Mechanical responses of anchored cemented gangue backfill materials subjected to static-dynamic combined loads

Abstract

The utilization of waste gangue concomitant with coal mining to construct roadway support structures embodies an advanced concept of resource recycling. However, these structures are inevitably subjected to continuous disturbances of static-dynamic combined loads during service life. This research explores the mechanical responses and reinforcement mechanisms of anchored cemented gangue backfill materials (CGBM) under static-dynamic combined loads. The fractal grading theory was introduced to control particle size distribution of aggregates, and the anchored cemented gangue backfill samples (CGBS) were casted by cementitious materials and waste gangue. Then, the static-dynamic combined loading tests regarding various pre-static loads (P_s), dynamic load amplitudes (P_d) and pre-tightening forces (P_t) were conducted. The results reveal that the mechanical properties, bolt axial force evolution, AE responses and failure modes of anchored CGBS exhibit marked differences. The peak stress of anchored CGBS decreases progressively with increasing P_s and P_d, while it initially increases and then decreases with increasing P_t. During dynamic loading, the irreversible strain exhibits an “accelerate-constant” increasing pattern, with corresponding hysteresis curves transitioning from “sparse-dense” characteristics. During dynamic loading, the expansion deformation induced by loading decreases, while the recoverable expansion deformation during unloading increases, resulting in a gradual decay of the upper and lower limit stresses of the bolt axial force. Stress concentration near the bolt hole region alters the stress transfer path, promoting the formation of shear failure surfaces. As the degradation effects of dynamic loading intensify, the ultimate failure mode transitions from inclined shear failure to conjugate shear failure penetrating the bolt hole. The findings offer a scientific foundation for coal gangue recycling and theoretical guidance for enhancing anchoring parameters and evaluating long-term stability of support structures along gob-side entry.