Permeability of polymer-modified kaolinite and fly ash-kaolinite mixtures under different confining pressures and OCRs

With the goal of promoting the treatment and reuse of fly ash, a series of permeability tests were conducted to investigate the hydraulic conductivity (K) of polymer (chitosan, PEO, xanthan gum)-fly ash-kaolinite systems under different confining pressures and OCRs. The addition of fly ash increased the K of kaolinite due to changes in particle size and gradation, and the effect is not significant when the fly ash content is below 30%. PEO and xanthan gum increased the K of kaolinite, with xanthan gum having a more significant effect, while chitosan reduces it. For fly ash-kaolinite mixtures, chitosan and xanthan gum had negligible impact on the K, whereas PEO increased it by an order of magnitude. In addition, confining pressure restricts the flow channel while increasing the effective contact area between polymers and soil particles. The Koc/Knc of polymer-modified kaolinite rapidly converges at high OCRs, while the that of polymer-modified fly ash-kaolinite converges at low OCRs. This study provides insight into the effects of polymer modification on the hydraulic conductivity of fly ash-clay mixtures and provides guidance for the application of polymer modification technology in soil improvement.