Abstract As part of the LEAP-UCD-2017 and the LEAP-ASIA-2019 exercises, dynamic centrifuge model tests were conducted at KAIST on a submerged 5° sloped medium-dense and dense model grounds of Ottawa F-65 sand. In this paper, the experimental procedure along with the testing results are presented. It was found that liquefaction occurred in the medium-dense model indicated by large lateral surface displacements and pore pressure buildup, while soil layers only partially liquefied in the dense models. The frequency characteristics of liquefied and partially liquefied models were observed using Fast Fourier Transform (FFT), ratio of response spectra (RRS) and time-frequency analysis of recorded accelerations. A shift in the fundamental frequency of the model grounds to lower frequencies due to softening associated with excess pore pressure buildup was seen in the FFT analysis. From the RRS, it was found that high-frequency amplification in accelerations due to soil dilatancy was similar within the liquefied zone in the medium-dense model regardless of confining pressure, while in the partially liquefied dense models, the high-frequency amplification was different according to the soil depth. Moreover, using time-frequency analysis, a shift in mean frequency of base motion (1 Hz) to lower frequencies was evident after liquefaction but not after partial liquefaction. Hence, by observing the frequency characteristics of liquefied and partially liquefied soil layers, the occurrence and depth of liquefaction can be ascertained. This provides an independent check for liquefaction in dynamic centrifuge testing using acceleration data.

中文翻译：

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在 KAIST 离心机试验中使用加速度记录的频率特性进行液化评估

摘要 作为 LEAP-UCD-2017 和 LEAP-ASIA-2019 演习的一部分，在 KAIST 对渥太华 F-65 沙子的淹没 5°倾斜中密和密集模型地面进行了动态离心模型测试。在本文中，介绍了实验过程和测试结果。发现液化发生在中等密度模型中，表现为大的侧向位移和孔隙压力增加，而在密集模型中土层仅部分液化。使用快速傅立叶变换 (FFT)、响应谱比 (RRS) 和记录加速度的时频分析来观察液化和部分液化模型的频率特性。在 FFT 分析中可以看到，由于与超孔隙压力累积相关的软化，模型的基频向低频移动。从 RRS 中发现，无论围压如何，在中密模型的液化带内，由于土壤剪胀引起的加速度的高频放大是相似的，而在部分液化密模型中，高频放大是不同的根据土壤深度。此外，使用时频分析，液化后基本运动的平均频率 (1 Hz) 向较低频率的转变很明显，但在部分液化后则不然。因此，通过观察液化和部分液化土层的频率特征，可以确定液化的发生和深度。