Time-Dependent Pillar Performance Influenced by Backfill Consolidation and Rock Creep: A Numerical Study

The intervening pillar plays a significant role in ensuring safety and ore recovery efficiency during sequential stope-and-fill mining. Its mechanical behavior, however, is strongly time-dependent due to the coupled effects of rock creep and backfill consolidation, which are often overlooked in conventional design. This study presents a numerical model based on FLAC3D that explicitly incorporates these time-dependent processes to investigate pillar performance under varying stope sequencing intervals. The results show that a short interval allows the partially consolidated backfill to provide effective lateral support when the adjacent stope is excavated, enhancing pillar stability. A longer interval permits further rock creep and backfill densification, leading to significant swelling pressure on the inner side of the pillar. This induces a beam-like bending and an asymmetrical stress state including a tensile minimum principal stress in the outer part of the pillar and high differential stress with elevated brittle shear ratio in the inner portion. Results also suggest that wider pillars exhibit markedly better resistance to both tensile spalling and shear damage, whereas narrow pillars are highly susceptible to instability as the stope sequencing interval increases. The findings underscore that managing sequencing interval and optimizing appropriate pillar width are critical for mitigating time-dependent risks of pillar in multiple stope-and-fill operations.