Formation mechanism and engineering application of the directionality of butterfly leaf in the butterfly plastic zone of roadway rock surrounded

The classical roadway pressure theory is not applicable to the analysis of deep roadway pressure.To solve this problem,based on the boundary equation of plastic zone around circular hole under non isobaric conditions and butterfly failure theory,the cosine fourth order implicit equation of the principal stress direction deflection angle of the surrounding rock of circular roadway and the polar coordinate angle of a point on the boundary of the plastic zone under the condition of non hydrostatic pressure field was deduced theoretically.Then,theoretical analysis,numerical simulation,and field test were used to study the evolution law of butterfly plastic zone distribution characteristics with the deflection of surrounding rock principal stress direction,and the formation mechanism of butterfly directionality in butterfly plastic zone of roadway was revealed.The applicability of butterfly directionality in the butterfly plastic zone of surrounding rock under different roadway section shapes (circular,rec tangular,arch),the mechanical parameters of surrounding rock (soft rock,medium hard rock,hard rock) and layered roof structure (lower soft upper hard type,lower hard upper soft type,weak interlayer type,hard interlayer type) were analyzed.Based on this,the relationship between butterfly directionality and the deformation and failure characteristics of surrounding rock was discussed,and the asymmetric deformation and failure mechanism of sur rounding rock of transport roadway in the working face of Zhaogu No.2 mine was studied.The results show that the butterfly leaf in the butterfly plastic zone will deflect with the deflection of principal stress direction,and the deflection angles of the two are approximately equal.The shape of roadway section,mechanical parameters of surrounding rock and roof structure of layered rock have no significant effect on the directionality of butterfly leaf,and the butterfly directionality is universal.Affected by the directionality of butterfly leaf,the distribution characteristics of butterfly plastic zone in the roadway are consistent with the deformation and failure mode of the surrounding rock,resulting in its deformation and failure at the butterfly leaf position in the butterfly plastic zone is more serious than that at other positions,and leading the non uniform deformation and failure characteristics of roadway.The failure mode of surrounding rock in the transportation roadway of working face is basically consistent with that of numerically simulated plastic zone.