Mechanical behaviour of rock discontinuities under seismic conditions

in order to investigate mechanical behaviour of rock discontinuities under dynamic loads and to relate them to real seismic phenomena, authors have set up an experimental device able to perform cyclic load tests on discontinuities. Experimental results showed that cyclic loads, even of small entity and well below peak strength, could determine asperities failure and therefore a decrease of shear strength along discontinuities. The asperities failure is proportional to the global displacement that is, in turn, proportional to the earthquake duration, amplitude and frequency. A treatment of the data based on regularization of acceleration spectrum similar to the methods used to estimate the fatigue in metallic structure is hereby proposed. The obtained experimental results as well as the law determination procedure are presented in the paper along with a UDEC model developed to reproduce the laboratory shear tests and to be applied for rock mass stability evaluation under cyclic loading