Method Statement for Construction of Drainage and Manholes

Penta-Ocean Construction Co., Ltd. Ref.: MS/C/024

Shatin to Central Link Contract 1102 – Hin Keng Station and Approach Structures

Revision : - Date: 8-11-2013

Method Statement for Construction of Drainage and Manholes Page: 1 of 15

Method Statement

For

Construction of Drainage and Manholes

For

Hin Keng Station & Approach Structures, Contract No. 1102

This document contains confidential information of Penta-Ocean Construction Co., Ltd. and shall not be copied or amended without approval of the Project Manager

Rev Issue Date Status Prepared by Reviewed by Reviewed by Engineer /

Construction Manager

QA Manager Safety Manager

- 29-10-2013 Submission

Joe Wong Helen Tong Alex Lam

Date: Date: Date:

Reviewed by Approved by Senior Construction

ManagerProject Manager

Colbert Cheung Wilson Chu

Date: Date:

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Content Page

1. The Scope of Works ……………………………………………………………… 3

2. Work methodology and Testing Procedure .….…………………………….…… 3

3. Material, Plants and Labour Resources ………………………………………... 9

4. Construction Programme ………………………………………………………… 9

5. Safety and Environmental Mitigation Measures ……………………………..….. 9

6. Flood Protection Measures ……………………………………………………… 10

7. Fire Detection and Protection Measures ……………………………………..… 10

8. Contingency Plan ………………………………………………………………….. 11

Appendices

Appendix A – Layout plan (1102/W/HIK/SWL/C14/011 to 018 and Suggested Drainage Layout in Hin

Tin Playground)

Appendix B – Typical section for drainage construction and manhole construction.

Appendix C – Inspection & Testing Plan

Appendix D – Risk Assessment

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1. The Scope of Works

This method statement is purposed to establish and illustrate the construction method for both

pipeworks (Storm and Sewerage) and manholes for Shatin to Central Link (Contract 1102 – Hin

Keng Station and Approach Structures) Project as specified in project specification. This method

statement outlines the procedure for constructing drainage pipes to fulfill the oncoming needs of

Hin Keng Station. In addition, this report will also intend to describe the concreting procedures of

manholes.

The proposed alignment and location of pipeworks and manholes please refers to the enclosed

drawings in Appendix A.

2. Work Methodology and Testing Procedure

Underground Services location plans made available by the Client/ Engineer will be viewed. A

Cable Avoidance Tool (CAT) will be used to identify the location of underground services before

excavation.

2.1 Procedures of pipe laying

2.1.1 Stormwater pipes – Precast Concrete Pipe

i) Set out the alignment on site according to approved shop drawings.

ii) Fence off the working area and plants.

iii) Install sheet piles along the alignment of pipeline at both side according to the ICE certified

design (Please refer to the section 1-1).

iv) Excavate a trench between sheet piles to approximate 500mm below 1st layer of wailing and

strut.

v) Install 1st layer of steel wailing and steel strut at level 1.0m below adjacent ground in

accordance with ICE certified design. (Please refer to the section 2-2 and 3-3).

vi) Further excavate the ground down to approximate 500mm below 2nd layer of wailing and

strut.

vii) Install 2nd layer of wailing and strut about 3.0m below the ground surface. (Please refer to the

section 4-4 and 5-5).

viii) Repeat Step vi) and vii) for remaining strut and wailing if required.

ix) Excavate the ground down to final formation level. (Please refer to the section 6-6).

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x) Install temporary pump and pump sump during construction if necessary. All water shall be

pumped to the waste water sedimentary tank and discharged to EPD’s approved water

discharge points.

xi) Place concrete blinding to the formation level to provide suitable working environment if

necessary.

xii) Construct the bedding for the pipe. For the bedding of storm water drains which is divided

into Type A bedding and Type B bedding.

(1) For Type A bedding, plain concrete cradle will be constructed to support the pipes.

(Please refer to the section 7-7a)

(2) For Type B bedding, the bottom of trenches will be filled with compacted filling materials.

(Please refer to the section 7-7b).

xiii) Cut pipe into appropriate length for installation if required.

xiv) Lay the pipes directly on the plain concrete cradle (Type A bedding) or compacted soils

(Type B bedding).

xv) Seal externally and internally with cement mortar for the joint between the cut pipe and the

pipe to which it is connected. And the cement mortar shall consist of cement and sand in the

proportions 1:3 by mass.

xvi) Carry out air test or water test for the installed pipeline.

xvii) Clean the pipeline by pigging, high pressure water jetting or other method approved by the

Engineer.

xviii) Carry out 1st layer of backfilling from the proposed formation level to 300mm above the top of

the pipe with lightly compact by hand rammers or manually operated power equipment. Fill

material within 1st layer of backfilling shall be compacted to at least 85% of the maximum dry

density and it shall be deposited in layers not exceeding 100mm. In addition, the difference in

fill levels between the two sides of structures or utilities during compaction shall not greater

than 250mm. (Please refer to the section 8-8).

xix) Carry out 2nd layer of backfilling from 300mm above the top of the pipe to 500mm below the

lowest layer of strut and wailing. Fill material shall be compacted by vibrating roller to at least

95% of the maximum dry density and it shall be deposited in layers not exceeding 250mm.

