基于地表及地下强震动加速度记录的场地液化判别

Identification of soil liquefaction using surface and borehole strong ground motions

依据强震动加速度记录快速判别土体是否发生液化及液化程度是地震实时防灾减灾的一项主要内容。目前,此类判别方法大多利用地表地震加速度记录进行判别,而对软土场地容易发生误判。针对有地表和地下加速度记录的场地提出一种基于系统辨识的方法,即在具有地表及地下加速度记录的情况下,将地下(一般为基岩位置)加速度记录作为系统输入,地表加速度记录作为系统输出,土体作为结构,利用地表及地下加速度记录组成输入、输出,计算土体的瞬时自振频率,并根据自振频率的改变判断土体液化情况。选取多组强震动记录作为样本,对提出的方法进行了验证,并用此方法对2011年东日本大地震造成的液化情况进行了判别,结果表明判别结果与日本震后的相关调查结果一致。

It is a main content in real-time earthquake disaster reduction to quickly identify the occurrence and extent of soil liquefaction based on strong motion records. Currently,most methods are based on the seismic acceleration records of the surface,which can easily lead to misjudgment in case of soft soil site. A new method based on system identification is proposed for the case that borehole records are available. The borehole( base rock) record is used as the input and the surface record is used as the response( output) with the soil between these two records as the structure( system). Modal frequency of the system can be calculated according to the input-output pair by using system identification methods. Then, the occurrence of liquefaction can be identified according to the modal frequency. Some strong ground motion records are selected to verify the proposed method. Results show that the method is reliable and robust. Finally,the sites which record the strong ground motions from the March 11,2011 Tohoku earthquake are identified and the result of the identification agrees with the disaster survey result after this earthquake.