1. What is the method statement for trenches of Gas Network & District Cooling?
This method statement for trenches defines the sequence and describes the control procedures for the excavation and backfilling of trenches for gas networks and district cooling.
Table of Contents
2. Definitions
QC-Quality Control
MS-Method Statement
BS-British Standards
IFC-Issued For Construction
HSE-Health Safety & Environment
PPE-Personal Protective Equipment
GIS-Geographical Information System
LPS-Loss Prevention System
GN-Gas Network
DC-District Cooling
3. References
BS 1377-4 Methods of test for soils for civil engineering purposes-Compaction-related tests
Health and Safety Plan
Construction and Environmental Management Plan
General Lifting Plan
Gas Distribution System Design Guidelines
District Cooling System Design Guidelines
MS- Trial Pits Excavation
MS- Protection of Existing Utilities
MS for Gas Network Installation
MS for District Cooling Installation
IFC Design Drawings
4. 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 non-conformance 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 monitor the site engineer’s strict implementation of the MS 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.
Advice for Health & Safety requirements and monitor the Hazard controls implemented on-site as per the Method Statement/Risk assessment.
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 the third party.
Ensure the validity and 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.
Survey Aide
Maintain and use Surveying equipment. Assist Surveyors in taking measurements, record measurements manually or electronically, and peg out boundaries.
Soils Competent Person
A person trained to identify unsafe hazards or working conditions in the workplace or working conditions with authority to have the hazards eliminated or controlled.
The soil competent person must have specific training in and be knowledgeable about, soil analysis, the use of protective systems, and the requirement of the standards.
A competent person must be on every job site when workers are exposed especially on deep excavation inspecting indications of possible cave-ins, failure of protective systems, hazardous atmospheres, and other hazardous conditions, inspecting materials or equipment if damaged to determine if usable, monitoring water removal equipment and operations, visual and manual tests of soils to determine type and inspection prior to the start or continuation of work after rainstorms or after any other hazard-increasing occurrences.
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 setups 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.
Third-Party Performs Laboratory
Performs the required testing and provides test results to certify that the work is in compliance with the project requirements.
5. Resources
1. Plant and Equipment
Excavator w/ Hammer
Bucket Excavator
Dump Trucks (MAN TGA 35.430)
Iron Rammers (weighing less than 5kg)
Vibrating Plate Compactors
Hand Compactors
Leica TS 15m Total Station
Leica NA2 Automatic Level
2. WorkForce
Soils Competent Person
Site Engineer
Land Surveyor
Survey Aide
Foreman
Equipment Operators
Banksman
Carpenter
Helpers/Laborers
Safety Engineer
First Aider
Third-Party Laboratory 1 Team
3. Light Tools
Power Tools (Various)-as per site requirement
Hand Tools (Various)-as per site requirement
6. Materials
Paints
Pins and pegs
Warning tapes
Concrete barriers
Approved bedding and surround materials
Approved pipes and accessories
7. Methodology
This document shall be read in conjunction with the approved Method Statement for Trenches of Gas Network Installation and District Cooling.
7.1 General
This methodology specifies the requirement for excavation and backfilling of trenches for the gas network in concurrence with the existing specifications and requirements of proper authorities and related project specifications.
All civil aspects of work involved in the utility network mentioned above shall be done and inspected as per this document.
The working area will be barricaded and restricted from the entry of unauthorized personnel.
It will be properly illuminated and necessary warning signs to be installed in the proper location.
All scaffolding works and ladders for access and egress shall be erected by certified scaffolders. All erected scaffolding access and egress shall be inspected and tagged prior to use.
The relevant permits are to be fully complied with by the construction team prior to commencing activity and ensure their validity.
All workers to be involved in the activity shall receive proper information, instructions, training, and adequate supervision during the activity. All workers shall be briefed as well on the safe system of work and procedure along with the use of proper PPE and emergency procedures.
7.2 Pre-Excavation Works
The working area shall be cleared with general rubbish and any obstructions that might hinder the continuous implementation of the activity.
Notwithstanding the information given on the as-built drawings, the contractor shall be responsible for locating all services crossing or in parallel with the line of the trench to be excavated.
Trial holes/pits will be dug by hand in sufficient numbers to ensure that all services on the route of the pipeline are uncovered. Trial holes/pits will be of sufficient size and depth to enable clear identification of service type. This activity shall be done in accordance with the approved Method Statement for Trial Pits Excavation.
