Page 89 - Buried Pipe Design

Chapter
3

Design of Gravity Flow Pipes

Design methods which are used to determine an installation design for
buried gravity flow pipes are described in this chapter. Soil types and
their uses in pipe embedment and backfill are discussed. Design meth-
ods are placed in two general classes—rigid pipe design and flexible
pipe design. Pipe performance limits are given, and recommended
safety factors are reviewed.
The finite element method for design of buried piping systems is rel-
atively new. The use of this powerful tool is increasing with time. A
detailed discussion of this method is included.

Soils
The importance of soil density (compaction) and soil type in contributing
to buried pipe performance has long been recognized by engineers. The
pipe-zone backfill, which is often referred to as the soil envelope around
the pipe, is most important. An introduction and a brief discussion of
embedment soils is presented in Chap. 1. In this chapter, additional
information on soil classification and soil-pipe interaction is provided.

Soil classes
Professor Arthur Casagrande proposed a soil classification system
for roads and airfields in the early 1940s. This system, now called
the Unified Soil Classification System (USCS), has been adopted by
many groups and agencies, including the Army Corps of Engineers
and the Bureau of Reclamation. The American Society for Testing
and Materials (ASTM) version of the USCS is entitled “Classifica-
tion of Soils for Engineering Purposes” and carries the designation
D 2487.

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