As a result of cyclic heating and cooling around the ambient temperature under drained conditions, normally consolidated and lightly overconsolidated fine-grained soils experience accumulation of irreversible volumetric contraction. Most existing thermomechanical models were developed for one heating–cooling cycle and are not suitable for multiple thermal cycles. An approach is proposed to simulate the volume change of fine-grained soil induced by thermal cycles. In the proposed approach, a thermal stabilization line is introduced to control the stabilized volumetric contraction under thermal cycles. Comparison with experimental results shows that the proposed approach can reproduce well the cumulative feature of volumetric contraction of fine-grained soil subjected to thermal cycles.

Horizontal stress changes of semi-floating energy piles subjected to cyclic thermal loading are investigated through finite element analysis adopting the hypoplastic model. By using the validated finite element model a parametric study is carried out, considering effects of amplitude of thermal cycles, pile diameter, pile length and relative density of sand. It is revealed that due to volumetric contraction of sand (loose or dense) at the interface under temperature induced cyclic shearing, a reduction of horizontal stress occurs. The degree of reduction in horizontal stress is most affected by the amplitude of thermal cycles and the pile diameter.

Energy piles serve as supporting structures and heat-exchange elements. They can provide thermal comfort much more efficiently than traditional air-sourced systems as the ground offers high thermal conductivity and a stable temperature below a certain depth. Energy piles are commonly installed as bored piles (replacement); however, driven (displacement) energy piles are also used in practice. A direct comparison of the performance of these two different types of energy piles subjected to thermal cycles is rarely explored not fully understood. In this study, two centrifuge energy model piles, one wished-in-place at one gravity (i.e. at low stress, simulating bored pile) and the other pile was jacked in at elevated gravity were constructed in saturated Toyoura sand. After construction, they were subjected to five heating and cooling cycles (7-37°C) under a constant working load. Cumulative settlement with a ratcheting pattern was observed for the 'bored' energy pile after five thermal cycles. In contrast, a slight heave was recorded for the jacked-in energy pile. The observed heave can be attributed to the densification effect and particle crushing of soil when the pile was jacked in, reducing or even eliminating thermal-induced contraction of sand and hence decreasing the reduction of horizontal stress during thermal cycles.

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