Revealing Cooperative Load-Bearing Mechanisms Between Mine Backfill and Rock Pillar Using a Bonded-Block Modeling Approach

This study investigates how mine backfill interacts with pillars to enhance load-bearing mechanisms in underground mining using the bonded-block modeling method. Through systematic numerical simulations of single- and three-pillar systems, we evaluate critical design parameters—backfill ratio, backfill’s cohesion, lateral confinement pressure, and pillar height-to-width ratio—to quantify their effects on cooperative load-bearing behavior. Key findings reveal that backfill provides essential horizontal passive support to pillars, with this stabilizing effect amplifying as the pillars fragment or undergo lateral expansion. Increasing the backfill-to-roof contact ratio due to the lateral expansion and squeezing effect of the pillar to the adjacent backfill strengthens the lateral constraints, reducing the tensile failures and axial crack propagation in the pillars at peak stress. In multi-pillar configurations, higher backfill cohesion improves system stability by redistributing loads across adjacent structures. Practical guidelines are proposed. Low-cohesion backfill with high filling ratios is recommended for single pillars to absorb energy during sudden failures, while high-cohesion backfill optimizes stability in multi-pillar systems. These insights advance the design of safer and more efficient backfill–pillar support systems in mining engineering.