Study On The Instability Mechanism Of Key Strata Structure In Repeat Mining Of Shallow Close Distance Seams

With the successive exploration of Shendong mining area, the exploration of the 2nd main mineable coal seam has been started in some area where the 1st seam has been explored. Due to the close distance of the two seams, the specific condition of repeated mining in close distance shallow seams has formed, specifically, in some particular area the strata behaviors of the lower seam are intense, and this can be seen from the multiple cases of instant descending of support active column and supports crushing, which has severely threatened the mine safety and its high efficiency production. Further research on instability mechanism of key stratum structure in close distance shallow seams repeated mining were studied using theoretical analysis, numerical simulation, physical simulation, field test etc.Key stratum of close distance shallow seams were classified into three kinds or four forms for the first time, that is the single key stratum structure including the thick and hard single key stratum structure and composed single key stratum structure, no typical key stratum structure, multiple key stratum structure while the upper seam has been excavated; instability characteristics of single key stratum in shallow seams while the upper had been excavated and its occurrence condition were analyzed. Uphill mechanical model was established, through which the influence of horizontal side force on the stability of single key stratum in shallow seams while the upper had been excavated and the main key stratum had been eroded was studied, the instability mechanism of single key stratum while the upper had been excavated and the surface was gully was revealed, influencing factors of dynamic strata behaviors were summarized, The key stratum structure mechanical model while crossing the pillar in close distance shallow seams was established, through which the influence of movement of key stratum block of upper seam on the key stratum stability of lower seam was analyzed, the instability mechanism of single key stratum while the upper seam had been excavated and crossing the pillar was revealed as well.Determining the suitable support resistance in Daliuta Mine Huojitu adit under the condition of single key stratum while the upper had been excavated. Consequently, the precaution measures of instability of key stratum in close distance shallow seams repeated mining of Daliuta Mine and Bulianta Mine were proposed, which has obtained remarkable economic effects.