Permeability and Seepage Flow - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 150

The equivalent permeability tensor of a rock mass composed of a sequence of N homo-
geneous layers of different permeability can be analytically described by expressions
derived by Terzaghi & Jelinek (1954) for layered soils.
Assuming steady-state, laminar fl ow and isotropic permeability of each layer the re-
lationship for the equivalent permeability = of the rock mass parallel to the
layers is obtained from the condition that the hydraulic gradient is equal in each layer:
(6.46)
where k jp is the equivalent permeability of layer j parallel to layer j and d j is the mean
thickness of layer j. Figure 6.17 shows an example of a rock mass with three horizontal
layers (Wittke 2000b).
Figure 6.17 Equivalent horizontal permeability of a rock mass composed of a sequence of horizontal
layers (Wittke 2000b)