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2012 Edition
architectural I civil I electrical I mechanical I structural
SUPERVISION GUIDE For Civil Engineering Works
Copyright © 2012 Housing & Development Board. All rights reserved.
This publication is reference material for Consultants to develop an effective quality
management system (‘QMS’) in their respective HDB-related projects. It is not a set
of exhaustive standards for Consultants to adhere to in their management of civil
works. Consultants are responsible for meeting the standards imposed by the
Building Control Act and related Regulations as well as relevant Codes of Practice,
and for observing good industry practices to develop and implement their QMS.
For the avoidance of doubt, if there is a difference between the contractual
obligations exacted on Consultants and the guidelines set out in this publication,
Consultants will be held to their respective contractual obligations.
This publication may not be reproduced or transmitted in any form or by any means
in whole or in part without the prior written consent of HDB.
While every effort has been made to ensure the accuracy of the information
contained in this publication, HDB and its employees shall not be responsible for any
mistakes or inaccuracies that may be contained here. Any liability and responsibility
to any party for losses or damage arising from this publication are expressly
disclaimed by HDB and its employees.
Foreword
Housing & Development Board (HDB) takes pride in housing more than 80% of the
population in Singapore. Delivering well-designed HDB flats of high quality has always
been our top priority.
HDB started to outsource the consultancy services for the design and supervision of
construction of HDB flats since 2003. We now have more than 100 consultants
participating in HDB projects. To ensure consistency in supervision practice and
standard, HDB has embarked on this project to produce a set of Supervision
Guide. They aim to serve as reference to the consultants in developing a
comprehensive Quality Assurance System for managing our projects.
There are altogether five Guides covering the supervision of architectural, structural
engineering, civil engineering, mechanical engineering and electrical engineering
works. These guides set out our expectations, share HDB’s requirements and illustrate
good practices.
These Guides are now available at HDB BGBiz Portal (http://bgbiz.hdb.gov.sg/) for
your easy reference. We hope you will find them useful and informative. We will be
reviewing the guides regularly and we welcome your valuable feedback to further
improve the guides. Let’s work together in the pursuit of quality excellence in our
projects.
Thomas Seow
Group Director
Building Quality Group
Housing & Development Board
Contents
1 Introduction Pg 1
2 Site Preparation Pg 2
3 Trial Bore Pg 4
4 Pre-piling Meeting Pg 6
5 Pile Load Test Requirements Pg 7
6
Bored Pile Records Pg 13
7 Pile Length Audit Pg 14
8 Service Road, Drain & Minor Sewer Pg 16
9 Good Practices Pg 23
10 Annex - Forms for Reference Pg 27
© 2012 Housing & Development Board
1 Introduction
This book serves to guide our Consultants in supervising piling, service road and minor
sewer works for new HDB development projects. HDB’s general requirements and the
examples cited are only for reference purposes. The Consultants shall develop their
own comprehensive supervision system and specific checklists/forms for each project.
The Consultant shall submit the following to the HDB Project Director (PD) according
to the proposed timeline to ensure timely completion of piling, service road and minor
sewer work:
1
S/n Description Timeline
1 QP’s responsibility in checking different stages of
works
Before contract
commences
2 Inspection forms for civil engineering works for
Site Supervisors
Before work commences
3 Pile construction programme
4 Bored piling machinery mobilization plan
5 Method statements
© 2012 Housing & Development Board
2 Site Preparation
Pre-Construction Survey
Consultants shall ensure that pre-construction survey is carried out to determine the
condition of existing buildings and structures adjacent or in close proximity to the piling
works. The consultant is required to exercise due diligence in monitoring the piling
works, assess the readings and instructs the contractor to take corrective actions
where necessary.
The owner of each affected building or structure shall be given a copy of the pre-
construction survey of their property. A complete set of the pre-construction survey
report should be kept on site.
Services Detection
The Contractor shall engage licensed cables/services detecting companies to carry out
cable/services detection work.
Copies of the latest services plans shall be kept on site.
Any cable/services detected shall be clearly marked on site and contractor shall take
the necessary precautionary measures to protect the cable/services throughout the
construction period.
