The overconsolidation ratio (OCR) is a critical factor in determining the mechanical behaviour of overconsolidated clays. On the basis of the three requirements for the peak strength line, a continuous and smooth peak strength line is constructed from the perspective of the peak stress ratio, and then a new yield function for overconsolidated clays is developed. The developed yield function in the stress space is characterized by an elliptical curve. The evolution of the developed yield function in the stress space is captured by a new hardening parameter, which is constructed by integrating the proposed peak strength surface with the subloading surface concept. By combining the developed yield function with the non-orthogonal plastic flow rule, a non-orthogonal elastoplastic constitutive model of overconsolidated clays is established to consider the influence of the OCR on strength and deformation. The proposed model requires seven material parameters, all of which have a clear physical meaning and can be easily determined via conventional laboratory tests. Three typical stress paths are employed to demonstrate the essential features of the proposed model. The effectiveness of the proposed model is confirmed by comparing the experimental data with corresponding model predictions.

Cohesion provided by pore ice is a critical component influencing the mechanical behavior of frozen soil, as it not only cements soil particles together but also shares the external loads with them. In view the crucial role of cohesion in developing an elastoplastic model for frozen soil, this paper employs triaxial tensile strength (TTS) to characterize cohesion and proposes a TTS degradation expression driven by plastic shear strain. By directly incorporating TTS into the yield function, a framework for a Non-Orthogonal Elastoplastic (NOEP) constitutive model that accounts for cohesion degradation in frozen soil is developed. Furthermore, a hardening parameter incorporating TTS is introduced and used in conjunction with the modified yield function to determine the magnitude of the plastic strain increment. The non-orthogonal plastic flow rule is used to determine the direction of the plastic strain increment based on the modified yield function. Ultimately, by combining the elastic strain increment determined by Hooke's rule, a NOEP constitutive model incorporating cohesion degradation for frozen soil is established. The validity and rationality of the proposed NOEP model in representing the stress-strain relationship of frozen soil are confirmed through comparisons with test results of frozen soil under the triaxial compression conditions. The proposed constitutive model provides a more comprehensive and precise representation of frozen soil's response to external loading, enhancing the understanding of its shear deformation behavior and providing a robust theoretical foundation for engineering design and construction in cold regions.