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

favorable to stringing out a long line of butt-welded pipes. Some pipe materials also have joints that can
be mechanically locked together. When this feature is invoked, the pipe string can be advanced by either
pulling or pushing or a combination of the two, thereby increasing the length that can be sliplined from
one access pit to the next. One of the limitations of using discrete pipe
lengths is that rubber ring joints will normally only allow angular rotations
ranging from about 1/2° to 3.5° depending on material and diameter.
Therefore, any deviations in the host pipe’s joints exceeding these values
may require special attention. Also, pipe lengths may have to be nonstandard
to accommodate short radius curves. For sewer force mains,
PVC, DI and GRP/FRP pipes could all be used for discrete sliplining.
Hobas Pipe USA, US Composite Pipe (Flowtite), Ameron, and Future
Pipe are manufacturers of large diameter GRP/FRP pipe that have been
used for sliplining of both pressure and non-pressure wastewater lines
(Figure 3-23). Pipe diameters from 12 to 144 inches (300 to 3,600 mm)
are available.
Figure 3-23. Hobas
Sliplining Pressure Joint
In the case of PVC, Certainteed Corp. manufactures the Certa-Lok restrained joint for trenchless water
and sewer applications. Certa-Lok is based on the use of a special coupling into which two nylon splines
are inserted that lock into grooves in the spigot end of the pipe. A rubber gasket is included for water
tightness. The C900/RJ and C905/RJ Certa-Lok PVC products are UL listed and suitable for pressure
applications ranging from 150 to 200 psi (10 to 14 bar) dependent on DR ratio and standard. Certa-Lok
pipe is available in diameters from 4 to 16 inches (100 to 400 mm). Another example of a restrained PVC
joint is the TerraBrute pressure pipe from IPEX. The TerraBrute joint is a steel ring and pin system,
that incorporates a rubber ring gasket for sealing. It is reported that the joint can take up to 120,000 lb of
axial force in the 12 inch (300 mm) diameter size. The TerraBrute joint was specifically developed for
horizontal directional drilling (HDD) applications, but can also be used for sliplining.
3.5.1.2 Pipe Bursting. 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 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. For
diameters 12 inches (300 mm) and under, upsizing up to 50% is possible and for diameters over 12 inches
(300 mm) upsizing by up to 25% is achievable with the right soil conditions and adjacent structures far
enough away to avoid damage. Upsizing by over 50% is considered experimental.
Pipe bursting has now been accomplished in diameters from 4 to 60 inches (100 to 1,500 mm). The
bursting method works best on friable pipes, including CI, asbestos-cement, non-reinforced concrete,
PVC, and clay pipes. There are three basic bursting methods ― static, hydraulic and pneumatic bursting.
Pipe splitting, which is a form of bursting for materials like DI and steel, is a fourth type that will be
covered in the next section. Fusible PVC replacement pipe should only be used with the static bursting
method.
The type of soil affects the ability of the bursting head to expand the hole and therefore the amount of
upsizing. Obviously bursting is not possible in rock or pipes that are concrete encased. Also, shallow
buried pipes risk surface displacement. As a general rule of thumb, the minimum depth of the existing
pipe should be 10 times the difference in diameters of the existing pipe’s OD and the expander’s OD.
With increasing depth of soil burial, the force needed to expand the hole also increases. The foundation
of adjacent structures and other utilities can be damaged if too close to the bursting activity. The distance
should be a minimum of 18 inches (450 mm) for normal bursting, larger for upsizing. Expansion pits can
be dug adjacent to structures or utilities to relieve the soil pressure.
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