Section 02300 EARTHWORK and the requirements specified below.
3.1.1
Trenching
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NOTE: Economic considerations should determine the
width of trench to be used in the design analysis
and to be specified for construction. Where it is
more economical to control trench width and thereby
use less costly pipe, the width of the trench shall
vary with the pipe diameter and should be held to a
minimum consistent with the space required for
proper installation of the pipe and the backfill at
the sides of the pipe. Where the sides of the
excavations are to be supported, proper allowance
should be made for the space occupied by the
sheeting and bracing.
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The width of trenches at any point below the top of the pipe shall be not
greater than the outside diameter of the pipe plus [_____] mm inches to
permit satisfactory jointing and thorough tamping of the bedding material
under and around the pipe. Sheeting and bracing, where required, shall be
placed within the trench width as specified. Contractor shall not
overexcavate. Where trench widths are exceeded, redesign with a resultant
increase in cost of stronger pipe or special installation procedures will
be necessary. Cost of this redesign and increased cost of pipe or
installation shall be borne by the Contractor without additional cost to
the Government.
3.1.2
Removal of Rock
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NOTE: Unless otherwise specified, material used to
replace unstable material or rock excavation should
be compacted to a minimum density of 90 percent for
cohesive soils and 95 percent for noncohesive soils,
as determined by ASTM D 1557.
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Rock in either ledge or boulder formation shall be replaced with suitable
materials to provide a compacted earth cushion having a thickness between
unremoved rock and the pipe of at least 200 mm 8 inches or 13 mm 1/2 inch
for each meter foot of fill over the top of the pipe, whichever is greater,
but not more than three-fourths the nominal diameter of the pipe. Where
bell-and-spigot pipe is used, the cushion shall be maintained under the
bell as well as under the straight portion of the pipe. Rock excavation
shall be as specified and defined in Section 02300 EARTHWORK.
3.1.3
Removal of Unstable Material
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NOTE: Coordinate with preceding paragraph.
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Where wet or otherwise unstable soil incapable of properly supporting the
pipe, as determined by the Contracting Officer, is unexpectedly encountered
in the bottom of a trench, such material shall be removed to the depth
required and replaced to the proper grade with select granular material,
SECTION 02630
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