A comparative analysis of terrain stability models for predicting shallow landslides in colluvial soils

Most of the slopes of the hilly areas of the Apennines are composed of colluvial soils originating from the weathering of the bedrock and down slope transportation. Shallow slides affect this superficial cover, depend largely on the surface topography and are a recurrent problem. SINMAP and SHALSTAB are terrain stability models that combine steady state hydrology assumptions with the infinite slope stability model to quantify shallow slope stability. They have a similar physical basis but they use different indices to quantify instability. The purposes of this study are to test and compare the approaches of SINMAP and SHALSTAB models for slope stability analysis and to compare the results of these analyses with the locations of the shallow landslides that occurred on November 2002 in an area of the Oltrepo Pavese (Northern Apennines). The territory of S. Giuletta, characterized by clayey–silty colluvial soils, represents the test site. The Digital Elevation Model was constructed from a 1:5000 scale contour map and was used to estimate the slope of the terrain as well as the potential soil moisture conditions. In situ and laboratory tests provided the basis for measuring values for soil hydraulic and geotechnical parameters (moisture content, soil suction, Atterberg limits, methylene blue dye adsorption, hydraulic conductivity). Soil thickness was extracted from a soil database. An inventory of landslide from interpretation of aerial photographs and field surveys was used to document sites of instability (mostly soil slips) and to provide a test of model performance by comparing observed landslide locations with model predictions. The study discusses the practical advantages and limitations of the two models in connection with the geological characteristics of the studied area, which could be representative of similar geological contexts in the Apennines.