A constitutive model for the mechanical behaviour of saturated frozen soils considering the dual effects of confining pressure

Data from the literature show that the mechanical behaviour of saturated frozen soils varies non-monotonically with total confining pressure in triaxial compression tests. Specifically, the shear strength of saturated frozen soils initially increases or remains nearly constant and then decreases as the confining pressure increases, regardless of soil type, temperature, or strain rate. This non-monotonic behaviour has yet to be well understood and incorporated into existing constitutive models. In this study, two mechanisms are considered to explain the influence of confining pressure: (i) prevention of crack growth within pore ice and (ii) onset of ice melting. At low confining pressures, the shear process can be affected by cracking in the pore ice, which is initiated by dilatancy-induced tensile stress or high deviatoric stress. As the confining pressure increases, these ice cracks are prevented, increasing the shear strength of the unfrozen soil. Simultaneously, confining pressure-induced ice melting occurs when confining pressure increases, leading to a reduction in shear strength. A constitutive model that addresses the mechanical behaviour of saturated frozen soils is proposed, incorporating these dual effects of confining pressure. The model is validated using triaxial test results for saturated frozen soils under various temperatures, pre-freezing mean effective stresses, and post-freezing total confining pressures. Comparisons between measured and predicted results demonstrate that the model can quantitatively capture the complex effect of confining pressure on the shear behaviour of saturated frozen soils, a capability rarely achieved by existing models.