Basal stability analysis method considering arc length and normal stress correction

When the traditional basal stability analysis methods based on homogeneous ground are used in layered soils, usually the shear strength is weighted average considering soil layer thickness, but they don’t consider either the actual arc length that the sliding surface goes through in every layer or the normal stress on the sliding surface. The factors that how distribution of soil layers influences the basal stability in layered soils are investigated. Two correction methods for the traditional basal stability analysis methods based on homogeneous ground assumption in layered soils are proposed, i.e. weighted average method considering arc length and weighted average method considering arc length and normal stress. Through the calculations of engineering examples, it is found that the results of the weighted average method considering soil layer thickness are far from the actual condition, but the two correction methods, especially the latter, can obtain a result that is close to that predicted by the layered integration method, and can better reflect the effect of soil layers beneath formation of excavation on the basal stability, and what’s more, the calculation process is simple and convenient. The calculated results indicate that the lower layer of sliding surface is extremely important for basal stability, so it’s better to embed the supporting structure fully or partially to the comparatively hard soil layer.