Relevant geological-geotechnical parameters to evaluate the terrain susceptibility for shallow landslides: Nova Friburgo, Rio de Janeiro, Brazil

This study aims to contribute to the analysis and classification methodology of geological derivation information regarding the detailed zoning of terrain susceptibility to the occurrence of shallow landslides. A geological-geotechnical classification model for the Corrego D'Antas basin (53 km(2)) was proposed from a geological map (1:10,000). The analysis was based on a set of data built through field investigations and laboratory experiments, later submitted to statistical treatment. Thirty samples were collected from five lithological units and then classified according to the type of material (COL, colluvium; MRS, mature residual soil; YRS, young residual soil) about the following geotechnical parameters: (i) particle size distribution, (ii) Atterberg limits, (iii) stability of aggregates, (iv) void index, (v) dry unit weight, (vi) in situ saturated hydraulic conductivity, (vii) effective cohesion, and (viii) internal effective friction angle. The results allowed the definition of the behavior of the types of materials and the division of the lithological units into three geological-geotechnical units: (i) unit I-gabbro, (ii) unit II-equigranular granite, (iii) unit III-diorite, granodiorite granite, and orthogneiss. These geological-geotechnical units showed a good correlation with the critical classes for landslides related to hydro-geomorphological conditions, vegetation and land use, and slope angle (> 30 degrees). The proposed classification represents an advance in the understanding of geotechnical parameters that are part of the prediction of models of terrain susceptibility to shallow landslides from the geo-hydroecological approach. In addition, it provides an input database for physics-based model predictions in mountainous region.