Influence of load interval on dynamic properties of subgrade fill in cold regions

The real simulation of vehicle loads is the key to studying the dynamic behaviors of subgrade fill in cold regions. Considering the time interval between adjacent vehicles, a series of dynamic triaxial tests with continuous and intermittent cyclic loading were conducted. The results show that the intermittent effect of cyclic load can enhance the stiffness of frozen subgrade fill, which is also strengthened by the increasing intermittent stages and ratios. The initial dynamic shear modulus of frozen subgrade fill can be effectively described using a function that accounts for the intermittent stage and intermittent ratio. Furthermore, a relationship between the maximum shear stress and the initial dynamic shear modulus has been established. A modified Hardin-Drnevich model is proposed to consider the interaction between the dynamic shear modulus, the intermittent stage, and intermittent ratio. The damping ratio increases nonlinearly as the increasing dynamic shear strain and intermittent ratio. A shear strain threshold exists and is slightly affected by the intermittent stage, but it decreases with increasing intermittent ratio. When the dynamic shear strain is larger than the shear strain threshold, the damping ratio increases with the increase in intermittent stage . The research results can provide a guidance for further understanding of the dynamic properties of frozen subgrade fill under the actual vehicle loads.