Research on mechanical properties and strength criterion of carbonaceous shale with pre-existing fissures under drying-wetting cycles

In order to investigate the influence of drying-wetting cycles and the fissure angle on the mechanical properties of carbonaceous shale with pre-existing fissures, uniaxial and triaxial compression tests on carbonaceous shale with pre-existing fissures after drying-wetting cycles(0, 5, 15 and 20 times) were carried out. The results show that the peak strength, cohesion and internal friction angle of carbonaceous shale gradually decrease with increasing the number of drying-wetting cycles, which manifests an obvious drying-wetting deterioration effect. The degree of deterioration is as follows:peak strength>cohesion>internal friction angle. The strength deterioration degree of carbonaceous shale after drying-wetting cycles gradually decreases with increasing the confining pressure, which indicates that the confining pressure has an inhibitory effect on the drying-wetting deterioration effect. The peak strength, cohesion and internal friction angle of carbonaceous shale show a trend of decreasing first and then increasing with increasing the fissure angle, which manifests an obvious angle effect. However, the angle effect and drying-wetting deterioration effect are mutually inhibited. In other words, as the number of drying-wetting cycles increases, the peak strength, cohesion and internal friction angle will decrease and the angle effect will attenuate. By introducing two mechanical parameters(c(a, n)andφ(a, n)) into the Drucker-Prager criterion, a strength criterion was established considering the drying-wetting cycles and the fissure angle, which can well describe the drying-wetting deterioration effect and angle effect of the strength. The research results can provide a reference for the strength estimation of carbonaceous shale in engineering practice and the stability analysis of slopes. © 2022, Science Press. All right reserved.