Load Transfer Method for Energy Piles in a Group with Pile–Soil–Slab–Pile Interaction

Abstract

The behaviour of an energy pile in a group is different from that of an isolated energy pile due to thermal and mechanical interactions. This study aims to extend the load transfer method to consider the mechanical and thermal interactions of energy piles in groups. The load displacement curve of an energy pile in a group is modified from that of the isolated pile through a displacement factor to account for group effects. This paper presents the results of a full-scale field test of four operating energy piles over 12 months, against which the proposed method is validated. Temperature changes of ∆T = 5, 10, 15, 20 °C were applied in the analyses. A comparison between the experimental and numerical results reveals the capability of the approach to provide information about the vertical displacement, vertical stress, and mobilised shaft resistance profile for an energy pile in a group subjected to both mechanical and heating thermal loads.

Energy geostructures: Theory and application

“…Load-transfer models fundamentally draw from the works of Winkler [68] to describe the load-displacement behavior of conventional walls and slabs, and Coyle and Reese [69] to describe the load-displacement behavior of conventional piles. In recent years, these models have been extended to describe single energy piles [59,[70][71][72][73][74], energy pile groups [75], as well as energy walls, slabs and cut-and-cover tunnels [66] subjected to both mechanical and thermal loads.…”

“…The available load-transfer models to address geotechnical aspects of energy geostructures include formulations for single energy piles [59,[70][71][72][73][74], energy pile groups [86,79,75,88], as well as energy walls, slabs and cut-and-cover tunnels [66]. For about two decades, in contrast to the widely established closed-form solutions allowing to describe the vertical displacements of single piles subjected to mechanical loads [89,90], no closedform solutions have been available for single energy piles subjected to thermal loads.…”

“…Not only the proposed closed-form solution allows a handy analysis of single energy piles subjected to mechanical and thermal loads [74]. It can also address energy pile groups when applied in combination with the interaction factor method [86,79], the equivalent pier method [88] or the modified load-transfer method [75].…”

“…While load-transfer models can be applied in combination with continuum models (e.g., the equations of Mindlin [84]) to directly address the mechanically and thermally induced interactions characterizing pile groups [91,79], this approach often leads to unsatisfactory predictions [79]. A valuable approach to overcome the limitation above is to indirectly address the mechanically and thermally induced interactions between pile groups through the modification of the load-transfer relationship of a single pile [92][93][94]75]. Highly adherent predictions of experimental observations can be achieved through this approach [75] and effectively serve the analysis of geotechnical and structural aspects.…”

“…A valuable approach to overcome the limitation above is to indirectly address the mechanically and thermally induced interactions between pile groups through the modification of the load-transfer relationship of a single pile [92][93][94]75]. Highly adherent predictions of experimental observations can be achieved through this approach [75] and effectively serve the analysis of geotechnical and structural aspects.…”