3D SEM Approach to Evaluate the Stability of Large-Scale Landslides in Nepal Himalaya

This paper deals with the stability of large-scale landslides with the aim of exploring reliable safety factor in 3-dimensions (3D) for the effective implementation of landslide stability enhancement measures (LSEM) in the mountainous country like Nepal. The paper uses ‘Specfem3D_Slope’, an open-source spectral element method (SEM) based program that can effectively handle the major challenges of 3D modeling to evaluate the stability of large-scale landslides. The SEM prefers p-refinement techniques (increasing the degree of interpolation or polynomial degree or spectral degree) instead of h-refinement (refining the mesh related to elemental budgets) unlike to FEM. Then the safety factors, thus obtained seem to be reliable values as per the material properties and slope model supplied, and that can encouragingly be used in effective design and implementation of various LSEM projects. Moreover, a complete draw down effect after the LSEM gives a complete sense of the effectiveness of the measures itself. In addition, the paper emphasizes some experimental tests to know the displacement behavior of landslide’s soils (e.g., Krishnabhir landslide). A theoretical model is chosen to do some deeper exercises on 3D for the reliability of the results and later implements such criteria for ‘Laprak landslide’ of Nepal Himalaya. With this modeling method (elasto-plastic) the paper incorporates all possible instability conditions like pseudo-static earthquake loading, structural loading over the sliding mass, partially saturated ground water profile, etc., the same conditions as implemented by previous researchers for Laprak landslide. The study of two major landslides of Nepal ‘Krishnabhir landslides’ (relates to major highway) and ‘Laprak landslides’ (relates to a large number of settlements over the moving mass) reflects the major issues of large-scale landslide stability modeling of Nepal Himalaya.