MS for Bored

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PROPOSED NEW ERECTION OF BUSINESS PARK BUILDING

ON LOT 8081W PT (PLOT 4A) MK 5

AT INTERNATIONAL BUSINESS PARK

REV: 0

METHOD STATEMENT

FOR

BORED PILE INSTALLATION

BY

PSL ENGINEERING PTE LTD

PROPOSED NEW ERECTION OF BUSINESS PARK BUILDING ON LOT 8081W PT (PLOT 4A) MK 5 AT INTERNATIONAL BUSINESS PARK – REV: 0 Method Statement For Bored Piling Works Date: 24 Sep 07

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Table of Contents

Chapter 1: Method Statement for Bored Pile Installation 1. System of Foundation

2. Specification of Concrete

3. Steel Reinforcement for Bored Piles

4. Piling Procedure

5. Safety Measures/Risk Assessement

Chapter 2: Site Records and Resources 1. Site Records

2. Resources

Appendix A Brochure for Polymer (Vinil-Mud)

Appendix B Safety Measures / Risk Assessment

Appendix C Forms for Site Records

Appendix D Site Organization Chart

Appendix E Machinery & Skill Proficiency Certificates

Appendix F Brochures for Plant and Machinery

Appendix G Construction Drawings


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CHAPTER 1

METHOD STATEMENT FOR BORED PILE INSTALLATION

1. System of Foundation

1.1 The system of foundation proposed is Bored Cast-In-Situ Reinforced Concrete Piles. (See Figure 1)

Cut-Off-Level

Figure 1

2. Specification of Concrete

2.1 Concrete Strength

2.1.1 The design characteristic strength of the ready-mixed concrete at 28 days shall be Grade 35, as per

specified in the drawings.

2.2 Type of Concrete

Grade 35 ready-mixed concrete of slump 175 ± 25mm shall be placed in the completed borehole by

tremie pipe.

3. Steel Reinforcement for Bored Piles

3.1 The steel reinforcement shall be high-strength steel to BS 4449. Details of reinforcement cage for

bored piles shall be in accordance with the piling plan issued by the Consultant, drawing no. P-1 Rev

1.


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4. Piling Procedure

4.1 Setting Out Pile Position

4.1.1 Setting out of piles shall be carried out from the main grid lines or the corner pegs of the proposed

structure.

4.1.2 The position of the casing can be checked by placing 2 reference pins, aligned perpendicularly to the

casing. The reference pins are placed at an equal a distance away from the actual proposed position.

(See Figure 2)

Figure 2

4.2 Temporary Steel Casing

4.2.1 To maintain the borehole stability in the soft strata, a temporary steel casing will be inserted. The

temporary steel casing will be inserted by means of a vibro hammer. Where stabilizing fluid is not

used for borehole stabilization, the temporary steel casing shall be driven to refusal or at least 1m below the soft strata (see Figure 3). The vibro hammer used for temporary casing installation shall

not generate ground vibrations that would exceed the limit of 10mm/sec set by the qualified person,

measured at the location of closest neighboring structure.

Figure 3

Temporary Casing

Soft Strata

Hard Strata

Reference Pin

Reference Pin Pile Position

1m


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4.2.2 In the event where extension of additional length of temporary steel casing is not feasible or would

make handling of the long casing difficult operationally, polymer shall be used to stabilize the

borehole. The level of stabilizing fluid shall be maintained close to ground level during the pile

construction. (See Figure 4). See Appendix A for brochure of polymer.

4.2.3 If collapsible soil is encountered below the toe level of the temporary steel casing, additional lengths

of temporary casings to seal off the collapsible layer shall be provided. Welding shall be used to join

the temporary steel casings.

Figure 4

4.2.5 The verticality of the temporary steel casing affects the eccentricity and verticality of the bored pile, therefore it is essential that the temporary steel casing is inserted upright.

4.2.6 The verticality of the casing shall be checked during the insertion of the temporary steel casing. This

can be done by using a plumb to visualise the verticality of the casing. This visual method of the

casing shall be checked in two perpendicular directions to ensure the verticality of the casing.

Figure 5

Temporary Casing

Soft Strata

Hard Strata

Stand

Plumb

Stabilizing Fluid


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4.2.7 Or alternatively, the verticality of the steel casing can be determined by placing a spirit level on the

temporary steel casing. This shall be carried out in two perpendicular directions to ensure verticality

of the temporary steel casing.

4.3 Verticality of Borehole

4.3.1 The verticality of the borehole and hence the pile shall be ensured by checking and maintaining the

verticality of the Kelly Bar of the boring rig. This can be done by using a plumb to visualise the

verticality of the Kelly Bar. This visual method shall be checked in two perpendicular directions.

4.3.2 The verticality of the Kelly Bar must be checked before commencement of boring. The Banksman

shall conduct subsequent checks periodically during boring. The frequency of checks shall be as (but

not limited to) the description below:-

(a) Before boring works commences;

(b) Immediately after insertion of Temporary Casing; and

(c) Every 6m of penetration beyond the toe level of the casing.

4.3.3 A guiding rod extending about 1m above the ground level and another guiding rod extending from

the piling rig shall be used to guide the rotational position of the piling rig. When the two rods are

aligned, the piling rig will be in the original position as it was when the center of the hole had been

checked. (See Figure 6)

Figure 6

4.4 Piling Tolerances

The positional and verticality tolerance of the piles shall not exceed the following limits:

Positional Tolerance

(eccentricity in any direction)

Verticality Tolerance

75mm 1:75 (1 horizontal to 75 vertical)


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4.5 Boring of Pile

4.5.1 Boring shall be carried down to the required strata and depth by either a hydraulic or mechanical

powered boring rig which are capable of sinking bored holes of diameter ranging from 450 mm to 1400 mm and up to a depth of 60 metres.

