Triaxial tests on dynamic properties of granite under intermediate and high strain rates

Experimental studies on the granite specimens under different confining pressures and strain rates are conducted using the improved split Hopkinson pressure bar (SHPB), and the impact response and failure mode of the rock subjected to intermediate and high strain rates are analyzed. Based on the test data, it is revealed that the dynamic compression strength and the peak strain of the granite increase with the increasing strain rate under the same confining pressure, and there is a logarithmic relationship between the dynamic strength and the strain rate. The elastic modulus of the granite is insensitive to the confining pressure and strain rate. The larger the strain rate is, the more serious the rock breakage is. Then, it is found that the compression strength of the granite increases with the increase of the confining pressure when the strain rate is identical. The failure mode of such granite takes on a change from the axial splitting at lower confining pressure to the compression/shear failure under high confining pressure. The stress-strain curve of the rock has a yield platform, being an apparent brittle-ductile transformation characteristic. Finally, the applicability of the famous Mohr-Coulomb criterion and the Hoek-Brown criterion to the biotite granite is further examined. It indicates that the granite can be well described by the Mohr-Coulomb criterion. The increase of dynamic strength of the granite is primarily due to the rate effect of cohesion.