On the fracture and energy characteristics of rock-backfill composite structure specimens exposed to fatigue-creep interaction loading

A series of stress-controlled fatigue-creep interaction loading tests were performed on rock-backfill composite structure (RBCS) samples. The testing results reveal the influence of cement/tailing (c/t) on deformation, energy dissipation, damage evolution, and macro-meso failure patterns. The equivalent lifetime of RBCS is the largest for a sample with smaller stiffness filling, a smaller stiffness filling leads to weaker volumetric expansion. Additionally, strain energy is relatively large for larger stiffness filling, indicating a larger proportion of energy release at failure. A dissipated energy-based damage evolution model is proposed to describe damage propagation at the entire fatigue-creep process which fits well with the experimental data. Moreover, the macro-meso failure pattern reveals the interactions between surrounding rock and filling material, failure seems to change from tension splitting to shear with increasing c/t. Good agreement was found among the volumetric deformation, energy dissipation, and failure pattern. It is suggested that flexible backfilling is benefit to prevent rock spalling and collapse.