Page 303 - Trenchless Technology Piping Installation and Inspection

Pr oject Considerations for Pipe Replacement Methods 267

forces (see Sec. 6.10). Lubrication of outside surface of the
pipe with suitable lubricant is an effective way to reduce
required pulling force on the new pipe by reducing the fric-
tion between the pipe and the soil. The key to applying this
solution is establishing a lubrication manifold and lubrica-
tion line and pumping the lubricant during the bursting
operation.
• Certain components or accessories of the system (for exam-
ple, the winch, air compressor, hydraulic components, cut-
ting accessories in front of bursting head, etc.) are under sized
or not compatible with the application. The addition of appro-
priate accessories in front of the bursting head is assumed in
order to cut PVC fittings, ductile clamps or fittings, and the
like, reducing the potential of stopping or slowing the burst-
ing operation. If necessary, these components should be
upsized (within the allowable range of that system).
• Breaking or shattering the existing pipe in running soil, below
the GWT, may result in the pipe filled with soil, converting
the bursting operation to a piercing operation. After verifying
that the bursting head did not damage any nearby waterline,
the site should be dewatered.

6.10 Sample Pipe Load Calculations

6.10.1 Introduction
A method for estimating pipe loads on HDPE pipe for a Mini-
horizontal directional drilling (Mini-HDD) operation was described
in Chap. 5. It would be advantageous to obtain similar estimates for
such loads due to a pipe-bursting operation. Unfortunately, such
attempts are hampered by the wide range of possible field conditions
and their effect on the loadings. Thus, only a rough guide or “rule-of-
thumb” may be obtained, based on a combination of theoretical pre-
dictions and review of practical field results. Nonetheless, the process
of arriving at such estimates yields valuable insight into the mechan-
ics of the pipe-bursting operation and an understanding of the sig-
nificant parameters impacting such a process, aiding the user in
achieving a successful installation.

6.10.2 Pulling Loads—Theoretical Considerations
In principle, the required pulling loads on the replacement pipe may
be determined by estimating the normal (perpendicular) pressures
applied to the pipe as it is pulled through the expanded borehole or
cavity created by the bursting head. In particular, the pulling load