堆载作用下既有桥梁群桩基础承载特性分析

发布时间：2018-09-03 11:02

【摘要】：随着我国铁路、公路建设规模的持续发展,铁路、公路桥梁的总里程不断增加,但由于施工条件和环境等各种因素的限制,经常会出现天然冲填土及施工中的弃方填土在桥下桩基周围大面积堆积的情况。堆填上荷载作用的结果主要表现在两个方面,一方面使桩周上产生水平位移,引起桥梁桩基产生弯曲变形,从而造成上部结构偏移甚至无法正常运营；另一方面使桩周土体进一步固结,上体与桩身发生相对位移,桩周产生较大的负摩阻力,进而降低桩基的承载力并产生不均匀沉降。可以看出,堆载作用对桥梁桩基础承载力及变形产生的不利影响对铁路运输及人民生命财产安全构成了严重的威胁,因此考察堆载作用下既有桥梁群桩基础承载特性及变形规律,评价其是否满足设计承载力及变形的要求是十分必要。木文在总结国内外近年来偏载作用对桥梁桩基承载特性的影响分析的基础上,由弹性理论推导出了在不同堆载等级、堆载距离下桩基承载力的理论计算公式;与理论计算相对应,建立了三维有限元模型,分析了随着堆载等级及距离变化单桩和群桩桩基承载力及变形的发展规律；在此基础上,建立了群桩基础三维有限元固结分析模型,研究了桩基沉降及内力随时间的变化规律,并与现场桥梁桩基础沉降实测数据进行了对比分析,验证了理论分析和数值计算的正确性。本文的主要研究成果如下：(1)调研了堆载作用下桥梁桩基础承载特性及变形的理论计算及分析方法,介绍了堆载作用下桩基受力特性及其复杂性,为本文的研究奠定了理论基础。(2)基于弹性理论中半无限空间表面上作用一竖向集中力F时,半空间内任一点的应力和位移的弹性力学解,针对应力及位移问题求解的复杂性,借助Matlab编程构建了相应的计算程序,推导出堆载状态下桩周土任一点的应力和位移,从而推导出任意堆载等级、堆载距离下单桩基础承载力的解析解；根据理论计算模型,建立了三维数值计算模型,研究了随堆载等级及距离变化,单桩及群桩基础的承载力及群桩效应系数的发展规律,与理论计算进行了对比分析,提出了不同堆载距离对应的安全堆载等级的计算公式。(3)以大丽线深厚软土区大区域堆载导致桥梁梅花桩群基础病害典型工点为背景,建立了梅花桩群基础三维有限元固结模型,研究了全堆载作用下群桩基础的沉降及受力特性随时间的变化规律。在此基础上,建立了桥梁现场梁梅花桩群基础及其上部结构沉降变形自动化监测系统,分析了各桥墩基础沉降变形变化规律,评估了其服役状态；为服务线路运营安全发挥了重要的指导作用。
[Abstract]:With the continuous development of railway and highway construction scale in China, the total mileage of railway and highway bridges is increasing, but due to the construction conditions and environment and other factors, Natural fill and abandoned fill are often accumulated in large area around pile foundation under bridge. On the one hand, the horizontal displacement around the pile causes the bridge pile foundation to bend and deform, which results in the displacement of the superstructure and even the normal operation of the superstructure. On the other hand, the soil around the pile is further consolidated, the upper body and the pile body have relative displacement, and the pile circumference produces greater negative friction resistance, thus reducing the bearing capacity of the pile foundation and producing uneven settlement. It can be seen that the adverse effects of heaps on the bearing capacity and deformation of the bridge pile foundation pose a serious threat to the safety of railway transportation and people's lives and property. Therefore, it is necessary to investigate the bearing characteristics and deformation law of existing bridge pile group foundation under the action of surcharge, and to evaluate whether it meets the requirements of design bearing capacity and deformation. On the basis of summarizing the influence of eccentric loads on the bearing characteristics of bridge pile foundation at home and abroad in recent years, the paper deduces the theoretical calculation formula of pile foundation bearing capacity under different heap-load grades and heap-load distance by elastic theory. Corresponding to the theoretical calculation, a three-dimensional finite element model is established, and the development law of bearing capacity and deformation of single pile and group pile foundation with the change of heaped load grade and distance is analyzed. The three-dimensional finite element consolidation analysis model of pile group foundation is established, and the variation law of pile foundation settlement and internal force with time is studied, and compared with the measured data of bridge pile foundation settlement on the spot. The correctness of theoretical analysis and numerical calculation is verified. The main research results of this paper are as follows: (1) the theoretical calculation and analysis methods of bearing characteristics and deformation of bridge pile foundation under heaped load are investigated, and the mechanical characteristics and complexity of pile foundation under surcharge are introduced. (2) based on the elastic theory, when a vertical concentrated force is applied on the surface of a semi-infinite space, the elastic solution of stress and displacement at any point in the semi-infinite space is obtained, and the complexity of solving the stress and displacement problem is discussed. With the help of Matlab programming, the corresponding calculation program is constructed, and the stress and displacement of soil around the pile at any point in the state of pile load are deduced, and the analytical solution of the bearing capacity of the pile foundation under any heaped load grade and the heap-load distance is derived, and the model is calculated according to the theoretical model. A three-dimensional numerical calculation model is established, and the development law of bearing capacity and pile group effect coefficient of single pile and pile group foundation are studied with the change of heap-load grade and distance, and compared with theoretical calculation. In this paper, the calculation formula of safety heap-load grade corresponding to different heap-load distance is put forward. (3) based on typical site of foundation disease caused by overburden in deep soft soil area of Dalian Line, a three-dimensional finite element consolidation model for foundation of Plum Blossom pile Group is established. The variation law of settlement and stress characteristics of pile group foundation with time under full surcharge is studied. On this basis, an automatic monitoring system for settlement and deformation of bridge site beam and Meihua pile group foundation and its superstructure is established, and the variation law of settlement and deformation of each pier foundation is analyzed, and its service status is evaluated. It plays an important role in guiding the operation safety of service lines.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U443.15

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