Finite Element Method (FEM) - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 282

Figure 10.58 Groundwater level versus time (Wittke 2000b)
The specific storage coefficients of S 0 = 0.03 m -1 assumed in the analyses (Fig. 10.56)
was estimated from relative joint volumes and layer thicknesses (Section 6.4.2).
The FE-mesh and the boundary conditions are represented in Fig. 10.54. The plane of
symmetry (y = 0) as well as the planes z = 0 and x = 0 were assumed to be impermeable.
A piezometric head of 38.7 m corresponding to the height of the groundwater table was
assigned to the nodes located on the planes x = 800 m and y = 400 m. As initial condi-
tion, a piezometric head of 38.7 m was assigned to all nodes. The phreatic surface was
determined with the aid of an iterative analysis (Fig. 10.54).
It is assumed that the tunnel is excavated up to the plane x = 400 m. In cases 3 and 4,
seepage water can flow into the tunnel via the temporary face and through the shotcrete,
whereas in cases 1 and 2, with impermeable shotcrete, seepage water is allowed to flow
into the tunnel only via the temporary face.