Modeling the stability of terraced slopes: an approach from Valtellina (Northern Italy)

This study focuses on the relationships between hydrological processes and the stability of terraced slopes. Emphasis is given to the presence of dry-stone retaining walls and how to explicitly consider them when performing a distributed stability analysis. Valtellina, an Alpine valley of Northern Italy, is selected as study area. In detail, the slope uphill the village of Tresenda, affected by several superficial landslides since 1983, is studied. Dry-stone walls heavily influence the hydrological and geotechnical processes at the slope scale, and it is therefore crucial to consider them when performing a stability analysis on mountainous terraced areas. Walls are usually 0.60-1.00 m wide, and therefore, base maps (Digital Elevation Models and soil depth map) with a horizontal resolution of 1 m have been appositely derived. Working at this horizontal resolution leads to the failure of some basic assumptions of the infinite slope method, usually applied for distributed stability analysis. In this study, we propose an alternative approach based on the global method of equilibrium applied to sections of single terraces one cell wide. A specific sensitivity analysis allowed to fix some constrains to the model, in order to improve the reliability of the results under different mechanical and hydrological conditions. The proposed stability model was calibrated and evaluated on recorded past rainfall events. It resulted to be a good instrument for the identification of the most unstable areas when stressed with high pore-water pressure conditions.