And then the lowest layer of strut and wailing will be removed. (Please refer to the section 9-

9).

xx) Carry out 3rd layer of backfilling from 500mm below the lowest layer of strut and wailing to

500mm below 1st layer of strut and wailing. Fill material shall be compacted by vibrating roller

to at least 95% of the maximum dry density and it shall be deposited in layers not exceeding

250mm. And then 1st layer of strut and wailing will be removed. (Please refer to the section

10-10). (It is noticed that if there are having 3 rows of strut and wailing in the trench, then the

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3rd layer of backfilling should only fill from 500mm below the lowest layer of strut and wailing

to 500mm below 2nd layer of strut and wailing, and then repeat step xix) till 500mm below the

existing ground level).

xxi) Carry out 4th layer of backfilling from 500mm below 1st layer of strut and wailing to the

existing ground level. Fill material shall be compacted by vibrating roller to at least 95% of

the maximum dry density and it shall be deposited in layers not exceeding 250mm. (Please

refer to the section 11-11).

xxii) Remove the sheet piles and reinstate the ground surfaces as per original. (Please refer to

the section 12-12).

xxiii) Carry out CCTV inspection before the pipeline is handed over.

2.1.2 Sewer pipes – Vitrified Clay Pipe

i) Set out the alignment on site according to approved shop drawings.


iii) Install sheet piles along the alignment of pipeline at both side according to the ICE certified

design.

iv) Excavate a trench between sheet piles to approximate 500mm below 1st layer of wailing and

strut.

v) Install 1st layer of steel wailing and steel strut at level 1.0m below adjacent ground in

accordance with ICE certified design.

vi) Further excavate the ground down to approximate 500mm below 2nd layer of wailing and

strut.

vii) Install 2nd layer of wailing and strut will be installed about 3.0m below the ground surface.

viii) Repeat Step vi) and vii) for remaining strut and wailing if required.

ix) Excavate the ground down to final formation level.

x) Install temporary pump and pump sump during construction if necessary. All water shall be


discharge points.

xi) Place concrete blinding to the formation level to provide suitable working environment if

necessary.

xii) Cut pipe into appropriate length for installation if required.

xiii) Lay the pipes.

xiv) Seal externally and internally with cement mortar for the joint between the cut pipe and the

pipe to which it is connected. And the cement mortar shall consist of cement and sand in the

proportions 1:3 by mass.

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xv) Carry out air test or water test for the installed pipeline.

xvi) Clean the pipeline by pigging, high pressure water jetting or other method approved by the

Engineer.

xvii) Construct concrete surround for the laid pipes for pipes protection.

xviii) Carry out 1st layer of backfilling from the proposed formation level to 300mm above the top of

the pipe with lightly compact by hand rammers or manually operated power equipment. Fill

material within 1st layer of backfilling shall be compacted to at least 85% of the maximum dry

density and it shall be deposited in layers not exceeding 100mm. In addition, the difference in

fill levels between the two sides of structures or utilities during compaction shall not greater

than 250mm.

xix) Carry out air test or water test for the installed pipeline.

xx) Carry out 2nd layer of backfilling from 300mm above the top of the pipe to 500mm below the

lowest layer of strut and wailing. Fill material shall be compacted by vibrating roller to at least

95% of the maximum dry density and it shall be deposited in layers not exceeding 250mm.

And then the lowest layer of strut and wailing will be removed.

xxi) Carry out 3rd layer of backfilling from 500mm below the lowest layer of strut and wailing to

500mm below 1st layer of strut and wailing. Fill material shall be compacted by vibrating roller


250mm. And then 1st layer of strut and wailing will be removed. (It is noticed that if there are

having 3 rows of strut and wailing in the trench, then the 3 rd layer of backfilling should only fill

from 500mm below the lowest layer of strut and wailing to 500mm below 2nd layer of strut and

wailing, and then repeat step xix) till 500mm below the existing ground level).

xxii) Carry out 4th layer of backfilling from 500mm below 1st layer of strut and wailing to the

existing ground level. Fill material shall be compacted by vibrating roller to at least 95% of

the maximum dry density and it shall be deposited in layers not exceeding 250mm.

xxiii) Remove the sheet piles and reinstate the ground surfaces as per original.

xxiv) Carry out air test or water test. And carry out infiltration test not more than 7 days before the

pipeline is handed over.

xxv) Carry out CCTV inspection before the pipeline is handed over.

