Abstract: A series of cyclic shear test on remolded unsaturated sandy soil with different water contents was performed using the cyclic simple shear test apparatus WFI25735. The effect of water content variation on dynamic properties of unsaturated sandy soil is examined at different shear strains. The experimental results show that there exists a critical moisture content of 11.2% corresponding to the normalized value of dynamic shear modulus Gd/Gdmax-? at large strain. When the water content is lower than critical moisture content, the value of Gd/Gdmax increases with the water content, and when the water content becomes higher than the critical moisture content, it decreases gradually with the increase of water content. The same critical water content can be found on the skeleton curve. When the water content is lower than the critical water content, the skeleton curve goes up slowly, and reaches a peak value at 11.2% water content. The skeleton curve decreases sharply with the increase of the water content when the water content is higher than the critical water content, and the strain softening appears, which can further explain the scatter diagram changing trend of Gd/Gdmax-?. At relatively high stress, the normalized damping ratio D/Dmax increases as the shear strain increases. The hysteretic energy dissipation of unsaturated sandy soil increases with the increase of the shear strain. As the water content increases, there exists a critical water content. The hysteretic energy curve shows a trend of first increasing and then decreasing and the critical water content can shift as the normal stress increases.

Key words: cyclic shear, dynamic shear modulus, skeleton curve, hysteretic energy dissipation, damping ratio