不同刚度约束对能量桩应力和位移的影响研究

能量桩是一种在传递上部建筑荷载的同时获取地热能源的新技术，其实际工作过程中，热荷载会引起桩体的膨胀或收缩，而桩顶建筑和桩底持力层则会对桩体变形产生约束，进一步影响桩体的应力和位移，但是目前对该问题的研究却十分有限。基于模型试验和数值模拟方法，对桩顶和桩底不同约束条件下两种埋管形式（单U和W型）的桩体位移和热应力进行了分析，并进一步探讨了位移零点随桩顶和桩底约束条件的变化规律。研究结果表明，随着桩顶上部荷载约束刚度的增大，桩体位移零点上移，桩体热应力随着深度增大而减小；随着桩端土体约束刚度的增大，桩体位移零点下移，桩体热应力随着深度增大而增大；相较于无外荷载，工作荷载作用下位移零点上移。

Study on stress and displacement of energy pile influenced by pile tip stiffness

Energy pile is an innovate technology which can simultaneously support building load and acquire geothermal energy. In the practical use, expansion or contraction of the piles induced by thermal load will be restrained by the upper structure and bearing layer of pile bottom. Thus, the pile stress and displacement will be significantly influenced. However, there are only few studies focusing on this issue. Based on model test and numerical simulation methods, the thermal stress and displacement of two types of heat exchange piles (U-shaped and W-shaped) under different pile head and pile tip restraints were analyzed. Furthermore, the position of null point influenced by the pile head stiffness restraint and pile tip soil stiffness restraint were evaluated. The results show that as the pile head load stiffness restraint increased, the null point moved upwards, and the thermal stress decreased with the increasing of depth. As the pile tip soil stiffness restraint increased, the null point moved downwards, and the thermal stress increased with the increasing of depth. Compared with the case with no load, the null point will move upward with a working load.