Method and Field Experiment of Stope Blast Boundary Control Based on 3D Laser Point Cloud

Precise control of blasting-induced excavation boundaries in deep phosphate stopes presents significant challenges under complex backfill constraints, with current overbreak/underbreak evaluation methods frequently lacking quantitative rigor. Using the 875-level stope of Shaft No. 2 at Guizhou's Xinqiao Phosphate Mine as a case study, this research develops an advanced methodology for blasting boundary characterization and control that leverages three-dimensional (3D) laser point cloud data analysis. High-precision post-blast point cloud data were collected using a mobile laser scanning system, followed by the development of a comprehensive analytical framework incorporating point cloud denoising, preprocessing, registration correction, surface reconstruction, and geometric discrepancy analysis. This system allows quantitative evaluation of the spatial distribution of overbreak and underbreak, volumetric deviation, and the degree of contour matching between the excavation boundary and the design profile. Utilizing point cloud diagnostic results from representative stopes, the effects of blasting energy distribution and initiation sequence on boundary formation were analyzed, subsequently developing a control strategy integrating zoned millisecond-delay initiation with optimized blasthole layouts. Field trials at the 875-13# stope confirmed the method's capability to precisely characterize post-blast boundary morphology and deviation characteristics, achieving over 90% contour matching accuracy for both A₁ and A₂ rows. Volumetric difference analysis of point cloud data provided a reliable quantitative basis for assessing overbreak and underbreak and for guiding blasting parameter optimization. The developed boundary control technique demonstrates consistent stability and robustness even under challenging conditions, including drilling deviations in the A₃ and A₄ rows. This methodology offers a quantitative, traceable technical solution for precision blasting design and boundary control in deep mining stopes, delivering practical value by minimizing ore dilution and enhancing stope extraction efficiency.