Landslide susceptibility evaluation in Alpine environment: 2. Thermo-hydro-mechanical modeling for the response to climate-related variables

This paper is Part 2 of two companion papers, proposing a multidisciplinary approach to assess stability and velocity evolution of a large landslide located in the Central Italian Alps (upper Valtellina region): the Ruinon landslide. Part 1 of this work presented a 3D stress–strain finite element analysis, which assessed the morphological and geomechanical predisposition of the slope to gravitational instabilities and defined the current stress state along the slope. In this paper, a thermo-hydro-mechanical (THM) numerical analysis is applied to the landslide shear zone, to assess the link between landslide driving factors and the shear band material response. Data used as input for the model were pore pressure, reference stresses and initial temperature at the sliding surface, as well as the monitored velocity of the landslide body, assumed to move as a rigid block. The shear band material was modelled as a visco-plastic medium with thermal softening and velocity hardening, thus thermal- and load-rate sensitivity of the material were estimated through laboratory testing. To this end, triaxial compression tests with thermal control were performed on rock samples representative of the shear band. To constrain the model, results of the analysis presented in Part 1 were used to define the stress state at the sliding surface and the relationship between pore pressure and shear stresses. Then, pore pressure data from in-situ piezometers relevant to the period 2014-2018 were introduced and a best fitting between modelled and monitored landslide velocities was obtained. Finally, velocities were forecasted for the period 2018-2020 and a process of validation was applied using field displacement. The outputs of the model adequately simulate the measured landslide velocity, reproducing the sliding behavior and its relationship with pore pressure. The presented approach may be applied to further case studies, aimed at defining a novel physics based early warning strategy for landslides.