Influence of brittleness of soft calcarenites in cliff stability problems: insights from FEM-DEM modelling

For soft rocks, brittle behavior occurring under low confinement stresses is generally underestimated or even neglected in the solution of boundary value problems, as for example those concerning the stability of rocky cliffs. In these cases, modelling approach should take directly into account processes such as the material detachment as well as crack opening and propagation, following fracture mechanics and rock brittleness concepts. This work is aimed at highlighting the role of post-peak brittleness in cliff stability problems involving soft calcarenites by means of the application of a hybrid finite-discrete element method (FDEM), which allows for a proper simulation of the brittle rock behavior and the related mechanism of fracture propagation. In particular, the paper presents the simulations performed for an ideal vertical cliff formed of soft calcarenites belonging to the Calcarenite di Gravina Fm. (Upper Pliocene - Lower Pleistocene) and largely outcropping in Apulia (Southern Italy). The numerical results highlight the impact of calcarenite brittleness in the stability assessment, the influence of the mesh dependency on the same results and the role of the combination of rock brittleness with joint sets to generate failure mechanisms in the cliff.