Page 305 - Analysis and Design of Energy Geostructures

Thermomechanical behaviour of single energy piles 281

Figure 6.8 Vertical head displacement history caused by a thermal load (Test 1) and combined
mechanical and thermal loads (Tests 2 7) in an energy pile. 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.

Fig. 6.8 shows a comparison between the vertical head displacement of the previ-
ously considered energy pile free to move vertically at its head and subjected to ther-
mal loading only (labelled Test 1 in the plot), and the vertical head displacement of
the same pile restrained at its head by a slab and subjected to both thermal loading and
increasing mechanical loading (labelled Tests 2 7 in the plot). In the considered case
study, thermal loading consisted of heating passive cooling cycles applied to the

energy pile of up to ΔT 5 22 C, whereas mechanical loading involved increasing
mechanical forces imposed at the head of the energy pile, following the construction
of the storeys of a building supported by the tested foundation. The maximum
mechanical load applied to the pile head was of P 5 1300 kN. The thermally induced
vertical head displacements of energy piles under free head conditions are higher than
those actually observed under the influence of a head restraint. However, the influ-
ence of heating passive cooling cycles can result in comparable and even greater head
displacements than those caused by mechanical loads (Laloui et al., 2003a).
Fig. 6.9 summarises experimental measures of thermally induced vertical head dis-
placements caused by thermal loads applied to full-scale energy piles, alone or in con-
junction with mechanical loads. Data obtained by Laloui et al. (2003a), Murphy et al.
(2015), Wang et al. (2014) and Akrouch et al. (2014) are presented. The upper and
lower bounding interpolation lines refer to the results of Laloui et al. (2003a) and
Wang et al. (2014), respectively. Thermally induced vertical head displacements from