On the influence of thermal cycles on the yearly performance of an energy pile

Thermo active piles have been studied as an efficient solution to minimize greenhouse emissions and achieve economic advantages. So far, this technology has received only partial acceptance by the industry, because of the impact on the serviceability of the system in the long-term. The aim of this work is to perform a tool able to numerically investigate the thermo-hydro-mechanical behaviour of a single energy pile, subjected to mechanical and thermal loads, in two sites: London (UK) and Napoli (Italy). The former location is used to validate the developed model against the experimental data available in the literature (Bourne-Webb et al. 2009), while the latter is proposed to evaluate the applicability of such technology in the Neapolitan area. Some analyses on the behaviour of the energy pile have been carried out for approximately one year (400 days), and the influence of daily cycles on modelling processes is underlined comparing the results of three different ways of simulating the same energy demand (considering daily temperature variations, neglecting them, and using average values of temperature). The outcomes show that the thermal-induced displacements, pore water pressure variations and axial loads are influenced by the mode of application of the thermal law and deserve to be taken into account in the geotechnical design, even if, in the Napoli case, are not detrimental to the structural functions of the soil–pile system. The main goals of the study can be summarized in the following points: (i) the geotechnical performance and the temperature variations provided during heat exchange operations, comparing three different ways of application of the same energy demand, (ii) the role of the hydraulic processes and the key factors that influence the pore water pressure generation, (iii) the thermal sustainability of the energy pile operations. These aspects are useful for the design practice as well as the numerical models.