Page 329 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

SITE UTILITY SYSTEMS

SITE UTILITY SYSTEMS 6.51

FIGURE 6.31 Coefficient for positive projection condition. (Courtesy: ANSI 21.1.)

Curves A, B, C, D, and E represent the following soils in Fig. 6.30.
A = sand and sandy loam
B = sand and gravel
C = saturated topsoil
D = average clay
E = saturated clay
Curve 0.70 is an average value used for standard calculations in Fig. 6.31 (incomplete
projection condition).

2 To determine W, refer to Table 6.8.
3. Trench width has an important influence on the soil load transmitted to the pipe. Any
trench must provide sufficient working space for the installation with tolerance allowed
for accepted construction practices and field conditions. Experiments have proven that
only the trench width at the top of the pipe need to be considered in calculating the earth
load. If the trench is widened above the top of pipe, it does not contribute any additional
load to the buried piping. If sheeting is used, the width of the trench is computed to the
inside of the sheeting if it is to be removed. It is recommended that the sheeting remain,
if possible.

At any given depth, for a particular pipe size and type of soil, a trench width is reached
beyond which there is no longer any additional load added to the buried pipe. This is called
transition width, and is the widest dimension that need to be considered to compute the

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