Method Statement for Diaphragm Wall Construction

Description of Works

Introduction

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

• Trench Excavation, Installation of Reinforcement Cages, and Concreting
• Anchor Construction
• Capping Beam
• Hoop Beam
• Waler Beam

Definitions

QC-Quality Control
HSE- Health Safety & Environment
PPE-Personal Protective Equipment
PMV-Plants, Machinery & Vehicles
LPS-Loss Prevention System
MEP-Mechanical, Electrical & Plumbing

Reference

Excavation Specification
Concreting Specification
HSE General Requirements
Method Statement for Shoring Guide Wall Construction
General Lifting Plan
Shoring Lifting Plan
Design for Shoring System
Construction Environmental Management Plan
Diaphragm Wall Concrete Mix Design (C50/60 OPC 70%+PFA 25%+MS 5%),
Concrete Mix Design (C50/60 OPC 70%+PFA 25%+MS 5
Grout Mix for Anchor
Method Statement for Monitoring of Sea Wall
Retaining System Specifications

Material References

Polymer, Bentonite & Soda Ash
Anchor Material
Steel Reinforcement
Coupler
Bonding Agent (weber ad 220 SVR)
Anchor Shop Drawings

Responsibilities

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.

Construction Manager

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

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.

Site Supervisor

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

Site Foreman

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

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.

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.

HSE Engineer

Ensure enforcement of safety procedures in accordance with the approved HSE Plan.
Closely monitoring the site engineer’s strict implementation of the Method Statement for Diaphragm 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 HSE procedures.

Advises on Health & Safety requirements and monitors the Hazard controls implemented on site as per the Method Statement/Risk assessment.

PMV Engineer

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

Chief Surveyor

Carry out pre-construction surveys 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 a third party.

Ensure the validity and the serial number of calibration certificates are available and posted on the survey equipment.

Ensure proper safety guarding of surveying equipment.
To maintain the records of all surveying equipment handled.

Survey Aide

Maintain and use Surveying equipment. Assist Surveyors in taking measurements, record measurements manually or electronically, and peg out boundaries.

Site Foreman

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

Equipment Operator

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

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.

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.

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.

Design Team

Responsible for the design of the project in coordination with the main contractor.

Shoring Team

Shoring subcontractor who will execute the main tasks at the site such as mobilization of equipment and plants, construction of diaphragm walls, construction of bored piles, and installation of anchors including stressing and destressing.

The main source of concrete to be used in the site from their batching plants and equipment such as concrete pumps and transit mixers.

Interfacing with other Operations

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

Duration, Phasing with the Subcontractors

All works associated with this Method Statement for Diaphragm Wall Construction shall be done within a minimum of 204 Working Days as per extracted Baseline Programme from the submitted Recovery Plan.

List of Subcontractors

Subcontractors for Shoring

Resources

Plant and Equipment

Base Carrier of Cutter – Bauer MC 128
Base Carrier of Cutter – Bauer MC 96
Trench Cutter- BC-40
Base Carrier of Cutter – Bauer MC 64
Gear Box, Drive unit, wheel set- 1200 mm
Gear Box, Drive unit, wheel set- 800 mm
Main Slurry Pump with Freq. Control Unit and Remote Control (Haberman)
Crawler Crane Liebherr LR 1160 (or equal) 100 Ton
Rough Terrain Crane Grove 70Te (or equal) 70 Ton
Polymer Storage Tank System (12m/11.5m/11m)- Bauer
Pipeline System for Slurry Handling and Circulation Ø 6”
SK Pipes 2000m
Pipeline System for Slurry Handling and Circulation Ø 4” SK Pipes 1000m Slurry Handling
Desander Units BE 500
High Speed Mixer BM 3000
Electric Main Boards and Distribution Boxes incl. Cables
Tremie Pipe Set Ø 250 mm incl. Hopper, Fork, and Rack
Lab Container – Fully Equip. for Testing of Slurry
Shovel Loader
Telescopic Handlers
Excavators w/ Rock Breaker and Bucket (CAT320/330D LME)
Generator
Drilling Rig (KR 806-2DB)
Hydraulic Hammer (Eurodrill HD) for KR 806
Grout Mixer and Pump “Domine- Anchorage Frame”
IC445/447
Flush Pump ETA 80
Mini Excavator
Crawler Crane 55Ton w/ 40m Boom & Auxiliary line
Anchor Lifting Beam
Air Compressor w/ 850cfm/10 Bar Ingersoll
Jack (ZPE 12 ST2)
Hydraulic Pump incl. Pressure Gauges EHPS-3/4H 3
Transit Mixer
Concrete Pump
Concrete Vibrator
Leica TS 15m Total Station
Leica NA2 Automatic Level

Note:

All 3rd Party Certificates shall be inspected prior to commencing operation.
Survey Equipment Calibration Certificate

Workforce

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

Light Tools

Various Power Tools
Construction
Various Hand Tools

Materials

Polymer
Soda Ash
C50/60N/mm² OPC Concrete
Bonding Agent
Shutters/Formworks
Steel Reinforcement

Test Certificates

Concrete Mix Design on Material Submittals

Material Submittal (Polymer, Bentonite & Soda Ash)

Site Planning

Duration of all works associated with Diaphragm Wall Construction referred to in this Method Statement shall be done within a minimum of 150 working days as per extracted Baseline Programme from the submitted Recovery Plan.

a. Preparation

The contractor shall ensure that all gate passes, permits, tools, and 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.

All necessary MEP clearances shall be obtained prior to starting the activity at the site.

Clash analysis will be done to verify that no MEP utilities will clash with the shoring system.

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.

Methodology for Diaphragm Wall Construction

1. Trench Excavation, Installation of Reinforcement Cages & Concreting

A. Description of Works

This method statement describes the procedure to be employed for the construction of a reinforced diaphragm wall.
Approximately 375 linear meters for a diaphragm wall thickness of 1200 mm
Approximately 475 linear meters for a diaphragm wall thickness of 800 mm

The excavation depth is approximately 20 m.

