大型河谷场地地震动特性研究

采用有限差分方法,通过算例研究了大型河谷场地地震动特性分析中的人工边界的选取方法,对比分析了不同人工边界的选取对数值模拟结果的影响,确定了散射场地震反应分析输入边界的地震动输入方法,认为在进行有限差分动力计算时,模型两侧施加自由场边界的模拟效果要优于两侧施加粘性边界的模拟效果;同时,对FLAC计算软件进行二次开发,对2个地形差异较大的河谷场地,采用线性和非线性摩尔-库仑模型进行了地震反应对比分析,研究了河谷场地地震动幅值和频谱特性随地形变化的规律。模拟数据表明,河谷场地谷底处地震动基本无放大作用,地势凸起处放大作用则较为明显;当考虑土体非线性时,随着地震动强度的增加,放大作用逐渐减小;谱分析结果表明,地势凸起处受高频地震动的影响显著,而地势平坦的谷底则受低频地震动的影响显著。

Research on Ground Motion Characteristics of Large-scale Valley

A finite difference method was used in a case for the selection of artificial boundary and the effects of different artificial boundaries on numerical simulation results were analyzed to determine the input method of boundary conditions for seismic response analysis of scattering field.Simulation results show that the free-field boundary is more effective than viscous boundary during dynamic finite-difference calculation. A new constitutive model was developed based on FLAC software,linear and nonlinear Mohr-Coulomb models were used for seismic response analysis of two significantly different terrain river valleys. Simulation data show that;the amplification of ground motion is negligible at sites of valley bottom but more obvious at sites of elevated places.When the non-linear is considered,the amplification reduces gradually with the increase of ground motion intensity.Spectral analysis result shows that the high terrains are mainly affected by the high-frequency ground vibration and the flat bottoms are significantly impact by low-frequency ground vibration.