Volume-II of IV - GAIL

MECON LIMITED
Delhi
PROCESS & PIPING
DESIGN SECTION
TECHNICAL SPECIFICATION
FOR
PIPELINE CROSSINGS USING
HORIZONTAL DIRECTIONAL
DRILLING METHOD
TECHNICAL SPECIFICATION NO. : MEC/S/05/62/75 REV-0 Page 3 of 11
2.0 DESIGN AND ENGINEERING
2.1 The limits of each crossing shall be determined by the Contractor on the basis
of crossing profile based on survey drawings, design, equipment, installation
technique and site condition. Contractor shall furnish all engineering design
calculation and crossing drawings etc. to owner for their approval prior to
execution of the work.
2.2 Within the entire limits of crossing, the minimum cover to top of coated pipe
shall be as specified in the Special Conditions of Contract (SCC).
However, wherever the drilled length for a crossing includes the crossings of
obstacles such as roads, railroads, cannals, streams, etc. The following
minimum requirements of cover to the pipe shall be satisfied unless specified
otherwise in the scope of work in SCC.
For Road Crossing : 1.4 m from top of road to top of pipe.
For railroad crossing : 1.7 m from base of Rail to top of pipe.
For canal crossing : 1.5 m from lowest bed level to top of pipe.
In case the pipeline crosses other utilities, viz., other pipelines, sewers, drain
pipes, water mains, telephone conduits and other underground structures, the
pipeline shall be installed with at least 500 mm free clearance from the
obstacle or as specified in the drawing or such greater minimum distance as
may be required by authorities having jurisdiction. Also in all cases, the
minimum covers specified above shall be maintained within the entire limits of
crossing.
2.3 The entry and exit points of the pipeline at ground level shall not come within
the limits of crossing as defined in the crossing drawings.
2.4 Contractor shall carry out calculations for determining the maximum
permissible overburden on pipe, to check that the empty pipeline is safe from
collapse at any point along the drilled crossing section. Contractor shall submit
these calculations to Owner for approval.
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