The purpose of this plumbing method statement is to define the procedure for the preparation and construction of gravity sewer sewage piping lines with GRP pipes with associated inspection chambers, manholes in accordance with the requirements specified in the relevant specifications considering safety and quality of the work activities.
Scope of work is as below:
- Gravity sewer lines with manholes 1500mm dia. Associated with house connection chambers to facilitate the project.
- G.R.P pipes 150mm dia., 200mm dia. and 300mm dia. laid in a trench width of 600mm + pipe diameter in a stable soil and 5 times pipe diameter in unstable soil.
- The limit of contract is gravity feed connection to the pumping station constructed by others adjacent to project boundary.
Roles and Responsibilities
Project Manager
To make sure that the project plumbing works are carried out in accordance with company policies and in accordance with the requirements of the project quality plan, specifications and contract.
Ensure full compliance of subcontractors with company quality policies and with the requirements of this method statement.
To ensure that all the equipment required to execute the sewage piping works according to the construction program are available, in good condition, and provide any additional equipment that might be required.
Co-ordinate with the Construction Manager, Project Engineer, Safety Engineer, Foreman and Surveyor for a safe and proper execution of the works.
To guide specific attention to all safety measures in co-ordination with the safety officer/engineer.
Construction Manager
Ensure area is ready and safe to start the works.
Set up required equipment and plant through discussion with the Project Manager and Project Engineer/Works Supervisor.
Ensure the works are carried out according to the specification and approved shop drawings.
Liaise and co-ordinate with the Project Manager for the agreed sequence of works with respect to the construction program.
Allocation of required manpower through co-ordination with the Project Manager.
Provide the risk assessments for the works in hand.
Provide sufficient and safe access for operatives, trucks and pumps.
Take precautionary measures with regards to protecting works from hot weather, wind, rain and sun.
Project Engineer
The engineer will carry out his duties in a manner that will be coordinated by the project manager on a daily basis, and will ensure proper distribution of the workforce and equipment at required locations.
To be aware of test frequencies related to the formation level.
Control disposal of waste excavated material according to the instructions received from the project manager.
Co-ordinate with the safety officer to maintain safe working and proper housekeeping of the site. To comply with the safety measures and ensure that all Safety Officer Teams are aware of the same to prevent accident and loss.
To inform the QC inspector of the areas ready for inspection and to prepare the inspection requests with complete attachments.
QA/QC Engineer / Inspector
Ensuring that consultant/client inspection requests are implemented.
Compilation of all necessary quality control checklists.
Assisting consultants during the inspections.
Coordinating with the third party lab regarding tests and results.
The control of work performance by means of checking the work before consultants’ inspection and issuing RFIs & punch lists as necessary.
Completion of documentation to verify the work performed.
Controlling all inspection activities on-site in line with ITPs.
Ensuring that all test equipment including surveying equipment is calibrated and is suitable for use on site.
Surveyor Responsibilities
To establish benchmarks from agreed reference points, provide required setting out and level markings and follow up with regular checks.
Co-ordinate with the Project Engineer / Foreman and ensure the approved shop drawings/construction drawings will be implemented properly.
Maintain survey details and reports, periodically check the progressing works and advise the Project Manager of any deviation from the drawings.
HSE Engineer/Officer
To ensure implementation of all health and safety measures related to the nature of works being carried out, and in accordance with the Project Safety Plan.
Ensure that all the persons involved in the works are aware of their responsibilities, and that they have enough understanding of the safety procedures.
The Safety Officer in co-ordination with the project manager will ensure that all the implemented safety measures are effective enough to maintain safe working on the site.
To maintain continuous inspections of the site activities, advise and train persons on a daily basis to prevent accidents and personnel injury.
Give special concern to housekeeping, and ensure that the site is maintained clean and tidy.
To ensure all the relevant safety sign boards for different works are in place.
Foremen/ Works Supervisor
Ensure the works are progressed in the sequence as agreed with the Project Manager.
