Experimental investigations of the dynamic mechanical properties and fracturing behavior of cracked rocks under dynamic loading

Cracked rocks are quite susceptible to dynamic loading from drilling, blasting, and impacting events. Understanding the dynamic response of cracked rocks under dynamic loadings is crucial for the assessment of rock structure stability. In this study, dynamic compression tests were carried out on rock specimens with multiple parallel cracks using a split Hopkinson pressure bar apparatus. Effects of strain rate and crack intensity on dynamic responses, including strength and deformation properties, progressive failure behavior, rock fragmentation characteristics, and energy dissipation of cracked rock specimens, were systematically investigated. Stress-strain curves migrate from class I curves into class II with increasing strain rate. Dynamic strength shows clear rate dependence while dynamic elastic modulus is independent of strain rate. Progressive failure behavior of cracked rock specimens under high loading rates was analyzed using high-speed photography and digital image correlation technique. Results show that the X-shaped shear failure mode is the final failure modes of all specimens, regardless of crack intensity. Fragmentation analysis indicates that increasing strain rate intensifies fragmentation, decreases mean fragment size, and increases fractal dimension of rock fragments. At low strain rates, specimens remain unbroken or slightly spilt; at high strain rates, specimens are systematically pulverized. Energy utilization efficiency decreases while energy dissipation density increases with increasing strain rate. For a given strain rate, crack intensity has no significant influences on energy dissipation and fragmentation characteristics of cracked rock specimens under dynamic loading.