Page 302 - Trenchless Technology Piping Installation and Inspection

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using the previously discussed techniques. However, if such a condi-
tion was discovered after initiating bursting, the contractor can repair
the sag by exposing the problematic location and adjusting the soil
beneath the pipe. Replacement of a section of pipe may be necessary at
this excavation. If direct excavation at the location is not feasible, grout-
ing or otherwise stabilizing the soil beneath the pipe may be possible.
If excessive ground movement is anticipated close to an existing
structure, a ground movement and vibrations monitoring plan should
be developed (see Sec. 6.9.7). If problematic levels (see Sec. 6.8.7) are
observed, a slower the rate of bursting is mandated. If the ground
movement remains excessive, the bursting operation should be halted
until an analysis of the causes and corrective options is conducted. If
there is a deteriorated or old gas line, waterline, or sewer line that is
particularly close to the bursting head and at risk of damage, exposure
of the line significantly reduces risk of damage. The corresponding
excavation should be performed using means that do not damage the
line, such as vacuum or manual excavation. If the existing pipe is shal-
low and there is a high risk of damaging the surface pavement, saw
cutting the pavement prior to bursting prevents the spreading of the
damage to the rest of the pavement. After the operation is completed,
the pavement over the trench can be repaired. In the absence of a viable
solution, one option includes abandoning the pipe-bursting method.
If the bursting is significantly slower or more difficult than antic-
ipated, the contractor should attempt to determine the cause and con-
sider available corrective actions. Possible reasons and solutions for
low bursting progress, or excessive pull force, include:

• The bursting system does not have sufficient power relative
to the application (upsize percentage, large diameter, length,
etc.). If the problem becomes evident shortly after the start of
the run, the bursting system should be upgraded with one
that has more power. If the problem occurs when the unit is
close to the pulling shaft, toward the end of the run, the oper-
ation should be continued until the bursting head reaches the
pulling shaft. At that point, the system may be upgraded for
performing the next run, unless it is determined that an iso-
lated problem, such as that due to a repair ductile clamp or a
fitting, and unlikely to occur again. As an alternative to
employing a more powerful bursting system, the length of
the runs may be reduced. If the problem arises in the middle
of the run, at a location where excavation is feasible, the burst-
ing head should be exposed by a new shaft and the system
upgraded. The introduced shaft can serve as an insertion
shaft for the remainder of the run.
• The soil around the pipe prone to flowing or running, possi-
bly leading to excessive friction and associated elevated pull