Damage Ratio Strength Criterion for Cohesionless Soils

Building upon the strain-decomposition model and the extremum-calculation model for the unit energy dissipation rate, a damage-ratio strength criterion for cohesionless soils is developed. A four-parameter expression for the damage ratio is formulated by assuming a closed, smooth, and convex triaxial failure envelope, as well as a monotonic decrease in the damage ratio with increasing hydrostatic stress. The theoretical failure curves of the proposed strength criterion are smooth and convex in the deviatoric plane and the meridian plane. In addition, the meridians intersect at a single point under isotropic triaxial compression, indicating that cohesionless soils experience plastic flow failure under this condition. Subsequently, the effectiveness of the proposed criterion is validated using existing experimental data on the triaxial strength and internal friction angle of cohesionless soils such as sand, gravel, granular soil, and coarse-grained soil. Finally, the proposed criterion is compared with the Mohr–Coulomb, Lade–Duncan, and spatially mobilized plane (SMP) criteria. The comparison reveals that the damage ratio strength criterion not only achieves high computational accuracy but also captures the variation of the internal friction angle with respect to the intermediate principal stress coefficient, mean stress, and minimum principal stress.