Page 266 - Trenchless Technology Piping Installation and Inspection

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cone-shaped bursting head operated by a reciprocating impact pro-
cess. This method was patented in the United Kingdom in 1981 and
in the United States in 1986; but expired in April 2005. When it was
first introduced, pipe bursting was used only in replacing cast-iron
gas distribution pipes and later was employed to replace water and
sewer pipelines. By 1985, the process was further developed to install
up to 16-in.-outer-diameter (OD) medium-density polyethylene
(MDPE) outside pipe.
Replacement of sewers in the United Kingdom using sectional
pipes as opposed to continuously welded polyethylene pipe was
described in a paper by Boot et al. (1987). Up to 2006, approximately
9000 mi of high-density polyethylene (HDPE) pipe has been installed
by bursting (Najafi, 2006). Currently, pipe bursting is used to replace
waterlines, gas lines, and sewer lines throughout the world.
Pipe bursting is too widely used to replace deteriorated pipes
with new pipes of the same or larger diameter, utilizing the same
existing pipe space (so more appropriate for urban conditions,
where usually underground space is crowded with utilities). This
method is an economic pipe replacement alternative that reduces
disturbance to business and residents when compared to the open-
cut technique. Pipe bursting is especially cost-effective if the exist-
ing pipe is out of capacity, deep, and/or below the groundwater
table (GWT). Upsizing refers to replacement of the existing pipe
with a pipe one standard size larger (e.g., replacing 8-in. pipe with
a 10-in. size is one upsize). Similarly, two-size upsizing is replace-
ment of the existing pipe with a pipe two standard sizes larger,
such as, replacing 8-in. pipe with a 12-in. size.
Pipe bursting typically involves insertion of a cone-shaped burst-
ing head into an existing pipe. The base of the cone is larger than the
inside diameter of the existing pipe and slightly larger than the out-
side diameter of the new pipe to reduce friction and to provide space
for maneuvering the pipe. The back end of the bursting head is con-
nected to the new—for example, polyethylene (PE)—pipe and the
front end is attached to a cable or pulling rod. The new pipe and
bursting head are launched from the insertion shaft and the cable or
pulling rod is pulled from the pulling shaft/pit or manhole (depen-
dent on the method and upsize required to retrieve the bursting
head), as shown in Fig. 6.1. The bursting head receives energy to
break the existing pipe from several possible sources: a pulling cable
or rod (static method), a hydraulic source (hydraulic method), or an
air compressor (pneumatic method). The energy breaks the existing
pipe into pieces and expands the diameter of the cavity. As the burst-
ing head is pulled through the existing pipe debris, it creates a bigger
cavity through which the new pipe is simultaneously pulled from the
insertion shaft. There are many variations to this method that are pre-
sented in the following sections.