Numerical modelling of heat exchanger pile in pyroclastic soil

Energy piles are an innovative technology that couples the role of the structural foundation to the role of the heat exchanger to satisfy the energy needs of buildings and infrastructures. In the last decade insight into the mechanisms governing the thermo-mechanical response of single energy piles have been gained via full-scale in-situ tests, numerical analyses and model-scale experiments. The numerical approaches allow testing a large variety of configurations, geometries, materials, thermo-mechanical loadings and boundary conditions in a rather controlled but relatively easy and cost-effective manner. As a widespread habit it should be remarked that the temperature changes adopted in the piles have been only rarely justified based on realistic heating and cooling demands of live buildings. This numerical study investigates the effects of combination of mechanical and thermal loads on the mechanical behaviour of a single energy pile embedded in a typical pyroclastic soil deposit of Campania region, in Southern Italy. Thermal loads over one year have been determined by means of Design Builder software analysing a building in Napoli; the intermittent operation of the heat pump over daily time scale is properly modelled in the coupled thermo-hydro-mechanical axisymmetric FE analyses. A sensitivity analysis has been carried out to investigate the effects of the surface thermal boundary conditions.