一维场地地震反应非线性有效应力分析法及其验证

A new nonlinear effective stress method for one-dimensional seismic site response analysis and its validation

液化所致的土体软化会影响地震运动规律,需进行有效应力分析以确定可液化场地的设计地震动参数。本文提出一种弱耦合形式的场地反应有效应力分析法。此方法将土的非线性滞回模型与剪切–体积应变耦合的孔压增量模型相结合,建立了循环加载过程中循环刚度退化与超静孔隙水压力增长的耦合关系;基于ABAQUS显式求解器开发了相应的材料子程序。该方法被用于模拟日本强震台阵非液化和液化场地的地震反应分析,在不同深度的水平地震动模拟和记录之间显示出很好的一致性:计算与记录的非液化场地井下台阵的地表峰值加速度仅相差2.6%(弱震)和11.8%(中强震);计算与记录的液化场地井下台阵在设置强地震仪深度处的土层峰值加速度的差异均在5%以内,且计算与记录的非液化和液化场地的谱加速度曲线吻合度较好。对比专业软件DEEPSOIL V6.0计算的强震台阵液化场地地震反应的结果,本文方法能更好地模拟高频地震波在多层液化土层中的传播以及液化土层的非线性放大与滤波效应。

Given modification of earthquake motions due to liquefaction-induced soil softening, the effective stress analysis should be conducted to develop the site-specific design ground motion parameters at liquefiable sites. A loosely coupled nonlinear effective stress method for the site response analysis is proposed. In this method, the nonlinear hysteresis model for soils is incorporated with an excess pore water pressure generation model characterized by cyclic shear-volume strain coupling, which establishes the coupling relationship between the degradation of cyclic stiffness and the generation of excess pore water pressure associated with earthquake events. The material subroutine in ABAQUS/Explicit platform is developed. The method is then used to simulate the seismic response of the downhole array non-liquefied and liquefied sites in Japan. The results show a good consistency between the simulations and the recordings at different depths:(1) The difference between the simulated and the recorded peak ground accelerations for the non-liquefied site is only 2.6%(weak motion) and 11.8%(moderate motion).(2) The difference between the simulated and recorded peak accelerations at different depths for the liquefied site is less than 5%.(3) The simulated and recorded spectral acceleration curves of the non-liquefied and liquefied sites are in good agreement. Compared with the responses of a downhole array multilayer liquefied site calculated by DEEPSOIL V6.0, those of the proposed method show a better agreement with the seismic recordings at different depths.