Centrifuge shaking table tests on evolution mechanism of sand mesostructure during earthquake liquefaction
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摘要: 已有研究表明地震液化历史是影响砂土抗液化能力的重要因素，相关研究学者认为这种影响的内在机理是砂土颗粒在前次地震液化后形成了稳定或者不稳定的细观结构，但是目前针对地震液化全过程中砂土细观结构演化行为的直接试验数据还很少。通过离心机振动台试验模拟了一个饱和砂土地基的地震液化现象，在试验过程中测试模型不同埋深处的加速度、孔压以及地表沉降，并基于细观图像获取设备记录了地震液化全过程中砂土细观数字图像。试验结果表明微振动会增加颗粒接触、减小颗粒间孔隙，随着振动强度增加，颗粒重新建立接触，颗粒间孔隙重新分布。受孔隙流体向上渗流作用，颗粒形成偏竖向和偏横向联通的大孔隙，偏竖向大孔隙周围的颗粒在渗流作用下长轴偏向竖直。Abstract: The existing studies demonstrate that the history of earthquake liquefaction is an important factor affecting the liquefaction resistance of sand. The researchers think the intrinsic mechanism of these effects is the generation of stable or unstable sand mesostructure after the previous liquefaction event. However, few studies have directly given the experimental results of the evolution behaviors of the sand mesostructure during the whole process of liquefaction. In this study, the centrifuge shaking table tests are conducted to model the earthquake liquefaction of a saturated sand deposit. The pore pressures and accelerations at different depths and the settlements of the sand deposit are measured. Besides, the mesoscopic digital images of the sand mesostructure are recorded simultaneously by a mesoscopic image acquisition system. The experimental results show that the small shaking increases the contacts and decreases the voids among sand particles. The particle contacts are reconstructed and the voids are redistributed with the larger shaking. Approximately vertically and horizontally linked large voids are caused by the upper seepage effects of the pore fluid. The sand particles nearby the approximately vertically large voids rotate vertically under the seepage effects.
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图 3 超孔压和超孔压比的时程曲线
Figure 3. Time histories of excess pore pressure and excess pore pressure ratio
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