2D and 3D Resistivity Imaging in an Investigation of Boulder Occurrence and Soil Depth in Glacial Till

The uncertainty regarding depths to bedrock and occurrence of boulders in glacial till can make the planning of a major road construction more difficult. Despite the fact that geophysics is frequently used in many applications and also occurs as a natural method to solve problems in geotechnical engineering, it has often a subordinate role as a site investigation method prior to road construction in Sweden. This project aims at evaluating 2D and 3D resistivity imaging to determine soil depths and track boulders in glacial till. Hopefully, the extent of the excavations preceding a road construction will thus be better estimated in the future, as the geotechnical investigations are suitably complemented. When compared with existing geotechnical data and brought together, both the 2D and 3D resistivity methods are regarded as good producers of reliable soil depth models. However reference data from alternative methods must always be used for validation and calibration of results. It is shown that a 3D resistivity dataset, consisting of a number of parallel CVES profiles, in some cases can give significantly improved resistivity models.