The scope of work specifically comprises of following major activities:

• Mobilization of staff and equipment to the project.
• Setup of plant and Equipment on site.
• Providing construction materials at the location of use which comprises ready mixed concrete, readymade steel rebar cages, anchor reservations, concrete spacers, and sweet water.
• Survey Works and setting out of Guide Wall by the contractor.
• Construction, demolition, and removal of reinforced concrete guide wall as per
• approved shop drawings by the contractor.
• Construct and maintain a firm, dry, and free working platform for the execution of works
• by the contractor.
• Trench excavation of 1200 mm and 800 mm thickness with lengths and depths as
• shown in shop drawings using two BAUER trench cutters.
• Maintain and circulate the support slurry in the trench as a drilling fluid and stabilize the open trench.
• Disposal of the waste slurries to an approved location.
• Pre-fabrication of reinforcement cages and horizontal transport to the installation
• location by the contractor.
• Lifting, lowering, and if required splicing of readymade steel rebar cage into the trench and securing it to sit at the proper alignment and elevation in the diaphragm wall as shown on the shop drawings.
• Concreting using tremie tube method in diaphragm wall.
• Disposal of excavated spoil, excess concrete, and cementitious material by the contractor.
• General site management related to the construction of the retaining walls.

Overall site management and coordination of traffic, site logistics, and other subcontractor works by the contractor.

• Disassembly and demobilization of plant and equipment.

B. Sequence of Activities

Working Platform and Ramps

Refer to the Layout showing Working Platforms and Ramps:

Shoring Layout. The conditions for stability will be checked and approved from HSE
department will be secured prior to the mobilization of rigs.

Setting Out

A layout drawing indicating the setting out of the diaphragm-wall coordinates will be
issued. These coordinates will indicate the position of the “internal” edge of the diaphragm walls.
These setting-out and panel layout drawings shall be submitted for approval of the
Project Manager prior to the start of construction.

Guide Walls

Please refer to the Method Statement for the Construction of the Guide Wall

Pre-Excavation

In order to start cutter excavation, a pre-excavation to a depth of 2.50 – 3.00 m is required.
This will be executed by a backhoe and if necessary by an excavator-mounted cutter wheel.
Loose material which might remain in this trench will be excavated within the guide wall using a backhoe excavator or a JCB.

Excavation Under Support Fluid

The requirements for the support fluid under applied loads have been checked via trench stability calculation. The calculation results are shown in Trench Stability Analysis.

The level of the slurry within the excavated trench will be continuously monitored and checked to ensure the stability of the open trench in accordance with the trench stability analysis.

The support fluid will consist of salt water, polymer, and soda ash. If required further additives might be added during the construction phase if deemed to be necessary.

Panel Excavation

The remaining excavation below the pre-excavation level down to the final depth will be done by the trench cutter BC 40 / BC 30 with a length of 2.80 m or 3.20 m.

The excavation process with primary and secondary panels will be done in accordance with the panel layout drawing, where secondary panels will overcut two previously concreted primary panels.

The figure below outlines the principal system of primary and secondary panels.

Please note: The above lengths of the panels will vary depending on the actual size of the cutter wheels and due to the geometrical boundaries of the project.

After having reached the final depth, and depending on the properties of the drilling slurry in the panel, it might be required to exchange the working slurry for fresh slurry.

The properties of the slurry will be checked on the sand content, density, shear strength, filtrate loss, temperature, viscosity, and PH- value prior to the commencement of reinforcement installation and the concreting procedure.

After the final depth has been reached, cleaning of the trench bottom with the trench cutter will be executed, and depending on the properties of the support fluid a complete change or desanding might be executed.

The final depth of each panel or bite shall be verified in addition to the displayed depth on the onboard computer of the cutter unit by manual measurements taken from the top of the guide wall by means of a measuring tape with attached weight.

Excavation of Primary Panels

Primary panels are constructed against the natural ground at both ends. After pre-excavation, the Trench Cutter will be positioned and the panel will be excavated in 1 or 3 bites. In the case of 3 bites, the outer bites will be 2.8 or 3.2 meters wide (refer to 0), whereas, the width of the center bite usually varies between 0.8 meters and 1.4 meters, depending on the geometry of the wall, the total panel length, and soil conditions.

Excavation of Secondary Panels and Forming of Joints

After the completion of the excavation of two adjacent primary panels, an intermediate secondary panel will be excavated. The distance of adjacent primary panels is set up to leave a clearance of 2.40 or 2.80 m for the excavation of a secondary panel.

The cutter with a frame length of 2.80 or 3.20 m (refer to 0) will be placed symmetrically in between the two primary panels. Therefore it will cut on each side 20 cm into the concrete of the two adjacent primary panels, resulting in a grooved rough surface of the primary panel concrete. The serrated surface at the primaries will ensure good interlocking with the secondary panel.

For reasons of verticality, the concrete strength of both primary panels should indicate comparable strength values.

Once pouring the secondary panel, the grooves within the exposed faces of the primary panels will provide intimate contact between the concrete of the primary panels and the freshly poured concrete of the secondary panel, thus ensuring a tight vertical joint.

Additional Measures for Primary Panels- Spacer Beams & Block-Out Elements

For primary panels only and prior to the installation of the cage(s), spacer beams (Hbeams) will be installed temporarily on both ends of the excavated panel (refer to the figure below).

Spacer beams will ensure good alignment of the reinforcement cages and that no reinforcement will be present in the overcutting areas.

The spacer beams of a total length of 2 x 12 m (total 24 m) will be installed at both sides of the panel to ensure the reinforcement is placed in the correct position. The spacer beams will be removed during concreting with the final 12 m being replaced by block-out elements of 2.5 m to 3.0m in length to provide the correct overcut for the secondary panel.

