Abstract: In water-filled borehole presplitting blasting,the incompressibility and high wave impedance of the water medium significantly alter the pathways of explosive energy transmission and the rock-breaking mechanisms.As a result, traditional parameter design methods developed for air-filled boreholes often lead to high overbreak ratios and excessive damage to the retained rock mass in water-bearing strata.Taking the water-rich slope of the Jianshan phosphate mine as the engineering background,this study establishes a coupled smoothed particle hydrodynamics–finite element (SPH–FEM) numerical model to systematically investigate the propagation characteristics of blast-induced stress waves,rock mass damage evolution,and crack propagation behavior under different borehole spacings and decoupling coefficients.The results indicate a strong correlation between the superposition of stress waves from adjacent boreholes and the coalescence of presplitting cracks.When the borehole spacing is 1.4 m and the decoupling coefficient is 2.34,the average crack propagation length reaches 49.48 cm,enabling the formation of regular and continuous through-going presplitting cracks while effectively suppressing excessive crushing around the borehole wall and the development of secondary cracks.Field tests further validate the reliability of the numerical simulations:under the optimized parameters,the half-hole rate of water-filled borehole presplitting blasting increases to 85%,and the acoustic reduction rate decreases by 18% compared with conventional blasting,demonstrating favorable damage control performance and crack-forming effectiveness under water-bearing conditions.The findings provide a useful reference for presplitting blasting parameter design in complex hydrogeological environments.