Macro-meso damage evolution mechanism of surrounding rock-backfill combination bearing

The backfill and surrounding rock collectively bear the in-situ stress, and revealing the macroscopic-mesoscopic damage evolution mechanism of the composite body can help to improve the theory of interaction between backfill and surrounding rock,as well as to optimize cement tailing ratios (CTR) and strength design of backfill. Uniaxial compression experiments and numerical simulations were conducted to investigate the surrounding rock-backfill composite specimens with different CTR. The stress-strain curves, mechanical properties, and failure modes at the macroscopic level were analyzed, as well as the crack propagation, energy evolution, and damage evolution mechanism at the mesoscopic level. The results show that with the increase of CTR, the peak strength and modulus of elasticity increase, and the peak strain decreases. The uniaxial failure mode is tensile-shear mixed. Fracture damage occurs at the contact interface when the CTR is low, whereas macroscopic cracks appear at the layered interface when the CTR is high. In the pre-peak stage, microcracks first appear in weak areas such as the contact interface and layered interface. The total energy is primarily transformed through elastic strain energy, with small amplitude energy loss and a low degree of damage. In the post-peak stage, dissipation energy increases rapidly and exceeds the elastic strain energy, leading to accelerated deterioration of internal damage. The number of cracks in the surrounding rock has increased significantly and rapidly, with macroscopic fracture surfaces appearing first. The internal cracks in the backfill converge and merge at the layered interface, which plays a significant synergistic support role when the CTR is high. © 2024 China University of Mining and Technology. All rights reserved.