Swelling Rock - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 195

ed by Equation (6.62). However, this requires an estimation of the mean discontinuity
apertures. Because of the difficulty of direct aperture determination, the apertures need
to be calculated from measured permeability coefficients using Equation (6.27) or (6.28),
respectively (Section 6.4).
If the shear strength on discontinuities is exceeded, dilatant displacements, which are
described by dilatancy angles

ψ J , respectively (Figs. 8.10 and 8.11, upper left),
lead to an opening of the discontinuities

ψ B and

2a iJ , respectively, and thus to an
increase of the rock mass permeability (Section 7.3.2, Fig. 8.10, upper right and lower
right). For tensile stresses normal to the discontinuities an opening of the discontinui-
ties and a corresponding increase in the rock mass permeability also occurs.

Δ 2a iB and Δ

Seepage flow and water uptake are described and coupled by Equations (8.8) and (8.9)
and controlled by

ω (Fig. 8.11, lower right).

Figure 8.11 Coupled model of stress-strain behavior, dilatancy, seepage flow, water uptake and swelling

Water uptake of the intact rock leads to swelling strains which are dependent on and

the state of stress as described in Section 8.4 (Fig. 8.11, lower left). For a stiff tunnel
lining the volume increase due to swelling is confined, which would lead to a build-up

ω