4.5.2 On completion of boring (achieving required penetration depth), a cleaning bucket shall be used. This

is to ensure that a good sound base can be achieved. The loose, disturbed or remolded soil shall be

removed from the base of the borehole by the Cleaning Bucket.

4.6 Placing Reinforcement Steel Cage

4.6.1 Reinforcement Details

Steel reinforcement cages will be prefabricated in sections complete with circular or spiral links,

appropriate spacers and stiffeners. The steel cages are generally composed of 12m and 6m long sub-

cage elements.

4.6.2 Spacers

Circular plastic spacers will be used to provide 75mm of concrete cover. The spacers will be affixed

on to the links. Spacing of spacer block along the reinforcement cage shall be 5m apart. A minimum

of three layers of will be provided for each 12m reinforcement cage. Each layer of spacer shall have a

minimum of three spacers.

4.6.3 Lapping of Cages If lapping of reinforcement cage is required, U-Clips or welding of minimum 50mm will be provided

to join the cages at the starter bars. Depending on the total cage length, the reinforcement cage may

be lapped prior to installation and lowered together into the borehole or lapped at the borehole

location and lowered after each lapping is completed. For the latter, the reinforcement cage shall be

properly supported on top of the temporary steel casing before lapping operations.

4.6.4 Lowering of Cages into Borehole

The service crane will be used to lift the cages using chains and hooks. For the lifting of cages during

installation, horizontal lifting supports will be welded to the rebar at the top of cage. Prior to

lowering into the borehole the lifting chain shall be slung around the horizontal lifting supports.

During the lowering of the reinforcement steel cage into the borehole, the hooks of the lifting chain

will be hooked onto the horizontal lifting supports. The steel cages shall be maintained at cut off

level by steel bars or wire ropes fastened to the temporary casing. The lifting chain will be dislodged

from the horizontal lifting supports once the temporary supports are in place.

4.6.5 Cleaning of Cages

When the cage is being installed into the bored hole, general workers will use wire brushes to remove

the unwanted soil material (if any) from the steel cage and also to ensure that cover spacers are not

dislodged.

4.7 Casting of Pile

4.7.1 Concrete shall be placed into the borehole via tremie pipe.

4.7.2 For dry boreholes that contain less than 300mm of water at the bottom, the overcast shall be kept to

about 0.5 metres above the cut off level.


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4.7.3 For wet boreholes, the overcast shall be kept to about 1.0 metres above the cut off level.

4.8 Tremie Pipe

4.8.1 Where concrete is to be placed into a wet borehole, tremie pipes shall be used to direct the concrete

to the base of the borehole without excessive contact with fluid inside it.

4.8.2 In the event that stabilizing fluid is used, Vermiculite shall be placed in the pipe. This is to prevent

direct contact between the first discharge of concrete in the tremie pipe and the stabilizing fluid.

4.8.3 The tremie pipe shall be extended to the base of the bored hole.

4.8.4 The tremie pipe will be reduced in length progressively during concreting but at least 3 metres of the

tremie pipe shall be embedded into the previously placed concrete. The pipe shall not be withdrawn

from the concrete until the completion of casting. (See Figure 7)

4.8.5 The internal diameter of the tremie pipe shall be large enough to allow for continuous pour with

minimal time.

4.8.6 The internal surface of the tremie pipe shall be cleaned immediately after use to prevent the pipe

from being clogged with concrete.

Discharged Concrete

Tremie Pipe

Concrete >3 m

Figure 7


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4.9 Removal of Temporary Steel Casing

4.9.1 Vibro Hammer shall be used to withdraw the Temporary Casing from the bored hole immediately

after concreting.

4.10 Backfilling of Empty Bored Hole

4.10.1 After each pile has been cast and the temporary steel casing removed, any empty bored hole above

the concrete level shall be backfilled with excavated material immediately. (See Figure 8)

Figure 8

Backfilled

Soil

> 500 mm Cut-Off-Level


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CHAPTER 2

SITE RECORDS AND RESOURCES

1. Records

1.1 Recording of all levels and timing shall be done by PSL Engineering site personnel. Leveling

instruments and measuring tapes shall be used for this purpose

1.2 Detail for the daily activity and bored piling will be recorded as follows: a) Daily Piling Record

b) Bore Pile Record

1.3 The penetration depth of the pile shall be taken by a measuring tape. The depth of the pile shall be

measured from either the existing Ground Level or the top level of the Temporary Casing to the toe

of the bored hole. Toe Level of the pile shall be equal to the Top Level of the casing or Ground Level

minus the piles penetration depth.

1.4 Eccentricity (ECC) of the bored shall be taken and endorsed by licensed surveyor. ECC of piles shall

be taken at the center of the concrete at Cut-Off-Level.

2. Resources

Plant / Equipment

The following key plant and equipment will be deployed:

No Description Quantity

1 Boring Rig Jin Tai SD 20

Soilmec R618

01

01

2 Crawler Crane R-B CH-50-HD

Linkbelt LS118RH-5

01

01

3 Excavator Kobelco K907 02

4 Vibro Hammer Mullar MH50

ICE 420

01

01

5 Welding Set 02

6 Container Office 05

APPENDIX A

BROCHURE FOR POLYMER

APPENDIX B

SAFETY MEASURES/RISK ASSESSMENT

APPENDIX C

FORMS FOR SITE RECORDS

APPENDIX D

SITE ORGANIZATION CHART

APPENDIX F

PILE LENGTH CALCULATION

APPENDIX E

MACHINERY & SKILL PROFICIENCY CERTIFICATES

APPENDIX F

BROCHURES FOR PLANT AND MACHINERY

APPENDIX G

CONSTRUCTION DRAWINGS

MS for Bored

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