Specifications Part 1 - Water Supply, Sewerage and Tube Well Works

9.18 Bedding and Back filling9.18.1 The pipe should be uniformly and continuously supported through its wholelength with firm stable bedding material. Pipe bedding material should be sandor gravel as per the requirements on the backfill material.9.18.2 The bedding should be placed so as to give complete contact between thebottom of the trench ands the pipe and should be compacted to provide aminimum compaction corresponding to 90% maximum dry density [ see IS2720 (Part 7 ) : 1980 ]9.18.3 If the pipe is supported on grade elevation with use of timber or of taperedwedges, they must be removed and not left in place. They can usually bepulled out after the bedding has been compacted to the specified minimumcompaction. The voids from which the timber has been removed must beproperly filled and compacted.9.18.4 Back filling should be placed in layers not exceeding a depth per layer whichcan be compacted to a minimum of 85% maximum dry density [see IS 2720(Part 7):1980] Lift should normally not be greater than 30 cm in height and theheight differential on each side of the pipe should be limited ok this amount soas to prevent lateral movement of the pipe.9.18.5 Most coarse grained soil are acceptable. This may comprise of gravel or sand.However, silty sand, clayey sand, silty and clayey gravel shall not be usedunless proposed to be used in conjunction with gravel or clean sand.9.18.5.1 It is very important that the pipe zone backfill material does not wash a way ormigrate into the native soil. Like wise, potential migration of the native soil intothe pipe zone backfill must also be prevented.9.18.6 Heavy earth moving equipment used for backfilling should not be brought untilthe Minimum cover over the pipe is 90 cm in the case of wide trackedbulldozers or 120 cm in the case of wheeled roaders or rollers compactor.9.19. Laying of pipes9.19.1 Each pipe shall be thoroughly checked for any damages before laying and onlythe pipes which are approved by the Engineer shall be laid.9.19.2 The following procedures should be followed so as to eliminate Potentialdamage to pipes and fittings and to maintain maximum safety during unloading,lifting and lowering.9.19.3 All the pipes and fittings shall be lifted with pliable strips, slings or ropes. Thesemay be canvas or polyester belts with a minimum width of 10 cms or nylonropes with a minimum diameter of 30 mm. Steel cables or ropes shall not beused for lifting and transportation of pipe. Ropes shall not pass through thesection of the pipe end to end.Urban Administration & Development Department Page 109