Method Statement for Shoring Guide Wall Construction

Description of Works

Introduction

This Method Statement for Shoring Guide Wall Construction defines the sequence and the control procedures to be followed for the project which includes but is not limited to the following:

• Setting out and Excavation
• Construction of a Concrete Blinding
• Construction of Vertical/Straight or L-shaped Guide Wall
• Backfilling Space Outside (Excavation Access Points) and Inside of Guide Wall

Definitions

CM-Construction Manager
QC-Quality Control
HSE-Health Safety & Environment
PPE-Personal Protective Equipment
PMV-Plants, Machinery & Vehicles
LPS-Loss Prevention System

Reference

Information sources may include, but not be limited to, verbal or written and graphical instructions, signage, work schedules/drawings/specifications, work bulletins, charts and hand sketches, and Material Safety Data Sheets (MSDS).

Excavation Specification

Concreting Specification

Health and Safety Guidelines

Guide Wall Design

General Lifting Plan

Responsibilities

1 Project Manager
Responsible for accomplishing the stated project objectives which include creating clear and attainable project objectives, building the project requirements, and managing the constraints of the project management triangle, which are cost, time, scope, and quality.

2 Construction Manager
Responsible for overall construction activities ensuring that all quality and safety procedures are implemented and required approved permits are obtained.

3 Temporary Works Manager
To support the project delivery teams, to support and lead the management and delivery of temporary works engineering whilst ensuring program, cost, quality, and safety objectives are achieved.

4 Site Engineer
Supervise operations in accordance with the approved Method Statement, shop drawings, specifications, material submittals, and schedules to achieve the acceptance of the project deliverables.

5 Site Supervisor
Supervise closely, the activities designated to them and ensure that all instructions and safety procedures are followed and strictly adhered to.

6 Site Foreman
To liaise with the Site Engineer and Supervisor for the work execution.

7 QA/QC Engineer
Ensure the proper implementation of the quality system and monitor the overall quality of the work is maintained. Conduct inspection and monitor tests. Determine and report any nonconformance and recommended corrective actions. Ensure that all personnel is aware of the quality requirement. Training of relevant personnel. Conduct surveillance and inspection duties at various stages to ensure compliance with QA/QC plan.

8 HSE Manager
Health, safety, and environmental (HSE) managers generally plan, coordinate, and implement issues and directives within the organization. They ensure safe environmental working conditions for all employees.

9 HSE Engineer
Ensure enforcement of safety procedures in accordance with the approved HSE Plan. Will be closely monitoring the site engineer’s strict implementation of the Method Statement for Shoring Guide Wall Construction and Risk Assessment, the use of proper tools and equipment to maintain safety, certifications of equipment and their adherence to safety regulations, reporting of any unsafe work or stopping work that does not comply with ES&H procedures.

He will advise on health & safety requirements and monitor the hazard controls implemented on site as per the Method Statement for Shoring Guide Wall Construction & risk assessment.

10 PMV Engineer
Ensure the equipment used are in good condition and monitor the equipment performance during operation.

11 Chief Surveyor
Carry out a pre-construction survey to fix the locations and corresponding elevations as per the approved shop drawings. Ensure quality and compliance during phases of surveying works and the regular checking of the surveying equipment or periodic calibration from third parties. Ensure the validity and the serial number of calibration certificates are available and posted in the survey equipment. Ensure proper safety guarding of surveying equipment. To maintain the records of all surveying equipment handled.

12 Survey Aide
Maintain and use Surveying equipment. Assist surveyors in taking measurements, record measurements manually or electronically, and peg out boundaries.

13 Site Foreman
Liaise with the Site Engineer and Supervisor for the work execution.

14 Equipment Operator
The only authorized person to operate any equipment to be used in the project.

15 Rigger
The rigger assists in the movement of heavy equipment and loads to be lifted. A rigger set ups machinery and secures it in place and signals or verbally directs workers engaged in hoisting and moving loads, in order to ensure the safety of workers and materials.

