Mechanical behavior and micro-damage evolution of quasi-homogeneous and quasi-heterogeneous backfill materials under uniaxial cyclic loading

As mining extends deeper, complex geostress environments demand greater underground stability. In mining operations, backfill materials play a crucial role in supporting underground structures, stabilizing mined-out areas, and mitigating the risks of ground subsidence. Therefore, studying the mechanical behavior and damage evolution of backfill materials is of great importance. This study systematically analyzed the mechanical behavior and micro-damage evolution mechanisms of quasi-homogeneous (QHOS) and quasi-heterogeneous (QHES) backfill specimens under different concentration and mix ratio conditions. The analyses were conducted using uniaxial cyclic loading and unloading experiments coupled with X-ray computed tomography (CT) and acoustic emission (AE) technology. The results showed that QHOS specimens exhibited higher compressive strength and structural stability, with cracks predominantly concentrated along a single primary fracture. In contrast, QHES specimens, due to their inherent microstructural heterogeneity, exhibited complex crack networks and failed at lower stress levels. AE analysis revealed that QHOS specimens exhibited stable and consistent cumulative AE signals, whereas QHES specimens displayed periodic fluctuations in AE activity. CT scanning further revealed significant differences in internal pore structures: QHOS specimens featured uniformly distributed and compact pores, while QHES specimens contained numerous interconnected small pores and throat structures that accelerated crack coalescence and early failure. Concentration significantly influenced the mechanical performance of the backfill materials, with higher concentrations leading to greater energy release. However, QHES specimens were less responsive to concentration changes compared to QHOS specimens. This study provides theoretical insights and scientific support for optimizing backfill material design and ensuring mine stability.