【作者】 李俊；

【导师】 周建；

【作者基本信息】 浙江大学 ， 土木工程， 2012， 硕士

【摘要】 目前高速铁路广泛采用的新型无砟轨道对路基下地基的工后沉降提出了严格的要求。在深厚软弱土地基上修建高速铁路必须解决地基承载力不足、工后沉降以及差异沉降过大的问题。如何在保证沉降控制要求的前提下尽可能的减小经济成本,需要考虑筒桩复合地基不同结构型式的应用。本文就此开展了路堤荷载下筒桩复合地基结构设计的相关研究工作。通过对筒桩复合地基进行三维有限元模拟,研究分析了有无桩帽、桩帽尺寸、桩间距大小和土工格栅对复合地基沉降变形性状的影响规律,并在此基础上提出了相应的筒桩复合结构的设计思路和方法,并选取具体复合体结构进行了计算,得到以下结论：1)桩帽对筒桩性状的影响很大,筒桩上设置桩帽可以较好地发挥其减小地基沉降,调节不均匀沉降的作用,对于减小筒桩的上刺位移量上有较好作用。在实际工程应用上建议筒桩上部设置桩帽；2)路堤下筒桩群桩复合地基的沉降在路堤中心线处最大,随距路堤中心线距离的增大而逐渐减小；在路堤荷载作用下,地基会产生侧向位移。桩间距的改变对加固区土体沉降的影响很大,对下卧层沉降及侧向位移的影响较小；加大桩间距会明显增大地基的总沉降及筒桩与桩间土之间的沉降差,实际工程应用中,桩间距不宜过大,建议选取S/D=3-3.5；3)土工格栅具有可以在整体上加强和改善复合地基性能的作用,能使沉降均匀化,对侧向形变的约束作用比较明显；采用土工格栅+桩帽的联合应用,能充分发挥桩帽与格栅各自的优势,在减小地基总沉降、调节不均匀沉降及控制地基侧向位移上取得比较理想的效果,是一种综合性能优异的筒桩复合结构型式；4)新型的分离式弹性接触筒桩复合结构,实现了桩帽与桩身结构上的分离,二者的弹性接触可以避免可能的冲切破坏；承受荷载时,将地基的沉降变形分为“分离”与“结合”两个连续的阶段,在“分离阶段”,桩帽会随地基浅层土体共同下沉,使地基下部土体被挤密压实,会使“结合阶段”的地基沉降减小、沉降不均匀的现象得到改善,是一种值得进一步深入研究的新型筒桩结构。更多还原

【Abstract】 The wild use of ballastless tracks on high-speed railway has raised a stringent requirement of post construction settlement. To build high-speed railway on deep soft soil the problem of inadequate foundation bearing capacity, excessive post construction settlement and differential settlement must be solved. How to reduce the construction investment under the premise of settlement control, the application of tubular piles with different structural types is one of the considerations. For this purpose, the paper carried out research work on the structure design of tubular pile composite foundation under the embankment.By3-D finite element simulation of tubular pile composite foundation, the impact of pile with and without cap, the cap size, pile spacing and geogrid on the settlement characteristics of composite foundation were analyzed. An appropriate design method for the tubular pile composite structure was then proposed on this basis, and the following conclusions were obtained:1) Pile cap has a great impact on the tubular pile characters. Tubular pile with cap can reduce ground settlement, adjust the differential settlement, and it also can prevent the upward penetration deformation of tubular pile. In practical engineering applications, it is recommended to set a cap on the top of tubular pile;2) In group tubular pile composite foundation the maximum settlement occurred at the centerline under the embankment. The settlement gradually decreases with the distance increasing from the embankment centerline. Under the embankment loading, lateral ground displacement will accumulate. Different pile spacing has significant impact on soil settlement of the reinforced area, but has less effect on the settlement of underlying layer and lateral displacement. Increased pile spacing will significantly deteriorate the total settlement of the foundations and differential settlement, hence in practical applications, large pile spacing is not suggested and the appropriate value S/D=3～3.5is recommended.3) Geogrid can strengthen and improve the overall behavior of the composite foundation. Therefore it has good effect on settlemental homogenization and constraint of the lateral deformation. The joint application of geogrid and pile cap was demonstrated to be a good type of tubular pile structure with integrated performance in terms of total settlement reducing, differential settlement adjusting and lateral displacement constraint.4) A new tubular pile was proposed, which has the feature of structural separation and elastic contact. Th elastic contact can avoid possible destruction of the punching. While using this novel pile, the total settlement consists of two parts, i.e. the settlement generated in the stage of "separation" and "combination". When loaded, the pile cap will move down with the soil in the separation stage, and this movement will help to reinforce the deep soil so less settlement in "combined phase" will be expected and the phenomenon of uneven settlement will be improved. This new type of tubular pile structure is worthy of further study.更多还原