The logarithmic-spiral (log-spiral) limit equilibrium procedure for slope stability analysis rigorously satisfies both force and moment equilibrium with a failure surface geometry formulated as a function of the soil’s angle of internal friction. Within the framework of limit equilibrium, this procedure has, in the past, been primarily limited to homogeneous soils. Herein, the log-spiral equation is modified to incrementally capture the complex failure mechanism and stability associated with heterogeneous soils and soils which exhibit anisotropic shear strength. Due to the unique properties of the log-spiral geometry, the critical failure surface and stability may be determined independent of any assumptions with regards to normal forces, which is often necessitated to render other limit equilibrium procedures determinate. This property of the log-spiral method enables full determination of internal statics allowing the demonstration of a rigorous solution through an explicit solution of force equilibrium along with the determination of the magnitude and direction of internal shear and normal forces. With the rigor of the method expanded beyond simply homogenous soils, the log-spiral method is applied in the context of layered soils to study the influence of transition zones between layers both in terms of their width and location within the soil layer. The methodology is also applied to slopes with anisotropic shear strength in which the influence on tension crack depth and stability are explored.