Page 209 - Buried Pipe Design

Chapter
4

Design of Pressure Pipes

The design methods for buried pressure pipe installations are somewhat
similar to the design methods for gravity pipe installations which were
discussed in Chap. 3. There are two major differences:
1. Design for internal pressure must be included.
2. Pressure pipes are normally buried with less soil cover so the soil
loads are usually less.

Included in this chapter are specific design techniques for various
pressure piping products. Methods for determining internal loads,
external loads, and combined loads are given along with design bases.

Pipe Wall Stresses and Strains
The stresses and resulting strains arise from various loadings. For
buried pipes under pressure, these loadings are usually placed in two
broad categories: internal pressure and external loads. The internal
pressure is made up of the hydrostatic pressure and the surge pres-
sure. The external loads are usually considered to be those caused by
external soil pressure and/or surface (live) loads. Loads due to differ-
ential settlement, longitudinal bending, and shear loadings are also
considered to be external loadings. Temperature-induced stresses may
be considered to be caused by either internal or external effects.

Hydrostatic pressure
Lamé’s solution for stresses in a thick-walled circular cylinder is well
known. For a circular cylinder loaded with internal pressure only,
those stresses are as follows:

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