HDB_Civil Engineering Supervision Guide 2012.pdf

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

http://bgbiz.hdb.gov.sg/









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


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


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


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.


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 ?


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


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 (scheduled by IRD)

Maximum Duration


*For buildings of 30 or more storeys, QP(Geo)/AC(Geo) are required for foundation design submission.


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.


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


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.


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


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



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


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



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


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.


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:


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.


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


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.


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:


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


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.


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.


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.


10 Annex - Forms for Reference

27

Record of Condition of UPVC Pipes Installed in Bored Piles


Summary of Load Tests Results

29


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.

HDB_Civil Engineering Supervision Guide 2012.pdf

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