Permeability Tests and Multi-Factor Analysis of Sand-Based Cemented Backfill Five-Component Samples With Different Mix Ratios

Extensive coal mining involves the challenge of liberating coal resources under buildings, railways, and water bodies. Sand-based cemented backfill (SCB) mining is considered an effective method to solve this problem while utilizing solid wastes in large quantities. Since the groundwater seeping into SCB pores in a complex mining environment deteriorates the SCB strength and stability, the permeability optimization of SCB samples under multi-factor conditions by adjusting their mix ratios is very topical. Therefore, in this study, a large number of SCB samples were prepared using aeolian sand as aggregates, cement and fly ash as cementing materials, and quicklime and water reducing agent as additives. The mass of the aeolian sand was a fixed value, while other ingredients' content ratios were expressed as a percentage of aeolian sand mass. With all other factors being constant, the level of one factor was changed at a time for univariate analysis. Four levels were set up for each of the four factors, and 16 tests were performed for a total of 13 mix ratios with an axial pressure of 1 MPa and confining pressure of 3 MPa. The effects of mix ratios, pore size, porosity, and surface structure on SCB's permeability were analyzed in detail. Experimental results show variations of quicklime and fly ash contents significantly changed the SCB's permeability, and variations of cement and water reducing agent contents had a minor impact on SCB's permeability. SCB's permeability positively correlated with porosity, primary pore size, and compactness of surface structure. These findings are considered instrumental in improving the SCB waterproof performance.