After installation of the block-outs into the panel, concreting will be proceeded up to the required level (incl. excess concrete).

The block-out elements will form a recess on the outside of the primary panels, i.e. a gap of 2.80 m and 3.2 m respectively in between two adjacent primary panels. The reasons for this slot are enabling works for the excavation of secondary panels:

a) The guide frame of the cutter can be mounted on top of the guide wall and proper
alignment of the cutter can be achieved.

b) The cutter can advance into the trench without cutting until the centrifugal pump will be immersed.

The block outs will be removed as soon as the setting of the concrete allows. Setting tests will be performed on-site to define the correct timing.

Construction Sequence for Block-Outs:

figure here*

Additional Measures for Secondary Panels-Cleaning of Joints

In order to ensure the best quality of the diaphragm wall joints, a brush will be used the cleaning the joints. The brush will be pushed along the joint of the previously installed primary panel to remove possible deposits of fines or such.

Fabrication and Installation of Reinforcement Cage

Fabrication of Reinforcement Cages:

The steel reinforcement cages will be manufactured in accordance with the approved shop drawings as two sections (each approx. 16 m long) and split over the open trench. The individual cage sections will be pre-fabricated and made available at the panel location prior to installation.

The steel cage will be provided with the reserve pipes for the anchors tied securely with the main bars of the cage in such a manner that they will not obstruct the tremie pipe during concreting.

Installation of Reinforcement Cages:

The cage lifting procedure will be in accordance with the Shoring Lifting Plan.
After the cage was transported to the installation location it will be offloaded in a horizontal position.

The cage will then be lifted from a horizontal to a vertical position and shifted over the panel.
The cage will then be carefully positioned over the panel and lowered at 3.0 meters intervals to allow fixing of concrete spacer blocks via tie-rods.

For the connection of the upper to the lower cage section, the lower cage section will be trapped off to the guide wall by means of steel trapping beams. Both cage sections will then be connected securely via a coupler and the complete cage lowered into the trench while concrete spacers will be mounted to the cage up to the top of the reinforcement cage.

Upon reaching the final level, the cage will be suspended from the guide wall at the proper elevation.

Each steel cage shall be lifted by special lifting points indicated in each steel cage shop drawing and shall be welded according to details in the shop drawing.

Concreting

Once all cage elements are placed in the excavated trench the tremie pipes will be installed in the trench down to the final depth.

The tremie pipe method assures that the concrete will be placed from the bottom of the trench to the top and displaces the slurry from the trench whilst rising. The displaced slurry will be pumped back to the desanding unit into the storage tank.

One tremie pipe string consists of:

• tremie pipes Ø 254 mm and 280 mm in section lengths of 0.5, 1, 2, 3, and 4 m with male and female connections
• rubber O-Rings for a water tightness of pipe connections
• tremie locking ropes
• 1 x lifting cap
• 1 x tremie support fork to rest the string on the guide wall
• 1 x 1.2-meter diameter conical shape hopper with lifting rope tremie hopper at the top.

Concrete with an approved mix design will be supplied to the trench locations by concrete mixer trucks at a rate sufficient to ensure a minimum pouring rate of 60 m³ per hour.

Concrete Mix Design for D-Wall, Mix C50/60 (Concrete Mix Design) will be used.

The volume of the concrete will be theoretically calculated and communicated to the concrete batching plant. During the casting operation, a concrete curve will be plotted and the concrete volume calculation will be refined. Forms of Quality Control and Recording will be issued separately together with the Inspection and Test Plan.

In order to guarantee a continuous pouring process of large panels and to minimize the risk of a failure during concreting a sufficient number of concrete mixer trucks will be provided (i.e. 2 nos. are pouring simultaneously, additional 2 nos. are waiting in line on-site and the remaining 4 nos. are loaded at the batching plant and/or on the way to the site).

Prior to the commencement of the concrete pouring process, proper quality checks for the workability of concrete will be made. The installed tremie pipe(s) shall be plugged with a temporary plug (concreting ball or polystyrene pieces in a bag, etc.) in order to avoid contamination of the concrete by the slurry contained in the tremie pipe during the priming (first pouring of the concrete).

The poured concrete through the hopper will force the temporary plug in the tremie pipe ahead of the concrete and prevent any contamination of the concrete by the slurry contained in the tremie pipe. After priming, the base of the tremie pipe(s) shall be kept at all times embedded in at least 2.00 m (standard situation) and 1.0 m (a special situation, which has been remarked in the concreting report) in the fresh concrete.

To ensure this requirement until the completion of the panel pouring procedure, the concrete supply shall be continuous and interruptions should not exceed 15 min.
To ensure an approximate horizontal level of the poured concrete in the panel at all times, two tremie pipe sets in large panels (> 4.0m) will be placed and charged with equal distribution.

In order to get non-contaminated concrete approx. 0.50 to 1.0 m over-placement on top of the designed cut-off level will be performed.

Earliest Time of Excavating Secondary Panels

Excavation of the secondary panels will be done after the poured concrete in the adjacent panel has gained sufficient strength to be freestanding. The required curing period shall be determined on-site for the particular properties of the concrete produced under mass production on-site.

Generally, the time for overcutting of primary panels will be a matter of several days. However, from experience with similar concrete mix designs used on other sites, a minimum of 24 hrs shall elapse before secondary panels are excavated in-between previously cast primary panels.

Disposal of Excavated Spoil

Spoil removed from the excavation shall be separated from the slurry employed in the
excavation process with the help of desanding unit BE 500. It shall be disposed of at the site after the water in it is evaporated sufficiently and as quickly as possible to an approved dump site by using dumpers and shovel loaders in such a manner that spillage and annoyance are minimized and as described in the waste disposal plan. Please refer to Construction Environmental Management.

