Plant & Guide Wall Construction

METHOD STATEMENT FOR SLURRY PLANT & GUIDE WALL CONSTRUCTION DOWNTOWN LINE C907

For Approval Mar 2008

PROPOSED PROPOSED DOWNTOWN DOWNTOWN LINE L INE (DTL) PHASE 1 C907

METHOD STATEMENT FOR SLURRY SLURRY PLANT PLA NT INSTAL INSTALLA LATIO TION N & GUIDE GUIDE WALL WAL L CONSTRUC CONSTRUCTION TION

Version: Initial Submission

Diaphragm Walls Version 1 prepared by GWT

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CONTENT 1. Introduction 2. Scope of Works 3. Essential Measures Prior to Work Commencement 4. Roles and Responsibil ities of Key Personnel 5. Organizatio n Chart 6. Curriculum Vitae 7. Site Safety 8. Health & Environmental Controls 9. Slurry Plant & Guide Wall Constr uctio n 9.1. Site Installation 9.1.1. Site Static Installation 9.1.2. Restricted Activities within the Railway Protection Zone 9.1.3. Site Mobile Plants 9.1.4. Temporary Site Installation 9.1.5. Earth Control Measures and Wash Bays 9.2. Guide Wall Construct ion 9.2.1. Guide Wall Construction Method 9.2.2. Essential Measures 9.2.3. Alternative to Elevated Guide Walls 10. Safe Work Practic e 11. Appendix

A.

Site Organization Chart

B.

Key Personnel Curriculum Vitae

C.

Site Utilization Plan, Silo Slab Design Calculation and Footing Anchorage Details; Engineering Evaluation Report on Existing North South Line Tunnel Section due to Silo Tanks Loading; Engineering Evaluation Report on Existing North South Line Tunnel Section due to Bentonite Pond Construction; Engineering Evaluation Report on Existing North South Line Tunnel Section due to Machineries Loading.

D.

List of Major Plant and Equipment

E.

Plant and Equipment Catalogues

F.

Guide Wall Settingout Cross-Section, Guide Walls Structural Adequacy Check, Trench Stability Analysis

G.

Risk Assessment


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1.0 Introd uctio n

Diaphragm Wall is required for DTL Phase 1 C907 Landmark Station and Cut & Cover Tunnels, constructed from ground level at approximately 103.0mRL ~ 103.5mRL to founding elevation at 38.0mRL ~ 45.0mRL, varied in thicknesses and depths at various locations according to load bearing requirements and soil stratum. This method statement shall describe the preceding work processes involve with diaphragm wall construction, commencing from site installation till guide wall construction. Subsequent work processes involve with diaphragm wall construction shall be separately addressed in the Method Statement for Diaphragm Wall Construction.

2.0 Scope of Wor ks

The scope of work involves setting up of slurry plant, guide wall construction for Cut & Cover Tunnels (East & West) and Landmark Station under DTL Phase 1 Contract 907.

3.0 Essential Measures Prior to Work Commencement

3.1 Project Survey Control, Underground and Surrounding Structures Survey It is imperative to establish Project Setting-Out Control, Existing Underground Structures and Surrounding Development Survey, and incorporate the same with construction tolerances provided in Section 9 of Particular Specifications into Propose Development Setting-Out Plans to eradicate erroneous setting-out and prevent damage causes to the numerous vital underground structures and utilities underlaying propose development. Setting out shall be carried out by qualified surveyor. 3.2 Trial Trench Trial trench shall be carryout by Licensed Cable Detection Worker along propose work to ascertain physical layout and function [live, abandon] status of known utilities. Appropriate measures [protection, diversion, termination, weep holes plugging, etc] shall be determined and carryout prior to guide walls construction to ensure against underground utilities damages and slurry outflow. 3.3 Restricted Activities in Railway Protection Zone and Common Service Tunnel All works within the Railway Protection Zone and within 6m of Common Service Tunnel shall adopt restricted activities guidelines stipulated in Code of Practice for Railway Protection and Standard Operating Procedure for Works within 6m of CST Structure.


