Abstract: As known, natural geotechnical materials always have the characteristics of structure and anisotropy. How to express their effects rationally in the constitutive model is the key point for evaluating the advantages and disadvantages of the constitutive model. On the basis of the modified Cam-clay model, a structural parameter was used to express structural characteristic of natural original soil in plain. An anisotropic parameter was used by rotating yield surface to express anisotropy effect. The anisotropic parameter also be used in the process of deducting the hardening rule. A modified Cam-clay model considering structural and anisotropic properties was established. Combined with the associated flow rule and consistency condition, the incremental stress-strain relationship from the constitutive model was derived. The model consisted of 8 parameters which can all be obtained by the conventional laboratory tests. At the last, the triaxial shear tests was carried out using natural original loess, the comparison of experimental results and model calculation shows that the modified Cam-clay model considering soil structure and anisotropy could simulate the mechanical characteristic of natural original loess correctly.

Key words: undisturbed loess, structural character, anisotropic character, modified cam-clay model, triaxial test