Dynamic Response of Large-span Jointed Rock Mass Chambers Under Repeated Blasting

Amid the dual challenges of advancing deep mining operations and achieving carbon peak and neutrality targets, maintaining safe production in underground mines has become a critical imperative for national resource security. Many underground mines in China have adopted large-diameter deep-hole mining as their primary production method, forming chambers with spans exceeding 20 meters under site-specific geological conditions. Given the complex underground conditions and recurring dynamic stresses from production blasting, analyzing the dynamic response of large-span chambers is critical. This study uses the Panlong lead-zinc mine as a case study and applies combined FEM-DEM numerical simulations to investigate how blast distance and chamber span affect the stability of the upper chambers. The results demonstrate that: (1) With a constant chamber span, decreasing blast distance from 27.5 m to 2.5 m increases post-blast plastic zone volume and fracture density by 251.41% and 42.12%, respectively, while repeated blasting significantly undermines chamber stability; (2) Reduced blast distances correspond to 66.25% and 373.37% increases in shear and tension-shear failure blocks per blast, evolving failure patterns, intensified peak particle velocity (PPV), and markedly compromised stability; (3) During cyclic blasting, larger spans induce roof displacement growth from 0.07 cm to 2.08 cm due to caving, alongside 195.35% and 208.49% increases in plastic zone volume and fracture density, respectively, progressively weakening large-span chamber stability; (4) Large-span chambers exhibit unstable conditions with extensive elastic energy accumulation at elevated levels post-excavation, where subsequent blasting disturbances promote further energy storage, substantially raising overall collapse risks. These findings provide valuable insights for underground mining operations regarding blasting design and support engineering.