Abstract: The purpose of this study is to establish a modified Yin’s double-yield-surface model based on the ratio of bioenzyme-based soil stabiliser, which can accurately describe the physical and mechanical properties of the bioenzyme-treated expansive soil. A series of drained triaxial shear tests was carried out to study the evolution laws of stress-strain, the elastic deformation, yield surface shape, dilatant yield surface, and failure line equation relating to the content of bioenzyme. Moreover, the effect of the bioenzyme content on the parameters of the Yin’s model was analysed. Finally, the bioenzyme content was introduced as a correction factor for the modified Yin’s double yield surfaces model. The results show that the bioenzyme can effectively improve the mechanical properties of the treated expansive soil. The modified Yin’s double-yield-surface model can well describe the constitutive relation of the bioenzyme-treated expansive soil. The theoretical calculation results of the modified Yin’s model show good agreement with the experimental results. Besides, the parameter determination method of the modified model is consistent with Yin’s original model.

Key words: highway engineering, expansive soil, constitutive relation, modified Yin’s double-yield-surface model, double yield surfaces, evolution law, soil triaxial shear test