TBM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 724

Conclusions
The loading and bedding of the segmental lining of a machine-driven tunnel in rock
may be completely different from in soil. This particularly applies to a sedimentary
rock with horizontal bedding-parallel discontinuities and vertical joints in which the
horizontal in-situ stress component normal to the tunnel axis is small. The design of
a single segmental lining for a tunnel driven in such a rock mass therefore requires a
realistic consideration of the interaction between the rock mass and the segmental ring
which can best be accomplished using the FEM but cannot be accounted for with con-
ventional approaches applied to tunnels in soil (Fig. 21.57). By means of examples, it
has been shown that the shear strength of the discontinuities and Young's modulus of
the annular gap grout have a considerable impact on the loading of the segmental ring.
Low shear strength on the steeply dipping joints and a low modulus of the mortar are
unfavorable for the loading and bedding of the segmental lining.