Application of a physically based methodology to define the input data of geotechnical slope model for the source areas to rapid landslides

The application of physically based models for susceptibility assessment in areas affected by debris flows requires the knowledge of topographical, geomorphological, stratigraphic, hydrogeological, geotechnical and rainfall input data. Among these, geotechnical data are of relevant importance for the results obtained by model implementation. If significant geotechnical properties of the soils involved by landslides are not available, any prediction deriving by their use could be a simplistic exercise. To overcome this issue, in the preliminary stage, data from the literature – for soil types like those involved in the debris flows – can be used as input parameters of model to localize, in the areas affected (or potentially affected) by landslides, the subsequent geotechnical investigations (in situ and laboratory) necessary to obtain an upgraded geotechnical slope model. The paper shows the application of the Transient Rainfall Infiltration and Grid-based Slope-Stability model (TRIGRS) to an area affected by debris flows for inception susceptibility assessment. Firstly, the model has been applied using geotechnical parameters available in literature, so the zones potentially affected by similar landslides have been identified. Based on these results, detailed in situ investigations have been located and carried out in the identified inception zones. By the results of in situ surveys and laboratory tests a more reliable geotechnical slope model for the study area has been defined. Therefore, TRIGRS has been applied a second time to the area using this geotechnical slope model. This last application of TRIGRS provided a more reliable inception susceptibility zoning map of the area as demonstrated by the obtained statistical performance metrics (TPR higher than 97%, FPR equal to about 33%, and AUC equal to 87,2%).