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180 Chapter 5 Water Hydraulics, Transmission, and Appurtenances

Figure 5.10 Concrete Water Pipe.
(Source: Wikipedia, http://upload.
wikimedia.org/wikipedia/commons/
2/2e/Concrete_water_pipe.jpg)

number of offsets from the tangent. Sharper curves can be formed by shorter or shortened
pipes. The smaller the pipe, the sharper can be the deflection. Welded pipelines less than
15 in. (400 mm) in diameter are sufficiently flexible to be bent in the field. The ends of
larger steel pipe must be cut at an angle that depends on the type of transverse joint, the
thickness of the steel plate, and the size of the pipe.
For sharp curves, transitions, and branches, special fittings are often built up or manu-
factured of the same materials as the main conduit.

5.7.3 Depth of Cover

Conduits that follow the surface of the ground are generally laid below the frost line, al-
though the thermal capacity and latent heat of water are so great that there is little danger
of freezing as long as the water remains in motion. To reduce the external load on large
conduits, only the lower half may be laid below frost. Along the 42nd parallel of latitude,
which describes the southern boundaries of Massachusetts, upper New York, and
Michigan in the United States, frost seldom penetrates more than 5 ft (1.5 m) beneath the
surface; along the 45th parallel the depth increases to 7 ft (2 m). The following equation
approximates Shannon’s (1945) observations of frost depth:

d 1.65F 0.468 (U.S. Customary Units) (5.41a)