2
Examples of cables/services that
require protection :
• Power cables
• Telecommunication cables
• Water main
• Sewer line
To carry out services detection before
work commencement
© 2012 Housing & Development Board
Site Monitoring Plan
Consultants shall ensure that the Contractor implements an effective site monitoring
plan when piling works are to be carried out in close proximity to existing
buildings/structures. For example, where site is near an existing slope, a basement or
LRT/MRT structure.
For piling works within the LRT/MRT railway protection zone, the Contractor is to seek
approval from relevant authorities before the commencement of piling work.
3
Examples of monitoring equipment:
Prism Tilt Plate
Inclinometer Vibration Monitoring Noise Meter
© 2012 Housing & Development Board
3 Trial Bore
Purpose
The Contractor shall carry out trial bore outside the working pile location to determine
the following:
• Soil condition against soil investigation report
• Condition of the side wall of the bored hole
• Casing length to prevent loose material from dropping from the side wall
• Method of casting ( Dry or Tremie casting)
• Speed of boring for the planning of construction resources
4
To commence trial bore
while waiting for permit to
commence piling work.
© 2012 Housing & Development Board
Review of Soil Conditions
Sufficient safety measures must be provided to ensure that the site has been hoarded
up before allowing the commencement of trial bore.
The Consultant shall review the outcome of the trial bore. Additional trial bore should be
conducted if soil condition detected differs from the soil investigation report or
undulating rock formation are detected.
The bored hole must be covered up immediately after it has been inspected.
5
Comparing of soil sample against soil investigation report
Socketing to
granite
Incline formation
Granite ?
© 2012 Housing & Development Board
4 Pre-piling Meeting
Purpose
The main purpose for the pre-piling meeting is to establish a mutual understanding among all stakeholders on the construction programme and supervision system, and to ensure that the piling works can be completed on time.
The following key personnel shall be invited for the pre-piling meeting:
The agenda for the pre-piling meeting shall include:
• Trial bore observations
• Casting method (Dry or Tremie)
• Soil/rock samples
• Casing Depths
• Resource Planning/ Piling duration
• Types of boring tools
• Zoning of Ultimate Pile Load Tests (ULT)
• Construction sequence
• Ultimate load test testing schedule and depth of test pile
• Founding depth of pile based on zone & pile sizes
• Consultant’s Quality Assurance/Quality Control system
• Documentation control
• Method Statement
• Pile installation daily cut-off time
• Pile Penetration Checks
• Any other piling related issues
6
HDB Consultant Main Contractor Piling Contractor
• PD
• PDA
• Project Manger
• QP
• RE
• RTOs
• Project Manger
• Site Supervisor
• Safety Officer
• Project
Engineer/Manager
• Site Supervisor
Approved method
statement
Consultant’s routing
form
© 2012 Housing & Development Board 7
5 Pile Load Test Requirements
Static Load Tests
The number of pile load tests required is specified in the contract drawings or
specifications.
In general, the number of pile load tests required are as follows:
Ultimate Pile Load Test : 0.5% of total working piles
(instrumented or non-instrumented)
Standard Pile Load Test : 1% of total working piles
Pile Load Test Using Kentledge System
In the preparation of pile load tests, the contractor shall ensure the rigidity of the
support. If necessary, piles or other strengthening methods shall be installed at
contractor’s expense. Only authorised personnel is allow to gain access to the
kentledge area. No worker shall use the kentledge as a shelter/ rest area.
The contractor shall submit the method statement on setting out of kentledge
system.
Item such as the followings shall be included :
• Geotechnical bearing capacity check
• Maximum allowable load on kentledge
• Maximum load to be applied on test pile
• Stability monitoring of the kentledge
Ultimate Pile Load Test (ULT)
The consultant is to plan the sequence and the schedule of the pile load tests.
The depth of the pile is to be decided by QP with reference to the approved design
penetration and observation made during the trial bore.
Proper erection of kentledge
© 2012 Housing & Development Board
Instrumented Ultimate Pile Load Test (iULT)
Upon the completion of each iULT, the Consultant is required to arrange for a Pile-
Design Optimisation Review with HDB.
The QP and AC must submit their respective evaluation reports on the test results to
HDB within 10 working days upon completion of each iULT.
The review is to be attended by QP, AC and/or PE(Geo) & AC(Geo).
