Brenner BT research may improve tunnel sustainability

23 February 2021

Drainage water from the Brenner Base Tunnel (BBT) could be used to supply sustainable energy to residential districts.

A research group headed by Graz University of Technology, Austria is trying to determine the geothermal potential of the tunnel and explore the concept of extracting heat from diverted tunnel water to supply both heating and cooling energy.

The researchers hope to establish simulation models within a year to allow an initial assessment of the infrastructural measures that will be needed to achieve the highest energy yield. This will see how the water temperature could be raised; how the use of absorber techniques such as energy anchors or sole plates attached to the tunnel interior can absorb mountain heat; how the heat can be economically distributed to households; and how heat pumps and heat exchangers may be adapted to assist energy extraction.

Set to become the longest rail tunnel in the world, the 64km-long BBT will link Innsbruck, Austria with Fortezza, Italy, and offers scope for cost savings and practicality. First, the tunnel slopes naturally toward the city of Innsbruck thereby enabling drainage water to flow without the need for pumping. Second, the almost completed exploratory tunnel running beneath the single-track twin tubes will be used to divert drainage water from the tunnels above, so any measures installed for energy generation will not impact the railway’s operation.

The interdisciplinary research draws on the fields of tunnelling, hydrogeology, process engineering and hydrochemistry to achieve optimal results. A basic aim is to identify the temperature and amount of drainage water that will be available after tunnel completion. In this the researchers will be supported by teams from the AIT and the Federal Geological Institute, as well as BOKU researchers from the Institute for Applied Geology and the Institute for Energy and Process Engineering.

Thomas Marcher, director of the Institute for Rock Mechanics and Tunnelling at Graz University hopes the project will serve as a role model for tunnel planners and operators globally. But he also urges caution: “We have to intensively check how heat extraction affects the thermophysical properties of the rock in the long term. Because what we all don't want [is] a cooling of such a dimension that diminishes energy generation in the long term."

Data for the project, which forms part of the FFG ‘City of the Future’ programme, has been supplied by BBT SE and Innsbrucker Kommunalbetriebe (Innsbruck municipality).