Related Rule Study of Subcritical Crack Growth and Threshold Values in Transversely Isotropic Slates

Elastic parameters and the subcritical crack growth of different bedding angle slate specimens were studied using uniaxial compression testing and the double torsion constant displacement load relaxation method using SANS and MTS Insight machines. To study the relations of the mode-I stress intensity factor KI versus the subcritical crack growth velocity V, the fracture toughness KIC, the stagnation speed, and the threshold values, the double torsion constant displacement load relaxation method was carried out. The related rules between the bedding angles (beta) and the uniaxial compressive strength, fracture toughness, and threshold values were investigated. Experimental results show that the uniaxial compression, the fracture toughness, and the threshold value curves move to the bottom then increase with the increase of the beta angle. In addition, its fracture toughness is minimal when the beta angle of the slates is 45 degrees, and crack initiation and crack propagation are generated under load, which can lead to the failure of the slate. lgKI-lgV relations of transversely isotropic slates measured by this method are in accordance with linear rules, which is in good agreement with the Charles theory. The range of K0/KIC for these different bedding angle slates is from 0.511 to 0.789. The test results would provide the basis for studying seepage and time-dependency of rock engineering stability.