Experimental study on layered cemented tailings backfill damage and failure mechanisms under blast loading

The stability of cemented tailings backfill (CTB) is critical for the safe operation of underground mines. Inevitably, operational constraints introduce two types of layered interfaces within CTB: transition heterogeneous structural interface (THSI) and continuous homogeneous structural interface (CHSI), thereby transforming CTB into layered cemented tailings backfill (LCTB). In this study, three-dimensional physical models were developed to simulate rock-backfill systems in underground mines. Five blasting tests were conducted to investigate the effects of charge position and LCTB strength configuration. The analyses focused on dynamic volumetric strain responses (Δk, defined as the attenuation ratio of the first peak volumetric strain εv(max) at identical distances), pre- and post-blast sonic velocity change rates (η, used to quantify damage severity), as well as damage morphology and failure evolution.The results indicate that the dynamic failure of the rock-backfill system proceeds through three sequential stages: crack initiation and backfill extrusion, crack propagation and blasting gas invasion, and rock-backfill system destruction. For LCTB containing a THSI, placing the charge within the high-strength LCTB layer accelerates the attenuation of εv(max), reflected by an increase in Δk (from 0.71 to 2.32), while the damage index η (from v(max) attenuation behavior, with Δk decreasing from 2.54 to 1.32, accompanied by reduced damage levels (η < 10%). These results suggest that, under the investigated model conditions, positioning the charge within the high-strength layer in the presence of a THSI, or aligning the charge with the CHSI, is favorable for mitigating LCTB degradation. The findings provide a mechanistic basis for understanding charge-layered interface interactions in two-step stope blasting and offer engineering-relevant insight into charge placement in layered cemented backfill systems.