Standard Pile Load Test (SLT)
The selection of the working pile for SLT should be made after the working piles have
been installed. It should not be preselected as it is also serve as a quality control for
assessment of the workmanship. It is recommended that the first SLT for the zone/block
be conducted early so that any remedial action, if required, can be carried out quickly to
minimise delay to the overall construction programme.
8
Flowchart for Pile-design Optimisation Review
Completion of instrumented ULT (iULT)
QP/AC evaluate pile design based on iULT results and submit evaluation reports to HDB (IRD Engineer & PD)
QP submits revised pile design to BCA and obtain BCA’s approval
QP/Contractor implement BCA-approved revised pile design for remaining piles on the next working day upon BCA’s approval
QP/Contractor commence piling works (based on
original pile design verified by ULT)
QP submits revised pile design
to HDB for verification
Within 5 working days
QP/AC present analysis of iULT results and recommend pile re-design at Pile Optimisation Review with HDB
Contractor submits iULT report to QP
Within 3 working days
Within 3 working days (scheduled by IRD)
Maximum Duration
Within 5 working days
*For buildings of 30 or more storeys, QP(Geo)/AC(Geo) are required for foundation design submission.
© 2012 Housing & Development Board
Calibration of Test Equipment
To ensure that the equipment used is accurate and in working condition, the
Consultant shall verify the validity of the certificate of calibration before the
commencement of pile load test.
Equipment to be calibrated:
• Dumpy level
• Pressure gauge
• Hydraulic jack
• Load cell
• Dial gauge
9
Serial No.
Date of calibration
Calibration validity is 3 months
from calibration date.
© 2012 Housing & Development Board
Tempered-Free Test Equipment
For safety reason and to prevent unauthorized loading or unloading of the load test, the
hydraulic pump for the jack shall be encased in a steel or wooden box under lock and
key.
10
Valve of hydraulic pump and
pressure gauge sealed with
tape initialled by RE/RTO
Equipment to be encased in a
tempered-free box during the
holding period of pile load test
© 2012 Housing & Development Board
Pile Test Records
The Consultant needs to ensure that the test loading sequence is according to the approved Method Statement, and witness and verify the pile load tests.
To prevent any pre-loading of the test pile, the pile top levels are to be recorded before the erection of kentledge platform and after the load test in the pile load test record.
11
ABC XYZ DEF
Pile Top Level
Before & After
Contractor
endorsement RTO
endorsement
RE
endorsement
QP to endorse and
to indicate follow-
action where
necessary.
Upon completion of all the pile load tests, Consultant is to provide summary of pile load
test result to HDB (PD).
Please refer to sample of the form in Annex A.
© 2012 Housing & Development Board 12
Pile load test settlement requirements
Ultimate Load Test (ULT)
2x Working Load (holding 24hrs) : not exceeding 25mm
2.5x Working Load (holding 72hrs) : no ultimate geotechnical failure
For instrumented ULT :
After testing to 2.5 x Working Load, the test pile is loaded up to 3x Working Load or as instructed by SO Rep.
Standard Load Test (SLT)
1x Column Load + 2x NSF : not exceed 10mm [if pile is designed for negative skin friction(NSF)]
2x Working Load (holding 72hrs) : not exceeding 25mm
© 2012 Housing & Development Board
Pile Record
13
6 Bored Pile Records
Rock Socket Level :___________
Pile installed with UPVC pipe: Yes/No
The Consultant shall ensure that the Contractor maintains and updates the bored
pile records after each pile installation and to be submitted to the RE/RTO by the
next working day. For the purpose of payment for coring through rock layer, the rock
socket level shall be clearly indicated on the pile records form. A sample of the form
is shown below. The form shall be endorsed by the Contractor’s Representative and
the Consultant’s RTO & RE.
Some essential records:
• Pile Reference
• Boring Details
• Soil Description
• UPVC Pipe
• Rock Socket Level
• Endorsements
Please refer to sample of the form in Annex A.
© 2012 Housing & Development Board
Audits by HDB on Pile Penetration Length
In addition to the quality and integrity of the piles, HDB conducts audit checks on pile penetration records (for bored piles with dry casting method only).
The purpose of pile penetration depth audit is to ascertain that the amount of piling work (pile size and depth) on record tallies with the actual piling work done on site.
