Mechanical properties and fracturing of rock-backfill composite specimens under triaxial compression

•Triaxial loadings have been conducted in the rock-backfill interface behavior.•Fracturing is monitored by traditional methods and modern CT scan technology.•Change of non-linear stress-strain behavior and fracturing has been presented. In the mining industry, backfill is used to stabilize mined-out underground excavations, and backfill made from mine tailings has the added advantage of being sustainable and eliminating the hazards of storing tailings on the surface. Triaxial compressive tests were conducted on laboratory specimens containing both rock and backfill, in order to better understand the effects of rock/backfill volume fraction and confining pressure on the strength and fracturing in rock-backfill systems. The importance of the interface between rock and backfill was also studied by conducting before and after CT scanning. The results are very interesting and show that shear and tensile fracturing in the rock as loading progresses occurs concurrently with slip and failure of the rock-backfill interface, resulting in unique stress-strain behavior, crack dilatancy, and failure types. The backfill shows very little fracturing but has a major effect on the effective strength and elastic properties of the combined specimens. The results provide important details on the failure process of rock-backfill systems and provide guidelines for the safe design of underground excavations in rock.