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

10.8.1.1 Width- The width of the trench above pipe level shall be as small as possiblebut shall provide sufficient space necessary for jointing the pipes. The trenchwidth shall be such as to provide a space of 300 mm on either side of the pipe.10.8.1.2 Depth The pipe shall have a minimum soil cover of 750 mm when laid underfoot paths and side walks, 900 mm when laid under roads with light traffic orunder cultivated soils and 1.25 m when laid under roads with heavy traffic.When the soil has a poor bearing capacity and is subject to heavy traffic, thepipes shall be laid on a concrete cradle. An extra trench depth of 100 mm shallbe provided for each jointing pit.10.9 Excavation10.9.1 The excavation of the trench shall be so carried out that the digging of thetrenches does not get far ahead of the laying operations.10.9.2 The wall of the trench shall be cut generally to a slope of ¼ : 1 or ½ : 1depending on the nature of the soil.10.9.3 If the trench bottom is extremely hard or rocky or loose stony soil, the trenchshould be excavated at least 150 mm below the trench grade.10.9.4 Rocks, stone or other hard substances from the bottom of the trench shall beremoved and the trench brought back to the required grade by filling withselected fine earth or sand (or fine moorum if fine soil or sand is not availablelocally) and compacted so as to provide a smooth bedding for the pipe.10.9.5 Where excavation requires blasting operation it shall be ensured that no pipesare stacked in the vicinity and completed pipeline in the vicinity have alreadybeen covered before starting of blasting operations; to prevent damage to theexposed pipes.10.9.6 Roots of trees within a distance of about 0.5 m from the side of the pipelineshall be removed or killed.10.9.7 The excavated soil shall preferably be deposited on one side of the trench, sothat it leaves a bench of about 0.5 m facilitating the workmen to move along thetrench without any difficulty.10.9.8 In places of heavy or light traffic the excavated soil shall be on the traffic sidefor the protection of the traffic from accidents. The other side of the trench maybe used for placing pipes and other accessories.10.9.9 To protect person from injury and to avoid damage to property, adequatebarricades, construction signs, red lanterns and guards as required shall beplaced and maintained during the progress of the construction work and until itis safe for the traffic to use the roadways.Urban Administration & Development Department Page 120