Experimental study of strength properties of coal-rock under non-uniformly distributed load

The strength characteristics of coal-rock under non-uniform distributed load are investigated using a self-developed mining-induced stress testing system under different conditions of initial vertical stresses, initial horizontal stresses and stress transfer velocity. The results show that the external damaged coal-rock block has strengthened effect on the bearing capacity of internal coal-rock blocks. When the initial vertical stress, the initial horizontal stress and the stress transfer velocity are fixed, the internal bearing capacity of coal-rock is approximately twice that of the external coal-rock. With the increase of the initial vertical stress, the later period bearing capacity of the whole coal-rock is reduced and is located in the range of different initial vertical stress. There exists a difference in decreasing characteristics between internal- and external coal-rock. When under a lower initial vertical stress range, the reduction of strength of external coal-rock in the later period is higher than that of internal coal-rock. When under a relatively high initial vertical stress range, the reduction of mechanical strength of external coal-rock in the later period is lower than that of internal coal-rock. The higher the initial horizontal stress is, the higher the bearing capacity of coal-rock is. No matter in a higher or lower initial stress range, the incremental quantity of the later period bearing capacity of internal rock-coal is larger than that of external rock-coal. With the increase of stress transfer velocity, the peak strength of coal-rock is increased, and the effect of stress transfer velocity on the mechanical properties of internal coal-rock is more significant.