Tunneling in Swelling Rock - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 758

swelling and thus heaving due to swelling is dependent on water supply, the in-situ per-
meability of the unleached Gypsum Keuper has a considerable influence on the amount
of heaving. After 11.5 years of swelling, vertical displacements of the invert of ca. 6 cm
and 2.5 cm are calculated for in-situ rock mass permeability coefficients of 10 -6 and
10 -8 m/s, respectively (Wittke 2012a).
For comparison, the case of a tunnel constructed according to the principle of yielding
support (Section 8.8) exhibiting a highly compressible yielding zone underneath the in-
vert, which is illustrated in Fig. 23.7 was investigated (Wittke 2012a). The tunnel invert
penetrates into the unleached Gypsum Keuper containing anhydrite. The remaining
cross-section is located in anhydrite-free Gypsum Keuper (Figs. 23.7 and 23.8). These
analyses also lead to the result that the in-situ permeability of the unleached Gypsum
Keuper has a considerable influence on the amount of heaving. For a permeability co-
eficient of 10 -8 m/s the calculated heaving remains relatively small, while a permeabil-
ity coefficient of 10 -6 m/s results in a large heaving of the invert, increasing with time
(Fig. 23.9). This heaving can be considerably reduced if the disturbed rock zone under-
neath the tunnel invert is sealed after excavation of the tunnel by means of grouting
(Wittke 2012a, Figs. 23.10 and 23.11).
Figure 23.7 Anhydrite surface in
the area of tunnel invert, principle
of yielding support