This study investigates the thermally induced mechanical interactions among closely spaced energy piles that partially operate as geothermal heat exchangers over a time-scale that is typical of practical applications. The analysis is based on the results of a full-scale in-situ test of a group of energy piles and a coupled 3-D thermo-mechanical finite element analysis. The work highlights two types of thermally induced mechanical interactions in energy pile groups, i.e., first- and second-kind interactions. The former interactions develop during early stages of geothermal operations of energy piles. The latter interactions develop during successive stages of geothermal operations of energy piles. The impact of these interactions on the variation of the mechanical behaviour of energy pile groups varies with time. Attention must be devoted to these interactions throughout the design process (e.g., geotechnical and structural) of energy piles because they play an important role in the serviceability performance of these foundations.