Page 362 - Trenchless Technology Piping Installation and Inspection

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• Water table and dewatering operations
• Load on the face of TBM
• Operational interruptions
• Overcut size
• Lubrication
• Alignment and/or grade corrections
• Intermediate jacking stations

4. If the operation is interrupted by more than a few (8) hours,
the jacking force required to install the remained of the pipe
may increase up to 20 to 50 percent of the original jacking
force estimate.

Figure 8.2 suggests a checklist for inspection of pipe-jacking
operations.

8.2 Microtunneling

8.2.1 Introduction
The work for microtunneling methods generally includes jobsite
planning and mobilization, construction of drive (jacking) and exit
(receiving) shafts, and simultaneous tunneling and jacking of the
pipe sections. After completion of the microtunneling operation, the
work continues for service lateral connections, construction of man-
holes over the drive and reception shafts, and all other necessary
related work items, such as site restorations.
Microtunneling is a remotely controlled, laser guided, pipe jack-
ing operation that provides continuous support to the excavation
face. Theoretically, pipes of 12 to approximately 90 in. or even more
can be installed using microtunneling. The process starts with jacking
of a microtunnel boring machine (MTBM) and pipe sections from a
jacking shaft (Fig. 8.3) to a reception shaft. The machine has a closed
faced shield. Figure 8.4 illustrates the front and back of a microtun-
neling machine.
Excavated soil is removed using auger removal system or hydraulic
removal system with slurry fluid (more common), which also
counterbalances groundwater and earth pressures. The MTBM is
guided by a laser or other survey device mounted in the jacking shaft,
which projects a beam onto a target in the articulated steering section
of the MTBM. The MTBM is steered by extending or retracting
remotely controlled steering jacks. Figure 8.5 illustrates the schematics
of microtunneling operation.
Most of the microtunneling machines are equipped with a cone
crusher. They are designed in such a way that cobbles, boulders, and