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In engineering practices such as backfill mining, the existence and characteristics of the rock-backfill interface significantly influence the propagation of explosive stress waves and the dynamic response of the rock mass. This study aims to reveal how, among these characteristics, different backfill media and their wave impedance differences with the rock specifically affect these processes. To this end, physical experiments were combined with numerical simulations, utilizing Digital Image Correlation (DIC) technology to capture strain field evolution under blasting, and LS-DYNA was employed for numerical analysis. The research indicates that the wave impedance difference between the rock and the backfill medium is key to controlling stress wave propagation and energy distribution. When the wave impedances are similar, stress wave transmission is dominant, leading to higher peak strain values at various points and a more uniform action of the stress wave on the rock mass, resulting in relatively uniform final failure. When the wave impedance difference is large, interface reflection is enhanced, forming a significant “blocking effect”; in this case, although the initial peak strain may be lower, the continuous action of the interface can lead to greater final strain and plastic deformation in the rock mass. Numerical simulations further show that the greater the wave impedance difference, the more pronounced the “guiding” and “blocking” effects of the backfill on crack propagation. This leads to intensified damage and crack accumulation in the rock mass adjacent to the backfill due to energy concentration, which also results in a higher fractal dimension of the cracks. Therefore, the type of backfill medium directly determines the strain response characteristics and final damage patterns of the rock mass by modulating the reflection and transmission behavior of waves at the interface. These findings have practical guiding significance for optimizing backfill material selection and blasting parameter design in backfill mining.

The stability of the “surrounding rock-backfill” composite system is crucial for the safety of mining stopes. This study systematically investigates the effects of steel slag (SS) content and interface angle on the strength and failure characteristics of rock and SS-cemented paste backfill composite specimens (RBCS) through uniaxial compression strength tests (UCS), acoustic emission systems (AE), and 3D digital image correlation monitoring technology (3D-DIC). The intrinsic mechanism by which SS content influences the strength of SS-CPB was revealed through an analysis of its hydration reaction degree and microstructural characteristics under varying SS content. Moreover, a theoretical strength model incorporating different interface angles was developed to explore the impact of interface inclination on failure modes and mechanical strength. The main conclusions are as follows: The incorporation of SS enhances the plastic characteristics of RBCS and reduces its brittleness, with the increase of SS content, the stress–strain curve of RBCS in the “staircase-like” stage becomes smoother; When the interface angle is 45°, the RBCS stress–strain curve exhibits a bimodal feature, and the failure mode changes from Y-shaped fractures to interface and axial splitting; The addition of SS results in a reduction of hydration products such as Ca(OH) 2 in the backfill cementing system and an increase in harmful pores, which weakens the bonding performance and strength of RBCS, and the SS content should not exceed 45%; As the interface angle increases, the strength of RBCS decreases, and the critical interface slip angle decreases first and then increases with the increase in the E S / E R ratio. This study provides technical references for the large-scale application of SS in mine backfill.

Understanding the shear behavior of the interface between surrounding rock and backfill is of significant engineering importance for enhancing stope stability in cemented tailings backfill mining. However, the evolutionary mechanisms of shear properties and damage under varying mechanical conditions remain insufficiently studied. This investigation employed tailings and surrounding rock from a Guangdong tailings pond, with basic mechanical parameters determined through laboratory tests. Numerical models of the rock-backfill composite were developed using PFC2D, considering different shear rates (0.3, 0.6, and 0.9 mm/min), lateral confinement levels (0.5, 1.0, and 1.5 MPa), and roughness coefficients. The analysis compared the interface’s peak and residual shear strengths, revealed crack evolution patterns, and explored damage mechanisms using acoustic emission monitoring and energy dissipation theory. Key findings include the following: (1) Shear stress–displacement curves under all conditions exhibited three stages, ascending, shearing-off, and sliding, with distinct peak and residual strengths. (2) Increasing lateral confinement, shear rate, and roughness transformed failure from localized to global sliding, with cracks occurring at the interface and propagating into the backfill. (3) Cumulative acoustic emission events increased with all three factors, with lateral confinement showing the most substantial effect on interface energy accumulation (83% increase). These results provide theoretical support for assessing interface stability in deep backfilled stopes.