Soil Strength and Slope Stability (pp. 88–90)

This excerpt from Duncan, Wright and Brandon’s textbook presents the derivation and assumptions of the Ordinary Method of Slices (Swedish Circle) for circular slip surfaces. It explains shear stress distributions, moment equilibrium, and the computation of factor of safety using total and effective stress formulations. Several worked equations highlight how pore-water pressure, slice geometry and assumed shear strength parameters influence the result. The text also discusses the limitations of the Ordinary Method compared with more advanced slice methods and emphasises when simplified assumptions remain acceptable for practice.