# Strength Characteristics and Slope Stability Analysis of Expansive Soil with Filled Fissures
## 6 Conclusions  
Fissured expansive soils were widely distributed in the mid-route of the South-to-North Water Transfer Project in China. Most of the fissures were filled fissures, which were filled with the gray-green clay. The gray-green clay was a typical strong expansive soil, and its content of clay particles and hydrophilic minerals was extremely high. The long-large filled fissures controlled the stability of the deep expansive soil slope. The limitations of the commonly used test methods for dealing with expansive soil filled fissures were analyzed, based on the conventional triaxial test sample preparation method; the mold was improved, the strong expansion fissure filler was manually placed in the sample, and the thickness and the inclination angle of the filled fissure were controlled. The layered filling--bevel cutting--refilling was the basic idea of the sample preparation device and method. A sample preparation device for triaxial test sample containing a filled fissure was designed. Triaxial tests of the expansive soil with filled fissure were carried out. Samples were prepared with filled fissures with inclination angles of \(15^{\circ}\), \(30^{\circ}\) and \(45^{\circ}\), and with a thickness of 7 mm, and a sample without filled fissures for comparison. After setting the filled fissures of gray-green strong expansive soil in the medium expansive soil matrix, it had a greater impact on the mechanical properties of the expansive soil, resulting in strength attenuation at various load levels in the triaxial tests. The strength attenuation was positively correlated with the inclination of the filled fissure. The strength parameters of expansive soils with filled fissures were basically stable, in which the cohesive force \(c\) was about 12 to 15 kPa and the internal friction angle \(\varphi\) was about \(3^{\circ}\) to \(6^{\circ}\). The deformation characteristics of the samples had a tendency to develop from strain hardening to strain softening after setting the filled fissures, and it was most significant when the fissure was filled with a \(45^{\circ}\) inclination angle. This provided parameters for the slope stability calculation of the actual project, and also provided a basis for the analysis of the strength of the filled fissure according to the geological survey on site, which was convenient for quickly predicting the possibility of landslide occurrence and the type, location and scale of the landslide. The spatial distribution of the filled fissures in the slope was included in the model, and the strength parameters of the filled fissures were considered. The geological model of the slope with filled fissures was generalized, and a stability analysis method for the expansive soil slope with filled fissures was proposed. A typical landslide in the South-to-North Water Transfer Project was selected as an example to analyze the slope stability. It could be found that the safety factor of the slope was about 0.9. The slope was in an unstable state. The sliding surface was affected by the vertical fissures on the top of the slope and the slow-inclined long-large fissures in the slope, and the shape of the sliding surface was a broken line, which was basically consistent with the actual failure characteristics of the landslide. Figure 11: Calculate sliding surface and actual sliding surface. (**a**) Homogeneous expansive soil slope; (**b**) expansive soil slope with filled fissures. **Author Contributions:** Conceptualization, H.L. and Z.D. ; methodology, Z.D. ; software, H.L. ; validation, J.L., J.G. and S.C.; formal analysis, Z.D. ; investigation, H.L. and J.G. ; resources, J.L. ; data curation, J.G. ; writing--original draft preparation, Z.D. ; writing--review and editing, H.L. ; visualization, J.L. ; supervision, S.C.; project administration, Z.D. ; funding acquisition, Z.D. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the National Natural Science Foundation of China, grant number 41702337.