Structures have to be built with depth foundations if difficult foundation conditions or very high loads occur.
Where pile foundations are needed, there is the opportunity of an additional geothermic use of the ground by using energy piles (geothermically activated in-situ concrete or ready-mix concrete piles, hollow piles, press piles).
First science-assisted, practical implementations of energy pile systems took place in the 1970s in Switzerland.
Meanwhile, this innovative energy technology has been successfully implemented in Germany (a.o. Katzenbach 1997, Brandt et al. 2003).
The thermal use of (near-surface) ground is defined, among others, in the VDI standard 4640 (sheet 2). Energy piles are categorized as "special heat source (reduction) plants" there.
Energy piles have two functions:
According to their main function, they transmit loads into the foundation. In addition, they can be used as geothermal heat transmitters.
Uses of the foundation piles as energy piles must not impair their load bearing capacity. Any reduction of the pile’s load capacity (occurrence of frost, diameter reduction by heat exchange pipes) has to be imperatively eliminated (temperature limitation, static tests).