Effect of the moisture content and dry density on the shear strength parameters of collapsing wall in hilly granite areas of South China

The changes in the mechanical properties of collapsing walls under the influence of natural factors in the hilly area of southern China need to be determined. We systematically studied the influence of the interaction of dry density ρ (1.0, 1.1, 1.2, 1.3, 1.4 g/cm³) and moisture content ω (0.05, 0.1, 0.15, 0.2, 0.25 g/g) on the stability of four soil layers in a collapsing wall. The soil cohesion decreased with increasing soil depth. The cohesion force initially increased and then decreased with increasing ω and increased with increasing ρ; the internal friction angle was mainly affected by ω and decreased with increasing ω. The cohesion could be used to effectively characterize the stability of the collapsing wall. The shear strength index was modeled based on interaction between the dry density and moisture content (R² > 0.95). The optimal combination of moisture content and dry density was obtained, and the collapsing wall was in the most stable state at a moisture content of 0.12–0.19 g/g and a dry density of 1.40 g/cm³. Based on the analysis of the critical height and safety factor (FS), the FS values of the sandy layer (C) was 0.53 and 0.57 for ω values of 0.25 g/g and 0.05 g/g, respectively. In the alternating process of soil wetting and drying, the basic properties of the soil changed; caused traceback erosion, and thereby affected the stability of the collapsing wall. Our study provides a theoretical basis for the investigation of the factors influencing the stability of collapsing walls.