Abstract: Firstly, the concept of stress path is extended by proposing the three-dimensional stress path considering the rotation of principal stress axis. Then the deep analysis of the stress path during excavation is carried out by numerical method. It is shown that whether the horizontal or the vertical stress exhibits characters of unloading during excavation; and the magnitude of unloading of the inner part of foundation pit is larger than that of the outer part of foundation pit, which cause the changes of both stress and rotation of principal stress axis of the inner part of foundation pit are larger than that of the outer part of foundation pit. As the distance from the centre of foundation pit increasing, both the changes of stress and rotation of principal stress axis of the inner part of foundation pit decrease. The effects of excavation on the change of stress and the rotation of principal stress axis of the outer part of foundation pit decrease as the distance from the wall increasing. The main performance of the stress path of the inner part of foundation pit is that the mean compressive stress p and the generalized shear stress q decrease while the rotation angle of principal stress axis ? increases. And the main performance of the stress path of the outer part of foundation pit is that q and ? increase while p decreases. So on the basis of the main performance of the stress path, the typical stress paths of both inner and outer parts of foundation pit during excavation are obtained to guide the practice design analysis and indoor experiment of foundation pit engineering.

Key words: excavation, stress path, principal stress axis rotation, stress change