A New Method for Fast Identification of Liquefied-Soil Site from Surface Acceleration Records

Abstract eng:
The methods for detection of soil liquefaction from seismic records are being developed recently. The developed detection methods make it possible to capture the alteration of the surface ground accelerations and then the occurrence of soil liquefaction can be indicated immediately after a earthquake happens. This kind of technique is useful in developing a system of seismic motion monitoring and the real-time disaster mitigation, and also provides a new approach to understand the mechanism of liquefaction. However, the existing detection methods generally result from the empirical estimation and there is shortage of the theoretical models. As a result, the soft sites by the methods are easily misdetected as the liquefaction sites and the misdetection have been explained reasonably. In the paper a new method for fast identification of the liquefied-soil site from surface acceleration records is presented in terms of the concept of the frequency decrease rate. By analyzing the main factors influencing the self-vibration period in the liquefied sites the frequency decrease rate is employed to describe the variation of the acceleration history during the liquefaction. The liquefiable site is simplified as a double-degree-freedom model and the formula for calculating the reduction of horizontal natural frequency induced by liquefaction is attained. And then the lower limit of frequency decrease rate is derived and based on it, the fast identification method of site liquefaction from surface acceleration records is proposed. The reliability of the method is examined by the actual earthquake records and the results indicate that by using the approach presented in the paper, not only the liquefied sites and the stiff non-liquefied sites are identified, but also the soft non-liquefied sites are detected correctly.

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