TBM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 670

Since the shield and thus the segmental lining are not positioned perfectly centrically
with respect to the excavated cross-section the actual location and width of the annu-
lar gap may deviate from the theoretical position illustrated in Fig. 21.7. In addition,
deformations of the rock mass and the segmental lining lead to varying widths of the
annular gap.
The annular gap is grouted with mortar to keep the bending moments and the deforma-
tions of the segmental lining small by means of attaining sufficient bedding. Between
the shield skin and the segmental lining a tail skin sealing is mounted to avoid leakage
of the mortar into the machine area (Fig. 21.7).
If there is excess excavation above the roof, there is a risk that mortar will penetrate
into the steering gap and also into the area of the cutterhead (Fig. 21.9). If the mortar
hardens within the steering gap this can lead to clogging of the shield skin and thus to
heading impediments.
Figure 21.9 Bypassing of a shielded TBM caused by excess excavation above the roof
(Wittke et al. 2006)
21.1.3 GripperTBM
A Gripper TBM (Fig. 21.10) is suitable for application in a rock mass in which a sup-
port of the excavated cross-section in the area of the temporary face and of the machine
is not required or may be achieved with minor efforts, such as rock bolts, steel sets and
shotcrete, applied locally at the tunnel roof.