Experimental and numerical investigations on damage mechanical behaviors of surrounding rock-backfill composite under uniaxial compression

The investigation into the damage evolution mechanism of surrounding rock-backfill composites contributes to understanding the combined bearing instability mechanism and interaction theory. Uniaxial compression test and 3D Particle Flow Code (PFC) numerical simulation were conducted to investigate composites with different combinations, cement tailing ratios (CTR), and backfill structures. The mechanical properties and macroscopic fracture characteristics were studied through uniaxial compression, while crack propagation and energy evolution laws were discussed through simulation. Finally, the damage evolution mechanism was revealed based on acoustic emission (AE) monitoring and dissipation energy. The results indicate that the composite specimens exhibit a mixed failure mode with tension failure as the primary and shear failure as the secondary. As the CTR decreases, the peak strength decreases while the peak strain increases; the layered structure leads to a deterioration in load carrying capacity and delays plastic deformation. The damage evolution process of the composites can be divided into three stages: In the damage slow accumulation stage I, almost no cracks and energy dissipation occur at the beginning. As the load increases, cracks mainly occur at the contact and layered interfaces with low energy dissipation and low damage; in the accelerated damage development stage II, the cracks accelerate and propagate with a slight increase in energy dissipation. As the peak stress is approached, the damage variables increase significantly; in the rapidly increasing damage stage III, the cracks propagate sharply in a short time, and dissipation energy increases rapidly. Macroscopic failure of the surrounding rock first leads to instability, which then extends to backfill by destroying bonds on contact interfaces as cracks further develop. The degree of damage intensifies, and damage variables increase sharply until complete damage occurs.