Thermo-mechanical behaviour of energy foundations

Thermally activated foundation elements have been successfully used in Austria for decades to harness near-surface geothermal energy for heating and cooling purposes. After a large number of projects on geothermally useable elements (energy piles, energy diaphragm walls, energy bored pile walls, energy floor slabs, energy fleeces, energy anchors, energy wells, etc.), the research focus of the Institute of Geotechnics is now on the investigation of the thermo-mechanical behavior of energy foundations.

In this context, two infrastructure projects in Vienna are scientifically evaluated. In one section of the Lainzer Tunnel, Hadersdorf-Weidlingau, the energy bore pile wall has been supplying heating energy for an adjacent school since 2004. The Taborstraße metro station of the Vienna U2 line has been using the existing energy diaphragm walls and other elements to heat and cool the station since it opened in 2008. In both cases, sensors in the thermally activated components provide long-term measurement data on temperature-strain behavior.

In addition, two energy piles were constructed as part of the research project "Unteres Hausfeld", which was completed in 2019, and are now the subject of further investigation. The piles were constructed and instrumented with different lengths to investigate the load transfer behavior in the two predominant soil layers of Vienna, the Quaternary sediments (sandy gravels, "Danube gravels") and the Miocene sediments (sands, silts, clays). In addition to conventional mechanical loading, thermal loads were applied and kept constant for several weeks to simulate heating and cooling scenarios.

The objectives of the scientific investigations are to study the load transfer behavior of energy foundations in general and the response due to the applied thermo-mechanical loading in particular. The measurement data generated in the large-scale tests will subsequently be used as a basis for numerical modeling of energy piles. The knowledge gained from the research project will ultimately be incorporated into the safe and economical dimensioning of energy piles produced in the future and thus contribute to the future of renewable, sustainable and locally harnessed primary energy sources.

Schematic representation of thermally utilisable elements of an underground station

© TU Wien, Institut für Geotechnik

Reinforcement cage of a diaphragm wall with absorbers and sensors

© TU Wien, Institut für Geotechnik

Numerical investigation of the thermal behaviour of an energy pile

© TU Wien, Institut für Geotechnik