Experimental Investigation of Spatial Particle Size Distribution and Segregation in Tailings Slurry for High-Goaf Backfilling

Tailings backfilling (TB) is widely recognized as an environmentally friendly and engineering safe technique to enhance mining efficiency. However, the heterogeneous particle distribution in TB slurry, also-named the segregation phenomenon, can significantly affect the mechanical strength of the backfill, especially under high goaf conditions. Therefore, elucidating the spatial distribution characteristics of particles during high-goaf filling has become a crucial research focus for improving the mechanical behavior of tailings backfill. A systematic experimental investigation was conducted in this study, incorporating the similarity principle, to analyze the migration behavior of backfill slurry particles and to clarify how the different backfill heights influence the spatial distribution of fine, medium, and coarse particles. The results indicate a clear vertical variation in PSD. Based on statistical analysis of samples collected from different backfill height experiments, coarse particle content increased progressively from the upper to lower layers (median: 16.2%, 23.6%, and 25.0%), while medium-sized particles remained relatively stable (37.0%, 37.3%, 37.0%). Fine particles dominated overall but decreased with layers (45.6%, 38.8%, 38.3%). Coarse particles tended to settle downward due to gravitational forces, whereas fine particles migrated upward. The distribution of medium-sized particles remained largely homogeneous. Fine and coarse particles were subjected to opposing driving forces. Meanwhile, particles maintained an approximately symmetrical distribution in the horizontal direction. Moreover, when the backfill height exceeded 800 mm, a notable intensification of stratification occurred, indicating a strong height-dependent transition in segregation behavior. In contrast, in the horizontal direction, the PSD showed no clear dependence on backfill height. These findings provide new insights into the mechanisms of particle segregation within backfill materials, offering a theoretical foundation and experimental support for optimizing PSD within the backfill body and elucidating the collapse mechanisms of high goafs.