Thermo-mechanical behaviour of floating energy pile groups in sand

Abstract

This paper presents the experimental results of small-scale model tests of an instrumented floating energy pile group in which the piles were embedded in dry medium-dense sand and subjected to the seasonal temperature pattern of the city of Nanjing in China. The study also included a model test to assess the effect of including nonthermal piles on the thermo-mechanical behaviour of the floating energy pile group. For comparison, a model test of a single floating energy pile embedded in the same soil and subjected to a similar temperature pattern was also conducted. The results show that the thermo-mechanical behaviour of an energy pile group is different from that of a single energy pile in terms of the thermally induced change in axial pile stress and the displacement of the pile top and tip. This difference in behaviour could be explained by the higher lateral confining pressure expected on a single pile than on a pile in a group due to pile interaction effects, which could lead to different end restraint boundary conditions. We conclude that the thermo-mechanical behaviour of an energy pile is controlled mainly by the end restraint boundary conditions.

摘要

目的

能量桩在工作状态下的热力学响应十分复杂,同时受到桩顶荷载、桩侧摩擦以及温度等多重因素 的影响。当群桩中出现部分能量桩不工作时,将造成上部结构的额外应力与变形。因此,本文重点探讨摩擦型能量桩群桩中部分能量桩在加热 制冷作用下的热力学响应,并与单桩的热力学效 应进行对比分析。

创新点

1. 通过建立摩擦型能量桩群桩模型试验,探讨桩侧摩擦对能量桩群桩的影响规律;2. 利用能量桩群桩与单桩对比,揭示能量桩群桩与单桩热力响应特性的区别;3.揭示部分能量桩加热制冷作用对能量桩群桩的影响机理。

方法

1. 建立摩擦型能量桩群桩及单桩的模型试验; 2. 将能量桩群桩与单桩进行对比,研究能量桩群桩与单桩热力响应特性的区别;3. 进行能量桩群 桩部分加热制冷试验。

结论

1. 对于长期工作的能量群桩,可以将其视为一个长宽高与整个群桩相同的热交换体,其表面温度与群桩的平均表面温度一致。2. 能量桩单桩在加热过程中,由于桩底受到的限制较大,所以桩顶位移大于桩底位移。3. 能量桩单桩在制冷过程 中,由于土体及桩体收缩,会出现明显的下沉。 4. 能量桩群桩桩帽在加热过程中,桩帽的位移与 群桩的上半部分长度相关;在本文的试验中,由于群桩上半部分受土的限制较小,因此其位移与桩自由膨胀的位移一样。5. 能量桩群桩在制冷期间,群桩的下沉量级要比单桩的大。6. 在制冷过程中,能量桩群桩在群桩效应作用下,内部桩的 桩底热位移较大。7. 能量桩群桩在部分加热的情 况下,会出现不均匀沉降,且在加热期间,沉降 主要受到不工作桩的牵制影响;而在制冷期间, 沉降主要受工作桩的下沉影响。8. 摩擦型能量桩 的热引起的桩身轴力是与桩侧的土压力大小相关的;由于群桩在群桩效应作用下,桩侧土压力要小于单桩,因此群桩的热引起的桩身轴力要大 于单桩。