Page 132 - Buried Pipe Design

Design of Gravity Flow Pipes 107

pipe performance as a function of height of cover is determined directly.
Equally good empirical approaches to study of the deflection mecha-
nism are

■ The study of actual field installations
■ The simulation of a large enough earth cover in a soil test box to
exceed the performance limits of the pipe

To avoid the problem of having to establish design data for the infi-
nite variety of installations and bedding conditions that are found in
the field, the following design bases have been chosen:

■ The embankment condition is selected as critical. (The results are
conservative for other than embankment conditions.)
■ Time lag or settlement of the embankment is included by analyzing
long-term values of deflection.
An added advantage of this system is that by a single test, not only
can ring deflection be determined, but also performance limits such as
ring crushing, strain, and wall buckling can be noted and analyzed.
The use of such data may be considered the most reliable method of
design and is recommended when available. Some of the pipe products
for which empirical test data have been determined are as follows:
Asbestos-cement (AC) pipe
Corrugated steel pipe
Ductile iron pipe
Fiberglass-reinforced plastic (FRP) pipe
Polyethylene (PE) pipe
Polyvinyl chloride (PVC) pipe
Reinforced-plastic mortar (RPM) pipe
Steel pipe (CMC-CML)

Substantial data are available for PVC sewer pipe made in accor-
dance with ASTM D 3034 with minimum pipe stiffness of 46 lb/in and
2
have been compiled by researchers at the Buried Structures
Laboratory, Utah State University. The results of many measure-
ments are categorized in Table 3.9 according to soil type, soil density,
and height of cover. Deflections presented in Table 3.9 represent the
largest deflections encountered under the conditions specified. Data
presented in this manner are designed to provide various options for
design engineers. Their use, in most cases, will show that several