Finite Element Method (FEM) - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 239

Figure 10.14 Displacement and
force boundary conditions, tunnel
in isotropic rock mass
Distributed loads are required to simulate external loads, for example due to the weight
of the rock mass overlying the computation section. They can be simulated by equiva-
lent nodal forces representing a surface load (Fig. 10.14) or a line load in the case of a
two-dimensional analysis.
The nodes lying on the lateral and lower boundaries of the computation section are
specified to be fixed in the direction perpendicular to their respective boundary. The
plane x = 0 represents a plane of symmetry (Fig. 10.14).
For an anisotropic rock mass it is generally not admissible to fix the nodes lying
on the computation section's vertical boundary planes in the directions perpen-
dicular to the latter, since even gravity can cause displacement components in the
horizontal direction.