Blasting response and charge optimization of slope smooth blasting layer using SPH–FEM coupling algorithm

To address over-excavation, strong vibration, and uneven rock breaking in slotted slope smooth blasting, a 3D blasting model is built with a smooth particle hydrodynamics-finite element method coupling, and the HJC constitutive model is adopted to simulate rock damage evolution. Simulations are conducted for reserved smooth blasting layers of 80, 100, and 120 cm to analyze rock damage, surface vibration, and fragment ejection. Taking the 100 cm layer with the best overall performance as the baseline, three charging patterns (continuous bottom charging, air-deck charging, and water-deck charging) are compared in terms of effective stress distribution. The results indicate that rock damage area and peak surface particle velocity drop as the smooth blasting layer thickens. The 80 cm layer causes over-excavation and intense vibration, while the 120 cm layer wastes blasting energy and results in poor fragmentation. The 100 cm layer produces well-graded rock fragments and achieves optimal blasting performance. Particle velocity along slots is larger than that in non-slot directions, and fragment ejection distance can be determined by the peak velocity of surface particles. With equal unit charge mass, water-deck charging reduces energy loss for similar wave impedance between water and rock; its peak effective stress is about 15.9% higher than air-deck charging and maintains a longer stress action time. Air-deck charging distributes blasting energy evenly over the slope. Continuous bottom charging gathers energy at the slope toe and aggravates local damage, which harms slope stability. This study provides numerical support for parameter selection and charge design of slope smooth blasting.