Hydroshield drive H3-4 in the lower Inn valley - construction experience / Hydroschildvortrieb H3-4 im Unterinntal - Erfahrungen der Bauausführung

In the lower Inn valley in the Tyrol, the existing railway line is being widened to four tracks as part of the TEN (Trans European Network) section Munich-Verona. The Brenner Railway Company has appointed the joint venture Porr Tunnelbau - Max Bögl for the construction of the section H3-4. At the time of writing the article, two thirds of the 5.8 km long tunnelled section had been bored, with daily advance rates of up to 32 m being achieved. A Hydroshield is being used to bore the main tunnel with a diameter of 13.03 m. The tunnel gradient lies completely under the groundwater table. For long stretches, the tunnel route runs through loose sandy or gravelly soil with high and very changeable permeability. At the borders of the contract section, silty clay soil dominates.
Eleven shafts are being constructed every 500 m along the tunnel route to act as emergency exits. The shafts are constructed with diaphragm walls and are connected to the main tunnel by pipe-jacked headings of 4.8 m diameter. Because of the groundwater pressure of about 3 bar throughout the site, a sealing block has to be constructed in advance at the junction area.