Study on Generation Mechanism of Boulders and Fragmentation Control in Production Blasting at Surface Coal Mines

To address the challenges of excessive boulder yield and inadequate methods for quantifying fragmentation during blast scale-ups in surface coal mining, this research theoretically analyzes the distribution law of explosion energy and identifies the causes of irregular energy dispersion in large-scale blasting operations. A theoretical calculation model was employed to establish optimal, reasonable delay intervals that effectively eliminate stress wave interference effects. Building on stress-wave propagation characteristics, the study implemented intermediate initiation for standard blasting zones and employed dual-point initiation to effectively fracture surface-hard rock formations based on detonation-position dynamics. The photographic analysis method was employed to perform polynomial fitting of observation point data, with the fitted curve representing overall blasting performance. The results indicate that the boulders mainly originate from three sources: (1) the rock mass between the bench slope face and the first row of blast holes, (2) the stemming section of the blast holes, and (3) the surface hard rock. Aiming at these boulder generation mechanisms in extensive blasting areas, three key modifications were implemented: installing inclined front-row holes, adopting central initiation for all blast holes, and supplementing auxiliary charges in hard-rock sections. Field implementation demonstrates significant improvements in blasting performance through optimized initiation positions and delay timing, resulting in enhanced hard rock excavation efficiency and reduced boulder processing costs. Post-blast analysis using fragmentation assessment software and data processing reveals an approximately 50 % reduction in boulder yield, validating theoretical models and establishing practical guidelines and design frameworks for subsequent large-scale blasting operations.