Accumulative plastic strain of heavy-haul clay subgrade subjected to freeze–thaw cycles: experimental investigation and prediction model

Accumulative plastic strain is a critical physical parameter for evaluating subgrade resistance to long-term traffic-induced deformation. In seasonally frozen regions, freeze-thaw (FT) cycles combined with heavy-haul traffic intensify subgrade deterioration. Cyclic triaxial tests were conducted considering FT cycles, initial moisture content, freezing temperature, deviator stress amplitude and confining pressure. The results show that accumulative plastic strain increases with higher content, more FT cycles and greater stress amplitude, but decreases with higher confining pressure and freezing temperature. Strain accumulation appears as plastic shakedown, creep or incremental collapse, while increasing confining pressure shifts the response from destructive to stable. A multi-factor prediction model was developed, demonstrating a good agreement with experimental results. These findings clarify the plastic deformation behaviour of low liquid limit clay under heavy-haul loading in seasonally frozen regions and guide safe and sustainable subgrade and pavement design.