TBM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 699

This rock mass has a high swelling potential, as was discussed in detail in Chapter 8.
Thus, not only the stability of the unsupported rock mass but also the extent of the
disturbed rock zone formed around the tunnel due to excavation, which may lead to
an increase in permeability of the rock mass and thus to accessibility of water, is of
special interest. For this purpose, the excavation of a tunnel with a diameter of 10 m
and an overburden height of 225 m located in unleached Gypsum Keuper excavated
using a TBM with a 10 m long shield was simulated by means of a three-dimensional
FE analysis.
Figure 21.36 shows the 59 m long, 25 m wide and 70 m high FE-mesh. Since the verti-
cal plane through the tunnel axis forms a symmetry plane only one half of the tunnel
cross-section is discretized.
Figure 21.37 Computation steps
The analysis was carried out in three computation steps. After simulating the primary
state in the first step of analysis, the excavation of the tunnel and the installation of the
segmental lining over a 19 m long section were modeled in the second step. The excava-
tion of a 10 m long unsupported section representing the machine area was simulated
in the third step (Fig. 21.37).