Page 274 - Trenchless Technology Piping Installation and Inspection

238 Cha pte r S i x

The n value for clay or concrete pipes is assumed to be between
0.012 and 0.015, in comparison to approximately 0.009 for PE
(Lindeburg, 1992).
In addition to PE, other pipe materials can be polyvinyl chloride
(PVC), ductile iron, VCP, or RCP. With exception of PVC and ductile
iron, VCP and RCP cannot be assembled into a single pipe string,
prior to the bursting operation, which allows a continuous pulling
operation. However, they can be jacked into position one by one
(thereby requiring less staging distance) behind the bursting head or
maintained in compression by towing them via a cap connected to
the cable or rod that passes through these pipes. Therefore, the static
pull system is the only bursting system that can be used with RCP
and VCP pipes. The joints of these pipes must be designed for jacking
applications.
For a comprehensive discussion of new pipe materials, refer to
Pipe Bursting Manual of Practice (MOP), No. 112, published by the
American Society of Civil Engineers (ASCE, 2007).

6.6 When Is Pipe Bursting a Preferred Solution?
For repair and replacement, conventional techniques require open-
cut excavation to expose and replace the pipe. Alternatively, the pipe-
line can be trenchlessly renewed by inserting a new lining, or replaced
by pipe bursting. Chapter 2 described several pipe-lining methods
such as cured in place pipe, close-fit pipe, and sliplining. The main
advantage of the lining methods over pipe bursting is the need for
little or no excavation for access to the pipeline. In contrast, pipe
bursting has the advantage of increasing the pipe capacity by more
than 100 percent, as described below.
Pipe bursting is most cost advantageous compared to the lining
techniques when:
• There are few lateral connections to be reconnected within a
replacement section.
• The existing pipe is structurally deteriorated.
• Additional capacity is needed.
For pressure applications, a 41 percent increase in the inside pipe
diameter doubles the cross-sectional area of the pipe and consequently
doubles the flow capacity of the pipe. For gravity applications, after
some algebraic manipulation to the Chezy-Manning equation
[Eq. (6.1)], it is shown that a 15 and 32 percent increase in the inside
diameter of the pipe combined, with the smoother pipe surface
can produce a 100 and 200 percent increase in the flow capacity,
respectively.