Fracturing mechanism of bedding shale under directional fracture-controlled blasting

The precise control of explosive energy to form an effective radial fracture network in shale is the key of shale gas dynamic extraction. In order to elucidate the damage and fracture mechanisms of shale under directional fracture-controlled blasting and establish a quantifiable relationship for shale damage and destruction under various blasting conditions, explosive tests were conducted on cubic shale specimens with four different fracture angles. The evolution of surface strain fields on the shale specimens was monitored using digital image correlation (DIC) technology. Additionally, the fractal dimensions of surface cracks on the shale specimens at different fracture angles were computed based on the box-counting theory. A programmed analysis of post-blast fragment size distribution was carried out using Matlab software, resulting in the development of a fully automated particle size analysis program with visual delineation of particle sizes. The experimental results demonstrate a negative power-law relationship between crack density and scaled distance within different scaled distances. The angle between the fracture direction and the weak plane of the bedding significantly influences the location of micro-damaged areas. Particularly, when the weak plane of the bedding is parallel to the fracture direction, damaged areas tend to concentrate along the weak plane, affecting the macrocrack propagation path and favoring the formation of a single crack. Energy dissipation at the weak planes of the bedding is identified as a crucial factor leading to suboptimal fracturing effects in shale blasting. When the fracture direction aligns with the weak plane of the bedding, a higher proportion of large fragments is observed in the post-blast specimens. The average fractal dimension of fragment size distribution is the lowest among all groups, measuring only 0.784 3. Conversely, when the fracture direction is perpendicular to the weak plane of the bedding, the distribution of post-blast fragment sizes becomes more uniform. The average fractal dimension of fragment size distribution increases to 2.5233, indicating relatively better blasting fragmentation results in such scenarios. © 2024 Explosion and Shock Waves. All rights reserved.