Abstract: The binary medium model has been widely studied in unfrozen geomaterials, however, it is still not well studied for frozen soil. In order to investigate the strength-deformation characteristics of frozen silty sand in triaxial test, the binary medium theory is introduced to interpret the stress-strain relationship of frozen soil. There are plenty of parameters for existing binary medium model, and the determination of parameters is with complexity. A binary medium model is proposed based on simplified breakage parameter. The triaxial tests of frozen soil were performed under five kinds of fine particle content and four kinds of confining pressure conditions, and the validity of proposed model was examined by test results. It is revealed that the stress-strain relationship can be divided into three stages with the increase of axial strain, namely, linear elasticity stage, elastoplastic stage, and strain softening stage. Based on binary medium model, all three stages can be well explained by the transformation theory of bonding element and friction element. Under the identical confining pressure conditions, both deviatoric stress and the maximum values of bulk expansion decrease, while the shear strength decreases linearly with the increase of fine particle content. Considering cross-section area correction, the silty sand with different fine particle contents presents softening characteristics, and the volume deformation shows the pattern from shrinkage to expansion with the increase of axial strain. The turning points of the three stages of deviatoric stress development are in good agreement with the extreme point of volume shrinkage and the turning point of volume expansion. Comparing the measured deviatoric stress in triaxial tests with the calculated by binary medium based on simplified breakage parameter, it is believed that the proposed model is able to simulate the stress-strain relationship of frozen silty sand in triaxial tests.

Key words: frozen silty sand, binary medium model, triaxial shear test, stress-strain relationship, breakage mechanism