摘 要

当前交通运输工程中，原有低等级道路设计已不能满足新兴发展的经济建设对交通设施的需求，东部地区土质较软，因此在拓宽路堤时，需强化地基承受荷载的能力。复合地基对拓宽路堤的沉降变形控制效果如何以及复合地基如何设计更加合理，是拓宽路堤工程中的关键科学问题之一。

本文运用有限元分析的方法，对拓宽路堤的沉降变形、单桩轴力和桩土荷载分担比进行分析。通过模拟路堤拓宽施工过程和桩基设计参数变化分析，研究了桩承式路堤的工作性状以及桩基参数对其的影响，主要工作及结论如下：

（1）使用PLAXIS程序模拟桩承式拓宽路堤有限元模型，以及拓宽路堤填筑施工过程，分析路堤沉降、桩基轴力和桩土荷载分担比在施工中的变化情况。结果表明：拓宽路堤的最大沉降量和最大水平位移量随着填筑高度的增加而增加，填筑施工期间的最大变形发生在填筑体内部；桩基变形模式和轴力分布都反映了路堤填筑到一定高度对桩基形成了倾斜的附加荷载作用；桩土荷载分担比随着填筑高度的增加而增大，桩基对于承担上部填筑荷载具有重要作用。

（2）以标准模型为参照，进行一系列桩基设计参数变化分析，结果显示：桩长、桩间距、桩身刚度等桩基设计参数改变时，对拓宽路堤沉降、单桩轴力及桩土荷载分担比都有一定的影响，减小桩长和桩身刚度、增大桩间距都会使得路堤沉降增加、桩土荷载分担比降低，这不利于拓宽路堤的正常工作。但是增大桩间距可以使单桩发挥出更大的轴力，从经济性上考虑，桩间距并不是越小越好。

关键词：软土地基；桩承式拓宽路堤；数值模拟；沉降；桩土荷载分担比

ABSTRACT

In the current transportation projects, the original low-grade road design can no longer meet the demand for transport facilities in the newly-developed economic construction. In the eastern region, the soil quality is relatively soft. Therefore, when the embankment is widened, it is necessary to strengthen the ability of the foundation to bear the load. It is one of the key scientific problems in the widening of embankment engineering that the effect of composite foundation on the control of settlement deformation of widening embankment and how the design of composite foundation is more reasonable.

In this paper, the method of finite element analysis is used to analyze the settlement deformation of the embankment, the axial force of the single pile and the load sharing ratio between pile and soil. By simulating the process of widening the construction process of the embankment and the analysis of the design parameters of the pile foundation, the work performance of the piled embankment and the influence of the parameters of the pile foundation were studied. The main work and conclusions are as follows:

(1) Using the Plaxis program to simulate pile anchors to expand the finite element model of the embankment and widen the construction process of the embankment filling, and analyze the changes of embankment settlement, axial force of the pile foundation, and load-sharing ratio of the pile and soil in the construction. The results show that the maximum settlement and the maximum horizontal displacement of the widening embankment increase with the increase of the filling height, and the maximum deformation during the filling construction occurs inside the filling body; both the deformation mode and axial force distribution of the pile foundation are reflected. The embankment filling to a certain height has formed an inclined additional load effect on the pile foundation; the load-sharing ratio of pile-soil increases with the increase of filling height, and the maximum value can reach 0.87. The pile foundation plays an important role in bearing the upper filling load.

(2) Using a standard model as a reference, a series of changes in the design parameters of the pile foundation are analyzed. The results show that the pile foundation, pile spacing, pile stiffness, etc., change the design parameters of the pile foundation, widen the embankment settlement, axial force and pile of the single pile. The ratio of soil load share has a certain effect. Decreasing the length of pile and the stiffness of the pile and increasing the spacing of piles will increase the settlement of embankment and reduce the load sharing ratio between pile and soil, which is not conducive to widening the normal work of embankment. However, increasing the pile spacing can make the single pile play a greater axial force. From the economical point of view the smaller the pile spacing is the better.

Key words: Soft Soil Foundation; Pile-supported Widening Embankment; Numerical Simulation; Settlement; Pile-soil Load Sharing Ratio

目 录

1 绪论 1

1.1 研究背景 1

1.2 路堤拓宽中土拱效应的研究 2

1.2.1 土拱形态与成拱过程的起源及近期发展 2

1.2.2 不同类型路堤中土拱效应的研究 2

1.3 不同路基对拓宽路堤的影响 4

1.4 路堤拓宽中的不均匀沉降及影响因素分析 5

1.5 路堤拓宽的性状分析 6

1.5.1 拓宽路堤的变形性转及安全因素的研究分析 6

1.5.2 土工格栅的力学效应研究 6

1.6 本文主要研究内容 7

1.6.1 存在的问题及不足 7

1.6.2 主要研究内容 7

2 计算模型的建立与参数选取 9

2.1 PLAXIS有限元分析软件 9

2.2 模型建立与网格划分 9

2.3 土体及桩、土工格栅参数选取 11

2.4 模拟施工步骤 11

2.5 本章小结 14

3 桩承路堤工作性状数值分析 16

3.1 路堤变形分析 16

3.1.1 竖向变形 16

3.1.2 水平变形 21

3.2 桩基变形分析 26

3.3 桩基受力分析 31

3.4 桩土荷载分担比分析 36

3.5 本章小结 37

4 桩基参数变化分析 38

4.1 桩基参数变化方案 38

4.2 桩长的影响 39

4.2.1 路堤变形分析 39

4.2.2 桩基轴力分析 40

4.2.3 桩土荷载分担比分析 42

4.3 桩间距的影响 43