Rock slope analysis on the complex Livorno coastal cliff (Tuscany, Italy)

Abstract

The landscape of the south coast of Livorno city (Tuscany, Italy) is characterized by sandstone headlands and sandy pocket beaches affected by serious stability problems. Lithological features and physical-chemical processes involve many slope failures concerning the sandstone cliff and extending all over the cliff height; these failures often threaten people and facilities. The most prominent positive relief landform is structurally controlled by three main closely spaced joint sets. The presence of leaning and collapsed rock blocks suggests that erosion and mass wasting maintain the cliff steepness and elevate risk conditions. The sandstone mechanical properties and discontinuity pattern have been investigated in order to determine the response of the rock mass to subaerial and marine stresses. The sandstone outcrops were characterized according to the Rock Mass Rating (Bieniawski, 1989) and the Slope Mass Rating (Romana, 1985; 1993). Such data has been reported in a GIS system in order to determine the landslide susceptibility of the cliff. Some numerical modelling, with a code at Distinct Element Method model, were carried out to evaluate stresses and displacement distribution near the free surface of a steep slope face, as a function of steepness, dip direction and rock mass quality. Then some fall simulations were carried out, to make a back analysis of previous events and to obtain a more general outline of possible movements. The results showed that rock mechanics and computer modelling can be effective tools in predicting the rock-mass stability, determining the mechanism by which blocks fall from steep slopes and their possible trajectories.