Effects of dynamic strain rate on the energy dissipation and fragment characteristics of cross-fissured rocks

Internal initiation and propagation of micro cracks in rock materials might result in macroscopic fragmentation and energy dissipation under dynamic strain rate. Understanding the internal mechanism of rock failure and energy consumption is significant in assessing the stability of engineering rock mass under dynamic disturbance. This study experimentally investigated the energy dissipation and fragment distribution of rock specimens containing symmetrical and asymmetrical cross fissures under static and dynamic loadings. Our results reveal that the dynamic strength of rock specimens evidently increases with increasing strain rate, while the dynamic elastic modulus does not depend on the loading rate. For a given dynamic strain rate, the rock specimens containing asymmetrical cross fissures (one of the fissures had a relatively large dip angle) had higher dynamic strengths than those containing symmetrical cross fissures. During loading process, tensile cracks and shear cracks significantly affect the failure patterns of cross-fissured rock specimens under static and dynamic loadings, respectively. All the cross-fissured specimens show similar "X" shaped shear failure mode regardless of fissure configuration subjected to dynamic strain rate. The cross-fissured rock specimens with higher strain rates feature smaller location parameter and scale parameter of the fragment size distribution by GEV fitting. The fractal dimension of cross-fissured specimens show an evident loading rate dependence, and the size distribution of the fragments in asymmetrically cross-fissured specimens under dynamic loading is most homogeneous. The dissipated energy density of all the rock specimens obviously increase as the dynamic strain rate increases, while the energy utilization efficiency is less affected by the strain rate.