Performance of coupling agent-amended clay/sand mixture under vacuum suction

This paper presents a comprehensive investigation on anti-seepage/erosion performance of a hydroxypropyl starch (HPS)-based coupling agent (CA) amended clay/sand as the cut-off wall materials under vacuum suction. The experiments, including the permeability, erosion, water-bleeding, viscosity, and microstructure by scanning electron microscopy (SEM) and mercury intrusion porosity (MIP) were conducted. It reveals that the very low CA incorporation can effectively reduce the clay mineral’s migration and bleeding volume of the soil slurry, and results in a lower hydraulic conductivity from 4.2 × 10^–5 cm/s to as low as 1.0 × 10^–6 cm/s, and a 45.4% decrease in erosion mass with just 0.2% CA addition. Microstructural analysis indicates that CA addition enhances hydrogel bonding, increases viscosity, and reduces bleeding volume, effectively mitigating clay erosion under vacuum suction. The findings not only are beneficial for the introduction of the hydroxypropyl starch (HPS)-based coupling agent into the sand/clay mixture’s modification, but also provide insights into the CA incorporation mechanism for improving the anti-seepage performance of clay/sand cut-off wall in vacuum preloading projects.