Analyses of the thermo-hydro-mechanical responses of energy pile subjected to non-isothermal heat exchange condition

Thermal resistance analysis of an energy pile and adjacent soil using radial temperature gradients

“…Heat exchanger pipes are commonly formed into Uloops and attached to the reinforcement cages of the piles, although spiral configurations have also been used (Brandl 2006;Zarrella et al 2013;Go et al 2014;Wu et al 2021). During GSHP operation, transient thermal gradients develop in the pile cross-section and the surrounding soil due to the thermal resistances of the pile material (often concrete) and the soil, respectively (Bourne-Webb et al 2016;Faizal et al 2016a;Ozudogru 2016a, 2016b;Caulk et al 2016;Han and Yu 2020;Moradshahi et al 2021a). The thermal resistances of energy piles and the surrounding soils are necessary parameters required in the thermal design and analysis of energy pile systems.…”

“…Several analytical and numerical modelling studies have characterized the internal heat transfer and thermal resistance of energy piles (e.g., Bozis et al 2011;Li and Lai 2012;Powrie 2013, 2014;Lee and Lam 2013;Zarrella et al 2013Zarrella et al , 2017Hu et al 2014;Ozudogru 2016a, 2016b;Caulk et al 2016;Park et al 2018;Maragna et al 2019;Han and Yu 2020;Moradshahi et al 2021a) but omitted transient internal temperature gradient measurements between the heat exchanger pipes and pile-soil interface typical of insitu conditions. The internal thermal resistances of borehole heat exchangers have been thoroughly studied (e.g., De Carli et al 2010;Lamarche et al 2010;Bauer et al 2011;Koenig 2015;Javed and Spitler 2017;Cui et al 2018) but the lessons learned cannot be applied to energy piles as different thermal behaviour of piles is expected due to differences in dimensions and number of heat exchanger pipes.…”

Cross-sectional thermo-mechanical responses of energy piles

“…Due to the transient changes in the temperature of the heat pump circulating fluid, the temperature across an energy pile's cross-section will also vary Ozudogru 2016a, 2016b;Caulk et al 2016;Han and Yu 2020;Liu et al 2020). However, the majority of field-scale studies on energy piles only measured their thermal response at a single location in the cross-section of the pile (e.g.…”

“…Numerical studies showed that non-uniform temperature and stress variations occurred between the centre and edge of the energy pile Ozudogru 2016a, 2016b;Caulk et al 2016;Han and Yu 2020;Liu et al 2020), but fewer field studies have been performed to validate these observations (e.g. Faizal et al 2019a;2019b).…”

“…The magnitudes of thermal stresses in energy piles depend on the magnitudes of inlet fluid temperatures (e.g. You et al 2014;Mimouni and Laloui 2015;Murphy and McCartney 2015;Faizal et al 2016;Han and Yu 2020). A recent parametric study based on field investigations showed that soil parameters (i.e.…”