Evaluation of shallow landslide susceptibility and Factor of Safety variation using the TRIGRS model, Serra do Mar Mountain Range, Brazil

Abstract

Mathematical models on physical bases were developed to predict which areas are susceptible to landslides. The TRIGRS (Transient Rainfall Infiltration and Grid-based Regional) model also offers the possibility of identifying the depth where the Factor of Safety (Fs) reaches values lower than one, thus constituting hypothetical rupture surfaces. The present study aims to assess the variation of the Fs according to depth and the susceptibility of slopes using the TRIGRS model in a basin in the Serra do Mar Mountain Range (Brazil) impacted by landslides in 1967, based on geotechnical and hydrological values collected both from the existing literature and field generated data. Two stability scenarios were generated through the model, with geotechnical and hydrological values available in the literature being used for the first one, and field values collected in the area itself for the second. The scenarios were validated by means of two indexes, Scar Concentration (SC) and Landslide Potential (LP), both taken from the 1967 scar mapping. In validation (SC index), both of them scenarios, albeit with different spatial distributions, presented the same values, that is, 67% (Fs ≤ 1) and 33% (Fs > 1), which indicates a high percentage of correct results. The results pointed to a rupture surface ranging between 2.00 m and 2.50 m. Due to the satisfactory results obtained, TRIGRS may be used by the public authorities interested in defining and monitoring areas of susceptibility and hazard to landslides.