Ensure ready mix concrete ordered from the approved supplier is delivered on time and with sufficient quantity for continuous casting of the planned pour.
Liaise with the Project / Site Manager for the allocation of the work force, ensuring adequate manpower is available.
Liaise with the site manager to ensure all the required plant / materials are available to construct the works.
Full time supervision will be required to ensure the works are progressing to the latest approved for construction drawings and specification.
EQUIPMENTS/ TOOLS / MANPOWER/MATERIALS
List of Equipment’s/Tools
- Transit Mixer (Concrete supplier) from Quick mix & Remix
- Vibrators
- Concrete Pumps
- Scabbler/Chipping Gun
- Masonry tools
- Mobile Crane (for contingency plan for breakdown of pump)
- Concrete Buckets (for contingency plan for breakdown of pump)
List of Manpower
- Project Managers
- Construction Managers
- Project Engineers
- QA/QC Engineers/ Inspectors
- Safety Engineers/Officers
- Lab Technicians
- Foremen/Work Supervisors
- Equipment Operators
- Skilled and unskilled labourers
List of Materials
- Ready mix concrete with approved design & trial mix of 40 N/mm² OPC
- Reinforcing Steel Bars, Assorted sizes, please refer to approved shop drawings
- 18mm thick Phenolic Board (Plywood)
- Assorted Wood
- Assorted Nails and Concrete spacer
- Tie Rods and Steel Clamps
- Cup-Lock with Steel Decking and Infill System
- Polyethylene sheets, Absorptive Mats and Water
- Poly Release WB Mould/Shutter Release Agent.
- Emaco S22 NB, Emaco S23 NB, Emaco R202 NB, Concresive 1450i, Concresive 1414, Masterflow 544 – Concrete Repair Materials
- Note: Quantity of manpower, equipment and materials will be submitted on the daily progress report.
General Method Statement for Construction of Gravity Lines Storm, Manholes & Chambers
General procedural matters
Upon formal receipt of construction approval from the Engineer, setting out for the sewer lines will be carried out by the Contractor’s Surveyor, which will be agreed with the Engineer’s Surveyor before proceeding with any permanent work.
Any obstruction observed during site inspection will be recorded and photographed and confirmed in writing for reference and records.
Following the issuance of the notices of intent to all the concerned authorities, we shall liaise with the Engineer and the Municipality to accurately record the conditions of existing manholes, wherever necessary (for connection to existing system).
Based on received approved drawings from the various authorities in response to our notices of intent, we shall carefully excavate a series of trial holes with a view to locate the exact position of the services.
Shop drawing for each line will be prepared and approved by Engineer prior to start the actual work.
Work will proceed in the event the proposed Storm line is unaffected by any obstruction.
In the event of obstruction conflict of any kind, necessitating relocation outside the allocated storm reserve, the necessary permission for such relocation will be acquired by the Engineer.
Prior to dewatering necessary approval will be obtained from the concerned authorities prior to discharge in existing system.
Dewatering
Where formation levels are below the groundwater table, dewater excavation utilizing well-point dewatering system.
Pre-drill the wells using Drill head fitted to the boom of a wheeled or chain excavator.
Well points of 6 meter in length will be installed into the pre drilled holes using jetting pumps.
The slotted filter heads of the well-points will be surrounded with sharp filter sand while jetting.
50 mm dia. UPVC well-points will be connected to 150 mm dia. Header pipes via 50 mm dia. Flexible hoses. The header pipes will be linked to 150 mm dia. Vacuum pumps which will pump the groundwater via 150 mm dia. Lay flat discharge lines, connected to 10 inch discharge lines laid up to approved discharge points.
Where rock is encountered:
A well-point dewatering system will be installed approximately for the first 30 metre length, in order to establish a sump, from where the groundwater will be slumped out by means of a suitable submersible pump or vacuum pump, if the formation area encountered by hard soil.
