饱和柔性桩复合地基表面振动特性研究

Surface wave has been used to investigate the composite foudation with cement mixing piles or gravel colunms.The fluid-soid coupling in saturated media and vertical cement mixing piles and gravel colunms will effect on the signal of the surface wave. The disturbance signals make the analysis of surface wave signal become more difficult. In this proposal,the formulations of 3D infinite elements for dynamic analysis of vibration problems in saturated composite foundation will be derived. Using the proposed finite-infinite element method, the vibration response of saturated composite foundation will be calculated to study the influences of the permeabilities of soil on the surface wave signals. At the same time, the surface wave scattering by cement mixing piles or gravel colounms was analyzed. The influences of pile-pile interaction on surface wave signal will be investigated. The regulations of amplitude and phase to frequency of surface wave in the composite foundation will be summarized to verify the limitation of equivalent method based on the theories of surface wave in stratified medias which has been used to investigate composite foundation. In the field of composite foundation, the surface wave tests will be performed to pursue the properties of surface wave dispersion curve. The influence of the pile spacing and the dimensions of pile will be studied.By using the 3D finite-infinite element hybrid method based on the saturated composite foudation, the sensitivity of surface wave signal to the parameters of the piles and soil will be numerically analyzed. A program with Levenberg-Marquardt method belonging to the least square method will be developed to inverse the parameters of the composite foundation. The results of the proposal will make the surface wave method more reliable to investigate composite foundation and be of significance on further perfect the dynamic theories of saturated composite foundation.

表面波技术一直试图被工程界用来检测竖向柔性桩复合地基的质量，但饱和土体中的流固耦合效应及竖向柔性桩对波动信号的干扰使该问题变得异常复杂。本项目针对饱和土中柔性桩复合地基，拟建立饱和介质三维动力有限元无限元耦合模型，分析地面点源激振作用下饱和柔性桩复合地基振动场，考察桩土渗透系数、柔性桩体的反射、透射和绕射作用以及柔性桩之间的相互干扰对表面振动信号的影响。研究地面振动信号的幅频、相频特性随振源和柔性桩空间位置变化而变化的规律。论证目前复合地基设计中套用水平层状地基等效计算方法的局限性。现场对水泥搅拌桩、砂石桩复合地基进行多道表面波试验，验证柔性桩的物理几何特性及空间布置形式在表面波频散曲线上的反应特征。并应用饱和介质有限元无限元耦合解分析桩土参数对实测信号的灵敏度，在此基础上，反演复合地基的工程参数。本项目研究成果将使表面波法测试复合地基的结果更加可靠，同时进一步完善复合地基表面振动传播理论

本项目针对饱和土中柔性桩复合地基，建立饱和介质三维动力有限元无限元耦合模型，编制计算程序，分析地面点源激振作用下饱和柔性桩复合地基振动场，考察桩柔性桩体的反射、透射和绕射作用以及柔性桩之间的相互干扰对表面振动信号的影响。通过分析发现，由于竖向增强体的反射、折射和绕射，在某些特定频段，地面震动具有几何衰减特性，呈现较为强烈的频阻效应；通过对弥散曲线的研究表明，在数倍柔性桩加固深度的波长下，表面波的波速高于天然地基的波速，两者之间的差别与柔性桩的尺寸、间距、材料强度等参数相关，因此难以从弥散曲线上的半波长估算复合地基的加固深度。而通过单桩饱和复合地基上块体振动响应及块体速度导纳灵敏度分析发现，单桩复合地基上块体振动规律与柔性桩尺寸，柔性桩和桩周土刚度、渗透性，以及块体尺寸有关。因完整桩临界桩长、缺陷桩缺陷临界深度的存在，将使块体振动法检测柔性桩完整性受到一定的限制。复合地基刚度与低频速度导纳的相关性良好，并给出了利用低频导纳值推求地基动刚度的修正公式以及基于有限元无限元耦合模型的反演柔性桩弹性模量的阻尼最小二乘方法。本项目研究成果进一步完善复合地基表面振动传播理论，对应用振动测试评估复合地基质量有更深入的认识。