7.3 Trench Excavation-Gas Networks
All trenches related to the gas network including for location of manholes are to be excavated with vertical sides to the width, lines, grades, and depths as shown on the approved shop drawings.
As per Gas Distribution System Design Guidelines, trench depths shall be sufficient to provide the required cover to the main piping and service piping. The cover shall be measured to the top of the pipe. Trench widths shall be a minimum of 400 mm or pipe diameter plus 150 mm on each side of the pipe, whichever is greater. Refer to Typical Trench Detail IFC drawing.
Prior to starting trench excavation, the route of pipes shall be surveyed and set out accurately in accordance with approved shop drawings.
The depth and width of the trench shall be established by installing sight rails or boning rods for checking bottom profiles at an adequate spacing set up using proper leveling techniques and to the levels shown on the drawings.
Rock encountered in trench excavations shall be so excavated that the clearance between the cables, when laid, and the rock sides and bottom of the trench are kept to the minimum limits necessary to provide for the specified thickness of bedding.
All existing services found during trial pit excavation will be adequately protected from damage and fully supported during excavation works in such a manner as to prevent any distortion or damage to the services.
This activity shall be done as per the approved Method Statement for the Protection of Existing Utilities during Excavation.
All excavated material must be removed from the site immediately to enable working areas to be clean and free from obstacles for the duration of the works.
For any possible presence of water at the excavated trench, the current water level at the site is controlled by an ongoing dewatering system at the site. In case the presence of water is detected, mobile diesel pumps or submersible pumps will be used to collect locally the water and ensure dry conditions throughout the performance of the work.
7.4 Placing of Bedding and Surround
Prior to placing bedding and surrounding materials, the formation level of the trench shall be inspected and approved by the consultant.
7.4.1 Bedding and Surround Materials
Pipe bedding and surround shall be provided as shown on the approved shop drawings.
Pipe bedding shall be well compacted and shall completely fill the whole width of the trench excavated.
Crushed limestone, 0-5 mm in size shall be used as bedding and surround for gas networks. The bedding shall be 200 mm thick.
7.5 Laying and Testing of Pipes
All works related to the Laying and Testing of Pipes shall be done as per the approved Method Statement for Gas Network Installation.
Laying of warning tapes and tracer wires.
After the laying of the pipes is approved, as-built for pipe laying shall be collected by an approved GIS Third party for preparing the final As-Built drawing.
7.6 Backfilling of Utility Trenches
Trenches are not to be backfilled until all required tests are performed on the utilities and until the Engineer has verified that the utilities have been installed as per approved shop drawings and in accordance with the project specification.
After the utilities have been laid, the trench refilling is to commence with approved fill not exceeding 50mm in size and in compacted layers not exceeding 150 mm in thickness. Each layer shall be well compacted by hand with iron rammers weighing not less than 5 kg until the trench has been filled to a height of 300 mm above the top of the utility.
The remainder of the trench is then to be refilled in compacted layers not exceeding 250 mm unconsolidated and 150mm consolidated thickness. Each layer is well compacted, with power rammers, vibrating plate compactors, or other mechanical means of a type to be approved until the ground is thoroughly consolidated up to the required level for surface reinstatement. Each layer is to be compacted to 95% of its maximum dry density as determined by BS 1377-4.
Where necessary or as instructed by the Engineer, the moisture content of the fill shall be adjusted either by drying out or adding potable water to assist the compaction of the material. During compaction, the backfill shall have a uniform moisture content of (± 2%) recorded in the compaction test.
PVC warning tape shall be laid above the utility pipe as shown in the approved Shop Drawings.
7.7 Trench Excavation-District Cooling
All trenches related to the district cooling network including for location of manholes are to be excavated with vertical sides to the width, lines, grades, and depths as shown on the approved shop drawings.
A table with the dimensions of the trenches within the different DC pipe diameters is shown in the approved IFC Drawing for District Cooling Typical Trench Section Detail and as per Typical Trench, Section drawing of the District Cooling Distribution System Design Guidelines for Civil Works.
The depth of the trench depends on the DC pipe dimension both also on the level of crossing existing underground structures. Covering above the top of the pipes shall not be less than 1000 mm measured from the highest point of the pipe to the ground surface.
Prior to starting trench excavation, the route of pipes shall be surveyed and set out accurately in accordance with approved shop drawings.
The depth and width of the trench shall be established by installing sight rails or boning rods for checking bottom profiles at an adequate spacing set up using proper leveling techniques and to the levels shown on the drawings.