2.2 Construction sequences of manhole:

2.2.1 Manhole – Max. depth more than 3.5m

i) Set out the location on site according to approved shop drawings.


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iii) Install sheet piles around the location of manhole according to the ICE certified design. (Please

refer to the section 13-13).

iv) Excavate vertically between sheet piles to approximate 500mm below 1st layer of wailing and

strut. (Please refer to the section 14-14).

v) Install 1st layer of steel wailing and steel strut at level 1.0m below the adjacent ground in

accordance with ICE certified design. (Please refer to the section 15-15)

vi) Further excavate the ground down to approximate 500mm below 2nd layer of wailing and strut.

vii) Install 2nd layer of wailing and strut about 3.0m below the ground surface. (Please refer to the

section 16-16 and 17-17).

viii) Repeat step vi) and vii) for remaining strut and wailing.

ix) Excavate the ground down to final formation level, and 3rd layer of wailing and strut will be

installed, if required. (Please refer to the section 18-18)

x) Install temporary pump and pump sump during construction if necessary. All water will be


discharge points.

xi) Place 75mm thick blinding layer under the manhole. (Please refer to the section 19-19).

xii) Carry out survey to locate the level of connection points.

xiii) Erect formwork and fixing reinforcement bars. (Please refer to the section 20-20).

xiv) 1st pour: Bedding and haunching will be constructed and it will only be cast within one time

provided with a longitudinal C.J. (Please refer to the section 21-21).

xv) 2nd pour: 1. 5m of manhole’s wall will be cast within one time provided with a longitudinal C.J.

(Please refer to the section 22-22).

xvi) 3rd pour: Reducing slab and wall below 0.15m high of ground level will be cast in one time.

(Please refer to the section 23-23).

xvii) Install certificated step irons and covers. (Please refer to the section 24-24).

xviii) Carry out air test.

xix) Clean the manhole.

xx) Carry out 1st layer of backfilling from the proposed formation level to 500mm below the lowest

layer of strut and wailing. Fill material shall be compacted by vibrating roller to at least 95% of

the maximum dry density and it shall be deposited in layers not exceeding 250mm. And then

the lowest layer of strut and wailing will be removed. (Please refer to the section 25-25).

xxi) Carry out 2nd layer of backfilling from 500mm below the lowest layer of strut and wailing to

500mm below 1st layer of strut and wailing. Fill material shall be compacted by vibrating roller to

at least 95% of the maximum dry density and it shall be deposited in layers not exceeding

250mm. And then remove 1st layer of strut and wailing. (Please refer to the section 26-26).

xxii) Carry out 3rd layer of backfilling from 500mm below 1st layer of strut and wailing to existing

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ground level. Fill material shall be compacted by vibrating roller to at least 95% of the maximum

dry density and it shall be deposited in layers not exceeding 250mm. (Please refer to the

section 27-27).

xxiii) Remove the sheet pile and reinstate the ground surfaces as per original.

2.2.2 Manhole – Max. depth less than 3.5m

i) Set out the location of site according to the approved shop drawings.


iii) Install sheet piles around the location of manhole according to the ICE certified design.

iv) Excavate vertically between sheet piles to approximate 500mm below 1st layer of wailing and

strut 1st layer of wailing and strut will be installed about 1.0m below the ground surface.

v) Excavate the ground to the proposed formation level.

vi) Install temporary pump and pump sump during construction if necessary. All water will be


discharge points.

vii) Place 75mm thick blinding layer under the manhole.

viii) Carry out survey to locate the level of connection points.

ix) Erect formwork and fixing reinforcement bars.

x) 1st pour: Bedding and haunching will be constructed and it will only be cast within one time

provided with a longitudinal C.J.

xi) 2nd pour: 1.75m of manhole’s wall will be cast within one time provided with a longitudinal

C.J.

xii) 3rd pour: Reducing slab and wall below 0.15m high of ground level will be cast in one time.

xiii) Install certificated step irons and covers.

xiv) Carry out air test.

xv) Clean the manhole.

xvi) Carry out 1st layer of backfilling from the proposed formation level to 500mm below the lowest

layer of strut and wailing. Fill material shall be compacted by vibrating roller to at least 95%

of the maximum dry density and it shall be deposited in layers not exceeding 250mm. And

then the lowest layer of strut and wailing can be removed.

xvii) Carry out 2nd layer of backfilling can be carried out from 500mm below the lowest layer of

strut and wailing to existing ground level. Fill material shall be compacted by vibrating roller


250mm. The sheet pile can be removed and then the ground surfaces should be reinstated

as per original.

