基于竖向台阵地震记录的非线性场地反应研究

Assessing nonlinear soil behavior using vertical array data:a case at TCGH16 station from KiK-Net in Japan

利用日本Ki K-Net台网中TCGH16竖向台阵在2009年1月到2014年6月间收集的1 646组地震记录,提取了原位等效应力-应变关系以及等效剪切模量比-应变曲线,建立了土动力学参数与地震动峰值加速度之间的关系,研究了非线性场地反应的阈值与程度。结果表明:(1) TCGH16台阵所处场地的等效剪切模量比曲线在等效应变超过线性阈值应变(约为2×10-5)时开始缓慢下降,在等效应变超过体积阈值应变(约为1×10-4)时迅速下降。(2)当地震动强度分别为100、200、400和800 cm/s2时,场地的等效剪切模量分别下降了约5%、11%、22%、42%。(3) TCGH16台阵发生场地非线性反应的阈值约为40 cm/s2,证实了非线性场地反应普遍存在于中等强度的地震动中。

In this study,we analyze acceleration time histories data at TCGH16vertical array in Japan,recorded between January 2009 to June 2014,to evaluate nonlinear soil behavior.Ground motion records provided by seismic vertical arrays allow estimation of in-situ soil dynamic parameters.Using classic hyperbolic models,we quantitatively assess the relationships between the soil dynamic parameters and level of ground motion.We found nonlinearity starts at a quite low level of strain of 2×10^-5 and becomes much more significant beyond a relative high level of strain of 1×10^-4.The threshold strains from ground motion observations are well consistent with those from previous laboratory tests.When PGA comes to 100,200,400 and 800cm/s^2,the shear modulus degradation is about 5%,11%,22%and 42%,respectively.Finally,we infer that the threshold acceleration for nonlinear response at TCGH16 array is about 40cm/s^2,which indicates clearly that nonlinear site response may occur during moderate- level ground motion.