【作者】 董晓明；

【导师】 谢永利；

【作者基本信息】 长安大学 ， 道路与铁道工程， 2013， 博士

【摘要】 由于湿陷性黄土特殊的结构特性，使得黄土地区的非均匀湿陷性时常会对桥梁桩基等一系列工程造成威胁，甚至产生严重破坏，因此，如何确定非均匀湿陷黄土区桩基承载力和桩侧负摩阻力大小是桥梁桩基设计中亟待解决的关键问题。本文依托山西河运高速大厚度黄土地区非均匀湿陷条件下的桥梁桩基项目，以研究非均匀湿陷条件下群桩受力特性和桩侧负摩阻力工作机理为主线索，以确定浸水前后桩基承载力和建立非均匀变形下桩基负摩阻力模型为主要目标，论文在总结国内外研究现状的基础上，利用现场试验、室内模型试验、理论方法和数值模拟，对非均匀湿陷黄土地区群桩基础承载特性和负摩阻力受力特性进行了系统的研究，研究成果为填补黄土地区非均匀湿陷条件下桥梁群桩负摩阻力研究方面的空白提供了理论依据和参考。主要研究成果如下：1．进行了现场桩基浸水载荷试验，将桩基沉降、桩身轴力和侧摩阻力进行了监测和分析，对黄土天然状态与浸水后的桩基受力特性进行对比研究，揭示了该地区黄土的非均匀湿陷特性，总结了地面浸水的时序问题对桩基受力特性的影响，归纳了浸水期间和停水后黄土湿陷和时间的关系，分析了天然状态、先浸水和后浸水三者桩基承载力的关系，并肯定了采用控制变量法桩基浸水试验来研究湿陷性黄土地区桩基负摩阻力的可行性和有效性。2．采用自行研发的一套室内模型装置，进行了土体非均匀变形条件下的单桩、群桩系列的模型试验，对桩顶沉降、桩身轴力、桩侧摩阻力、桩端阻力等一系列受力特性进行研究，探讨了黄土非均匀变形条件下荷载传递的工作机理，首次研究了黄土非均匀变形对桩基承载力的影响，分析了黄土非均匀变形条件下不同位置的基桩的受力特性，并进一步研究了不同桩端土、不同桩间距对群桩效应的影响。3．开展了桩-土界面摩擦性状试验，探求黄土增（减）湿对桩侧摩阻力的影响，通过改变桩侧土的含水率，研究了黄土增（减）湿对桩侧剪应力的变化规律，确定了最大剪应力与相对位移的关系，提出了该类似地区桥梁桩基桩-土界面的剪力传递函数。4．基于桩基负摩阻产生机理，结合负摩阻力的影响因素和现场桩侧负摩阻力的受力特性，确定了桩土相对位移的计算模型，推导了中性点和最大负摩阻力的位置，建立了“抛物线”式的单桩负摩阻力计算模型，并在单桩负摩阻力模型的基础上提出了群桩负摩阻力的计算方法和群桩负摩阻力修正系数，并将理论结果与现场工程实测数据进行对比验证，进一步预估了不同桩数群桩的下拉荷载。5．运用有限元ADINA软件，基于黄土湿陷的机理，提出了用密模修正法模拟黄土湿陷变形的新方法，用图形可视化和数据分析软件对数据处理，验证了密模修正法模拟自重湿陷性黄土湿陷变形的可行性，并结合现场桩基浸水试验，确定了该类似黄土地区的密模修正系数，推导了黄土湿陷后土体任一深度的沉降关系式。6．依托山西河运高速桥梁桩基项目，运用强大的有限元软件对群桩载荷试验和群桩浸水负摩阻力受力特性进行数值模拟，研究了群桩在竖向荷载作用下的承载力性状、承台性状、桩-土位移、桩身轴力和基桩侧摩阻力的变化规律，并运用密模修正法对黄土湿陷条件下的群桩负摩阻力进行研究，分析了不同位置的基桩的受力特性，结合理论分析和现场试验，预估非均匀湿陷黄土地区群桩的下拽力，为今后类似工程提供一定的借鉴意义。更多还原

