas of

limestone formation with floaters/boulders, cavities & erratic rock

profile, (d) uncontrolled fill ground, (e) off-shore of marine environment

such as jetty project and (f) residual subsoil with inclined/laminated

weathered shale for:

driven RC piles

driven spun piles

jacked RC piles

jacked spun piles

bored piles

micropiles?

What are the common causes/mechanism of the problems? Effective

mitigations?

i) What are the purposes and basic scope of contents of a

comprehensive method statement for installation of:

bored piles

micropiles

driven RC piles

driven spun piles

jacked RC piles

jacked spun piles?



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What are the important information & data that shall be checked and

verified with the Contractor before acceptance/approval to method

statement can be given by the RE?

j) What are the important pre-installation inspection/measurements/ tests

that should be carried out to ensure the required quality of

materials/products delivered to site have complied with the

specification for:

driven RC piles

driven spun piles

jacked RC piles

jacked spun piles

bored piles

micropiles (Reinforcement cage or API pipes).

k) What are the important inspection/measurements/tests that should be

carried out during installation stage to check and ensure the required

construction workmanship/tolerances have complied with the

specification for:

driven RC piles

driven spun piles

jacked RC piles

jacked spun piles

bored piles

micropiles

l) Pile designers may specify various types of pile testing methods to

check structural integrity and performance (capacity & settlement). As

a site supervisor, what are the important information and data or

process that should be checked and verified/clarified with the

Contractor to ensure the tests are properly carried out as specified?

m) For static load test or maintained load test for piles, what are the

important inspection/measurements/document/clarifications that

should be checked and verified with the Contractor before approval

to proceed is given?

n) For high strain dynamic pile test/PDA test for driven RC piles or spun

piles, what are the important inspection/measurements/document

/clarifications that should be checked and verified with the Contractor

before approval to proceed is given?

o) For statnamic pile test for driven RC piles or spun piles or bored piles,

what are the important inspection/measurements/document

/clarifications that should be checked and verified with the Contractor

before approval to proceed is given?



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p) For bidirectional or O-cell pile test for spun piles or bored piles, what

are the important inspection/measurements/document /clarifications

that should be checked and verified with the Contractor before

approval to proceed is given?

q) For driven RC or spun piles, what are the basic criteria of selection of

piles for load tests?

r) For jacked RC or spun piles, what are the basic criteria of selection of

piles for load tests?

s) For bored piles, what are the basic criteria of selection of piles for load

tests?

t) For micropiles, what are the basic criteria of selection of piles for load

tests?

u) For driven RC piles that are suspected of structural integrity problems

through driving records or PDA tests with low BTA ratio, what are the

relevant tests that should be carried out to verify the conditions?

Typical remediations?

v) For driven Spun piles that are suspected of structural integrity problems

through driving records or PDA tests with low BTA ratio, what are the

relevant tests that should be carried out to verify the conditions?

Typical remediations?

w) What are the typical subsoil conditions and construction methods that

are prone to have structural integrity problems for bored piles? What

are the reliable test methods to verify the conditions? Effective

mitigations vs. the problems?

x) What are the typical subsoil conditions and construction methods that

are prone to have structural integrity problems for micropiles? What

are the reliable test methods to verify the conditions? Effective

mitigations vs. the problems?

y) What are the common construction disputes and contractual claims

related to inadequate specification for (a) bored piles, (b) driven RC

piles, (c) jacked spun piles & (d) micropiles?

z) What is meant by a bored pile according to BS EN 1536:2000? What are

the main applications, advantages and limitations of bored piles?

aa) What are the relevant Codes of practice or established design

guides commonly used by pile designers in Malaysia? What is meant

by good engineering practice? Acceptable established design &



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construction guides & guidelines? What are the main differences in

design methods by ASD, LFRD and limit state design for pile designs?

bb) What are the most important prerequisites and information to

enable engineers to design bored pile properly?

cc) What should be the scope of GI/SI methods to obtain the necessary

subsoil properties & information required to address the problems of

bored pile design & construction for normal high-rise building projects?