The availed bore hole results will have due significance while deciding upon the method of dewatering for a particular area.
Notes on excavation
The existing ground level will be recorded.
Excavation will proceed after successful dewatering wherever required.
As trunk sewer lines are located in areas unaffected by space restriction and are in areas of stable ground conditions, an open-cut to the safe angle of repose of the soil will be adopted.
The deep excavation will be in stages as per depth band.
Where the proposed deep lines are located near an existing service or structure, we will use trench shoring support for excavation prior to commencement of any such excavation.
Due care will be taken to maintain and support the existing services and structures.
Night watchman will maintain a vigil on the excavation and dewatering installations, to keep the excavation free of water or loose materials at all times.
Diversions will be carried out by safety barriers.
Access ladders will be provided for ease of entry and exit from the excavations.
Inspection requests, will be given to the Engineer/Inspectors, for obtaining approvals at various stages.
The available bore hole results have due significance upon the method of excavation and dewatering for a particular area.
Excavated material will be moved to a safe distance from the trench sides.
Adequate shoring, battering of excavation sides will be undertaken to ensure the trench remains stable & safe working environment.
General Method Statement for Construction of Gravity Storm Water Lines
Pipe laying – GRP pipes (gravel surround)
Drawing shall be re-viewed by the Engineer & communicated to foreman in charge of the Pipe Laying. GRP Pipes will be laid in accordance with the manufacturer’s instructions concerning the laying of pipes and bedding for the same, as submitted for approval.
Written inspection request’s will be given to the Engineer/Inspectors for approval of various stages of work, such as –
- Setting out
- Excavation & formation
- Side and above bedding
- Pipe Laying
- Water Test
- Deflection Test
- Backfilling
Upon receipt of the Engineer’s approval of the compacted formation, the bedding material will be carefully placed in the trench on the spread geotextile.
The bedding material 150 mm depth increased to 300 in unstable grounds a directed by the Engineer will be spread and levelled to the pipe gradient to a level of 2.0 cm above the invert level, so as to have a compacted invert level.
The stalked pipes will be lowered by and laid from downstream to upstream.
GRP pipes will be laid in granular bed and surrounded of 10 mm single size natural aggregate, contained within approved geotextile trench lining material, to have an overlap of 300 mm.
The GRP Pipes for Dia above 500 will be joined by using tirfors.
Pipes will be checked for line and level jointly by surveyors and the engineer’s inspectors.
Each pipe joint will be enclosed with approved PVC wrapping tape. Side bedding will be placed carefully by means of a crane and side discharge skip, discharging the materials centrally. The side bedding will be compacted in layers, by 2 No. hand compactors, simultaneously on either side of the pipe to impart symmetrical compaction.
Following this, the pipe surround material will be placed carefully in the same manner, to a level of 30 cm in two layers above the crown of the pipe and compacted. The Geotextile Fabric overlapping will be 30 cm.
Selected materials previously excavated from the trench will be utilized to backfill the trench in 150 mm layers, carefully compacted by hand rammers, up to a level of 600 mm above the crown of the pipe.
Water test in accordance with your Specification will be carried out as per the attached method statement.
When pipe laying is not in progress, we will ensure that the pipe ends are closed at all times by timber plugs.
Subsequently, backfilling will continue in layers, compacted in the lower regions by mechanical plate compactors and in the upper region by hand-operated drum rollers.
Deflection test will be carried out immediately after 100 % backfilled (to allowable limit).
Compaction tests will be carried out for the backfilling, as directed by the Engineer in unmade areas, to a minimum Proctor density of 90%. In areas under roads, the compaction tests will be carried out in accordance with the ‘Abu Dhabi Municipality Specification for Backfilling of Trenches & Excavation in Asphaltic Roads, Tiled/Paved Parking’s and Roads’.
150mm wide service warning tape will be placed 800 mm below the finished ground level.
