Underground Infrastructure - July 2023 - 30

Rehab Technology
by robotic cutters or externally excavated and reconnected,
resin/epoxy requires precise design and mixing, and the need
for specialty equipment.
CIPP is also challenged by geometry, such as 22- and 45-degree
bends that can cause the liner to wrinkle and/or " fold
over " on itself, potentially creating an annulus that could compromise
the integrity of the liner. CIPP is best fit for relatively
straight pipe alignments. CIPP also requires constant, diligent
QA/QC throughout the application process as ambient factors
can influence the integrity of the liner.
Like the rest of the industry, CIPP manufacturers continue
to make advances. The advent of UV-cured liner minimizes the
potential for the catalyst setting off before the liner is in place, as
it requires UV light rather than simple heat. Robotic cutters for
re-instating services are constantly evolving, as well. Because
of these and other advances, CIPP will continue to evolve and
play a role in the rehabilitation of pressure pipelines.
Pipe bursting
Pipe bursting as a trenchless pipeline replacement method was
developed and introduced domestically in the 1970s. The concept
is relatively straightforward: a bursting or splitting head is
pulled through the host pipe, breaking it by exceeding the pipe's
shear strength and tensile limits. Simultaneously, the bursting
assembly expands the surrounding material to facilitate the
pulling of a new pipe behind it.
Pipe bursting is a popular solution for replacing old, compromised
or otherwise defective pipelines, as well as for upsizing
a line due to capacity needs. Upsizing is generally limited
to single " step " increases (e.g., bursting a 10-inch-diameter line
and pulling in a new 12-inch pipe), although larger upsizing can
be accomplished with the appropriate soil/surface conditions
and host pipe depth.
There are two general methods of pipe bursting: pneumatic
and static pulling. A pneumatic burst utilizes dynamic force to
burst the existing pipeline, while static bursting is performed
under constant pull force. Many factors must be considered
when selecting the appropriate bursting method, including but
not limited to, soil characteristics, groundwater presence, diameter
and material of both new and existing pipelines, and depth.
Static bursting uses rods and a hydraulic system to pull the
bursting head through the host pipe. It has become the most
popular method largely due to the reduction of energy transition
into the surrounding soil. The magnitude of energy waves
associated with bursting can be extremely high and carry the
risk of damaging nearby utilities or heaving at the surface (exacerbated
if the pipeline travels below a roadway or structure).
Upsizing the host pipe is exclusive to the static bursting method.
In general, high-density polyethylene (HDPE) pipe is the
material of choice for pipe replacement via bursting. The flexibility
and material characteristics of HDPE offer the ability to
withstand pulling forces without deformation, the ability to
string out long segments of pipe above ground (via weld fusion),
and it has natural anti-corrosive properties.
Bursting offers key benefits when compared to other
trenchless options, including no loss of pipeline internal diameter,
the ability to upsize (if conditions are met), the ability to
install long sections in a single day, and little-to-no host pipe
preparation. Compared to traditional open-cut pipe replacement,
installation time is reduced significantly, as well as necessary
traffic control, restoration and permitting.
Pipe bursting is not without challenges and limitations,
however. While gradual horizontal and vertical bends can be
navigated successfully, bursting is limited to relatively straight
alignments. Bends in the line must be identified and can limit
the distances installed for a particular run. Appurtenances
such as valves, tees, wyes, etc. must be removed before bursting
and reestablished after.
Additionally, the risk exists for the bursting head to become
stuck or go off-course at which point it must be located and excavated.
A proper bursting effort requires extensive project planning
to understand the existing pipe, soil and site conditions as
well as the selection of the proper approach and materials.
30 JULY 2023 | UndergroundInfrastructure.com
http://www.UndergroundInfrastructure.com

Underground Infrastructure - July 2023

Table of Contents for the Digital Edition of Underground Infrastructure - July 2023

Underground Infrastructure - July 2023 - 1
Underground Infrastructure - July 2023 - 2
Underground Infrastructure - July 2023 - 3
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