Permeability and Seepage Flow - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 147

Figure 6.15 Rock mass with persistent horizontal bedding-parallel discontinuities and vertical joints of
negative exponential spacing ending at the bedding (Doolin & Mauldon 2001)

When the individual values of these quantities are replaced by the mean values ,

, and , k yy can be calculated as

(6.40)

The permeability parallel to the bedding can be expressed by

(6.41)

Equation (6.40) refl ects connectivity of joints and bedding-parallel discontinuities while
(6.41) corresponds to (6.28). c is a factor depending on the distribution of the joints'
spacing (Doolin & Mauldon 2001). If the latter is constant then c = 2 is valid. c = 4 ap-
plies if the spacing of the joints follows a negative exponential distribution (cf. Section
13.9.2) which has been validated in a large number of discontinuity measurements in
the fi eld (Priest & Hudson 1976, Beacher et al. 1977, Hudson & Priest 1979, Priest &
Hudson 1981, Wittke 1990).
If , the permeability k yy normal to the bedding is dominated by the
permeability k J of the joints and can be approximated by (Doolin & Mauldon 2001)

(6.42)

In this case the connectivity of joints and bedding-parallel discontinuities can be neglected.
If , k yy is controlled by the permeability k B of the bedding-paral-
lel discontinuities. In consideration of (6.41) k yy can be approximated by (Doolin &
Mauldon 2001)