地热能源载体条件下静钻根植桩承载及变形特性研究

Static drill rooted pile is a new type pile with convenient construction and quality assurance. As geothermal energy carrier, the embedding method of heat-exchanger tube of this new type pile is different to that of cast-in-place pile, and there are few research reports about the influence of temperature on capacity and deformation characteristic. In this project, the influence mechanism of temperature on capacity and deformation characteristic would be studied by laboratory model test, laboratory test and microcosmic test. The influence of temperature load on the strength of cement soil was studied by laboratory tests, evaluation method for application of this new type pile as geothermal energy carrier would also be proposed. And the influence of temperature load on the friction resistance of soil-cement-prefabricated pipe pile was studied also by indoor test laboratory tests. The effects of temperature variation on the microstructure of cement soil were investigated by micro-test and the quantitative characterizations of microstructure with macroscopic mechanical strength would be discussed. The influence of temperature variation on pile-side friction, pile axial force, displacement of pile top and pile, stress of cement soil and the soil and stress distribution were tested by model test. Based on the experimental analysis, the pile side friction resistance model considering the influence of temperature is established, and the bearing and deformation analysis methods for static drill rooted pileconsidering the influence of temperature are proposed, providing a more reasonable and applicable theoretical guidance for the related l engineering application.

静钻根植桩作为一种新型桩基形式，施工方便且质量得到保障，作为地热能源载体其热交换管埋置方式与使用较多的灌注能源桩不同，温度荷载对其承载及变形特性影响的研究罕见报道。本项目拟通过室内模型试验、室内试验及微观测试等方法分析温度荷载对其承载及变形特性的影响机理。通过室内测试研究温度荷载对水泥土强度的影响规律，为静钻根植桩作为地热能源载体的适用性提供评估方法；通过室内测试研究温度变化对土体-水泥土-预制管桩接触摩阻力的影响规律；通过微观测试探究温度变化对水泥土微观结构的影响及其与宏观力学强度的定量表征；通过室内模型试验测试温度变化对桩侧摩阻力、桩身轴力、桩顶与桩端位移、水泥土应力、土体应力分布的影响。在试验分析的基础上，建立考虑温度影响的桩侧摩阻力发挥模型，进而提出考虑温度影响的静钻根植桩承载及变形分析方法，为相关应用提供更加合理、适用的理论指导。

作为一种建筑节能技术，地源热泵系统在建筑暖通与空调领域得到越来越广泛的应用。地热能源桩（Geothermal Energy Piles）是利用建筑物的基桩，将换热管置于基桩内，其优点是不需额外钻孔和回填，节约工程造价，而且获得的能源具有可再生性、稳定可靠、清洁持久、经济和环境效益显著等特点。因此，该技术有较大的发展潜力和广泛的应用前景。基于上述优点，本项目开展了室内试验测试，探讨了影响软土热物性变化的因素，研究了法向应力对砂土中温度传导的影响及温度对桩-砂土接触力学性能的影响。开展模型试验，研究温度沿桩深的分布规律，结合数值计算分析结果，提出了温度荷载作用下附加桩身位移和附加桩身轴力的简化计算方法。室内试验测试结果表明，软土导热系数随干密度增大呈线性增长，法向应力对温度在砂土内的传导没有明显影响，温度荷载对桩-砂土接触力学性能几乎没有影响。模型试验测试结果表明，升温和降温后桩体温度沿深度的变化并不均匀，其温度分布规律与桩周土性质和换热管埋设方式有关；模型试验测试表明桩身位移变化零点的位置与桩顶荷载和约束条件有关。综合分析模型试验与数值计算结果，指出了温度荷载作用下附加桩身位移变化零点的存在，给出了确定该点的简化计算方法。测试结果同时表明，桩周土压力和桩端阻力在多次冷热循环作用下循环变化，升温引起桩顶上抬位移，降温引起桩顶附加沉降，在多次冷热循环作用下，静钻根植能源桩桩顶和桩周土表面均会产生累积沉降，且随着桩顶荷载和冷热循环次数的增加有增大的趋势；温度引起的预制桩和水泥土均产生的附加温度应力分布，与温度变化值、桩顶荷载和约束条件等因素密切相关。研究结果为该新型能源桩的后续研究提供了一定的理论基础，为其推广应用奠定了一定的试验和理论依据，为今后该领域的发展提供了一定参考。