Effects of coupled static and dynamic strain rates on mechanical behaviors of rock-like specimens containing pre-existing fissures under uniaxial compression

Rocks containing pre-existing fissures in underground engineering are likely to be subjected to static pre-stress and dynamic loads simultaneously. Understanding the deformation and failure mechanism of fissured rocks under coupled static and dynamic strain rates is beneficial for the stability assessment of rock engineering structures. This study experimentally investigates the mechanical behaviors of fissured specimens under coupled static and dynamic loads with different loading parameters. Our experiments reveal that the coupled static-dynamic strain rates significantly affect the strength, deformation, energy characteristics, and failure mode of fissured specimens. For each dynamic strain rate, the strength and elastic modulus of specimens feature an increase first as the static pre-stress increases up to half of the uniaxial compression strength, and then a decrease. However, for each static pre-stress of coupled loads, the strength and elastic modulus increase noticeably with increasing dynamic strain rate. From the perspective of energy partition, for each static pre-stress, the higher dynamic strain rate induces greater energy dissipation of the specimens during the coupled loading, and more elastic energy is released at the end of loading. Moreover, for each dynamic strain rate, the pre-stress of half uniaxial compression strength induces the highest released elastic energy.