Koralm Tunnel as a Case Study for Sinter Formation in Drainage Systems

The drainage systems of several tunnels in Austria are heavily clogged with calcite precipitates. Cleaning and water conditioning are cost-intensive for the operating company. The results of the case study Koralm tunnel show that the dissolved calcium in the drainage solutions derives from the ground water and especially from the dissolution of portlandite at the shotcrete. Accordingly, the drainage solutions are often strongly alkaline and as sufficient supersaturation with respect to calcite is reached, calcite precipitates. The carbonate in the calcite sinter is obtained from the ground water or from the absorption of atmospheric CO₂. Extensive chemical, mineralogical, and isotopic analyses as well as hydrogeochemical modelling permit to decipher the effective parameters in order to develop recommendations for retaliatory action. In-situ experiments in the Koralm tunnel simulate the conditions for the designed drainage system, which should provide an appropriate evaluation of the sinter formation in the drainage and the application of inhibitors. Sinter formation will be reduced by using tailored construction materials.