1 March 1997
a. Thrust restraint. Force mains will be restrained to resist thrusts that develop at bends,
tees, wye connections and plugs in the pipe. The magnitude of such forces can be calculated
with the use of formulas found in standard hydraulics textbooks. Required methods of restraint
will consist of mechanical joint restraints or concrete thrust blocks, and will be designed in
accordance with Appendix C, TM 5-813-5.
b. Depth of cover. Force mains will be installed with sufficient depth to prevent freezing, and
to protect the pipe from structural damage. A minimum cover depth of 1 meter (3 feet) will
ordinarily be required for freeze protection. However, in unusually cold climates, a greater depth
may be required.
c. Protection of water supplies. Force mains and sewers will not be installed closer than 3
meters (10 feet) horizontally to potable water lines. If conditions prevent a 3 meters (lO-foot)
clearance, a minimum distance of 2 meters (6 feet) will be allowed provided the bottom of the
water pipe is at least 300 mm (12 inches) above the top of the force main or sewer pipe. Where
a force main must cross a potable water line, it will always be installed below the water line with
a minimum vertical clearance of 600 mm (2 feet). Where water lines cross under a gravity
sewer, the sewer pipe for a distance of at least 1 meter (3 feet) on each side of the sewer shall
be fully encased in concrete or shall be made of pressure pipe. Pressure pipe joints will not be
closer than 1 meter (3 feet) horizontally to the crossing unless fully encased in concrete.
d. Asbestos-cement pipe. Due to the dangers associated with cutting asbestos products, no
asbestos-cement pipe shall be installed. Safe procedures for cutting existing asbestos-cement
pipe are given in the Asbestos Cement Pipe Producers Association publication Recommended
Work Practices for A/C Pipe.