Use of a borehole shear test method for geotechnical mapping of landslide risk areas

Landslides are the natural disasters that cause the highest number of fatalities in Brazil, many of which could be prevented by measures for managing land use and occupation. In order to indicate acceptable ranges of occupation and urban expansion, there is a need to generate maps that take into account the susceptibility of the terrain to shallow landslides. To do this, we used the methods proposed by Regina Davison Dias, in which lithological and pedological maps are combined to generate geotechni-cal maps. Parameters from the characterization of the geotechnical units were inserted in the SHALSTAB (Shallow Slope Stability) model, together with a hydrological model and a Digital Terrain Model (DTM). Each pixel of the map is analyzed individually, and all are combined to produce a susceptibility map for shallow landslides. It is therefore necessary to choose and analyse methods to determine soil-strength parameters that are easy and quick to produce. In Brazil, the most commonly used method for obtaining strength parameters is direct shear, while in situ assays, such as the Borehole Shear Test (BST) are still little explored. The present work evaluates the use of the Borehole Shear Tests to generate maps of susceptibility to shallow landslides. For that, we chose a hydrographic basin and applied the methodology of Regina Davison Dias, comparing the results obtained from both direct shear and borehole tests, based on the final maps and on the envelopes obtained by Mohr-Coulomb criteria.