Geomechanical behavior and properties of cemented paste backfill under passive interface loading and their influences on field-scale stability

After placement into underground mined-out voids (called stopes), a passive interface loading develops between cemented paste backfill (CPB, an artificially cemented soil) and surrounding rock mass, which results in the spatiotemporal changes in the geomechanical behavior and properties of CPB, and thus affects its field stability. In this study, meter-scale curing columns with rough inner surfaces were developed to investigate the effect of passive interface loading on the geomechanical behavior and properties of CPB, and field-scale stability of CPB mass was conducted through a series of 3D numerical analyses. The obtained results discovered that the passive interface loading not only weakens the compressive and shear behaviors of CPB, but also leads to highly spatiotemporal changes in elastic modulus, unconfined compressive strength, cohesion, and angle of internal friction. Meanwhile, through the integration of the measured degradation in mechanical properties, the field-scale analysis reveals that consideration of stress arching and homogenous mechanical properties substantially overestimate the stability of CPB mass, especially in the narrow stopes with a relatively small height. The simultaneous consideration of stress arching and associated heterogeneous mechanical properties are required for the reliable and accurate assessment of the field stability of CPB mass and its safe engineering design.