ORIGINAL PAPER Cyclic Thermo-Mechanical Analysis of Energy Piles in Sand Rajni Saggu · Tanusree Chakraborty Received: 25 November 2013 / Accepted: 20 June 2014 / Published online: 8 July 2014 © Springer International Publishing Switzerland 2014 Abstract Geothermal energy piles in sand sub- jected to cyclic thermal loading with fifty thermal cycles and constant mechanical axial load are analyzed numerically in the present work using the nonlinear transient finite element analysis method. The resulting soil–structure interaction is investigated through these analyses. The stress–strain response of sand is simulated herein using the Mohr–Coulomb constitutive model. Mechanical behavior of energy piles is simulated using the concrete damage plastic- ity model. Analyses are carried out for floating and end bearing piles in both loose and dense sands subjected to different constant axial load magnitudes at the pile head. Parametric sensitivity studies are performed for different amounts of temperature variation on the pile. It is observed from the results that the mechanical load governs the response of the piles when the piles are subjected to higher mechan- ical loads close to the limit load value on the pile. However, at low to moderate axial load magnitudes, thermal expansion of the pile causes uplift of the piles. Due to pile uplift, negative shear forces are generated at the pile–soil interface near pile head. The radial strains induced in the pile due to thermo- mechanical loading are observed to be higher than that induced due to only mechanical loading. The axial stress in the piles also increases when pile is subjected to heating. Keywords Energy pile · Finite element method · Sandy soil · Thermal cycle · Thermo-mechanical response 1 Introduction Geothermal energy piles provide sustainable energy alternative for residential and commercial buildings worldwide (Laloui et al. 2006; Brandl 2006; Bourne- Webb et al. 2009; Boe ¨nnec 2009; De Moel et al. 2010; Amatya et al. 2012). The energy piles provide structural support to the building and also fulfill the building’s heating–cooling requirements. For manu- facturing of energy piles, the reinforced concrete drilled shafts are often preferred over the steel pipe piles because of good thermal storage capacity and thermal conductivity of concrete that make these piles an ideal medium for geothermal energy absorber (Brandl 2006). In spite of the growing recognition on the benefits of energy piles, there is still knowledge gap in understanding the load transfer mechanism of these piles under thermo-mechanical loading (Laloui et al. 2003, 2006; Boe ¨nnec 2009; Knellwolf et al. 2011). Also, the effect of long-term R. Saggu · T. Chakraborty (&) Department of Civil Engineering, Indian Institute of Technology (IIT) Delhi, Hauz Khas 110 016, New Delhi, India e-mail: tanusree@civil.iitd.ac.in R. Saggu e-mail: rajnirupal@gmail.com 123 Geotech Geol Eng (2015) 33:321–342 DOI 10.1007/s10706-014-9798-8