Mechanical properties of organic-inorganic hybrid fiber reinforced cemented tailings backfill considering energy evolution and damage fracture characteristics

The backfill method is widely used in underground mining operations. However, challenges such as the high temperatures in deep shafts and the frequent use of pH-imbalanced wastewater as filling water require tailored filling materials. By leveraging the high-temperature resistance of inorganic fibers and the acid-alkali resistance of organic fibers, we propose a hybrid fiber-reinforced cemented tailings backfill (HFRCTB) that includes both polypropylene (organic) and basalt (inorganic) fibers. This study utilizes advanced techniques such as 3D digital image correlation, computed tomography, and scanning electron microscopy to examine the mechanical properties and failure patterns of HFRCTB across multiple scales. Our findings suggest that polypropylene fibers contribute more to the strength improvement of HFRCTB than basalt fibers, as indicated by compressive and tensile strength tests and energy dissipation analysis. Optimal mechanical properties were achieved when the content of both polypropylene and basalt fibers was 0.3%. The inclusion of different fiber types alters the failure mode and damage extent in the backfill material, with organic fibers having a more pronounced effect than inorganic fibers. Notably, the HFRCTB with optimal mechanical properties exhibited the lowest initial porosity, but the highest post-test porosity and three-dimensional fractal dimension. The microstructural failure patterns of polypropylene fibers provide direct insights into the internal failure mechanisms. Polypropylene fibers that failed solely through tension or shear exhibited lower strength compared to those that experienced combined tensile-shear failure, while the extent of fiber damage was lower in HFRCTB specimens with higher overall strength.