Pseudodynamic Analysis of Strength Nonlinear 3D Soil Slopes Based on Multicone Failure Mechanism

Accurate evaluation of the stability of three-dimensional (3D) slopes in seismically active regions is crucial. However, conventional assessments of slope stability often utilize the classic Mohr–Coulomb criterion to describe the strength parameters of geotechnical materials, which does not correspond to the actual situation. In this study, the multitangent technique is employed to determine the strength envelope of the nonlinear power-law criterion, addressing soil strength nonlinearity. Meanwhile, a new multicone failure mechanism is introduced to better capture 3D slope instability characteristics. The spatial-temporal effects of seismic acceleration are characterized through the modified pseudodynamic method. Two stability evaluation measures—the stability factor and the stability number—are derived, with optimal solutions obtained through a hybrid optimization algorithm. Comparative analysis with existing research confirms the efficiency and reliability of the proposed approach. Parameter study results indicate that soil strength nonlinearity significantly influences the impact of seismic forces on slope stability. The increase in seismic acceleration coefficients correlates negatively with slope stability, a trend that is accentuated as the nonlinear coefficient reduces. The average reduction rate of the slope stability factor is 27.22%. The back-calculated stress points indicate that at a nonlinear coefficient of m = 2.0, there is increased discreteness in the distribution of stress points on the strength envelope and equivalent strength parameters, with a higher number of points located within the tensile stress region.