Unified Slip Line Solution for Seismic Slope Stability in Cohesive-Frictional Soils Considering the Intermediate Principal Stress Effect

Traditional methods for slope stability analysis usually do not consider the influence of the intermediate principal stress, though it has certain favorable impacts on the strength of geomaterials, such as soil and rock. Hence, this study presents the unified slip line solution for classical slope stability problems under seismic conditions. The analysis is conducted based on an integrated framework of the unified strength theory and the slip line approach. The unified strength theory incorporates the effect of the intermediate principal stress on slope stability by introducing a specified parameter, b. In contrast, the slip line theory precludes the need for any predefined slope geometry and slip surface in the analysis. Instead, the slope geometry required to sustain the stability with a prescribed factor of safety (FS) is derived for slopes in cohesive-frictional soils. In addition, the earthquake effect is captured using the pseudo-static approach. The slope profiles thus derived from the current formulation are found to have a reasonable morphological similitude with natural slopes. Additionally, the results indicate that the unified strength theory parameter b substantially affects the seismic slope stability. With an increase in b, the slope profiles are generally seen to form a steeper layout, revealing the fact that the potential strength of the slope medium is effectively utilized. Further, a rational comparison of the present results with the solutions available in the literature affirms the legitimacy of the proposed approach in providing practical design guidelines for optimal slope profiles and intimating the need for slope-strengthening measures to prevent any imminent slope failures in advance.