Experimental investigation of energy piles: From laboratory to field testing

Geothermal operation of energy piles involves an interplay between the multi-physical phenomena governing the behaviours of soils, geostructures and the interactions between them, which are mainly characterized by the associated temperature variations. This state-of-the-art paper brings together the experimental findings from several field and laboratory investigations to attain a thorough understanding of the responses of soils and soil–structure interfaces under non-isothermal conditions, which is of paramount importance for the analysis of energy geostructures. First, the outcomes from thermal oedometer and triaxial tests are presented, revealing the related volumetric strains and changes in shear strength experienced by soils near the vicinity of energy piles. Next, the results from the direct shear tests performed on soil–concrete​ interfaces under thermal and mechanical conditions, similar to those experienced by soil–energy pile interactions, are introduced. Finally, full-scale field tests focusing on the responses of single and groups of energy piles to monotonic and cyclic temperature variations are presented. The design and development of the laboratory testing devices, as well as the experimental setup for the field tests, are also detailed in the paper, preceding the corresponding outcomes.