非饱和土中桩的动力响应与循环荷载试验研究

发布时间：2019-05-18 18:15

【摘要】：摘要：桩的动力响应研究是桩支承建筑物抗震设计和桩基完整性检测的理论基础。由于问题的复杂性,已往研究大多将桩侧土简化为单相或饱和两相弹性介质。众所周知,工程环境所处的近地表土层往往处于非饱和状态,为固、液、气三相的多孔介质材料。因此,本文在非饱和土动力学最新研究成果的基础上,基于三相多孔介质波动方程,充分考虑各相材料间的惯性和粘性耦合效应以及毛细压力作用,通过理论分析和模型试验对非饱和土-桩动力相互作用问题,非饱和土弹性半空间中埋置振源时的基本解以及桩的长期荷载循环特性进行了系统的研究,主要研究内容包括以下几个方面： (1)针对半空间埋置振源下的三维Lamb问题,运用方位角的Fourier级数展开和径向Hankel变换技术,直接对频域内的非饱和土波动方程进行求解,并结合地基表面的边界条件以及荷载作用面上的连续性条件,求得了非饱和均质弹性半空间内部作用任意振源时的动力Green函数,退化到饱和土中的解与已有文献的结果相吻合。 (2)考虑基质吸力对土体动剪切模量的影响,建立了竖向简谐振动作用下非饱和土和单桩耦合动力响应模型,求解了轴对称条件下非饱和土体的动力控制方程和基桩的一维波动方程,根据桩土界面衔接条件以及桩端不同支承形式,给出了嵌岩桩和非端承桩的桩顶复动刚度、速度导纳以及土层阻抗在频域内的解答。 (3)通过Helmholtz矢量分解及分离变量法解耦波动方程,并将桩等效为能考虑其剪切变形的Timoshenko杆件,采用Novak三维连续介质模型对非饱和土中端承桩的稳态水平振动进行了研究；同时利用半空间水平动力Green函数,建立了非饱和土中水平受荷单桩的Fredholm积分方程,得到了单桩动力阻抗的封闭形式解答,考察了桩身位移、弯矩和剪力沿深度的分布规律。 (4)在Novak平面应变模型的基础上,利用散射域中的水平位移衰减函数,通过位移场的叠加考虑桩-桩间的波动干扰和群桩效应,推导了水平稳态谐振下非饱和土中单桩及群桩基础的阻抗函数以及各单桩分担的荷载,并讨论了饱和度、频率和桩间距等参数对基础振动特性的影响。 (5)推导了两种不混溶流体饱和多孔介质中Rayleigh波的弥散特征方程,讨论了波速、自由场位移分布及粒子运动轨迹,随后在求得非饱和土半空间自由波场解的基础上,采用Winkler地基梁模型,考虑上部结构惯性力的作用,对频域内全埋入单桩和部分埋入单桩在Rayleigh波作用下的横向动力响应进行了研究,分析了饱和度、轴向荷载和自由段桩长等因素与桩的地震反应之间的相互影响关系。 (6)通过开展红黏土中单桩轴向循环荷载模型试验,对不同循环荷载比和加载频率下桩的长期动力特性进行了研究,并从桩侧土剪切刚度和侧阻退化两方面出发,对循环荷载作用下桩顶累积沉降机理进行了分析。在FLAC3D中,实现了能够反映剪切刚度疲劳退化的修正Hardin-Drnevich(H-D)模型,并对常法向刚度(CNS)循环剪切下侧阻退化进行了数值模拟。
[Abstract]:Abstract: The dynamic response of the pile is the theoretical basis of the seismic design and the integrity test of the pile foundation. Because of the complexity of the problem, most of the research has simplified the pile-side soil into single-phase or saturated two-phase elastic medium. It is well known that the near-earth surface soil layer in the engineering environment is often in an unsaturated state, and is a solid, liquid and gas three-phase porous medium material. Therefore, on the basis of the latest research results of unsaturated soil dynamics, based on the three-phase porous medium wave equation, the inertia and the viscous coupling effect and the capillary pressure effect among the phase materials are fully considered. Based on the theoretical analysis and model test, the basic solution and the long-term load cycle characteristics of the pile in the unsaturated soil-pile dynamic interaction problem, the unsaturated soil elastic half-space and the long-term load cycle characteristics of the pile are studied. The main research contents include the following aspects: (1) Aiming at the three-dimensional Lamb problem under the half-space embedded vibration source, using the Fourier series expansion and the radial Hankel transformation technique of the azimuth angle, the non-saturated soil wave equation in the frequency domain is directly solved, and the boundary condition on the surface of the foundation and the continuity strip on the load acting surface are combined. In this paper, the dynamic Green's function in unsaturated homogeneous elastic half-space is obtained, and the degeneracy to the saturated soil is the same as that of the existing literature. (2) Considering the influence of matrix suction on the dynamic shear modulus of soil, the dynamic response model of unsaturated soil and single pile under the action of vertical simple harmonic vibration is established, and the dynamic control equation of unsaturated soil and one-dimensional wave of the foundation pile are solved. The dynamic equation, according to the interface condition of the pile and the different bearing form of the pile end, gives the pile top complex dynamic stiffness, the velocity admittance and the soil layer impedance in the frequency domain. (3) Uncoupling the wave equation by the Helmholtz vector decomposition and the separation variable method, and the pile is equivalent to the Timoshenko rod which can take into account the shear deformation of the pile, and the steady-state horizontal vibration of the non-saturated soil middle-end bearing pile is carried out by using the Novak three-dimensional continuous medium model. In this paper, the Fredholm integral equation of horizontal load-bearing single pile in unsaturated soil is established by using the Green's function of the semi-space, and the closed form solution of the dynamic impedance of the single pile is obtained. The displacement, bending moment and shearing force of the pile are also studied. (4) On the basis of the Novak plane strain model, using the horizontal displacement attenuation function in the scattering field, the fluctuation of the pile-pile is taken into account by the superposition of the displacement field. In this paper, the impedance function of single pile and pile foundation in unsaturated soil under the horizontal steady-state resonance and the load of each single pile are derived, and the parameters such as saturation, frequency and pile spacing are also discussed. In this paper, the dispersion characteristic equation of Rayleigh wave in two immiscible fluid saturated porous media is derived, and the wave velocity, the free field displacement distribution and the particle motion trail are discussed, and then, on the basis of obtaining the free wave field solution of the unsaturated soil semi-space, Win The transverse dynamic response of a single pile and a partially embedded single pile in the frequency domain under the action of Rayleigh wave is studied by the kler foundation beam model considering the action of the inertial force of the upper structure, and the factors such as saturation, axial load and length of free segment pile and the seismic response of the pile are analyzed. (6) The long-term dynamic characteristics of the pile under different cycle load ratio and loading frequency are studied by carrying out the model test of single-pile axial circulation load in red clay. On the basis of the two aspects of side resistance and degradation, the pile top under the action of cyclic load The cumulative settlement mechanism is analyzed. In the FLAC3D, a modified Harin-Drnovich (H-D) model, which can reflect the fatigue degradation of the shear stiffness, is realized, and the normal method is subjected to cyclic shear of the stiffness (CNS).
【学位授予单位】：中南大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU473.1

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