Reloading Mechanical Properties and Particle Flow Simulation of Pre-Peak Confining Pressure Unloading Sandstone

The excavation-unloading damage effects of western high-geostress slopes on rock were explored by testing the pre-peak confining pressure unloading sandstone reloading mechanical properties. The deformation and failure mechanisms were studied from a mesoscopic perspective using the particle discrete-element method. (1) Approaching the unloading failure, confining pressure increased the specimen bearing capacity attenuation. (2) The confining pressure unloading promoted microdefect propagation and development; the specimens increased rapidly to the damage stress value after reaching the initiation stress value. The penetration fracture zone was more evident and expansive in the model, and the distribution of the dense crack areas was more concentrated in the fracture zone and area. (3) The average interval of the tangential contact force was the largest in the direction of crack expansion and propagation. The strong force chains were shown to primarily bear external loads, whereas the weak force chains played a key auxiliary role in maintaining stability. (4) The number of cracks developing in the confining pressure unloading damage process indicated that the loading process did not cause damage to the specimens. The fracture zones further propagated and formed on the dominant fractures based on the damage caused by the confining pressure unloading disturbance.

Automated summary

The excavation-unloading damage effects of western high-geostress slopes on rock were investigated using sandstone reloading mechanical tests under pre-peak confining pressure unloading. The deformation and failure mechanisms were analyzed using the particle discrete-element method. (1) As unloading failure approached, increasing confining pressure led to a decrease in specimen bearing capacity. (2) Unloading of confining pressure promoted microdefect propagation and development, with specimens rapidly reaching the damage stress value after reaching the initiation stress value. Penetration fracture zones were more pronounced and expansive in the model, with dense crack areas concentrated in the fracture zone and surrounding area. (3) The tangential contact force exhibited the highest average interval in the direction of crack expansion and propagation. Strong force chains primarily bore external loads, while weak force chains played a key role in maintaining stability. (4) The number of cracks developing during the confining pressure unloading damage process indicated that the loading process did not cause damage to the specimens. Fracture zones further propagated and formed on dominant fractures due to the damage caused by confining pressure unloading disturbance.