Permeability and Seepage Flow - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 133

where

and

(6.11)

is referred to as “permeability coeffi cient” of the discontinuity.

Figure 6.6 Kinematic viscosity of water as a function of temperature (Wittke 1990)

Discontinuities encountered in nature usually are not smooth as it has been assumed
so far. The hydraulic roughness of the discontinuity's walls is described by a relative
roughness, defi ned as the quotient of the maximum roughness amplitude k of the dis-
continuity, which is also known as “absolute roughness”, and the hydraulic diameter
D h . The latter is proportional to the ratio of the cross-sectional area A and the wetted
perimeter P of the discontinuity (Fig. 6.7, upper):

(6.12)

(6.13)

In (6.12) w is the width determining the wetted perimeter P of the discontinuity which
can be selected arbitrarily and

is the aperture averaged over the entire surface of

the discontinuity.