Verification of shear wave velocity versus cyclic stress ratio to cause liquefaction using centrifuge modeling

目前，室内最常用的试验是动三轴试验，与真实的现场情况相比，动三轴试验存在着明显的不足。在实验室中验证这些程序的一种更好的技术是通过小规模物理建模。然而，在小规模模型试验中不可能进行可靠的标准贯入试验或静力贯入试验。在最近由NSF赞助的一个项目中（使用弯曲元件确定飞行中离心机模型的土壤性质，CMS-9728860），我们已经开发了一种技术，可以精确地测量离心机模型在离心机飞行过程中不同深度处的剪切波速度。这种技术使得有可能验证剪切波速度与循环应力比引起液化。由于剪切波速度测量具有无损性和可靠性，近年来，利用剪切波速度评价液化势的方法得到了迅速发展。由于该技术目前已广泛应用于岩土地震工程设计中，因此迫切需要对该程序进行独立可靠的验证/确认。在本研究中，具有不同相对密度的饱和砂土模型将经受相当于标准7.5级地震的模型地震。在地震发生前，将在模型中的不同深度处测量剪切波速度。将在模型中放置加速度计和孔隙压力传感器，以记录土壤中的循环应力比和超孔隙压力。根据记录的数据，可以计算模型中不同深度处的循环应力比和修改的剪切波速度。根据孔隙压力传感器的记录，还可以检查特定深度的土壤是否膨胀。因此，这些试验的数据将提供独特的数据点，以验证经验剪切波速度与循环应力比引起液化曲线，这将是一个重大的贡献，岩土地震工程。

Currently, the most commonly used test in the laboratory is cyclic triaxial test, which has some significant shortcomings when comparing with the real field situation. A much better technique to verify these procedures in laboratory is through small-scale physical modeling. However, it is not possible to conduct reliable SPT or CPT tests in a small-scale model test. In a recent project sponsored by NSF (Determination of soil properties for in-flight centrifuge models using bender elements, CMS-9728860), we have developed a technique that can accurately measure the shear wave velocity at different depths in a centrifuge model during the flight of a centrifuge. This technique makes it possible to verify the shear wave velocity versus cyclic stress ratio to cause liquefaction. The method of using shear wave velocity to evaluate liquefaction potential has been developing rapidly in recent years since shear wave velocity measurement is non-destructive and quite reliable. Since this technique is now widely used in geotechnical earthquake engineering design, an independent and reliable verification/validation of this procedure is urgently needed. In this study, saturated sand models with different relative densities will be subject to a model earthquake equivalent to a standard magnitude 7.5 earthquake. Before the earthquake, shear wave velocity will be measured at different depths in the model. Accelerometers and pore pressure transducers will be placed in the model to record the cyclic stress ratio and excess pore pressure in the soil. From the recorded data, it is possible to calculate cyclic stress ratio and modified shear wave velocities in the model at different depths. From the recording of pore pressure transducers, it is also possible to check whether the soil at a specific depth liquefies. Thus the data from these tests would provide unique data points to verify the empirical shear wave velocity versus cyclic stress ratio to cause liquefaction curve, which would be a major contribution to geotechnical earthquake engineering.