Borehole Electromagnetics – A Case Study from Hamburg, Germany

As part of the Grasbrook redevelopment in Hamburg, Germany, borehole electromagnetics was applied to support unexploded ordnance (UXO) detection across a 120,000 m² former port area. Approximately 77,000 boreholes were drilled, including through reclaimed water zones to depths of up to 15 meters. The work was carried out with high-precision, carriage-mounted drilling equipment integrated with GIS, allowing for accurate positioning and vertical alignment of each borehole.

The survey method is based on Transient Electromagnetics (TDEM) and uses four directional measurements to assess the surroundings of each borehole. This directional approach improves the ability to distinguish between isolated metal objects and natural conductive layers. In areas with strong magnetic interference—such as near drill piles or steel foundations—electromagnetics helped clarify UXO assessments.

Field data show that true UXO objects produce consistent signals in both magnetic and electromagnetic data, while anomalies lacking an EM response could be excluded. The case examples demonstrate that borehole electromagnetics improves interpretation quality, especially in complex subsurface conditions, and supports more reliable object identification before excavation.