Mining induced stress rotation trace and its sensitivity to face advance direction in kilometer deep longwall panel with large face length

Due to the quick depletion of coal resource in shallow buried coal seams,the mining of deep buried coal resource becomes critical in the eastern mining area of China.Deep mining is characterized by high ground stress,strong disturbance and well developed fractures,which result in a series of surrounding rock instabilities,such as drastic face sloughing,large scale roof falling and large displacement experienced by the gate road.In order to improve ground control,a kilometer deep longwall panel with large face length in Kouzidong mine in Huainan,China,is taken as a typical engineering background.Field measurement,lab experiment,numerical simulation and theoretical analysis are applied to the study of mining induced stress rotation and its sensitivity to face advance direction.In the kilometer deep longwall panel with large face length,the spatial distribution of front abutment stress presents regional pattern,divided by the boundary of peak point influenced zone.Influence scope and failure region reach 150 m and 8-12 m,respectively,in the coal seam.Large amplitude rotation occurs to mining induced stress.High stress level and stress rotation result in a drastic failure of surrounding rock.After the extraction of coal seam,mining induced stress dips to gob area at the position 200 m ahead of face line.The stress on two sides of the face dips to gate road.Influence scope of the side gate reaches 15 m in dip direction.By taking the vertical plane parallel with face advance direction as a reference,the stress rotation trace is divided into slow deviation stage,fast approaching stage out of the reference plane and cooperative rotation stage within the plane.The rotation trace is strongly influenced by face advance direction.When the face advance direction is parallel with or perpendicular to minimum ground stress,the mining induced stress rotation trace presents a symmetrical distribution on the stereogram.Otherwise,the rotation trace presents an asymmetrical distribution.With increase in the angle made by face advance and minimum ground stress directions,the slow deviation stage shrinks while the fast approaching stage expands out of the reference plane.But the cooperative rotation stage remains in the reference plane constantly.Based on fracture distribution,the stress orientation sensitivity area of surrounding rock stability is identified on the stereogram.If the fracture orientation remains stable,the stress orientation sensitivity area covers local region of the stereogram.If the fracture presents a random distribution,the stress orientation sensitivity area realizes full coverage.Moreover,a determination method is proposed for favorite stress rotation trace,which helps to choose and optimize face advance direction,and provides new method for ground control in deep mining.