Abstract
Landslides can substantially impact the fluvial systems, which is why the continuous mapping of their extent, evolution and stability assessment is crucial. However, in such environments, material identification (e.g. colluvium) and subsurface characterization by the methods used for geologic mapping and geotechnical investigation is often a challenging task. Thus, these classical invasive methods may benefit from geophysical techniques to enable and enhance our understanding of the subsurface in these areas. To examine such integrated approach, Multi-Channel Analysis of Surface Waves (MASW) combined with Electrical Resistivity Tomography (ERT) were applied on a geomorphologically active fluvial valley in Sobradinho (the Federal District of Brazil). The subsurface materials showed a specific range of resistivity values as dry soil, saprolite, and landslide slip surface. The 1D shear wave velocity (Vs) model showed an increasing trend of Vs with depth at a location away from the landslide mass, while the longitudinal profile (over the landslide) showed an anomalous change in Vs (~ 250 to 400 m/sec). Based on the existing information about the landslide, the ERT appeared to be an effective method over MASW. This study shows how the integration of geophysical data with the geological and geotechnical investigation helps to obtain a more realistic or unambiguous model of the subsurface.
Highlights
The instability of colluvial slopes, which are usually encountered around fluvial valleys, presents a significant challenge for geohazard risk assessment in many countries around the world, including Brazil
A geophysical investigation combining Multi-Channel Analysis of Surface Waves (MASW) and Electrical Resistivity Tomography (ERT) methods was carried out in this study to examine if such combination could improve the characterization and delineation of the slip surface of the Sobradinho landslide located in a morphologically active fluvial valley
A bimodal propagation of the Rayleigh wave was observed over the dispersions obtained from all three seismic lines taken in the study
Summary
The instability of colluvial slopes, which are usually encountered around fluvial valleys, presents a significant challenge for geohazard risk assessment in many countries around the world, including Brazil. Several studies of this phenomenon have been conducted to understand the mechanism of instability (Ehrlich et al, 2018 and references therein; Hussain et al, 2019a), which can be attributed to different factors and processes that lead to deterioration of the geotechnical conditions as changes of the shear strength and effective stress (Keefer and Larsen, 2007). Liquefaction caused by a combination of saturated materials and seismic loading can trigger mass movement in colluvial slopes. The correct identification of colluvial materials, as well as geomorphological units, surficial fractures, and cracks (that provide permeable paths to the rainfall water) are crucial for landslide risk assessment around fluvial valleys
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