Modelling of Fatigue Damage Evolution of Two Natural Rocks Under Cyclic Loading

Many civil, mining and transportation structures located in rocks are subjected to repeated loading and unloading cycles. Each cycle of load causes fatigue damage which accumulates with increasing cycles. In the present study, damage evolution of two natural rocks namely Garhwal gneiss and Shivpuri sandstone from India has been studied through laboratory tests. The Garhwal gneiss specimens were studied under uniaxial cyclic loading by adopting incremental loading scheme. Load was applied through load control mode and four different loading rates were employed. The Shivpuri sandstone was tested under low confining pressure conditions adopting the similar incremental loading scheme but under displacement-controlled environment. Damage evolution of these rocks was discussed in the form of modulus, irreversible strain, and dissipated energy. Applicability of inverted S-curve model to represent the damage evolution was evaluated. It is observed that irreversible strain and dissipated energy modelled the fatigue damage evolution in better way as compared to modulus. It was also observed that for tests conducted under load-controlled environment, the irreversible strain evolution was more systematic whereas for tests performed under displacement-controlled environment dissipated energy was a better indicator of fatigue damage evolution.