Pipe laying – uPVC pipes (gravel surround)
As built drawing shall be reviewed by the Engineer and communicated to foreman in charge of Pipe Laying.
UPVC Pipes will be laid in accordance with the manufacturer’s instructions concerning the laying of pipes and bedding for the same, as submitted for approval.
Written inspection requests will be given to the Engineer/Inspectors for approval of various stages of work, such as:
- Setting out
- Excavation & formation
- Side and above bedding
- Pipe Laying
- Water Test
- Deflection Test
- Backfilling
Upon receipt of the Engineer’s approval of the compacted formation, the bedding material will be carefully placed in the trench on the spread geotextile.
Bedding material will be spread and levelled to the pipe gradient to a level of 2.0 cm above the invert level, so as to have a compacted invert level.
The stalked pipes will be lowered by downstream to upstream.
UPVC pipes will be laid in granular bed and surrounded of 10 mm single size crushed aggregate, contained within approved geotextile trench lining material.
The pipes will be checked for line and level jointly by our Surveyors and the Engineer’s Inspectors.
Each pipe joint will be enclosed with approved PVC wrapping tape.
Side bedding will be placed carefully by means of a crane and side discharge skip, discharging the materials centrally. The side bedding will be compacted in 150 mm layers, by 2 No. hand compactors, simultaneously on either side of the pipe to impart symmetrical compaction.
Following this, the pipe surround material will be placed carefully in the same manner, to a level of 30 cm in two layers above the crown of the pipe and compacted The Geotextile Fabric overlapping will be 30 cm.
Selected materials previously excavated from the trench will be utilized to backfill the trench in 150 mm layers, carefully compacted by hand rammers, up to a level of 600 mm above the crown of the pipe.
Water test in accordance with your Specification will be carried out as per the attached method statement.
When pipe lying is not in progress, we will ensure that the pipe ends are closed at all times by water-tight plugs.
Subsequently, backfilling will continue in layers, compacted in the lower regions by mechanical plate compactors and in the upper region by hand-operated drum rollers.
Upon completion of the backfilling, the 1st pig test will be carried out (allowable limit: 3%)
A 2nd Pig test will be carried out immediately prior to issue of the P.A.C. (Allowable limit: 5%).
Compaction tests will be carried out for the backfilling, as directed by the Engineer in unmade areas, to a minimum Proctor density of 90%.
In areas under roads, the compaction tests will be carried out in accordance with the Municipality Specification for Backfilling of Trenches & Excavation in Asphaltic Roads, Tiled/Paved, parking’s and Roads’.
A final mirror test is carried out to ascertain the alignment.
150 mm wide service warning tape will be placed 800 mm below the finished ground level.
Procedure for water test for GRP & uPVC pipes
Complete the granular bedding up to the soffit of the pipeline.
Fix stoppers end plugs both at the upstream and downstream with tow pipes ½” dia. the upstream will be the ‘air release pipe’, while the downstream one will act as ‘filling pipe’.
Fill the line from downstream pipe (Filling Pipe).
Keep the Air Release Pipe open to release the air.
When water starts coming from the Air Release Pipe, the pipe will be closed.
A pump will be fixed at the downstream end, fitted with a gauge and pressure applied equivalent to 5 m. of water head or depth to invert plus 1.0 m. whichever is greater.
Measure the head at the downstream end.
The pressure will be maintained for a period of 30 minutes.
If there is any drop in pressure, water will be added from a measuring vessel at 10 minute intervals.
A record will be kept of the quantity of water added.
The added quantity of water should not exceed 1 liter per day, per millimeter of nominal internal diameter, per kilometer of pipe.
Pipelines will be tested in length between manholes to manholes.
Procedure for the storage of pipes
The Pipes & Fittings will be stored in a shaded in a shaded area for uPVC pipes and GRP pipes with tarpaulin form direct sun and in accordance with manufacturer’s recommendations.
It will be ensured that the Pipes & Fittings do not come into contact with sharp projections.