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4.0 Roles and Responsibil ities o f K ey Personnel

The responsibilities of the key personnel are specified herein. The number of site personnel will be provided according to production demand. Project Manager

- Plan and control overall project activity and budget, - Prepare production schedule, - Select and engage Subcontractors, - Promote safety, quality and productivity

Construction Manager

- Prepare work process methods, - Engineering proposals with applicable measures, - Temporary site installation structural adequacy checks and submission to Relevant Authorities, - Promote constructability, reduce waste and environment pollution

Site Manager (s)

- Requisite lifting appliances, construction accessories and consumables products, - Sequence work activities and resources availability, - Provide safe working space, - Work quality assurance

Site Engineer

- Work process inspections, - Coordinate all site activities, - Prepare daily report, casting record, panel report, consolidate data

Safety Supervisor(s)

- Prepare and seek work process permits, - Coordinate overall site activities - Carryout and enforce safe work practice, - Implement preventive measures to reduce risks and minimize work accident - Coordinate machinery and work processes - Controlling of manpower

Draft Person

- Coordinate dimensions, details, - Prepare, submit and issue shop drawings - Update amendments and as-built drawings

Purchaser

- Ensure product specification conformance and supply from reliable sources

Operator(s)

-Service crane, grab, cutter, excavator slurry plant operators conduct daily plant inspection and carryout works in their specialization

Skill Worker(s)

- Carrying out daily site activities.

5.0 Organizatio n Chart Propose Organization Chart is enclosed in Appendix A. Diaphragm Walls Version 1 prepared by GWT

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6.0 Curriculum Vitae Curriculum Vitae of the key personnel involve in this project is enclose in Appendix B. 7.0 Site Safety Safety is an indispensable construction process. Diaphragm wall production carryout from existing ground shall require work staffs to be provided with essential personnel protective equipment (PPE) such as safety boots, hard hats and gloves to protect the operatives from falling objects, hands abrasion, corrosive substances and hot works. High reflective vests shall also be worn to highlight operative visibility to moving vehicles / plant, particularly during night works.

Additional PPE example body harness, goggles, welding shields, filter masks shall be provided to others working at height, or involved in specialize operations alike blazing and welding works. All hot works shall be equipped with fire extinguisher. All new work staffs shall attend Safety Induction Course prior to carrying out site work. This process shall reinforce work staffs safety awareness and provide the opportunity to impart the Restricted Activities on site. Risk Assessment Report is enclosed in Appendix G. Safety Supervisor shall concenciously carry out the following to promote site safety: Issue personal protective equipment to work staffs with clear application instructions and keep record of all safety protective equipments issued to work staffs. Conduct toolbox meeting prior to the starting of work in the morning on a daily basis. Ensure good housekeeping on site. Refrain use of defective or worn lifting gears and tools and replace the same. File and verify certificates validity of all the lifting machinery, lifting gear etc. and inspect their condition worthiness. Notify, conduct investigation and prepare Dangerous Occurrence and Accident Reports. Practice safe works inspection and attend Safety Committee Meetings. •

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8.0 Health & Environmental Contr ols Noise The construction equipment used for diaphragm wall works shall not exceed 65dbl Noise limits set by the Ministry of Environment. Ai r B or ne Parti cl es Cont ro l Air pollution on site shall be effectively controlled through use of suitably power rated and properly maintained diesel engines. Employ screw conveyor and automated bentonite powder batching and mixing system to eliminate air borne pollution during bentonite mixing. Situate bentonite bulk bag over opening of dry bentonite silo will stopple air borne pollution during stock replenishment. Waste and Recycli ng The waste produced from this activity is limited to the use of Bentonite slurry. In order to protect the environment, the bentonite shall not be discharged into the public drain and would be disposed at the authorized disposal areas. Pest Contro l Maintain well drain working platform and drains free from stagnant water, reticulate stored slurries will eradicate mosquito breeding. All trash bins shall be covered to prevent crows and flies infestation. Conduct weekly inspection and carryout selective fogging and larvarciding.


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METHOD STATEMENT FOR SLURRY PLANT & GUIDE WALL CONSTRUCTION DOWNTOWN LINE C907 9.0 Slurry Plant Constru ctio n

9.1.

Sequence of Work

FLOW CHART

COMMENCEMENT APP. POWER/ WATER SURVEY SURVEY

REVIEW

PLANNING CONFIRMATION

SURFACING

REINFORCEMENT PEINFORCEMENT

SET UP OF SLURRY TREATMENT PLANT

MOBILIZATION MOBILIZATION

WORKSHOP

BAR BENDING

TESTING

BENTONITE MIXTURE

EXCAVATION EXCAVATION

SLURRY TREATMENT

CHECKING SPOILS REINFORCEMENT CAGE CAGE INTO POSITION

TREMIE PIPE

RECOVERY OF STABILZER

CONCRETING CONCRETING

WORK DONE WORK DONE

DISPOSAL


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METHOD STATEMENT FOR SLURRY PLANT & GUIDE WALL CONSTRUCTION DOWNTOWN LINE C907 9.2.


