考虑土的多孔多相性条件下复杂局部场地波动问题研究

The ground amplification effects caused by irregular surface topography and geological conditions have been the focus of research by both seismologists and earthquake engineers for the last three decades. In current study the soil in local site are supposed as the single-phase medium or saturated porous medium. But in fact, soil is consist of solid phase, liquid phase and gas phase sometimes, and presents the character of porous and multi-phase. So,in the analysis of the wave propagation in complex local site the porosity and muliti-phase of soil should be taken into account. Howerver, there is no analysis about this so far. In this project, the theory about the dynamic of three-phase unsaturated porous medium is introduced into the analysis of the wave propagation in complex local phase. The soil in local site is suppose three-phase saturated porous medium or two-phase porous medium. Analytical method and finite element numerical simulation method are used in the analysis. At first, a series of analytical solutions for scattering of plane waves by unsaturated soil local irregular site were developed using Fourier-Bessel series expansion technique. On the base of the analytical solutions, the physical mechanisms of wave propagation in local site with unsatuerated soil are studied quantatively, the dynamic responses of local site are explained directly. At the same time the analytical solutions can be used to evaluate the computation results. For the second, finite element numerical simulation method used to solve the problem are present also. More practical and detail models are used to analyse the seismic responses of the complex local site with unsaterated soil. Through the effective integration of analytical explanation and numerical simulation, the ground amplification effects caused by irregular surface topography and geological conditions considering the porosity and muliti-phase of Soil are studied systematically.

局部场地条件对地震波传播的影响，无论从理论分析或从工程应用上来说，一直备受关注。但目前的研究中场地岩土多被假定为单相介质或饱和多孔介质，很少考虑场地岩土的多孔多相性。本项目首次将三相非饱和多孔介质动力模型引入到局部场地地震地面运动分析中，即将场地岩土考虑为三相非饱和与两相饱和的情况，分别运用解析方法和有限元数值模拟方法对局部场地波动特性进行分析和研究。首先建立解析方法求解简单的典型非饱和局部场地条件对地震波的散射，定量地分析非饱和的局部场地波动问题的本质和物理机制，给出地震时场地反应的直观解释，并为数值计算的精度和收敛性提供判据；其次建立相应的有限元方法，对含非饱和岩土的复杂局部场地的地震地面运动进行数值模拟，以便更真实、细致地反映（与饱和场地相比）非饱和复杂局部场地条件对地震动的影响；通过解析方法的理论解释与数值方法的有效结合，系统地分析具有多孔多相性的局部场地条件对地震地面运动的影响。

局部场地条件对地震波传播的影响，无论从理论分析或从工程应用上来说，一直备受关注。但目前的研究中场地岩土多被假定为单相介质或饱和多孔介质，很少考虑场地岩土的多孔多相性。本项目首次将三相非饱和多孔介质动力模型引入到局部场地地震地面运动分析中，将场地岩土考虑为三相非饱和与两相饱和的情况。建立了非饱和成层地基地震波散射问题的解析分析方法、局部场地地震地面运动解析分析方法、非饱和多孔介质有限元分析方法以及地震波斜入射下多孔多相地基场地波动输入方法。运用这些方法，分别从解析和数值两个不同角度对局部场地波动特性进行研究，在考虑场地土多孔多相条件下，系统地分析典型局部场地（包括水平成层非饱和土场地、非饱和土半空间中凹陷场地、圆柱形空穴、夹塞等局部场地）地震地面运动特征，研究结果表明当土体孔隙率较大及骨架刚度较小时，进行局部场地地震动分析时，必须考虑土体的多孔多相性，尤其要注意饱和与非饱和的区别。土体的初始饱和度会影响场地地震动的峰值和特征频率，从而影响局部场地地震地面运动。通过精细化局部场地分析模型，以及解析方法的理论解释与数值模拟方法的有效结合，定性定量地分析非饱和土局部场地波动问题的本质和物理机制，为复杂局部场地地震地面运动提供合理的解释，为地震小区化工作提供理论依据，并为复杂局部场地地区大型结构的抗震设计提供技术支持。