Accumulative plastic strain of thawed saturated clay under long-term cyclic loading

Accumulative strain of subgrade soil is crucial for designing the subgrade structures and maintaining the long-term performance of pavements. Due to the effects of freeze-thaw cycles in seasonally frozen region, subgrades filled with clayey soil usually are exposed to an increasing risk of turning into a saturated condition. The thawed saturated clay can generate notable accumulative strain under long-term cyclic loading. This study investigated the effects of freeze-thaw cycles, dynamic stress amplitude, confining pressure, number of cyclic loading and multi-stage cyclic loading on the evolution of accumulative plastic strain for thawed saturated clay by using dynamic tri-axial tests. An empirical model for calculating the accumulative strain was proposed based on the experimental data. The test results indicate that the normalized accumulative strain increases with the increasing number of freeze-thaw cycles, as well as the increasing dynamic stress amplitude and loading cycles, but decreases with the increasing confining pressure. Evolution of the accumulative strain under multi-stage cyclic loading can be divided into three phases by two threshold CSRs (cyclic stress ratio), i.e., the gradual stabilization phase, the rapid growth phase and the failure phase. The accumulative plastic strain model, which can reflect the effects of freeze-thaw cycles, dynamic stress amplitude, confining pressure and loading cycles, was proposed and validated. Results achieved in this study contribute to a better understanding of deformation behavior for cohesive subgrade soils in seasonally frozen region.