Numerical Simulation and Parameter Optimization of Fan-shaped Hole Blasting in Backfilled Sublevel Open Stoping

To address the issues of backfill damage and stope boundary irregularities caused by fan-shaped borehole blasting in sublevel open stoping with subsequent backfilling, this study focuses on the underground stope of Xinqiao Phosphate Mine as a case study. Numerical models were developed using LS-DYNA finite element software to comprehensively analyze the blasting performance of fan-shaped medium-deep holes under various operational conditions. Field-measured blasting contours of the stope were compared with numerical simulation results to evaluate the influence of different loading application methods on the blasting damage prediction accuracy. The simulations employed both experimentally recorded borehole wall pressure time-histories and a constitutive explosive material model coupled with the JWL equation, revealing that the measured load time-histories yielded more precise blasting effect representations. Building upon this foundation, the study systematically simulated fan-shaped blasting under one-step mining, two-step mining, and special stope conditions by examining two key variables: inter-sidewall distance and initiation delay time. Subsequent analysis focused on surrounding rock mass damage distribution patterns and blastinginduced vibration characteristics. Results indicate that in one-step mining scenarios, inter-sidewall distance exhibits limited impact on surrounding rock mass stability, while initiation delay time emerges as the predominant factor governing blast fragmentation efficiency. At a 0.3 m inter-sidewall distance, blasting damage primarily concentrated within the ore caving zone, achieving effective bulk fragmentation while substantially mitigating surrounding rock damage risks. In two-step mining scenarios, backfill stability demonstrates high sensitivity to toe burden distance, with damage risks markedly damage decreasing when exceeding 0.6 m. While sequential hole initiation enhanced fragmentation, it exacerbated backfill damage. Special stope conditions required asymmetric sidewall parameter design and optimized borehole arrangement to minimize backfill impacts. These findings culminate in an optimized fanshaped blasting parameter system tailored for Xinqiao Phosphate Mine's A-orebody, delivering both theoretical frameworks and practical methodologies for backfill mining blasting operations.