Abstract: When the natural soil is influenced by the unloading induced by the excavation, its stress-strain relationship shows a quite difference with the relationships obtain from the conventional loading test of undisturbed natural soil. At present, commonly applied soil constitutive models are established based on the conventional tri-axial test, where soil is subjected to isotropic confine pressure and uni-axial loading stress. In addition, these constitutive models do not take the influence of initial K0 consolidation and the unloading induced by excavation into consideration. In this paper, a new model is proposed based on the Cam-clay model and the principles of Ohta-Sekiguchi model. In the proposed model, to adjust the elastic region and reflect the influence of the initial K0 consolidation, the hardening axis in p–q stress space is rotated by introducing a stress ratio. To describe the three-dimensional anisotropic stress state, the transformation stress method is introduced to the model. By all these approaches above, this newly proposed model is able to reasonably describe the strength and deformation of soil under initial K0 stress and complex stress-train relationships under unloading induced by excavation. The rationality of this proposed model is verified by comparing the predicted results with the results obtained from typical laboratory tests.

Key words: excavation, elastoplastic model, anisotropy, constitutive model