Effects of vibration history on nonlinear shear modulus and damping ratio of sand

The effects of vibration history on nonlinear dynamic properties of dry sand are studied by applying torsional previbration using the non-resonant vibration mode by means of the Stokoe resonant column apparatus. The study shows that, for a given sand sample, there is a threshold number, below which G_max decreases and beyond which it increases with the number of cycles. Normalized shear modulus is not affected by preloading frequency but damping ratio increases with preloading frequency under the confining pressure under which previbration is applied. The normalized shear modulus decreases and the damping ratio increases with the number of cycles. Reloading confining pressure may decrease and unloading confining pressure may further magnify the effects of the vibration history on the normalized shear modulus and the damping ratio. The effects of vibration history on the normalized shear modulus and the damping properties result from for the jointed effects of wear process and reorientation of interparticles in vertical direction.