Civil Engineering Reference
In-Depth Information
The drawdown curves resulting for the four different cases are plotted in Fig. 10.57 in the
vertical section through the tunnel axis (y = 0). The maximum lowering versus time is
represented in Fig. 10.58. When an impermeable shotcrete membrane is assumed (cases
1 and 2) the maximum lowering of the groundwater table is very small. In cases 3 and
4, with permeable shotcrete membrane, a significantly larger maximum lowering of the
groundwater table was computed, even when the permeability of the claystone is only
10
-7
m/s.
Thus, the permeability of the shotcrete membrane is decisive for the lowering of the
groundwater table. A shotcrete with a low permeability was therefore used, and the wa-
ter loading on the shotcrete membrane was considered in the stability analyses for the
tunnel. The tunnel was carried out with a circular cross-section using a full-face exca-
vation. By these means, the subsidence of the ground surface could be limited to values
between 4 and 7 mm that did not hinder the air traffic (Section 20.3).
10.7
FEM Program Systems and Related Modules Provided by WBI
10.7.1 Program System FEST03
Based upon the models described in Chapter 3, the finite element program system
FEST03 (Fig. 10.59, left) allows us to carry out stability analyses assuming iso-
tropic and anisotropic, elastic-viscoplastic stress-strain behavior and accounting
for discontinuity systems with user-defined orientations. Strength criteria of the
Mohr-Coulomb type with tension cut-off for soil, intact rock and discontinui-
ties are implemented. Boundary conditions and forces due to self-weight, traffic,
seepage, hydrostatic uplift, water pressure and temperature as described in Section
10.5.1 can be introduced into the analysis. In addition, construction stages and
support measures, as described in Sections 10.5.2 and 10.5.4, can be simulated. The
results consisting of stresses, displacements and stress resultants can be represent-
ed in various ways (Section 10.5.5). The calculation of stress resultants enables the
dimensioning of structural elements such as the lining of a tunnel.
The program system FEST03 has been used by WBI for more than three decades on
a great variety of rock engineering problems and has been updated several times with
respect to computational efficiency, pre- and post-processing as well as the implemen-
tation of stress-strain laws for swelling rock (SWELL1 and SWELL2) and rock salt
(SALT), which are included in the program system as separate modules. Further mod-
ules related to FEST03 are routines for dynamic time history analyses (DYN), con-
solidation analyses for cohesive soils according to Biot's theory (CON), stress-strain
analyses for cohesive soils according to the Cam-Clay model (CAM) and stress-strain
analyses accounting for geometric nonlinear behavior (HAMMOCK). All the modules
listed in Fig. 10.59 (left) allow fully three-dimensional analyses.
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