Formation mechanism and prevention and control of underground debris flow induced by roof-cutting of pressured support in deep-buried face

With the large-scale development and utilization of coal resources in Huanglong coalfield in Western China,a new type of roof disaster has emerged in this area:debris flow disaster caused by roof cutting of roof support. Because of the large burial depth and thick bedrock,it is different from that of the shallow seam in Northwest China and the loose seam in North China in terms of material and power sources. In order to prevent the recurrence of this type of disaster, this paper analyses and studies the characteristics of overburden failure,reasonable working resistance of support,occur- rence of joints and fissures in working face,the superposition effect of abutment pressure of inclination of adjacent work- ing face,hydraulic gradient condition of aquifer,physical and mechanical characteristics of weak cemented stratum and mineral composition by means of theoretical analysis,numerical calculation and laboratory test from the angle of material source,power source and its influencing factors of disaster formation,and reveals the formation conditions of roof cutting by pressured support in accident face and the internal relationship between them. The results show that the formation of this type of disasters includes necessary natural conditions and inducing factors. The necessary natural conditions are weak cemented strata (provenance) of the mudstone roof of the Zhiluo Formation containing a large amount of hydro- philic minerals and sliding instability (power source) of the composite key strata. The inducing factors are too small re- sistance of support work,superposition effect of inclined abutment pressure near working face,slow advancing speed of working face,large hydraulic gradient of roof aquifer and occurrence characteristics of roof joints and fissures in working face,that is to say,when necessary natural conditions exist,the superposition of multiple disaster-inducing factors leads to disaster. Therefore,aiming at this disaster type,the paper has formed the prevention and control technical route of “finding out the necessary natural conditions,controlling and avoiding the inducing factors”.