16 First Aider
The first aider responds promptly when requested, operates with competence, knows how to secure additional help when needed, reports incidents and actions taken, and complies with requirements for certification.

17 Banksman
The role of a banksman is to provide additional eyes and ears to assist the operator of the equipment to navigate or operate safely.

18 Security
A security guard shall be clearly visible, and vigilant, respond quickly and correctly during crises, observe and report, check and monitor, maintain order among workers, and offer safety warnings and tips.

19 Carpenter
A carpenter construct erects, install and repair structures and fixtures of wood, plywood, and wallboards using the carpenter’s hand tools and power tools.

20 Helpers/Laborers
Perform tasks involving physical labor in the building, assists the skilled workers, and remove the trash, and residual building debris. Assist in constructing and later disassembling reinforcement braces, concrete forms, scaffolds, and temporary structures.

Interfacing with other Operations

Limit and Boundary of Work
Re-routing of existing Temporary Roads

Resources

Plant and Equipment

Excavators with Rock Breaker
Bucket (CAT320/330D LME)
Petrol/Electrical Powered Poker
Stihl Saw 220V
Plate Compactor
Generator
Leica TS 15m Total Station
Leica NA2 Automatic Level

Note:
All 3rd Party Certificates shall be inspected prior to commencing lifting operation.
All machines shall fulfill project requirements if required.

Workforce

Site Engineer
Land Surveyor
Survey Aide
Foreman
Equipment Operator
Banksman
Security Guards
Carpenter
Steel Fixers
Helpers/Laborers
Safety Engineer
First Aider

Light Tools

Power Tools (Various)
Hand Tools (Various)

Materials

C30/20N/mm² SRC Blinding Concrete
·C30/37N/mm² OPC Reinforced Concrete
·Shutters/Formworks
Steel Reinforcement
Hessian Cloth

Test Certificates

Test Certificates for the above materials are not applicable since these are only for temporary works and do not require full control of QA/QC department.

Site Planning

The duration of works for Guide Wall Construction referred to in this Method Statement for Shoring Guide Wall Construction is scheduled to be finished within 30 Working Days.

a. Preparation

The contractor shall ensure that all gate passes, permits, tools, materials for safety precautions, manpower, and equipment are available before the commencement of work.

The Site Team shall make sure that access roads are always clear from any obstruction and site is always accessible.

b. Site clearance

Before commencing the work, the area shall be cleared of all debris, materials, or other obstructions.

c. Traffic Management

The Site Team with the assistance of the Safety Officers shall coordinate logistics and materials movement through the site following the direction and road signs displayed on site. The required diversion routes shall be marked on drawings including the required traffic signs.

The Work Permits and Operator Certificates shall be compiled and filed for reference by authorized personnel.

Temporary traffic signs, barriers, and flagmen will be deployed to control traffic flow in accordance with the Roadwork Construction and Traffic Management of the HSE Plan.

At the end of each ramp, there will be a transition area to give the driver the opportunity to watch the access roads before joining thereto.

d. Pre-construction Safety Meetings

The meeting shall be scheduled prior to the beginning of the work and before any subcontractor starts on the project.

Safety awareness meetings will be conducted every working day morning/every other day to brief the workforce on the safety prevention measures. The equipment check for safety shall be recorded/ documented during the daily Safety Awareness Meeting.

Traffic safety will be discussed to emphasize these meetings.

Each worker will be instructed to follow specific safety requirements related to his trade. They will be required to follow installed safety signs, observe barricades and use opens.

The safety team will perform hazard risk analysis by identifying all steps, and hazards identified in those steps, with a focus on the relationship between the work task, the tools, and the work environment. After identifying uncontrolled hazards; The contractor will take steps to eliminate or reduce them to an acceptable risk level.

General contractual Safety, Health, and Environmental requirements.

Roles of the contractor, subcontractors, authorized representatives, and all project workers.

