Cumulative damage characteristics of rock samples under cyclic low energy inclined plane impact

The ore pass wall in underground mines is often damaged by the impact and wear caused by unloaded ores. Studying the mechanisms of rock damage and failure under different impact angles can provide technical insights for the design and maintenance of the ore passes. This study employed an inclined impact experimental device along with a drop hammer loading test machine to perform cyclic low-energy impact tests on sandstone samples at five different inclined plane angles. The porosity of the rock samples was measured using a nuclear magnetic resonance (NMR) detection system, which provided data on porosity, T₂ spectrum distribution, and NMR images of the samples after different numbers of impacts at different slope angles. The results indicate that: (1) Under cyclic inclined plane impact loading, an increase in the inclination angle, leads to reduced damage to the rock sample. The rock sample impacted at a 45° inclined plane exhibited the most severe damage. Rock samples with large inclination angles are more prone to experience rupture fractures at the tip of the inclined plane, primarily due to shear-tensile failure. The porosity changes dramatically at initially slope angles, resulting in greater damage. (2) As the number of impacts increases, the porosity of the samples first decreases, then increases, and subsequently decreases again. This progression corresponds to the closure of large pores following the first impact, followed by the expansion of micropores into macropores after 5 impacts, ultimately leading to gradual degradation of the samples until failure. (3) As the number of impacts increases, new cracks form within the rock sample and small cracks expand. Despite an increase in the number of micropores, the macropores still exert a significant influence on the rock samples, with the macropore spectrum area accounting for over 95%.