Numerical prediction of crater blasting and bench blasting

Abstract

As an anisotropic and jointed material, shale has been extensively investigated due to the rich unconventional gas reserved in the shale rock mass. In the process of hydraulic fracturing in jointed shale, joints may significantly affect hydraulic crack behavior under dynamic disturbance loads, such as crack propagation direction, speed and distance, which has a great effect on the efficiency of hydraulic fracturing and gas production. Therefore, it is of great significance to study crack dynamic propagation characteristics in shale with different orientation joints and dynamic strength. Impacting experiments were conducted on the single cleavage triangle (SCT) shale specimens with joint orientation 0°, 30°, 45°, 60° and 90°, respectively. A modified split Hopkinson pressure bar (SHPB) system was applied and AUTODYN code was used to simulate crack dynamic fracture behavior. For the case of a single joint and multiple parallel joints, crack propagation directions and trajectories were numerically analyzed. The experimental and numerical results indicate that joints have a great influence on crack dynamic propagation direction. In addition, the crack propagation speed of shale is positively related to the loading rate under dynamic loads. If joints are considered as thin layer material, dynamic tensile strength and elastic modulus of joints have a great effect on dynamic crack propagation behavior under impact loads.