In engineering practice, energy pile foundations are often designed for the lifetime of the building. Thermal exchange between a pile and the surrounding soil depends on the annual energy needs of the building, as heating mode in winter and cooling mode in summer. Thus, energy pile foundations will undergo a heating–cooling cycle per year. In the present work, an experimental method based on a small-scale pile model installed in saturated clay was used to study the thermo-mechanical behaviour of energy piles under thermal cycles. Thirty cycles were applied (to represent a 30-year period if the daily cycles are neglected) while a constant pile head load was maintained. Four tests were performed corresponding to pile head loads equal to 0, 20, 40 and 60% of pile resistance. The results obtained show an increase in irreversible pile head settlement with the thermal cycles. In order to interpret the experimental results better, the finite-element method is used to simulate the experiments numerically. This allows the important role of pile thermal contraction/expansion in the pile–soil interaction under thermo-mechanical loading to be highlighted.

中文翻译：

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粘土中能量桩的长期热力学行为

在工程实践中，通常在建筑物的使用寿命中设计能量桩基础。桩与周围土壤之间的热交换取决于建筑物的年能源需求，例如冬天的采暖模式和夏天的制冷模式。因此，能量桩基础每年将经历加热-冷却循环。在目前的工作中，基于安装在饱和黏土中的小规模桩模型的实验方法被用来研究热循环下能量桩的热力学行为。施加了30个周期（如果忽略了每日周期，则表示30年），同时保持恒定的桩头载荷。进行了四个测试，分别对应于桩头载荷等于桩阻力的0％，20％，40％和60％。获得的结果表明，不可逆桩头沉降随热循环而增加。为了更好地解释实验结果，采用了有限元方法对实验进行了数值模拟。这使得在热力作用下桩热收缩/膨胀在桩-土相互作用中的重要作用得以突出。