Characterization of landslides: a vertical electrical sounding approach

Abstract

The high groundwater activity typically found in landslide bodies favors electrical resistivity methods to characterize the subsurface of landslides. The more water present, the more the current injection into the ground and thus greater the depth of penetration. Furthermore, this generates a higher contrast between the stable and the unstable mass of the landslide. Being a cost-effective and a flexible approach to characterize landslides, 1-D electrical resistivity surveys have the ability to acquire point data similar to borehole logs, thus allows to detect and highlight anomalies of groundwater flow and groundwater build up. These parameters could change from point to point due to the inherit disturbed nature of landslides. A preliminary vertical electrical sounding survey using Schlumberger electrode configuration was carried out along the axis of a creep-type landslide in Badulusirigama, Badulla, Sri Lanka. Four survey points were established for the preliminary VES survey. Each survey line spanned 140 m in length. The data revealed the presence of two types of layers with high (200–370 Ω m) and low (20–60 Ω m) apparent resistivities. Another resistive layer with an apparent resistivity around 100–140 Ω m was found to be sandwiched in the clay layer which was significant to the landslide body and interestingly was not observed in the borehole logs. Furthermore, the southwest inclination of this sandwiched layer explained the southwest region of the landslide being highly active in terms of groundwater discharge through horizontal drains. The bedrock was not detected at three of the survey points highlighting the thick clay layer present in the landslide body. This preliminary survey revealed the general anatomy of the landslide along its axis in terms of the number of layers, type of layers, their thicknesses, the presence of water, and their resistivities.