Particle-Scale Insights into Extraction Zone Development During Block Caving: Experimental Validation and PFC3D Simulation of Gradation-Dependent Flow Characteristics

To investigate the evolution trend of the extraction zone above the drawbell in block caving, an experimental apparatus incorporating the drawbell structure was designed. Ore drawing experiments were conducted using materials with varying particle size gradations. The results demonstrate that the extraction zones for all three gradations exhibit an ellipsoidal shape in the vertical direction, with elliptical cross-sections. As the draw height increases, both the major and minor axes of the extraction zone’s maximum cross-section continuously enlarge, stabilizing beyond a draw height of 80 cm. The ore fragment size significantly influences the extraction zone dimensions. Gradation I, characterized by the smallest average particle size, yielded the largest extraction zone, whereas Gradation III, with the largest average particle size, resulted in the smallest. Numerical simulations of ore drawing for the different particle sizes were performed using PFC3D. The extent of the extraction zone in the numerical results was determined by reconstructing the initial positions of the drawn particles. The simulations show good agreement with the experimental findings, particularly regarding how the major and minor axes of the extraction zone cross-section vary with increasing draw height. Moreover, the simulations confirm that smaller average particle sizes enhance particle flowability, leading to larger extraction zones, as anticipated.