Page 301 - Analysis and Design of Energy Geostructures

Thermomechanical behaviour of single energy piles 277

Figure 6.4 Comparison between the thermally induced vertical strain measured in a single energy
pile free to move vertically at its head and the corresponding vertical strain under free expansion
conditions. 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.

Observed thermally induced vertical strains in energy piles caused by heating ther-
mal loads are often associated with a reversible, that is thermoelastic, character. This
evidence was noted, for example, by Laloui et al. (2003a) and is reported in Fig. 6.5
considering the evolution of vertical strain variation at selected depths along a single
energy pile free to move vertically at its head for different temperature variations
applied to the pile.

6.6 Thermally induced radial strain variations

Radial strains develop in energy piles because of the applied thermal loads along with
the thermally induced vertical strains. For the same temperature variation applied to
energy piles, comparable vertical and radial strains caused by the temperature variations
can be observed. However, due to the different dimensions characterising the length
and the diameter of energy piles, the vertical and horizontal pile displacements associ-
ated with the considered strains are markedly different, the former being much more
significant than the latter.
Observed thermally induced radial strain variations in energy piles can be associated
with a reversible behaviour (Mimouni and Laloui, 2015; Rotta Loria and Laloui,
2017). In other words, lateral contact is maintained between the energy pile and the
ground after a thermal cycle. Fig. 6.6 shows the evolution of radial strains for an