Further case studies:
  • Geophysical investigations within the scope of the recycling of an idle site 
Case study 2: Investigation of coal diapirs and gravel banks

After the sedimentation of the coal in Central Germany steep dipping coal seams -so called coal diapirs- were formed by glacial stress. At the same time gravel banks sunk into the coal seams. As the coal seams are not horizontal in those areas, the geological situation should be investigated as precise as possible by geophysical measurements.

With a maximum exploration depth of 12 m below surface, 2D geoelectric surveys with a spacing of 2 m between the electrodes were performed.

In fig. 3 the result of the investigation along one profile is shown. At the lower picture, showing a map of the resistivity distribution, a bed of gravel that causes the high resistivities (red-brown colours) could clearly be seen. The real side-cut presented in the photo above is situated nearly parallel to the surveyed profile. It shows a very good co-incidence between the geoelectical results and the real geological situation. With that network of 2D geoelectrical profiles, the knowledge concerning the distribution of coal diapirs and gravel subsidences could be precised. Existing wells were used to calibrate the geoelectrical results thus providing a very good estimation of the base of the gravel horizon.

Fig. 3: Comparison of the geoelectrical resistivity map and the real side-cut of the same area