Disposal of Waste Slurry

After a certain number of cycles, the working slurry will not be recyclable anymore due to contamination of cement & fines. The physical properties of the slurry will be monitored to decide when to dispose of the slurry. The slurry will be disposed of at designated locations as described in the waste disposal plan. Please refer to Construction Environmental Management Plan in conjunction with Construction Environmental Management Plan.

Tolerances/Requirements

Panel Excavation:

The plan position for panels at the commencing surface will be within 25 mm in the longitudinal direction.

The verticality of the panels shall be within 1 % in both transverse and longitudinal directions.

Panel Overcut:

In general, overcut of 200 mm will be executed.

Concrete:

The overbreak in concrete consumption may not exceed 15%; however, for soft areas, the consumption might be higher.

Reinforcement Cages:

Reinforcement shall be maintained in its correct position during concreting of the panel within a vertical tolerance of +150/-50mm (i.e. a maximum of 150mm high) on the level of the reinforcement projecting above the final cut-off level.

The longitudinal tolerance of the cage at the final cut-off level measured along the excavation shall be ±75mm within the panel.

Installation of Inclinometer Casing in Diaphragm Wall

• Direct installation of an inclinometer casing in the diaphragm is not recommended.
  The inclinometer casing will get distorted and stressed when firmly tied to a steel structure from bottom to top.
• It is also no good to directly expose the casing to the heat of hydration and stresses generated during the concreting process. The casing may distort and even get cracked.
• Fix a 150 mm nominal bore diameter steel guide pipe vertically within a reinforced bar cage as shown in the Figure below. The pipe length to be installed should be worked out in such a way that its top remains around 0.5 m above the existing ground level after the cage is fully lowered to the bottom of the slurry trench. The bottom of the guide pipe should be around 0.5 m above the bottom level of the cage. It should be sealed at the bottom with a concrete plug/plastic cap. Make sure that the jointing of tube lengths is waterproof to prevent any grout/concrete from entering it, while the cage is being concreted. Use of dented or distorted pipes shall not be done as this will make installation of inclinometer access tube difficult or even impossible.

Note: It is recommended that an auxiliary guide pipe be installed adjacent to the main guide pipe at 1.25 m approx. center to the center distance at critical monitoring locations.

This auxiliary pipe can be used in case the main pipe gets choked and becomes useless due to any reason.

• Weld guides the pipe firmly to the cage. Ensure that it remains vertical and is least distorted during the lowering of the cage.
• Concrete cage after covering the mouth of guide pipe.
• Flush the guide pipe clean with water and verify depth with the help of a suitable depth measuring device (e.g. a sounding chain) that it is fully open up to the bottom.

Note: Ensure that the heat of hydration of mass concrete has dissipated before installing the access casing in the guide pipe. Use a temperature probe for this purpose. The temperature should not exceed 40°C. The heat of hydration, if present may warp the access casing and render installation useless.

• Lower casing with bottom cap into guide pipe gripping it with the safety clamp secured around 500 mm from the top.

Note: Maintain one pair of casing grooves parallel to the direction in which lateral movement is to be measured i.e. perpendicular to the diaphragm wall.

• Take a casing pre-assembled with a fixed coupling, having a safety clamp secured around 500 mm from its top end, and mate it with the pipe already lowered through the coupling end. Pop-rivet the fixed coupling to the lowered casing at four places.
• Seal the joint with mastic waterproof tape and BOPP tape. Remove the safety clamp from the first casing and lower jointed casings into the guide pipe.

Note: Always use a safety clamp such that the casing does not accidentally fall into the guide pipe while installing.

• To counteract buoyancy, if required fill the casing with clean water to lower it into the guide pipe.
• Repeat the above procedure for all the casings to be installed in the guide pipe.

Note: It is preferable to use 20 mm nominal diameter rigid PVC pipe lengths jointed using threaded sockets for grouting. Lower above tubes say up to 0.5 m above the bottom of the guide pipe.

Prepare a grout mix to be filled in the annular space between the guide pipe and casings as directed by project authorities. If no instructions are available, the suggested grout mix is as follows:

Cement 50 kg
Bentonite 10 kg
Water 75 liters

• It is recommended to flush the inside of the casing with water after grouting. This is to prevent any leaked grout from sticking in the casing and impairing the movement of the probe.
• The top of the uppermost casing should be 25 mm above the top of the steel pipe. Cut the top of the pipe suitably with a hacksaw. Use a flat file to make the pipe end smooth.

Note: The depth of the top of the grout face from the top of the steel casing should be at least 100 mm (125 mm from the ABS casing top). This is necessary for fixing pipe extension jig over casing for taking readings.

• Clean the exposed portion of the casing top and fix the top cap.
• When not taking readings, the gauge well should be protected with a cover fixed on top of the steel casing by four M6 Allen head bolts.
• Mark tag no. of installation in paint on the inner side of the steel guide pipe. Also mark casing grooves as ‘A+’,’ A-’,’ B+’, and ‘B-’ with a permanent ink marker pen. If the uppermost probe wheel is pointed in the direction of the major principle plane of movement, the casing groove pointing in this direction is marked as ‘A+’. Looking down the well, directions ‘B+’,’ A-’, and ‘B-’ are clockwise from ‘A’.

Additional Precautionary Measures and Arrangements

• Coordinate with the M&E department to keep provisions and make arrangements for future utility penetrations through the wall.
• Tremie pipes should remain embedded 2.0m into concrete during concreting.
• Introduction of depth surroundings or lowering of polymer sampler into trench prior to the withdrawal of cutter frame is prohibited to avert any bodily injury through entanglement with lead wires reeled with cutter wheels.
• Mixer openings should be covered during mixing. P2 grade dust masks together with gloves and goggles should be provided to avoid inhalation of hazardous particles.
• Hard barricading and safety signage must be installed on the seaside as a safety requirement.
• All open trenches must be barricaded and displayed on warning signboards.
• Precautionary measures are to be taken to prevent any slurry from going toward the seaside and creating an environmental hazard.
• Proper functional PMV should be in place prior to the start of construction activities. No major repair will be allowed at the site as an environmental requirement.
• Ensure that dust control (water spraying) shall be done regularly when using trench cutters.
• Exclusion zones shall be provided around trench cutters, and adequate barriers and signs are to be posted.

