竖向荷载作用下小间距摩擦型群桩基础承载特性分析

发布时间：2018-09-09 17:03

【摘要】：随着经济的迅速发展,国家为改善二、三线城市特别是滇西北地区的交通出行问题,为高速公路的建设投入大量资金,这有利于推进滇西北旅游业的发展,促成边区实现跨越式发展和构建小康社会。工程实践中常会遇到群桩桩距距过小的情况,传统的理论分析和室内试验明显滞后于工程实践的需求。因此在保证桥梁工程的安全性并充分发挥群桩承载性能的同时,对小间距群桩桩基的承载性状进行深入研究是非常有必要的。论文在分析国内外室内试验和理论计算的基础上,通过建立有限元三维数值模型对云南某桥梁工程的小间距群桩竖向承载特性展开分析,主要研究工作及成果如下:(1)基于查阅国内外群桩基础的相关文献基础上介绍了计算单桩承载力、群桩承载力、群桩沉降、有效桩长的方法,对比分析几种常用经典计算方法的优缺点及适用范围,并在此基础上对群桩承载力采用群桩效应系数法和极限平衡法、群桩沉降采用分层总和法、有效桩长采用桩顶沉降控制法分别进行计算。(2)对有限元软件在岩土工程中的适用性进行了简要分析,简明阐述本论文Abaqus数值模拟软件的建模步骤及分析材料本构模型的选用:桩体采用线弹性模型、土体采用摩尔-库伦模型、相互作用采用摩擦接触(切向行为采用罚函数、法向行为采用硬接触)和绑定接触,面-面离散化的方法。(3)采用Abaqus有限元软件,对小间距低承台群桩基础进行三维数值模拟计算,探讨不同桩距、桩长、桩数、桩径等工况对群桩竖向承载性状的影响,并就不同桩距工况下采用数值计算和理论计算得出的群桩效应系数进行对比分析,通过分析荷载-沉降曲线得出结论:在竖向荷载较小时,不同工况下的群桩沉降差别不大;当竖向荷载增大,桩距在2d-6d工况下沉降量由大变小;桩长由50m增至80m工况下群桩竖向承载力逐步增大,沉降变形逐步减小,但桩长增加到一定程度后再增加长度,群桩承载力和沉降变化幅度较低;随桩数增加,荷载-沉降曲线呈现较大变化,但桩数增加到一定量时,沉降减小幅度趋于平稳。对比分析数值计算和理论计算不同桩距工况下的群桩效应系数相差不大,验证了采用数值模拟的可行性。(4)对依托工程分别采用以群桩效应系数法和极限平衡法两种不同方法来计算群桩竖向承载力,并对结果进行了对比分析,验证了有限元数值计算出的群桩效应系数的适用性;对依托工程群桩沉降、有效桩长分别采用理论计算和数值计算进行对别分析,得出群桩设计的合理性。
[Abstract]:With the rapid economic development, in order to improve the transportation and travel problems of the second and third tier cities, especially in northwest Yunnan, the state has invested a large amount of money in the construction of highways, which is conducive to promoting the development of tourism in northwest Yunnan. Promote the border region to achieve leapfrog development and build a well-off society. In engineering practice, the group pile spacing is often too small, and the traditional theoretical analysis and indoor test obviously lag behind the demand of engineering practice. Therefore, while ensuring the safety of bridge engineering and giving full play to the bearing capacity of pile groups, it is necessary to deeply study the bearing behavior of small spacing pile groups. Based on the analysis of indoor tests and theoretical calculations at home and abroad, the vertical bearing characteristics of small spacing pile groups in a bridge project in Yunnan Province are analyzed by establishing a finite element three-dimensional numerical model. The main research work and results are as follows: (1) based on the reference of the domestic and foreign pile group foundation, the method of calculating the bearing capacity, settlement and effective pile length of single pile group is introduced. The advantages and disadvantages of several classical calculation methods are compared and analyzed. On this basis, the pile group effect coefficient method and limit equilibrium method are adopted for pile group bearing capacity, and the stratified summation method is used for pile group settlement. The effective pile length is calculated by means of pile top settlement control method. (2) the applicability of finite element software in geotechnical engineering is analyzed briefly. In this paper, the modeling steps of Abaqus numerical simulation software and the selection of material constitutive model are briefly described. The pile body adopts linear elastic model, the soil body adopts Moore Coulomb model, the interaction adopts friction contact, and the tangential behavior adopts penalty function. (3) Abaqus finite element software is used to simulate the pile group foundation with small spacing and low cap, and the different pile spacing, pile length and pile number are discussed. The influence of pile diameter and other working conditions on the vertical bearing behavior of pile group is analyzed, and the effect coefficient of pile group under different pile-spacing conditions is compared and analyzed by numerical calculation and theoretical calculation. Through the analysis of load-settlement curve, it is concluded that the settlement of pile group under different working conditions is not different when the vertical load is small, and when the vertical load increases, the settlement of pile spacing changes from large to small under 2d-6d condition. When the pile length increases from 50 m to 80 m, the vertical bearing capacity of pile group increases gradually, the settlement deformation decreases gradually, but the pile length increases to a certain extent, and the variation range of bearing capacity and settlement of pile group is lower, which increases with the number of piles. The load-settlement curve varies greatly, but when the pile number increases to a certain amount, the settlement decreases steadily. There is no significant difference in the effect coefficient of pile group between the numerical calculation and the theoretical calculation under different pile-spacing conditions. The feasibility of numerical simulation is verified. (4) pile group effect coefficient method and limit equilibrium method are used to calculate the vertical bearing capacity of pile group respectively, and the results are compared and analyzed. The applicability of the effect coefficient of pile group calculated by finite element method is verified, and the rationality of pile group design is obtained by theoretical calculation and numerical calculation of effective pile length for pile group settlement of relying engineering.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U443.15

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