ABSTRACT
Illinois coal basin mines are associated with weak floor strata immediately below the coal seam. Weak floor strata control the failure behavior of pillars and mine openings and the extraction ratio is generally limited to about 50%. Stability of underground structures in such mines can be improved if mine openings are partially or completely backfilled. A simplified concept was developed to assess the stability of pillars and openings due to partial backfilling. The concept indicated that the effective pillar width at the floor-pillar interface is increased due to backfilling that increases safety factor against floor failure. In addition, the backfill provides confining pressure to the pillar and permits larger vertical loads to be carried by the pillar. After validation using finite element analyses, this concept was incorporated into a program PANEL.3D developed by SIU for structural analysis of mining layouts with capability of backfilling and probabilistic analysis.
After a brief description of the developed concepts and the program, this paper primarily focuses on the effects of backfilling on pillar and floor safety factors for a mine layout in central Illinois USA. More specifically, the paper focuses on an approach for optimization of injection boreholes’ location to maximize mine working stability over the long term. The approach is illustrated for a typical mine layout in central Illinois. The analyses revealed that the backfill height in an opening was an important variable for improved stability. The results indicated that both the pillar and floor safety factors were increased and failure probability of pillars decreased significantly after the openings were backfilled.
