Due to its unique composition and fabric characteristics

loess exhibits structural and hydrological sensitivity

with its mechanical properties

including yield stress

shear strength

and deformation characteristics

being closely related to saturation and structural integrity. Considering the influence of saturation on the structural strength of loess

structural parameters such as yield stress

friction strength

and cohesion strength are introduced

and a functional relationship between these parameters and initial saturation was established. An evolution equation for structural parameters during plastic deformation was derived based on the structural degradation characteristics observed in shear deformation of loess. On this basis

the yield function for structural loess was developed by drawing inspiration from the Cambridge model. By taking yield stress and structural parameters as hardening parameters

an elastoplastic constitutive model for loess

accounting for saturation and structural evolution

was proposed using the associated flow rule

and the corresponding constitutive matrix was derived. Based on triaxial consolidation drainage test data for undisturbed Q loess from Dongjiahe Town

Tongchuan City

Shaanxi Province

stress-strain curves under varying confining pressures and saturations were predicted

and the model’s rationality was verified. The results indicate that under low saturation conditions

loess exhibits high structural strength

which decreases significantly after yielding

accompanied by pronounced strain softening characteristics. As soil saturation increases

structural strength and corresponding yield stress decrease

with stress-strain curves becoming less steep

indicating increased plastic deformation and progressively less pronounced softening characteristics. The model effectively captures the relationship between loess structure and initial saturation

enabling a more accurate description of mechanical behavior under varying saturation conditions and reflecting how strain softening characteristics vary with saturation.