The method statement for earthworks below describes the whole construction procedures including material and equipment required for earthworks. Detail of the procedure contained herein could be modified based on actual site condition.
WORKING METHOD AND PROCEDURE FOR EARTH WORKS
All heavy equipment, as mentioned hereunder, required for excavation works will be supplied by company.
• Backhoe Excavators (+Buckets, Hydraulic hammers)
• Wheel Loaders
• Dump Trucks
Mini Skid Loaders
• Roller compacter
• Water Tanks Trucks
• Air Compressor
Contractor will utilize supplied equipment operated by certified operator for the excavation works.
All previous equipment will be provided by Proximity Warning Alert System except air compressor.
Excavators with bucket will be used for soft and/ or rock excavation.
Excavators attached with hydraulic rock breakers (hammer) will be used for rock excavation. Hydraulic hammer will break rocks into pieces would be collected by the Buckets and load them into dump trucks for transport (if needed).
Excavation permit is a designated work permit process and Gas testing will be done by approved vendor if the depth of excavation exceeds 1 .2 m.
• Setting-out will be done in accordance with the IFC drawings. Prior to the commencement, reference benchmark position shall be verified and limits/centerlines of excavation shall be marked. All benchmarks shall be maintained for future check/verification.
• Precise survey instruments will be used for setting-out.
• Excavation dimensions at the ground level will be calculated based on the dimensions of the structure, working space, depth of the excavation & slope to be maintained etc.
• Safety at workplace is to be ensured.
• Excavators attached with buckets will excavate soft soil strata
• As per as dump trucks can reach near the excavator, excavated soil will directly loaded into the dump trucks and transported to the dumping area. This helps to maintain a tidy site.
• Proper access for dump trucks will be maintained.
• When excavation reaches to harder strata where the buckets don’t work, remove buckets and fix
hydraulic jack hammers.
• Jackhammers will break rocks into smaller pieces.
• Collect rock pieces by excavators attached with bucket. Transport by dump trucks.
• Excavation will be done in layers.
• Excavate to grades as required to accommodate the works and provide adequate working space
around the foundations, but not less than 1.2 meters.
• Excavated material which is suitable for General fill shall be stockpiled for future use.
• Care shall be taken to avoid any disturbance to the bottom of excavation. If the bottom is disturbed, the loose material shall be removed.
• When several close excavations are needed, the entire adjoining area may be excavated.
• Adequate access for vehicles to the bottom, if needed, shall be maintained.
• Ensure that all sides of open excavations are maintained in a safe and stable condition by shoring or adequate slopes.
• All Necessary requirements will be taken consideration if the excavation around or near any existing
structure according to Engineer instruction.
• Excavation shall not allow below the existing structures.
• Excavation should be done up to the level shown on the approved drawings.
• Once excavation reaches to sub-grade elevation, make the sub-grade smooth, and free from loose earth.
Selection of backfill Material
Backfill Material shall be selected in compliance with SAES-A-114 Para 6.2.
Regardless of the source of supply, any fill material shall be sampled and test by approved Independent Laboratory in order to verify its compliance with SAES-A-114 Para 6.2 standard.
General fill material shall be selected from common excavation material which is free from organic
material and debris. It shall contain no rock over 75mm in greatest dimension and shall be capable of being compacted in accordance with the requirements of Project Specifications.
• Maximum particle Size 200mm except rocks or stone for which it shall be 73mm (3 inches).
• Shall be free of frozen lumps, organic matter, trash, chunks of highly plastic clay or other unsatisfactory material.
The material shall consist of only in organic materials.
That portion of the material passing the No. 40 sieve shall have a maximum liquid limit of 35 and a
maximum plasticity index of 12 per ASTM 04318. Liquid limit and plastic limit tests are not required for select fill material with less than 15% passing the No. 200 sieve (SAES-A-114 para.6.2.2).
Water used for compaction of fill material shall be reasonably free of salts, oil, acid alkalis, organic matter, or other deleterious substances. Used of water with a TDS in excess of 1 O,OOOppm such as brackish water, seawater or water obtained from ground pits such as subkha water is not allowed unless it is proven and verified by the Company representative and the Project inspection representative that there is no other source of water available within 20km and all concrete to be supported by or buried within the fill is designed for either exposure type II or Ill as defined in SAES-Q-001 Table1.
Only suitable, approved materials shall be used.
> All excavations or surface to receive backfilling shall be cleaned of all trash and debris.
> Prior to backfill, concrete structure and waterproofing must be inspected and released for backfill.
> The following areas shall be filled or backfilled with select fill material.
• Beneath or immediately surrounding foundations
• Beneath slabs, roadways, area pavement, and parking areas
• Where otherwise indicated on design drawings
Backfilling shall be placed in uniform layers of the specified thickness and wetting operation, if required, shall be carried out in a way so that uniform moisture content is assured throughout each layer.
• Sub-grade of all Building and Structure shall be compacted to 95% of maximum Density determined as per (SAES-A-114 Para 126.96.36.199).
• Granular select fill material shall be compacted to 90% of the maximum Modified Proctor Density determined by ASTM D-1557, or 70% relative density as determined by ASTM 0-4253, (SAES-A-114, para 188.8.131.52)
• The sand bedding shall be free of debris and rocks and compacted to at least 70% relative density, or 95% proctor density as per ASTM D-698, which ever gives the greater density. (SAES-S-070, para
9. 7.2), (SAES-S-070, para 21.1).
In-place Density Test
To verify that the specified degree of compaction has been achieved, in-place tests shall be carried out of each layer according to ASTM D 1156 or D6938 as follows;
• Rock sub grade: no tests are required (only visual inspection) .
• Sub grade other than rock: One field density test is request for each foundation when several foundations are closer and entire adjoining area has been excavation.
• Final approved Drawings.
• Applicable Contract Documents.