【Abstract】 Due to the special structural characteristics of collapsible loess, loess area non-uniform Collapsibilityoften poses a threat to bridge pile foundation or other series of engineering works in loess areas, that evenresult to serious damage. Therefore, how to determine the foundation bearing capacity and pile sidenegative frictional resistance of loess non-uniform collapse area is a key problem in the design of bridgepile foundation which should be solved. This paper is based on the project of bridge pile foundation underthe condition of non-uniform collapse of loess areas in Heyun high speed, shanxi. To study the pile groupmechanical characteristics under the condition of non-uniform collapse a working mechanism of pile sidenegative frictional resistance is set up as the main clue, to determine the bearing capacity of the pile beforeand after immersion and a non-uniform deformation of pile foundation negative friction resistance model isset up as the main aim, of this paper on the basis of summarizing the present situation of research at homeand abroad, making a system to study the non uniform pile load-bearing characteristics of loess collapsearea and mechanical characteristics of pile side negative frictional resistance, using field tests indoor modeltest, theoretical method and numerical simulation. The research results offer theoretical basis for referenceon filling the blank of bridge pile side negative frictional resistance under the condition of non-uniformcollapsibility of a bridge pile group in loess area. Main research results are as follows:1．Conducted field Pile foundation soaking load test, monitoring and analyzing the settlement of pilefoundation, pile axial force and pile side friction, making a comparative study about loess under naturalstate and soaking state, revealed non-uniform collapsibility characteristics of this loess region, summed upthe influence of ground soaking timing problems on pile foundation stress characteristics, summarized therelation between loess collapse and time during and after water immersion, analyze the relationship ofpilefoundation bearing capacity was analysed under three conditions of, natural,immersed and after immersion states, and affirmed the feasibility and effectiveness of pile foundation negative friction resistanceusing controlling variable method of pile foundation soaking test.2．Used a set of self-invent indoor model device, conducted model test of single pile and pile groups,under the condition of soil non-uniform deformation, studied a series of mechanical characteristics of thepile top settlement, the axial force of pile, pile side friction resistance, pile side negative frictionalresistance, discussed the mechanism of the load transfer under the condition of non-uniform deformationof loess, studied the non-uniform deformation of loess influence to the bearing capacity of pile foundation,analyzed different position of the stress characteristics of pile under the condition of loess non-uniform deformation and further studied of the pile group effect of the different pile side soil and different pilespace.3．Conducted Friction properties test of pile-soil interface, explored the influence of pile sidefriction under increased or reduced water in loess, studying the change law of pile side shear strain underincreased or reduced water in loess through changing pile lateral soil water content, affirmed therelationship between the maximum shear stress and relative displacement, put forward the shear transferfunction of bridge pile foundation pile-soil interface in similar regions.4．Based on the mechanism of foundation negative frictional resistance, together with the effectivefactor of negative frictional resistance and the force characteristic of negative friction resistance in the field,ascertain the calculational model of pile and soil of relative displacement, rationalize the locality of neutralpoint and the maximum negative friction resistance, built a calculational model of single pile negativefriction resistance of a parabola shape, and put forward a calculation method and calibration coefficient ofpiles foundation negative friction resistance at the base of single pile foundation negative frictionresistance, compare the theory result with the field test data, further more, compute the down-drag load indifferent number of piles.5．Used the finite element software ADINA, based on the mechanism of collapsible loess, putforward the new method of density model revision to simulate the collapsible loess deformation, used thefigure visualization tool of the software of for data analysis, validate the feasibility of the method ofdensity model revision to simulate the deformation of collapsible loess, combined immersion test of pilefoundation, to get the result of the density coefficient model revision of this loess area, rationalize therelated expressions of settlement in discretional depth after the loess collapsed.6． Based on piles foundations items of Hejin-Yuncheng expressway, use the finite element softwareto get the numerical simulation of piles load test and the force characteristic of piles load immersion test,study the transformation law of the character of bearing capacity, pile caps, displacement of pile and soil,axial force of pile and frictional resistance of pile side, apply the density method of the model revision toresearch piles foundation negative friction resistance under the condition of loess collapsibility, analyze theforce characteristic of piles in different locations, and combine the theory analysis and field test, toestimate the down drag of loess non-uniform collapse area, provide certain reference significance forfuture similar programme.更多还原