Field and numerical investigations of free-water surface oscillation effects on rock slope hydromechanical behaviour - Consequences for rock slope stability analyses

In order to better understand the role of groundwater-level changes on rock-slope movements, a highly fractured carbonate rock slope was extensively instrumented with surface tiltmeters and internal extensometers and pressuremeters set both at discontinuities and within rock matrix. Water level changes within the slope aquifer were controlled by opening and closing of a gate set on the aquifer spring. When a 70 kPa pressure fall is induced, complex and contrasted movements are measured. The movements are characterized by deformation magnitudes in discontinuities of 0 to 5 x 10-6 m and surface tilts of -0.6 to -4 x 10-6 rad. Analysis of field data with three different coupled hydromechanical numerical models and associated sensivity studies show that slope movements are mainly rotations at the basal saturated part of the slope linked to the hydromechanical behaviour of a few discontinuities.