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2.3 Testing procedure

2.3.1 Sequence of air test:

i) Remove all obstructions, debris and superfluous matter from the pipelines.

ii) Seal the end of all the pipelines and associated branches under test by expanding drain

plugs or inflatable canvas or rubber test bags.

iii) Connect a U-tube manometer to the pipelines.

iv) Pump air into the pipeline until a test pressure of slightly more than 100 mm of water is

registered on an U-tube manometer connected to the pipeline. 5 minutes shall be

allowed for stabilization of the air temperature and the air pressure shall then be

adjusted to 100 mm of water.

v) Read the pressure from the U-tube at the end of a 5 minutes period without further

pumping.

vi) Measure the air pressure inside the pipelines upon test start.

vii) Measure the loss of air pressure inside the pipelines.

2.3.2 Sequence of water test:

i) Remove all obstructions, debris and superfluous matter from the pipelines.

ii) Secure all drain stoppers and/ or bags in the end of the pipelines and all associated

branches under test.

iii) Fill water to the pipelines at least 2 hours before the test to allow for water absorption.

iv) A test pressure of 1.2m head of water above the soffit of the pipe at the high end shall

be applied at the standpipe and maintained for 30 minutes; the test pressure applied

shall not exceed 6m head of water at the invert the low end of the pipe.

v) The head of water at the standpipe shall be topped up at 5 minutes intervals during the

test and shall be filled to the specified head at the end of the test period by adding

measured quantities of water to the standpipe.

vi) The leakage of water from the pipeline shall be measured as the amount of water

added to maintain the specified test pressure.

2.3.3 Sequence of infiltration test:

The procedure for the infiltration test shall be accordance with BS8005: Part 1 Clause 13.6.

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3 Material, Plants and Labour Resources

5 - 10 workers at peak time,

Working and lifting platform with Certificate,

Backhoe,

Welding machine,

Vibrator,

Rigger,

Steel stairways,

Generator,

Pumps and concrete pump,

Wooden chutes, and

Small hand tools and/ or other tools necessary for in-situ concrete casting work.

4 Construction Programme

Tentative Start: Mid-October 2015;

Tentative Finish: Mid-March 2016.

5 Safety and Environmental Mitigation Measures

i) All workers are required to attend pre-work health check by Site Nurse before attending

Safety Induction Training and a Site Gate Pass will be issued to workers who pass the

pre-training written test.

ii) All workers are required to wear safety helmet, safety shoes and reflective vest. In

addition, appropriate PPE, such as, eye protector, approved ear protector, duct mask,

safety harness and so on, should be used in accordance with the nature and hazards of

the works.

iii) Temporary shoring system shall be properly designed. ICE shall check and certify the

temporary works design. After completion of shoring system, ICE shall check and

certify the construction of temporary works construction before carrying out any soil in-

site test.

iv) Weekly regularly inspection and checking will be carried out by Competent Person.

v) Lifting appliances should be equipped with safe load indicator. The lifting appliances

and lifting gears should be certified by RPE with valid testing and examination

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certificates. Operator should also enter the result of weekly checking into the prescribed

inspection Form 1.

vi) No load should be allowed to be carried out outside the site boundary and no worker is

allowed to work below the lifting route.

vii) Waste water sedimentary tank shall be provided on site. All water shall be properly

discharged to EPD’s approved water discharge points.

viii) Permit to Operate, Permit to Move, Permit to Dig and Hot Work Permit should be strictly

implemented.

ix) All bodily injury, accident incident or near miss should be reported to foreman or Safety

Officer immediately.

x) All mobile crane and generator shall be silent type.

xi) Regularly check the generator and electrical tools by registered electrician. Provide

proper earth-rod; provide emergency stop button; Stop the generator when refuelling.

6 Flood Protection Measures

Temporary soak away pit and temporary pump pit should be provided at low-point area to avoid

water flooding.

7 Fire Detection and Protection Measures

Smoking is prohibited on site

Provide sufficient fire extinguishers in good conditions at working place.

8 Contingency Plan

The movement monitoring on tracks and adjacent Operational Railway Facilities shall be conducted

concurrently to review any impact caused by construction of pipelines and manholes.

If the movement due to construction processes exceeding the Alert values be observed, the

Contractors shall revise his method excavation and enhance the monitoring scheme including real-

time monitoring tract. The Contact will resubmit the method statement to the Engineer and Railway

Operator for Approval.

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Appendix A

Layout plan (Drawing Number: 1102/W/HIK/SWL/C14/011 to

018).

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Appendix B

Typical section for drainage construction and manhole

construction

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Appendix C

Inspection and Testing Plan

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Appendix D

Risk Assessment

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Method Statement for Construction of Drainage and Manholes

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