Permeability and Seepage Flow - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 128

In unjointed rock such as tuff or rock salt (Section 2.7.1, Figs. 2.19 and 2.20), the poros-
ity of the intact rock may lead to a permeability k IR that cannot be neglected (Fig. 6.1,
center). Then we talk about a “pore aquifer”.

Figure 6.2 Joint aquifer

In some highly porous sedimentary rocks containing voids such as pores, capillaries and
cracks the permeability of both the intact rock and the discontinuities must be account-
ed for (Fig. 6.1, right).

6.2 Porous Intact Rock

6.2.1 Porosity
In general, all intact rocks contain a proportion of voids. To be relevant for permeabili-
ty and to allow seepage fl ow, at least part of these voids must be interconnected to form
passages through which water can permeate. From a hydraulic point of view therefore
a distinction must be made between (a) the total proportion of voids including isolated
pores and pores fi lled with capillary bounded water, which is not hydraulically effective
(total porosity) and (b) the proportion of interconnected, hydraulically effective voids.
The latter is referred to as “effective porosity”, also called “open porosity”.
Total porosity is defi ned as

(6.1)