TBM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 700

Figure 21.38 shows the calculated principal normal stresses and the zone in which the
strength of the discontinuities is exceeded, representing the disturbed rock zone, in a
longitudinal section (plane x = 0) and a cross-section located in the middle of the un-
supported machine area (cross-section 1-1), respectively. In Fig. 21.39 calculated nor-
mal and shear stresses in horizontal sections represented in the longitudinal section
(plane x = 0) are plotted. The load-carrying action of the rock mass in the unsupported
machine area is clearly visible in these figures.
Figure 21.38 Principal normal stresses and disturbed rock zone, computation step 3
The maximum displacement in the unsupported machine area amounts to 13 mm (Fig.
21.40, left) and the viscoplastic displacements converge (Fig. 21.40, right). Thus, the
tunnel can be considered as stable. Since the displacements are sufficiently small, the
steering gap between shield and rock mass remains open and so the shield skin is not
loaded by the rock mass.