Maintenance of the Trench Cutters

The hydraulic oil and gear oil level will be continuously monitored by the operator, in case of an oil leak the work will be automatically stopped and the cutter will be taken out of the trench to a designated maintenance area and a drip tray will be placed below the cutter in order to repair the damaged hose.

2. Anchor Construction

A. Description of Works

The scope of works comprises the installation of 5 years of design life ground anchors in up to 5 levels for the anchorage of shoring elements and walls, in total 3,420 ground anchors.

The anchors are five (5) to six (6) strands of both types of removable and non-removable ground anchors and lengths between 25m and 37m. The non-removable anchors are designed for a lifetime of 5 years.

The scope of work specifically comprises the following major activities:

• Mobilization of Staff and Equipment to the Project
• Setup of plant and Equipment on Site
• Providing construction materials at the location of use which comprises anchoring tendons, anchor heads, post-grouting pipes, and spacers
• Uncovering and Cleaning of Pre-Installed Anchor Reservations
• Drilling of Boreholes by Rotary Drilling
• Supply and Mixing of Cement Mortar
• Supply and Installation of Ground Anchor Tendons
• Grouting and Post-Grouting of Drill Holes
• Supply and Installation of Ground Anchor Tendons and Anchor Heads
• Stressing/Tensioning of Anchor Tendons
• General Site Management Related to the Construction of the Ground Anchors
• Disassembly and Demobilization of Plant and Equipment

B. Sequence of Activities

General

Briefing:
Before starting work, the construction manager will familiarize the anchor crew with the tasks and the features of the construction site. In the safety training session, the site personnel will
– on the basis of the risk assessment – be given instructions pertaining to general anchor drilling hazards and the specific hazards posed by construction sites.

Anchor Installation Sequence:

Anchors will be installed in sequence 1 – 3 – 5 – 7 … where remaining anchors 2 – 4 – 6 – 8 … will be installed earliest 24 hours after grouting of the first anchors.

Working Platforms and Ramps

The design, construction, and maintenance of the working platform and ramps required for the safe installation of anchors shall be executed in accordance with the approved Method Statement.

The conditions for stability will be checked and approval from HSE Department will be sought prior to the mobilization of rigs.

The top-level anchor working platforms will be approx. 500mm – 800mm below the anchor starting point.

The working platform will be maintained in a dry and stable condition.

Uncovering of Anchor Reservations

Elevations of the individual anchor layers will be marked on the diaphragm wall after bulk excavation and construction of the working platforms. The pre-installed anchor reservations within the diaphragm wall will be uncovered by the use of small hand tools and Hilti hammers. The cover plates will then be removed by the use of torch sets.

Drilling of Borehole

All coring and/or drilling works shall be performed in a manner that affects adjacent structures, foundations, and services if any, shall be minimized.

The anchor drilling rig is set up in front of the anchor point of entry and the anchor inclination is determined and set as required, with a gradient indicator. The anchor boreholes will be then started through the pre-installed sleeve pipes.

Two drilling methodology may be applied according to site & soil conditions, these are as follow:

a) Percussion Drilling with Top Drifter: Drill bits with an outer diameter of 160mm are attached to drill rods of 152mm outer diameter. Through this setup, a bore with a minimum diameter of 160 mm will be constructed. The drilling will be supported by a water flushing technique. In steps of 4.0 m, the drilling rods will be extended until the final length of the anchor is reached.

The process is to be understood that the first drilling rod is provided with a drill bit for loosening the materials, while water is pumped simultaneously through the drilling rods for transportation of the loosened material. The loosened material, mixed with water, will be flushed out in the annulus space between bore and drill rod which will be banked up inside a platform excavated bit then to be pumped by a submersible pump to a segregation/storage tank then to be reused for the next drilling works.

At the end of drilling works, all rods will be dismantled and water flow will be visually monitored prior to the anchor installation stage.

b) ODEX Drilling System: Drilling will be carried out using the bottom DTH Hammer version ODEX installed on the drilling rods using compressed air. The rods will be protected by a temporary casing through the full borehole till the final depth is achieved. The external diameter of the drilling column will be 178mm with an inner casing diameter of 168mm.

At the end of drilling works, all drilling rods will be dismantled including the ODEX DTH head and water flow will be visually monitored prior to the installation of the anchor. The casings will be removed progressively during grouting.

In the event that soil conditions as described in the borehole logs are differing from those encountered on site, the Engineer will be notified accordingly. As the case may be adjustment of drilling tools and flushing technique as well as parameters of anchorage could be resulting from the actual findings while drilling.

After reaching the final depth the rods will be flushed clean with water until reasonably clean water flows out from the top of the borehole.

Disposal of Drill/Injection Spoil

Drilling/grouting & backfilling spoil shall be disposed of in accordance with the Construction Environmental Management Plan

Filling of Bore with Cement Grout

The following cases will require filling the borehole stage:

If the borehole collapse inside the uncased borehole: the borehole will be primarily grouted via the drilling rods to stabilize the uncased bore while dismantling these rods using 1200kg cement + retarders & superplasticizer in order to allow a smooth anchor installation stage.

If cavities occurred during drilling works: the borehole and cavity will be backfilled using 350kg cement + 100kg fly ash + 4% Silicate. Re-drilling works will be carried out after 48hours and followed by a primary grout mix of 1200kg cement + retarders & superplasticizer in order to allow a smooth anchor installation stage.

