Structurally Constrained 4D ERT Monitoring to Image Hydrological Processes Leading to Landslide Reactivation

Future environmental and climate change will affect the frequency and magnitude of landslide occurrences. A major focus of research is therefore to gain an improved understanding of the processes contributing to unstable slopes and the associated triggering mechanisms. This study considers the use of a combination of one-off seismic and geoelectrical monitoring measurements (from a 34 month period leading to landslide reactivation) to gain detailed understanding of the hydrological conditions leading to landslide reactivation. The study site is the Hollin Hill landslide field observatory that comprises a suite of geophysical, geotechnical and environmental sensors, thus offering the opportunity to compare and inform interpretation of the different data streams. The 4D electrical resistivity tomography (ERT) inversion was structurally constrained employing results of a combined P- and S-wave seismic refraction tomography (SRT). The ERT results were temperature corrected and translated into values of gravimetric moisture content (GMC) using laboratory derived GMC-resistivity relationships. The results show seasonality effects for the first year of monitoring, followed by imaging of crack built up and deep moisture penetration leading to failure of the back scarp. Elevated moisture contents, as an effect of prolonged rainfall, were imaged throughout the landslide prior to its reactivation.