Permeability and Seepage Flow - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 148

(6.43)

Thus, the connectivity of joints and bedding-parallel discontinuities has to be con-
sidered particularly if the aperture or permeability, respectively, of the bedding-parallel
discontinuities is low compared with that of the joints. In horizontally bedded and ver-
tical jointed sedimentary rock in which the bedding-parallel discontinuities are largely
closed or fi lled with cohesive soil this is often the case.
As an example, Fig. 6.16 shows the equivalent permeability tensor of a rock mass with
persistent horizontal bedding-parallel discontinuities B fi lled with cohesive soil and one
set of open vertical joints J terminating on bedding-parallel discontinuities. The super-
position of the permeability tensors of B and J yields:

(6.44a)

with

(6.44b)

(6.44c)

(6.44d)

According to (6.29), the permeability parallel to the bedding is expressed by the
permeability coeffi cient k F of the fi lling. Inserting the values specifi ed in Fig. 6.16
(k F = 10 -8 m/s, , , ) into (6.44) and
assuming a negative exponential distribution of joint spacing (c = 4) yields (Fig. 6.16)

(6.44e)

Thus, in this example the vertical permeability k zz normal to the bedding is four times
higher than the permeability k xx normal to the joints and 1.25 10 7 times lower than the

⋅

permeability k yy .