Accident reporting requirements.

Specific details of the work to be performed along with the use of personal protective equipment.

Emergency procedure.

e. Operating Procedures:

A site investigation has to be carried out to develop safety precautions and measures prior to the commencement of the work. After such investigation, relevant sign boards will be displayed and barricades will be installed where and as necessary, such as but not limited to the following:

• Advanced signs e.g. “Work Area” signs will be placed ahead approximately 300m before the activity zones on both sides of the road.
• Relevant information, warning, and mandatory signs such as Narrow Road Signs, One-Lane Traffic signs, etc. will be placed approximately 25m from the last advanced signs.
• “One Way traffic ahead” signboards would be placed 90 m ahead of the working area in order to notify incoming drivers of the new road layout.
• Traffic Controllers would be deployed on both sides in order to control “One-way traffic”.
• Photographs would be taken for information to maintain traffic safety recordkeeping.
• A radio communication system would be used where normal communication is impossible.
• After completion of the work, safety cones and barricades have to be removed accordingly.

Methodology

This method statement describes the procedure to be employed for the construction of a reinforced concrete guide wall:

• Approximately 400 linear meters for a wall thickness of 1200 mm.
• Approximately 500 linear meters for a wall thickness of 800 mm to facilitate the construction of the Diaphragm Walls.

The top of the guide wall is + 1.80m from a reference point.

The guide walls are used to provide positional accuracy for the initial placement of the Bauer trench cutters during the construction of the diaphragm walls. They are also used to trap off reinforcement cages, spacer beams, and block out elements.

A. Description of Works

The guide wall construction will be carried out in several phases. Each section will
comprise 15-25 linear meters of guide wall for the Diaphragm Wall. Generally, the depth of the guide wall is 2000mm.

Construction of the guide walls will involve the placing and fixing of mesh and reinforcement, erection of shutters, and mechanical placement of concrete within a pre-excavated trench. It is envisaged that excavation will be battered back to a safe angle of repose or contained by existing retaining structures.

The site-specific activities under the scope of work comprise the following:

1. Setting out and excavating
2. Construction of a concrete blinding
3. Construction of vertical/straight or L-shaped guide wall
4. Backfill space outside (excavation access points) and inside of the guide wall. The opposing walls for the guide wall of the diaphragm wall will be constructed
   simultaneously.

