CEMP-E
EI 11C201
1 March 1997
(2) Where unstable soil extends to considerable depths, more stringent measures must
be taken. The sewer will be fully encased in concrete and supported on piles at each end. The
pipe and encasement will be designed to act as a beam when the span distance is relatively
short.
(3) For extremely severe cases, where unsatisfactory material covers a large area, and
extends well below the trench bottom, a row of piling capped with concrete or wood cradles will
be required to support the sewer. Dwarf piling may be suitable substitute for conventional piling
in certain situations.
b. Installation in rock. Where sewers must be constructed in rocky terrain, trenches will be
sufficiently wide to provide clearance between the sides and bottom of the pipe, and any rock in
the trench. Pipe must be installed to avoid all contact with rock, or any other unyielding material
in the trench. A granular type bedding or concrete cradle will normally be provided along the pipe
bottom, and trenches will be backfilled with satisfactory materials.
c. Sewers in embankments. The need to install sewers above original ground surface in an
embankment or fill does not arise frequently at military installations. Occasionally, an
embankment will be required in low lying areas to raise the grade, or will be provided to avoid
placing sewers aboveground, as discussed below.
d. Aboveground sewers. Sewers are normally laid underground, and at sufficient depths to
be protected from impact and freezing. However, in cases where valleys, watercourses,
structures, or other obstacles must be crossed, it is sometimes more advantageous to install
sewers aboveground. Sewers supported from bridges, piers, suspension cables, or pipe beams,
etc., will be designed with adequate structural capability. Protection against freezing and
prevention of leakage are important design considerations. Expansion jointing may also be
required.
e. Jacking, boring, tunneling, and microtunneling. In situations where sewers must be
constructed more than 5 to 6 meters (15 to 20 feet) below ground surface, through
embankments, under railroads, primary access roads, or airfield pavements, or where the Facility
Engineer determines that conditions make it difficult or impractical to excavate open trenches, it
will be necessary to install the pipe by other methods. In these cases, pipe may be pushed,
jacked, bored, tunneled or microtunneled into place. A casing pipe will normally be required for
sewers installed using these methods except for microtunneling in which rigid pipe is pushed,
jacked, bored, or tunneled into place. A casing pipe will always be required to protect sewers
under railroads, primary access roads, and airfield pavements. The void space between the
sewer pipe and casing will be filled with special aggregates capable of being blown into place, or
with commercially available polyethylene or other type spacers, saddles, and seals. Depending
on soil resistance, rigid extra strength pipe can be forced underground by machine for distances
of 15 to 45 meters (50 to 150 feet). Commercially available machines used hydraulic power to
produce forces ranging from 29 to 670 kilonewtons (6500 to 150,000 pounds). Horizontal boring
(augering) and reaming machines placed in excavated pits simultaneously remove material and
hydraulically jack extra strength pipe through the ground in sizes up to 900 millimeters (3 feet) in
diameter.
f. Anchoring Sewers. Normally sewers do not have to be anchored in place. However large lines laid
underwater or below the high groundwater level may have to be anchored, using saddles and piling or
concrete, to avoid floating. Guidance from the pipe manufacturer should be used in designing anchoring
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