Page 373 - Trenchless Technology Piping Installation and Inspection

Inspection and QA/QC for Trenchless Installation and Replacement Methods 323

and pipe diameters experienced in an evaluation program. These
jacking load curves can only be used as a guide (rough order of mag-
nitude) and comparison purposes for different pipe diameters and
soil conditions, and cannot be used for estimating jacking loads on an
actual project. It should be noted that the actual jacking loads may
fluctuate during pipe installation but will increase as jacking distance
increases.
Figure 8.12 suggests a checklist for inspection of microtunneling
operations.

8.3 Pilot-Tube Microtunneling

8.3.1 Introduction
Pilot-tube microtunneling (PTMT) is a hybrid version of conventional
microtunneling. Pilot-tube microtunneling combines the accuracy of
microtunneling, the steering mechanism of a directional drill, and
the spoil-removal system of an auger-boring machine. PTMT
employs augers to transport spoil and a guidance system that
includes a camera-mounted theodolite. The target uses electric
light-emitting diodes (LEDs) to secure high accuracy in line and
grade. When project conditions are suitable, pilot-tube microtun-
neling can be a cost-effective tool for the installation of small-
diameter pipes of sewer lines or water lines. This technique can also
be used for house connections direct from the main line sewers.
Typically, pilot-tube machines can be used in soft soils and at rela-
tively shallow depths. Jacking distances of 500 ft have been accom-
plished with newer guidance systems.
PTMT requires various components to function simultaneously
for a successful installation. The integration of these components
with each other plays a key role in productivity of a PTMT installa-
tion. Discussed below are the important components of PTMT.
8.3.2 Design of the Pipe
Design of the pipe must include the following:

1. Service loading of the pipe: The permanent (service) loading of
the pipe for the specified designed life including, but are not
necessarily limited to internal operating, transient and test
pressures, soil overburden, surface loads, and external static
water head. The installation loads that the pipes would be
subjected to, which include but are not limited to, jacking
forces, external pressure from groundwater, soil loads, sur-
face loads, and annular space lubrication injection.
2. Pipe diameter: The pipe diameter is determined by the capac-
ity of flow required. After the diameter and material of the