Study on mechanical properties and energy characteristics of carbonaceous shale with different fissure angles under dry–wet cycles

To experimentally investigate the stability of underground excavations under dry–wet cycles and different fissure angles, several rock samples with prefabricated fissure angles were prepared and subjected to the coupled influence of dry–wet cycles and axial loading until failure. Results show that the rock strength is affected by the dry–wet cycles and fissure angle, thereby yielding the strength expression. Based on the characteristics of elastic and dissipation energy ratios, the energy evolution process of the rock samples is divided into the initial dissipation energy stage, stable dissipation energy–growth stage, dissipation energy–acceleration stage, and dissipation energy–surge stage. The sensitivity of the peak total energy and elastic strain energy of the rock samples to the fissure angle decreases as the number of dry–wet cycles increases. The difficulty degree of rock deformation and failure caused by energy exhibits a difficult–easy–difficult evolution characteristic as the fissure angle increases, while the evolution characteristic gradually weakens with an increase in the number of dry–wet cycles. The failure modes of the rock samples are controlled by the fissure angles and the dry–wet cycles. Tensile failure requires more energy than shear failure. As the number of dry–wet cycles increases, the elastic strain energy decreases, rock failure intensity weakens, and surface shedding reduces. The findings of this study provide a significant understanding of the instability and failure of underground rock engineering.