Study on Effect of Blasting Vibration on Stability of Safety Roof Pillar for Open-pit to Underground Transition in Longshou Mine

This study aims to investigate the stability evolution of the safety roof pillar during the transition from open-pit to underground mining in Longshou mine under the influence of blasting vibration. A numerical calculation model was established based on the current mining area conditions. The most critical position of the safety roof pillar was determined through calculations, and a two-dimensional numerical model for this position was developed using top-level mining as an example. By calculating blasting parameters and equivalent elastic boundaries, we obtained the peak blasting load transmitted from cutting holes, auxiliary holes, and peripheral holes to the excavation surface. Subsequently, numerical calculations were conducted to assess the stability of the safety roof pillar after applying an equivalent blasting load to the excavation face. The results indicate that each delayed blast caused displacement and vibration velocity peaks, with maximum displacement observed at monitoring points inside the safety roof pillar closest to the blast site. Vibration velocity spreads spherically around the blasting operation position into surrounding rock mass. Based on criteria related to blasting vibration velocity and rock damage assessment, it can be concluded that overall there is no or only slight damage present in the safety roof pillar. Additionally, analysis reveals that maximum principal stress remains lower than tensile strength of rock mass without any significant formation of a tensile fracture plastic zone on the safety roof pillar. In general, the designed thickness of the safety roof pillar meets requirements for open-pit to underground mining. However, due to actual geological complexities beyond what is captured by the numerical model, it is essential to continuously observe and monitor changes in the safety roof pillar to ensure its stability during ongoing mining operations.