Chen Guo-xing

Calibration of V s -based empirical models for assessing soil liquefaction potential using expanded database

The shear wave velocity (Vs)-based method of assessing the liquefaction susceptibility of soils has given geotechnical engineers a promising alternative for determining soil resistance to seismic liquefaction. Through the use of an expanded global case histories of soil liquefaction, the authors obtained a new calibrated correlation equation for liquefaction triggering analysis. This new liquefaction triggering correlation was found to be reasonably conservative, and yet insensitive to the variations in the components of the adopted simplified analysis framework. A probabilistic version of the liquefaction triggering correlation, obtained with the weighted maximum-likelihood technique, was validated using a weighted empirical probability approach. Three zones of liquefaction potential, transitioning from non-liquefaction to liquefaction, were then defined based on liquefaction probability contours.

COMPARISON OF 1D EQUIVALENT-LINEAR AND NONLINEAR SEISMIC SITE RESPONSES IN DEEP SEDIMENT LAYERS

Abstract. A reasonable description of soil hysteretic constitutive relation has a significant impact on the evaluation of design ground motion parameters. These parameters play an important role in predicting seismic damage and taking further effective anti-seismic measures. In this study, based on the 200m-deep-borehole profiles in Suzhou region (China), the 1-D seismic site responses are compared by two analysis methods. One is an equivalent linear analysis (ELA) modeling in frequency domain, the other is a nonlinear analysis (NLA) using a multi-degree-of-freedom, lumped mass model in term of the modified Matasovic constitutive modeling in time domain. The effects of bedrock motion characteristics (amplitude, frequency content and duration) on the predictions from the two site response analyses in deep sediment layers have also been analyzed. Using the results from a broad range of bedrock motions, we can find the difference between the two site response analyses in different strain levels. Specifically, the surface peak ground acceleration (PGA) calculated by ELA increases monotonically as the PGA of bedrock motion increases. However, the surface PGA calculated by NLA first increases rapidly and then decreases gradually or keeps constant. Moreover, the surface acceleration response spectra (Sa) for short periods computed using ELA and NLA are significantly different. The high-frequency contents of bedrock motions exhibit obvious filtering in ELA while the high-frequency contents in NLA first magnify and then attenuate as the PGA of bedrock motion increases. In addition, for the medium or strong bedrock motions, the surface ground motion duration is not only related to bedrock motion characteristics, but also closely related to the cyclic behavior of nonlinear soil medium. The influence of bedrock motion intensity on the duration prolongation of surface ground motion can be reasonably evaluated using NLA.

NONLINEAR ANALYSIS ON SEISMIC RESPONSE OF A MULTI-GEOMORPHIC COMPOSITE SITE

Abstract: Based on the explicit FE method and parallel computing cluster platform of ABAQUS, a large-scale two-dimensional (2D) nonlinear analytical model for a multi-geomorphic composite site consisting of valley flat, terraces, undulating hilly terrain was established by considering the inhomogeneity of ground soils and influence of terrain change. Nonlinear seismic effect characteristics of the composite site were analyzed, including the peak ground acceleration (PGA), spectral acceleration, duration and acceleration transfer functions. The main results demonstrated that: (1) the PGA of different observation points on the ground surface vary with each other, which was caused by the terrain differences. For the same input motions, the ground surface PGA of valley flat area show obviously larger than that of the first terrace area. (2) the horizontal spectral acceleration of ground surface appears a double-peak or multi-peak phenomena, the spectra shape peak moves to a larger period in the floodplain area compared with that in first terrace area and the period difference comes to be from 0.05s to 0.25s. (3) the sensitive frequency band of seismic site response was 0.5Hz to 1.75Hz, when the frequency is lower than 0.2Hz or higher than 2Hz, the seismic amplification characteristics is not apparent.(4)PGA exhibits spatial variation characteristics which varies in both lateral and depth directions, and there is a non-monotonic decreasing characteristic with soil depth, greater motion amplification and focusing effect of some shallow soil layers were found. In some degree, the 2D results can reflect nonlinear site effect and the influence of lateral heterogeneity of soils on seismic wave propagation.