State of Technology Report for Force Main Rehabilitation, Final ...
State of Technology Report for Force Main Rehabilitation, Final ...
State of Technology Report for Force Main Rehabilitation, Final ...
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Since the original pipe is destroyed in the bursting process, the new pipe must be designed to carry all <strong>of</strong><br />
the operational loads, including internal pressure, external soil pressure, and traffic loads. After insertion<br />
<strong>of</strong> the new pipe behind the bursting head, the soil will tend to close back on the pipe providing support.<br />
The design <strong>of</strong> the pipe is similar to direct burial pipe based on soil-pipe interaction. Actually, some <strong>of</strong> the<br />
most demanding loads may be exerted on the new pipe during the installation. The new pipe will see<br />
flexural loads as it enters the launch pit, axial tensile loads due to friction and pipe weight, external<br />
buckling pressure due to soil fill and groundwater, and possible surface damage from contact with shards<br />
<strong>of</strong> the old pipe.<br />
Static Pipe Bursting<br />
Static bursting was originally developed by British Gas to replace CI<br />
gas mains. It works well with CI and asbestos cement pipes. Pipe<br />
diameters from 2 to 60 inches (50 to 1,500 mm) can be burst using the<br />
static method, which relies upon brute <strong>for</strong>ce to shatter the existing<br />
pipe. Lengths up to 400 feet (122 meters) typically can be burst using<br />
the static approach although much longer lengths can be burst under<br />
the right combination <strong>of</strong> ground conditions and bursting equipment.<br />
TT Technologies Grundoburst ® and Hammerhead Hydroburst ® are<br />
two examples <strong>of</strong> equipment designed <strong>for</strong> static bursting, as<br />
illustrated in Figure 3-24.<br />
Figure 3-24. Static Bursting Head<br />
Pneumatic Pipe Bursting<br />
With pneumatic bursting, an air operated hammer shatters the old pipe<br />
with impact as the bursting head is pulled through the line. Pneumatic<br />
bursting works well with the same materials as the static method, plus<br />
PVC. Broken pieces are pushed outward by a rear expander, which<br />
can also upsize the resulting void. Diameters from 4 to 60 inches (100<br />
to 1,500 mm) and lengths up to 500 feet (152 meters) typically are<br />
burst with the pneumatic method. TT Technologies Grundocrack ® is<br />
an example <strong>of</strong> pneumatic pipe bursting equipment (Figure 3-25).<br />
Figure 3-25. Pneumatic Bursting Head<br />
Hydraulic Pipe Bursting<br />
Hydraulic pressure is used to expand the burster, which breaks the old pipe and pushes the pieces into the<br />
surrounding soil. An expansion cone can also be accommodated <strong>for</strong> upsizing. The hydraulic method can<br />
be used with the same materials as the static method and in diameters from 6 to 20 inches (150 to 500<br />
mm). Xpandit is an example <strong>of</strong> equipment designed <strong>for</strong> hydraulic pipe bursting.<br />
Tenbusch Insertion Method<br />
The Tenbusch Insertion Method (TIM) deviates from the static and dynamic pipe bursting methods.<br />
Instead <strong>of</strong> using the bursting head to pull a new pipe into the void created by the burst, Tenbusch jacks the<br />
new pipe in place <strong>of</strong> the existing deteriorated pipe. The leading element is a heavy steel guide pipe,<br />
which maintains alignment within the center <strong>of</strong> the old pipe. Behind the lead is the cracker, which<br />
fractures the old pipe, followed by a cone expander that radially expands the fractured pipe into the soil.<br />
This is followed by the front jack which is a hydraulic cylinder that acts like an intermittent jacking<br />
station to provide the axial thrust to the leading equipment. The front jack bears against the pipe (via an<br />
adapter) that is also being jacked into the void. Lubricant is introduced at the adapter to minimize<br />
friction. The lead equipment is designed to be disassembled at a 4 feet (1.2 meters) diameter receiving<br />
manhole and removed. With the Tenbusch method, only rigid pipes that can withstand the high axial<br />
jacking loads are used <strong>for</strong> the replacement. This is mainly clay and DI pipe.<br />
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