Trenchless Piping Technology
Fiberglass Tank & Pipe Institute
Sullivan D. Curran PE, Executive Director
Introduction
The conventional approach to pipeline installation is to dig an open trench,
place the pipeline and then bury it. Although this method does not pose much of
a problem in rural or sparsely populated areas where vehicle traffic is light,
it can create havoc in busy urban areas, industrial complexes, when crossing
waterways or in environmentally sensitive areas. Prolonged pipe replacement
projects can cause major disruptions and economic impacts for industry and other
activities affected by excavation and construction. In a sensitive wetland
environment such as a river crossing, wildlife habitats would be destroyed and
extensive mitigation efforts would be required. As a result, trenchless or
"no-dig" technology has been used extensively in Europe, Japan and other parts
of the world, but is a recently applied technology in the United States to
minimize the disruptive effect of open trench pipeline construction.
Industrial Applications
The 1972 passage of the Clean Water Act (CWA) highlighted sewer rehabilitation
as a way to reduce hydraulic loads on pipelines, pumping stations and treatment
plants. Later in 1987, the CWA was expanded to include certain industrial
storm-water discharges. Then in 1995, the EPA further expanded their rules to
include discharges from commercial and light industrial facilities. Typically
the permitting of storm-water discharge requires the identification of areas
that may contribute to pollution in a discharge. For example, older bulk
petroleum, chemical or other liquid storage terminals may experience
infiltration into the existing sewer system making it difficult to meet
permitted storm-water discharge quality levels. As a result, sewer renovation or
replacement may be necessary. Trenchless methods are likely to be less
disruptive and more cost-effective in those areas where excavation may impact
other aboveground or underground structures.
Scope
Trenchless construction technology methods include the new construction (or
replacement) of piping and the renewal (i.e., renovation or rehabilitation) of
existing piping. Following is a discussion that describes the difference between
installing or renewing pipe underground without digging a trench.
New or replacement piping requires new construction at or near the
existing pipeline or at a location along a new alignment. One commonly used
method is the directional boring of small diameter horizontal holes up to six
inches in diameter to bury underground utility pipe and cable. However, the
focus of this paper is on the installation of large diameter fluid carrying pipe
in sizes ranging from 6 inches up to 108 inches (9 feet).
Renewal of existing piping involves one of two methods that may be
determined after conducting an assessment of the structural condition and degree
of inflow/infiltration exposure.
- Renovation is the
first option if the existing piping is found to be structurally sound. Then
the objective is to reduce inflow/infiltration by injection or sealing
techniques to repair limited damage. However, often the host pipe has
structurally deteriorated (i.e., missing pieces/cracked joints in masonry
piping, hydrogen sulfide corrosion of concrete piping or corrosion of steel
piping) and "rehabilitation" is necessary.
- Rehabilitation
measures restore the pipeline’s structural condition while still operating
the original "host" pipe. Construction techniques may include sliplining
with a new pipe; interior lining with cements or installing cured in-place
liners and others. This paper is limited to trenchless pipe replacement
using slip lining and pipe jacking methods.
Trenchless Technology Methods
Following are a number of trenchless technology methods that are described in
ascending order, with small diameter methods listed first:
New Pipeline Construction or Replacement
- Auger Boring – This is a
trenchless construction method used to install a casing by hydraulically
pushing the pipe through the ground and removing the spoil through the pipe
using an auger. This method is limited to amenable soil conditions,
relatively short distances and relatively small diameter piping (e. g., 24
inches).
- Direction Drilling - This is
a trenchless construction method that employs a directional drill to bore a
horizontal tunnel (e. g., 2,200 feet in length and up to 36 inches in
diameter). The tunnel is then reamed to remove the spoil and may be filled
with bentonite slurry to maintain tunnel stability. The pipeline is
assembled aboveground, pulled or pushed into the tunnel and anchored.
- Micro Tunneling and Pipe
Jacking – This is a trenchless piping construction method that pushes the
pipe into place (i.e., pipe jacking) behind a micro tunnel boring
machine that is remotely controlled. The boring machine is connected to the
head of the pipe that follows the slightly oversized tunnel as it is
drilled. The minimum diameter is 12 inches, which is limited by the
available machines. The practical maximum internal diameter is 84 inches.
- Utility Tunneling and
Carrier Pipe –This construction method involves excavating the ground at the
leading edge of a shield or boring machine and erecting a lining system from
within the excavated space. The minimum size is approximately 48 inches in
diameter, which is the size required to allow personnel access to erect a
liner from inside the opening. The lined tunnel acts as a host for the
installation of the carrier pipe system which is grouted in place.
