Environmental Engineering Reference
In-Depth Information
Figure 3.6
.
Example of a three-dimensional calculation in non-linear viscosity:
the Chlöwena landslide in Switzerland, 1994 [VUL 96]
To complicate matters, the natural variability of the materials implies a major
uncertainty. It has been shown by statistical studies on samples of
a priori
homogenous soils that the standard deviation of the cohesion is in the order of half
the mean, and that of the angle of internal friction is in the order of one-tenth of the
mean.
In conclusion, the instability threshold (corresponding to a global safety factor of
F = 1
) cannot be determined precisely, but only approximated. Values of safety
factors below
F = 1.1
already often correspond to a critical situation where slow
movements can be observed. “Stability” in its engineering sense is generally
accepted for
F
varying between 1.3 and 1.6.
3.3.2.
Infinitely long slope
The simple case of an infinitely long slope is very useful in practice, because the
geometry of certain natural slopes corresponds roughly to these conditions (see
Figure 3.7). We will suppose, in addition, that the flow is parallel to the slope.
