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Pr oject Considerations for Pipe Replacement Methods 237

deteriorated. The diameter of the existing pipe typically ranges
from 2 to 30 in., although bursting of larger diameter existing pipes
is becoming more common. A segment of 300 to 400 ft is a typical
length for bursting, although significantly longer runs have been
completed using more powerful bursting systems. However, point
repairs on the existing pipe, particularly using ductile materials; can
create problems. For a comprehensive discussion of existing pipe
materials, refer to Pipe Bursting Manual of Practice (MOP), No. 112,
published by the American Society of Civil Engineers (ASCE, 2007).

6.5 Replacement (New) Pipe Material
High- and medium-density polyethylene (HDPE or MDPE), collec-
tively called “PE”, have been the most widely used replacement pipes
for pipe bursting applications. Polyethylene pipe may utilize high-
performance PE4710 material, with somewhat greater strength capa-
bility than conventional pipe. The main advantages of PE pipes are its
continuity, flexibility, and versatility. The continuity, which is obtained
by butt fusing together long segments in the field, reduces the possi-
bility of stopping the installation process. For small diameters (4 in.,
or less), the pipe may also be supplied in continuous lengths on a reel.
The PE pipe flexibility allows bending the pipe for convenient inser-
tion in the field. In addition, it is a versatile material that meets other
requirements for gas, water, and wastewater applications. The rela-
tively smooth interior surface reduces the friction between the fluid
flow and the pipe wall, which allows increased flow capacity. The
smooth exterior surface also reduces the friction between the soil and
the pipe, facilitating the pulling operation (see Sec. 6.10.2). The rela-
tively higher thermal expansion coefficients of HDPE pipes, requires
proper installation and restraint.
The internal surface of PE pipe is smoother than that of the con-
crete or clay pipe. For gravity applications, the following Cheesy-
Manning equation [Eq. (6.1)] demonstrates that the flow capacity of
the PE pipe is 44 percent greater than those of the concrete or clay
pipes, assuming the internal diameter for the existing clay or concrete
pipe equals that of the replacement PE pipe.

.
Q = 149 Ar () 23 S (6.1)
/
n H
3
where Q = flow quantity (ft /sec)
n = Manning roughness coefficient (dimensionless)
2
A= internal cross-sectional area of the pipe (ft )
r = hydraulic radius (ft)
H
S = slope of the energy line, which is parallel to the
water surface and pipe invert if the flow is uniform
(dimensionless)