Study On The Effect Of End Structure On The Position Of Gob-side Entry In Extremely Thick Coal Seam With Large Mining Height And Fully Mechanized Caving Face

The position and control of gob-side entry driving in extremely thick coal seam with large mining height and fully mechanized caving face is largely determined by the end structure characteristics of overlying strata in the face of the upper section.In order to keep the stability of entry and isolate the gob in case of water and harmful gas overflow and spontaneous combustion of coal seam,Tashan Coal Mine protects the entry by using wide pillar,whose width is 38~45m.It results in some problems,such as heavy loss of coal pillar,heavy strata behaviors.To solve the problems,it is proposed to adopt the technology of remaining small coal pillar along the goaf.Based on the engineering background of 8204 working face of Tashan Coal Mine3-5# coal seam,this thesis studied the end structure of gob-side entry driving in extremely thick coal seam with large mining height and fully mechanized caving face.The relationship between the end structure characteristics and mining parameters,lateral abutment pressure,fracture field,mechanical model of end structure,the reasonable width of coal pillar and the evolution of the end structure were studied by using methods such as engineering analogy,theoretical calculation,numerical simulation and field observation.The study results shows: Low key strata formed to cantilever structure,high key strata formed to voussoir structure before stability.Triangular slip region was formed after stability.The lateral support pressure peak was 32.09 MPa and the position was 34 m,the low stress region was 0~17m,the influence range was about 99 m.The pressure peak decreases with increasing mining thickness.Peak position,range of low stress region and influence range increase with mining thickness.With the increase of mining thickness,the overburden structure has changed obviously.Slip region was formed obviously when the mining height was more than 9m,it's suitable to set up small coal pillar.It's not suitable to set up small coal pillar when the excavation length at the end is more than 13~15m.The smaller the length,the more benefit to adopt the technology of small coal pillar with gob-side entry driving.The size of small coal pillar was determined as 6m and it had achieved good control effect of surrounding rock in practice.