Pipeline Renewal Technologies
- Sliplining – This is a
construction method used for pipeline installation inside an existing host
pipeline. Although sliplining reduces the inside diameter of the pipe, the
reduced inflow and infiltration combined with the smooth interior of plastic
or fiberglass sliplining materials increase the hydraulic flow. A typical
construction method involves digging insertion pits (e. g., 10 feet wide and
up to 25 feet long) over the existing pipeline at approximately 600 to over
1,200 foot intervals. Workers enter the pits and remove the top of the
existing pipe. After cleaning buckets are pulled through the line, sections
of the slipliner are lowered and either pulled or pushed into place. Final
installation may include pumping a grout between the host pipe and slipliner
if the structural integrity of the host pipe is in question.
- Pipe Bursting – Pipe
bursting tools are used in sliplining to provide access in collapsed or
narrow sections of the host pipe and if the pipe diameter is being
increased.
Typical Applications
Following are typical applications for new, replacement or rehabilitation of 2
through 102-inch diameter piping systems:
- Storm-water
- Industrial Effluents
- Sewer Interceptors
- Sewer Lines
- Force Mains
- Water Supply
- Salt Water Lines
Fiberglass Trenchless Piping
Benefits
Directional Drilling
Flexibility permits the adhesive bonding of up to 16 inch diameter pipe
aboveground and then pulling or pushing lengths exceeding 2,000 feet through a
normal size insertion trench and through the drilled tunnel.
Micro Tunneling and Pipe Jacking
Outside (OD) Dimensional Consistency and Smooth Exterior Surface: The
computer controlled production process achieves dimensional consistency and
smooth exterior surfaces. Both of these qualities minimize friction forces
created when jacking the pipe and cutter head forward through the soil to create
the tunnel. Minimizing friction when pipe jacking has two advantages:
- Smaller versus larger
capacity jacking equipment (i.e., hydraulic capacity and framing size)
needed to push heavier pipe materials (e. g., concrete or steel) with large
outside diameter tolerance ranges.
- Longer drives up to 800 to
1,000 feet with small diameter piping e. g., an average of 500 feet pushing
36-inch diameter pipe through stiff clays and silt-clays.
High strength to weight ratio
fiberglass has a higher compressive strength than other large diameter piping
materials. For example, fiberglass pipe weighs six to eight times less than a
similar strength concrete in 72-inch diameter pipe.
Smaller lifting equipment required off-loading and positioning pipe in the
insertion pits.
Slip Lining
High compressive strength of 2.5 times greater than typical concrete
permits equal pipe strength with a thinner pipe wall. The thinner wall results
in a larger inside diameter and minimizes any flow reductions from the original
pipe design capacity.
Smooth inside diameter wall reduces friction and typically improves flow
rate of the original piping system.
Gasket sealed joints are optional and permit the deflection of pipe
couplings such that existing piping curves may be negotiated without special
mitered or beveled fittings.
In-service installation when by-pass pumping is not feasible or allowed.
Sewage or other wastewater flow may continue through the insertion pits while
the pipe is being inserted into the host pipe. This is a significant advantage
over re-routing the outflow and developing an Environmental Impact Report.
All Applications
Long life corrosion resistance externally to an underground environment
and, internally to acids and caustics.
Leak-free joints by using adhesive bonded or rubber-ring seal bell-spigot
joints for leak free service.
Easy joining methods by using push-together joints for simple and quick
assembly without welding or grouting.
Standard fittings that are compatible with traditional ductile iron
dimensions.
Summary
While fiberglass is widely used in direct burial piping applications, it is
uniquely suited to micro tunneling/pipe jacking for new construction and
slipling into existing host piping systems. As a result, some one-third of the
fiberglass pipe footage has been installed using trenchless methods.
References
- Trenchless Technology June
1996 article "What is Trenchless Technology Anyway?"
- Public Works September 1996
article "Pipeline Renewal Technologies"
- Public Works December 1996
article "Major Sliplining Project for Baton Rouge"
- Public Works March 1997
article "Trenchless Technology Protects Wetlands Habitat"
- Ameron, Fiberglass Pipe
Group Bondstrand fiberglass Pipe Systems literature
- HOBAS Pipe USA, Inc.
Newsletters, literature and papers.
- Smith Fiberglass Products
Inc. literature
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