Liquefaction-Induced Lateral Flow on Gentle Slope With a Focus on Post-Seismic Behavior

Motivated by the flow deformations observed in Uchinada Town during the 2024 Noto Peninsula Earthquake and similar phenomena reported in the 1964 Niigata Earthquake, and inspired by existing theories such as the water film effect and void redistribution, this study conducts a comprehensive numerical investigation of liquefaction-induced lateral flow in gentle slopes. The research focuses on key parameters including the inclination angle, relative density, and permeability. Using OpenSees, two models are developed: the “Inclination Model” (equivalent slope by adjusting gravity) and the “Slope Model” (realistic slope). Both adopt PDMY02 and PIMY constitutive soil models. The results reveal a non-monotonic relationship between slope angle and horizontal displacement, as increasing slope angle shifts the position of shear strain localization. Loose sand undergoes significant and continued lateral deformation after shaking, while dense sand remains mostly stable, indicating that loose sand is more susceptible to lateral flow. Surface conditions, such as low permeability or a clay cover, significantly affect post-seismic behavior. The observed sliding of the clay layer supports the water film effect and void-redistribution theories. Comparing the two models, the realistic slope model shows smaller deformation, emphasizing the importance of slope geometry and boundary constraints. Overall, permeability and drainage conditions govern post-seismic behavior, where delayed dissipation of excess pore water pressure leads to prolonged lateral flow.