Civil Engineering Reference
In-Depth Information
Figure 8.20
Irrigation of the invert of the test gallery
Fig. 8.21 shows the FE-mesh used for a block constructed according to the principle of
resisting support. Since the vertical plane through the axis of the gallery represents a
symmetry plane, only one half of the gallery is modeled by finite elements. The bound-
ary conditions specified in Fig. 8.21 are selected for the stress-strain analysis. On the
upper boundary a surface load is applied, simulating the overburden up to the ground
surface. On the other boundaries, sliding supports or fixed bearings are specified.
Figures 8.22 - 8.25 show the essential results for the block carried out according to the
principle of resisting support.
In Fig. 8.22, the vertical stresses on the bedding-parallel discontinuities and the perme-
ability of the rock mass in the horizontal direction underneath the invert of the gallery
are represented, which were calculated for the state after excavation of the gallery and
before installation of the internal lining. As a result of excavation and unloading and
the corresponding opening of the discontinuities, a loosened rock zone is formed that
leads to an increase in permeability from the original 10
-9
m/s up to
10
-6
m/s.
Figure 8.23 shows the corresponding results after installation of the internal lining,
irrigation and 20 years of swelling. Near the boreholes, where water can permeate into
the rock mass, the vertical stresses increase considerably up to 6 MPa due to swelling,
and permeability decreases from 10
-9
m/s to
≥
10
-11
m/s. Between the boreholes and at
greater distance from the boreholes the rock mass remains dry and the stress state and
the permeability do not change significantly compared with the state before swelling.
Thus, in the irrigated areas swelling has led to a self-sealing of the rock mass.
≤
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