Effect of freeze-thaw cycles on the accumulative deformation of frozen clay under cyclic loading conditions: experimental evidence and theoretical model

The accumulative deformation behaviours of subgrade soil under cyclic loading conditions are crucial for designing the foundations of structures and maintaining the long-term performance of pavements in the frozen regions. Dynamic triaxial tests were conducted on frozen Qinghai-Tibet clay under different conditions to investigate the effect of freeze-thaw on the accumulative deformation behaviours. The development characteristics of axial permanent strain for frozen clay are sensitive to the freeze-thaw process. The permanent strain curve of samples gradually decreases with the progress of the freeze-thaw process until reaching the critical cycle number for the steady state. The microstructure variations induced by the thermodynamic cycles are discussed and analysed to study the micro-mechanism for property degeneration. In addition, this paper shows the effects of the dynamic stress amplitude, confining pressure, and loading cyclic number on the evolution of accumulative strain based on experimental observations The experimental results demonstrate that the normalised accumulative strain curve rises with the increase in the number of freeze-thaw cycles, the stress amplitude and the number of loading cycles but decreases with increase in the confining pressure. Finally, a modified accumulation model (HCA) is presented to simulate the development process of plastic strain under cyclic loading conditions. The influence factors, such as the freeze-thaw procedure, the loading cyclic number, the confining pressure and the dynamic stress amplitude, are considered and supplemented in this theoretical model. The predicted results reveal good agreement between the experimental data and the simulation responses.