On the integrated use of geophysics for quick-clay mapping: The Hvittingfoss case study, Norway

Quick-clay landslides are a known hazard in formerly glaciated coastal areas; hence, large efforts are devoted to map the distribution of quick clays. In this paper, we focus on one particular Norwegian site (Hvittingfoss, 80 km south-west of Oslo), which was remediated against potential landsliding 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., seismic and resistivity Cone Penetration Testing with pore pressure measurement) in order to improve our geological understanding of the site and to establish a suitable, integrated and multi-disciplinary approach to better map the special extent of the quick-clay zone. The integration of the different geophysical methods and geotechnical measurements allow a more precise imaging and characterisation, both spatially and vertically, of the sedimentary sequences and of the underlying bedrock. The resulting geological model is then populated with the quantitative parameters derived from the geophysical measurements. 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.