TBM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 713

Figure 21.56 Proof regarding the tensile splitting at the circumferential joint, loads due
to jacking forces (Wittke et al. 2006)
21.5.2 Loading and Bedding of the Segmental Lining
Loading and Bedding Approaches
In recent years, TBM driven tunnels in sedimentary rock have been carried out more
frequently by means of a single segmental lining. However, the loading and bedding
approaches that have been applied for many years to TBM headings in soil are often
transferred to rock without critical consideration (DGGT 1995, ERCT9 1997). These
approaches assume that the segmental lining along its entire periphery is loaded and at
least partly bedded by the ground (Fig. 21.57). This implies that the tunnel after excava-
tion is not stable without support.
In rock, however, the tunnel may be stable in the machine area and also in the area
behind so that the segmental lining remains largely unloaded. If, in such a case, the
grouting of the annular gap is carried out too late, the segmental ring is loaded only by
its self-weight and remains unbedded.