长期竖向循环荷载作用下桩的变形特性试验及理论研究

发布时间：2018-03-31 23:24

本文选题：桩基础　切入点：竖向循环加载　出处：《浙江大学》2013年博士论文

【摘要】：随着国民经济的持续快速发展,风力发电、海上石油平台及高速铁路等新型能源及高速交通工程陆续兴建。在这些工程中,桩基础在其服役期内不但要承受上部结构自重所产生的静荷载,还要长期承担由风、浪或列车等所引起的具有显著周期性的竖向循环荷载的作用。竖向循环荷载作用下桩的承载及变形特性愈发受到设计人员的关注,特别是对于高速交通、风力发电机等这些对基础不均匀沉降较敏感的结构,长期循环荷载作用下的桩基累积沉降已成为此类工程设计中最需控制的关键参数。然而目前循环下桩基的受荷性状及控制方法尚未明确,因而开展对竖向循环荷载作用下桩基承载及变形性状的研究具有重要的现实及理论意义。本文通过大比尺模型试验、数值模拟等方法系统研究了长期竖向循环荷载作用下桩的承载及变形性状及累积沉降调控方法,提出了基于服役性能设计的循环下桩基设计方法。本文研究受到国家自然科学基金(50878193、51225804及U1234204)的资助。本文所做的主要工作和研究成果如下： (1)建立了竖向荷载作用下单桩有限元分析模型,研究了单次加卸载过程中的桩身荷载传递及变形规律。研究结果表明,桩顶卸载回弹下的桩身上部会产生负摩阻力,负摩阻力的分布深度主要受卸载幅值、长径比、桩土刚度比及桩端土体模量的影响。负摩阻范围随卸载幅值的增大而变大；相同卸载幅值下,负摩阻范围随桩长的增加、桩土刚度比的增大、桩端土体模量的减小而减小。 (2)设计并制作了大比例模型试验桩,提出了孔压、土压及轴力传感器的桩身安装、测试及标定技术,基于浙江大学大型土工物理模型试验系统开展了25组刚性单桩循环加载试验,对饱和粉土地基中的刚性单桩在静力及循环加载条件下的承载及变形性状进行了系统试验研究。 (3)基于模型试验,获得了不同循环荷载加载条件下,粉土地基中刚性桩的承载及变形性状、桩-土界面应力变化规律及荷载传递变化规律；分析了单桩循环承载弱化及累积沉降产生的机理；提出了考虑组合循环荷载特性的桩基长期累积沉降预测公式。研究结果显示,累积沉降随振次的增加而增大,随循环荷载幅值的增大而变大；循环加载将导致桩-土界面土体发生剪缩,引起界面超静孔压的累积及法向有效应力的下降,孔压及有效应力的变化幅度随剪切幅值的增大而变大；循环下侧摩阻的弱化是由于界面法向有效应力的降低所引起的。 (4)利用通用有限元软件ABAQUS所提供的二次开发平台,开发了基于Mortara静力/循环界面弹塑性模型的用户界面子例程序UINTER.通过与砂-钢界面剪切模型试验结果的对比,验证了本文UINTER的正确性。利用有限元模型,对界面循环加载性状及影响因素进行了分析,提出了基于法向应力降低的界面剪切循环弱化简化分析模型。 (5)基于理想塑性模型,采用幂函数描述法向应力随循环次数的弱化规律,建立了桩土界面循环弱化模型；基于双曲线型模型建立了桩端循环滞回模型。建立了基于荷载传递法的竖向循环加载条件下单桩的一维分析模型,编写计算程序ACLPAP。采用该模型对竖向循环加载下的桩-土相互作用问题进行了分析,研究了长径比、桩土刚度比、下卧层性质、桩周土模量分布等因素对桩基循环加载性状的影响。研究结果显示,循环下桩基的竖向荷载传递规律、承载及变形性状主要决定于桩顶循环荷载幅值水平,桩基的循环加载效应随循环荷载比的增大而变大,存在一最小循环荷载比,当荷载比小于MCLR时,桩基性状不会因循环加载而受到影响；相同循环荷载幅值下,桩基的循环加载效应随桩长的增加而减小,随桩土刚度比的增大而变大,随桩端土体模量的增大而减小。 (6)分析了循环下桩基设计中的关键问题,提出了基于界限循环荷载比控制的基本设计思想。讨论了组合循环荷载下桩基的变形及承载性状,提出了循环稳定沉降分析图的概念。提出了循环下桩基的基本设计方法及一般流程。采用该设计方法对一个实例工程进行了验算分析,并与实际监测结果进行了对比,验证了该方法的有效性。本文研究采用模型试验及理论研究手段对竖向循环下桩基性状进行了较为细致的研究,所得结果对于考虑循环荷载影响的桩基设计具有重要的参考意义。本文研究结果丰富了桩基研究内容,为循环下桩基的优化设计奠定了理论基础。
[Abstract]:With the sustained and rapid development of the national economy, wind power, offshore oil platforms and high-speed railway and other new energy sources and high-speed traffic engineering were built. In these projects, the pile foundation during its service period should not only bear the weight of the superstructure load generated by the longer period shall be borne by the wind, waves or caused by train the significant periodic vertical cyclic loading. The bearing and deformation characteristics increasingly emphasized by designers of pile under vertical cyclic loads, especially for high-speed traffic, the structure is sensitive to the uneven settlement of wind turbines on the basis of these, the long-term cyclic loading of pile foundation has become the key parameters of such cumulative settlement in the engineering design of control. However, the current cycle of under the pile foundation load characteristics and control method is not yet clear, so the study on pile foundation under vertical cyclic loads The study of bearing and deformable characters has important practical and theoretical significance.
In this paper, through large scale model tests and numerical simulation method to study the long-term system of vertical cyclic loading pile bearing and deformation and cumulative settlement control method, put forward the design methods of pile foundation design based on the service performance of the cycle. This research was supported by the National Natural Science Fund (5087819351225804 and U1234204) of the funding. The main work and research results are as follows:
(1) a finite element analysis model of single pile under vertical load, the pile load transfer and deformation of single loading and unloading process. The results show that the upper part of the pile pile under unloading will produce negative friction, the depth distribution of negative friction resistance is mainly affected by the magnitude of unloading, long diameter than, the influence of pile soil stiffness ratio and pile modulus. Negative friction range increases with the amplitude of the unloading is larger; the same unloading amplitude, negative friction range with the increase of pile length, pile soil stiffness ratio increases, decrease the soil modulus of pile end decreases.
