Page 29 - Trenchless Technology Piping Installation and Inspection

4 Cha pte r O n e

carbon emissions due to higher fuel consumptions), safety hazards
of trenching (cave-in hazards, traffic accidents, falls into trench, and
so on), damage to trees and tree roots, reduction in service life of
∗
pavement, and possible damage to existing utilities and structures
due to trenching operations. Najafi (2005) presents a breakdown of
the social costs including an analysis of the life-cycle cost of the project.
As such, and considering all the project parameters, the open-cut
method in most cases could be a time-consuming and inefficient
method of pipe installation.
Trenchless technology is a process for construction, renewal,
and replacement of underground pipelines and utilities with mini-
mal surface and subsurface disruptions. Trenchless technology
methods provide more opportunities for direct installation of pipe-
lines and ducts with welded and fused or bell and spigot and
retrained joints, thereby, reducing possibilities of leaks and joint
misalignments and settlements. Jacking pipes, commonly used in
trenchless installation, have higher degree of accuracy, which
requires the installation by specialized and qualified contractors.
Due to the larger wall thickness requirements, higher strength mate-
rials, and lower tolerances requirements, jacking pipes have a higher
resistance to stresses due to shear loads. The pushing-in of the jack-
ing pipes guarantees a higher positional accuracy and a lower dis-
turbance of the natural soil in the embedment area so that optimum
bedding is achieved.
Another important benefit of trenchless technology is the fact
that in open-cut method, through the soil prism above the pipe,
soil backfill and traffic loads act directly on top of the pipe, caus-
ing pipe deflections in flexible pipes and more stress in rigid pipes.
In comparison, studies have shown that due to arching effects of
soil in trenchless technology installations, the loads on the pipe
are considerably less and more uniformly distributed around the
pipe surface, resulting in minimum pipe deflections. Figure 1.2
illustrates a comparison of pipe loads in trenchless and open-cut
methods.
Trenchless installation methods significantly reduce the amount
of excavation, backfilling, compaction, and pavement replacement.
In the trenchless installation method, the most costly item is the pipe
installation, usually estimated on a linear foot basis, while in the
open-cut method excavation, backfilling, pavement replacement, and
shielding or shoring are the major cost items and are estimated on a
cubic yard or square foot basis.

∗ Studies have shown approximately up to 60 percent reduction in the life of
pavement due to lateral cracking after pavement cuts.