From microstructure to subsurface characterization. Spectral information from field scale time domain induced polarization

Sammanfattning: A large variety of subsurface infrastructure projects of different types can gainvaluable information from tomographic measurements of subsurface physicalproperties.With resistivity and time domain spectral induced polarization (IP),the distributions of the conductive and capacitive properties of the subsurfaceare obtained. Technical developments of time domain IP equipment and newinversion algorithms have led to the possibility of collecting large amounts ofdata and invert for spectral IP parameters. In this way, much more informationabout the subsurface can be extracted from a single measurement compared towhat was possible previously. It is well-known that spectral IP effects arisethrough redistribution of ions at the pore scale, and that spectral IP parameterscan be linked to microscale surface chemical and structural properties.However, much remains to be known about how to analyse and interpretspectral IP parameters from field scale time domain IP measurements.Therefore, the main objective of this licentiate thesis is to focus on these issues.In soils contaminated with free phase non-aqueous phase liquids (NAPLs), thecontaminant phase affects the microgeometry inside the pore spaces of the soil.The results from paper I show that different configurations of the NAPL phaselikely affect the spectral IP response of the soil in different ways. This isexemplified by measurements at a field site, where IP responses are absent inthe NAPL source zone. In contrast, elevated IP responses are observed in thedegradation zone, where the NAPL probably is configured as isolated dropletsin the pore space. In order to investigate probable sources to observed varyingIP responses in a Cretaceous limestone bedrock, the measured spectral IPparameters were compared with the investigations of the microstructure andcomposition of thin sections in paper II. Several characteristics that can affectthe measurements were found, such as presence of certain minerals andvarying texture of the limestone. However, more research is needed in order tounderstand the polarization mechanisms in limestones. Although mostprevious research has been carried out in sand- and claystones, there is a greatpotential to reveal textural and structural properties in any kind of bedrock bymeasurements of spectral IP parameters.