Study on the fracture characteristics controlled by filling ratio in cut-and-fill mining

To mitigate surface subsidence and stope instability induced by an insufficient filling ratio in cut‑and‑fill mining, this study investigates overlying strata fracture characteristics and instability mechanisms by means of similar material simulation, PFC numerical modeling, and theoretical analysis. Filling ratio acts as the dominant factor for overburden and stope stability: full (100%) filling suppresses roof displacement and key-stratum breakage to realize reliable gangue-pillar bearing and overburden control, whereas 50% insufficient filling triggers key-stratum fracture and domino-style chain failure starting from central goaf gangue pillars, further producing severe overburden destruction and large-magnitude surface subsidence. PFC simulations prove cut-and-fill mining forms a composite three-arch structure, whose evolution under gangue compaction controls overburden damage and surface subsidence. Analysis confirms the criticality of middle gangue pillar stability, so Cut-and-fill mining design should strengthen middle and end gangue pillars. This study clarifies filling ratio control mechanisms, providing technical support for filling parameter optimization and safe, efficient Cut-and-fill mining.