# Strength Characteristics and Slope Stability Analysis of Expansive Soil with Filled Fissures
## 1 Introduction
A numerical exercise was performed on a slope in Regina, Canada, using a program that implemented the constitutive model into infinite slope formulation to reflect the influence of the stress regime change and associated softening on unsaturated expansive soil slope stability [30]. Major landslides that occurred on the mid-altitude slopes of Mount Elgon, eastern Uganda, were studied through the analyses of soil particle size distribution, Arterberg limits, shear strength and the factor of safety [31]. In the stability analysis of expansive soil slopes, the soil with fissures was usually homogenized [32]. In the analysis, the strength parameters obtained from the experiment were used as the overall strength parameters of the slope soil. On this basis, the stability of the slope was analyzed by reducing the strength parameters to reflect the influence of the fissures [33]. The calculated sliding surface of the slope was often arc-shaped (Figure 1a), and after surveying the 19 excavated channel landslides in the Nanyang section of the South-to-North Water Transfer Project, the landslides were mainly controlled by various fissures. The sliding surface was controlled by the vertical fissures at the trailing edge and the slow-inclined long-large filled fissures. The shape of the sliding surface was basically a broken line (Figure 1b). Figure 1: Conventional generalized sliding model and actual sliding model of expansive soil slope. (**a**) Arc-shaped sliding surface; (**b**) broken line sliding surface. It is impossible to objectively consider the characteristics of the fissures in expansive soil, especially the spatial distribution and strength of the fissures, when equivalent homogeneous soil was used to calculate the slope stability, and the effect of fissures on slope stability was reflected by strength attenuation. It was difficult to analyze how these fissures could constitute potential sliding surfaces [34; 35]. Even if the strength parameter used in the calculation was the lowest strength of the fissure surface, for the actual slope, it was only correct when the sliding surface was along the fissure surface, which often resulted in the calculation parameters being too conservative and the safety factor was too small. In this paper, a sample preparation device for preparing triaxial test samples with filled fissures was developed. Using the gray-green strong expansive soil in the Nanyang section of the South-to-North Water Transfer Project as the filling material and the brown medium expansive soil as the matrix of the expansive soil, triaxial samples with filled fissures were prepared. By carrying out triaxial tests, the strength properties of expansive soils with filled fissures are studied. On this basis, a slope stability analysis method that could reflect the impact of filled fissures, with calculation conditions which were close to the true state of the fissured expansive soil slope, was proposed, and the stability analysis of the fissured expansive soil slope was carried out. This method can provide a reference for solving the slope stability problem in the expansive soil distribution area.