Dealing with corners and changing geometry - The Boundary Element Method with Programming - page 340

may also change. An example is the modelling of a tunnel excavation process 6 . Here the
domain is assumed to be of infinite or semi infinite extent and only the boundary of the
tunnel has to be meshed by elements.
Figure 12.10 Example for a staged excavation process in 3D (only half of the mesh shown)
As shown in Figure 12.10 the multiple region BEM 7 is used to model the excavation.
In tunnelling with the New Austrian Tunnelling Method, excavation advances in steps of
several meters, either by excavating the full cross section or parts of it. In the example
shown in Figure 12.10 a two stage excavation (top heading and bench) is shown. Figure
12.11 illustrates how excavation is modelled with a multi-region BEM.
Figure 12.11 The steps in modelling excavation
The volumes of material to be excavated are discretised by boundary elements and
represent boundary element regions in a multi-region analysis. According to the multi-
region algorithm explained in the previous chapter, stiffness matrices are calculated for
each region separately. Each excavation step is simulated by the deactivation of a region.