【作者】 陈长流；

【导师】 朱彦鹏；

【作者基本信息】 兰州理工大学 ， 结构工程， 2014， 博士

【摘要】 桩基础作为一种重要的深基础形式,具有沉降量小和承载力高的优点,目前在大厚度黄土地区得到非常广泛的应用。工程实践证明桩的侧摩阻力在不同工况下取值会有很大的差异,为能深入研究桩与土体之间的相互作用,把握侧摩阻力取值的规律,本文通过现场试验、缩尺模型试验和数值模拟分析相结合的方法进行研究,对考虑湿陷的大厚度黄土地区桩基负摩阻力特性有了更全面和深入的认识,主要完成的工作和取得的成果如下：(1)借助实际工程,通过现场大型试验研究桩基在天然状态下及浸水条件下桩顶荷载与桩体沉降的关系；通过对黄土地区土体湿陷、沉降特点及不同深度土层的沉降变化特征的研究,分析了桩周土体沉降与桩身荷载传递规律之间的关系；分析了试桩在预浸水条件下桩身承载力和正负摩阻力的变化规律,并与未进行预浸水的试桩进行了对比分析,研究了桩身轴力分布和中性点位置变化以及桩身摩阻力的分布规律。(2)以相似理论为基础,通过对国内外桩基负摩阻力的试验方案分析与研究,将原型桩和缩尺模型桩进行相似关系转化,自主设计了一套考虑湿陷的桩基负摩阻力的缩尺模型试验方案及方法,对大直径沉管灌注单桩承载力进行缩尺模型试验研究,并进行了负摩阻力试验,得到了桩的中性点位置以及负摩阻力产生和发展的规律。(3)基于ADINA大型有限元分析软件对黄土地区单桩和群桩的负摩阻力进行了分析。主要研究内容包括：有限元模型的建立、浸水计算模型的设置、桩基P-S关系分析、桩顶加载工况下桩身轴力分析、浸水工况下桩周土体沉降分析、浸水工况下桩身轴力分析和浸水工况下桩侧负摩阻力分析。(4)以西北黄土地区实际工程为背景,借助数值分析软件ADINA,建立了有限元分析模型,计算了桩顶加载及浸水工况下,桩身轴力及负摩阻力,并对影响桩身轴力及负摩阻力特性的参数进行了分析。主要研究了黄土弹性模量、黄土粘聚力、桩顶荷载、桩体刚度和浸水压力等对桩身轴力及负摩阻力的影响。更多还原

【Abstract】 As an important form of deep foundation, pile foundation has the advantages of small subsidence and high bearing capacity. It gets very extensive application in large thickness loess area at present. Pile can be considered as cylindrical component buried in the soil. The interaction between soil and pile was produced under the external force. And the interaction was very complex because of the layered characteristics of soil and the geological features of the differente soil. Engineering practice shows that the side friction value of the pile was great differente under different conditions.In order to study the interaction between pile and soil, and master the law of side friction values of the pile, this paper would study the characteristies of pile negative friction in the large thickness loess area considering the collapsibility through the combining method of field test, scale model test and numerical simulation analysis. The main work and achievements are as follows:(1) With the aid of actual engineering, the relationship between the pile settlement and the pile top load was studied through the field test study on large pile foundation under water immersion and natural conditions. The relationship between the soil settlement and the pile load transfer law was studied by the analysis of soil collapsibility, settlement characteristics, and settlement change features of different soil layer depth in loess area. The pile bearing capacity and the positive and negative friction changing rule was analyzed under pre-water immersion, and the testing pile was compared analysis was carried out between prewatering and non-pre-water immersion. The pile axial force distribution, the change of neutral position, and the friction distribution on the pile was studied.(2) According to the similarity theory, through the analysis and research of the domestic and overseas pile foundation testing scheme of negative friction, the prototype is turned into scale model by similarity relation, and then the testing scheme and method of the pile negative friction laboratory scale model considering the collapsibility was designed. The bearing capacity of large diameter sinking pipe was researched by scale model test, and the negative friction test was also carried out. Then, the neutral point position and the produce and development rule of negative friction were get.(3) The negative friction of single pile and pile group in loess area was analyzed by Nonlinear (ADINA). Main research contents include:the FEM model establishment, the water immersion calculation model set, the P-S relationship analysis of the pile foundation, the axial force analysis of pile top loading condition, the soil sedimentation analysis under water immersion condition, and the axial force and negative friction analysis under water immersion condition.(4) Based on the practical engineering in the northwest loess area, nonlinear FEM (ADINA) is used to established the finite element analysis model. The pile axial force and negative friction was calculated under pile top loading and water immersion conditions. And then parameters which influence the axial force and negative friction were analysed. The influences of loess elastic modulus and cohesive force, pile top loading, pile stiffness and water immersion pressure on the pile axial force and negative friction were mainly studied.更多还原