Specifications Part 1 - Water Supply, Sewerage and Tube Well Works
Specifications Part 1 - Water Supply, Sewerage and Tube Well Works
Specifications Part 1 - Water Supply, Sewerage and Tube Well Works
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12.8 Trench:-(See Drawing No.3)12.8.1 Location: Drinking water pipelines should not be located below seweragepipelines. Where a pipeline runs parallel to other pipelines or cables, thedistance between them should not be less than 0.4 m.12.8.2 At points of congestion, a distance of 0.2 m should be maintained unless stepsare taken to prevent direct contact.12.8.3 Width: Trenches should be of adequate width to allow the burial of pipe, whilebeing as narrow as practical. If expansion <strong>and</strong> contraction are not problems<strong>and</strong> snaking of pipe is not required, minimum trench widths may be obtained byjointing the pipe outside the trench <strong>and</strong> then lowering the piping into the trenchafter the testing. A trench width of two or three times the pipe diameter is agood rule of thumb. Narrow (unsupported) trench width <strong>and</strong> supported trenchwidth shall be as given under:Nominal pipe size(Diameter in mm)Table No.12.2Unsupported NarrowTrench Width (Minimum)Number ofpipe DiameterWidth (mm)Supported Trench Width,(Minimum)Number of pipeDiameterWidth(mm)90 5.0 450 10.0 900110 4.0 450 8.2 900125 4.0 500 7.2 900140 3.9 550 6.4 900160 3.5 560 5.6 900180 3.2 580 5.0 900200 3.0 600 4.5 90012.8.4 Where necessary to prevent cave-ins, trench excavations in unstable soil shallbe adequately supported. As backfill is placed <strong>and</strong> sheeting withdrawn, the voidleft by the withdrawn sheeting shall be filled <strong>and</strong> compacted before withdrawingthe next increment.12.9 Trench Bottom12.9.1 The trench bottom shall be constructed to provide a firm, stable <strong>and</strong> uniformsupport for the full length of the pipeline. There should be no sharp objects thatmay cause point loading.12.9.2 Any large rocks, hard pan, or stones larger than 20 mm should be removed topermit a minimum bedding thickness of 100-150 mm under the pipe.12.9.3 For pipes of diameters 100 mm or greater, bell holes in the bedding, undereach socket joint, shall be provided by removing some of the bedding material,Urban Administration & Development Department Page 140
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