In situ large size non conventional shear tests for the mechanical characterization of a bimrock in The Santa Barbara open pit mine (Italy)

A high mine slope in the disused Santa Barbara open pit mine (Tuscany, Italy) is cut in the Shale-Limestone Chaotic Complex (SLCC), which is a typical bimrock made up of a scaly-fabric clayey matrix including heterometric calcareous blocks. The slope shows evidence of instability phenomena: mainly rotational landslides and toppling countercracks. In order to characterize the mechanical behaviour of the SLCC bimrock, in situ large size non conventional shear tests were performed. The aim of in situ tests is to overcome the size limitation of laboratory specimens and namely to take into account the influence of calcareous blocks on the strength of the bimrock. Bimrock’s strength parameters under natural conditions can be evaluated by means of a limit-equilibrium analysis taking into account shear test data and the geometry of the sliding surface.