Stability Analysis of Coastal Slopes Based on a Semi-Diurnal Tidal Water Level Variation Model

To investigate the impacts of tidal level fluctuations on the groundwater dynamics and stability of coastal slopes, a numerical simulation framework was developed using the SEEP/W and SLOPE/W modules in GeoStudio. By combining saturated–unsaturated seepage mechanics with the finite element limit equilibrium method, the semi-diurnal tidal cycle was simulated to derive analytical solutions for the internal water-level distribution within the slope, and to assess the factor of safety as well as the geometry of the potential slip surface. By examining the evolutionary patterns of the phreatic surface and pore-water pressure inside the slope, this work elucidates the failure mechanisms of coastal slopes under tidal forcing. The findings demonstrate that tidal fluctuations induce periodic, hysteretic variations in the slope’s phreatic surface, which peaks at the conclusion of the rising tide (t = 0 h) and reaches its trough at the end of the falling tide (t = 6 h). Pore-water pressure alterations are predominantly localized in the near-surface region of the slope. The slope’s factor of safety exhibits pronounced oscillations in tandem with tidal levels, attaining a maximum at the end of the rising tide (t = 0 h) and a minimum at the end of the falling tide (t = 6 h), thus identifying the falling tide phase as the critical window for instability. Tidal changes exert a comparatively limited influence on the spatial positioning of the slip surface, underscoring the concealed and abrupt nature of tidal impacts on slope stability. Numerical simulation outcomes align closely with theoretical calculations, with small relative errors, which verifies the consistency and effectiveness of the simulation and theoretical calculations.