18. Geophysical Data Integration for Quick-Clay Mapping: The Hvittingfoss Case Study, Norway

Quick-clay landslides are a known hazard in formerly glaciated coastal areas. Some of Norway’s most densely populated areas are located in potential quick-clay zones and, hence, large efforts are devoted to map the distribution of quick clays. Here, we focus on one particular Norwegian site (Hvittingfoss, 100 km south-west of Oslo), which was remediated against potential sliding in 2008. A set of geophysical methods including Electrical Resistivity Tomography, P-wave seismic refraction tomography, S-wave seismic reflection profiling, and Ground Penetrating Radar, were jointly analysed and complemented with laboratory data and in-situ geotechnical measurements (i.e., CPTU, SCPTU and RCPTU) in order to establish a suitable, integrated and multi-disciplinary approach to map the extent of the quick-clay zone. Through careful integration and interpretation of the different data, the main deposits were identified. Both the clay deposit and the overlying sand layer were precisely imaged and their lateral variations were determined. The underlying moraine deposit and the bedrock were also identified, thereby yielding an idea of the preferential leaching paths. Considering the inherent complexity of quick-clay mapping, the collected data illustrate the benefit of an integrated approach, and emphasise the need for high resolution, proper imaging, calibration and ultimately joint inversion of the different data.