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.

Rock's mechanical parameters and fragmentation characteristics significantly change under the freezing and thawing environment in high-altitude cold regions, and it is difficult to directly apply traditional blasting parameters for excavation. Therefore, researching blasting design parameters in freeze-thaw environments is of great importance. This study analyzed the impact of freeze-thaw cycles on rock mechanical properties and conducted the crater experiments of single-hole and double-hole simultaneous blasts in ore rocks under freeze-thaw conditions based on Jurong Copper mine. Futhermore, the geometric parameters and block size distribution of the crater were measured after blasting, and the reasonable parameters for blasting design were determined using the mathematical fitting methods. Additionally, the changes in the blasting crater parameters of the mine were also compared and analyzed under four different rock conditions. The results show that the mechanical properties of rock mass significantly deteriorate with a decrease in uniaxial compressive strength and elastic modulus of up to 40.6% and 54.0% under freeze-thaw cycles, respectively. The optimal burial depth ratio for single-hole blasting of freeze-thaw ore rocks is 0.678~0.789 under different lithological conditions, and the ratio of the optimal charge burial depth to crater radius is distributed in the range of 0.875~1.076. For Chibula mining area, the hole diameter is 152 mm, the diorite hole net parameter is 4.5 m×3 m, the corresponding explosives consumption is 0.56 kg/m³, and the tuff hole net parameter is 5 m×4 m with a 0.63 kg/m³ explosives consumption. For Jurong mining area, the hole diameter is 310 mm, the tuff blasting hole net parameter and explosive consumption is respectively 7 m×5 m and 0.61 kg/m³, and the granite porphyry hole net parameter and explosive consumption is respectively 8 m×5 m and 0.64 kg/m³.