Temperature dependence of soil-structure interface behaviour in the context of thermally-activated piles: A review

Thermally-activated (TA) piles are cost-effective technologies with the dual role of transferring structural loads to the ground while exchanging heat with the surrounding soil as part of shallow geothermal energy systems. As TA piles are subjected to both thermal and mechanical loads, the behaviour on the soil-structure interface is particularly complex and is key for the analysis and design of these structures. The present paper aims to review the current state of knowledge regarding the thermal dependency of soil-structure interface behaviour and provide an overview of experimental results obtained from non-isothermal tests investigating soil and soil-structure interface behaviour. This overview includes comparison of the different experimental equipment and procedures, soil types, initial soil state overconsolidation ratio (degree of consolidation or relative density) and thermal loadings. It was found that it is not straightforward to reach a unique interpretation regarding possible variation of the soil-structure interface behaviour at different temperatures: the framework of the experimental evidence is very complex due to the wide variation in testing conditions. Therefore, it was not possible to compare the studies like-for-like, leading to an apparently ambiguous interpretation of the results. Overall, the consensus across this and other studies is that the potential variation of interface resistance with temperature typically appears to be limited and not very significant.