• If we got (10% 50% over grout) this will be no problem because it’s a backfilling of microcavities
  and fissure in the rocks.
• But if we get (-10% less grout) then the trench should be cleaned once again and grouted.

Note: All additives (or similar) which are mentioned in this MS will be used in case it is required during the grouting & filling works for special cases on-site.

Insertion of Anchor Tendon into Borehole

As the next step, the drill rig will be removed from the anchor location in order to facilitate the installation of the anchor tendon.

The installation of the anchor tendon into the bore shall be made with care in order not to damage the anchor set, not to damage the PE sheath surrounding the steel strand, and to avoid any contact with harmful soil or oil.

Primary Grouting

Normal primary grouting operation (between borehole inner surface & corrugated pipe or free length strands zone) will initially commence upon insertion of the anchor tendon via tremie method under the pressure of 5-6 bar. The tremie pipe shall be fixed to the ground anchor unit where grouting will be commenced from the lower end of the tremie pipe, i.e. toe of the bore.

The grouting shall be carried out in one continuous operation until the consistency of the grout emerging is the same as that of the injected grout (volume of grout ≈ 40 to 50 liter / per linear meter depending on geological soil condition). The top of the borehole will be plugged by a means of a cap of cement mortar with a grout observation tube in order to control that full of the anchorage borehole is completely filled by grout.

The full project estimated primary grouting quantity is between 4,000,000 to 5,000,000 Liter + 40% to 50% over consumption (depending on geological soil condition) for a total of 3420 anchors.

In the special case that after completion of drilling works the water flow is more than 50 liter/min, an anchor tendon will be placed inside the borehole then a special top packer (or) cement plug will be installed inside the reservation steel pipe, the primary grouting process to be commenced under higher pressure condition in order to fill the external area of the anchor duct.

Achieving “Free Anchor Length”

Finally the “free anchor length” will be achieved by using greased strands covered by a polyethylene sheath for each strand at the free length position + smooth plastic duct will be installed around these sheathed strands, to avoid loads from the bond lengths being transferred into the diaphragm wall.

Secondary Grouting

Once the primary grout is completed, a secondary grouting operation (inside the corrugated pipe) will be carried out in order to fill the corrugated pipe with strands inside of the bond zone under the pressure of 5-6 bar and a volume of grout ≈ of 20 to 30 liter / per linear meter. Pumping will continue until the grout arises out of the observation tube which is located outside of the borehole.

Cube samples (3 samples per anchor: 1 for 7 days + 2 spares) shall be taken from the outflow of grout from the secondary observation tube. Samples will be suitably stored for compressive strength testing. No anchor shall be stressed until the grout has reached a minimum strength of 30 MPa. The full project estimated secondary grouting quantity is between 2,000,000 to 3,000,000 Liter + 10% overconsumption for a total of 35000 Anchors.

C. Anchor Testing, Stressing, and Lock-off

General

Testing and stressing of anchors and recording will only be carried out by experienced personnel under the control of a suitably qualified supervisor under the following premises:
a) Stressing will commence once the specified minimum grout strength is achieved, which will be monitored by means of grout cubes’ compressive strength results – usually after 7 days.

b) Anchor stressing force shall be obtained with respect to the anchor working load ‘P’.
c) A calibrated VSL (or other) hydraulic stressing jack & pump shall be used for the stressing works.
d) A calibration certificate of the hydraulic jack and gauge shall be provided to the project consultant and available for inspection during the stressing works.

Stressing Process

Stressing Preparation

Uncoiling of PE anchor sleeves, installation of sealing (if required), bearing, and anchor head plate. The anchor head is fixed in position after 2 wedges are tightened. Tightening is especially important in the case of spherical caps (twisting of the sphere). The hydraulic jack will then be installed (supported by auxiliary lifting equipment) and aligned to the given anchor installation.

Pre-Stressing

Until tensioning up to the pre-load of 10% of the working load, the tensioning assembly might need to be lifted in position. Then the remaining wedges will be installed into the wedge plate.

Acceptance Testing and Locking-Off

After pre-stressing and installation of all wedges, the tensioning will be continued in accordance with BS EN 1537 (2000).

Test Load for Anchors:

Design load: As per the final approved design calculation and according to the anchors’ design table.

Proof test load ‘Pp’ = 1.25 x ‘P’ (i.e. 1.25 Working load)
For the acceptance test, the anchor will be loaded from the datum load Pa to the proof load PP as per the below-mentioned increments. The proof load will then be maintained constant for 15 min. Stressing is carried out by stressing all strands in each tendon in one continual operation.

During stressing the working condition of the hydraulic pump, stressing jack and gauge, power source, hydraulic hoses, and connection will be carefully monitored in order to ensure good working for the whole setup. After testing the anchor it will be locked off as per the set design value (‘P0‘= 0.9 x working load ‘P’).

The steps of Stressing Operation for Loading Test are as below:

Evaluation of the Apparent Tendon Free Length:
The following equation is generally used to calculate the apparent tendon-free length:
L app = (At .Et .Δs) / ΔP,

Where:
L app : is the apparent tendon-free length;
At : is the cross-section of the tendon = 15.24mm;
Et : is the elastic modulus of the anchor tendon = 200 kN/mm2;
Δs : is the elastic extension of the tendon (various according to load increment);
ΔP : is the proof load “Pp” minus datum load “Pa” (various according to anchor load)

Acceptance Limits of L app:

• Upper Limit:
  Lapp ≤ Ltf + Le + 0.5 Ltb;
  Lapp ≤ 1.1Ltf + Le
  Whichever is the larger
• Lower Limit :
  Lapp ≥ 0.8Ltf + Le

Where:
L app : is the apparent tendon-free length;
Ltf : is the tendon-free length (various according to anchor design table);
Ltb: is the tendon bond length = 10m;
Le : is the external length of the tendon measured from the tendon anchorage in the anchor head to the anchorage point in the stressing jack (various according to jack fixing point on site).

