Mechanical properties, deformation response, energy evolution, and failure pattern of stratified cemented tailings backfill under triaxial compression

The backfill should keep stable in the primary stope when mining an adjacent secondary stope in subsequent open stoping mining methods, and the large-size mined out is usually backfilled by multiple backfilling before the recovery of a secondary stope, resulting in a layered structure of backfill in stope. Therefore, it is significant to investigate the deformation response and mechanical properties of stratified cemented tailings backfill (SCTB) with different layer structures to remain self-standing as an artificial pillar in the primary stope. The current work examined the effects of enhance layer position (1/3, 1/2, and 2/3) and thickness ratio (0, 0.1, 0.2, and 0.3) on the mechanical properties, deformation, energy evolution, microstructures, and failure modes of SCTB. The results demonstrate that the incorporation of an enhance layer significantly strengthens the deformation and strength of SCTB. Under a confining pressure of 50 kPa, the peak deviatoric stress rises from 525.6 kPa to 560.3 kPa, 597.1 kPa, and 790.5 kPa as the thickness ratio of enhance layer is increased from 0 to 0.1, 0.2 and 0.3, representing a significant increase of 6.6%, 13.6% and 50.4%. The slopes of the curves in the elastic stage become steep, and the plastic phase is extended accordingly. In addition, the peak deviatoric stresses and total/elastic strain energy at the peak point also increased. As the thickness ratio of the enhance layer increases from 0 to 0.1, 0.2, and 0.3, the elastic energy rises from 0.54 MJ·m-3 to 0.67 MJ·m-3, 0.84 MJ·m-3 and 1.00 MJ·m-3, representing a significant increase of 24.1%, 55.6% and 85.2%. With the increase of confining pressure, the cohesion and internal friction angle of SCTB are both increased, however, the cohesion is more susceptible to enhance layer position and thickness ratio than the internal friction angle. The failure style of the SCTB specimen changes from shear failure to splitting bulging failure and shear bulging failure with enhance layer. The crack propagation path is significantly blocked by the enhance layer. The findings are of great significance to the application and stability of the SCTB successfully fulfilled in subsequent stoping backfilling mines.