Non-associated elasto-plastic constitutive model of frozen sand considering the influence of phase transition state and temperature

Frost heave is the main factor affecting the mechanical properties of frozen soil，which will lead to more significant strain softening and dilatancy characteristics of frozen soil during the shear process. To accurately describe the mechanical characteristics of frozen soil，this paper introduces the concept of phase transition state concept to describe the dilatancy of frozen soil，solving the problem of difficult to unify the softening and dilatancy characteristic point displacement laws using only critical state theory. Furthermore，by combining the fractional order differentiation，the non-associated plastic flow law of stress-strain of frozen soil is described，avoiding the additional construction of plastic potential surfaces. The mechanical response of frozen soil is described by introducing the yield function considering the influence of temperature. Based on the hardening rule considering phase transformation and the yield condition considering temperature effect，an improved elasto-plastic constitutive model is proposed to evaluate the mechanical properties of frozen sand. The model unifies the temperature effect，phase transition state，critical state and non-associated plastic flow in the theoretical framework of elasto-plastic mechanics，and all model parameters have clear physical meaning. Finally，by simulating the stress-strain behavior of frozen sand，and comparing with the experimental data，the results show that the constitutive model can effectively capture the phase transition and strain softening law of frozen sand at different temperatures and confining pressures.