Evolution And Spontaneous Combustion Characteristics Of Mining Induced Air Leakage In Shallow Contiguous Seams Coal

In China,Shenyu,Lingwu and Shengdong coalfield is a important occurrence in the depth of 80 ~ 240 m shallow and short distance coal seams,due to relatively shallow buried coal seam,large mining height,mining top caving zone and fractured zone has penetrated through the surface stratum,so the surface leakage is very serious.With a mine in Shendong mining area of the upper plate of the individual main coal mining have been completed,began to lower main coal mining,most of the wording seam is the level 1 aptitude coal seam,because the interval between the two layers of coal is small,the two levels of coal goaf communicate after the influence of the lower coal mining,the upper coal has the risk of spontaneous combustion and it has an impact on the lower coal mining period.In order to study how the ground air leakage caused by repeat mining at shallow and closed distance coal seam group influence the spontaneous combustion of coal in goaf.Represented by Shen Dong mining area of western China,analysis the plastic zoned 、 porosity and displacement of overlying strata at different extraction stages,which caculated by FLAC3 D.The results show that:1)maximun crack height is 130 m after the mining of upper seam,the height do not connect the surface;maxinmm crack height has devoloped to 162 m and connected the surface after the mining of underlying seam.There is a ‘U’ shape of strata fracture distribution.2)There is an separation area at around 62 m over upper working face after the mining of upper working face,With the mining of undelying seam,the separation area and the deflection of the strata has further developed.3)At the same stage of extraction,the porosity rate of both sides of strata is bigger than the middle of the strata′s;The porosity of strata has further developed with the mining of undelying seam.In the process of repeated mining of the shallow buried and contiguous seams,the coal pillar in the goaf has experienced three stages: stress concentration(steady),pressure relief(crushing)and compaction(crushing)The results of similar simulation experiments show that the risk of spontaneous combustion of coal in these three states is increasing in turn.In the actual production process,due to the special occurrence conditions of shallow and contiguous seams,along with the recovery,air leakage passage through surface、old space and working face of the adjacent layer is formed,then increasing the spontaneous combustion risk of coal and pillar in Goaf.