Geothermische Bohrungen in Staufen im Breisgau: Schadensursachen und Perspektiven

Geothermal drillings in Staufen/Breisgau (Germany): damage causes and perspectives.

In 2007 seven geothermal borehole heat exchangers with a planned depth of 140 m were installed of a small square next to the historic town hall of the City of Staufen for its heating and cooling. Some weeks after completion of the borehole heat exchanger drillings an uplift movement started, causing heavy damages to the surrounding buildings. Officially 269 buildings are currently affected, some are deemed structurally unstable. One office building had to be evacuated. An artesian aquifer was connected hydraulically to the anhydrite bearing Gipskeuper Formation. Anhydrite reacts to gypsum which causes volume extension. The swelling process, once initiated, cannot be stopped easily because the process itself opens and closes water paths. Furthermore Staufen is located on the eastern graben flank of the Upper Rhine Valley on a strongly tectonized massif. Due to these fissured and faulted formations, the prediction of water movement and the swelling process is very difficult. With a newly developed grouting some major cavities near the wellbores were sealed off. This has been partly successful because the maximum uplift rate of about 10 mm/month decreased to less than 4 mm/month (data of May 2012). Additional problems could arise from the good solubility of gypsums in water, which may cause sinkholes. In the last months some small subsidence phenomenon already occurred locally within the uplift area.