Monitoring of the movements of a deep, slow, clayey landslide and 3D interpretation

The Costa della Gaveta landslide is an active, deep and very slow landslide which is being monitored and studied since 2004. Recently new boreholes have been carried out and inclinometer tubes have been installed to deepen the comprehension of the 3D geometry and kinematics. Localized displacement on a slip surface is confirmed to be the prevailing movement mechanism. Thanks to the long term monitoring, even the slow internal viscous deformations of the landslide body have been evaluated and interpreted. Soil discharge (i.e., the volume rate of soil crossing transversal sections) is confirmed to be constant in the track. This characterizing kinematic feature allows a first approximation prediction of the landslide behaviour on empirical basis. To further improve the prediction of the landslide behaviour and the risk management of the area, a theoretical model has been constructed by a 3D finite element code. First results show the large difference in the safety factor between 2D and 3D analyses for the considered landslide. The influence of pore pressure distribution on the local safety factor is also analysed.