【作者】 蔡国军；

【导师】 刘松玉；

【作者基本信息】 东南大学 ， 岩土工程， 2004， 硕士

【摘要】 在高速公路与桥梁的连接段,通常需要将路基加高加宽,如果桥头路基下,存在较大厚度的软土层时,路基软土将在上覆路堤荷载作用下,发生侧向变形,此时的桥台桩将承受来自于土体水平移动引起的侧向荷载。特别是在路堤施工完毕以前,建造的桥台桩将承受更大的侧向土压力。土的侧向荷载对桥台桩基的水平位移和弯曲变形具有重大影响,往往导致桥台桩身发生挠曲,严重时将导致桥台或桥梁结构的破坏。针对上述问题,本文在总结和阐述现有被动桩土压力理论、试验成果和计算方法的基础上,结合具体的工程问题采用有限元方法对桥台桩与土体相互作用问题展开了初步的研究。首先,根据国内外文献资料,主要就软土地基上桥头路基填筑对桥台桩的侧向影响研究现状进行分析,总结了目前包括软基上桥头路基填筑对桥台桩基影响的试验、有限元分析以及路堤下覆软土侧向变形引起的桩身土压力计算等诸多方面的研究成果。其次,总结了侧向变形土体常见的位移模式,分析了桥台桩的变形机制,然后分别阐述不同模式下桩侧压力的产生机理及桩的几种破坏模式,在此基础上提出桩土间相互作用力与桩土间相对位移的双曲线关系模型和理想弹塑性关系模型。本文从填土荷重作用下土体位移的机理分析入手,总结了桥台桩位移的判断与分析方法,并提出了软土地基上桥台桩设计应考虑的两个问题和避免桥台桩产生过大位移的处理对策。对软土地基上的桥台桩,先从抗滑桩的角度分析了桥台桩所承受的侧向土压力以及桩的变形情况,探讨了桥头路基填筑过程中下覆软土侧向变形引起桥台桩侧向位移的计算方法,并对这些方法进行了进一步的评价。最后,结合连云港软土形成的地质背景,对该地区软土的工程性质进行了分析总结,对某一具体的桥梁工程,通过(平面应变)有限元方法研究了桥头路基填筑高度、填筑速率、下覆软土层厚度以及土性参数变化等对相邻桥台桩的侧向影响,得出了一些相关结论,可供工程设计参考。更多还原

【Abstract】 Piles supporting bridge abutments on soft clay may be loaded laterally from horizontal soil movements generated by the approach embankment. Construction of embankments on soft clay results in the development of time dependant vertical and horizontal sub-soil displacements. Where the embankment on soft clay forms an approach to a piled bridge abutment, time-dependant movements within the clay may produce significant lateral loading and deflection of the piles. This loading, and any additional lateral loading derived from backfill earth pressure in cases where the approach embankment is retained by the abutment structure, will induce bending moments and deflections in the piles. In severe cases, this may lead to structural distress or failure of the piles or bridge structure.To solve the problems mentioned above, based on the systematic summary of existing theories, tests and analytical approaches, the behavior of piled bridge abutment against soil lateral movements has been studied thoroughly by FEM. The main contents and conclusions can be given as follows:Firstly, according to geotechnical literatures, the current research situation of embankment lateral effects on the piled bridge abutments on soft clay is analyzed. The field observation results and centrifuge model tests of piled bridge abutments on soft ground, finite element analysis of the soil-pile interaction and various computation techniques of the lateral earth pressure acting on the piles from horizontal soil movements are summarized.Secondly, displacement mode of unstable soil and the deformation mechanism of passive pile are analyzed, then a elastic perfectly plastic model and a hyperbolic curve model about the behavior of piled bridge abutment against soil lateral movements are developed on the basis of the previous research.In this paper, a plane strain finite element approach is described for analysis of pile groups influenced by lateral soil movements from the approach embankment in Lian Yungang. The piles are replaced by an equivalent sheet-pile wall with flexibility equal to the average stiffness of the piles and soil it replaced in the approach. Then, the relation between lateral deformation effects on the piled bridge abutment and the surrounding issues such as the thickness of soft clay, embankment height, loading speed is summarized. Some conclusions are drawn regarding application of the analytical method to the design problems of this nature.更多还原