The Pipes & Fittings will be stored in a flat level area and raised above the ground on timber so that the lowest point of any Pipe or Fitting is not less than 150 mm above the ground.
Pipes will be stacked in such a manner so that the height of the stacked pipes does not exceed 2 meters.
The Spigot and Socket Pipes will be stacked in such a manner so as to ensure that Pipe layer have Sockets protruding at opposite ends of the stack.
Rubber Joint Rings will be stored in an air-conditioned Store.
Procedure for backfilling
Backfilling will be carried out in accordance with specifications.
Selected material previously excavated from the trench will be utilized to backfill the trench in 150 mm layers, carefully compacted by hand rammers, up to a level of 600 mm above the crown of the pipe.
Subsequently, backfilling will continue in layers of 30 cm, compacted in the lower regions by mechanical plate compactors and in the upper region by hand-operated drum rollers.
Compaction test will be carried out for the backfilling, to a minimum Proctor density of 90%.
In areas under roads, the compaction tests will be carried out in accordance with the ‘Municipality Specification for Backfilling of Trenches & Excavation in Asphaltic Road, Tiled/Paved Parking and Roads’.
The frequency of tests will be in accordance with the requirements of the specification.
Backfilling will start immediately after the pipeline is tested and approved.
The Marking Tape will be laid 50 cm from the finished ground level.
Method of Concrete Bed & Surround for G.R.P., H.D.P.E. / UPVC Pipes
All the procedures and methods will be the same as above except for the following:
50 cm thick class c blinding concrete with hooks embedded to hold the pipes in position & level.
Concrete blocks for adjustment of t pipe level placed at 3 meter intervals.
Concrete class c pipe surround Ø +300 < 900 with flexible joint at pipe joints.
General procedure for construction of new port at existing storm manhole
After completion of open cut excavation for the portion between existing manhole and proposed manhole/chamber, the location of connection will be exposed and marked on the external face of existing manhole wall.
Client shall be notified, before any activity in manhole to ensure condition of the down storm flow is in continuous operation to avoid any backflow and maintain normal flow to carry out the respective works in sequence.
Cutting of existing manhole wall protection for the marked location will be carried out prior to breaking of concrete will be preceded by using small electrical hammer till reaching the internal face of manhole wall.
The GRP new port will be installed inside the cut portion as per the required level and alignment.
Grouting will be done surround the new port by using the approved grouting materials.
Once the curing time of grouting is completed, the protection for the disturbed portions (external and internal) will be rectified as existing.
The outer connection from the proposed manhole/chamber to the newly constructed port will be done and encased by Concrete/Gravel Bed and surround.
Backfilling for the laid line and the exposed part around the existing manhole will be carried out on layers as specified.
Client is notified to check condition of existing manhole.
Procedure for Construction of Inspection Chambers & Catch Basins
Construction of these drainage units shall be carried out in the following sequences details below and it shall be understood throughout this method statement that every activity will be inspected and approved by the engineer prior to the commencement of subsequent activity.
Pre-cast Yard: Proposal for establishing a pre-cast yard will be submitted with location & the yard’s area.
Shop Drawings: Proposed location for chambers will be surveyed based on approved drawings.
Preliminary setting out will be carried to assess the feasibility of fixing the chambers.
Shop drawing are attached with this method statement that include plan view, section view, arrangement for base wall and roof slab.
Dewatering: Depending on the location of chamber and ground water presence, dewatering is required, shall be carried out as per method statement.
Setting out: Setting out of manhole shall be done as per the approved shop drawings, excavation will be carried out along with the pipeline trenches.
Base: Shutter will either be steel or wooden shutter (Marine Plywood). Detailed sketches are attached for all types of manholes & chambers.
Steel reinforcement shall be fixed and placed where required according to the drawings.
Sufficient cement cover blocks shall be placed to maintain a 70 mm clear concrete cover at the bottom of base in case of reinforced chambers.
