Study On Ground Pressure Of The Ultra Longwall Mining In The Shallow Coalseam Of Shendong Mine Area

With the development of Shanbei coal area, the shallow seam with thin bed rock is deeply studied by researchers in our country,especially the minging face less than 300 meters and mining height under 5 meters.But less research to over 300 meters of the minging face and more than 5 meters of minging height, with the extension of the mining face and the mining height in Shendong coal area, the study of the mining pressure behavior of shallow coal seam and roof control is more and more important.This paper takes the 22209 mining face of Halagou Coal Mine (320m) as research object and has made the complete Mine Pressure Observation of the Mining Face. Comparison with the mine pressure behavior law of the 22209 mining face (240m) shows that the extension fully mechanized mining face regularity of first-weighting and periodic-weight of main roof. The study have analyzed the weighting mechanism over working face and method of calculating working resistance by"key strata theory"and"step voussoir theory",combining with the real working load of working face.It take the rational evidence for support chosen.Finally,the sdudy have investigated the optimization of reasonable working face length,which came up with the evidence for designing appropriate length of working face.The study to the 2-2 coal seam with lengthening working face (320 meters) of Halagou Coal Mine shows that, the first weighting step distance is 62~77 meters and the average periodic weighting step distance is 9.9~12.9 meters. A small periodic-weighting may exist in a periodic-weighting when the length of working face more than 300 meters. The pressure distribute irregularly and weighting is nonsynchronous. The support resistance is relatively large when weighting, and the mining face pressure is big in the middle and small in two sides. The weighting of the mining face changes periodically and heterogenely, and the suitable working resistance range is 9827~11752kN per shelf. Appropriate length of working face should made overall by rate of advance,economic returns,working resistance and difficulty of roof control. With the length of minging face being oversize, rate of advance slow down and roof caving fully , which can lead to frequent periodic-weighting.Through analyzing the shelf using in the 2-2 coal seam of Halagou Coal Mine,it is found that the present shelf adapt reluctantly to 320 meters ,the length of mining face. The study reach a conclusion that safety and economical efficiency are optimal when the length of working face under 300 meters.Mining practice shows that the result of study can take technical support for shelf chosen ,length of minging face made,roof control during the extraction under safe minging.