反复地震荷载作用下砂土再液化特性的演化机理

After strong earthquakes occur, saturated sandy grounds might liquefy for many times during the main shock and the following aftershocks，i.e. the phenomenon of re-liquefaction. Historical earthquake cases proved that sand re-liquefaction resistance is probably lower than the first liquefaction, and exhibit completely different liquefaction characteristics. This application aims to explore the evolution mechanism of the re-liquefaction characteristics of sandy ground under repeated earthquake loading condition, and develop the constitutive model and numerical simulation method for re-liquefaction considering the influence of liquefaction history. First, the evolution rule of the liquefaction characteristics under repeated loading conditions will be summarized through dynamic triaxial shear tests and shaking table tests; Second, the micro structure change of sand before and after re-liquefaction will be observed through Cryo-SEM to investigate the micro mechanism for the evolution of re-liquefaction characteristics, and then the relationship between the macro evolution rule and the micro mechanism of re-liquefaction will be establish; Third, the characteristic parameters which can reflect the influence of liquefaction history will be identified, and then the constitutive model for re-liquefaction of sand can be established and applied in numerical method to simulate the re-liquefaction phenomenon of real sandy grounds; Finally, dynamic centrifuge model test will be carried out to verify the calculation model, and the prediction method that can properly evaluate the re-liquefaction response of sandy ground in engineering will be established. The research results can provide scientific evidence for the risk assessment of ground re-liquefaction.

强震发生后，饱和砂土地基在主震和余震的反复作用下可能发生多次液化，即砂土的"再液化"现象。历史的地震案例证明，砂土地基的再液化抵抗能力有可能低于初次液化，并表现出与初次液化完全不同的液化特性。本项目旨在探索反复地震荷载作用下砂土再液化特性的演化机理，建立考虑液化历史影响的砂土再液化本构模型与数值模拟方法。首先，通过动三轴试验与振动台模型试验归纳与总结连续加振条件下砂土再液化特性的演化规律；然后利用冷冻扫描电镜技术（Cryo-SEM）观测砂土再液化前后微观结构的变化，探索砂土再液化特性演化的微观机理；接着，确定反映液化历史影响的本构表征参数，建立砂土再液化本构模型，并应用到数值方法中对真实场地的再液化现象进行数值模拟；最后利用动态离心机试验结果验证砂土地基的再液化数值模型，确立具有工程实用价值的砂土地基再液化动态响应预测方法。其研究成果将为砂土地基的再液化风险评估及危害性评估提供科学依据。

强震发生后，饱和砂土地基在主震和余震的反复作用下可能发生多次液化，即砂土的“再液化”现象。历史的地震案例证明，砂土地基的再液化抵抗能力有可能低于初次液化，并表现出与初次液化完全不同的液化特性。本项目旨在探索反复地震荷载作用下砂土再液化特性的演化机理，并建立考虑液化历史影响的砂土再液化本构模型与数值模拟方法。首先，通过振动台模型试验归纳与总结了连续加振条件下砂土再液化特性的演化规律，发现砂土在经历过一次液化历史以后，再液化时间比初次液化时间更快，表明砂土的再液化抵抗能力有显著的下降趋势，但是这种变化趋势仍然与砂土的密度变化紧密相关；然后利用显微镜数字成像技术拍摄了砂土多次液化前后土颗粒的细观图像，观测了砂土再液化前后细观结构的变化，并根据砂颗粒的细观参数特征，探索了砂土再液化特性演化的细观机理，发现砂土在液化后再固结阶段的土粒重排列现象是引起再液化抵抗强度下降的主要原因；接着，确定反映液化历史影响的本构表征参数，建立了砂土再液化本构模型，并应用到数值方法中对真实场地的再液化现象进行数值模拟，确立了具有工程实用价值的砂土地基再液化动态响应预测方法。其研究成果能够为砂土地基的再液化风险评估及危害性评估提供科学依据。