Roof Breaking Characteristics And Overburden Migration Law Of Repeated Mining In A Short Distance Coal Seam Group Of A Mine In Guizhou Province

In view of the high proportion of short-distance coal seams in Guizhou Province and the unclear characteristics of roof fracture and overburden migration after repeated mining due to the special karst landform,the safety production of the working face is seriously affected in the actual production process.Based on the engineering background of 17101 working face in Panjiang Coal Mine,Guizhou Province,this paper studies and analyzes the characteristics of roof fracture and the law of overburden migration after repeated mining in close seam group by means of theoretical analysis,numerical simulation and similar simulation comparison.The results show that the roof pressure is not strong when mining the coal seam which is repeatedly mined in short distance,but there are three kinds of pressure phenomenon in different layers of the overlying strata,the pressure is more frequent,and the coal wall is easy to be damaged under the repeated mining of the coal seam group in short distance.The mechanical model of "coal wall support roof" is constructed.After the mechanical analysis,the reasonable calculation formula of support resistance is determined by using the mechanical knowledge(2.5).In FLAC3 D numerical simulation experiment,because the roof of 17#coal seam is affected by two times of mining,the structure is relatively broken,so the direct roof subsidence is large.In the similar simulation experiment,when the working face of 17× coal is advancing to 30 m,the direct roof collapses.At this time,the overlying goaf is also compacted downward.Because the 17#coal roof has become relatively soft under the influence of repeated mining,the roof collapses as the working face advances.In the experiment affected by single mining,because the coal body is soft and the coal seam above the working face will collapse along with the advance of the working face,but the direct roof of the coal seam above will not collapse along with the collapse,but will have a supporting effect on the goaf above,which is different from the situation under repeated mining.By using UDEC numerical simulation software modeling and operation analysis,it is found that under the influence of repeated mining in 15 and 16 coal seams,roof pressure is more frequent,the stability of end face roof becomes worse,and roof caving is more serious.The research results provide a theoretical basis for coal mining under similar conditions,and play a good reference role for the next mining.