Structural design verifications, structural analysis of tunnels - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 115

Figure 3-16 Numerical
model of the movement
slot [236].

A further important property is the sliding process between the shotcrete layer fixed to the
rock mass by rock bolts and the rock mass. The sliding elements described here, which are
also based on the theory of decoupled finite elements, can also describe this process very
well by using a Coulomb failure criterion.

For the modelling of the shotcrete shell, a beam element is used, which delivers normal
forces, moments and shear forces without subsequent integration of stresses.

3.7.2 Determination of the loosening of the rock mass from blasting
Another possible application of FEM in tunnelling is described in [237]. This is a calcula-
tion model intended to provide the first method of considering the changed load-bearing
of the rock mass due to drilling and blasting.
The particular feature of this application is the fact that a dynamic loading has to be simu-
lated, which propagates in waves in the continuum. For example the wavelength and the
reflection of the waves at the edges have to be considered in the discretisation. Since, for
example, reflection at the edge of the discretisation can influence the results of the calcula-
tion, elements were included at the edge to simulate viscous damping. Fig. 3-17 shows the
modelling of a wedge cut, and Fig. 3-18 shows the entire FE mesh with the configured load
function of the blasting effect and the stress curves as result, each plotted against time.

Figure 3-17 Wedge cut with FE
model [237].

Figure 3-18 Stress curves with FE mesh [237].