桩—土接触面力学性质的模拟研究

发布时间：2019-01-26 10:15

【摘要】：桩基础承载力通常由侧摩阻力与桩端承载力组成。对于桩体侧摩阻力的大小，目前多假定其与法向应力呈线性比例关系，但对于土体与混凝土桩体剪切过程中的土体的应力应变传递规律研究较少。桩-土接触面的剪切性质与剪切过程中土颗粒的运动形式紧密相关，为讨论土体与混凝土接触面剪切性质，本文结合肇源松花江特大桥工程实例，采用室内试验结合数值模拟的方法，研究了土体与混凝土的剪切特性，为进一步理解土体与混凝土剪应力的发挥机理提供了一定参考。首先，选取该工程中土体与混凝土试样，进行了土体与混凝土的接触面中型剪切试验，其中试验土样包括粘性土、细砂、粗砂，法向荷载根据实际工程确定。中型剪切试验结果显示，桩-土接触面的峰值剪切强度与法向应力呈较好的线性关系，对于粘性土，剪切过程中还表现出一定的粘聚力特征。因此，完全可以借鉴土体中库仑-摩尔理论描述接触面的剪切强度。在试验过程中无法从土样中提取足够多土体应力应变信息，故考虑采用数值模拟的方法反演中型剪切试验过程，研究土体剪应力在剪切过程中的传递规律。颗粒流方法被引入剪切试验的数值模拟研究中，以研究砂土与混凝土的剪切破坏特征。颗粒流作为一种离散元方法，很好反映了砂土颗粒之间的法向、切向、滑动作用，从颗粒之间的相关作用为出发点构建本构方程，具有其他方法不具备的诸多优点。在颗粒流模型建立的过程中，颗粒之间的细观参数决定了模型的宏观性质。为了准确获得模型颗粒细观参数，第四章中采用正交试验的方法，基于砂土的三轴试验，研究了孔隙率、摩擦系数、法向刚度、切向-法向刚度比等四项细观参数对三轴试验中砂土内摩擦角、泊松比、弹性模量的影响规律。结果显示：砂土的内摩擦角通常与颗粒的摩擦系数、切向-法向刚度比有关；砂土的弹性模量通常与颗粒的法向刚度、切向-法向刚度比有关；砂土的泊松比主要由颗粒的切向-法向刚度比、孔隙率决定。而后，在确定了颗粒细观参数的基础上，建立了砂土与混凝土中型剪切试验的颗粒流模型，进行了不同法向荷载下砂土的剪切试验。数值模拟结果与中型剪切试验结果达到了较好的吻合，再次证明了离散元方法在砂土性质模拟中的合理性。通过对比土体颗粒的应力、位移、孔隙率等分布特征，总结了土体与混凝土剪切过程中颗粒位移与应力的传递规律。同时，采用支持矢量机的方法，准确划分了土体中剪切带的范围，讨论了法向应力、颗粒尺寸对剪切带最大厚度的影响，结果显示：颗粒尺寸越大，，法向应力越小，则土体中剪切带厚度越大。本研究结果对于深入认识土体与混凝土结构体之间的剪切破坏机理以及了解土体中剪切带的相关性质具有促进作用。
[Abstract]:The bearing capacity of pile foundation is usually composed of side friction resistance and pile end bearing capacity. At present, it is assumed that the frictional resistance of pile is linear proportional to normal stress, but there is little research on the law of stress and strain transfer between soil and concrete pile in shear process. The shear properties of pile-soil interface are closely related to the movement of soil particles during shear. In order to discuss the shear properties of soil and concrete interface, this paper combines with the example of Zhaoyuan Songhua River Bridge. The shear characteristics of soil and concrete are studied by the method of laboratory test and numerical simulation, which provides a certain reference for further understanding the mechanism of shear stress between soil and concrete. First of all, the medium shear test of the interface between soil and concrete is carried out by selecting the soil and concrete samples in this project. The test soil samples include cohesive soil, fine sand, coarse sand, and the normal load is determined according to the actual engineering. The results of medium shear test show that the peak shear strength of the pile-soil interface is linear with the normal stress, and the cohesive force is also shown in the shear process of the clay. Therefore, the shear strength of the contact surface can be described by using the Kulun-Moore theory in soil. Enough information of soil stress and strain can not be extracted from the soil sample during the test, so the numerical simulation method is considered to invert the medium shear test process and to study the law of soil shear stress transfer in the shear process. The particle flow method is introduced into the numerical simulation of shear tests to study the shear failure characteristics of sand and concrete. Particle flow, as a discrete element method, well reflects the normal, tangential and sliding effects of sand particles. The constitutive equation is constructed from the point of view of the correlation between particles, which has many advantages that other methods do not have. In the process of establishing the particle flow model, the macroscopic properties of the model are determined by the meso-parameters between particles. In the fourth chapter, the porosity, friction coefficient and normal stiffness of sand were studied by orthogonal test based on triaxial test of sand. The influence of four mesoscopic parameters, such as tangential to normal stiffness ratio, on the internal friction angle, Poisson's ratio and elastic modulus of sand in triaxial test. The results show that the internal friction angle of sand is usually related to the friction coefficient of particles and the tangential to normal stiffness ratio, and the elastic modulus of sand is usually related to the normal stiffness and tangential normal stiffness ratio of sand. The Poisson's ratio of sand is mainly determined by the tangential-normal stiffness ratio and porosity. Then, on the basis of the determination of the particle meso parameters, the particle flow model of medium shear tests of sand and concrete is established, and the shear tests of sand under different normal loads are carried out. The results of numerical simulation are in good agreement with the results of medium shear test, and the rationality of the discrete element method in the simulation of sand properties is proved again. By comparing the distribution characteristics of soil particle stress, displacement and porosity, the transfer law of particle displacement and stress in the shear process between soil and concrete is summarized. At the same time, by using support vector machine, the range of shear band in soil is accurately divided, and the normal stress and the effect of particle size on the maximum thickness of shear band are discussed. The results show that the larger the particle size, the smaller the normal stress. The thickness of shear band in soil is larger. The results of this study can promote the understanding of shear failure mechanism between soil and concrete structure and the properties of shear band in soil.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU473.1

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