Effect of Frequency on The Dynamic Properties in Resonant Column Testing

Abstract

Dynamic properties of soils are needed to conduct seismic analysis according to building code of UAE. Research on the effect of loading frequency on dynamic properties such as shear wave velocity of geomaterials remains inconclusive mainly due to unquantified biases in available test methods. Resonant column (RC) is a laboratory device that is considered superior to other laboratory and field methods for evaluation of dynamic properties in-spite of testing biases. Effect of frequency on dynamic properties can be masked or unrealistically imposed if known testing biases are not quantified. Contribution from the base of RC device during testing can affect the results either directly or indirectly by affecting the mass polar moment of inertia (MPMI) of the drive plate of RC device. The MPMI of the drive plate is evaluated for every RC using conventional technique in which calibration probes of known dynamic properties are tested. The calculated value of MPMI strongly depend on the stiffness of calibration probes. A new method based on suspension of drive plate instead of mounting on probes is used in this study for evaluation of MPMI. The suspension of drive plate removes connection to base, and contribution of base is minimal. The results of new method are compared with the results of conventional method by testing seven calibration probes and also with selected studies from the literature. The findings of this study agree with previous studies that MPMI from the conventional method has a large scatter with in tested frequencies. Consequently, the variation in the calculated shear wave velocity is also large. The degree of contribution from the base of RC device is found to be comparable with one of the previous study. The effect of base contribution increases with increase in stiffness of calibration probe. The new method on the other hand shows insignificant variation in MPMI of the drive plate within the tested frequencies. The small variations can be attributed to device resolution and measurement errors. The new method is expected to increase the reliability of shear wave velocity by improving the estimate of the MPMI of drive plate.