Numerical Study Of Landslide Entire Process Based On Coupled Eulerian-Lagrangian Finite Element Method

Landslides are one of the major geological disasters in China.The consequence of landslides have made strong impacts on the economics and development of our society.Due to complex physical and mechanical processes and various influencing factors of landslides,the existing methods have the following drawbacks and limitations.(a)the strength reduction method of slope stability is based on the Lagrangian finite element method.The obtained factor of safety is not reliable because the commonly failure criterion which is used to determine the factor of safety is non-convergence of numerical simulation,which may be severely influenced by mesh distortion in the Lagrangian finite element method.(b)For the problem of rainfall-induced landslides,which has strong coupling effect of seepage and stress,most previous studies analyzed the pre-failure and post-failure stages separately and hence the physical continuity cannot not be guranteed;(c)For natural slopes with spatial variability,most previous studies focus on the effect of spatiability on slope stability.Limited studies have been conducted to investigate the effects of spatial variability on large deformation behaviors in the post failure stage.For addressing the above problems,the present study utilized the advantage of the coupled Eulerian-Lagrangian(CEL)finite element method and developed three methods with implementation in the platform of ABAQUS.(1)A CEL-based method of slope stability analysis is proposed.The method combines the CEL finite element simulation and the strength reduction method of slope stability analysis.The energy-based failure criterion is introduced to calculate the factor of safety.The proposed method can avoid the mesh distortion in the conventional strength reduction method and obtain a factor of safety based on energy conservation and hence is capable of handling problems with strong nonlinearity.Three example problems are conducted to verify the applicability and effectiveness of the proposed method.(2)An entire process simulation method which combines the coupled seepage and stress numerical analysis of unsaturated soils and the CEL method is proposed for modelling rainfall-induced landslides.The method adopts a two-stage analysis approach:the coupled hydro-mechanical finite element analysis in the pre-failure stage and the large deformation CEL simulation in the post-failure stage.An equivalent state concept is used to ensure the physical continuity between the pre-failure and post-failure stages.The effectiveness of the method are demonstrated by the case studies of the Hongyanzi landslides,Three Gorges Reservior,China and the Tokai-Hokuriku Expressway landslide,Japan.(3)A random coupled Eulerian-Lagrangian(RCEL)method which combines the random field simulation and the CEL method is proposed.With integration of the seepage analysis for unsaturated soil slopes,the RCEL method is further developed for the rainfall-induced landslides.The effects of spatial variability on the failure modes,post-failure deformations and the impact on pipelines are investigated through the example problems.The influences of the coefficients of variation,the correlation lengths of strength parameters and different seepage boundary conditions are discussed.