TBM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 697

Figure 21.35 Case B, displacements at the temporary face and the tunnel contour (Wittke et al. 2006)

The required jacking force to overcome the skin friction between the shield and the rock
mass can be determined from σ r according to Equation (10.15). With a friction coef-

ficient between the shield and the rock mass of

= 0.274 the required jacking force to
overcome the skin friction comes to T = 98 MN (Wittke-Gattermann & Wittke-Schmitt
2004, Wittke et al. 2006). A considerable proportion of the calculated radial pressure
on the shield, however, is due to the water pressure, which does not contribute to the
friction between the shield and the rock mass.

μ

21.3.6 Conclusions
For TBM tunneling in difficult geological conditions the shield design should be carried
out with the aid of FE analyses, in order to understand and to account for the complex
interactions between rock mass and shield. Details such as the required thickness of
the steering gap can be derived from the results of these analyses. Furthermore, design
loads may be derived for the dimensioning of the shield, which is carried out by the
machine manufacturer.