Page 48 - Buried Pipe Design
P. 48
26 Chapter Two
Pipe and Soil Working Together
P
P
Δ
Figure 2.11 Graphic of pipe and soil working together as
a system.
Load
Side Side
Support Support
Figure 2.12 Graphic showing the contribution of sidefill
soil in the performance of a flexible pipe.
Equation (2.10) has become known as the Marston-Spangler load
equation for flexible pipes. It should be remembered, however, that the
assumption of soil friction resisting the downward movement of the cen-
tral soil prism has been used in its development, and that it should not
be used merely because a pipe is flexible. The maximum loads on rigid
and flexible pipes as predicted by the Marston equations, Eqs. (2.4) and
(2.10), do not take place instantaneously and may not occur for some
time. In certain cases the initial load may be 20 to 25 percent less than
the maximum load predicted by Marston, and the long-term load may
be greater than that predicted.
