城市区域尺度复杂深厚不均匀场地非线性地震效应机理及空间差异性特征

Based on Suzhou city area scale site as research region, through the cyclic triaxial tests with low and high consolidation pressures, the constitute model and its parameters of the soils are given which can describe the influence of both sedimentary environments and soil depth on the nonlinear hysteretic characteristic of soils. 3-D stratum shear wave velocity structure is constituted to establish large-scale site refined finite element model of 2-D seismic wave field numerical simulation. The oblique incident and vertical incident SH waves are respectively used to simulate the input ground motion of near-field medium-strong earthquake and far-field large earthquake. The Quaternary soil layer bottom is selected as the ground motion input interface and the parallel computing explicit algorithm is used to simulate the propagation of 2-D seismic waves. The mechanism of the nonlinear seismic site effects is studied with regard to different engineering geological zoning and their sub-zones within the city area scale site under the impulsive waves of different characteristics. The mechanisms of the site micro-topography features, soil layer condition and input ground motion characteristic on the effects of the following phenomena during the propagation of seismic waves are revealed: the reflection effect of slowly-inclined deeply-buried bedrock interface, the edge effect of the inclined interface betwwen hill rock and soils, the focusing effect of the upheave or depression zone of the bedrock and/or ground surface, the clustering effect induced by the horizontal heterogeneity of soil layers,the strong amplification of long-period component waves in the deep soft site and the increase of high frequency component waves induced by the distortions of wave propagating. The strong-motion recordings on bedrock of the near-field medium-strong earthquake and far-field large earthquake, similar to the near source and far-field seismogenic structure background of the Suzhou research region respectively, are chosen as the input ground motion to study the spatial variability characteristics of nonlinear seismic site effects and surface ground motion parameters at different geology engineering zoning and their sub-zones.

以苏州为研究区，通过低、高固结应力的循环三轴试验研究，给出能反映土沉积环境与土层深度对土体非线性滞回特性影响的本构模型及参数；构建三维地层剪切波速结构，建立二维地震波动数值模拟的大尺度场地精细化有限元模型，采用斜入射SH波模拟近场中强地震、竖向入射SH波模拟远场大地震的地震动输入，以第四系地层底面为地震动输入面，采用并行计算显式算法进行二维地震波动数值模拟，研究不同特征的脉冲波作用下不同工程地质区及其子区场地非线性地震效应机理，揭示场地微地形特征、土层条件及地震动特性在地震波传播过程中发生的反射效应、边缘效应、聚焦效应、深软土层低频放大效应及土层横向不均匀性诱发的聚集效应、地震波传播畸变诱发的高频放大效应的机理；选择与研究区的区域/近场地震地质构造环境相近的近场中强震、远场大地震基岩强震记录作为输入地震动，揭示不同地质工程区及其子区场地非线性地震效应及地表地震动参数的空间差异性特征。

以苏州中心城区和河口盆地为研究区，研究复杂场地非线性地震效应机理及空间差异性特征。提出一组新的不规则加载-卸载准则及将一维本构模型拓展到二、三维动力分析的高精度等效应变算法。这一新的本构模型改进了计算效率。提出一个基于应变的新的孔压模型。该模型用于预测不排水循环加载下饱和砂的孔压增长特征。耦合新的本构模型与孔压模型，提出新的场地非线性地震反应的分析方法。以苏州中心城区为研究目标区，基于446个钻孔实测资料，建立了目标区第四纪地层剖面与三维地层结构可视化模型；研究了第四纪深厚沉积层剪切波速结构空间变化特征，建立了vs30地图绘制的多尺度随机场模型，提出单孔浅层剪切波速外推深层剪切波速的逐步外推法，给出剪切波速不小于700 m/s的基岩面埋深等深线图及微震动场地卓越周期等值线图；应选取剪切波速不小于700m/s的土层顶面作为地震输入基岩面；揭示了深厚第四纪沉积层土动力特性与地震反应特征，试验给出250m深第四纪地层标准钻孔的土动力特性参数，应采用时域非线性法计算深厚第四纪地层的地震反应；给出了近场中强震、远场大震和巨震作用下研究目标区的峰值加速度PGA和卓越周期均值等值线图；给出了远场大震作用下深厚第四纪地层地表设计地震动参数及沿土层深度的PGA折减系数。以典型河口盆地为研究对象，试验给出代表性土体动力特性参数，采用二维模型研究了基岩起伏和土体横向非均匀的盆地非线性地震反应特征，发现了基岩起伏土层的地震动聚集效应、盆地边缘效应及中长周期地震动的显著放大效应，给出了盆地地表PGA、卓越周期均值等值线图、地表加速度反应谱放大因子和地表设计地震动参数。提出合理保守的基于剪切波速的地震液化临界曲线，并给出了相应的评价场地液化的概率方法及不同液化概率等值线图。基于多相孔隙介质波动理论，提出了针对不同饱和状态下场地中地震波传播特性的研究方法，建立了地震波在深厚场地不同土层之间的反射与透射的分析理论。建立了不同边界条件下非饱和软土场地地基中的Rayleigh波的理论模型，揭示了Rayleigh波的弥散特性受到地基主要力学参数的影响规律。