Mechanical properties, damage evolution, and constitutive model of rock-encased backfill under uniaxial compression

The backfill does not exist independently in the stope, but is in contact with the surrounding rocks to form a combination body to jointly bear pressure. In order to study the joint pressure-bearing mechanism of rock and backfill in the stope, the rock-encased backfill (RB) samples are produced, and the uniaxial compression tests and acoustic emission (AE) monitoring are carried out. The results show that: (1) The encased rock can strengthen the uniaxial compressive strength (UCS) and elastic modulus (EM) of the backfill. The UCS and EM of the RB samples are greatly affected by the cement-tailings (c/t) ratio and radius (r/R) ratio. When the c/t ratio decreases from 1:4 to 1:10, the UCS and EM decrease by about 14% and 29%, respectively; when the r/R ratio increases from 0.2 to 0.8, the UCS and EM decrease by about 63% and 72%, respectively. There is a positive linear function relation between UCS and EM. (2) AE energy release and AE event location characterize the crack growth rate and the crack spatial position of the RB samples respectively. (3) A damage constitutive model of the RB sample is established based on the principle of conservation of energy. The total damage D consists of the damage at the centre of the backfill D-1 and the damage in the encased rock D-2. All the damage curves are S-shaped. The damage first evolves at the centre of the backfill, then in the encased rock, finally co-evolves, leading to the overall instability and failure, which is mutually verified with the locations of AE events. (C) 2021 Elsevier Ltd. All rights reserved.