Environmental Engineering Reference
In-Depth Information
The distortions are concentrated in these shearing zones (also called sliding or
failure surfaces ), for which the laws of plastic materials are generally used. Such
failures can lead to movements of several meters in very little time (minutes or
hours), followed in general by a new state of equilibrium.
Figure 3.1 . Categories of movement: a) creep; b) slide; and c) flow
The third category concerns the flow of loose material, often with water, over
comparatively great distances from the area of departure: debris flows, mudflows,
etc. The velocities reach several meters per second and the distances covered can be
many kilometers. Fluid dynamics come into play here, as covered elsewhere in this
topic.
In reality, a juxtaposition of several mechanisms is often observed, as well as the
presence of multiple sliding surfaces. In addition, the geometry is three-dimensional,
the lithology complex and the hydro-geological conditions complicated. Figure 3.2
presents the profiles of a complex slide. Such slides remain a challenge for current
methods of slope stability analysis.
The causes of movements have several origins, including the action of gravity or
of earthquakes, variations in hydro-geological conditions, erosion by rivers at the
bottom, overload at the top by rock falls, evolution at a geological scale (glacial
retreat, tectonic movements), and anthropogenic action.
This chapter will be limited to the treatment of three types of analysis, namely
the modeling of slopes in slow movement (creep), the calculation of a safety factor
for the case of slopes that could potentially slide, and the impact of non-saturation
on behavior.
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