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.

Accurately describing the solid-like and fluid-like behaviors of granular media is crucial in geotechnical engineering. While the unified frictional-collisional model, integrating rate-independent frictional and ratedependent collisional stresses, is widely used for solid-fluid phase transitions, an effective model is still under investigation, and comprehensive analyses are lacking. This study addresses these gaps by developing an enhanced elastoplasticity-based frictional-collisional model. The frictional stress is modeled using a critical-statebased elastoplasticity approach, and the collisional stress is formulated through an enhanced kinetic theory incorporating particle stiffness. Subsequently, comprehensive element simulations are conducted to explore the effects of concentration, particle stiffness, and strain rate paths on the model. The proposed model's effectiveness is also validated against experimental data. Finally, a detailed comparison with the typical mu(I) rheology model and a state-equation-based phase transition model is conducted. Our analyses show that the developed model effectively captures strain rate path and particle stiffness through the collisional stress component, while concentration-dependent characteristics are captured through both frictional and collisional stress components. Through comparative analyses, we also found that both the state-equation-based and elastoplasticity-based models depict solid-like behavior and replicate the rheology of granular media in a fluid-like state, similar to the mu(I) model. However, they differ in implementing critical state theory: the state-equation-based model acts as a partial-range phase transition model, describing stress evolution from the critical state to the fluid-like state, while the proposed elastoplasticity-based model serves as a full-range phase transition model, covering stress evolution from the initial to the fluid-like state.

Accurate continuum modelling of granular flows is essential for predicting geohazards such as flow-like landslides and debris flows. Achieving such precision necessitates both a robust constitutive model for granular media and a numerical solver capable of handling large deformations. In this work, a novel unified phase transition constitutive model for granular media is proposed that follows a generalized Maxwell framework. The stress is divided into an elastoplastic part and a viscous part. The former utilizes a critical-state-based elastoplasticity model, while the latter employs a strain acceleration-based mu(I) rheology model. Key characteristics such as nonlinear elasticity, nonlinear plastic hardening, stress dilatancy, and critical state concept are incorporated into the elastoplasticity model, and the non-Newtonian mu(I) rheology model considers strain rate and strain acceleration (i.e., a higher-order derivative of strain) to capture changes in accelerated and decelerated flow conditions. A series of element tests is simulated using the proposed unified phase transition model, demonstrating that the novel theory effectively describes the transition of granular media from solid-like to fluid-like states in a unified manner. The proposed unified model is then implemented within the material point method (MPM) framework to simulate 2D and 3D granular flows. The results show remarkable consistency with results from experiments and other numerical methods, demonstrating the model's accuracy in capturing solid-like behaviour during inception and deposition, as well as liquid-like behaviour during propagation.

The majority of existing effective stress-based constitutive models approach thermal effects through the temperature dependency of surface tension and its effects on the soil-water retention curve (SWRC) and effective stress. Experimental tests and theoretical studies, however, suggest that the temperature effect on surface tension alone is not sufficient to properly explain thermal-induced changes in the effective stress and SWRC. This study focuses on the temperature-dependent elastoplastic behavior of low plasticity unsaturated soils by developing a set of constitutive-level relations that incorporate temperature-dependent SWRC and effective stress models. These models account for the effect of temperature on the enthalpy, contact angle, and surface tension. The application of the presented constitutive relations was demonstrated and validated for low plasticity soils, specifically incorporating temperature effects into the hardening modulus, specific volume change, yield stress of the modified Cam-Clay model, and stress-strain relationships. The proposed relationships are incorporated in any effective stress-based constitutive model for modeling temperature dependency of elastoplastic response in low plasticity unsaturated soils. Employing these relationships can enhance the numerical simulation of low plasticity unsaturated soils under thermo-mechanical or other coupled processes involving temperature-dependent conditions.

In this paper, by introducing a new yielding mechanism based on the widely acknowledged double-structure theory, the original UH model for unsaturated soils is extended to capture the behaviour of expansive clays. A novel expansion potential is further established to evaluate the effect of overconsolidation on the volume change of unsaturated expansive clays during wetting. With only one additional parameter, the proposed model can describe the behaviour of both wetting-collapse and wetting-induced swelling for unsaturated clays. Comparisons between model predictions and test results show a good agreement which verifies the capability of the proposed model in charactering the features of unsaturated expansive clays under various stress histories and stress paths.

This article presents a critical discussion of the repercussion of overshooting effects on element tests and finite-element simulations. For exemplification purposes, three advanced constitutive models for sands that had already achieved a certain level of accuracy in the simulation of monotonic and cyclic loading were carefully selected; namely, a bounding surface plasticity model, a hypoplastic model with intergranular strain, and a hypoplastic model with elastoplastic anisotropic intergranular strain. Cyclic loading laboratory data and scale tests on Karlsruhe fine sand were considered to support the analyses. The obtained results suggest that the overshooting issue is one of the most serious limitations of the selected models and has a major impact on elemental and finite-element simulations. Therefore, models' end-users should be aware of this drawback when performing simulations under certain conditions involving unloading-reloading episodes with different strain amplitudes.