Mechanical behavior and reloading reinforcement characteristics of fractured coal under low confining pressure

To study the basic mechanical behavior and the reloading reinforcement characteristics of fractured coal, conventional triaxial loading tests with different fissure angle were first carried out. On this basis, conventional triaxial loading and unloading tests were conducted to investigate the reloading reinforcement characteristics of fractured coal. The results reveal that when the fissure angle was small, the stress-strain curve exhibited the multi-peak phenomena. As the fissure angle increased, the stress drop phenomenon in the peak region was weakened. With the increase of the fissure angle, the peak stress of the specimens increased and then decreased, while the elastic modulus showed an overall increasing trend, demonstrating the controlling effect of the crack angle. Meanwhile, the cyclic loading exhibited a certain enhancement effect on the strength of the fractured coals when the specimens was unloaded near the crack closure stress. The findings can provide a better understanding of the failure mechanism and reloading reinforcement characteristics of fractured coal.