Method Improvements of Testing Modulus of Soil Based on Free-Vibration Column

It is difficult to directly measure the dynamic elastic modulus of soils when the strain is less than 10⁻⁴, though the dynamic shear modulus can be easily obtained by the free-vibration testing method. Some improvements were adapted to the traditional free-vibration column for measuring dynamic elastic modulus of soil precisely with lateral vibration in small strain (10⁻⁴∼10⁻⁶). Differing from the traditional lateral vibration theory, a new dynamic elastic modulus testing method based on bending vibration equation of cantilever beam was put forward based on the improved free-vibration column of GZZ-50. Firstly, some descriptions about calibration process of needed testing parameter (moment of inertia of drive board) were made, and then, Poisson’s ratio of standardized column was used to confirm the measured results. Four main improvements were applied, including the shape of drive board which made the bending vibration equation solved, laser displacement sensors for correcting specimen’s height parameter with uncontacted manner which can reduce the influence of specimen, a hoop with plug used to make the split mould be removed, and air duct used when installing drive board to increase the success rate of installing specimen. Finally, standard process of installing specimen was described, which can be used as reference of similar test.

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