Finite Element Method (FEM) - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 277

Figure 10.52 Seepage flow analysis for a dam, FE-mesh and boundary conditions, view from upstream
Figure 10.53 Seepage flow analysis for a dam, FE-mesh and boundary conditions, view from
downstream
Special cases of Dirichlet boundary conditions are the phreatic surface and the seepage
surface. The piezometric head of all nodes lying on the phreatic and the seepage surface is
equal to their geodetic height (h = z). The extent of the seepage surface as well as the loca-
tion of the phreatic surface are usually unknown at the beginning of the analysis and have
to be determined iteratively as described in detail in Wittke (1990) and Wittke (2000b).
In a transient seepage flow analysis, time-dependent Dirichlet boundary conditions re-
ferred to as “piezometric head hydrographs” and time-dependent Neumann boundary
conditions denoted as “flow hydrographs” can also be introduced. Flow hydrographs
may be applied, for example on the surface of the computation section as flow rates due
to precipitation.