What are the important CP requirements need to be met?

dd) What are the important/critical or mandatory requirements

specified in the Codes of practice (BS 8004 & EC 7) for bored pile

design?

ee) What are the fundamental scopes of design verification/analysis/

calculations for bored piles to show compliance with the design

criteria /requirements specified in CP/BS 8004?

ff) What are the important scope/methods of design validation to ensure

the design requirements specified in the CP are met at site with

particular reference to structural integrity, capacity and settlement?

gg) What are the major factors that will affect ultimate unit friction fsu &

ultimate end bearing fbu for bored piles?

How to estimate unit ultimate skin friction fsu & end bearing fbu for bored

piles in clay, sand, intermediate geomaterial (IMG) & rock? What

factors that can influence fsu & fbu significantly? Why fbu is commonly

ignored in the estimation of end bearing in practice? When end

bearing can be considered substantially and partly? Basis?

hh) What are the usual permissible limits/tolerances for bored pile

position, verticality and rake for displacement piles? How to inspect

and check/verify/test these limits at site? In case some of the piles are

found out of alignment or position exceeding the tolerable limits, what

are the acceptable methods of remediation or rectification? Who

should bear the additional costs involved according to JKR

Specification for Piling Works (JKR/SPJ/2010-S10)?

ii) What are the main & critical information sought from GI/SI aimed for

bored pile design & construction?

jj) What are the basic 3 types of bored pile construction? Applications &

limitations plus advantages of each method of construction? What are

the common types of unstable strata in bored pile construction & how

to address the problems involved?



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kk) What are the basic requirements for boring operation related to boring

machine & drilling tools for bored pile construction in soft to

hard/dense soil & rock (soft to hard rocks)? When can boiling

phenomenon happen & how to address boiling problem? When can

the problem of excessive outflow of drilling fluid happen and how to

address the problem? When can the excessive inflow of groundwater

and/or soil to the bores happen & how to address such problem?

ll) What are the common construction methods for rock socket for bored

piles? How to estimate ultimate friction for rock socket? What are the

factors that shall be considered when adopting the ultimate rock bond

strength?

mm) What is meant by drilled shaft stabilization in bored pile

construction & the engineering principles involved? What are the

common methods for drilled shaft stabilization & the engineering

principles involved? Their applications, advantages and limitations?

What are the important QC tests & their acceptance criteria that should

be carried out to ensure performance

nn) What is meant by base cleaning in bored pile construction? What are

the common methods for base cleaning & the principles involved?

Their applications, advantages and limitations? What are the common

tests that should be carried out to ensure the base is clean?

oo) What are the important construction requirements for fabrication

and placement of reinforcement cage in bored pile construction to

ensure performance? What are the common defective construction in

handling & placement of the reinforcement cage and the

consequence to the bored pile performance? What factors influence

the amount of reinforcement (As) required? In case soft ground or high

lateral load and 2% of reinforcement are required, what are the typical

problems that may arise? How to address these problems to ensure

performance of bored piles?

pp) What are the desired properties of concrete mix for tremie

concreting in bored pile construction? What are the important QC tests

on tremie concrete that should be checked and carried out at least

once daily?

qq) What are the common construction defects in tremie concreting for

bored piles and what are the possible consequences to bored pile

performance?

rr) How slump of insitu concrete for bored pile can affect the performance

(integrity & capacity) of bored piles critically? How slump should be

monitored during the whole process of concreting especially for the



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concreting for big & long bored piles that takes more than 1.5 hours to

complete?

ss) BS EN 1536 recommends that the concrete-depth for all bored piles

should be recorded. What are main purposes for this record?

tt) What are the requirements, extent & scope of site supervision,

inspection & recording for bored pile installation as required by BS 8004

and BS EN 1536:2000?

uu) What are the common structural integrity problems in bored pile

construction? Methods of mitigations against these problems? Methods

to identify and assess/determine the extent/existence of these

problems?

