Structural Behaviour of Concrete Energy Piles in Thermal Loadings

Authors: E. H. N. Gashti, M. Malaska, K. Kujala

Abstract:

The thermo-mechanical behaviour of concrete energy pile foundations with different single and double U-tube shapes incorporated was analysed using the Comsol Multi-physics package. For the analysis, a 3D numerical model in real scale of the concrete pile and surrounding soil was simulated regarding actual operation of ground heat exchangers (GHE) and the surrounding ambient temperature. Based on initial ground temperature profile measured in situ, tube inlet temperature was considered to range from 6oC to 0oC (during the contraction process) over a 30-day period. Extra thermal stresses and deformations were calculated during the simulations and differences arising from the use of two different systems (single-tube and double-tube) were analysed. The results revealed no significant difference for extra thermal stresses at the centre of the pile in either system. However, displacements over the pile length were found to be up to 1.5-fold higher in the double-tube system than the singletube system.

Keywords: Concrete Energy Piles, Stresses, Displacements, Thermo-mechanical behaviour, Soil-structure interactions.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1097269

References:

[1] E. H. N. Gashti, V.-M Uotinen, and K. Kujala, “Numerical modelling of thermal regimes in steel energy pile fondations: A case study,” Energy and Buildings, vol.69, 2014, pp.165-174.
[2] L. Laloui, M. Nuth, and L. Vulliet, “Experimental and numerical investigations of the behaviour of a heat exchanger pile,” International Journal for Numerical and Analytical Methods in Geomechaics, vol.30, 2006, pp.763-781.
[3] D. Adam, R. Markiewicz, “Energy from earth-coupled structures: foundations, tunnels and sewers,” Geotechnique, vol.59(3), 2009, pp.229–36.
[4] D. Pahud, M. Hubbuch, “Measured thermal performances of the energy pile system of the dock midfield at Zurich Airport,” In: European Geothermal Congress. 2007.
[5] H. Quick, S. Meissner, J. Michael, “Innovative foundation systems for highrise buildings,” In: The 1st Intelligent Building Middle East Conference. 2005.
[6] B. L. Amatya, et al., “Thermo-mechanical behaviour of energy piles,” Geotechnique, vol.62 (6), 2012, pp.503-519.
[7] J. Gao, et al., “Thermal performance and ground temperature of vertical pile-foundation heat exchangers: A case study,” Applied Thermal Engineering, vol.28 (17–18), 2008, pp. 2295–2304.
[8] Comsol Multiphysics, Finite element analysis and engineering simulation software (Version 4.3a), Software material library, 2013.
[9] Swiss Standard SN 670 010b, Characteristic Coefficients of soils, Association of Swiss Road and Traffic Engineers
[10] P. J. Bourne-Webb, B. Amatya, K. Soga, “A framework for understanding energy pile behaviour,” Proceedings of the Institution of Civil Engineers, Geotechnical Engineering, DOI: 10.1680/geng. 10.00098, 2012.