B. Sequence of Activities

1. All operatives/sub-contractors will be required to attend the site induction. All plant operators will be certified with the relevant operator card for the plant. In addition to the site induction, a method statement briefing and daily task briefing will be held for all operatives before the commencement of the day’s task. A site induction, Method Statement for Shoring Guide Wall Construction briefing, and task briefing attendance form for the briefing will be signed by the operatives and a copy is available on request.
2. A permit to dig will be issued by the contractor prior to the start of excavation. The positions of all known services will be clearly marked at ground level and overhead services shall be preferably removed prior to the commencement of the works.
3. For setting out for the excavation works steel pins shall be placed centrally on the wall axis every 25 m by the surveyor (tolerance ± 25mm). Prior to the excavation, the outline of the excavation berms will be marked with marking spray on the ground.
4. The trench for the guide wall will be excavated to a given level, 2100mm deep (including a 100mm kicker), using a 360-degree excavator and jackhammer. The excavation level will be controlled via horizontal laser or surveyors’ direction. Spoil will be placed/stored adjacent to the excavation 1.2-1.5 m away from the edge of the excavation, approximately 30% will be used as backfill material, and the remaining will be removed as muck away.
5. During the excavation, a temporary demarcation zone will be installed around the excavation. This demarcation will consist of a combination of fence elements and appropriate signage at a minimum of 1m from the edge of the trench.
6. Access and egress of the trench will either be by means of a ladder rested against the batter and secured at the toe or a staircase with a handrail at either end of the trench.
7. Setting out: Steel reference pins shall be firmly inserted in the ground centrally on the wall axis with a tolerance of ± 3mm. The maximum distance between single reference pins shall not exceed 10m.
8. A 50mm deep timber frame shutter will be placed upon the formation level in the center of the excavation and fixed in position using steel road pins fitted with protective caps as shown below. Blinding / Kicker construction: Timber frame shutter to be set out and fixed by steel road pins.
9. The frame will allow accurate placement of the blinding concrete to the underside of the opposing guide walls whilst maintaining an 850mm respectively 1250 mm void along the center of the trench from which to position the wall formwork at a later stage. Concrete blinding will be placed using an excavator with a concrete skip under the direction of a banksman, and finished by hand.
10. When the blinding concrete has set (at a minimum to be left overnight) the timber
    frame will be removed, cleaned, and repositioned for the subsequent pour. This procedure will be repeated ahead of guide wall construction until the blinding level is complete.
11. Pre-fabricated base formwork will be lifted into the trench and fixed into position using steel road pins and timber props.
12. Reinforcement will be placed and vertical wall starter bars or vertical mesh
    reinforcement will be fixed. The vertical starter bars shall be installed prior to casting blinding concrete at a minimum 600mm spacing. Temporary support shall be installed prior to cast blinding to ensure that starter bars are adequately installed, aligned, and strong enough to support the installed main reinforcement.
    Protective caps will protect personnel from any protruding reinforcement bars. Steel will be prefabricated outside the trench and lifted into a place where possible.
13. Once the alignment and level of the base shutters (kicker) have been checked by the surveyor, concrete will be placed by using the bucket of the excavator or a concrete skip. The banksman will control all plant and concrete delivery vehicle movements during the operation. Concrete will be vibrated using a poker.
14. When the base shutters (kicker) have been stripped and recycled, vertical reinforcement will be fixed. Where possible, reinforcement will be pre-fabricated out of the excavation and lifted into place. Vertical wall formwork will be lowered into the trench and positioned.
15. Stop ends will be constructed from timber. They will be placed where necessary and will allow for continuity of the reinforcement into the subsequent part of the wall. All projecting reinforcement bars will be capped. Laps and spacing of the reinforcement will be as per design.
16. Once completed, the line and level of the formwork will be checked by the surveyor. The Site Supervisor and/or Engineer will also inspect the formwork to ensure that adequate bracing and support are in position. Level control of horizontal shutters via horizontal laser or surveyors’ direction.
17. Concrete will be placed using a concrete skip suspended from the excavator, via an excavator bucket, or discharged directly from the truck. The concrete will be poured evenly into each opposing wall to ensure balanced pressure on the formwork. The final form and levels will be checked by the surveyor and the finishing of the concrete will be undertaken by hand float to a level.
18. Wall shutters will be struck the following day, and temporary timber struts will be positioned between each wall as per the design to provide additional resistance to lateral earth pressure until diaphragm wall construction is commenced. The opening between the walls will also be backfilled with a granular material with a max 150mm thickness per layer.
19. The same procedure will be repeated until the completion of the guide walls, with corner guide walls being constructed in the same way.

C. Curing of Concrete

1. General

Curing shall continue for at least 7 days and until it attains an in-place compressive strength of the concrete of at least 70% of the specified compressive or flexural strength, whichever period is longer. Curing shall not stop unless otherwise approved by the engineer.

Concreting shall not take place until all Hessian, polythene and a supply of fresh water are on the site and ready for use.

2. Water for Curing

Water shall be used for concrete and during the curing period and shall generally conform to the requirement of the project specifications.

The use of an approved curing compound as another option for curing shall be as per the manufacturer’s recommendation and approval of the consultant.

D. Backfilling and Compaction

1. Backfilling

Excavation is only to be backfilled after the permanent works therein have been approved and after the removal of any debris or deleterious material from the excavations.

Selected excavated material will normally be used. Where the excavated material is not considered suitable, selected material from an approved source is to be used.

