Civil Engineering Reference
In-Depth Information
11.5.2.3 Tunnel boring machine with shield (TBM-S)
For rock with a short standup time or in rock liable to rockfall, tunnel boring machines are
fitted with a shield skin. In this case, installation of the lining in the protection of the shield
skin is appropriate (segments, pipes etc). As it advances, the machine can support itself off
the lining, so the gripper equipment is usually omitted. Otherwise, the statements already
made about tunnel boring machines apply correspondingly.
11.5.3 Double shield machines (DSM)
Double shield machines (DSM) consist of two parts one behind the other. The front part
is equipped with the cutterhead and the main thrust cylinders, and in the back part are the
auxiliary cylinders and the grippers. The front part of the machine can be extended for-
wards from the back part by a complete ring length with a telescoping mechanism.
In a stable rock mass, the grippers resist the torque and the thrust forces during advance.
The back part of the machine is securely fixed by the grippers and the assembly of the
segment ring can continue as the machine advances. In stable rock, the installation of seg-
ments may not be necessary.
In an instable rock mass, in which the grippers cannot grip adequately, the advance can be
supported from the last ring of segments. The front and back parts of the machine in this
case are telescoped together and the thrust forces are transferred to the segment ring by
the auxiliary cylinders.
It is usually not possible to provide active support to the face and the excavated sides of
the tunnel.
The rapid advance of the back part of the machine to reposition the grippers after the com-
pletion of a boring stroke means that the rock mass must be able stand up without support
until the annular gap has been fully grouted or filled with pea gravel.
11.5.4 Shield machines (SM)
These are differentiated into shield machines for full-face excavation (with a cutting
wheel; SM-V) and shield machines for partial excavation (with a cutting head, excavator;
SM-T). Shield machines are used in soft ground above and below the groundwater table
and the ground around the excavated cavity and the face normally have to be supported.
Shield machines can be further categorised according to the type of face support (Fig. 2).
11.5.4.1 Shield machines for full-face excavation (SM-V)
Face without support (SM-V1)
If the face is stable, e.g. in clay with stiff consistency and sufficient cohesion or in solid
rock, open shield machines can be used. A cutting wheel fitted with excavation tools ex-
cavates the ground and the excavated material is cleared on a conveyor belt.
In rock liable to rockfall, shields are mostly used, which are fitted with a largely closed
cutterhead fitted with disc cutters and fully protected from instable ground by a shield
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