基于设计地震动的覆盖层场地空间自由场构建

地震波在覆盖层场地的传播、透射及反射特性异常复杂，合理构建及表达覆盖层场地空间自由场是非一致地震动输入的关键。建立了覆盖层场地空间任一点地震动关于入射SV波、P波时程和入射角的表达式，基于地表水平和竖直两向设计地震动获得入射SV波和P波时间历程及入射角，考虑界面多次反射和土层阻尼引起的幅值衰减，构建了基岩-覆盖层场地空间自由场。与La Cienega场地实测台阵记录对比结果表明:不同深度的特征点两向地震动模拟值与实测记录符合良好，场地任意点水平和竖直地震动时程具有空间非一致性。该文提出的空间自由场构建方法为覆盖层-坝体系统非一致地震动输入提供基础。

CONSTRUCTION OF FREE FIELDS IN BEDROCK-OVERBURDEN SITE SPACES BASED ON DESIGNED GROUND MOTIONS

The propagation, transmission and reflection characteristics of seismic waves in overburden sites are extremely complex. The reasonable construction and expression of the free field of bedrock-overburden sites is the key to generating nonuniform ground motion input. The expressions between two directional ground motions at any point in an overburden site space and the incident SV and P waves are established. The time history and incident angle of the incident SV and P waves can be obtained from the measured ground motions in the horizontal and vertical directions of the ground surface. By considering the multiple reflections at the interface and the amplitude attenuation caused by soil damping, the free field of the bedrock-overburden site space is constructed. The results of the comparison with the measured array records at La Cienega site show that the simulated values of the two directional ground motions at different depths are consistent with the measured records. The time histories of the horizontal and vertical ground motions at any point in the free field are inconsistent. The spatial free field construction method proposed in this paper provides a basis for non-uniform ground motion input of overburden-dam systems.