Initial topography and inherited structural discontinuities are known
to play a dominant role in rock slope stability. Previous 2-D physical
modeling results demonstrated that even if few preexisting fractures
are activated/propagated during gravitational failure all of those
heterogeneities had a great influence on mobilized volume and its
kinematics. The question we address in the present study is to determine
if such a result is also observed in 3-D. As in 2-D previous models
we examine geologically stable model configuration, based upon the
well documented landslide at Randa, Switzerland. The 3-D models consisted
of a homogeneous material in which several fracture zones were introduced
in order to study simplified but realistic configurations of discontinuities
(e.g. based on natural example rather than a parametric study). Results
showed that the type of gravitational failure (deep-seated landslide
or sequential failure) and resulting slope morphology evolution are
the result of the interplay of initial topography and inherited preexisting
fractures (orientation and density). The three main results are i)
the initial topography exerts a strong control on gravitational slope
failure. Indeed in each tested configuration (even in the isotropic
one without fractures) the model is affected by a rock slide, ii)
the number of simulated fracture sets greatly influences the volume
mobilized and its kinematics, and iii) the failure zone involved
in the 1991 event is smaller than the results produced by the analog
modeling. This failure may indicate that the zone mobilized in 1991
is potentially only a part of a larger deep-seated landslide and/or
wider deep seated gravitational slope deformation.