Characterization of Deposition in Tunnel Drainage

In water pressure-relieved tunnels, calcium carbonate scaling occurs in tunnel drainage systems. Mostly the drains have to be cleaned to prevent an increase of the water pressure on the tunnel lining, which can cause damage to the tunnel structure or water ingress. In order to organize the cleaning procedures efficiently, a measurement of the thickness and zones of the calcite scaling is required. This contribution lists various measurement methods and discusses electrical impedance tomography (EIT) as a representative in detail. EIT is based on measuring the impedances of all combinations between two electrodes and subsequent reconstruction of the material distribution. The basics of this measurement principle are explained and a characterization of the electrical properties of calcite is presented.