3.2.5.2
Removal of Unyielding Material
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NOTE: Minimum of 100 mm (4 inches) should be
removed to produce a suitable cushion for the pipe.
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Where [overdepth is not indicated and] unyielding material is encountered
in the bottom of the trench, such material shall be removed [_____]
millimeters inches below the required grade and replaced with suitable
materials as provided in paragraph BACKFILLING AND COMPACTION.
3.2.5.3
Removal of Unstable Material
Where unstable material is encountered in the bottom of the trench, such
material shall be removed to the depth directed and replaced to the proper
grade with select granular material as provided in paragraph BACKFILLING
AND COMPACTION. When removal of unstable material is required due to the
Contractor's fault or neglect in performing the work, the resulting
material shall be excavated and replaced by the Contractor without
additional cost to the Government.
3.2.5.4
Excavation for Appurtenances
Excavation for manholes, catch-basins, inlets, or similar structures shall
be [sufficient to leave at least 300 mm 12 inches clear between the outer
structure surfaces and the face of the excavation or support members] [of
sufficient size to permit the placement and removal of forms for the full
length and width of structure footings and foundations as shown.] Rock
shall be cleaned of loose debris and cut to a firm surface either level,
stepped, or serrated, as shown or as directed. Loose disintegrated rock
and thin strata shall be removed. Removal of unstable material shall be as
specified above. When concrete or masonry is to be placed in an excavated
area, special care shall be taken not to disturb the bottom of the
excavation. Excavation to the final grade level shall not be made until
just before the concrete or masonry is to be placed.
3.2.5.5
Jacking, Boring, and Tunneling
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NOTE: In situations where utility lines must be
installed more than 5 to 7 meters (15 to 20 feet)
below ground surface, through embankments, under
minor roads or parking areas, or where surface
conditions make it difficult or impractical to
excavate open trenches, utility lines may be
installed by jacking, boring, or tunneling as a
contractor option. Where operational requirements
preclude installation by trenching, the use of
jacking, boring, or tunneling should be specified as
mandatory alternatives. This requirement will
normally exist where utilities must cross railroads,
highways, primary access roads and airfield
pavements. Pipe and conduit smaller than 900 mm (36
inches) in diameter will normally be installed in
smooth steel pipe casing. Designing engineers must
coordinate with installation facility engineers to
identify and validate utility crossings where
SECTION 02300
Page 26
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