Abstract

Flow liquefaction is a catastrophic failure phenomenon of loose sand when subjected to wave or seismic load, and an instability state can be regarded as the onset of flow liquefaction. Most of the previous studies focused mainly on the static instability state, while the investigations on cyclic instability state (CIS) are very limited and unsystematic. The characteristics of CIS are complex and there is no clear consensus about the determination of CIS. Therefore, this study aims to investigate the characteristics of CIS in flow liquefaction via a series of undrained triaxial tests performed on saturated loose sand. The testing program covers a broad range of initial deviatoric stresses q_s, cyclic stress amplitudes q_cyc, and relative densities D_r. The test results indicate that CIS will occur at either compressive side or extensive side, depending uniquely on the ratio of q_s/q_cyc. The slopes of CIS lines increase with an increase in the relative density. Under the same q_cyc, the mean effective stress at CIS first decreases and then increases as q_s increases. Finally, CIS is predicted by a useful method, which is able to monitor CIS both in situ and in laboratory tests.

摘要

流动液化是松散砂土在受到波浪或地震荷载作用下发生的灾难性破坏现象，不稳定状态可视为流动液化的开始。以往的大部分研究主要集中在静态不稳定状态，而对循环不稳定状态（CIS）的研究非常有限且不系统。CIS的特点比较复杂，对于CIS的确定没有明确的共识。因此，本研究旨在通过对饱和松散砂土进行的一系列不排水三轴试验来研究 CIS 在流动液化中的特性。测试程序涵盖了广泛的初始偏应力q _s、循环应力幅值q _cyc和相对密度D_r。测试结果表明 CIS 将发生在压缩侧或扩展侧，具体取决于q _s / q _cyc的比率。CIS 线的斜率随着相对密度的增加而增加。在相同的q _cyc下，CIS 处的平均有效应力随着q _{s 的}增加先减小然后增加。最后，通过一种有用的方法预测 CIS，该方法能够在原位和实验室测试中监测 CIS。