Page 31 - Buried Pipe Design

Chapter
2

External Loads

Loads are exerted on buried pipes by the soil that surrounds them.
Methods for calculating these loads are given in this chapter.
Marston’s theory for loads on buried conduits is discussed along with
the various factors which contribute to these loads. Underground pipes
are placed in tunnels, buried under highways, buried under railways,
and buried under airports. Methods are given for the determination of
loads which are imposed on pipes in these and other applications.

Soil Pressure
The subject of soil structure interaction has been of engineering interest
since the early 1900s. The horseless carriage had its volume-production
start with the Oldsmobile in 1902, and the need for improved roads was
immediately apparent. Many projects for road drainage were begun
using clay tile and concrete drain tile. One major problem existed, how-
ever. There was no rational method of determining the earth load these
buried drains would be subjected to. As a result, there were many fail-
ures of pipelines.
The loads imposed on conduits buried in the soil depend upon the
stiffness properties of both the pipe structure and the surrounding
soil. This results in a statically indeterminate problem in which the
pressure of the soil on the structure produces deflections that, in turn,
determine the soil pressure.
When designing rigid pipes (for example, concrete or clay pipes), it
is customary to assume that the pipe is affected mainly by a vertical
pressure caused by soil and traffic; a horizontal reacting pressure is
either nonexistent or negligible. For flexible pipes, the vertical load
causes a deflection of the pipe, which in turn results in a horizontal

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