The procedure required are as follows:
14
Audit on Pile Penetration Length
PM/RE notifies HDB PD to arrange for pile audit check by IAD
(to provide pile layout plan & piling record)
IAD and PD select 5% of the total number
(dry piles with UPVC pipes only)
Contractor prepares piles for checking within 7 days
PM/RE inform IAD and PD for checking
IAD, PD, RE and Contractor to conduct physical check on site
RE prepares the record for Physical Checking, to be signed by RE,
Contractor’s PM & HDB rep (IAD & PD/PDA)
IAD and PD inform PM/RE on selected piles
During partial/full completion of piling works (by block)
7 Pile Length Audit
© 2012 Housing & Development Board 15
To provide UPVC pipe for checking on pile
length (for bored piles with dry casting
method only)
RTO to document the record
of UPVC pipe installation
Contractor is to take the necessary precautionary measures to prevent damage to the UPVC pipe before the pile penetration check.
For bored piles with dry casting method, the Contractor shall install a 16mm internal
diameter hollow UPVC pipe of approved quality with a pre-laid 3mm wire.
UPVC pipe is cut and
capped after concreting
Please refer to sample of the form in Annex A.
© 2012 Housing & Development Board
8 Service Road, Drain and Minor Sewer
16
Construction of the service roads shall not commence until the construction of drains is
sufficient to permit drainage of the road formation.
Existing level constraints
In drain construction, the proposed invert level may not match the existing drain invert
level at the discharge point. Adjustment to the upstream level may needed to ensure that
the proposed gradient is achieved. Hence, it is important to conduct check to these levels
before the drain construction so that any adjustment to the drain depth / gradient can be
made, if necessary.
Service roads have been incorporated to HDB development to provide access to the Multi-
storey carparks and other services such as the Electrical Sub-station, Central Refutes
Chutes and in some cases serve as Fire Engineer Access. Parking lots for handicapped
drivers and service bays as alighting and pick-up points are provided along service roads
where required.
Service Road and Drain Construction
Service Road with drain within driveway
© 2012 Housing & Development Board
Bakau Piling to Drain Culvert
Bakau Piling
Depending on the soil condition, bakau piling to drain may be required as specified by the
QP and indicated on the drawings.
Bakau pile shall be driven with piling frame with a drop hammer of approved weight of not
less than 200kg to a final set of 200mm for the last 10 blows from the drop of 1.0m to
1.5m height.
The Contractor shall submit the method statement to the Consultant before commencing
the bakau piling. All piling information shall be recorded.
Preparation for lean concrete and
subsequent drain base construction
Bakau Pile installation in progress
17
The centre
line and the
positions of
the piles
shall be
pegged.
© 2012 Housing & Development Board 18
Galvanised Grating
Galvanised gratings shall be tested for their zinc mass coating. 2% of the total
number of gratings installed or a minimum of 3 numbers of gratings shall be
selected for testing.
Grating and frame to
drain opening
The mass of zinc coating on each grating shall comply with the following average
coating mass:
© 2012 Housing & Development Board 19
Interlocking Paving blocks
Sampling and Test Requirements
A total of 16 blocks shall be tested for each
550m2 of interlocking pavement.
The maximum dimensional deviations from
the standard work sizes for the paving blocks,
measured in accordance with BS 6717: Part
1o or SS 76M , shall be as follows :
Length : ±2mm
Width : ±2mm
Thickness : ±3mm
Homogeneous or Non-homogenous Coloured Paving Block
Coloured paving blocks formed by addition of pigments may be either homogeneous
or non-homogeneous in colour. Non-homogeneous coloured paving blocks are
considered as composite concrete paving blocks.
The coloured surface shall not be less than 5mm thick. A total of 5 composite
concrete blocks shall be checked for surface layer thickness compliance for each
550m2 of interlocking pavement.
Non-homogeneous
(composite concrete paving block)
Homogeneous
The average compressive strength shall not be less than 49N per mm2 and crushing
strength of any individual blocks shall not less than 40N per mm2.
© 2012 Housing & Development Board 20
Interlocking Pavement Construction
Typical Section of Service Road
Interlocking paving
blocks (80mm thk)
Crusher run (200mm thk)
Hardcore (150mm thk)
Subgrade ( 500mm thk)
Bedding sand (50mm thk)
Interlocking concrete pavement are introduced to service roads because of their myriad
design, pattern arrangement and colour scheme in lieu of the dull concrete and bituminous
pavements
Bedding sand shall be
well- graded sand passing
a 4.75mm sieve.
