Analysis of instability mechanisms of a high rock prism standing on a cliff face

The analysis of possible failure mechanisms of a 50-m-high rock prism is presented. The case well represents a situation typical of many rock cliffs. The reconstruction of the geometry through remote and direct surveys and the mechanical characterization through laboratory and in-situ tests allowed to build a geotechnical 3D model. Analyses were conducted with the finite difference code FLAC3D where discontinuities are reproduced by interface elements. Under different hypotheses, the severity of the state of stress was evaluated to investigate which mechanism, between the failure of the rock sustaining the prism at its base or shearing along discontinuities, is more critical. The results of the numerical analyses address a more realistic evaluation of safety margins and criteria for design of stabilization measures.