Numerical Analysis of the Behaviour of Energy Micropiles Used for Heat Storage: A Case Study in Turku (Finland)

Energy Micropiles (EMPs) are a promising emerging technology thanks to their dual function of providing both structural support and energy supply to both pre-existing and new buildings. However, further experimental and numerical research is needed to fully understand their thermal and mechanical behaviour. In this work, a geothermal heat storage case study consisting of a group of EMPs installed in Turku (Finland) is presented. Beneath the main historic square of the city an underground car park was built, supported by more than 2000 end-bearing micropiles, including 561 EMPs consisting of a steel tube equipped with one U-shaped heat exchanger. Thermal energy is stored underground using solar collectors placed beneath the square’s stone floor. In wintertime, geothermal heat is used to de-ice the square floor and for parking space heating. During site construction, thermal response tests (TRTs) were carried out on EMPs with different lengths and filling materials to assess the mean thermal conductivity of the soil. 3D numerical finite element simulations are presented to back-analyse the TRTs and investigate the effects of the thermal conductivity of the filling material and U-pipe shank spacing in EMP thermal performance. Further analysis is ongoing to assess the thermo-mechanical behaviour of EMPs and the surrounding soil at the Turku site.