Geotechnical Analysis of Heat Exchanger Piles

Energy piles: current state of knowledge and design challenges

“…The experimental results by Shoukry et al (2011) disagree with the second assumption of Knellwolf et al (2011), Amatya et al (2012 and Bourne-Webb et al (2012), as it shows that Young's modulus of concrete is temperature dependent. Furthermore, as the pile crosssection is subjected to differential temperatures due to the existence of U-tube heat exchange elements where the temperature of the in-leg is different than that of the out-leg, non-uniform thermally induced axial strain in the pile could be generated.…”

“…Therefore, there is a need for a better understanding of the engineering behaviour of energy piles as it will allow more refined design guidance and avoid excessive conservatism. Knellwolf et al (2011) introduced a one-dimensional finitedifference method for designing energy piles. The proposed method was formulated under the load transfer approach by Seed and Reese (1957) and Coyle and Reese (1966).…”

“…The proposed method was formulated under the load transfer approach by Seed and Reese (1957) and Coyle and Reese (1966). The design method by Knellwolf et al (2011) relies on the following simplifications/assumptions:…”

“…Although the energy pile concept has been used successfully in some countries such as the UK (Knellwolf et al, 2011), Austria (Brandl, 2006) and Germany (Ennigkeit and Katzenbach, 2001), other countries are reluctant to accept this technique mainly due to concerns regarding the potential impact of temperature cycles on the structural performance of the pile (load capacity and settlement issues), as shown in Figure 2. The energy pile differs from the conventional pile as it is subjected to mechanical and thermal loads.…”

The Average Temperature of Energy Piles

“…The geotechnical design of energy piles requires confirmation that the foundations can carry safely the required load from the overlying structure and that no detrimental effects from the additional imposed temperature changes will occur (GSHPA, 2012). These additional design checks may be carried out by adapted load transfer methods, by numerical simulation or by design charts (e.g Knellwolf et al, 2011, McCartney & Rosenberg, 2011, Laloui et al, 2006, Bodas-Freitas et al, 2013. With the exception of full numerical simulation, which is computationally very expensive, most of these approaches require simplifying assumptions to be made about the heat transfer rate or temperature boundary conditions related to the pile.…”