改进的虚土桩法及其在非等截面桩纵向振动中的应用研究

发布时间：2018-05-30 05:29

本文选题：桩-土相互作用 + 虚土桩　；参考：《浙江大学》2013年博士论文

【摘要】：目前,国内外研究桩与桩底土相互作用关系的模型,大多数是非连续模型,且缺乏对桩底土作用的研究。为了建立桩与桩底土的严格耦合关系,本文提出了一种改进的虚土桩法。并基于该方法,分析了桩底土对单桩纵向振动特性的影响,研究了焊缝在多级混凝土管桩完整性检测中的作用及不同条件下静钻根植竹节桩这一新桩型的动力特性。主要的工作与创新成果如下： (1)基于地基中圆形竖向荷载下的Mindlin附加应力,提出了考虑应力扩散效应的虚土桩法。进一步结合平面应变模型,通过Laplace变换和卷积定理等数学方法,求得任意激振力作用下的桩体振动频域响应解析解和时域响应半解析解。通过分析桩底土体参数对桩动力响应的影响,发现土体剪切模量是决定桩底支撑刚度的重要因素,土体模量提高,将引起桩底支撑刚度和阻尼显著增大。桩底土对桩身动力响应的影响存在临界厚度,约5-7倍的桩体半径,在此范围内,桩体刚度与桩底土层厚度成反比关系,阻尼与之成正比关系。 (2)将虚土桩法从平面应变模型发展到轴对称连续土体模型中,考虑土体的径向和竖向两相位移,建立三维波动效应下的桩土体系纵向振动模型。通过引入位移势函数和Laplace变换的手段,采用分离变量法将竖向和径向位移进行解耦,进而通过阻抗传递法求得桩体的频域响应,通过Laplace逆变换得到桩体的时域响应。根据所求得的解,对比了轴对称连续模型与平面应变模型下虚土桩法的差异,发现轴对称模型能更好地反映桩土体系的自振频率。 (3)提出了混凝土管桩焊接缝的简化模型,将影响焊缝质量的物理因素转化到等效的刚度体系中,从而实现了可对焊缝进行理论拟合的目的。借助本文所提出的虚土桩法,求得多级混凝土焊接管桩桩顶的动力响应。经过分析有效焊接断面、焊接高度等参数的大小对桩顶速度响应的影响,表明焊接深度不应小于5mm,焊缝高度宜控制在2mm范围内。实测数据的拟合结果表明,该简化模型能有效地反映焊缝质量对管桩反射波信号的影响,可为桩基完整性检测提供指导。 (4)根据静钻根植竹节桩的成桩机理,确立了径向非均质理论与虚土桩法相结合的桩土动力模型。结合系数矩阵传递法,求得径向非均质土体下竹节形根植桩的桩顶动力响应。分析了竹节及桩周水泥土等对桩顶动力响应的影响,结果表明桩体刚度与竹节密度和竹节半径成正比,桩侧水泥土的硬化程度越高,桩顶刚度越大,阻尼越小,且泥浆的水泥配合比为40%时,性价比较高。通过对工程数据的反演拟合验证了桩侧水泥土的硬化规律。完善地模拟桩与桩底土的作用关系是本文的核心,即文中提出的虚土桩法。以此来解决工程中出现的实际问题是本文的目的。基于此,本文提出的新方法、得到的新结论可为桩基工程设计及检测工作提供参考。
[Abstract]:At present, most of the models used to study the interaction between piles and subsoil are discontinuous models and lack of research on pile-subsoil interaction. In order to establish a strict coupling relationship between pile and subsoil, an improved virtual soil pile method is proposed in this paper. Based on this method, the effect of pile bottom soil on the longitudinal vibration characteristics of single pile is analyzed, and the role of weld seam in the integrity detection of multistage concrete pipe pile and the dynamic characteristics of the new type of pile with static drilling and planting bamboo section pile under different conditions are studied. The main results of work and innovation are as follows: 1) based on the Mindlin additional stress under the circular vertical load in the foundation, a fictitious soil pile method considering the stress diffusion effect is proposed. Combined with plane strain model, by means of Laplace transform and convolution theorem, the analytical and semi-analytical solutions of vibration frequency domain response and time domain response of pile subjected to arbitrary excitation force are obtained. By analyzing the influence of soil parameters on pile dynamic response, it is found that the shear modulus of soil is an important factor in determining the supporting stiffness of pile bottom, and the increase of soil modulus will result in a significant increase in the stiffness and damping of pile bottom bracing. The influence of pile soil on the dynamic response of pile body has a critical thickness, about 5-7 times of the radius of the pile body. In this range, the stiffness of the pile is inversely proportional to the thickness of the soil layer of the pile bottom, and the damping is proportional to it. 2) the pseudo-soil pile method is developed from plane strain model to axisymmetric continuous soil mass model. Considering the radial and vertical two-phase displacement of soil, the longitudinal vibration model of pile-soil system under three-dimensional wave effect is established. By introducing the displacement potential function and Laplace transform, the vertical and radial displacements are decoupled by the method of separating variables, and the frequency domain responses of the piles are obtained by the impedance transfer method, and the time-domain responses of the piles are obtained by the Laplace inverse transformation. According to the obtained solution, the difference between the axisymmetric continuous model and the plane strain model is compared. It is found that the axisymmetric model can better reflect the natural frequency of pile-soil system. The simplified model of welding joint of concrete pipe pile is put forward. The physical factors affecting weld quality are transformed into the equivalent stiffness system, so that the purpose of theoretical fitting of weld seam can be realized. The dynamic response of multistage concrete welded pipe pile top is obtained by using the virtual soil pile method proposed in this paper. The effect of effective welding section, welding height and other parameters on the velocity response of the pile top is analyzed. The results show that the welding depth should not be less than 5mm, and the weld height should be controlled within the range of 2mm. The fitting results of measured data show that the simplified model can effectively reflect the influence of weld quality on the reflected wave signal of pipe pile and can provide guidance for pile foundation integrity detection. 4) according to the pile forming mechanism of static drilling and planting bamboo section pile, the dynamic model of pile and soil is established, which combines radial heterogeneity theory with fictitious soil pile method. Based on the coefficient matrix transfer method, the dynamic response of the pile top of the bamboo-shaped root pile under the radial heterogeneous soil is obtained. The influence of bamboo section and cement soil around pile on the dynamic response of pile top is analyzed. The results show that the stiffness of pile is proportional to the density and radius of bamboo section, the higher the hardening degree of cement soil is, the greater the stiffness of pile top is and the smaller the damping is. And when the cement mixture ratio of mud is 40, the ratio of performance to price is higher. The hardening law of cement soil on the pile side is verified by inverse fitting of engineering data. It is the core of this paper to simulate the interaction between pile and soil perfectly, that is, the virtual soil pile method proposed in this paper. The purpose of this paper is to solve the practical problems in engineering. Based on this, the new method and the new conclusion can provide reference for the design and testing of pile foundation engineering.
【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

【参考文献】