Abstract: The loess in Shaanxi Province exhibits heavy metal contamination, primarily concentrated in the Guanzhong region. In addition, the main heavy metal ions in loess are Pb, Cu, Ni, Cd and As. Among them, the Pb concentration is the highest, reaching up to 545.6 mg/kg. To mitigate pollution spread at contaminated sites, a loess/bentonite cutoff wall was implemented, and its hydraulic conductivity and pollution retardation behavior were experimentally investigated. Experimental results demonstrate that increasing bentonite content in the cutoff wall significantly reduces both hydraulic conductivity (k) and pollution retardation coefficient (C_ad). To aid in subsequent engineering design, quantitative models for predicting k and Cad were formulated. Using this characterization, the minimum bentonite addition required to meet cutoff wall permeability standards was calculated (28.52%), exceeding the project’s specified value. Consequently, bentonite modification is necessary. Simultaneously, colloid migration during polluted liquid seepage through the cutoff wall was identified, contributing to pollution diffusion and pollution retardation coefficient reduction. Consequently, subsequent research should focus on developing a cost-effective modified material to enhance colloid fineness and reduce its mobility within the cutoff wall. This approach would reduce hydraulic conductivity, improve pollution retardation coefficient, and prevent pollution spread caused by colloid migration.

Key words: loess heavy metal pollution, loess/bentonite cutoff wall, hydraulic and pollution prevention retardation behavior, quantitative characterization, colloid migration