Geoelectrical and IP imaging used for preinvestigation at a tunnel project

At a large tunnel project in Southern Sweden a number of geoelectrical and IP imaging were carried out. The tunnel is drilled through a horst with a complex geology which includes fractures, high water content and weathered zones. The measurements where carried out to compile a geologic model to use in the further planning of the project. The resistivity and IP complements each other very well since they focus on different specific characteristics. IP proved to be useful at locating dolerites and resistivity was useful for the general distribution of fractures. An advantage is that with the seven-channel Lund Imaging system both types of data can be measured in a fast and cost efficient way. Magnetic measurements are a good supplement to pinpoint the exact position of the dolerite. Based on the general geologic information, resistivity and IP measurements recommendations can be given on where to drill in order to improve the geological model.