Site Installation

9.2.1. Site Static Installation Main static installation include bentonite slurry plant (mixer, ponds, storage silos, desanding plant and pumps); generators, site offices, workshops, store, changing rooms, steel storage and fabrication yard. The Site Utilization Plan, Silo slab design calculation and footing anchorage details are enclosed in Appendix C. The silo slab design shall be adopted for all remain static plant experiencing lighter loading capacities. The following procedures are applicable for slabs and walls construction and slurry plant erection: Setout propose structure layout and determine slab elevation according to existing ground level. Remove top soils, lay, level and compact 300mm thick hardcore. Lay required top and bottom steel reinforcement to slab with applicable spacer chairs to maintain required covers. Install adequately supported formwork shutters [with tie rods for walls] along propose slab or wall layout. Setout elevation markers at 3.0m x 3.0m intervals to maintain min. 300mm slab thickness elevation during casting. Place Grade 25 N/mm2 ready mixed concrete through skips or concrete pump; vibrate and trowel level to finish. Provide adequate curing from 9 hours after casting. Remove shutters after 24 hours, and proceed with propose silo and slurry plant layout and orientation markings on slab. Detect for presence of utilities prior to breaking ground and repeat the above steps and for spoil pit walls construction. Erect silos and slurry plants; properly orientated and aligned to receive pipe fittings. Install pipes and fittings between silos, slurry plants and pumps, and extend pipelines with control fittings to required workplace. •

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9.2.2. Restricted Activities within the Railway Protection Zone The layout of plant, storage and office areas are captured in Site Utilization Plan enclosed in Appendix C. The various Restricted Zones shall be visibly identified on plan and prominently and sturdily set-out on site and Application for Verification of Reserve Lines & Drilling Positions submitted for Authority verification and approval. All Restricted Activities within the Railway Protection Zone and within similar zones to the Common Service Tunnel shall be effectively addressed and permission obtained from the Authority prior to works execution. Engineering Evaluation Report on Existing North South Line Tunnel Section due to Silo Tanks Loading and Bentonite Pond Construction is enclosed in Appendix C. 9.2.3. Site Mobile Plants Mobile plant consists of excavation rigs, backhoes, dump trucks, concrete trucks, service cranes to hoist, splice and install steel reinforcement cages, stopends and concrete casting. The most critical mobile plant loading from service crane and its vicinity from open trench is carryout to determine platform capacity adequacy to undertake mobile plant loading. Engineering Evaluation Report on Existing North South Line Tunnel Section due to Machineries Loading.is enclosed in Appendix C. Meanwhile, all heavy machineries above 50-ton shall be kept away from the 2nd Reserve prior to the Authority’s grant of approval to access within the Restricted Zones. List of Major Plant and Equipment is enclosed in Appendix D.


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9.2.4. Temporary Site Installation All electrical installation shall be appropriately installed by Licensed Electrical Worker with adequate earthing, and power plant shall be registered with Energy Market Authority prior to operation. Diesel tanks shall be located within impermeable bund walls of adequate containment capacity, and installation shall be registered with the Singapore Civil Defense Force for Petroleum & Flammable Materials Storage Licensing. A list of fuel burning equipment together with Temporary Bentonite Plant Installation shall be separately submitted to Pollution Control Department, National Environment Agency. All lifting machines shall be Inspected and Certified by Approved Persons prior to operation. 9.2.5. Earth Control Measures and Wash Bays Earth Control Measures, treatment processes for rainwater and wash bay discharges shall be separately addressed.

9.3.

Guide Walls Construct ion

A pair of 0.30m thick x 1.20m deep concrete guide walls will be constructed along the near face alignment of diaphragm wall with the other parallel leaf constructed at diaphragm wall thickness + 50mm clearance to provide sturdy reference for diaphragm wall works elevation, layout markings, as well as guide to attain trench verticality during initial grab excavation. The guide walls shall also sustain loads from steel reinforcement cages, stopends, tremie pipes and other equipment suspended over the open trench. This concrete structure will further reduces soil erosion within the splash-zone of open trench and soil raveling at trench opening highly susceptible to mechanical notching. The guide walls structural adequacy check, steel reinforcement details, wall thickness and depth are enclosed in Appendix F. Trench stability analysis shall be referred for applicable guide wall elevations. Slurry elevations shall be maintained to at least 1m above the highest piezometric level and guide walls will be provided to 0.20m above minimum slurry levels identified in the trench stability analysis. The effects from equipment surcharges, widths of open trench, properties of underlain soil stratum, piezometric level and slurry density are collectively analyzed to verify stability of ground surrounding the open trench. Trench stability analysis is enclosed in Appendix F. Where applicable wider open trench within the guide walls will be excavated to increase the slurry head reservoir to minimize slurry spillage and head drop during introduction and withdrawal of excavation equipment. Cable detection works shall be carried out by a licensed cable detector, and report submitted to the authority, together with Notice to Commence Excavation application. Excavation shall be started only after Notice to Commence Excavation is approved. 9.3.1. Guide Wall Construction Method The typical construction processes and sequence of guide walls are addressed herein. •

