This method statement describes the procedure and inspection instructions to be followed during the Excavation and Backfill for all kind of related works. Document will ensure that all activities are in full compliance with project specifications.
Roles and Responsibilities
Foremen will coordinate day-to-day activities of direct Labor and Sub-Contractors and responsible for the on-going Quality and production at the work force.
Site engineer will provide technical information and oversee on the basis of day-to-day activities of field supervision.
Quality engineer will witness all tests performed in his designated area and carry out detailed inspection prior to raising an RFI. All such tests should be signed and certified by the individual performing the test. Perform daily surveillance Inspection of workmanship and documentation activities.
Site manager manages and directs project construction activities performed by the project team composed of personal assigned by the various functional departments.
Tools and Equipment’s
- Excavator
- Loader
- Roller Compactor
- Plate Compactor
- Jumper
- Water Tank
Safety Requirements
All risks involved in Excavation and Backfill will be indicated in risk assessment sheet.
All construction work will be undertaken in accordance with the organization safety manual.
Permits will be obtained (when required) prior to any work being carried out and work will commence in accordance with specific measure itemized on the permit.
All necessary (PPE) Personal Protection Equipment will be provided and worn in accordance with Procedure of safety manual.
All Access/Exit points shall be maintained free from obstacles, material or equipment etc.
Temporary safety signs shall be provided at all working areas where needed.
At site all the work activities will be kept in a clean and tidy manner.
Signal man must be provided for equipment’s on site.
Sequence of Work
Excavation
Excavations shall comply with all structural drawings of the project.
Excavation boundary work shall be set out in accordance with the Approved IFC Drawings. A clear space of at least 1 meter shall be maintained on all sides of excavation to allow circulation and setting of formwork.
All excavation will be adequately protected for safety. All local excavation will be hard barricaded at sufficient distance from the edge of excavation (1.0m). Banks more than 1.5 shall be shored on laid back.
All trench of 1.5m in depth or more than will be provided by sufficient egresses and proper side slopes will be provided and maximum allowable angle of slope is 45 degrees.
Blasting shall not be permitted without prior approval. Rocker breakers will be used in hard strata where excavators and /or shovel loaders are efficient, immediately after the client approval.
Excavation material that is suitable for backfilling either will be placed so as to minimize any inconvenience to vehicular traffic and other construction activities or stockpiled in an agreed unconstructive location for later use.
If unsuitable material beneath the specified depth is encountered. The unsuitable material will be removed (over excavate) as directed by client. Resultant excavation will be filled with approval suitable material is loose layers not exceeding specified thickness for each type of fill material.
All excavation across existing roads, accesses paving will be carried out in a manner with no disturbance to the other executing works in the area.
The width of all trenches for culvert and underground utilities shall be sufficient to allow inspection of pipe, pipe joints and proper compaction of backfill at bottom section of lines.
Dewatering Process
The purpose of dewatering is to ensure good condition of soil during excavation and backfilling operations within the scope of work.
All work shall be kept well drained at all times and shall ensure that all work is carried out in the dry conditions.
Remove water to prevent softening of foundation bottoms, undercutting footings, and soil changes, detrimental to stability of sub grades and foundations, and shall convey water removed from excavations and rain water to collecting or run-off area.
Once the excavation reaches below the water table and depending on the dimension of the pit, side ditches will then be excavated submersible pump will be placed for pumping out the water.
Discharge water shall be pump through flat hoses to a final water discharge location approved and within moderate distance.
Dewatering progress will continue till the backfilling activity is completed.
Adequate measure shall be taken to deal with the presence of water and inflow of water when placing the fill material.
Backfilling and Compaction Method
In general the placement and compaction of all classes of fill material shall be constructed to the lines and levels as indicated on the drawings.
Curing must be exercised during the placement of fill against buried pre-cast units, vessels, or a structure to ensure that uneven placement of fill on one side does not move or destabilize the unit.
Fill material belonging to a particular class shall well graded placed, spread and compacted in uniform layers of equal thickness a maximum size of 100mm and shall be free of deleterious, debris, vegetation, organic and foreign material and shall comply with project requirement:
Type I
Graded sands and gravel, gravel-sand or silty-sand mixtures, crushed graded rock; little or no fines, no well-defined moisture versus maximum density relationship (GW, SW, GP, SP).
Plasticity Index: NP to 5.
Gradation: Less than 12% passing No. 200 sieve.
Type II
Clayey gravels and sands, poorly graded mixture of sand, gravel and clay, clays (inorganic) of low to medium plasticity, sandy clays, silty clays, lean clays (CM, SM, GC, SC, CL).
Liquid Limit: 20 to 50.
Plasticity Index: 5 to 22 maximum
Prior to placing the back fill material the civil inspector shall inspect the excavation for clean lines and must ensure that backfilling location is dry ad clear form foreign matter (free paper, wood, rags and other organic matter). The backfilling operation will not commence unless the area to be filled has been inspected and approved by consultant.
Fill material shall be mixed at stock with fresh water to the moisture content within+/-2% of the optimum moisture content using wheel loader. This will be controlled by visual and FDT respectively.
For paved areas, dune sand fill material around cables shall be used.
For unpaved areas, dune sand fill material shall be used from bottom of trench up to 100mm above the cables.
The site foreman shall be responsible for applying the required number of passes by compaction equipment in use.
Results of compaction achieved will be confirmed by necessary soil tests required by earthwork.
Soil testing (field density, water content, classification etc.) in general, shall be carried out at frequency stated in “Earth work” specifications.
Inspection and Testing Requirements
Work execution, material approval and test shall be monitored, witnessed and recorded as per the project quality plan and ITP requirements.
Contractor will issue a written RFI, 24 hour in advance of test/inspection to permit QC Engineer to verify the readiness of the test inspection.
Verbal notices of readiness for inspection are not acceptable.