Permeability and Seepage Flow - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 152

where k jn is the mean permeability of layer j normal to layer j. In the example illustrated
in Fig. 6.18 three horizontal layers are considered and (6.47) is derived for this particu-
lar case (Wittke 2000b).
If a coordinate system is selected in which the z axis is directed vertically, the equivalent
permeability tensor of a rock mass consisting of a sequence of N horizontal isotropic
homogeneous layers is composed of the permeability coeffi cients (6.46) and (6.47) as
follows:
(6.48)
Transient seepage fl ow
The continuity condition, which is equivalent to the principle of mass conservation, in
consideration of Darcy's law leads to the following equation of transient seepage fl ow
(Wittke 2000b):
(6.49a)
or in a more compact matrix form
(6.49b)
where S 0 is the so-called “specifi c storage coeffi cient” defi ned as