RFQ023, Annex II - Technical Specifications of water supply.pdf

Technical Specification
ANNEX-II
2.1.2. Pipe Bedding and Laying
Laying instructions of the manufacturer shall be explicitly followed.
a. The bottom of the excavation trench shall be compacted to 90% M.P. before placing
the bedding material.
b. Bedding for pipes shall be constructed by spreading and compacting screened
granular bedding material over the full width of the pipe trench, by layer of 200mm
and compacted to 95% M.P. After the pipes have been laid, additional material shall,
be placed and compacted equally on each side of the pipes, and where practicable,
this shall be done in sequence with the removal of the trench support.
c. Where socket-jointed pipes are required to be laid on a granular or sand bed, or
directly on a trench bottom, a depression shall be left in the supporting material at the
joint to provide a bed support throughout the length of the barrel of the pipe and to
prevent contamination of the rubber gasket immediately before being forced home.
d. All pipes shall be sound and clean before laying. When pipe laying is not in progress,
the open ends of the pipes shall be satisfactorily covered by plugs or other approved
means to prevent entry of any foreign matter into the pipe. Good alignment shall be
preserved in laying.
2.1.3. Backfill to Pipe Trenches
a. As soon as the excavation is complete to normal grade of the bottom of the
trench, selected granular material filling shall be placed where required by layer
of 200mm thick, compacted and graded to provide firm, uniform and
continuous support for the pipes. This layer shall be compacted to 95% M.P
determined under laboratory conditions or to the pipe manufacturers'
recommendation. Bell holes shall be excavated so that only the barrel of the
pipes bears upon the bedding.
b. Selected granular material shall be placed evenly on each side of the pipes to
mid-diameter and hand tools shall be used to force the selected granular
material under the haunches of the pipes and into the bell boles to give firm
continuous support for the pipes.
c. Granular material shall then be placed to 200 mm above the top of the pipes.
The initial meter of backfill above the selected granular material shall be placed
in 200 mm layers and carefully compacted to 95% M.P.
d. Generally the compaction shall be done evenly on each side of the pipes and
compaction equipment shall not be operated directly over the pipes until
sufficient backfill has been placed to ensure that such compaction equipment
will not have a damaging effect on the pipes.
e. If not enough suitable material is available, the Contractor shall either screen
the excavated soil to remove stones and other materials liable to damage the
pipes or use suitable material from other excavations as proposed by the
contractor and accepted by the Engineer or imported from outside the Engineer
may direct.
f. The remainder of the trench may be backfilled with selected approved material
Plumbing Works Page: 6