Modelling the post-failure stage of rainfall-induced landslides of the flow type

The geomechanical modelling of failure and post-failure stages of rainfall-induced shallow landslides represents a fundamental issue to the proper assessment of failure conditions and recognizes the potential for long travel distances of the failed soil masses. Considering that these phenomena are among the most catastrophic natural hazards, as a contribution to the topic this paper discusses the potential of a hydromechanical coupled finite element model (FEM) to analyze the post-failure stage using an advanced constitutive model. In particular, simple undrained triaxial tests and experimental evidence of centrifuge tests are reproduced first, for both loose and dense soils. Then, two slope scale benchmarks are analyzed in the cases of vertical downward or horizontal water seepage and for both loose and dense soils. Compared with results obtained through standard limit equilibrium analyses, the coupled FEM provides a new comprehensive framework for failure and post-failure scenarios that includes a significant reduction of mean effective stresses, also in the case of a loose soil slope subjected to vertical downward water seepage. The obtained results are particularly encouraging because they outline the possibility to analyse both the failure and post-failure stages in a unique framework. Moreover, the numerical analyses indicate that the post-failure mechanisms are intimately tied to specific predisposing factors and boundary conditions, rather than to a single mechanical or state parameter of soil, such as, for instance, the soil relative density.