厚层淤泥质粉质黏土的动力特性参数对地表地震动参数的影响

以天津滨海某软弱场地为例,在不同强度不同相位的地震动时程输入下,用等效线性化技术考虑土的动力非线性特性,计算水平成层场地的地震反应,研究天津地区厚层淤泥质粉质黏土的动剪模量比和阻尼比与剪应变幅值的关系曲线的变异性对深软场地地表峰值加速度及其反应谱的影响。结果表明:(1)在阻尼比较均值加减一倍标准差对地表地震动参数变化影响不大;(2)在动剪模量比均值增加或减1倍标准差,对2%超越概率水平下地表峰值加速度影响显著,对应地表峰值加速度可能增加或减小20%~30%,其地表反应谱谱型也有变高变瘦或变矮变胖的趋势;(3)在动剪切模量均值减1倍标准差时,对10%超越概率水平下的地表峰值加速度的影响比较显著,减小幅度在15%左右,反应谱也存在变矮变胖的趋势;在动剪切模量均值加1倍标准差时,对10%超越概率水平下的地表地震动参数影响不明显;(4)在动剪切模量或阻尼比均值加减1倍标准差时,对63%的地表地震动参数影响均不明显。

Influence of Dynamic Characteristic Parameters of Thick MuckySilty Clay on Surface Ground Motion Parameters

A soft site in the coastal area of Tianjin is used for analysis as an example of the seismic response of a site with horizontally-layered soil. The ground motion time history with different intensities and phases was input, and the equivalent linearization method was used to consider the nonlinear dynamic characteristics of the soil. This study also presents the effects of a relation between variability in the curves of dynamic parameters of a thick layer of mucky silty clay in the Tianjin area (including the soil dynamic shear modulus ratio and damping ratio) on the peak value of ground surface acceleration and its response spectra in deep soft sites. Numerical results obtained from a number of case studies were used to make a comparison with a standard condition, and the following was determined. Firstly, adding or reducing one standard deviation to the mean of the damping ratio has little effect on ground motion parameters. Secondly, addition or reduction of one standard deviation to the mean value of the dynamic shear modulus ratio has a prominent effect on the peak value of ground surface acceleration; when the ground motion time history input is 2% of the 50 years transcendental probability the corresponding peak value of ground surface acceleration increases or decreases by 20% to 30%, and the surface response spectra is changed into a thin-high or short-fat trend. Thirdly, the mean value of the dynamic shear modulus ratio when one standard deviation is added, has a significant effect on the peak value of ground surface acceleration for 10% of the 50 year exceedance probability, the corresponding peak value of the ground surface ratio decreases by about 15% and the response spectra is changed into a short fat trend. Finally, when one standard deviation is added or subtracted from the mean value of the dynamic shear modulus ratio or damping ratio there is little effect on the value of ground motion parameters.