DEM Simulation of the evolution of unstable rock faces: an alternative approach to modelling and back-analysis

The evolution of unstable rock slopes is a process characterised by a succession of discrete events, each one giving rise to a new configuration of the rock face. If these events are put in a wider time frame, they can be seen as a local step contributing to the overall process. The advances in recognition systems, such as laser scanning or georadar techniques, allow to build numerical models of higher and higher precision, where the topographic and geostructural configurations may be precisely reconstructed. These improved capabilities open the possibility for defining highly representative numerical models that can be used for back analysis purposes or the design of risk mitigation works. One possible drawback of such approaches is that they superimpose structural and topographic data, whose compatibility is not independent on the mechanical behaviour of the rock mass. In fact, the initial geometry is depending on the (usually complex) rock slope history, which has a two-fold relationship with the whole set structural and mechanical features of the rock mass. In order to investigate this point, a series of Distinct Element analyses of an unstable rock face located in Bolzano province is performed. The model is characterised by a very simple geometry, and slope evolution is studied by adopting the strength reduction technique. Structural and mechanical information is obtained from an extensive in situ survey. The aim of the simulations is to show how a model based on the available geomechanical information can be used to reproduce the main topographic features of the rock slope, and to perform a back analysis of a selected case history.