The development of the unsaturated soil thermo-hydro-mechanical (THM) coupling model plays a very important role in solving certain geotechnical engineering problems and has been a topic of significant research in recent years [1–8]. Many classic elastoplastic models for unsaturated soils have been developed within the framework of critical state theory [9–14]. For instance, Alonso et al. [10] proposed the famous Barcelona Basic Model (BBM) model by using the matrix suction and net stress as dual stress variables. The BBM model describes the stress-strain relationship with the modified Cambridge model and captures the yield behavior of unsaturated soils using the wetting-collapse yield curve (LC yield). As a classic model, it has been widely cited and improved by researchers [15, 16]. Sheng et al. [17] proposed a model (SFG) to describe the volumetric changes in unsaturated soils, which can predict deformations during drying and loading processes. However, many of these models use dual stress state variables, considering the effect of suction but neglecting the impact of saturation on the strength and deformation of unsaturated soils. A large amount of experimental data shows that even when matrix suction and net stress are identical, the mechanical properties of soils with different saturation levels can still vary. Therefore, some scholars [18–20] have introduced saturation degree into constitutive models to describe its influence on soil properties. Additionally, the soil-water characteristic curve (SWCC) of unsaturated soils exhibits significant hysteresis, meaning that the curves for drying and wetting processes are different. Some researchers [21–24] have incorporated the SWCC into constitutive models, leading to the development of hydro-mechanical coupling models for unsaturated soils.