Analysis of thermo-mechanical behaviour of energy piles

The use of pile foundations as heat exchangers in combination with heat pump conditioning systems are becoming increasingly popular. Quite a large number of small scale laboratory tests and field scale experiments are available and allow to gain an insight in the mechanisms governing pile-soil interaction under thermo-mechanical loading. In the paper, numerical FEM simulations are carried out on published experimental small scale laboratory tests. The paper focus is on the load-settlement relationship and on the load-transfer curves with depth. The tests show that under purely cyclic thermal loading reversible strains are predominant, while the preliminary application of an axial load causes the development of irreversible deformations during the thermal loading. Numerical FEM simulations carried out with two different constitutive soil models confirm such a finding. A simple procedure to calibrate the model’s parameters is proposed and validated