非饱和土自由场地地震地面运动的解析分析

发布时间：2018-06-16 11:46

本文选题：非饱和孔隙介质 + 自由场地模型　；参考：《北京交通大学》2015年硕士论文

【摘要】：我国位于世界两大地震活动带之间,据史料记载,几乎各省都曾发生过破坏性地震。随着我国经济建设的迅速发展,更多大型建设项目开始不断出现。为保证这些建设项目在地震作用下的安全性,必须研究自由场地地震响应问题。目前对于自由场地运动的研究大多是将场地简化为单相或两相饱和状态下进行研究,而实际上我们自然环境中的介质大多数是处于非饱和状态的,即介质孔隙中存在气体。因此对含有三相非饱和孔隙介质的自由场地地震地面运动的解析分析显得尤为重要,目前,对非饱和土自由场地中波动问题的研究还不够成熟,关于非饱和弹性孔隙介质场地的波动问题的相关研究亟待展开。本文首先介绍了线弹性变形条件下的三相非饱和孔隙介质波动方程,通过对波动方程中的矢量进行Helmholtz分解,采用Fourier变换求解方程,得到在非饱和孔隙介质中存在三种压缩波和一种剪切波。并分析了不同场地弹性常量下非饱和孔隙介质中产生的四种体波的传播特性受非饱和孔隙介质饱和度的影响情况。在研究非饱和孔隙介质波动特征的基础上,建立非饱和土自由场地模型,分别对平面P波和SV波入射情况下场地中的波场进行分析,根据场地边界条件,求解波场中的待定系数,从而得到平面P波和SV波入射情况下非饱和土自由场地地震地面运动的解析解。根据解析解,计算分析了饱和度、入射角度、入射波频率、土层刚度、孔隙率等因素对非饱和土自由场地地震地面运动的影响,得到以下结论：(1)随入射角度的增加,饱和度的变化对位移放大系数的影响在最大值附近时相对较大；(2)非饱和状态下自由场地共振频率相同,达到饱和状态时发生变化；(3)随土层刚度的减小,饱和度的改变对各振幅比和位移放大系数的影响逐渐增加；(4)随土层孔隙率的增加,饱和度的改变对位移放大系数的影响逐渐增加；(5)随着非饱和土层深度的增加,水平位移放大系数并不是呈现出单一变化趋势的；(6)当自由场地模型中均匀非饱和土层的厚度趋于无穷时,场地交界面处的位移放大系数发生一定的改变。由于在四种不同体波中P1波和S波传播速度较快且衰减速度较慢,因此本文主要考虑这两种体波的变化特性。可以看出由于孔隙中气相的存在,非饱和自由场地中不同体波的传播特性发生了显著的变化。本文给出了平面P波和SV波入射下非饱和土自由场地地震地面运动的解析解答,得到了非饱和土自由场地地震地面运动的一般规律和结论。为复杂场地地震地面运动提供合理的解释,为复杂场地地区大型结构的抗震设计提供技术支持。
[Abstract]:China lies between two major seismicity zones in the world. According to historical records, destructive earthquakes have occurred in almost all provinces. With the rapid development of China's economic construction, more and more large-scale construction projects began to appear. In order to ensure the safety of these construction projects under earthquake action, it is necessary to study the seismic response of free site. At present, most of the research on free site motion is to simplify the site to single-phase or two-phase saturation state, but in fact, most of the media in our natural environment is in unsaturated state, that is, gas exists in the pore of the medium. Therefore, it is very important to analyze the seismic ground motion of the free site with three-phase unsaturated porous media. At present, the research on the wave problem in the unsaturated soil is not mature enough. The research on the fluctuation of unsaturated elastic porous media is urgently needed. In this paper, the wave equation of three-phase unsaturated porous media under the condition of linear elastic deformation is introduced. By Helmholtz decomposition of the vector in the wave equation, Fourier transform is used to solve the equation. Three compression waves and one shear wave are obtained in unsaturated porous media. The propagation characteristics of four kinds of bulk waves produced in unsaturated porous media under different site elastic constants are also analyzed, which are influenced by saturation of unsaturated porous media. On the basis of studying the wave characteristics of unsaturated porous media, the free site model of unsaturated soil is established, and the wave fields in the field under the incident conditions of plane P wave and SV wave are analyzed, respectively, according to the boundary conditions of the site. The undetermined coefficients in the wave field are solved, and the analytical solution of seismic ground motion in the unsaturated soil free site under the incident conditions of plane P wave and SV wave is obtained. Based on the analytical solution, the effects of saturation, incident angle, incident wave frequency, soil stiffness and porosity on seismic ground motion in unsaturated soil free site are calculated and analyzed. The following conclusion is obtained: 1) with the increase of incidence angle, The effect of saturation on the displacement magnification factor is relatively large near the maximum value. (2) the resonance frequency of the free site is the same in the unsaturated state, and the variation of the free site resonance frequency occurs when the saturation state is reached, which changes with the decrease of soil stiffness. The effect of saturation on amplitude ratio and displacement magnification factor increased gradually with the increase of soil porosity, and the effect of saturation on displacement magnification factor gradually increased with the increase of unsaturated soil depth. The horizontal displacement magnification factor does not show a single trend.) when the thickness of the uniform unsaturated soil layer in the free site model tends to be infinite, the displacement magnification factor at the site interface will change to a certain extent. Since P _ 1 and S waves propagate faster and attenuate more slowly in four different body waves, the variation characteristics of these two kinds of bulk waves are mainly considered in this paper. It can be seen that the propagation characteristics of different bulk waves in unsaturated free sites have changed significantly due to the existence of gas phase in pores. In this paper, the analytical solution of seismic ground motion in unsaturated soil free site under the incident of plane P wave and SV wave is given, and the general law and conclusion of earthquake ground motion in unsaturated soil free site are obtained. It provides reasonable explanation for seismic ground motion of complex site and provides technical support for seismic design of large structure in complex site area.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU435

【引证文献】