土层平均剪切波速确定及其可靠性验证——基于钻井台阵强震动记录

Shear wave velocity based on analysis of geotechnical downhole array records

震害资料显示,场地条件对地震动特性以及工程结构破坏程度影响显著。为减少因场地效应而造成的经济损失和社会影响,在进行场地地震反应分析时,需最大限度地减小因场地土层模型参数的不确定性引起的地震动评估偏差,为工程结构地震反应分析选取并生成适当的地震动输入。随着强震动观测技术的逐渐发展,大量可靠的钻井台阵记录为地震过程中场地观测点的动力反应提供了直接数据。以美国加州地区La Cienega钻井台阵强震动观测数据为基础,利用互相关函数,对不同强度地震作用下场地土层的平均剪切波速进行分析,并在此基础上,以Cyclic 1D为模拟平台,建立一维自由场地地震反应有限元分析模型。分析结果表明:通过钻井台阵地震动观测数据识别,得到场地平均剪切波速,能够反映该场地的动力特性,数值模拟计算结果和台阵地震动记录基本吻合,可为数值模型参数选取提供依据。

Seismic downhole-array monitoring in-situ earthquake motions at the ground surface and in soil profile provides valuable information on local soil dynamic characteristics under seismic motions. In particular, with the help of system identification techniques insights are obtained for relationships between local geologic conditions and real time ground motions. In this paper, La Cienega geotechnical array installed by California Strong Motion Instrumentation Program（CSMIP） was employed to evaluate shear wave velocity, examine the nonlinear soil response during earthquake shaking and investigate the site seismic response. Thirteen earthquakes recorded by La Cienega geotechnical array, where the strongest shaking event of West Hollywood earthquake on Sep.9, 2001 was recorded with the peak ground acceleration of 0.49 g, were employed to perform cross-correlation analyses. A 1-D numerical analysis model is developed with the identified shear wave velocity. Comparisons between the computed response and the downhole array records show good agreements. This validated model can be used to predict the site response during future shaking events.