Falling principle and support design of butterfly-failure roof in large deformation mining roadways

The roof falling control of large deformation mining roadways has been an important hurdle for safety and high-efficiency production in the past decades in China. This paper, based on the field engineering background of Baode mine and the butterfly-failure theory of mining roadways,analyses the non-uniform evolution law of mining stress field and the characteristics of plastic zones under its influence. The results show that the plastic zone of mining road- ways could be a butterfly-failure distribution under the high deviatoric stress condition,and the butterfly-failure zone is direction independent which means the position of butterfly-failure wing is variable with the direction change of princi- ple stress. High deviatoric stress may occur around the roadways under the influence of mining disturbance,and the di- rection of maximum principle stress tilts towards working face,which keeps the butterfly-failure wing stay at the road- way roof direction. The roof strata staying in this butterfly-failure wing suffers heave damage companying with strong di- lation and deformation. In addition,when the rock weight in this butterfly-failure wing exceeds the loading threshold of bolts or anchor cables,it triggers the roof falling. Also,the authors proposed a support design with long bolts to control the butterfly-failure-trigged roof falling,and the field application gives a good feedback. The long bolts support design offers a new solution for roof falling control in large deformation roadways.