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Soft bands may widely exist in sites, and their presence complicates the analysis of slope stability, particularly when the limit analysis method is adopted. Note that the use of the limit analysis method is capable of providing rigorous lower and upper bound solutions and hence is widely used in soil slope stability analyses. To account for soft band effects, finite-element lower-bound (FELB) and finite-element upper-bound (FEUB) approaches are introduced in this study. Finite element discretization aids in the construction of a statically allowable stress field and kinematically admissible velocity field, which are prerequisites for limit analysis. In combination with a modified pseudodynamic approach, seismic slope stability analysis is evaluated through linear programming. Lower and upper bound solutions of the slope safety factor (FoS) are optimized with an interior point algorithm, which aids in better estimating the true FoS of seismic slope stability. The nonassociated flow rule is also discussed herein. After validating the upper and lower linear programming models by limit equilibrium and FEM, the soft band's effects on seismic slope stability are discussed, and a rotational-translational failure mechanism is revealed by critical velocity fields. A less than 5.1% difference between lower- and upper-bound solutions is favourable for providing a reliable reference for slope design. [ABSTRACT FROM AUTHOR]

A finite-element upper-bound procedure is presented to assess the stability of a soil slope under reservoir drawdown and rainfall conditions. In order to overcome the scientific challenge of generating a kinematically admissible velocity field, discretizing the problem of interest into finite elements is carried out for this specific purpose, and based on which the upper bound formulation of slope safety factor is derived. The slope stability analysis is transformed to the optimization of a linear programming model under four constraint conditions, by virtue of an interior-point algorithm. Steady-state and transient water flows are discussed. Based on the soil–water characteristic curve (SWCC), matric suction above the phreatic surface is considered so as to provide a reliable assessment for unsaturated slope stability. True cohesion of soils and apparent cohesion stemmed from matric suction are combined to describe the shear strength of unsaturated soils. After validating the robustness of the proposed procedure by limit equilibrium and FEM, it is further applied to evaluate the slope stability under (rapid, general, slow) reservoir drawdown and rainfall conditions. [ABSTRACT FROM AUTHOR]