In situ X-ray computed tomography (CT) investigation of crack damage evolution for cemented paste backfill with marble waste block admixture under uniaxial deformation

Cemented waste rock backfill (CWRB), which is a mixture of tailings, waste rock, cement, and water, is subjected to the combination actions in underground mining operations. While the strength requirement of CWRB has been widely studied, the mesoscopic damage evolution mechanisms of waste block proportion (WBP) on its geomechanical characteristics are still not well understood. In the present paper, the crack damage evolution of CWRB samples were characterized using real-time X-ray CT under uniaxial compression. The effects of waste block on the stress strain responses, stress dilatancy behaviors, meso-structure changes, and the cracking behaviors were investigated. The results show that strength of CWBR is influenced by waste block proportion, and strength increases are due to geomechanical effects related to propagation of tortuous failure surfaces. Besides, for sample with high WBP, interlocking among the waste blocks also improves the overall stiffness and strength of CWRB compared with tailing paste sample. Volumetric dilatancy caused by the damage and cracking behavior has a close link with the meso-structural changes, which are controlled by the interactions between the waste rock and cemented tailing paste. The crack damage behavior is quite inhomogeneous and strongly influenced by the waste block size, shape, and distribution. Our study demonstrates that it is feasible to reveal the physical mesoscopic mechanism of crack damage evolution for CWRB by using X-ray CT, and the meso-damage cracking behaviors should be deeply studied to ensure stability of pillar during mining activities.