Analysis of unsaturated shear strength and slope stability considering soil desalinization in a reclamation area in China

The unsaturated soil shear strength is a crucial parameter for the evaluation of erosion and slope stability analysis. In this study, we collected unsaturated and undisturbed soil samples in Aug 2018 and investigated the relationship between the unsaturated soil shear strength, soil salt content (SSC) and particle content in coastal reclamation areas. A combination method of the direct shear test and soil water characteristic curve (SWCC) was used on undisturbed soil to determine the unsaturated soil shear strength in 79 soil sampling sites. The shear strengths of four gradient salt content soils with different matric suctions were selected to perform a slope stability analysis using the strength reduction method (SRM) for an agricultural engineering slope model considering soil desalinization. The shear strength of unsaturated soils increased with increasing matric suction, especially when the soil salt content was high. The soil effective cohesion was found to be significantly positively correlated with the SSC and clay content, while the soil effective internal friction angle was significantly negatively correlated with the SSC and clay content. The internal friction angle related to matric suction was independent of the soil properties. The location of the critical failure surface was deeper, and the factor of safety (FS) was higher on a slope with a high SSC at all slope gradients than that with a low SCC. The FS decreased with increasing saturation and decreasing SSC. This implies that the agricultural engineering slope, especially for drainage ditch slopes rammed with high salt content soils, was at the stable stage after its establishment but had higher potential to fail during desalinization and saturation. This study aims to evaluate slope stability using unsaturated soil shear strength and increase the current understanding of the soil desalinization of saline-sodic soils and their efficacy in soil shear strength in coastal reclamation areas.