The impact of natural sodium bentonite on the microstructure, permeability and strength characteristics of bentonite-modified loess (BML) were evaluated by scanning electron microscope (SEM) test, triaxial flexible wall permeability test, uniaxial compression test and direct shear tests. The experimental results indicate that bentonite can be used for loess solidification attributed to its effective particle filling, water absorption and expansion characteristics. The quantitative parameters of SEM images such as the average pore area, width, length and surface porosity of BML declined first and then increased with bentonite content, and the lowest was observed at a bentonite content of 15%. The hydraulic conductivity of BML declined with increasing bentonite content and was lower than the maximum allowable limit of 1.0 × 10⁻⁹ m/s. The uniaxial compressive strength and shear strength parameters of BML increased initially and subsequently declined as bentonite content increased. A normalized prediction model was established for modified loess based on the correlation between mechanical characteristics and the microscopic pore parameters, which was verified to be rational in estimating the macro- and micro-scale properties of BML. Therefore, when the anti-seepage landfill layers are constructed in the Loess Plateau area, 15% of bentonite is recommended in modified loess, which has optimal impermeability and mechanical properties.

Sodium carboxymethyl cellulose (Na-CMC) was used to improve the chemical compatibility of natural sodium bentonite (NaB) used in vertical cutoff walls for containing acid mine drainage (AMD). Ab Na-CMC content from 2% to 15% was examined to determine the minimum Na-CMC content of sodium carboxymethyl cellulose-amended bentonite (CMCAB) needed to yield a low hydraulic conductivity (<10⁻⁹ m/s). Hydraulic conductivity (k), swell index, viscosity, XRD spectra, FT-IR spectra, and microstructures were measured for CMCAB to assess the hydraulic performance of CMCAB for containing AMD and to elucidate the mechanism of reduced k due to the addition of Na-CMC. The results show that the k of CMCAB decreased with the increase in Na-CMC content and stress. A 10% or higher content of Na-CMC is required to reduce the k of NaB down to 10⁻⁹ m/s. Na-CMC did not impact the interlayer structure of NaB but increased the viscosity of CMCAB. CMCAB with increased viscosity retained the Na-CMC within the pore spaces, narrowing the flow paths for AMD and yielding low k.