Experimental investigations of static mechanical properties and failure characteristics of damaged diorite after dynamic triaxial compression

To investigate the static mechanical properties and failure characteristics of damaged rocks after impact under realistic in-situ stress, dynamic triaxial compression tests with different strain rates and confining pressures were conducted on diorite by a modified split Hopkinson pressure bar. The damage factor was calculated according to the change of the longitudinal wave velocity of rocks before and after the impact, and the residual strengths of the damaged diorite were obtained by uniaxial compression and Brazilian tensile tests. In addition, three brittleness indexes based on the residual strength were adopted to evaluate the brittleness of damaged specimens, and fractal dimension was introduced to study the fragmentation characteristics. The results show that the dynamic peak stress, strain, elastic modulus, damage factor and plastic deformation of diorite all increase with increasing strain rate, i.e., rate dependence, and the increasing rate decreases with increasing confining pressure. The increment in confining pressure leads to the increase of dynamic peak stress, elastic modulus, static residual strength and brittleness, and the increasing rate increases with increasing strain rate, while other physio-mechanical parameters decrease with confining pressure. The post-peak behavior of dynamic stress-strain curves is divided into two classes according to the strain rate and fracture state of rocks under dynamic loading. Upon the strain rate increases above 87 s−1, the brittleness of damaged specimens generally decreases to moderately brittle or even low brittle, and the corresponding drillability becomes much easier. The fractal dimension of damaged specimens increases with the increase of confining pressure and decreases linearly with the increase of strain rate.