Mechanism and control method of roof fall resulted from butterfly plastic zone penetration

In this study,the problems of frequent roof fall accidents and support difficulties in the layered roof of road- way were investigated using theoretic analysis,numerical simulation,field detection and field engineering test,the dis- tribution of the butterfly plastic zone of layered roof roadway was revealed,and the mechanical mechanism of roof fall due to butterfly plastic zone penetration was elucidated. The research shows that the butterfly plastic zone has the char- acteristic of penetrating across strata,and no plastic failure rock cannot block the formation of butterfly plastic zone in soft strata;The distribution of penetration of butterfly plastic zone in the roof is accompanied with strong deformation pressure,the lower no plastic failure rock under soft strata plastic zone is subjected to a continuous huge squeeze load which makes the no plastic failure rock fractured and failed,this is the intrinsic reason of roadway roof fall hazards. The key to prevent roof fall of the roadway is to keep the stability of plastic zone of surrounding rock,the length of rock bolts (or cables) should be longer than the plastic zone,and the rock bolts ( or cables) should have the ability to withstand a large deformation without breaking. Based on the research,strengthening support and field test were conducted in the 81306-2 tailgate of Baode Colliery in Shendong,the field test shows that the support method proposed can maintain the stability of roadway roof effectively.