Use of Electrical Resistivity Tomography for Detecting Quick Clay in Norway

Quick clay landslide is a major natural hazard in a number of northern countries including Norway. Detecting and mapping of quick clay is one of the most important measures to reduce quick clay risk. In Norway, the mapping of quick clay relies mostly on geotechnical boreholes with sampling and rotary sounding or total sounding. Geophysical methods such as Electrical Resistivity Tomography (ERT) have been tested at a number of sites, but their use in practice is generally limited. In this study, ERT survey was tested at three sites: a flat benchmark geotest site at Tiller-Flotten, Trondheim municipality in central Norway, a sloping agricultural site at Buvika, Skaun municipality central Norway and a post-landslide site in Ask, Gjerdrum municipality in southern Norway. The purpose is to compare the use of ERT for detecting quick clay for different topographic, geological and historical settings. The results show that ERT can be used to complement information from boreholes and reduce uncertainties in detecting quick clay. However, local variabilities must be taken into account when deciding on survey parameters and processing ERT measurements. Particularly, ERT surveys indicate potential quick clay with resistivity values 20–80 Ωm for Tiller-Flotten, 8–80 Ωm for Buvika and 20–120 Ωm for Ask.