Circular Slip Surface
All methods of limit equilibrium assume that the soil body above the slip surface is subdivided into blocks (dividing planes between blocks are always vertical). Forces acting on individual blocks are displayed in figure.
Static scheme of slice
Here, Xi and Ei are the shear and normal forces acting between individual blocks, Ti and Ni are the shear and normal forces on individual segments of the slip surface, Wi are weights of individual blocks.
Individual methods of slices differ in their assumptions of satisfying the force equations of equilibrium and the moment equation of equilibrium with respect to the center O.
The program allows for adopting one of the following methods:
Ground water specified within the slope body (using one of the five options) influences the analysis in two different ways. First when computing the weight of a soil block and second when determining the shear forces. Note that the effective soil parameters are used to relate the normal and shear forces.
Introducing anchor forces and water above the ground surface into the analysis
Anchor forces are considered as external load applied to the slope. They are taken with respect to one running meter [kN/m] and introduced into the moment equation of equilibrium. These forces should contribute to additional stability, if that cannot be achieved in a different way. There is no limitation to the magnitudes of anchor forces and therefore it is necessary to work with realistic values.
Influence of water above the ground surface is considered as set forces acting perpendicular on the ground surface together with pore pressure along the slip surface, which is derived depending on the depth of slip surface measured from the ground water table. The forces acting on the ground surface enter the moment equation of equilibrium as forces acting on respective arms measured towards the center of the slip surface.
Optimization of circular slip surface searches the most critical surface (the lowest SF).