Resistivity measurements as a tool for outlining quick-clay extent and valley-fill stratigraphy: a feasibility study from Buvika, central Norway

Thick, marine clay deposits in valleys along the Norwegian coast are occasionally subjected to large landslides involving quick clay. Detailed mapping of the extent of quick clay is of great interest for planning and protection purposes, as the position of quick clay within slopes has a major impact on the landslide risk. Ground conditions in the small valley of Buvika, mid-Norway, are characterized by thick occurrences of quick clay, which are documented in numerous geotechnical investigations. The resistivity method is potentially well suited for outlining pockets of quick clay since quick clay has a slightly higher electric resistivity (10-80 Omega m) than intact unleached clay (1-10 Omega m). This is due to a higher salt content in the latter. These relations are supported in this study by pore-water salt content measurements. The acquired resistivity profiles are compared with other geophysical data and geotechnical drilling information. Results are promising, and acquired resistivity profiles are interpreted in terms of quick-clay extents, stratigraphy, bedrock influence, and groundwater drainage patterns. Mismatch between intersecting resistivity profiles may be an indication of local geological variations.