PACKAGE : I Bid Document VOLUME : II - Public Health Engineering

5.4 Trench excavation.
General: Trench excavation means excavation of trenches into which the pipe is to
be laid. Before commencing trench excavation, the route of the trenches shall be
pegged out accurately and the natural ground levels and the alignment shall be
agreed with the Engineer in charge. The contractor shall dig probing pits or
appropriate size and depth including cutting the road at every 100m interval or as
directed by Engineer in charge.
Stripping surface materials: Before the surface of any part of the site is disturbed
or the works there on are started, the Contractor shall take and record levels in the
presence of the Engineer or his representative. Before commencing the excavation,
the surface materials shall be carefully stripped and set aside for reuse as directed
by the Engineer.
5.5 Width of trench.
The width of the trench at bottom between the faces of sheeting shall be nominal
diameter of the pipe plus 300mm clearance on either side of the pipe. Trenches
shall be of such extra width, when required as will permit the convenient placing of
timber supports, strutting and planking and handling of specials.
The width of trenches measured at the crown of the pipe shall permit adequate
working space. The trenches shall be widened at sockets and other structures as
may be found necessary.
Care should be taken to avoid excessive trench width and thereby increasing the
load on the pipes.
5.6 Depth of excavation of trenches.
The depths for the trenches will be calculated from the surface to the bed of the
pipes and in case when a layer of bedding is to be placed below the pipeline, the
depth to the bottom of the bedding will be paid.
GTS : General Technical Specification. Page 34