Slope stability analysis with nonlinear failure envelopes

The nonlinearity of shearing resistance in soil could be explained as interlocking or dilatancy. The dilatancy is generally stress level dependent and it lies on the stress range of interest in particular problems, especially for slope stability. Based on such a concept, analytical expressions for the nonlinear failure envelopes in terms of effective stresses are critically reviewed. They are classified in three major groups as power type, parabolic type, and hyperbolic type. The nonlinear failure envelopes can be obtained from routine laboratory shear test and triaxial test by optimization technique using commonly used SPREADSHEET software, and then they can be used in limit equilibrium, stress-stain analyses, and the development of the constitutive models as better approximation than the classical linear relation. On the base of Janbu's generalized procedure of slice (GPS), an iterative method that incorporated several nonlinear failure envelopes in the SPREADSHEET setup by the authors is presented. The basic principle is to transfer equivalently the shearing resistance of each point on the concerned nonlinear envelope to the Mohr-Coulomb linear relation that is tangent to the nonlinear envelope with relevant cohesive and frictional parameters. Finally, an example is resolved to show the methodology that how the iterative technique is used.