Geophysical and geotechnical investigations for a major highway in a quick-clay area

Abstract

The paper presents results from site investigations for a major public highway project close to Trondheim in Mid Norway. The planned road is located in an area with thick deposits of sensitive and quick clays, and is expected to represent both local and global stability issues. The site investigations included 2D resistivity measurements and conventional geotechnical borings, such as rotary pressure soundings, total soundings, cone penetration tests (CPTU), undisturbed piston sampling and pore-pressure measurements. Extensive laboratory investigations were also carried out, including salinity measurements. The 2D resistivity measurements were carried out to detect the distribution of leached clay, and the results were used for planning of the subsequent geotechnical investigations. This is one of relatively few Norwegian studies using 2D resistivity measurements in evaluation of ground conditions in an industry project. There was very good agreement between the data sets with respect to presence of sensitive or quick clays. The investigation hence clearly points out that the combination of resistivity measurements and geotechnical borings has the potential of becoming a powerful site investigation strategy, particularly in mapping of large areas or long-stretched road corridors.