Underground Infrastructure - July 2023 - 32

Rehab Technology
Sliplining
Loose-fit pipe lining (commonly referred to as sliplining) is one
of the oldest forms of lining, with roots dating back to the 1960s.
Like pipe bursting, sliplining is performed by pulling or pushing a
new pipe through a larger-diameter host pipe. Unlike pipe bursting,
the host pipe remains intact and acts as a conduit for the
new pipeline. As the name suggests, the new pipeline fits loosely
inside the host pipe, leaving an annular space between the two.
This method of trenchless pipeline rehabilitation is perhaps
one of the simplest and easiest to perform, and can be executed
inexpensively. As with pipe bursting, HDPE is a popular choice
for sliplining due to its advantageous material characteristics and
structural capacity. However, other materials are frequently utilized,
as well.
A clear limitation with sliplining as a rehabilitation method is
the inherent reduction in internal diameter. Pressurized HDPE
pipelines can require very thick pipe walls, therefore when sliplining
high-pressure pipes with HDPE, the internal diameter is even
further reduced and capacity can be impacted significantly enough
to make the option unfeasible (although the smooth HDPE pipe
typically carries a lower friction factor than the host pipe).
Preparation becomes critical in terms of understanding the
alignment and cleaning the host pipeline to ensure that the new
pipe can be properly installed. Any service or lateral lines must
be excavated and reinstated after sliplining. The annular space
between the new and host pipe is typically grout filled to close
the void and provide support.
Modified sliplining or close-fit lining - what is colloquially
known as Swagelining, is similar to sliplining in that a new standalone
pipe is inserted into a host pipeline. Swagelining differs in
that the pipe diameter is modified or reduced for insertion to the
host pipe but restored to its original size and shape afterwards.
Once again, HDPE is the material of choice for this trenchless
rehabilitation method because of its elastic properties. The
desired length of HDPE pipe is fused together (up to about a
mile in length) and then pulled through a dye stationed at the
access point to the host pipe.
The dye temporarily compresses the HDPE as it is pulled
into the host pipe; constant tension is applied to the pipe as it is
being pulled to maintain the compressed shape. When the new
pipe reaches the limit of the rehabilitation span, the tension is
released, and the HDPE returns to its original shape and size.
The clear benefit of Swagelining as opposed to basic sliplining
is that less of the original internal diameter is given up because
the new pipe fits closely to the interior of the host pipe. The remaining
benefits and challenges encountered with Swagelining
are quite similar to sliplining, with additional equipment being
needed to deform the new pipeline.
Flexible Fabric Reinforced Pipe
Flexible Fabric Reinforced Pipe (FFRP) has been successfully
utilized in the United States for over 10 years but on the
timeline of trenchless technology is still considered the newest
rehabilitation option. There are currently two types of FFRP
approved for use in the United States and both are considered
AWWA Class III liners.
At a glance, the two available liners share many common
traits both in material properties and installation method. Both
options, in their standard form, consist of three layers:
* A modified, abrasion resistant polyethylene outer
* An inner fabric layer that provides the majority of the
tensile strength
* A polyethylene inner layer that has a C-Factor of 150
Both products are best suited for pressure applications, as they
cannot be tapped without compromising their integrity. Each
FFRP option has a modified abrasion resistance polyethylene
(PE) outer layer, a middle layer of fabric reinforcement (including
options such as seamless woven polyester, aramid or a combination
of the two fabrics), and a modified PE layer on the inside.
FFRP is an excellent solution for a wide variety of applications,
especially those in which traditional open cut is challenged
by above ground infrastructure, where CIPP is challenged
by geometry, and where sliplining reduces the finished
diameter too greatly. Other benefits include rapid installation
times, long pull distances, small termination portals, small
overall project footprint, NSF 61 approval for potable water,
32 JULY 2023 | UndergroundInfrastructure.com
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Underground Infrastructure - July 2023

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