Civil Engineering Reference
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Figure 5.5 shows the result and back analysis of a triaxial creep test carried out with a
confining stress of
σ
3
= 15 MPa and six deviatoric stress levels
Δσ
=
σ
1
-
σ
3
. The
Δσ
level
second to last represents an unloading. During the first five
levels only primary and
secondary creep deformations occurred. At the last and highest level (
Δσ
= 22 MPa)
very large strain rates representing tertiary creep followed by a creep failure were meas-
ured. The comparison of the strains back analyzed with the parameters given in Fig. 5.5
and the measured values yield good agreement between measurement and back analysis
(Kiehl et al. 1998, Wittke 2000b).
Δσ
Figure 5.5
Back analysis of a multi-stage triaxial creep test including unloading on rock salt using the
stress-strain law of WBI (Kiehl et al. 1998, Wittke 2000b)
In a 500 m deep drift of a salt mine near Morsleben, Germany, the so-called “Wetter-
strecke” (ventilation drift) was excavated. After excavation horizontal and vertical rela-
tive displacements
δ
V
of the drift's walls were measured (Fig. 5.6). After a period
of approximately 3 years, displacements of approximately 35 mm were monitored in
both directions. The parameters with which the monitoring results could be back ana-
lyzed using the finite element method (FEM, see Chapter 10) do not significantly differ
from those obtained from the results of the creep tests (cf. Figs. 5.4 - 5.6).
δ
H
and
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