深厚非均匀沉积土场地非线性地震反应特征研究

Seismic site effect is a major factor of the earthquake risk of urban cities with deep covering sediments. The study of this project expects to help understanding of seismic effect of deep site, which focuses on the influence of soil dynamic characteristics and soil distribution on seismic surface wave propagation. The sites along the metro lines in Suzhou city are taken as the research object, and based on the abundant and detailed geological survey data in the study area as well as the dynamic triaxial test results of typical undisturbed soil samples obtained within 200m in depth, the influence of soil types, sedimentary environment and depth on the dynamic characteristics of soils are studied. A modified model which may reasonably reflect the sedimentary history of inhomogeneous sedimentary soil site of the study area is put forward, and the corresponding soil dynamic parameters of the 200m deep profile are given. Meanwhile, the equivalent linear method and the modified constitutive model are used to describe the nonlinear characteristics of soil, respectively, and the seismic response of the soil layers as well as its difference are studied under different seismic waves and input bedrock surfaces, nonlinear characteristics of seismic site effect are revealed. Finally, large-scale two-dimensional nonlinear numerical simulations of the studied area are established to analyze the mechanism and characteristics of seismic site response, the spacial characteristics of ground motion are given. The results of this study may provide theoretical and scientific basis for the earthquake resistance and disaster mitigation planning work of coastal (or riverside) cities.

场地地震反应是覆盖层深厚城市评估地震风险的一个主要方面。本项目着重描述土动力特性与土层结构对地震面波传播特性的影响。以苏州地铁沿线地层为研究对象，基于翔实的岩土工程勘察资料及200m深钻孔原状土样的动力试验结果，研究土的类型、沉积环境和深度对土动力特性的影响，构建能合理反映苏州研究区复杂沉积物土动力特性的本构模型，给出200m深标准剖面随土层深度变化的土动力参数。考虑输入地震动特性和地震基岩面深度的影响，比较研究等效线性方法、集中质量非线性方法分析给出的深厚场地非线性地震反应特性，揭示深厚复杂一维场地非线性地震波动机理；基于大尺度二维精细化场地非线性地震波动数值模拟，探究横向非均匀深厚场地非线性地震波动机理及地震效应特征，揭示地震动参数的地表展布及沿深度方向的空间差异性特征。该研究成果可为沿海(江)城市抗震设防与减灾规划提供基础性的科学依据。

场地地震反应是城市评估地震风险的一个重要方面。本项目以苏州地铁沿线地层为研究对象，基于翔实的岩土工程勘察资料及200m深钻孔原状土样的动力试验结果，研究了土的类型、沉积环境和深度对土动力特性的影响，构建了能合理反映苏州研究区复杂沉积物土动力特性的本构模型，给出了200m深标准剖面随土层深度变化的土动力参数。建立了不同特征脉冲波作用下苏州城区凹陷沉积场地地震效应研究模型并分析沉积土层特性、输入地震动特性对其影响的规律，揭示了深厚复杂一维场地非线性地震波动机理；输入不同强度的脉冲波时，地表加速度都随脉冲波峰值频率的减小而增大，但增大的幅度在不同位置表现不同，位于凹陷沉积分布明显的东部区增大更为明显，反映了凹陷沉积层对高频地震动有更为显著的过滤效应。基岩输入不同PGA及不同频率的脉冲波时，地表加速度时程曲线则明显区别于对应的基岩脉冲波波形，这与土层的基本物理状态有关。基岩输入峰值频率1Hz的脉冲波时，土层最大峰值剪应变分别为0.29%和0.93%，即此时土体表现出强烈的非线性特征，造成脉冲波波形出现“畸变”。同时，基于大尺度二维精细化场地非线性地震波动数值模拟，探究了横向非均匀深厚场地非线性地震波动机理及地震效应特征，结果表明地震动的中、长周期分量有显著的放大效应，给出了不同超越概率水平下苏州城区PGA放大系数均值等值线图，还给出了苏州城区遭遇6-6.5级近场中强地震、7-7.5级中远场大地震和8级以上远场特大地震威胁时的地表PGA放大系数均值等值线图，地表PGA放大系数均值的空间分布规律与场地工程地质分区相关。该研究成果可为沿海(江)城市抗震设防与减灾规划提供基础性的科学依据。