The Engineer shall inspect all formworks and reinforcement works before placing the concrete.
A polypropylene formwork liner will be provided to the surfaces of the formwork to improve the finished surface of the concrete.
Approved concrete shall be placed in accordance with the contract requirements and it shall be thoroughly compacted with vibrating pokers.
Shuttering will be removed after concrete has gained sufficient strength to carry its own weight and imposed loads. Curing of concrete will start after initial setting of concrete.
Wall & Cover Slab:
Construction of wall will be done to the entire height of the wall in a single pour.
Internal & external shutter work will be carried out and proper support will be given to the shutter to avoid any deformation.
The concrete cover slab will be constructed separately with respect to road levels.
Procedure for pouring concrete, de-shuttering and curing shall be the same as described in base section above.
Blinding: After obtaining approval from the Engineer for the formation, blinding of class C concrete shall be laid to a minimum of 75 mm.
Protection of external concrete surfaces: External surfaces for concrete structures shall be protected with approved water proofing membrane system as per specification and our method statement of waterproofing.
Backfilling: Backfilling shall be done after water proofing works and it shall be as per specification and our method statement for backfilling.
Fixing the Cover & Frame: Frame and cover fixing shall be as per the specifications and Method Statement for Fixing of D.I. Covers & Frames.
Internal finishing for drainage manholes will be an approved Epoxy paint as per specification
General Procedure for Construction of Manholes
1500 mm Dia. MANHOLE ON 200-500 mm Dia. SURFACE WATER LINES UP TO 6 m. DEPTH :
Use a Pre-Cast manhole units as per standard details approved with internal coating and to use tanking externally for concrete protection.
Safety procedures will be adopted as described in the safety manual submitted and will generally comply with the requirements.
All manholes shall have a circular base unit above which a circular shaft shall be constructed. The base will be cast in a single part. (Pre-Cast)
Upon receipt of the Engineer’s approval for the formation, concrete blinding to a depth of 50 mm will be poured and trowel finished to a top level 55 mm below the invert of the manhole.
Prior approval of the Manhole Production Schedule will be obtained.
The ‘torch-applied’ Water-proofing Membrane (5mm) will be placed in accordance with the manufacturer’s instructions, membrane will be protected with 50 mm screed.
Pre-Cast base pre painted is fixed on line & level followed by shafts, adjustments rings cover slabs.
Fixing procedure is maintained by fixing 2 no. Gasket strips of 20 mm width between each joint, as per the detailed drawings.
250 mm thick removable concrete class b cover slab with 600 Ø circular opening will be (eccentric) as shown on plan.
I. Cover & Frame (class D400/B125) as specified will be fixed to line & level as per road camber by block work.
General method statement for construction of manholes
2000 mm Dia. MANHOLE ON 600-900 mm Dia. SURFACE WATER LINE (DEPTH >6.0 M.):
The method for the construction of the drainage manhole will be identical to that described in method statement expect for the SA, base to be casted on site. (app 20 T)
Upon completion of screed, the steel reinforcement for the base unit will be cut, bent and assembled at the steel yard as per contract drawings and as well as the approved Bar Bending Schedules.
It will then be brought to the site and with the help of a crane, placed above the concrete spacers between the screed and the steel cage.
Upon receipt of the Engineer’s approval for the steel reinforcement, the base top circular plywood will be positioned above the reinforcement using spacers between the steel and plywood.
The prevention of uplift during concreting will be ensured by placing a sufficient number of sand bags and tying the lifting hooks to plywood.
After placing the external shutters and having the same checked and approved by the Engineer, rest will be as per method statement except that the first lift of shaft will be of 2000 mm Dia including the reducer slab, both of which will be concreted separately and the reducer slab will have reinforcement.
The manhole construction detail for 2000 mm Dia is shown on Shop drawing.
ATTACHMENTS
- Inspection Checklists
- Inspection and Testing Plan
- Approved Drawings
- Risk Assessment
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