Abstract
Two sets of dynamic centrifugal model tests were designed and implemented in this study: the overlying waterless surface and the water-covered surface. Based on the use of the El Centro waves with different intensities as the base input, the seismic time history at the surface of two sets of free site models was obtained. According to the results of the site response at two sets of the free site surface obtained with a traditional spectral ratio, the coherence functions at the surface and the base were used to modify the traditional spectral ratio for analysis and to evaluate the effect of the ground motion coherence function for site amplification. The modal characteristics and the amplification effect of a typical saturated soil water free site were summarized at the same time. The results showed that the ground response results of the two groups of typical free site centrifugal models were greatly influenced by the coherence function. In the low frequency phase, the coherence function of the amplification spectrum of the site response decreased significantly, while in the high frequency phase, the decrease trend decreased. The coherence function had a significant effect on the first-order mode of the free site. The first-order mode frequency and the amplification factor of a typical free site could be identified effectively. Compared with the saturated land free site model, the saturated soil water free site model had higher-order modes due to the overlying water. It was shown that the overlying water, as part of a complex medium system, could be ignored in the site response and basic cycle estimation.
Highlights
The coherence function is a physical quantity that describes the statistical characteristics of the correlation between two points in the ground motion space, and it can reflect the relationship between the correlation of each frequency component of the ground motion and the frequency and the distance between the two points
Wang et al [5] and others analyzed the seismic records of the California Strong Motion Instrumentation Program (CSMIP), and they showed that the coherence of the ground motion decreased with the increase of the epicenter distance and the depth from the surface, and the coherence of the ground motion had a greater impact on the low frequency band of seismic waves
With the ground motion of different intensities as the base input, the amplified spectrum of the site response was calculated with the traditional spectral ratio method
Summary
The coherence function is a physical quantity that describes the statistical characteristics of the correlation between two points in the ground motion space, and it can reflect the relationship between the correlation of each frequency component of the ground motion and the frequency and the distance between the two points. Because centrifugal model can truly reproduce the prototype stress state, more and more geotechnical problems can be solved by centrifugal model test, which is the mainstream and hot spot in the field of geotechnical seismic engineering It is widely used in slope stability analysis, dynamic simulation of underground space and tunnel engineering, soil seismic liquefaction, and so on. Chen and Shen [15] designed two groups of square tunnel models with and without isolation layer by using the dynamic centrifuge test and explored the seismic effect of the isolation layer on the square tunnel by inputting different vibration loads. The research results helped to improve and deepen the understanding of the site of marine soil dynamics and sea ground motion site effects These results have certain reference value and engineering significance for improving the accuracy of marine engineering seismic design and reducing engineering seismic risks
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