Procedure of Dewatering of Excavated Area at Site

This procedure describes the steps to be taken and sequence of events necessary to enable satisfactory completion of each activity.

1. Ensure that all IFC and reference drawings have been issued to responsible personnel handling the work.

Ensure Dewatering works shall be conducted in accordance with the latest revision of the IFC drawings that distributed in controlled manner. 

2. Project END document control section provides all relevant personnel this procedure after approved by OWNER/GENCON in control manner.

3. The Civil Supervisor shall confirm and check the following items prior to the commencement of dewatering system installation:

• a. Water table elevation.
• b. Disposal locations designated or approved by OWNER.
• c. Water sample shall be tested by an Independent Laboratory to assure it is within the limit of allowed disposal requirements (if required).
• d. Detail and construction drawings of dewatering system.
• e. Approved procedure. (This procedure).
• f. Availability of dewatering system equipment & pipe disposal materials.
• g.  IFC drawings (Structures Drawings subject for dewatering) are available.

Secure work permit and check work areas, soil type and condition of adjacent structures. 

4. The Safety officer shall ensure that work is performed according to the instructions and precautions specified in the work permit. Ensure that barricades/ steel barriers/ tapes are erected where required and safety equipment is readily available at the work areas. 

5. The Engineering Department shall provide drawings of dewatering system indicating installation layout of well points, headers, flexible hoses and other accessories. SUBCON Engineering shall locate the possible disposal point and submit to client for approval. Please refer to Attachment 7.1 “Sketch drawing for Dewatering Layout and Details” for the proposed ditch to dispose pumped water.

6. Civil Section shall asses and decide when:

• a. The quantity of water present in the excavation is minor, dig a collection sump below the excavation level, where collected water can be pumped out using an ordinary suction pump.
• b. The quantity of water entering the excavation is deemed excessive and continuous flow is evident, use a dewatering system consisting of well points, multi-dewatering pumps, headers, flexible connections, cargo hoses and collecting tank erected at height considering the water heads for disposal of water to the approved canal/ pits, etc. This method will reduce seepage and prevent any breakdown of the excavation sides / base due to turbulence and flow. Well points will be installed at one side of excavation and if necessary at around the excavation at least 1.00 meter away from the edge. Well point must have sufficient depth at 1.0 to 1.5 m below the bottom of excavation to reduce the water level. The water level should be kept below the excavation finish level in order for compaction of the foundation base. The water removed from the excavation must be disposed to the approved disposal canal / pits. 
• c. Well point method (system) shall be utilized for dewatering works at site. 

Continuously operate dewatering equipment until work within the excavation has been completed and then continuously operate until the work on concrete and backfilling has been completed. The tank shall be checked periodically by SUBCON and shall remove the sand accumulation as necessary. Standby pump unit will be provided at work site in case running pump gets trouble.

7. Civil Supervisor shall submit request for inspection (RFI) to site QC section.

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1. Purpose

2. Scope of Work

3. Definition

4. References

5. Responsibilities

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7. Dewatering Inspection

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