被动桩水平位移荷载施加位置的探讨

被动桩是指一种由于土体水平位移而发生挠曲变形的桩。目前不论是室内试验还是数值计算，常在模型边界对土体施加水平位移荷载（位移边界条件）形成土体的位移场，用来研究被动桩的变形特征，但不同研究者采用的水平位移施加位置（边界位置）与被动桩的距离存在较大差异。结合一个工程案例，采用有限单元法对水平位移加载位置进行了单变量参数分析。研究表明，随着水平位移加载位置与被动桩距离的增加，桩身变形显著减小。这表明了施加位移边界后地基中存在明显的应力扩散。当该距离小于5.5倍桩径时，在模型边界施加同等大小的水平位移所需应力显著增加。同时讨论了水平荷载加载位置与被动桩距离的合理范围，认为应在5～8倍桩径范围之内。

Distance between location of displacement applied boundary and passive pile

Passive pile is a kind of pile deformed due to horizontal movement of soil. To study the deformation behavior of passive pile in both indoor experiment and numerical calculation, a horizontal displacement is normally applied on the model boundary (as a displacement boundary condition) to form a displacement field of soil. However, various distances between the position where horizontal displacement applied (usually the model boundary) and the location of passive pile are chosen by different researchers. According to an embankment field case, the loading position of horizontal displacement is analyzed using one univariate parameter in finite element method. The results show that the deformation of the pile decreases with increasing the distance between loading position and the location of passive pile, which indicates that stress dispersion occurs obviously in the soil after applying the displacement boundary condition. When the distance is less than 5.5 times of the pile diameter, there is much more stress required to achieve the same level of displacement at the model boundary. The distance from loading position to the pile location is also discussed, and it is found that the reasonable distance is in the range of 5-8 times of pile diameter.