Abstract: The morphology of the plastic zone of roadway surrounding rock has an important influence on the failure mode and degree of roadway. In order to explore the evolution of plastic zone morphology under three-dimensional stress field, this paper derives the axial stress expression based on elastic mechanics, and determines the approximate solution method of 3D plastic zone under 3D strength criterion according to the idea of solving the boundary equation of butterfly plastic zone. By determining the surrounding rock stress loading scheme through equal spherical stress p and equal deviatoric stress q with different Lode angles θσ , the morphological evolution of the plastic zone under different 3D strength criteria is studied in depth, and the low sensitivity of the criterion for butterfly failure is demonstrated. Based on the butterfly failure theory, the asymmetric deformation failure mechanism and control technology of 160206 return roadway in Yangchangwan are analyzed. The results show that: 1) Under the same p, q and different θσ stress loading conditions, the morphology of the plastic zone under the five strength criteria shows the evolution patterns of round, oval and butterfly shapes, and the morphology of the plastic zone of surrounding rock is basically consistent for each strength criterion under the same θσ . 2) Under the loading scheme with same stress state and different stress directions, the plastic zone morphology of surrounding rock varies greatly. The shape of the plastic zone is largely determined by the horizontal lateral pressure ratio. The axial lateral pressure has a greater influence on the size of the plastic zone, but less influence on the shape of the plastic zone. 3) Under the influence of superimposed mining, the roof of 160206 return roadway presents asymmetric large deformation and failure. Based on the support idea of butterfly plastic zone, the collaborative support technology of ' asymmetric anchor cable + advanced unit support + borehole pressure relief ' has been applied, and good supporting effect has been achieved.

Key words: plastic zone boundary, butterfly plastic zone, strength criterion, mining influence, roadway surrounding rock control