海洋土动剪切模量比和阻尼比预测不确定性特性

UNCERTAINTIES OF SHEAR MODULUS REDUCTION AND DAMPING RATION CURVES OF MARINE SOILS

土体动剪切模量比G/G_(max)和阻尼比λ随剪应变幅值γ_(a)的变化曲线的不确定性对场地非线性地震反应分析结果的不确定性有重要影响。以莱州湾海床110 m以浅的原状粉质黏土试样G/G_(max)和λ的试验数据为例,采用Davidenkov骨架曲线描述G/G_(max)曲线,λ表示为小应变阻尼比λ_(min)和G/G_(max)的函数,发现描述G/G_(max)曲线的参数A、B、γ_(r)及λ_(min)的预测方程均为海床深度H的函数。基于点估计法的不确定性传递分析表明,参数A、B和γ_(r)三者的不确定性共同引起的预测G/G_(max)的总体不确定性以及仅由单一参数A、B、γ_(r)值的不确定性引起的预测G/G_(max)的单变量不确定性均随γ_(a)的增大而先增大后减小。预测G/G_(max)的总体不确定性和仅由B或γ_(r)的不确定性引起的预测G/G_(max)的单变量不确定性均随H的增加而降低;参数A的不确定性引起的预测G/G_(max)的单变量不确定性随H的增加而增大。由G/G_(max)和λ_(min)两者的不确定性引起的预测λ的总体不确定性以及仅由G/G_(max)的不确定性引起的预测λ的单变量不确定性均随γ_(a)的增大而略有先增大后减小的趋势,且均随H的增大而略有减小。由λ_(min)的不确定性引起的预测λ的单变量不确定性与γ_(a)无关且随H的增大而略有增大。

The uncertainties of soil shear modulus reduction(G/G_(max))and damping(λ)increase curves with shear strain amplitude(γ_(a))have important influence on the uncertainty of the results of nonlinear site seismic response.Based on the test data of undisturbed marine silty clay samples taken from seabed surface to 110 m depth at the Laizhou Bay,the G/G_(max) curve is described using the Davidenkov skeleton curve function,and theλcurve is expressed as a function of two variables,i.e.,the λ_(min)(small strain damping)and G/G_(max).The laboratory investigation reveals that the prediction equations of parameters A,B,andγ_(r),which describe the G/G_(max) curve and λ_(min),are all functions of the seabed depth H.The uncertainty transfer analysis based on point estimation method shows that the total uncertainty of the predicted G/G_(max) caused by the parameters A,B,andγ_(r) and the single univariate uncertainty of the predicted G/G_(max) caused by one of the three parameters increase first and then decrease withγ_(a).The total and univariate uncertainty of the predicted G/G_(max) caused by the variable B orγ_(r) decrease with H,whereas the univariate uncertainty of the predicted G/G_(max) caused by the variable A increases with H.The total uncertainty of the predictedλcaused by G/G_(max) andλ_(min) and the univariate uncertainty of the predictedλcaused by G/G_(max) increase slightly first and then decrease slightly withγ_(a),while both decrease slightly with H.The univariate uncertainty of the predictedλcaused byλ_(min) is independent ofγ_(a) and increases slightly with H.