A unified thermodynamics-based constitutive model for granular soils with and without particle breakage

Particle breakage substantially alters the stress–strain response and critical state behavior of granular soils, complicating constitutive modelling. A thermodynamically consistent hyperelastic-plastic constitutive model is therefore developed within a unified mathematical framework to describe granular soils with and without particle breakage. The normalized breakage index is introduced as an internal state variable and embedded directly in the elastic potential, from which the corresponding energy-conjugate thermodynamic force is derived. The state boundary is subsequently derived from the stability condition of the breakage-dependent elastic potential and evolves consistently with particle breakage. Plastic deformation and particle breakage are formulated as coupled dissipative processes constrained by non-negative dissipation, thereby avoiding separately prescribed yield functions and breakage criteria. Granular temperature is introduced to characterize grain-scale fluctuations and regulate the evolution of these irreversible processes. The model is validated through drained and undrained triaxial tests on granular soils with and without particle breakage and satisfactorily reproduces the stress–strain relation, pore pressure response, and particle breakage evolution under different loading conditions.