Dynamic shear modulus and damping ratio of thawed saturated clay under long-term cyclic loading

Dynamic properties of subgrade soil under the long-term traffic loading are crucial for designing the subgrade structures and evaluating the long-term performance of traffic infrastructures in seasonally frozen regions. In this study, the dynamic shear modulus and damping ratio were employed to evaluate the long-term dynamic behaviors of thawed saturated clay by conducting a series of cyclic tri-axial tests. Effects of freeze-thaw cycles, dynamic stress amplitude, confining pressure and multi stage cyclic loading on the evolution rules of dynamic shear modulus and damping ratio versus shear strain were analyzed. The results indicate that both dynamic shear modulus and damping ratio decrease with the increasing shear strain during the long-term cyclic loading. Repeated freeze-thaw cycles have tremendous effects on decreasing the dynamic shear modulus and increasing the damping ratio. Increasing dynamic stress amplitude has a decreasing effect on dynamic shear modulus, and an increasing effect on damping ratio. Increasing confining pressure has no obvious effect on the evolution of damping ratio, but has an increasing effect on increasing the dynamic shear modulus before the shear strain reaches a certain level. Multi stage cyclic loading can be an alternative method to determine the evolution of dynamic shear modulus during the long-term cyclic loading, but it is not applicable for the damping ratio. Finally, the Martin-Davidenkov model and a hyperbolic model which can be used for predicting the evolution of dynamic shear modulus and damping ratio, respectively, were proposed and validated. The results show that both the two models can give satisfactory prediction. The results achieved in this study contribute to a better understanding of the long-term dynamic behavior for cohesive subgrade soils in seasonally frozen region.