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

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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.