TBM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 680

the extreme wear of the machine components, repeated extensive maintenance and
repair became necessary and the expected lifetime of the TBM, especially that of
the cutterhead, was reduced.
2. A complete annular gap grouting could not be achieved in the majority of cases.
Instead, the grout was washed out in the area of water bearing joints, such that
channels were formed. This led to a high water inflow into the tunnel from the area
behind the shield in the order of 100 l/s. The water inflow into the temporary face
and machine area amounted to approx. 5 to 10 l/s, resulting in a total inflow of
around 125 l/s (Fig. 21.17). Thus, it was difficult to cope with the maximum water
inflow requested by the environmental court, which led to standstills of heading
forced by the respective control, and which forced the use of closed mode opera-
tion with the corresponding higher wear.
Figure 21.17 Wash-out of annular gap grout and water inflow (Lundman et al. 2009)
21.2.5 Reasons for the Delay and Cost Increase
On the basis of the ground conditions described in the contract documents three-di-
mensional FE analyses were carried out by WBI to prove the subsequently described
effects which, however, could also be derived without such analyses from the conditions
described and on the basis of a profound rock mechanical experience and knowledge.
With regard to the problems described in Section 21.2.4, the analysis results clearly
show the following effects:
1. Because of the high intact rock strength an essential pre-condition for the instabi-
lity of the temporary face is a discontinuity system allowing the formation of rock
wedges, that is, a sufficiently small spacing and large persistence of the discontinu-
ities. According to the results of mapping, steeply dipping joints with varying ori-
entation and gently dipping schistosity-parallel discontinuities have to be expected