Post-peak behaviour of rocks under cyclic loading using a double-criteria damage-controlled test method

Cyclic loading-induced hazards are severe instability problems concerning surface and underground geotechnical projects. Therefore, it is crucial to understand the rock failure mechanism under cyclic loading. An innovative double-criteria damage-controlled testing method was proposed in this study to capture the complete stress-strain response of porous limestone, especially the post-peak behaviour, under systematic cyclic loading. The proposed test method was successful in applying the pre-peak cyclic loading and then in controlling the self-sustaining failure of rock during the post-peak cyclic loading. The results showed that the strength of the rock specimens slightly increased with an increase in the fatigue life in the pre-peak region due to cyclic loading-induced hardening. Additionally, a combination of class I and class II behaviours was observed in the post-peak region during the cyclic loading tests; the class II behaviour was more dominant by the increase in fatigue life in the pre-peak region. Damage evolution was assessed based on several parameters, such as the elastic modulus, energy dissipation ratio, damage variable and crack damage threshold stress, both in the pre-peak and post-peak regions. It was found that when the cyclic loading stress is not close to the peak strength, due to a coupled mechanism of dilatant microcracking and grain crushing and pore filling, quasi-elastic behaviour dominates the cyclic loading history, causing more elastic strain energy to accumulate in the specimens.

Automated summary

Cyclic loading-induced hazards pose severe instability problems for surface and underground geotechnical projects. This study proposed an innovative double-criteria damage-controlled testing method to understand rock failure mechanisms under cyclic loading. The results showed slight increase in strength of rock specimens with increase in fatigue life in the pre-peak region due to cyclic loading-induced hardening, and a combination of class I and class II behaviors in the post-peak region during cyclic loading tests.