Influence of joint angles and in-situ stress on blasting effects in layered rock mass

Drilling and blasting in layered rock masses faces significant challenges, as pre-existing joints cause unbalanced energy distribution, leading to poor forming effects and severe over-excavation. However, a comprehensive understanding of the complex coupling mechanisms between key joint parameters and the in-situ stress field on the final blasting outcome is still lacking. The model tests are used to quantitatively analyze the macroscopic crushing characteristics and crack propagation velocity. The numerical simulation then reveals the underlying mechanisms of stress wave propagation and energy partitioning, which are validated against the experimental results. The results indicate that the joints and the in-situ stress field play distinct, competitive roles in the blasting outcome. First, the joints control the anisotropy of the damage: crack propagation is primarily guided along the joint direction (the channel effect), and the apparent crack velocity exhibits a Ⅴ-shaped trend with the joint inclination angle (0° - 90°). Second, the in-situ stress state controls the overall extent of the damage: Increased confining pressure (both equal and unequal) inhibits crack propagation by increasing the failure threshold of the rock mass. Mechanistically, while this locking effect enhances stress wave transmission (i.e., reduces the locking effect), this is secondary to the dominant inhibitory effect of the increased overall rock mass strength. The primary contribution of this study is the identification of this dual control mechanism, revealing that the final blasting effect is a non-linear competition between the joint's structural guidance and the dominant strengthening effect from the in-situ stress field, which clarifies the complex energy partitioning mechanisms at the blast source.