Fracture mechanism study applied to limit equilibrium analysis of un unstable rock mass

Analisi stabilità "Madonna deIn geotechnical field, the Limit Equilibrium Method (LEM) is one of the most used analysis to solve the stability problem of an unstable rock cliff. A limit of the LEM is the impossibility of considering the evolution over the time of the rock’s mechanical parameters and also the effect of the crack tip stress concentrations, which may trigger a crack propagation. The aim of this thesis is to overcome these limitations of the LEM model, proposing the application of a fracture mechanism approach on the real unstable rock mass of “Madonna del Sasso”. In this thesis, the effects of degradation of rock joint are evaluated through a time-dependent reduction of rock bridge along the discontinuity. After a preliminary characterization of the granite samples, many laboratory experiments were carried out on the CCNBD specimens for the investigation of mode I and mode II fracture toughness of the rock under different types of load. The intact granite specimens have been thermally treated in order to have a better representation of the possible in situ degradation of the rock and, in the end, the subcritical crack growth parameters have been computed to apply the fracture mechanism approach to the LEM analysis. The final result shows the decrease of the safety factor F_s over the time which becomes critical after 193 years. Nevertheless, some critical issues have arisen during the development of this fracture mechanism approach that do not make it appropriate for a large scale prediction.l Sasso"