Rock encountered in trench excavations shall be so excavated that the clearance between the cables, when laid, and the rock sides and bottom of the trench are kept to the minimum limits necessary to provide for the specified thickness of bedding.
All existing services found during trial pit excavation will be adequately protected from damage and fully supported during excavation works in such a manner as to prevent any distortion or damage to the services. This activity shall be done as per the approved Method Statement for the Protection of Existing Utilities during Excavation.
All excavated material must be removed from the site immediately to enable working areas to be clean and free from obstacles for the duration of the works.
For any possible presence of water at the excavated trench, the current water level at the site is controlled by an ongoing dewatering system at the site. In case the presence of water is detected, mobile diesel pumps or submersible pumps will be used to collect locally the water and ensure dry conditions throughout the performance of the work.
7.8 Placing of Bedding and Surround
Prior to placing bedding and surround materials, the formation level of the trench shall be inspected and approved by the Consultant.
7.9 Bedding and Surround Materials
Pipe bedding and surround shall be provided as shown on the approved Shop Drawings.
Pipe bedding shall be well compacted and shall completely fill the whole width of the trench excavated.
Crushed Limestone, 0-5 mm in size shall be used as bedding and surround for the district cooling network.
7.10 Laying and Testing of Pipes
All work related to the laying and testing of pipes shall be done as per the approved Method Statement for District Cooling Network Installation.
After the laying of the pipes is approved, as-built for pipe laying shall be collected by an approved GIS Third party for preparing the final as-built drawing.
7.11 Backfilling of Utility Trenches
Trenches are not to be backfilled until all required tests are performed on the utilities and until the Engineer has verified that the utilities have been installed as per approved shop drawings and in accordance with the project specification.
After the utilities have been laid, the trench refilling is to commence with approved fill not exceeding 50mm in size in compacted layers not exceeding 150 mm in thickness. Each layer shall be well compacted by hand with iron rammers weighing not less than 5 kg until the trench has been filled to a height of 300 mm above the top of the utility.
The remainder of the trench is then to be refilled in compacted layers not exceeding 250 mm unconsolidated and 150mm consolidated thickness. Each layer is well compacted, with power rammers, vibrating plate compactors, or other mechanical means of a type to be approved until the ground is thoroughly consolidated up to the required level for surface reinstatement. Each layer is to be compacted to 95% of its maximum dry density as determined by BS 1377-4.
Where necessary or as instructed by the Engineer, the moisture content of the fill shall be adjusted either by drying out or adding potable water to assist the compaction of the material. During compaction, the backfill shall have a uniform moisture content of ( ± 2%) recorded in the compaction test.
PVC warning tape shall be laid above the utility pipe as shown in the approved shop drawings.
8. Risk Assessment
Please refer to the attached document in Appendix B.
9. Permit and Licensing Requirements
Refer to Appendix C for the Permit to Work.
10. Drawings, Diagrams, Maps, and Survey Data
Refer to approved Shop Drawings.
11. Pre-Start Safety Briefing Arrangements
Refer to Risk Assessment in Appendix B.
1. Protective and Safety Equipment
All workers involved shall be equipped with adequate PPE as stated below:
a. Safety Helmet with Company Logo
b. Safety Boots
C. High Visibility Vest
d. Safety Goggles
e. Hand Gloves
f . Coveralls
2. Information to Personnel
a. Safety Induction
b. Job training
C. Superintendents Notices/Memos
d. Toolbox talks
e. STARRT Card
3. Special Safety Requirements
a. All necessary personal/protective equipment (PPE), as well as harness, be provided.
b. Banksman, wearing distinctive vests, shall be assigned to help operators maneuver their equipment.
c. The equipment operators shall possess the required licenses and certificates.
d. Generated dust shall be controlled by periodic water spraying.
e. 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.
f. All working activity shall comply with client safety procedures.
g. First aid material.
h. General management of protection/operation hazards is to be observed.
i. In case of working at night, please refer to Method Statement for Night Works
12. Environment and Quality Issues
1. Precautionary Measure
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 the Construction and Environmental Management Plan and as per government-approved disposal areas.
3. Inspection, Test, and Sampling
Request for Inspection and Testing will be submitted prior to and after execution of works.
4. Quality Assurance Requirements Table
Refer to Project Quality Plan and Project Specifications
13. List of Appendices
Appendix A: Related Drawings
Appendix B: Risk Assessment
Appendix C: Inspection and Test Plan (ITP)
Appendix D: Permit to Work
