Page 253 - Buried Pipe Design

Design of Pressure Pipes 227

AWWA C950 can be summarized as follows:

Manufacturing processes:
■ Type I filament-wound
■ Type II centrifugally cast
Resins: Epoxy and polyester for RTRP and RPMP construction
Liners: none, thermoplastic, reinforced thermoset, nonreinforced
thermoset
Size range: 1 to 156 in
Diameters: inside diameters, outside diameters (IPS), outside diam-
eter (CI), metric dimensions
Pressure classes: 50, 100, 150, 200, 250, and over 250 lb/in 2
Hydro safety factors—service and distribution pipe:
■ 2 to 1 (including surge)
■ Transmission pipe 1.4 to 1 (including surge)

Strains induced by combined loading in buried pressurized flexible pipe
Introduction. It is well known that flexible pipe deflects under normal
installation and when pressurized, it rerounds, which reduces the
bending strains. Studies of the combined strain behavior of flexible
pipe have been reported in the literature, and a summary is presented
here.
Also, results are compared to the AWWA (ANSI/AWWA C950-81)
standard. The comparison shows that there exists a discrepancy in the
region where Spangler’s curve and Molin’s curve cross. Note that the
discussion on combined loading found in AWWA C950-81 has been
omitted from AWWA C950-07, which is the current version at the writ-
ing of this book.
Tests. A test program was run at Utah State University to deter-
mine the rerounding behavior when a buried flexible pipe is pressur-
ized. The test design permitted the efficient study of many variables
simultaneously. Variables for this program were haunch type, pipe
stiffness, soil compaction, and initial pipe deflection as controlled by
overburden pressure.
The pipe and measuring device. In the 6-in-diameter pipe, a single
linear variable differential transformer (LVDT) was mounted on a
shaft that could be rotated. The LVDT and shaft were enclosed in a
rubber bladder that was reinforced with a rubberized canvas covering
on the outside of the rubber bladder. The entire mechanism was then
placed inside the pipe. It was, therefore, possible to start the shaft and
trace out the profile of the pipe. The LVDT readings were digitized via