1 March 1997
11-5. CURED IN PLACE PIPE (CIPP). In this process a soft, pliable tube, general referred to as
a soft liner, is forced by water or air into the sewer. The tube negotiates displaced pipes and
cures to a rigid liner. It is an expensive process but does not require excavation and service can
be continued after only one day. In a one CIPP process the tube is felt, impregnated with
thermo-setting polyester or epoxy resins. Other materials are also available but many CIPP
processes are patented and could potentially require sole source justification. Generally CIPP
should be allowed as one of several options or with performance specifications that do not
prevent competition among manufacturers or other rehabilitation methods.
11-6. DEFORMED/FOLDED LINERS. Another method for restoring pipe integrity is that of
installing a deformed or folded liner into an existing pipe and then reforming the liner with heat
and pressure to fit tightly to the inside diameter of the original pipe. This results in a rigid liner.
Various manufacturers have different names for their products.
a. Deformed/Reformed. In this process, high density polyethylene pipe is deformed in a "u"
shape at the manufacturing plant during the manufacturing process and supplied in long
continuous lengths on coils. The pipe is pulled into place through existing openings and
reformed by means of steam and low pressures. This method utilizes sufficient wall thickness to
be considered a "stand alone" product which does not rely entirely on the host pipe for its
structural strength. This process is controlled by guidelines given in ASTM F 1533 and offers the
advantage of being able to reinstate service laterals internally by means of a remote controlled
b. Folded. Currently PVC is used as the "folded liner", specifications for which are given in
ASTM F 1504. This product is folded flat at the manufacturing plant, delivered to the site in coils,
preheated, and then pulled into place in the host pipe. Once in position, the product is formed by
hot water, steam, or hot air and pressure. Service laterals can also be remotely installed.
11-7. PIPE BURSTING. Each of the previous methods for rehabilating sewers reduce the
interior diameter of the pipe. A method of replacing existing pipe with equal or larger pipe (up to
50 percent larger in cross sectional area) and without excavating the pipe is known as pipe
bursting, impact mole, or the pipeline insertion method (PIM). The process, first developed for
replacing gas mains, uses an impact mole to burst the existing pipe outward into the surrounding
soil and replaces it with new pipe (generally high density polyethylene). An entry pit is prepared
at one end of the existing pipe and a pneumatic pipe bursting mole, which can include an
expander, is set up at the pipe opening. A winch is positioned at the exit point and a steel cable
guides the mole toward the end. The percussive action of the pneumatic equipment and the
constant tension of the winch forces the mole through the existing pipe. When replacing
pressure pipe the new pipe is towed behind the mole, while with gravity sewers, the new pipe
can also be hydraulically jacked behind the mole, which increases the distance between entry
pits. Generally, entry pits are required between every other manhole. Connection of laterials
also requires excavation. The mole can burst even cast iron pipe but can not maneuver through
bends. Further information can be found in USACERL Technical Manuscript N-91/08, "Review of
PIM (Pipeline Insertion Method) Technology".
11-8. PIPE CRUSHING. The pipe crushing process is also a trenchless construction method. In
it, high density polyethylene pipe is installed in the same operation as the pipe crushing.
Essentially the process involves the use of a crushing head that implodes and crushes the
existing pipe inward thus causing minimum disturbance to the surrounding soil and allowing
close uses to existing utilities or structures. Just behind the crushing head, a steel cone clears
away the crushed pipe and excess soil, making room for the new pipe. Forward progress of the