能源桩热-力学特性模型试验与数值模拟

能源桩是集地源热泵与建筑桩基于一体的建筑节能技术，具有经济、环保和节省地下空间资源等优点，因热-力耦合作用导致其承载性状不同于普通工程桩。基于室内模型试验和数值模拟研究，针对多次温度循环下饱和黏土地基中能源桩热-力响应展开研究，分析了桩周温度场、桩土沉降、桩侧摩阻力的变化，得出如下结论：升温时桩身温度沿深度逐渐减小，土体温度沿径向逐渐降低；降温所引起的桩顶沉降量大于升温的膨胀量，多次温度循环导致桩顶产生不可逆的累积沉降，其累积变形可能会对上部结构的安全造成影响。桩周土由于土体的热固结也发生不同程度的沉降，距离桩身越近沉降越大，且土体沉降速率随循环次数的增加呈逐渐减小趋势，三次循环后B4点沉降达到1.42%D(D为桩直径)；温度荷载所引起的侧摩阻力随温度的升高和循环次数的增加而逐渐增大；升温时桩体上部产生负的侧摩阻力，下部产生正的侧摩阻力，降温时恰好相反，工作荷载的作用导致桩身产生负摩阻力的区域逐渐变小，位移零点也逐渐上移。运用COMSOL Multiphysics软件建立三维数值模型可较好地模拟热-力耦合作用下能源桩的承载力特性，数值模拟结果与模型试验结果吻合度较高，为试验设计及工程应用给出建议。

Model test and numerical simulation of thermal-mechanical properties of energy pile

The energy pile is a building energy-saving technology which integrates ground source heat pump and building pile foundation. It has the advantages of economy, environmental protection and saving underground space resources, and its load transfer behavior is different from that of ordinary engineering piles due to thermal-mechanical coupling. Based on the laboratory model test, the thermal-mechanical response of the energy pile in saturated clay foundation under multiple temperature cycles was studied. The temperature field around the pile, the settlement of pile and soil, the additional heating stress of pile and the shaft friction were analyzed. The results show that the temperature of pile and soil decreases along the depth and radial direction respectively, when the temperature rises. The settlement of pile top caused by cooling is greater than the expansion caused by heating. The irreversible accumulated settlement of pile top caused by multiple temperature cycles may affect the safety of superstructure. The settlement of soil around pile in different degrees occurs due to the thermal consolidation. The settlement decreases with the distance from the pile, and the sedimentation rate of the soil decreases with the increase of the number of cycles. After three cycles, settlement at B4 reaches 1.42%D (D is the diameter of pile). The additional stress and the shaft friction of pile caused by temperature load increase gradually with the increase of temperature and number of cycles. When heating, the negative shaft friction occurs in the upper part of the pile and the positive shaft friction occurs in the lower part. When cooling, it is just the opposite. Under the action of the working load, the negative shaft friction area of the pile becomes smaller and the zero-displacement point moves upward gradually. The three-dimensional numerical model established by COMSOL Multiphysics software can better simulate the bearing capacity characteristics of the energy pile under thermal-mechanical coupling. The numerical simulation results are in great agreement with the model test results, which provides some suggestions for experimental design and engineering application.