Abstract: Establishing a constitutive model that reflects the local bonding breakage process has always been a core task in soil mechanics and is crucial for solving engineering stability issues. Based on thermodynamic principles and breakage mechanics, this paper proposes a macro-micro thermodynamic constitutive model. This model quantitatively describes the thermodynamic behavior of local bonding breakage and the non-uniform distribution of stress-strain at the microscale. It improves the prediction accuracy of the model for deformation characteristics, which is similar to the Cambridge model in mathematical form. Firstly, based on the law of conservation of thermodynamic energy, the mathematical expression of structural breakage work during compression deformation was determined. It was found that the dissipated energy of breakage can be mainly divided into two parts: the frictional effect between bonded elements and frictional elements, and the irreversible transformation from bonded elements to frictional elements. Furthermore, a macro-micro constitutive model framework considering the thermodynamic behavior of local bonding breakage was established. Secondly, based on the constitutive framework and the deformation mechanism of loess (frictional, bonded, and damaged), the expressions for free energy, dissipated energy, and damage dissipated energy were determined. The damage yield function and elastic-plastic constitutive model considering the evolution laws of volume breakage and shear breakage were derived. Finally, the established model was used to predict the experimental data of other scholars, and its rationality and simulation advantages were verified through comparison. This model aligns better with thermodynamic principles, and its parameters are easy to determine.

Key words: structural loess, constitutive model, local broken, thermodynamics, binary-medium model