Crusher run material
consists of hard, clean,
durable and angular
material with a nominal size
of not more than 125mm.
Hardcore shall be
composed of approved
broken stone, brick,
concrete not exceeding
150mm or less than 60mm.
Sub-grade material should have
a minimum soaked CBR of 5%
and compacted to minimum of
95% of maximum dry density
using AASHTO compaction test
© 2012 Housing & Development Board 21
Testing of Water-tightness of Sewers
Records of water tightness test to
be endorsed by Consultant’s &
Contractor’s Reps
All sewers below 600 mm in diameter before being surrounded and covered shall be
tested by filling with water. The pressure shall be measured from the highest point of
the pipeline under test and shall be 1.5 metre head of water. Pipelines should not be
accepted until they have withstood the required pressure for 30 minutes without a
loss in excess of 1.5 litres for 100 m for each 300 mm in diameter.
© 2012 Housing & Development Board 22
Materials Test
Service Road/Drain Material Relevant Tests
Precast Concrete Drain Channel, Kerb Water Absorption Test
Interlocking Concrete Paving Block Compression Test, Surface Layer
Thickness
Hot Dipped Galvanised Hinged Grating Zinc Mass Coating Test
Compaction of Road Formation Compaction Test (Dry Density-Moisture
Content Relation), In-situ Field Density
Test
Compaction of Sub-grade CBR Test
The Consultant shall plan and schedule the materials for testing. To avoid abortive work, the
test results should be obtained before allowing the use of materials for construction.
Sample list of materials for testing:
© 2012 Housing & Development Board
The Contractor is required to submit to the Consultant the daily programme showing
the piles to be installed as below :
23
9 Good Practices
Piles In Close Proximity
The Consultant is to check the sequence of the pile installation to ensure that piles
in close proximity are not installed on the same day. This is to avoid any disturbance
to shaft friction and setting of the concrete.
Sequence and Daily Pile Installation Programme
Indicate location of the
piles to be installed for
the day
Update the date of
installation and pile
length
16/4/09
38.2m
Daily programme for BLK XXX
Date :
Pile Dia (mm) Pile location
900 G9/1
900 G12/4
900 G1/2
1100 G20/1
900 G5/4
© 2012 Housing & Development Board
Measuring Tapes
To ensure measuring tapes used are not tampered with, the Consultant shall check the
measuring tapes used on site for the measurement of pile penetration depth.
24
The Consultant is to ensure measuring tapes used are not tampered with.
© 2012 Housing & Development Board
Temporary Casing
For the safety of workers and to prevent loose materials from dropping into the bored
holes, a temporary casing of at least 1 m height from the ground level shall be
provided.
25
Proper storage of reinforcement cage
The contractor shall designate a proper storage area to store the reinforcement cage.
> 1m casing
above ground
Reinforcement
cage shall be
elevated from the
ground.
© 2012 Housing & Development Board
Interlocking block around services/ manhole covers
Site Supervisors should know the details well and to conduct checks to ensure that
work is carried out according to the drawings.
26
Edges of manholes should be surrounded with paving blocks.
Kerb details around turning corner
Corner kerb formed with sharp
turn
Correct type of kerb as
shown in drawing should be
installed.
© 2012 Housing & Development Board
10 Annex - Forms for Reference
27
Record of Condition of UPVC Pipes Installed in Bored Piles
© 2012 Housing & Development Board 28
© 2012 Housing & Development Board
Summary of Load Tests Results
29
© 2012 Housing & Development Board
Acknowledgements
The Supervision Guides Editorial Team would like to express its thanks and
appreciation to Mr Tan Thu Liak, Mr Lim Seam Teong, Mr Alan Tang Liang Yah,
Mr Patrick Ng Hak Wue, Mr Chan Yee Soo, Mr Shaifuddin Bin Md Salleh and all
others who have in one way or another contributed towards the success of this
Guidebook.
The Editorial Team Mr Neo Poh Kok
Ms Magdalene Tan Ee Yin
Mr Lim Kee Thiam
Ms Fauziah Bte Jaafar
Ms Kelly Foo Siew Lin
2012 Edition
Together, we provide excellent project management to deliver quality homes in a sustainable environment.