RESEARCH ON BEARING DEFORMATION OF SINGLE PILE UNDER VERTICAL FORCE-THERMAL LOAD-TORQUE LOADING PATH
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摘要: 正常服役过程能量桩受复杂的力学行为，目前针对多向荷载作用下能量桩的承载变形特性研究相对较少。为探讨能量桩在竖向力、温度荷载和扭矩共同作用下的承载特性，依次施加桩顶竖向力、温度荷载和桩顶扭矩，通过考虑温度荷载对桩侧摩阻力及边界条件的影响，基于荷载传递法及边界元法构建了桩身位移控制方程，提出竖向力→温度荷载→扭矩加载路径下的能量桩承载变形特性的分析方法，通过与已有试验和ABAQUS有限元结果进行对比，均具有比较好的吻合度。研究表明，温度荷载会改变单桩的荷载传递特征，影响桩身轴力和桩侧摩阻力分布。竖向力→温度荷载→扭矩加载路径下，温度变化引起的附加荷载会导致单桩抗扭承载力降低。进一步的参数分析表明，增大竖向荷载会使桩侧极限环向摩阻力减小，导致能量桩单桩抗扭能力降低26.2%(75%Pu，Pu为竖向极限荷载)；随着长径比的增加，桩身承载力逐渐增大，可选取合适的长径比抵消温度荷载带来的影响；随着温度增量的增大，桩身变形量逐渐增大，其中桩身0.6L以上部分变形较大，因此作为能量桩使用的工程桩基需要对地基上部进行加固。Abstract: The energy pile exhibits complex mechanical behavior, and there is relatively little research on the bearing deformation characteristics of the energy pile under multi-direction loads. To investigate the bearing characteristics of energy piles under vertical load, thermal load, and torque, the thermal load and torque were applied after preloading the vertical load to the pile top. By considering the effect of thermal load on the shaft resistance and boundary conditions of the pile, the pile displacement control equation is derived based on the load transfer method and boundary element method, and the analysis method of the bearing deformation characteristics of energy pile under vertical force → thermal load → torque loading path is proposed. The proposed method is in good agreement with the existing experiments and ABAQUS finite element results. The results show that thermal loading changes the load transfer characteristics of the monopile and affects the axial force and lateral frictional resistance distribution of the pile. Under the vertical force → thermal load → torque loading path, the additional load caused by the temperature change leads to the reduction of the monopile torsional resistance. Further parametric analysis shows that increasing the vertical load decreases the ultimate circumferential frictional resistance on the pile side, resulting in a 26.2% reduction (75%Pu, where Pu is the ultimate load) in the torsional resistance of the energy pile monopile. With the increase in the length-diameter ratio, the bearing capacity gradually increases, and thus the effect of thermal load can be offset by selecting a suitable length-diameter ratio. With the increase of temperature increment, the deformation increases gradually, and the deformation of the upper 0.6L is more significant, so the engineering pile foundation used as an energy pile needs to be reinforced on the upper part.
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Key words:
- multidirectional loads /
- energy pile /
- bearing characteristic /
- load transfer /
- theoretical analysis
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图 7 竖向力→温度荷载加载路径桩身轴力分布曲线
Figure 7. Axial force distribution curve under vertical force → thermal loading path
图 8 桩侧环向摩阻力分布
Figure 8. Distribution of circumferential friction resistance on pile side
图 10 三种竖向力工况下$T{{ - }}\theta$曲线对比
Figure 10. Comparison of $T{{ - }}\theta$ curves under three vertical load conditions
图 11 三种竖向力工况下桩身扭转角分布情况
Figure 11. Distribution of pile torque angle under three vertical load conditions
图 12 不同长径比L/D对桩顶承载力包络线的影响
Figure 12. Effect of different ratio L/D on the envelopes of pile top bearing capacity
图 13 不同温度增量下$T{\text{ - }}\theta $曲线对比
Figure 13. Comparison of $T{\text{ - }}\theta $ curves under different temperature increments
图 14 不同温度增量下桩身扭转角分布情况
Figure 14. Distribution of torsion angle of pile under different temperature increments
表 1 桩-土材料参数
Table 1. Pile and soil parameters
参数 砂土 混凝土 密度ρ/(kg/m3) 1571 2640 弹性模量E/MPa 11 27.8×103 泊松比ν 0.2 0.25 热膨胀系数α/(με/℃) 10 2.2 
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