Evaluation of Creep Characteristics:

The displacement due to creep at proof load should be measured between the 3rd & 15th min.
The corresponding (α) should be less than 1.8mm.

Note: The documentation of tests is done in the Stressing Report which will be filled and updated prior to the test of each anchor depending on the anchor design load table and following the above-mentioned equations & acceptance criteria.

D. Anchor Head Installation

After the anchors are stressed, the anchor strands of the non-removable anchor type will be cut off, then a protection cap will be installed and finally filled with grease for protection.

For the removable anchor type, strands shall not be completely cut after the anchor head should remain for removal operations after the service period is completed.

E. Anchoring Materials

All materials used in the works covered by this method statement shall be mutually compatible.

This applies in particular to adjacent materials with a common interface. Materials shall conform to those referred to under the applicable standards with properties not changing during the foreseen design life of the completed ground anchor in such a way that the anchor loses its serviceability.

Anchor

All anchors are constituted of a multi-strand removable and non-removable anchor consisting of five (5) to six (6) strands with a minimum design life of 5 years

A complete Ground Anchor consists of:

• Tendon strands – Steel strand will be protected by grease and PE sheath, these sheaths and grease will not be applied on the bond length area of the non-removable type anchor body structure:
• A corrosion-resistant aluminum anchor body, manufactured in Aluminum die-casting technique for the removable anchor type.
• Corrugated & Smooth Plastic Ducts for the non-removable anchor type.
• Plastic Spacers & Centralizers
• Grout body
• Anchor head

Strands

Bonded PC Strand conforming to ASTM A416 Grade 270 shall be used.

Anchor Body Structure

Typical anchor bodies for removable anchor type.

Corrugated and Smooth Plastic Ducts (for Non-Removable Anchor Type)

These ducts are to be placed around the anchor tendon as part of the corrosion protection system for the lifetime of 5 years of ground anchors, the corrugated duct will be placed inside the bond length area and the smooth type will be inside the free-length area.

Corrugated and Smooth Plastic Ducts (for Non-1.4 Plastic Spacers and Centralizers)

Spacers and centralizers will be placed along the anchor tendon in order to centralize it inside the borehole and to make sure that sufficient grout is covering the perimeter of the anchor tendon & ducts.

Anchor Head

The wale, bracket, anchor bearing plate, and fixing components used for the head part of the anchor shall have necessary functions, and sufficient strength, and shall not cause transformation that has a negative influence on the necessary anchoring force.

Each Ground Anchor shall be provided with sufficient excess strand length to enable the removal of the strand at the end of the anchor service life (for removable anchors type only).

The bracket shall be manufactured according to the anchor installation angle, and be sufficiently strong to cause no change in the vertical and horizontal component force of the anchoring force.

Grout Material and Admixture

Mixed grout shall consist of the following properties/components:

Cement: The cement to be used for grouting SRC ( Sulphate Resistant Cement )

Proposed grout mix proportion:

• Water / Cement ratio 45% – 50% by weight of cement ( 1200kg/m³)
• Bleeding = max. 2% after 3 hours and max. 4% at any time.
• Compressive Cube Strength = min. 20 N/mm² at 07 days min. 30 N/mm² at 28 days
• Mixing time = min. 4 minutes
• Water: Clean sweet water, free from oil, organic matter, or deleterious substances.
• Grout mix will be tested for 7 days of compressive strength after installation of site setup

(Grouting Plant)

• Viscosity (using 8mm Marsh Cone)
• Temperature (≤ 35°)

F. Lifting and Installation Procedure of Anchor Tendons

Once the anchor preparation works are completed at the fabrication area, the approved anchor tendons will be installed inside the drilled borehole using 2 methods:

1) Manual Method: Crane will lift up the anchor tendon using multiple wire ropes/belt slings and deliver it to the installation point where an appropriate number of adequate manpower will handle the anchor carefully in order to install it inside the borehole manually till it reaches the end bottom (toe) of the drilled borehole.

2) Lifting Beam Method: Crane will get a special attachment of a designed certified lifting beam with a full-length holding bracket with inside running wheels which will be hung by both crane cables from the lifting eyes position. The fabrication team will place the approved anchor tendon inside this bracket and secure it by means of some belts.

The tendon will be delivered to the installation point using the crane where adequate manpower will handle it properly from inside that bracket towards the borehole with the help of the crane which will start to slowly lift the beam from the backside and lower the front side in order to allow the tendon sliding easily with rolling above the bracket wheels to go inside the borehole till the end bottom (toe) of the drilled borehole.

2. Capping Beam

Construction Methodology

After completing the diaphragm wall, construction of a capping beam at the top of the diaphragm wall or piles shall commence. The work shall be done by removing first the guide wall to enable the construction of the capping beam. The work shall be done as follows:

1. After the removal of the guide wall and the area is clean and free to start the work, the Surveyor shall verify the top of the diaphragm wall and shall conform to the approved plan and drawing.
2. As the markings were finalized, installation of reinforcement shall be done as per Shop Drawing, Reinforcement Details D-Wall (Capping Beam)
3. All reinforcement shall be assembled using black annealed mild steel tie wire with ends directed into concrete.
4. Once the reinforcement is complete and appropriate concrete spacers are installed, formworks shall follow.
5. All reinforcements shall be provided with requisite spacers, chairs, ties, bracing, and temporary and permanent supports for reinforcement using approved compatible material as per BS 7973.
6. Supplementary bar spacers shall be provided to ensure the adequacy of cover and stability and to fix cast-in items and tie bars as required.
7. Mechanical splices shall comply with EN 1992-1-1 or BS 8666, and shall be used as and where indicated on the drawings.
8. Correct concrete cover to reinforcement shall be maintained with the aid of an approved spacer.
9. The formwork in contact with the concrete shall be treated with a suitable non-staining mold oil to prevent adherence to concrete.
10. Apply bonding agent prior to casting concrete as follows:

• The surface of piles shall be sound and scrubbed using a stiff-bristled nylon brush to remove laitance, dust, dirt, grease, wax, and any other foreign materials that might affect the proper bonding of new concrete on the old ones. The surface should be damp with no excess, free-standing water.
• Weber ad 220 SBR liquid is directly added to a previously prepared mixture of cement/sand or cement/sand/gravel and mixed by a power mixer with a low rotation speed (300 rpm). Total mixing time should not exceed 5 minutes from the time liquid is added to the solid material.
• Prime the prepared surface by applying a thin cement slurry mix with Weber.ad 220 SBR, using stiff nylon bristled brush, and proceed for concrete casting.

