Dynamic Mohr-Coulomb and Hoek-Brown strength criteria of sandstone at high strain rates

To investigate the dynamic Mohr-Coulomb and Hoek-Brown strength criteria under the low confining pressures at high strain rates, the dynamic uniaxial and triaxial compression tests of sandstone were conducted with a conventional and modified triaxial SHPB system, respectively. The confining pressures are 5.0 MPa, 7.5 MPa, 10.0 MPa, 12.5 MPa and 15.0 MPa, and the strain rates varied from approximately 40 s(-1) to 160 s(-1). The results show that the cohesion is a linear positive correlation with the logarithm of strain rate, and the internal friction angle is a linear negative correlation with the logarithm of strain rate. The change of cohesion is more obvious than that of the internal friction angle. The rock parameter m also exhibits a linear positive correlation with the logarithm of strain rate. Furthermore, the relationships between cohesion, internal friction angle and rock parameter m and strain rate were obtained. On this basis, the unified dynamic Mohr-Coulomb and Hoek-Brown strength criteria at high strain rates were established. According to the established dynamic strength criteria, the strength of sandstone under high strain rates and low confining pressures can be estimated theoretically. By comparing the theoretical curve and test data, it can be concluded that established dynamic Mohr-Coulomb and Hoek-Brown strength criteria of sandstone are appropriate for both high strain rates and low confining pressures.