The equivalent pier method for energy pile groups

This study presents a method for estimating the average vertical displacement of energy pile groups subjected to thermal loads. The method consists of replacing any regular energy pile group with a single equivalent pier of the same length and an equivalent diameter. This equivalent pier is described by material properties that are a homogenisation of those of the piles and the surrounding soil and by a load-displacement relationship of a characteristic energy pile in the group. The load-displacement relationship of the equivalent pier differs from that of a single isolated energy pile because it is modified to account for the group effects. These effects include a greater vertical displacement of the piles subjected to loading in the group compared to the case in which they are isolated, thus involving a more pronounced average group displacement. Comparisons with results obtained through the interaction factor and finite-element methods prove that the proposed approach can accurately estimate the average vertical displacement of energy pile groups. This novel formulation of the equivalent pier method may be used at both preliminary and successive stages of the analysis and design of energy pile groups to assess expediently the thermally induced displacement response of such foundations.