Further case studies:
  • Investigation of coal diapirs and gravel banks 
Case study 1: Geophysical investigations within the scope of the recycling of derelict land

New buildings shall be erected on a brown field site formerly covered with buildings for a longer period. Unexpected foundation remains were found during investigation drilling, although a deep rubble clearance has been performed. For further planning it is very important to get information about the dimensions of remaining foundations and about possibly existing additional ruins at the investigation site because they will strongly hinder the intended works. The near-surface subsoil can be investigated with non-invasive geophysical measurements providing maps with indications of remaining foundations, cellars and possibly existing contaminated areas.

Geoelectric surveys were performed to derive information about the different buried materials as well as existing ruins and possibly existing openings. These surveys were completed by magnetic surveys that are particularly sensitive to ferrous reinforcements and other ferrous burials. As the both methods are measuring different physical parameters, the combined interpretation of both methods will result in a higher level of confidence e.g. for the assignment of materials.

Figure 1 shows resistivity models of the subsoil down to a depth of 12 m that were derived by a 2D inversion of geoelectrical data. Whereas along line 1 below 2.5 m of rockfill nearly everywhere the natural ground is found, along line 2 several anomalies are detected which were produced by ruins and metallic burials. Figure 2 shows a map of the total magnetic field for the whole investigation area. The distribution of the foundation remains in the subsoil with their ferrous reinforcements can clearly be seen. Between the two nearly E-W striking linear structures several crossing elements and smaller anomalies are visible that indicate further building remains but also possible tubes and pipes.

The results of the geoelectric and magnetic investigations provide a very good review about the remaining ruins in the ground. Due to the complementary information of both methods it is partly possible to characterize the materials. For this reason the geophysical investigations provide a good basis for the planning of all further works.

Fig. 1: Resistivity models of two lines derived by 2D inversion of geoelectrical data

Fig. 2: Total magnetic field for the whole investigation area.