Detection of soil liquefaction from strong motion records

Abstract

During the recent earthquakes in Japan and the U.S.A. a number of records from liqueÿed-soil sites have been obtained. The ground motion parameters from these sites were studied and several methods for detection of liquefaction from seismic records were developed. The methods, however, focus mainly on the horizontal ground motion and may interpret as liquefaction-induced some records from soft-soil deposits or records with dominant surface waves, at which sites the phenomenon was not observed. Besides, not all of the available records from liqueÿed sites were processed. In this paper, after examination of the ability of di erent types of ground motion parameters to indicate alone soil liquefaction we propose a new liquefaction detection method that simultaneously analyses instantaneous frequency content of the horizontal and the vertical ground acceleration. We also compare performance of the proposed method with that of the other liquefaction detection methods. The computations are carried out using a common data set including records from liqueÿed and non-liqueÿed sites. Results show that the frequency-related parameters and the proposed method detect more e ciently the occurrence of liquefaction from the seismic records. damage assessment systems within them can predict structural damage not only due to the ground shaking, but also due to ÿre, soil liquefaction or tsunami.Since the 1964 Niigata earthquake, a number of ground motion records from liqueÿedsoil sites have been obtained. The records show that the horizontal ground acceleration alters uniquely after the onset of liquefaction -its frequency abruptly drops o to the range 0.5-1 Hz and its amplitudes decrease -while the vertical acceleration is rather stable ( Figure 1). This alteration of the horizontal acceleration is triggered by the decreasing of the soil shear modulus as a consequence of the pore-water pressure buildup under undrained condition. An adequate description of the alteration can be used as a method for detection of liquefaction from the seismic records. Such a method can operate data from a seismometer network and identify the occurrence of the phenomenon immediately after an earthquake. It can also function as a standalone liquefaction sensor in combination with an accelerometer. Liquefaction has been recognized as the main reason for collapse of earth dams and slopes, failure of foundations, superstructures and lifelines and its early detection might be of great interest.A practical approach to capture the alteration of ground motion is to calculate appropriate ground motion parameters and compare their values with limit ones that correspond to soil liquefaction. The advantages of this approach are that the alteration is expressed in terms of physically meaningful quantities and that computations are simple. The disadvantage is the incompleteness of the alteration description. Another possible approach is to perform nonlinear e ective-stress analysis of the soil. This model-based approach is more comprehensive, but involves knowledge...

Variation process in stiffness inferred by nonlinear inversion during mainshocks at Kushiro Port vertical array site

“…According to previous studies conducted by Kostadinov and Yamazaki (2001) and with the results of our STFT analysis for the observed horizontal ground motions, liquefaction can occur during the mainshocks due to abrupt changes in the predominant frequency. Liquefaction is a process by which sediments below the water table temporarily lose strength gradually and behave as a viscous liquid rather than as a solid, as shown in Fig.…”

“…Ground motion parameters from liquefiedsoil sites have been examined in a number of studies which have employed several methods for assessing liquefaction based on strong motion records. Nakayama et al (1998), Miyajima et al (1998), Ozaki (1999), and Kostadinov and Yamazaki (2001) reported various methods that consider ground motion parameters such as peak horizontal ground acceleration, maximum spectrum intensity, and maximum horizontal ground displacement. The respective method evaluates the occurrence of liquefaction either positively or negatively if these parameters exceed certain limit values.…”

Impact of Ground Freezing on Seismic Performance of Bridge Pile Foundations Subject to Liquefaction-Induced Lateral Spread

“…Considerable changes were observed as the motion propagates from the dense sand layer to the ground surface: more long-period components were present within the loose sand layer and in the ground surface when the main shaking occurred, and the peak amplitude of acceleration decreased. The alteration of acceleration time histories including frequency and amplitude indicates liquefaction in the loose sand layer (40).…”

General description and classification of the models of ecological and technological objects ground-space monitoring

“…Разжижение почвы представляет собой процесс, в котором в течение очень короткого периода времени (несколько секунд или десятков секунд) при сотрясении грунта, почва трансформируется из своего нормального состояния в состояние тяжелой, жидкой массы [24]. Несколько моделей мониторинга описаны в литературе [25,26,27,28,29] для наземного или космического наблюдения. Одна из них показана на рис.…”