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Licensed cable detection worker shall ascertain propose layout of guide walls are free from utilities, and Notice to Commence Excavation duly approved prior to carrying out trench excavation. Where existing utilities are detected the functional [live or abandon] status of such utilities shall be verified and appropriate measures [protection, diversion and work sequencing, termination, weep holes plugging, etc] shall be determined and implemented prior to guide walls construction.


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METHOD STATEMENT FOR SLURRY PLANT & GUIDE WALL CONSTRUCTION DOWNTOWN LINE C907 •

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Excavate to required depth and width of proposed guide walls after establishing setting out alignment to proposed work. Lean mix 30mm ~ 50mm thick, grade 10N/mm² concrete to base of guide wall to provide a firm base for guide wall formwork erection. Re-peg positions of diaphragm wall with required tolerance and clearance from lean concreted surfaces to provide reference for formwork erection. Install 2 x 2 nos. of T40 steel reinforcement to bottom end of each guide wall; together with 2 layers of A10 wire mesh [Ø10mm x 200mm x 200mm square grid] along the faces with 25mm concrete cover. All steel reinforcement shall be provided with 45 x bar diameter laps. Erect formwork along the peg alignment of proposed diaphragm wall with adequate bracing to prevent dislodgement and distortion during casting. Mark elevation to propose top of guide wall against the formwork to provide indication to control elevation of guide walls during casting. Evenly introduce Grade 25N/mm² concrete into both sides of guide walls to avert displacement or movement of formwork. Trim all under-sized inner face of guide wall until diaphragm wall thickness + minimum 25mm clearance tolerance is obtained if over-break occurs to guide wall inner faces. Guide walls shall be constructed continuously and propped against internal faces to reduce susceptibility to dislocation and movement. It shall be constructed against soil faces and in firm medium. Formwork to guide walls may be removed on the next working day or minimum12 hours after casting. Introduce 50mm x 75mm timber props against opposite faces of constructed guide wall at lower quarter and upper quarter at 3.0m interval before backfill with suitable excavated soil to inner face of guide wall.

9.3.2. Essential Measures It is imperative that essential measures in above Section 3 are addressed and approved prior to guide walls construction to eradicate erroneous setting-out and ensure against underground structures and utilities damages. 9.3.3. Alternative to Elevated Guide Walls Enhanced trench stability afforded by raised slurry head from elevated guide walls will be physically constrained by feasibility of works elevation and platform accessibility needs. Under circumstances where increased piezometric level are caused by high ground water level within the fill stratum, welling to reduce piezometric level may be considered a viable alternative to substitute raising slurry and guide wall elevations to improve trench stability. Welling where applicable shall be separately and appropriately addressed prior to works practice.


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METHOD STATEMENT FOR SLURRY PLANT & GUIDE WALL CONSTRUCTION DOWNTOWN LINE C907 10.0


Safe Work Practic e

To avoid any danger to life and health during diaphragm wall works the following measures may be taken: 

Protect all working and storage areas by temporary fencing clearly marking any hazardous or dangerous areas, which shall be off limit to the public.

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Cover up or protection of all trenches in progress or completed but not backfilled during rest days and rest hours or fencing at least 1.5 m height.

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Store safety and lock all tools & machinery during rest days.

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Adequate platforms and lighting during night works.

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Continuous maintenance and safety precautions on equipment and machinery according to the manufactures recommendation.

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Proper working attire to be worn by all persons engaged on site production.

10.1. Contingency Plan In the unlikely event of a major trench collapse, the excavation will be immediately back-filled with lean mix concrete. Excavation will only re-commence after a review of and implementation of any necessary precautionary measures.

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In the unlikely event of the sudden loss of bentonite slurry, the excavation will be immediately stopped and back-filled with the excavated materials until the loss of bentonite slurry is stopped. Excavation will only re-commence after a review of and implementation of any necessary precautionary measures.

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Plant & Guide Wall Construction

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