(2) the design and fabrication of the large scale model test pile, put forward the pore water pressure, earth pressure and axial force sensor of pile installation, calibration and testing technology, Zhejiang University large geotechnical physical model test system was carried out in 25 groups of single rigid pile based on cyclic loading tests of saturated silty soil, the rigidity of single pile carrying on the static and cyclic loading conditions and deformation properties were studied.
(3) based on the model test, obtained in different cyclic loading conditions, the bearing and deformation behavior of rigid pile in silt foundation, pile-soil interface stress variation and load transfer regularity; analysis of the single pile bearing mechanism of cyclic weakening and cumulative settlement generated; the settlement prediction formula of pile foundation considering combined cycle load characteristics of long-term accumulation. The results showed that the cumulative settlement increases with the time of vibration, with the increase of the amplitude of cyclic load increases; cyclic loading will cause the pile-soil interface soil shear contraction caused by decreased accumulation of interface of the pore pressure and the effective stress, variation pore pressure and effective stress decreased with increasing shear amplitude becomes larger; lower friction weakening cycle is caused by reducing the interfacial normal effective stress of the Institute.
(4) two development platform using ABAQUS finite element software provided by the development of the Mortara static / cyclic elastoplastic model interface of the user interface sub cases program UINTER. by comparing with the sand steel interface shear model based on test results, verified the correctness of UINTER. Using the finite element model of factors cyclic loading characteristics and influence of interface are analyzed, put forward a method based on the simplified model of weakening interfacial shear stress reduced circulation to.
(5) the ideal plastic model based on the power function to describe the normal stress with the weakening regularity of cycle times, a cyclic weakening of pile-soil interface model; hyperbolic model was established based on the pile cyclic hysteretic model. Analysis model of load transfer method under cyclic loading conditions of single pile is established based on one dimension using this model, calculation program ACLPAP. of vertical cyclic loading of pile-soil interaction problems in compiling are analyzed, on the long diameter ratio, stiffness ratio of pile and soil, substratum properties, effects of soil around the pile modulus distribution of pile loading traits. The results showed that the vertical load transfer law pile foundation under cyclic loading and deformation properties of pile mainly depends on the amplitude of cyclic load, cyclic loading effect of pile foundation with the cyclic load ratio increases, there is a minimum cycle load ratio, when the load ratio is less than M When CLR is applied, the pile foundation behavior will not be affected by cyclic loading. Under the same cyclic load amplitude, the cyclic loading effect of pile foundation decreases with the increase of pile length, and increases with the increase of pile soil stiffness ratio, and decreases with the increase of pile end soil modulus.
(6) the analysis of key issues in the design of pile foundation under the circular, puts forward the basic design idea of control than a limit cycle load is discussed. Based on a combination of pile foundation deformation under cyclic loading and bearing characteristics, puts forward the concept of settlement cycle stability analysis diagram is proposed. The basic design method of pile foundation under cyclic and general process of using. The design method of an instance of engineering checking and analysis, and the actual monitoring results were compared to verify the validity of the method.
In this paper by means of model test and theoretical research on characters of pile vertical circulation is studied, the results have important reference value for the design of pile foundation considering the effect of cyclic loading. The results of this study enriches the research content of pile foundation, laid the theoretical foundation for the optimization design of pile foundation under cyclic.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU473.1

【共引文献】