Page 34 - Trenchless Technology Piping Installation and Inspection

New Pipeline Installations 9

New installation
methods

Conventional pipe jacking Utility tunneling Horizontal Earth boring

FIGURE 1.5 Trenchless installation methods.

removed and a new pipe is installed in its place. In the inline replace-
ment method, the existing pipe acts like a pilot hole to guide the
installation of the new pipe in the same space as the existing pipe
occupied originally. It is understood that sometimes point repairs
may be required before a renewal or replacement method can be
used. Many times, most cost-effective new installation, renewal, or
replacement may include utilization of several trenchless methods to
adapt to the specific conditions of the project. For a safe, successful,
and cost-effective trenchless operation, certain conditions and require-
ments must be met as explained in this book.

1.6 Trenchless Installation Methods
Trenchless installation methods include all the methods of installing
new pipelines or utility systems below ground surface without direct
installation into an open-cut trench. As Fig. 1.5 illustrates, trenchless
installation methods are further divided into two broad categories of
worker-entry and nonworker-entry installations. Conventional pipe
jacking (CPJ) and utility-tunneling (UT) techniques require workers
inside the tunnel during the excavation and pipe installation. How-
ever, horizontal Earth-boring methods includes techniques in which
the tunnel or borehole excavation is accomplished through mechanical
means without workers being inside the tunnel or borehole. Conven-
tional pipe jacking is differentiated from utility tunneling by the soil
support structure. It can be identified as a “one-phase” installation,
where pipe sections are installed at the same time when soil excavation
is made. In utility tunneling, first the tunnel is excavated and lined
with a tunnel liner plate or wood lagging and steel ribs. After comple-
tion of the tunnel, the pipe sections are “transported” one by one and
installed in the tunnel. After all pipe sections are installed, the annual
space between the liner and the outside face of the pipe may be grouted.
Both conventional pipe jacking and utility tunneling may utilize the
same excavation equipment [such as a tunnel boring machine (TBM)].

1.6.1 Conventional Pipe Jacking
Conventional pipe jacking (PJ), a method of pipe installation where
prefabricated pipe sections are jacked or pushed behind the tunnel
boring machine or other tunnel excavation methods. In this method,