深厚第四纪沉积土非线性性能对地表地震动特性的影响

Influence of Nonlinear Behavior of Quaternary Deep Sediment Layers on the Characteristics of Surface Ground Motions

土体非线性性能对地表地震动的影响主要体现在其频谱成分和强度的改变上。采用修正Matasovic本构模型描述土的动力非线性特性,利用专业软件DeepSoil对深厚场地的50个钻孔剖面土柱模型进行了场地地震反应分析。采用加速度反应谱卓越周期Tp、平均谱周期Tavg及加速度傅氏谱平均周期Tm表征地表地震动频谱特性;以Arias强度Ia和地表峰值加速度PGA表征地表地震动强度。结果表明:(1)特定场地条件下,Tp不能反映土体非线性对地震动从基岩传播至地表时频谱成分变化的影响;Tavg和Tm在表征地震动频谱成分特性时具有较高的一致性;(2)基岩地震动高频丰富时,Tavg和Tm随着基岩地震动峰值加速度的增大而呈现出线性增长的趋势;而基岩地震动低频较发育时,Tavg和Tm的增长趋势线存在明显的拐点;(3)PGA与Ia值随基岩地震动峰值加速度的增大呈现出基本一致的非线性增长趋势,且其离散性均随基岩峰值加速度的增大而增大。

The nonlinearity of soil has a great influence on the spectral characteristics and intensity of ground motions. The modified Matasovic model is accepted to well characterize the nonlinear behavior of soil. The profile soil models of 50 boreholes for the quaternary deep sediment layers are established for site seismic response based on software DeepSoil. The predominant period Tp,average spectral pe-riod Tavg of the acceleration response spectrum and the mean period Tm of the Fourier amplitude spec-trum of an acceleration time history are employed as the proxy to characterize the spectral characteris-tics of surface ground motions. The ground motion intensity is characterized by the Arias strength Ia and the peak ground acceleration(PGA). The results show that:(1) Tpdoesn′t characterize the changes of seismic motions spectral characteristics during the seismic wave propagating from bedrock to surface ground. Tavg and Tm have a good similarity in characterizing the spectral characteristics of seismic motions.(2) When the seismic bedrock motions are rich for high frequency components,Tavg and Tm show a linear growth trend with increasing peak bedrock acceleration. However,there are inflection points in the growth trend lines of Tavg and Tm if the seismic bedrock motions are rich in low frequency components.(3)The nonlinear generation rates of PGAs and Ia with increasing peak bedrock acceleration are essentially consistent,and the values of PGAs and Ia show much greater dis-persion with increasing peak bedrock accelerations.