ROCK MECHANICS STUDIES TO ANALYSE TOPPLING FAILURE

The study is devoted to the analysis of toppling failure of a rock slope. The rock wall is part of a quarry of ornamental stone, situated in Ossola valley (Italy). The rock mass is constituted by ortogneiss and is interested by a main set of discontinuities, the foliation. Three minor sets of joints are also present, isolating slabs and blocks, leading to flexural toppling and block flexural toppling kinematism. A face of the quarry was interested in the past by an instability phenomenon (figure 1), due to water seepage along joints and due to the height of the overhanging rock wall. This phenomenon was back analysed by a 2D numerical modelling based on the DEM (Deangeli et al., 1996). On the basis of this analysis a new stable configuration of the rock face has been verified, and the exploitation activity in this zone is exhausted. The excavation is presently moved to a zone of the quarry with the same geostructural scenery but with a lower weathering degree of the rock mass (figure 2). The exploitation planning of the future development of the quarry has been carried out by means of analytical and numerical procedures. Parametric analyses of the main structural and mechanical features of the rock mass have been set up taking into account different values of the joint spacing and dip, tensile strength and deformability of the rock matrix in different geometrical configuration of the rock face. The results of the geomechanical studies together with some insights for the interpretation of toppling phenomena allowed the optimisation of the quarry layout in a safe stability condition