Particle flow simulation of fracture responses and anchoring mechanisms of cemented materials subjected to static-dynamic combined loads

This study aims to reveal the evolution of energy, cracks, force chain, and ultimate failure modes of cemented gangue backfill materials subjected to static-dynamic combined loads, as well as the reinforcement mechanisms of pre-tightening bolts on mechanical performance and progressive damage. The particle flow models with various fractal dimensions (D) of particle size distribution were established, and irreversible damage accumulation during dynamic loading was achieved through a nonlinear parallel-bonded stress corrosion model. The simulation results show that, compared to uniaxial compression, the energy release lag at peak strength is eliminated under static-dynamic combined loading, and the brittle failure feature becomes more pronounced. The filling effect of fine aggregates optimizes the uniformity of internal stress distribution, with the peak parallel bond strain energy increasing by 9.60%, 8.42%, and 14.81% as D increases from 2.1 to 2.85. At initial dynamic loading, the instantaneous increase in axial stress reaches the crack initiation stress, significantly increasing the number of tensile cracks. As pre-static load increases, the model sample is subjected to a higher internal stress environment during dynamic loading, leading to more remarkable force chain breakage observed at peak strength. Shear failure, including oblique shear failure and tensile-shear mixed failure, is the primary failure mode under static-dynamic combined loading. The additional constraints provided by bolts increase strain energy stored in particles and contacts and reduce the crack number at peak strength, with the constraining effect exhibiting more pronounced as preload increases. For anchored samples, the end of pallets is the initiation point for shear cracks, which extend along the edge of the preload concentration area, while tensile cracks initiating from the sample ends propagate toward the preload concentration area.