Technology And Engineering Practice Of Gob-side Entry Retaining Without Filling Wall In Medium-thickness Seam Of Lanhua Baoxin Mine

The design yield of Lanhua Baoxin Coal Mine is 0.9Mt/a,it is mining No.3 coal seam at present.The average coal thickness is 1.77 m,pitch of 4~10°,depth of 400 m,located in the middle of the Shanxi group,K7 fine sandstone above.There is a tension of face continuity,the slow recovery rate of resources and other issues,therefore,this paper takes the No.3 coal seam of Baoxin Coal Mine as the engineering background,studies on the technology of gob-side entry retaining without filling wall,the main results are as follows:(1)This paper analyzes and studies the evolution and stability of the large-scale structure of gob-side entry retaining without filling wall,puts forward the view that there is a large structure of the overburden rock.Before mining the next face,the triangular block B is supported by the immediate roof and gangue,and hold by the adjacent blocks,so the large structure can reach the equilibrium state;During the second mining effect,the load on the large structure is constantly increasing,and the stress state between the blocks changes,but the bearing condition does not change,so the large structure will maintain a random balance until the next working face pushed over.(2)This paper puts forward a small structure of gob-side entry retaining without filling wall,it refers to the anchor bearing system composed of the combination support by anchor and cable,the roadway auxiliary support and the surrounding rock of anchorage range.The roof caving of gob-side entry retaining without filling wall is simplified as a mechanical model of rectangular superposition plate,the calculation formula of the auxiliary support load in the process of the initial roof caving,periodic roof caving and the later destruction activity are given.(3)Based on the geological conditions of No.3 coal seam in Baoxin Coal Mine,the 3DEC discrete element numerical analysis method was used to simulate the mining process of 3103 face and 3105 face without roadside filling,and the deformation law and stress variation of surrounding rock during the two mining processes are studied.When the 3103 face is recovered,the roof sinking is the most severe in the range of 10~30m after the face,and the sinking velocity is 12.2 ~ 18.1mm / d,the maximum sinkage to 122 ~ 175 mm,is the coal seam thickness of 6% to 9%;When the 3105 face mining,in the range of 10 m in front of face and 25 m in the rear face,the roadway roof is sinking sharply,the velocity reaches 35.5 ~ 41.1mm / d,and the maximum sinkage is 350 ~ 435 mm,for the coal seam thickness of 17% to 22%.In the 3105 face mining process,the stope roof near the 3103 goaf first form the arc triangle collapse,and then to the O-type collapse development.Therefore,it is inferred that the roof of gob-side entry retaining without filling wall will form a "X-O" type of collapse in the case of the current geological conditions.(4)Lanhua Baoxin Coal Mine uses the way of strong support and the natural collapse of the roof to achieve the technology of gob-side entry retaining without filling wall.As of January 2017,3103 face has been successfully completed,leaving the length of 650 m,more than about 39,800 tons of coal recovery,an increase of about 1061.18 million yuan of income,achieved a stage of success.This project solves the difficult problem of excavation replacement tension,and now reduces three heading faces,improves the coal recovery rate by 10 ~ 20%,and prolongs the service life of the mine.