Laboratory experiments to determine the hydraulic heterogeneity of sediments with SIP

The investigation of preferential flow paths in the subsurface is necessary e.g., for the prediction of contaminant transport. Usually, hydraulic methods are applied for that, however, the geophysical method Spectral Induced Polarization (SIP) offers a different approach. As it can be applied from the earth’s surface, the groundwater state does not get disturbed and it is capable of continuous imaging. As hydraulic heterogeneity is a key factor that causes preferential flow paths, it was our aim to describe hydraulic anisotropy and heterogeneity in a series of laboratory experiments electrically and hydraulically.

The experimental set up consists of a sample holder that can contain samples of 18 cubic decimeters in size. Electric and hydraulic measurements can be carried out without disturbing the sample. In two measurement series we investigated a combination of two different sands and a combination of sand and sandstone. The samples were investigated under pressurized groundwater conditions. In the measurement series we varied the volume share of the two components of the sample and the orientation of the layer boundaries relative to the direction of flow.

The results indicate that the electrical parameters like imaginary part of conductivity, phase shift and chargeability are dependent on the sample orientation, but only if there is a significant contrast in the conductivity amplitude of the two components. Otherwise, only the volume share of both components can be determined. The results can be useful for an improved interpretation of field measurements. Future work could be aimed at validating these findings in further measurement series with different material and field measurements.