Research on the Strength Damage and Permeability Characteristics of Cemented Paste Backfill under Chlorine Salt Erosion and Dry-Wet Cycles

Cement paste backfill (CPB) suffers serious damage and deterioration under the dual erosion conditions of the dry-wet cycle caused by the high chloride salt concentration in mine water and the fluctuation of mine water level. In order to discuss the mechanical properties and permeability characteristics of CPB under erosion, this study designs an immersion experiment for CPB under chloride salt and dry-wet cycle conditions. Through a uniaxial compressive strength (UCS) test, the change law for the mechanical parameters of the CPB was investigated, the strength constitutive equation of the CPB was constructed and the deterioration process of the CPB was analyzed. The penetration test was used to investigate the diffusion characteristics of the packing under chloride salt and dry-wet cycle conditions. The results showed that the strength and Young's modulus of the CPB initially increased and then rapidly decreased, with maximum decrease rates of 32.2% and 38.2%, respectively. The CPB structure exhibits an initial undamaged stage, an initial damaged stage, a damaged development stage, a damaged destruction stage and a residual damaged stage. The chloride ion penetration depth gradually increased with the number of dry-wet cycles, with a maximum diffusion depth of 20.5 mm. The maximum apparent diffusion coefficient of chloride ion was 18.99 x 10-10 m2/s, and the maximum concentration was 0.303 mol/L. Under the double erosion conditions of chloride salt and dry-wet cycle, the CPB structure was severely damaged.