Mechanism and prevention of strong strata behaviors induced by the concentration coal pillar of a room mining goaf

In order to overcome the problem of strong strata behaviors at the No． 31201 working face due to the overly- ing coal pillars of a room-and-pillar mining goaf at Shigetai Coal Mine in Shendong mining area,based on field obser- vations and theoretical analysis,the authors studied the mechanism of strong strata behaviors and the prevention meas- ures through analyzing the critical width of the elastic nuclear of a small pillar that remains stable under the advancing abutment pressure,and the strata structures under dynamic load and support load. The results show that during the pe- riod of working face moving out the area of the overlying coal pillars,the face strata rotation reduces the supporting width of the overlying coal pillars that support the overburden strata,if the advancing abutment pressure leads to the instability of those coal pillars and the small coal pillars at front large-area,the movement of the unstable pillars and o- verburden strata will lead to the face overburden under the dynamic load,which destructs the bearing structure of the face overburden,then the strong strata behaviors will occur. Hereby,the prevention measure is proposed as blasting the overlying coal pillars in advance. Also,the safety distance between the working face and the overlying coal pillars dur- ing the blasting is determined. The measures was proved to have obvious effect in the field application.