Mechanical properties and failure characteristics of layered cemented backfill with different height ratios

The mechanical properties of layered cemented backfill are critical factors governing the movement of overlying strata in mined-out areas and surface subsidence. To reveal the mechanism by which the layered structure influences the stability of backfill, this study systematically investigates the mechanical behavior, acoustic emission (AE) evolution characteristics, and internal crack propagation patterns of layered cemented backfill under different height ratios using uniaxial compression tests combined with AE monitoring technology. The results show that: (1) the uniaxial compressive strength and elastic modulus of layered cemented backfill decrease exponentially with increasing height ratio of the low-strength zone; (2) the macroscopic failure mode exhibits a pronounced "barrel effect," with failure concentrated primarily in the low-strength region. As the height ratio increases, the failure mode gradually shifts from tension-dominated to shear-dominated; (3) the cumulative AE ringing count significantly increases with rising height ratio, and RA-AF analysis indicates that the overall failure mode of the specimens is shear-dominated. Both the height ratio and loading rate significantly affect the crack propagation pattern. This study clarifies the mechanical response and damage evolution mechanisms of layered cemented backfill, providing a theoretical basis for safety assessment and parameter optimization in backfill mining operations.