Liang Cui

Cemented paste backfill (CPB)/rock interface shear resistance results in a spatiotemporal stress reduction in CPB and thus affects the mechanical stability of CPB structure in underground excavations. To study the stress distribution in CPB structure, an integrated model consisting of a cohesive zone model for CPB/rock interface behavior and a multiphysics model for hydrating CPB behavior is developed. The predictability of the proposed model is validated against measurements from laboratory tests and field studies. Thereafter, the validated model is used to investigate the influence of curing time, stope geometry, and field backfilling operation on the spatiotemporal stress development in CPB structure. It has been found that the CPB/rock interface loading is able to reduce the stress levels in CPB by up to 75%, and taking advantage of this phenomenon can significantly reduce the operation cost. Moreover, there exists a critical stope width that governs the extent of stress reduction in CPB. In addition, continuous mining activity in the secondary stope exerts limited impact on the stress redistribution in the primary backfill body. These findings provide practical guidance for the safe design of a CPB structure as well as a more strategic mining plan for the adjacent ore body.

Cemented paste backfill (CPB) that contains alkali-activated slag (AAS) produces more desirable properties and performance (enhanced fluidity, higher strength, lower cost, and limited carbon emission) as compared with CPB made with cement. Significant efforts have been devoted to the study of the effect of the individual factor on the rheology of AAS-CPB. However, the synergistic effect of curing temperature, time, and activator nature is still unclear. Therefore, the current research aims to investigate the time-dependent rheology of AAS-CPB under the combined influence of curing temperature, silica modulus (Ms), and activator concentration (AC). The findings revealed that a higher curing temperature results in a reduction in fluidity and an increase in the thixotropy of CPB. The evolution of rheological parameters of AAS-CPB is more insensitive to the curing temperature as compared to that of OPC-CPB. During the initial 2 h, higher AC can weaken the rheological parameter. However, a more rapid growth rate of rheological properties was observed after 2 h. The rheological parameters of AAS-CPB with higher Ms are always lower than those of AAS-CPB with lower Ms at all temperatures studied. In addition, the discrepancy in the linear correlation between thixotropy and plastic viscosity for OPC-CPBs and AAS-CPBs indicates the different hydration rates of slag and Portland cement. These findings are beneficial in guiding the mix proportion design of AAS-CPB in mines with various underground temperatures.

The inclusion of fiber in cemented paste backfill (CPB) can significantly alter the mechanical response of the CPB body. The intrinsic defects in CPB and the potential dynamic loading condition make it necessary to investigate the fracture properties of fiber‐reinforced CPB (FR‐CPB). The mode‐I fracture behavior and properties are crucial to the successful engineering application of FR‐CPB technology used in underground mines. The contribution of fiber length and content to the evolutive mode‐I fracture behavior and properties of FR‐CPB was examined in this study. The results show that the addition of fiber reduces the prepeak stiffness but improves the mode I fracture toughness (K_Ic), and the improvement in K_Ic increases with fiber length. In contrast, the initial increase in fiber content (from 0% to 0.5%) benefits the K_Ic acquisition, while a further increase in fiber content from 0.5% to 0.75% poses a negative influence on the K_Ic development. Moreover, with the adoption of the cement hydration model, four predictive functions are proposed to describe the contribution of fiber length and content to the development of fracture properties. In addition, K_Ic is identified as a more reliable fracture property for assessing the immediate ground support role played by the FR‐CPB structure. The findings are helpful when it comes to the determination of the fiber length and content in FR‐CPB design.