2.2 Soil slope Stability Analysis Circular Arc Method 2.2.1 Basic Principles The calculation is based on the ultimate equilibrium stability of soil slope. The natural homogeneous soil slope loses stability, and the sliding surface is curved, as shown in Figure 5. Usually the sliding surface is close to the arc, which can be calculated by the arc, called the arc method. The arc method was first developed by Swedish scientists. Sweden, which is located in the eastern half of Scandinavia and has a narrow north-south terrain, has a large area of thick, high-sensitivity clay deposited during the glacial period and the post-glacial period. Disturbing the structure of soil during the construction of houses and railways reduces the strength of soil.