Objective  The study aimed to explore the effects of water-soil chemical interaction on the shear characteristics of Benggang, and to provide a theoretical basis to understand the causes and mechanism of Benggang.

  Method  The soil samples from 3 soil layers in a soil profile (red soil layer, sandy soil layer and detritus layer) of a typical Benggang located in Changting County, Fujian Province, were collected and then exchanged with two kinds of electrolyte solutions (Na ⁺ and K ⁺ ) at four different concentrations (0.005, 0.01 and 0.1 mol L⁻¹) to analyze their shear characteristics (deviatoric stress, cohesion and internal friction angle).

  Result  ① The red soil layer had the highest in deviatoric stress, cohesion and internal friction angle, followed by the sandy soil layer and the detritus layer. ② The cohesion of the three soil layers exchanged with K ⁺ significantly increased as the electrolyte concentration increased, while exchanged with Na ⁺ showed the opposite trend. The cohesion of the red soil layer exchanged with K ⁺ (0.10 mol L⁻¹) was 17.39% higher than that of the pure water treatment, whereas the internal friction angle of the soil did not differ significantly as the electrolyte concentration increased. ③ The deviatoric stress and cohesion of the three soil layers exchanged with K ⁺ were significantly greater than those exchanged with Na ⁺ , and the cohesion rates of the red soil layer, sandy soil layer and detritus layer exchanged with K ⁺ were 9.99%, 3.37% and 9.65% higher than that exchanged with Na ⁺ , respectively. However, the internal friction angle of the soil did not differ significantly. The effect of the water-soil chemical interaction on cohesion was significantly greater than that of the internal friction angle.

  Conclusion  The influence of the concentration of Na ⁺ and K ⁺ on cohesion is significantly greater than that of internal friction angle. K ⁺ can increase the soil shear strength by increasing the soil cohesion and then improve the erosion resistance of the collapsed soil, and the soil shear strength increase with the K ⁺ electrolyte solutions.