When off loading, the drainage pipe shall be lowered to the ground either manually or with crane. Timber supports of at least 3” wide shall be placed beneath the pipes with spacing not greater than 2 mtrs. Closer supports will be required for sizes below 160mm.
Drainage pipes shall not be stored under direct sunlight to avoid ultra violet degradation. Larger pipe sizes of thicker class shall always be placed at the bottom of the stack.
The width of the trench at the crown of the pipe shall not be less than the outside diameter of pipe 300mm to allow proper compaction of side fill material. The bedding shall consist of a free running granular material passing a 19mm sleeve, but with a minimum of fine particles.
The thickness of the prepared bed shall be at least 100mm. It shall be well compacted and brought to an even surface so as to provide uniform support for the pipe. Trenches shall be kept free of water by pumping the water out, if any.
Installation Procedure for Underground Drainage Piping
Pipes are brought to the work place manually from the store to the hoist area and are shifted to the respective floors through the hoist. Ensure that the mating areas of spigot and socket are thoroughly clean and square. Set the rubber ring into groove. Assess the full socket depth by simple measurement and mark spigot accordingly. Apply lubricant to the spigot side and to the inside of the joint on rubber.
Accurate axial alignment of the spigot and socket prior to jointing is important, hand feed spigot into rubber joint until resistance from the inner sealing section is felt. Complete the joint by applying leverage to the following socket and using a timer block to prevent damage.
Back-Filling Procedure
Before commencing to place any side fill material; any leveling pegs or temporary packing shall be removed. Filling around the pipes shall be done with the same bedding material to a minimum height of 100mm and a maximum of 300mm and be thoroughly compacted. Normal filling of trench shall then proceed in layers of 150mm with selected materials.
Hydrostatic Testing of Drainage System
Water test is conducted to ensure and prove the tightness of the joints and ensure there are no leaks in the underground piping system. The water pressure test can be applied to the system in its entirety or in sections. No section of the pipe shall be tested to less than 1.5 meter head of water.
In testing successive sections of piping, at least the upper 3 meters of the next proceeding section will the tested. Except the upper most 3 meters, the whole system shall have been subjected to a height of less than 1.5 meter head of water.
The water shall be kept in the drainage pipe system or in the portion under test for at least 30 minutes before inspection starts. While the system is under pressure, a careful inspection shall be made on all pipes and joints. If any leaks in joints or evidence of defective pipe or fittings are revealed, the defective pipe / fitting should be immediately replaced with new joints and materials.
Testing will be inspected by main Contractor / Consultant to their satisfaction and document for correct test will be maintained by getting approval in test certificate by Consultant and Main Contractor. Only after approval of testing back filling of trench will be allowed. Work Inspection Request shall be raised for Consultant’s inspection and sign off.
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