Fatigue behaviour characteristics and life prediction of rock under low-cycle loading

The fatigue characteristics of rock materials significantly impact the economy and safety of underground structures during construction. Hence, it is essential to conduct further investigation into the progressive damage processes of rocks under cyclic loading conditions. This research utilised both laboratory experiments and discrete element simulations to investigate how confining pressure and fatigue upper limit stress influence the mechanical behaviour and crack development of marble under low-cycle fatigue conditions. By introducing synthetic displacement and reasonable assumptions, the classical damage evolution law was updated, resulting in a fatigue life prediction formula applicable to various rock materials and loading conditions. The results indicate that lower fatigue upper limit stress can delay the accumulation of damage and extend the fatigue life of the rock, but it results in more severe ultimate failure. The damage variable’s correlation with the relative number of loading cycles for different fatigue load upper limits under the same confining pressure can be approximated by the same functional relationship. The modified damage evolution model provides an effective characterisation of this trend. The proposed fatigue life prediction method comprehensively accounts for different rock materials, confining pressures, loading frequencies, and initial damage, showing a close match with actual results.