Supporting Effects of Backfilling at the Hishikari Mine

The Hishikari Mine consists of epithermal vein type Au-Ag deposits. The veins are extracted mainly by drifting and bench stoping with backfill. Blasted waste rocks are generally used as backfilling materials and crushed waste rocks with cement are used for larger stopes. Although backfilling controls the displacement of excavation surface and increases the stope stability, practical evaluation for stope dimension in conjunction with backfilling effects is not established. In this study, supporting effects of stope ends were evaluated and available support lines were drawn by using a three-dimensional elastic finite element analysis. Based on available support lines, the properties of backfilling materials were evaluated. The behavior of rock mass in bench stoping was compared with a two-dimensional elasto-plastic finite element analysis. The results indicated more remarkable influence on the stope stability with the backfill stiffness. The Young's modulus of the backfilling materials containing cement at the Hishikari Mine changed from 10 MPa to 1 GPa by numerical analyses and field measurements.