Page 37 - Trenchless Technology Piping Installation and Inspection

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FIGURE 1.8 Open hand shield. (Source: Pipe Jacking Association.)

Open shield excavator tunnel boring machine (TBM) is an open
face shield in which a mechanical excavator is mounted for excava-
tion purposes. Figure 1.9b shows the excavator tunnel boring
machine
Closed shield is divided into two categories, i.e., worker entry oper-
ation and microtunneling remote operation. Worker entry operation
is further divided into three categories which are defined as follows:

1. Earth-pressure balance machine (EPBM): A full face tunnel bor-
ing machine in which the excavated material is transported
from the face by a balanced screw auger or screw conveyor.
The face is supported by excavated material held under pres-
sure behind the cutter head in front of the forward bulkhead.
Pressure is controlled by the rate of passage of excavated
material through the balanced screw auger or valves on the
screw conveyor. Figure 1.10a shows the worker entry EPM
machine.
2. Slurry machine: A soft ground full face tunnel boring machine
in which the excavated material is transported from the face
in a slurry. Various cutting heads are available to suit broad
range of ground conditions. The pressure of slurry is used to
balance the ground face pressure. Figure 1.10b shows the
worker entry slurry machine.