# Strength Characteristics and Slope Stability Analysis of Expansive Soil with Filled Fissures
## 5 Stability Analysis of Expansive Soil Slope Considering Filled Fissures  
### Engineering Geological Survey of the Landslide  
The landslide in Nanyang section of the middle route of the South-to-North Water Transfer Project was selected as an example to analyze the slope stability (Figure 9a). The Nanyang section was located in the southern part of the South-to-North Water Transfer Project and was a typical strong expansive soil distribution area. The expansive soils in the area were mainly Middle and Lower Pleistocene flood sedimentary clays, and Neogene lacustrine sedimentary clays, including brown clay and gray-green clay.  
The landslide was located in the medium expansive soil area, the original slope ratio was 1:2, the top elevation of the slope was 145.695 m, and the bottom elevation was 131.384 m.  
Figure 9: The landslide characteristics. (**a**) Site location; (**b**) landslide plan; (**c**) landslide profile and landslide engineering geological information.  
The formation was the Middle Pleistocene alluvial (Q2 al+pl) clay, and according to the detailed geological survey on site, it was found that the slope could be divided into three layers (Figure 9c). The first layer of the landslide was reddish brown clay containing a small amount of iron manganese nodules--the thickness was about 3 m. The second layer was brown-yellow clay with a thickness of about 4 m, and the content of calcium nodules and black iron manganese nodules was low. The third layer was brown clay and gray-green clay, containing some black iron manganese nodules.  
The sliding direction of the landslide was 130\({}^{\circ}\), and the total length of the landslide body was about 38.48 m. The trailing edge of the landslide was generally vertical, with a length of about 3.4 m. The left side of the landslide was heavily deformed and severely broken. The maximum height of the steep silk was 1.8 m, and the height of the right side was 0.2 to 0.8m. The front edge of the landslide cut out along the bedding gentle fissure at the slope foot. The landslide profile is shown in Figure 9.  
Geology cuts were arranged on both sides of the slope and fissures were recorded. It was concluded that there were 105 fissures in the length of \(L>1.0\) m in the slope. The fissures developed mainly in two groups, and they were mainly low inclination fissures, followed by medium inclination. One group of along-slope fissures had the tendency of 120\({}^{\circ}\) to 140\({}^{\circ}\) and the inclination of 5\({}^{\circ}\) to 50\({}^{\circ}\), the other group of anti-slope fissures had the tendency of 310\({}^{\circ}\) to 325\({}^{\circ}\)and the inclination of 3\({}^{\circ}\) to 60\({}^{\circ}\).  
The steep inclination fissures along the slope developed in the upper part of the slope, the inclination angle was 75\({}^{\circ}\) to 84\({}^{\circ}\), and the fissure surfaces were flat and smooth, filled with gray-green clay. At the foot of the slope, low inclination angle fissures along or against the slope developed, the inclination angle was 11\({}^{\circ}\) to 28\({}^{\circ}\), and the fissure surfaces were also flat and smooth, filled with gray-green clay.