Evaluation of field sand liquefaction including partial drainage under low and high overburden using a generalized bounding surface model
Evaluation of field sand liquefaction including partial drainage under low and high overburden using a generalized bounding surface model
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DOI：
10.1016/j.soildyn.2021.107059
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发表时间：
2022-01
影响因子：
4
通讯作者：
W. El-Sekelly;R. Dobry;T. Abdoun;M. Ni
中科院分区：
文献类型：
--
作者：
W. El-Sekelly;R. Dobry;T. Abdoun;M. Ni
本文采用FLAC3D程序和P P S本构模型，对密实疏松的渥太华纯砂在离心机低覆盖层和高覆盖层条件下的地震液化响应进行了模拟。本文首先用循环应力控制三轴试验对PPand进行了标定，然后用两次离心机试验的信息对其进行了修正。校准后的模型被用来模拟4个离心机试验，涵盖的相对密度从45%到80%，覆盖压力从大约100 kpa(∼1 atm)到600 kpa(∼6 atm)。这四个数值计算是完全耦合的有效应力模拟，考虑了孔压在每个时间步长的积聚和消散。在所有四个离心机实验中，数值结果与实验结果都得到了很好的匹配，建议在类似清洁沙子中使用校准后的P2P和输入参数。模拟结果证实了之前从离心机结果得到的高覆盖层下砂层的扩散率增加。这是因为P P S and假定砂土的体积模数与平均有效应力的平方根成正比，这与作者根据离心机数据得出的类似结论是一致的。校准后的PPS模型也被用来对相同的四个离心机实验进行“无流”模拟，在这些离心机实验中，液体在摇动过程中或摇动后不允许流动。在实际应用中，有时没有使用流动模拟来减少数值工作量，假设场地中的液化基本上不排水。结果表明，对于1 大气压的低覆盖层，这一假设可能会产生有用的工程结果，但对于较高的覆盖层，该假设可能变得越来越不正确和过于保守。这是因为在某些现场条件下，由于砂土扩散系数的增加，在高覆盖层下的振动过程中，流体流动变得更加明显。
The article presents simulations of the seismic liquefaction response of dense and loose clean Ottawa sand under low and high overburden in the centrifuge, using Program FLAC3D and the P2Psand constitutive model. P2Psand was initially calibrated in the paper with cyclic stress-controlled triaxial tests and then modified with information from two centrifuge experiments. The calibrated model was used to simulate four centrifuge tests covering relative densities from 45% to 80% and overburden pressures from about 100 kPa (∼1 atm) to 600 kPa (∼6 atm). The four numerical computations were fully coupled effective stress simulations that allowed for pore water pressure buildup and dissipation at every time step. The calibration yielded very good matches between numerical and experimental results in all four centrifuge experiments, and calibrated P2Psand input parameters are suggested for practitioners in similar clean sands. The simulations confirmed the increased diffusivity of the sand layer under high overburden obtained before from the centrifuge results. The reason is that P2Psand assumes that the sand bulk modulus is proportional to the square root of the mean effective stress, consistent with the similar conclusion derived from the centrifuge data by the authors. The calibrated P2Psand model was also used to perform “no flow” simulations of the same four centrifuge experiments, in which fluid flow was not allowed during or after shaking. No flow simulations are used sometimes in practice to reduce numerical effort, on the assumption that liquefaction in the field is mostly undrained. It was found that this assumption may produce useful engineering results for a low overburden of 1 atm, but it may become increasingly incorrect and too conservative at higher overburden. The reason is that for certain field conditions, fluid flow becomes more significant during shaking under high overburden due to increased sand diffusivity.