Environmental Engineering Reference
In-Depth Information
Figure 3.12.
Test on a reduced model: field of displacement
These tests have made it possible to validate the newly-designed computer code
and then to conduct parametric studies on the impact of non-saturation on the
behavior of slopes. In the case where the instability is caused by a supply of water in
the interior of the mass, which often corresponds to reality, it is no longer so much
the slope of the terrain that is the determinant, but the subtle interplay of all the
constitutive parameters. In addition, it is the transitory dimension of the
phenomenon that has to be considered to explain the triggering of instability.
In more detail, it has been noted that:
- the geometric permeability K affects not only the moment when the instability
is triggered, but also the form of the mechanism;
- the shape of the suction curve (
S
r
−
s
) affects the soil response. A highly
contrasting curve (abrupt transition from complete saturation to low saturation)
causes an abrupt mass response, while a more gentle curve (in a clay soil, for
example) somehow cushions the response of the slope;
- the type of material law for the solid skeleton very obviously influences the
calculated displacement field, even its the influence on the pore-water pressure field
is weak;
- the initial position of the piezometric surface (
u
w
=
0) affects the response
because it defines the thickness of the non-saturated zone; it has been shown that the
most critical case is reached for a piezometric surface located at a certain depth. In
this case, the non-saturated layer somehow plays the role of a “waterproof cover”
under which interstitial under pressures develop;
- the shape of the hydrograph (the temporal distribution of the water supply)
plays a major role. In effect it is not the hydrograph leading to a maximum volume
of water injected into the terrain that leads to the most critical cases, but rather one