vv) What are the common methods used to estimate/check lateral load

capacity & deflection of bored piles? When & how external lateral

loads (ground movement) can be imposed on piles? How to improve

lateral load capacity of bored piles in loose or weak/soft soils near the

ground level?

ww) What is meant by bidirectional load test? What are the main

differences between the conventional maintained load tests and

bidirectional load tests? Can the bidirectional load tests be considered

static load tests? What are the advantages & disadvantages of

bidirectional load tests when compared with the conventional

maintained load tests?

xx) What are meant by high-strain dynamic load test/PDA and statnamic

load test? What are the main differences between these 2 tests? What

are the advantages & disadvantages of PDA & statnamic load tests

when compared with the conventional maintained load tests?

yy) What are the important acceptance criteria for load tests on bored

piles? What are the load test acceptance criteria according to

JKR/SPJ/2010/S-10? Basis of the acceptance criteria?

zz) What are the typical conditions/situations that bored piles are practical

and cost-effective? When bored can be very competitive when

compared with other piling systems?

aaa) What are the main purposes of pile testing for bored piles? How to

ensure the results of pile testing are representative and meaningful?

What are the common test methods/types & their applications,

advantages & limitations for tests to check structural integrity and

capacity?



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bbb) SI Report given in the Tender document usually attached with

statements such as “The SI Report is intended solely as a preliminary

guide and the completeness nor accuracy of the information

provided is not guaranteed. No responsibility is assumed by the SO for

any opinion or conclusion given in the SI Report. The Contractor shall

study the SI Report in detail and oblige to place his own interpretation

on the information provided and to make due allowance for the

effect of the site and subsoil conditions on his construction operation. If

necessary, the Contractor shall carry out his own SI.”

If the actual subsoil conditions differ significantly from the SI Report

given and this has resulted in:

a) The actual driven RC pile penetration/set depth is significantly

shorter resulting in loss due to large wastage

b) The drilled shaft stabilization methods of bored piles have to be

changed from normally by water to bentonite/polymer slurry

resulting in additional cost & delay.

Can the piling Contractor be entitled to claim for the above

additional loss and costs?

ccc) Generally, can the piling Contractor be entitled to claim for the

additional cost of repair/rectification of the adjacent

buildings/structures/utilities due to piling works according to JKR

Specification for Piling Works (JKR/SPJ/2010-S10)?

ddd) What are the common bored pile construction disputes and

contractual claims related to:

Boring operation

Subsoil conditions

Rock socket construction methods & depth

Drilled shaft stabilization methods

Base cleansing methods

Concreting

Placement of reinforcement cage

7. Case Histories/case studies

Refer slide presentation: introduction & background/site history subsoil

conditions, problems encountered, scope of investigation & findings, proposed

remediations & engineering principles involved.

a) Installation of 125mm micropiles for distressed RC anchored wall, Teluk

Kumbar, Pg.



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b) Installation of 100mm micropiles as underpinning works for settled

school building in Mersing.

c) Installation of 300mm micropiles as foundation for 2 tier flyover, Jalan

Ampang, KL.

d) Bored pile Construction for Puchong Utama Interchange. Problems of

excessive soft toe up to about 1m thick for bored piles (1.2m

diameter) in thick sandy silt (20m). Qd=600 ton with 5m rock socket

(RQD<5%, highly weathered sandstone/schist). Investigation &

remediation proposal?

e) Large diameter bored piles for high-rise building (1.5m to 2m), PJ.

45m to 65m long with 3m rock socket in weathered granite installed

by reverse circulation machine & BG 38. Instrumented test pile by MLT

to 2Qd=7000 ton. Statnamic load tests & PDA tests. Results

interpretation, etc.

8. Attachment: slide presentation

WORKSHOP NOTES - E-Geo Consultant Sdn Bhdegeo.com.my/papers/About Pile Foundations/Workshop...

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