The freeze-thaw cycle tests were conducted on the remoulded soil samples taken from a highway subgrade in a seasonally frozen area. The triaxial compression tests under the consolidated-drained condition were carried out on the remoulded samples subjected to freeze-thaw cycle

and stress-strain data were obtained. Based on the experimental results and the theory of elasto- plasticity

an elliptic equation is proposed to fit the yield surface in the p-q coordinate system

while a parabolic equation is proposed to fit shear yield surface

from which an elastic-plastic constitutive equation was developed following an associated flow rule with considering freeze-thaw cycles. By comparing the theoretical calculation with the experimental data

it is shown that the proposed double-yield surface constitutive model can accurately predict the frozen soil stress-strain relationship. The model provides a theoretical basis for long-term stability analysis and engineering prediction of subgrade soil in seasonally frozen areas.