Centrifuge modelling of lead retardation in soil–bentonite cut-off walls

Soil–bentonite (SB) walls are commonly used as barriers for in situ containments at landfills. SB walls are designed to control the movement of persistent pollutants such as heavy metals in the long term. This paper presents centrifuge and numerical modelling of 50 years of performance of a loess-amended SB (LSB) wall in comparison with a conventional SB wall. Both walls were 28 m high and subjected to a hydraulic head difference of 2 m in the prototype. A purposely designed apparatus was developed to impose the hydraulic head and a pollutant loading of 200 mg/l lead(II) on two barriers simultaneously. The apparatus was loaded on the ZJU400 geotechnical centrifuge and spun to 100g. Similitudes of dispersion and adsorption of lead(II) in a centrifuge are discussed. Stress redistribution was observed in small-scale walls due to the enhanced soil arching effect. The lead(II) migration distance in the LSB wall after 50 years was 44.3% shorter than that in the SB wall. The predicted breakthrough time for the LSB wall was 149.1% longer than that for the SB wall when the thickness was 0.6 m. Retardation effects could be attributed to the significant ability of loess to absorb lead(II).