Failure characteristics of large unconfined cemented gangue backfill structure in partial backfill mining

For the subsidence prevention purpose, partial backfill mining is employed. The mined-out area is supported by carefully designed backfill piers and strips. The stability of these unconfined backfill structures (UBS) is very important to the mining operation. In order to study the failure characteristics of UBS, the stress-strain curve of a large cemented gangue backfill material (CGBM) test block (800 x 800 x 800 mm) was derived through uniaxial compression test. The failure process of the test block was monitored by digital image correlation (DIC) and ultrasonic testing (UT) techniques. The internal pressures and deformations were monitored by sensors embedded at different depths in the test block. It is found that: 1) The curves of internal pressure and deformation can be divided into four stages. 2) A hard core is formed in the central part of the test block under uniaxial compression load. 3) The three manifestations of the curves of internal pressure or deformation can be used as the failure precursor point, critical instability point, residual bearing capacity or residual deformation of the test block respectively. The experimental findings could be used to guide the design, stability monitoring and reinforcement of UBS in partial back fill operations. (C) 2018 Elsevier Ltd. All rights reserved.