Method Statement for Manhole Construction

The purpose of this method statement is to define the procedure for the construction of manhole in accordance with the requirements specified in the relevant project specifications and drawings.

This method statement should be implemented in conjunction with MEP method statement for pipe laying. All the procedures shall comply with the requirements of the municipality and works shall be carried-out in accordance with shop drawing approved by both the municipality and consultant where applicable.

Project manager is overall responsible for the implementation of this method statement including the HSE and quality requirements, in coordination with other team members including construction manager, site engineer, quality engineer, supervisor and workers.

List of necessary Tools:

  • Masonry tools
  • Grinders and Cutting Disks
  • Mechanical Mixers

List of materials

  • Solid Blocks – Assorted sizes- depend on the approved drawings.
  • Cement
  • Sand
  • Water
  • Mixing Board / Mortar Bin
  • Waterproofing materials as per approved material submittal
  • Steel Bars, Assorted sizes, please refer to approved shop drawings
  • 18mm thick Phenolic Board (Plywood) (as applicable)
  • Assorted Wood
  • Assorted Nails and Concrete spacer
  • Tie Rods and Steel Clamps
  • Polyethylene sheets, Absorptive Mats and Water
  • Poly Release WB Mould/Shutter Release Agent.
  • Concrete Repair Materials Emaco S22 NB, Emaco S23 NB, Emaco R202 NB, Concresive 1450i, Concresive 1414, Masterflow 544

Note: Quantity of manpower, equipment and materials will be submitted on the daily progress report.

Procedure for Construction of Manhole

Setting out

The Surveyor will establish the location, axis/gridlines, invert level and lay-out of manhole.

Check the level of blinding, concrete base and invert level of pipes, axis/gridlines, and dimensions and ensure that works are carried out in accordance with approved shop drawings and coordination with approved external ground levels and pipes level.

The manhole top level must comply with approved level, shop drawing and coordination in the pavement lay-out and final level.

Excavation and Compaction Works

Excavate the location of manhole in the location as per approved shop drawings.

Excavation for manhole to be in accordance to dimension and levels shown in the approved drawings.

Clean and remove all debris found in the manhole excavation.

If the manhole is over excavated then fill using approved fill material.

Manual compaction required for the base of each manhole.

The contractor to submit the work inspection request for all holds points as shown in the ITP of manhole construction.

50mm thick concrete blinding under manhole foundation:

Formwork for the blinding shall be prepared by contractor after approval of excavation level from the consultant.

Anti-termite treatment shall be done by the approved subcontractor and immediately polyethylene sheets will be installed prior to placement of the blinding concrete.

Method Statement for Manhole Construction Method of statement

Placement of Blinding

The blinding concrete is C20 N/mm² MSRC and constructed in accordance to approved dimension shown in the drawings.

Contractor shall maintain and follow the proper curing time for blinding.

Before casting the Manhole base the approved material for waterproofing will be applied to the top of the blinding.

Pouring of 150mm. thick Concrete Base:

Contractor must comply to the formwork requirements for base concrete in accordance to approved dimensions as shown in the drawings.

The concrete base is C40 N/mm² MSRC.

After casting the concrete, the contractor shall maintain and follow the proper procedure for curing of concrete.

Casting of Manhole walls:

The contractor will cast RCC walls as per approved shop drawings and details for manhole having depth of more than 1000mm using C40 N/mm2 MSRC and for depth less than 1000mm solid block manhole shall be constructed.

Laying of Block Walls for Manhole

Lying of solid blocks is conformed to the project specifications unless otherwise mentioned in this method statement.

The Block work mortar shall be mixed in proportions of 1 part cement and 6 parts of fine aggregates.

Mixing will be done using mechanical mortar mixer, when a mechanical mixer is unavailable the mortar will be mixed manually.

The plumb and level of block walls shall be maintained.

Joints shall be uniform and well filled.

Unsatisfactory works shall be removed and replaced immediately.

Lying of Block works with MEP Pipes:

The Contractor shall check the exact location of pipes and their invert levels to ensure compliance to approved drawings.

Block-outs / openings at the required location of pipes can be provided.

If a pipe box out is not installed or added later then the point of pipe penetration will be marked and the solid block wall will be cut using a grinder.

As per the requirements of the MEP Engineer and after verifying the size of pipes passing through the opening the pipe shall be installed.

After the installation of pipes, the voids/holes around the pipes and the openings should be closed by concrete.

Plastering the Manhole Walls

The internal and the external surfaces of the manhole shall be plastered as per the approved method statement for plastering the standard practice and specifications.

Contractor shall make the floor slope at 1:6 towards the centre of manhole or in accordance to approved slope shown in approved drawings.

Above the C40 N/mm2 MSRC concrete base slab  of manhole benching will be done using SRC cement sand mortar mixed at ratio of (1:2).

Benching and channel will be formed as per the site conditions and approved drawings.

Pouring of 100mm thick concrete make up cover:

Contractor shall prepare the formwork for concrete cover in accordance to approved dimension shown in the drawings.

Concreting of the manhole concrete cover shall be carried out in accordance with the approved dimensions shown in the drawings.

Level and the location of the manhole cover shall be checked to ensure it matches the approved drawings and the site conditions.

After casting the concrete, the contractor shall maintain and follow the proper procedure for curing of concrete.

Formwork shall be removed through the manhole cover opening.

The inside of the manhole shall be cleaned of debris after curing is complete.

Waterproofing Works

To treat the surface of the benching, the contractor shall apply the two (2) coats of sodium silicate or as per approved material for the manhole treatment as shown in the approved drawing and material submittal.

The interior face of walls or inside the manhole shall be applied by two (2) coats of chemical resistant epoxy paint or approved equal brand based on the material submittal and approval.

Exterior face of the walls shall be applied with (primer +two (2)) coats of Flexkote or any other material approved for substructure waterproofing.

The waterproofing works shall be carried out in accordance to approved materials and manufacturers recommendations for proper application.

Backfilling, Compaction and Termite treatment

After completion of manhole work backfilling will be done by filling with approved material.

All filling should be done in layers of 200mm compacted and field density test of final layer should be conducted.

Termite treatment shall be done by approved subcontractor on backfill periphery to treat backfill soil and immediately polyethylene sheets will be installed.

Contractor shall submit the work inspection request as per the ITP for manhole construction.

error: Content is protected !!