To investigate the impact of underground multiple stress disturbances on the long-term stability of cemented tailings backfill (CTB), this study conducted experiments under different disturbance levels (20–80% of static strength) and frequencies (1–4 times). By comprehensively utilizing mechanical testing, wave velocity monitoring, digital image correlation (DIC), and scanning electron microscopy (SEM), the “heterogeneous” evolution mechanism of macro-micro damage was revealed. The results indicate that disturbance level and frequency exert distinctly different driving effects on the deterioration of CTB, rather than a simple linear superposition. Specifically, low-frequency disturbance produces a compaction strengthening effect, microscopically promoting the generation of Ca(OH)₂ and ettringite (increased Ca/Si ratio). In contrast, the combination of high disturbance and high frequency induces free water extrusion and inhibits hydration, leading to an advanced damage threshold based on energy evolution and the accelerated coalescence of microcracks, which favors the formation of C-S-H gel (decreased Ca/Si ratio). Within this heterogeneous mechanism, the disturbance level acts as the dominant controlling factor. This study clarifies the nonlinear mechanical and chemical evolution paths under composite disturbances, providing theoretical support for the dynamic stability control of backfill in deep multi-step mining.

In the subsequent backfilling mining method, the composite structure formed by the ore pillar and the backfill is the key element in ensuring the stability of the working face. Its mechanical behaviour directly affects mining safety and ore recovery rates. In order to elucidate the mechanical response and failure mechanisms of rock-like backfill composite structures (RLBCS) under biaxial loading, specimens with different water-to-cement (W/C) ratios (0.5, 0.6, 0.7 and 0.8) for the rock-like backfill were prepared in this study. Biaxial loading tests were conducted, with digital image correlation (DIC) technology employed simultaneously to monitor the evolution of strain and displacement on the specimen surface. The results indicate that the biaxial strength of RLBCS decreases exponentially as the W/C increases. When the W/C exceeds 0.7, the strength reaches a plateau. The strength contribution of the backfill increases relatively. The axial stress–strain curve exhibits four distinct phases. A pronounced bimodal distribution is observed when the W/C exceeds 0.5. The evolution of lateral strain exhibits a transition point where compression is followed by expansion. The threshold for lateral expansion stress exhibits a non-monotonic variation. The modulus of elasticity decreases as the W/C increases. The apparent structural strain ratio exhibits a non-monotonic variation. The failure pattern exhibits marked asymmetry. The rock-like side shows tensile failure. Where the interface is present, this manifests as localised crushing at the top of the rock-like layer, cracking along the interface, and bulging of the backfill. The W/C ratio of the rock-like material governs the failure mechanism of RLBCS. The strain localisation modes in backfill materials are classified into two types: post-peak abrupt and pre-peak gradual. The evolution of interface strain exhibits four distinct stages: an initial abrupt change, cooperative deformation, crack initiation, and post-peak instability. The spatiotemporal evolution of interfacial delamination and the deformation of the backfill was quantified through displacement field analysis. The research findings provide a theoretical basis for the design of underground mining operations.