Long-term thermo-mechanical behavior of energy pile in dry sand

Abstract

International audienceA small-scale pile has been developed in the laboratory to investigate the thermo-mechanical behavior of energy piles subjected to a significant number of thermal cycles. The pile (20 mm external diameter), installed in dry sand, was initially loaded at its head to 0, 20, 40 and 60% of its ultimate bearing capacity (500 N). At the end of each loading step, 30 heating/cooling cycles were applied. The long-term behavior of the pile was observed in terms of head settlement, axial force profile, soil and pile temperature, and stress in soil. The results evidence the irreversible settlement of the pile head induced by thermal cycles under constant load head. In addition, the incremental irreversible settlement that accumulates after each thermal cycle decreases when the number of cycles increases. The evolution of irreversible pile head settlement versus number of cycles can be reasonably predicted by an asymptotic equation

Experimental and Numerical Study on the Behavior of Energy Piles Subjected to Thermal Cycles

“…ey suggested that the pile head settled after the initial thermal cycles and then heaved during the subsequent thermal cycles. is finding is different to that observed in the model tests [6,8], in which an accumulated downward displacement of the pile was evident. As pointed out by Suryatriyastuti et al [17], the cyclic hardening/softening behavior of the pile-soil interface and the soil should be considered in the long-term performance analysis of energy piles.…”

“…On the basis of the measured strain and the deduced axial force along the pile, the mobilized skin friction was found to change significantly during the thermal cycles. Nguyen et al [8] adopted a relatively high number of thermal cycles (30 cycles). e additional pile stress induced by heating did not fully recover during the subsequent cooling phase.…”

FEM Analysis and Simplified Approach for a Single Energy Pile Subjected to Thermomechanical Loads

“…Model tests were also carried out to examine the heat transfer performance and bearing characteristics of piles with embedded tubes under normal working conditions over repeated temperature cycling, and the results show that the thermal stresses were superimposed with the mechanical stresses [11][12][13][14]. Centrifuge modeling of soilstructure interaction in energy foundations was also carried out to measure the transient thermomechanical response of end-bearing energy pile during heating-cooling cycles, and the result shown that the model pile was affected by the heating and cooling cycles [15,16], being consistent with the conclusion that the effect of temperature on the shear strength of sand, clay, and the clay-concrete interface is negligible [17,18].…”

Effects of Cyclic Temperature Variations on Thermal Response of an Energy Pile under a Residential Building

“…Small-scale physical model studies with thermal cycles on energy piles (Kalantidou et al, 2012;Stewart and McCartney, 2014;Yavari et al, 2014Yavari et al, , 2016aWang et al, 2017;Nguyen et al, 2017) have indicated that the thermally induced axial settlement of the pile is reversible for pile head loads corresponding to as low as 20% of the ultimate pile capacity, but becomes irreversible for higher pile head loads closer to the ultimate pile capacity. The field tests conducted by Faizal et al (2018) indicated that the axial and radial thermal responses of an unrestrained energy pile embedded in dense sand followed linear reversible paths for heating and cooling cycles, suggesting that both the pile and the soil did not undergo significant thermally induced deformations.…”

“…The field tests conducted by Faizal et al (2018) indicated that the axial and radial thermal responses of an unrestrained energy pile embedded in dense sand followed linear reversible paths for heating and cooling cycles, suggesting that both the pile and the soil did not undergo significant thermally induced deformations. As highlighted in the smallscale physical model studies reported by several investigators (Kalantidou et al, 2012;Stewart and McCartney, 2014;Yavari et al, 2014Yavari et al, , 2016aWang et al, 2017;Nguyen et al, 2017), it is conceivable that building loads could lead to irreversible axial and radial thermal responses along with associated deformations of the pile and the surrounding soil during cyclic temperature changes. Therefore, further investigations are deemed necessary to evaluate the reversibility of the axial and radial thermal responses of energy piles under building loads when subjected to daily cyclic temperature changes.…”