Page 304 - Analysis and Design of Energy Geostructures

280 Analysis and Design of Energy Geostructures

Figure 6.7 Evolution of thermally induced vertical head displacement in an energy pile free to
move vertically at its head throughout a heating passive cooling cycle. Redrawn after Laloui, L.,
Moreni, M., Vulliet, L., 2003a. Comportement d'un pieu bi-fonction, fondation et échangeur de chaleur.
Can. Geotech. J. 40 (2), 388 402.

mechanical loads is associated with energy pile displacements in a unique direction
(e.g. downward for compressive loads applied at the pile head).
Based on the previous considerations, the combined influence of mechanical and
cooling thermal loads applied to energy piles involves an increase of their head settle-
ment (with respect to the case of downward mechanical loading only). In contrast, the
combined influence of mechanical and heating thermal loads applied to energy piles
causes a decrease of their head settlement (with respect to the case of downward
mechanical loading only) that can even result in an overall heave of such foundations.
This latter phenomenon is associated with the opposite influence of downward
mechanical loads and heating thermal loads on the behaviour of the pile head. It may
be observed for piles subjected to limited mechanical loads and significant heating
thermal loads. The commented influence of mechanical and heating thermal loads
holds unless energy piles subjected to heating thermal loads in normally consolidated
soils are considered. In these latter conditions the thermal collapse of the soil would
result in a head settlement of the energy pile instead of a head heave, despite the pile
expanding under the influence of the heating thermal load.