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

10.9.10 During excavation, large stones and rubble shall be separated and removedfrom the excavated soil and stacked separately.10.9.11 Where loose earth is encountered during excavation and where the trench isvery deep, the side walls shall be properly shored for the safety of workmen.10.9.12 The bed of the trench shall be excavated to the pipe grades so that uniformsupport is assured for the full length of the pipe.10.10 Laying10.10.1 The pipes shall be lowered into the trenches either by hand passing or bymeans of two ropes. One end of each rope shall be tied to a wooden or steelpeg driven into the ground and the other end shall be held by men which whenslowly released will lower the pipe into the trench.10.10.2 The pipe shall rest continuously on the bottom of the trench. The pipes shallnot rest on lumps of earth or on the joints. Four-meter long wooden templatesmay be used to check the level of the bed. Clearance of approximately 100 mmin depth and width equal to length of the collar plus 30 mm on both sides shallbe provided at the joint which shall be refilled form sides after the joint is made.10.10.3 In unstable soils, such as soft soils and dry lumpy soils it shall be checkedwhether the soils can support the pipelines and if required suitable specialfoundation shall be ensured.10.10.4 Some clayey soils (for example black cotton soil)are drastically affected byextremes of saturation and dryness. In changing from totally saturated to acompletely dry condition, these soils are subjected to extra ordinary shrinkage.10.10.5 This shrinkage is usually seen in the form of wide and deep cracks in the earthsurface and may result in damages to underground structures, including pipematerials. The clay forms a tight gripping bond with the pipe, subjecting it toexcessive stresses as the clay shrinks.10.10.6 In such areas, it is recommended that in such cases an envelope of a minimum100 mm of tamped sand shall be made around the pipeline to avoid anybonding.10.10.7 In place where rock is encountered, cushion of fine earth or sands shall beprovided for a depth of 150 mm by excavating extra depth of the trench, ifnecessary, and the pipes laid over the cushion, where the gradient of the bedbe necessary to anchor a few pipes against theirsliding downwards.10.11 Jointing10.11.1 Before commencing jointing, the pipes shall be cleaned; the joints and the endsof the pipe shall be cleaned, preferably with a hard wire brush to remove looseparticles.Urban Administration & Development Department Page 121