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 K

0

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 p

rinciples of Ohta-Sekiguchi model. In the proposed model

to adjust the elastic region and reflect the influence of the initial K

0

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 K

0

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.