Earthwork excavation Method statement

EARTHWORK EXCAVATION, BACKFILLING AND COMPACTION

1.0 OBJECTIVE

1.1  To define the requirement and describe the procedure for earthwork excavation, backfilling and compaction works for the contract no GTC.101/ED/01 Engineering, Procurement, Installation and Commissioning (EPIC) of Ras Laffan Utilization Project –Buildings and utilities and support service Phase 1-Utilities.

2.0 SCOPE

2.1 Applicable to all the buildings and utilities at Service Base Area, Service Berth Area, FSO Marine and Telecom buildings.

3.0 REFERENCE

3.1  Project Approved Drawings

• Qatar Petroleum standard Spec. Vol. 1, section 2.3, 2.10
  • British Standard BS  1377 test 13
  • Qatar Construction Spec. Sect. 12, Part 2

4.0 PROCEDURE

4.1 GENERAL:

• Approval of location and settingout is to be obtained from QP engineer prior to proceeding with excavation works.

• Proper work permit should be in place before commencing the works.

     4.2 SHORING AND STRUTTING

• Prior to commencing any structural excavation work which is 1.5 m or greater in depth, a design should be submitted to QP engineer for approval.

• The system is to be designed so that no members extend through surfaces exposed in the finished construction, and no shoring or bracing is placed under permanent structures.

• The detail calculations of lateral earth pressure for the full excavation depths, surcharge loads of any description, equipment loads, forces at various stages of support during excavation, the maximum design loads to be carried by various members of the support system and strut pre-load forces.

     4.3 DEWATERING:

• At locations where the excavation extends below ground water table, a dewatering system is to be provided .The resulting ground water level shall be at a depth below the excavation level so as to allow the safe and proper execution of works.

• Complete working drawing showing the type of dewatering, ground water control system, equipment, arrangements, location and depth of the proposed dewatering system, including stand by equipment and power supply, proposed locations for the discharging of extracted ground water should be submitted to QP for approval.

• The dewatering system design should also include the details of measures required to prevent damage due to settlement of roads, pavements, utilities, sewers, buildings and other structures outside the excavation but within the area affected by the dewatering.

      4.4 EXCAVATION:

• The marking out for structures is to be carried out as per approved drawings and necessary approval is to be obtained from QP engineer before proceeding with excavation works.

• The depth of excavation for foundations will be as per approved drawing.

• The excavation to the required levels will be carried out either manually or by machinery by making necessary precautions with regard to the stability of the excavations, adjoining properties, any underground utilities and the safety of workforce.

• Excavated surplus material suitable for filling will be placed in fill areas with in the limits of the works.

• Excavated material un suitable for filling shall be hauled away and dumped in to spoil areas as directed by the QP engineer.

• The excavation has to be approved by  QP engineer before proceeding with further works.

     4.5  BACKFILLING AND COMPACTION:

• Once concreting and protection works are completed and approved, a request is to be made for the inspection and approval of QP engineer for the back filling works.

• Selectfill material will normally be used, where excavated material is considered unsuitable for backfilling.

• Care should be taken to avoid damage to structures and waterproofing works while backfilling.

• The backfill material is to be watered and mixed as necessary to ensure that prior to compaction the moisture content of the whole layer is 6 3 % of the optimum moisture content.

• It shall be placed in layers not exceeding 250 mm thick, compacted by a suitable compactor.

• Compaction of each layer is to continue until a density of at least 95 % of the maximum dry density has been achieved by means of Nuclear Gauge Testing to determine the Field Dry Density.

• The backfilling and compaction in layers to continue till the required level is achieved.

      5.0  RECORDS :

• Inspection reports.

• Checklist.

Approval for fill material