This paper presents a micro-mechanical analysis of the macroscopic behavior of natural clay. A micro-structural stress-strain model for clayey material has been developed which considers clay as a collection of clusters. The deformation of a representative volume of the material is generated by mobilizing and compressing all the clusters along their contact planes. The model is then used to predict multistage drained triaxial stress path tests on Otaniemi clay. Numerical simulations are compared to the experimental ones in order to validate the modeling approach. Then, the numerical results obtained at the microscopic level are analyzed in order to explain the induced anisotropy observed in the clay behavior at the macroscopic level. Finally, the evolution of the state variables at each contact plane during loading can explain the changes in shape and position in the stress space of the yield surface at the macroscopic level, as well as the rotation of the axes of anisotropy of the material.