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

目前，实验室最常用的试验方法是循环三轴试验，与现场实际情况相比，这种试验方法存在着明显的不足。在实验室验证这些程序的一个更好的技术是通过小规模的物理建模。然而，不可能在小规模模型试验中进行可靠的SPT或CPT试验。在美国国家科学基金会（NSF）资助的项目（利用bender elements测定飞行中的离心机模型的土壤性质，CMS-9728860）中，我们开发了一种技术，可以准确测量离心机飞行过程中不同深度的离心机模型的剪切波速度。这种技术使验证引起液化的剪切波速与循环应力比成为可能。近年来，利用横波测速评价液化潜力的方法得到了迅速发展，因为横波测速具有无损、可靠等优点。由于该方法已广泛应用于岩土抗震工程设计，因此迫切需要对该方法进行独立可靠的验证。在本研究中，具有不同相对密度的饱和砂模型将受到相当于标准7.5级地震的模型地震。地震前，在模型中测量不同深度的横波速度。在模型中放置加速度计和孔隙压力传感器，记录土壤的循环应力比和超孔隙压力。根据记录的数据，可以计算出模型中不同深度的循环应力比和修正横波速度。从孔压传感器的记录中，还可以检查特定深度的土壤是否液化。因此，这些试验数据将为验证经验横波速度与循环应力比引起液化曲线提供独特的数据点，这将对岩土地震工程做出重大贡献。

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.