State of Technology Report for Force Main Rehabilitation, Final ...

The use of close-fit liners is often called modified sliplining. It involves the use of a thin walled liner
with an outside diameter that is similar to the inside diameter of the host pipe. The key to installing the
liner is to temporarily reduce the liner diameter to facilitate its insertion into the host pipe. Once the liner
is in place, it is reverted back to its original outside diameter forming a close fit to the host pipe. The two
methods of temporarily reducing the diameter of the liner is symmetrical or fold-and-form. Polyethylene
(PE) pipe is used for the symmetrical reduction process, and both PE and polyvinyl chloride (PVC) for
fold-and-form.
CIPP is by far the leading method for the rehabilitation of gravity sewers. With the expiration of the
original patent on CIPP, many new variants have been introduced. The main differences are based on
tube construction, method of installation, curing method, and type of resin.
Woven hose linings differ from ordinary CIPP products by the construction of the tube reinforcement.
Rather than being made of a felt-type material, hose liners are made from either polyester, glass, or
aramid fibers that are woven into a hose-type configuration, similar to the type of construction used for
fire hoses. Three types of woven hose lining systems are discussed including adhesive-backed linings,
non-adhesive backed linings, and glass-reinforced thermoplastic linings.
Replacement
Replacement involves the installation of a new fully structural pipe to take over the functions of the
deteriorated force main. Several technologies are available for online and offline replacement.
Historically, the most common method has been offline replacement by open cut, as the work can be
undertaken with the existing main in operation and it results in a brand new pipe with a known design
life.
The second most common method of replacement has been sliplining. Sliplining involves the insertion of
a new pipe with a smaller outside diameter than the inside diameter of the pipe to be rehabilitated. Pipe
lengths can be fused together to create a long continuous string, frequently done with PE and Fusible
PVC, which is then pulled into the host pipe. Alternatively, especially when site conditions prevent
pre-joining long strings of pipe, discrete pipe sections can be jointed one at a time and pushed into the
host pipe. PVC, DI, and fiberglass reinforced plastic/glass reinforced plastic (FRP/GRP) pipes are
typically sliplined in this fashion. Mechanically restrained joints can also be employed with these
materials, which would allow pulling of the pipe into place.
Pipe bursting involves the breaking up of the old pipe and pushing it into the surrounding soil by passing
a bursting or splitting device through it, while pulling a replacement pipe in behind the bursting head.
The replacement pipe is usually high density polyethylene (HDPE), PVC, or DI. In some cases, the
process can be used to expand the void created thus upsizing with the insertion of a larger diameter. Pipe
bursting has now been accomplished in diameters from 4 to 60 inches (100 to 1,500 mm). The three basic
bursting methods include static, hydraulic, and pneumatic bursting.
Offline replacement simply involves the installation of a new pipe without regard to the line and grade of
the existing pipe. Normally, the existing deteriorated pipe being replaced is kept in service (at reduced
operating conditions if necessary), while the new replacement pipe is being installed. Typically, methods
of offline replacement include open cut excavation and newer trenchless methods such as directional
drilling and microtunneling/pipe jacking. For microtunneling, FRP/GRP, polymer concrete, and steel
pipes can be used.
vi