11. Prior to cast concrete, ensure the cleanliness of the forms. When using wood forms, it shall be oiled or wetted with water in advance of placing concrete so that joints will tighten and prevent seepage of cement grout from the mix. The reinforcement shall be sprayed with a small amount of water prior to starting the pour.
12. The location of the expansion joint and contraction joint shall be as per the approved shop drawing.
13. Concrete dropped into place shall be dropped vertically. It shall not strike the formwork between the point of its discharge and its final place in the Work, and except by approval of the Engineer, it shall not be dropped freely through a height greater than 1.5 m.
14. Further discussion and information pertaining to concrete works shall be discussed on a separate Method Statement for Concrete Works.

3. Hoop/Waler Beam

Construction Methodology

The Hoop Beam shall begin construction once the diaphragm wall is done. Hoop Beam construction shall be done in sequence as follows:

• Once the diaphragm wall is done and the guide wall was demolished, the excavation shall advance in preparation for the installation of anchors and the construction of hoop beams.
• Please note that during the lowering and installation of reinforcement cages, the preinstalled reservation/block-outs for the location of hoop beams were already installed.
• The Surveyor shall monitor the excavation and verify the location of the pre-installed reservation/block-outs once exposed.
• Any deviation in the location or position of the hoop beam due to the installed block-outs shall be corrected as per survey verification.
• Clean the block-out location for the hoop beam to locate the embedded coupler.
• The hoop beam shall be connected to the diaphragm wall with a 32mm ø embedded U-bar with a coupler.
• The bottom formworks shall be installed first.
• Dowel bars 32mm ø will be connected to the U-bars by a coupler that will hold the main reinforcement of the hoop beam.
• All reinforcement shall be assembled using black annealed mild steel tie wire with ends directed into concrete.
  10. Once the reinforcement is complete and appropriate concrete spacers are installed, formwork installation shall follow.
• All reinforcements shall be provided with requisite spacers, chairs, ties, bracing, and temporary and permanent supports for reinforcement using approved compatible material as per BS 7973.
• Supplementary bar spacers shall be provided to ensure the adequacy of cover and stability and to fix cast-in items and tie bars as required.
  13. Mechanical splices shall comply with EN 1992-1-1 or BS 8666 and shall be used as and where indicated on the drawings.
• Correct concrete cover to reinforcement shall be maintained with the aid of an approved spacer.
• The formwork in contact with the concrete shall be treated with a suitable non-staining mold oil to prevent adherence to concrete.
• Apply bonding agent prior to casting concrete as follows:
  The concrete surface shall be sound and scrubbed using a stiff-bristled nylon brush to remove laitance, dust, dirt, grease, wax, and any other foreign materials that might affect the proper bonding of new concrete on the old ones. The surface should be damp with no excess, free-standing water.
  Weber ad 220 SBR liquid is directly added to a previously prepared mixture of cement/sand or cement/sand/gravel and mixed by a power mixer with a low rotation speed (300 rpm). Total mixing time should not exceed 5 minutes from the time liquid is added to the solid material.
  Prime the prepared surface by applying a thin cement slurry mix with Weber ad 220 SBR, using stiff nylon bristled brush, and proceed for concrete casting.
• Prior to casting concrete, ensure the cleanliness of the forms. When using wood forms, it shall be oiled or wetted with water in advance of placing concrete so that joints will tighten and prevent seepage of cement grout from the mix. The reinforcement shall be sprayed with a small amount of water prior to starting the pour.
• The location of the expansion joint and contraction joint shall be as per the approved shop drawing.
• Concrete dropped into place shall be dropped vertically. It shall not strike the formwork between the point of its discharge and its final place in the Work, and except by approval of the Engineer, it shall not be dropped freely through a height greater than 1.5 m.
• Further discussion and information pertaining to concrete works shall be discussed on a separate Method Statement for Concrete Works.

Risk Assessment and Job Hazard Analysis

Permit and Licensing Requirements

Drawings, Diagrams, and Maps

Pre-Start Safety Briefing Arrangements

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

Safety Requirements:

All necessary personal/protective equipment (PPE), as well as harness, be provided.
Banksman, wearing distinctive vests, shall be assigned to help operators maneuver their equipment.
The equipment operators shall possess the required licenses and certificates.
Generated dust shall be controlled by periodic water spraying.
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.
In case of working at night, please refer to Method Statement for Night Works.

Environment and Quality Issues

1. Precautionary Measures
   All precautionary measures shall be briefed to all workers prior to commencing the activity.
2. Disposal Requirements
   All waste shall be disposed of as per Environmental Compliance and Management Plan
   and as per Government approved disposal areas.
3. Inspection, Test, and Sampling
   a. Request for Inspection and Testing will be submitted prior to and after execution of works. Inspection and Test Plan (ITP) shall be provided.
4. Quality Assurance Requirements Table
   Refer to Project Quality Plan
   Inspection and Test Plan (ITP) shall be provided.

tag: Method Statement for Diaphragm Wall Construction