ANISOTROPIC MECHANICAL BEHAVIOR OF SHALE UNDER UNIAXIAL COMPRESSION WITH DIFFERENT STRAIN RATES

Shale is a kind of sedimentary rock with well-developed bedding planes. It is proved by conventional mechanical tests under static loading that bedding planes is the main influence factor on the anisotropic behavior of shale. However, as an experimental factor, strain rate is supposed to have a nonnegligible influence on the anisotropic behavior of shale as well. To investigate the effects of strain rates on the anisotropic mechanical properties of shale and the corresponding failure modes, the experiment on the shale samples with varied bedding plane angle β from 0°to 90åt the interval of 15°is conducted under strain rates of 10^-4 s^-1, 5×10^-4 s^-1, 10^-3 s^-1 and 10^-2 s^-1, respectively. The tests give the following results. (1)The anisotropic behavior of elastic modulus of shale samples becomes less obvious under high strain rates, while the Poisson's ratio of shale samples is rarely affected by strain rate. (2)The increase of compressive strength of shale samples for β=45°~60°is the most obvious one if compared with the rest shale samples. The anisotropic behavior of peak strength of shale samples is weakened by high strain rate. (3)The failure modes of shale samples are relatively less affected by bedding planes under high strain rates and the anisotropic behavior of shale samples becomes less obvious under high strain rates. In conclusion, the anisotropic behavior of shale is weakened by high strain rate. The results can provide references for a deeper understanding of the mechanical properties of shale.