Abstract: A new method to define slippage line under local loading condition is presented based on Hill’s principle of strain bifurcation and the elastoplastic constitutive model of soil. It can tail how slippage line formed and developed, and can reveal process of onset and evolution of slippage point and directions in elastoplastic slope body also. In practice, it is convenience to define the location and movement direction of slippage line in the slope by the elastoplastic continuum with finite element increment numerical method. During each step in elastoplasticity, whether the determinant of acoustic tensor on each Gauss point equals zero or not should be checked, once it equals zero or near to zero, mark the point and the movement direction. With some points are marked and arrayed regularly, the slippage line will be formed.

Key words: slope stability, elastoplastic constitutive model, strain localization, slip line