Monday, February 10, 2020

Work method statement : water recticulation works



A. Excavation and Backfilling For Pipe Trenches.

  1. Before commencing for the excavation of pipe trenches, the routes of pipelines shall be pegged out accurately.  Interval of each peg shall not exceed 60m apart and clearly marked with level to which the pipe to be laid. Pegs alignment and level for the gradient in which the pipe to be laid shall be jointly checked and verified between Resident Engineer and Contractor representative. All pegs shall be maintained in position and at the correct level from the time excavation commences until back-filling completed.
  2. The trench shall have a working space of 150mm on either side of the outside pipe when properly aligned. At all joints the trench shall be excavated to give a working space of not less than 300mm all-round the joint.

3. The trench shall be excavated to the depth as shown in the drawings.

4. At all time, the trench shall be kept free from standing water.

5. Trenches shall only being backfill after the pipe laying works is accepted and approved by Resident Engineer. Before the pipelines have been satisfactorily tested, only sufficient backfilling of the trench to prevent “snaking” and to maintain the pipe in position shall be allow as directed by Resident Engineer. However all joints shall be left exposed until pipeline have been satisfactorily tested and approved by Resident Engineer.

6. Backfilling material for the trench shall be free from stones or rocks or other hard materials. Backfilling material shall be carefully spread along the trench bottom between the pipes and trench walls and shall be compacted by method of hand rammed.

B. Pipe Jointing, Pipe Laying and Testing.

1. No pipe shall be laid until the trench has been inspected and approved by Resident Engineer. The trench shall be kept sufficiently dry for making jointing.

2. All joints shall be done in accordance to the construction drawings and to the Manufacturer recommendations.
3. Laying of pipe shall be gently lowered into the trench manually or by means of combination usage of excavator and sling ropes or any other method as seen fit or as instructed by Resident engineer. No pipe shall be rolled and dropped into the trench.

4. Before any pipe, special and valve is laid in position ready for jointing , its internal surface shall be inspected and ensured free from any dirt, stones, etc.

5. At all time when works is not actually being carried out at such open ends, Suitable stops shall be fixed to all open ends of the pipelines in the trench as to prevent entry of foul water, earth and other foreign matter into the pipelines.

6. Once each jointed section of pipeline reach minimum length of 100m or more but not exceeding 1500m or as directed by Resident Engineer, the pipeline shall be lowered into the trench and partially backfill and all joint shall be left exposed. The Pressure test shall then be conducted on the pipeline in the present of Resident Engineer or his representative. Pressure test shall be conduct in accordance to the Manufacturer recommendation or gradually pressurised until the required test pressure of 1.5 X maximum working pressure is achieved and hold for 15 minutes before the pressure are released.

7. Testing of pipeline shall not been carried out in the middle of the day or even towards the late afternoon.