Study on permeability performance of cemented tailings backfill based on fractal characteristics of pore structure

The permeability of the backfill has a significant impact on the leaching and transport ability of pollutants to groundwater through the backfill area, and the way of pollutants enter the backfill mainly depends on the pore structure inside the backfill. Therefore, permeability is also a reflection of pore structure characteristics. The test used mine tailings as aggregate, Portland cement (PC 32.5) as cementing material, and added different additives (lime, fly ash, and anionic polyacrylamide (APAM)) to make backfill samples with a mass concentration of 74% and a cement-sand ratio of 1:4 and 1:6, respectively. Four groups of backfill samples with curing ages of 3d, 7d, and 28d were tested by nuclear magnetic resonance (NMR) and centrifugal testing machines, and the T-2 spectrum distribution characteristics of the samples before and after centrifugation were obtained. According to the test results and fractal theory, it is found that the four groups of backfill have double fractal characteristics. With the increase of curing age or cement-sand ratio, the fractal dimension of small aperture distribution (D-min) of backfill pore structure generally increases, while the fractal dimension of large aperture distribution (D-max) and permeability gradually decrease. D-max represents the number of large pores and has a high correlation with porosity, indicating that it has a great influence on porosity. The high degree of correlation between permeability and D-min indicates that the formation of water passage in backfill is related to fine pores. Meanwhile, the permeability prediction results using the correlation between the fractal bound water saturation model and the Coates model show that the measured and predicted values of the bound water saturation, and the predicted permeability values and the calculated values of the Coates model all fit well, which verifies the feasibility of this method.

Automated summary

The permeability of backfill affects the leaching and transport of pollutants to groundwater, which is determined by the pore structure. The study used different additives to make backfill samples with varying curing ages and cement-sand ratios. It was found that the backfill exhibits fractal characteristics, and the permeability is correlated to the pore structure and porosity. The feasibility of the fractal bound water saturation model and Coates model was validated in predicting the permeability.