Abstract Thermo-active piles are capable of providing both structural stability as foundations and low carbon heating and cooling as ground source heat exchangers. When subjected to heating or cooling, the soil surrounding the pile restricts its expansion or contraction, giving rise to thermally-induced axial stresses, which need to be considered during design. Previous numerical studies often assume axisymmetry of the problem and/or a simplification of the heating or cooling mechanism of the pile. To simulate accurately the development of thermally-induced axial stresses, this paper presents a computational study comprising three-dimensional fully coupled thermo-hydro-mechanical finite element analyses conducted using the Imperial College Finite Element Program (ICFEP), where the heating of a thermo-active pile is simulated by prescribing a flow of hot water through the heat exchanger pipes within the pile. The effects of pipe arrangement on thermally-induced axial stresses are investigated by considering three different cases – single U-loop, double U-loop and triple U-loop. Since three-dimensional analyses are computationally expensive, a simplified method using a combination of two-dimensional analyses is proposed to estimate the thermally-induced axial stresses, which is subsequently validated and shown to yield accurate results.

中文翻译：

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一种计算用作换热器的桩基中热致应力的实用方法

摘要 热活性桩既可以作为地基提供结构稳定性，又可以作为地源换热器提供低碳供热和制冷。当受到加热或冷却时，桩周围的土壤会限制其膨胀或收缩，从而产生热致轴向应力，这是设计时需要考虑的。以前的数值研究通常假设问题的轴对称和/或桩的加热或冷却机制的简化。为了准确模拟热致轴向应力的发展，本文提出了一项计算研究，包括使用帝国理工学院有限元程序 (ICFEP) 进行的三维全耦合热-水-机械有限元分析，其中通过规定热水流过桩内的换热器管道来模拟热活性桩的加热。通过考虑三种不同的情况——单 U 形环、双 U 形环和三 U 形环，研究了管道布置对热致轴向应力的影响。由于三维分析的计算成本很高，因此提出了一种使用二维分析组合的简化方法来估计热致轴向应力，随后对其进行验证并显示可产生准确的结果。