2. Compaction Fill

Compaction fill to be compacted by a suitable plate type vibrator, pedestrian-operated vibrator
roller, a small tandem roller, or other approved compaction plant.

The material is to be placed in layers within the effective range of compaction of the plant provided that the maximum loose (uncompacted) thickness of each layer does not exceed 200 mm. Each compacted layer shall have a maximum thickness of 150mm.

No completed fill layer shall be covered by the next layer until it has been tested, inspected, and approved by the Engineer.

The material is to be watered and mixed as necessary to ensure that prior to compaction the moisture content of the whole layer is ± 3% of the optimum moisture content. Compaction of each layer is to continue until a density of a least 95% of the maximum dry density has been achieved.

The dry density/moisture content relationship will be determined by the heavy compaction test (4.5% rammer method) of BS 1377.

E. Lifting Procedures

The construction of the guide wall do not involve any critical lifting and all lifting operation will be carried out in accordance and in full compliance with the requirements mentioned in the approved General Lifting Plan.
Moreover, prior to commencing the lifting operation, a lifting operation plan permit will be in place.

F. Tolerances

The finished internal face of the guide wall closest to any subsequent main excavation shall be vertical to within a tolerance of 1:200 and the top edge of the wall shall represent the reference line. There shall be no ridges or abrupt changes on the face and its variation from its specified position shall not exceed ±15mm in 3m. The minimum clear distance between the guide walls shall be the specified diaphragm wall thickness plus 25mm and the maximum distance shall be the specified diaphragm wall thickness plus 50mm.

Risk Assessment and Job Hazard Analysis

Please refer to the document in Appendix.

Permit and Licensing Requirements

Please refer to the “Permit to Work” in Appendix.

Drawings, Diagrams, and Maps

Please refer to the document in Appendix.

Pre-Start Safety Briefing Arrangements

1. Risk Assessment

Refer to Risk Assessment Appendix.

2. Protective and Safety Equipment

All workers involved shall be equipped with adequate PPE as stated below:

Safety Helmet with Company Logo
Safety Boots
High Visibility Vest
Safety Goggles
Hand Gloves
Coveralls

Information to Personnel

Safety Induction
Job training
Superintendents’ Notices/Memos
Toolbox talks
STARRT Card

Special Safety Requirements

All necessary personal/protective equipment (PPE), as well as harness, be provided.

Banks man, wearing distinctive vests, shall be assigned to help operators maneuver their equipment.

The equipment operators shall possess the required licenses and certificates.
Generated dust (By the end or equipment operations), shall be controlled by periodic water spraying.

The required permit to work by Dorsch shall be obtained prior to the commencement of work.

The required TSTI will be prepared prior to the commencement of work and positively implemented.

The project safety officer is responsible along with the project zone site engineer for ensuring that all operations are carried out with due regard to the safety of all project personnel & property.

No working at height issues anticipated.

In case of working at night, please refer to Method Statement for Night Works.

Environment and Quality Issues

Precautionary Measures

All precautionary measures shall be briefed to all workers prior to commencing the activity.

Disposal Requirements

All waste shall be disposed of as per Environmental Compliance and Management Plan
and as per Government approved disposal areas.

Inspection, Test, and Sampling

a. Request for Inspection and Testing will be submitted prior to and after execution of works. An inspection and Test Plan (ITP) shall be provided.

Quality Assurance Requirements Table

Refer to Project Quality Plan
Inspection and Test Plan (ITP) shall be provided.

Attachments

Appendices

Sketch and Drawings

1. Guide Wall Layout
2. Guide Wall Design
3. Expansion Joint & Steel Reinforcement Arrangement

Risk Assessment and Job Hazard Analysis
Permit to Work (Excavation Works) & Lifting Operation Permit
Inspection and Test Plan

Material Submittals

1. Concrete Mix Design
2. Formworks Drawings
3. Structural Design Calculation

Baseline Programme
Survey Equipment Calibration Certificate

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