Abstract: Solving the stress state of the slip surface constitutes the core issue in the stability analysis of subgrade slopes. To facilitate the engineering application of analytical methods for slip surface stress, this study introduces a methodology for determining slip surface stress in subgrade slopes, grounded in the stress superposition principle within an elastic semi-infinite space. This approach treats the slope surface as the boundary of an elastic semi-infinite space and computes the stress state at any point within the slope body by the hypothetical resistive force acting on the slope surface (derived from the Mindlin solution). Based on this framework, the slip surface stress can be determined accordingly. Furthermore, this study introduces a model test method for measuring slip surface stress. Building upon this, two example slopes with potential slip surfaces were designed. The slip surface stresses obtained from the analytical method and the model test method were comparatively analyzed to verify the rationality of the analytical method. Concurrently, a calculation method for the stability coefficient based on the analytical solution of slip surface stress was proposed, and its engineering application value was explored. The research findings are as follows: Example calculations show that the proposed analytical method aligns fundamentally with model test results. Statistical analysis indicates that the correlation coefficients for normal stress and shear stress between both methods exceed 0.5, with the p-values of the correlation coefficient tests greater than 0.05, demonstrating a strong correlation and insignificant differences. The proposed stability coefficient method enables the simultaneous determination of local stability coefficients and global stability coefficients, reflecting both the overall landslide stability and the failure mechanism of potential landslides. Based on the explicit principle of stress superposition and facilitated by straightforward programming implementation, the proposed theoretical calculation method not only extends the existing analytical framework for stress calculation in homogeneous subgrade slopes, but also provides a clear pathway for its extension to more complex conditions. It offers a novel analytical tool for both stability evaluation and failure mechanism analysis of subgrade slopes.

Key words: subgrade slopes, stress state, Mindlin solution, model test, statistical analysis, local safety factor