Theoretical and numerical investigation of the effects of in-situ stresses and dual-borehole combinations in eccentric decoupled charge blasting

Eccentric decoupled charge (EDC) blasting is a widely used technique for rock fragmentation and tunnel excavation, yet the underlying rock damage mechanisms, particularly in relation to in-situ stresses and multi-borehole combinations, remain underexplored. First, we developed an analytical model for single-borehole EDC blasting, providing insights into the theoretical relationship between the formation of different rock damage zones around the borehole and various influencing factors, including decoupling coefficient, in-situ stress, rock and explosive properties, and peak blast pressure. Using a finite element fluid-solid coupling algorithm, we performed numerical simulations for a simple case of single-borehole EDC blasting, verifying the effectiveness of the adopted numerical approach. We then performed numerical simulations for dual-borehole EDC blasting with varying in-situ stress conditions and borehole combinations. The results indicate that: (1) rock damage is primarily concentrated on the eccentric side of the borehole due to its smaller decoupling coefficients and the resulting larger peak blast pressure; (2) the formation of through cracks between two boreholes is highly dependent on the relative angle φ between them, while the extent and direction of the cracks are largely controlled by the application of in-situ stress. This work provides a theoretical basis and reference for optimizing the design of multi-borehole contour blasting in deep rock excavation under significant in-situ stresses, facilitating desired crack propagation while minimizing damage to the surrounding rock.