软土地基上堆载对临近桥梁桩基的影响

发布时间：2018-01-24 22:21

本文关键词： 软土地基被动桩堆载土体侧移修正剑桥模型　出处：《福州大学》2014年硕士论文　论文类型：学位论文

【摘要】：在路基和桥梁等建设工程中,往往因地基土的工程性质较差,使得在土体上的堆载诱发土体发生较大侧向位移,使邻近桩基础受到附加水平荷载甚至竖向摩阻力的作用,严重影响桩的承载性能乃至上部结构的破坏,这类桩即称作“被动桩”。被动桩问题有着深刻的工程背景和惨痛的经验教训,特别是近年来桥梁堆载问题日益突出。本文首先利用有限元软件Geo-Studio进行软基上堆载对邻近桥梁桩基的受力形状二维模拟分析,主要讨论了不同堆载高度、宽度、位置、桩径大小、桩长、桩身弹性模量、净空高度、软土层厚度和桩顶荷载等因素对被动桩的位移变化、桩身应力和弯矩分布规律的影响,研究发现：(1)堆载大小和软土层厚度对于桩基位移影响较大,起到至关重要的作用,桥梁尺寸和桩顶荷载等对桩基位移也有一定的影响,但影响不大,说明与桩基位移直接相关联的是桩侧软基沉降的大小。(2)桩身应力大小受堆载大小、桩身弹性模量、净空高度、桩顶荷载等因素影响较大。在左桩基的软基段左侧,桩底持力层交界处右侧,右桩基软基段左侧,桩底持力层交界处右侧,以及系梁部位的应力较大,出现一定程度应力集中现象。(3)桩身弯矩大小与堆载大小、位置、桩长、弹性模量、净空高度、软土层厚度和桩顶荷载等因素关系较大,在软土层以下约1 Om左右位置和桩底嵌入持力层处弯矩均较大。其次,针对福州闽侯荆溪特大桥的6个墩位的堆载问题进行了相应分析,根据相关钻探资料和设计资料建立相关模型,通过计算结果发现,69#桥墩处位移较大,达到5.4cm。因此,结合相应的桥梁加固设计规范提出了不同的加固和治理措施；同时,对桥侧软基上堆载问题提出了不同的预防措施,认为采用复合地基加固软基的方式能够最有效地防治堆载所引起的的桩侧位移,而采用卸载、换填土、隔离桩和桩基加固等方法,只适合于堆载较小或桩基位移较小的情况。说明若要明显改善堆载对桥梁桩基的影响,应着手于改善软土地基的承载力状况,减小软土地基沉降,从而减少软基变形对桥梁桩基带来的影响。
[Abstract]:In the subgrade and bridge construction projects, because of the poor engineering properties of the foundation soil, the surcharge on the soil caused a larger lateral displacement of the soil. The adjacent pile foundation is subjected to additional horizontal load or even vertical friction, which seriously affects the bearing capacity of the pile and even the damage of the superstructure. This kind of pile is called "passive pile". The problem of passive pile has profound engineering background and painful experience and lessons. Especially in recent years, the problem of bridge surcharge is becoming more and more serious. Firstly, the finite element software Geo-Studio is used to simulate the stress shape of adjacent bridge piles on soft foundation. This paper mainly discusses the displacement change of passive pile with different heaped height, width, position, pile diameter, pile length, elastic modulus of pile body, clearance height, soft soil layer thickness and pile top load. Under the influence of stress and bending moment distribution of pile body, it is found that the size of pile load and the thickness of soft soil layer play an important role in influencing the displacement of pile foundation. The bridge size and pile top load also have some influence on the pile foundation displacement, but the influence is not obvious, which shows that the pile displacement is directly related to the pile side soft foundation settlement. The elastic modulus of pile, clearance height and load on top of pile have great influence on the left side of the soft foundation, the right side at the junction of the bottom bearing layer, the left side of the soft foundation section of the right pile foundation, and the right side of the bearing layer at the bottom of the pile. The bending moment and pile load size, position, pile length, elastic modulus, clearance height of pile body are larger than that of tie beam, and the phenomenon of stress concentration occurs to a certain extent, I. E. pile bending moment and pile load size, position, pile length, elastic modulus and clearance height. The thickness of soft soil is related to the pile top load and so on. The bending moment is larger at about 1 Om below the soft soil layer and at the pile bottom embedded in the bearing layer. Secondly. Based on the relevant drilling data and design data, this paper analyzes the surcharge problem of 6 piers of Fuzhou Minhou Jingxi Bridge, and establishes the relevant model. Through the calculation results, it is found that the displacement at the pier of Gui69# bridge is large. Therefore, combined with the corresponding design code for bridge reinforcement, different reinforcement and treatment measures are put forward. At the same time, different preventive measures are put forward to the problem of pile load on the soft foundation of bridge side. It is considered that the composite foundation can be used to strengthen the soft foundation effectively to prevent the pile side displacement caused by the surcharge, and the unloading method is adopted to replace the fill. The method of separating pile and strengthening pile foundation is only suitable for the case of small heaped load or small displacement of pile foundation. It shows that if the influence of pile load on bridge pile foundation is to be improved obviously, the bearing capacity of soft soil foundation should be improved. The settlement of soft soil foundation is reduced, and the influence of soft foundation deformation on bridge pile foundation is reduced.
【学位授予单位】：福州大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：U443.15

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