Study On Gas Migration Law And Extraction Of Lower Protective Layer Mining In Close Coal Seams

The gas controlling of the working face under the mining conditions of lower protectivelayer in close distance coal seam group is a problem that restricts the production safety. Thegas controlling of lower protective layer mining in close distance coal seam group in Jinjiamine of Guizhou Panjiang Coal Limited by Share Ltd is taken as the engineering background,using field measurements, theoretical analysis, numerical simulation and other means, thestress distribution, movement and deformation,and destruction of upper overlying coal afterlower protective layer mining are analyzed, on the basis of which the migration rules ofpressure relief gas in lower protective layer mining are researched, the results are as follows:(1)Through the analysis on the formation of "three zones" overburden rock in protectivelayer mining, get that the height of caving zone and fractured zone of mining overburden rockin11223working face were about6m and15.5m (+4m). Using elastic-plastic mechanics,establishing mechanics model of upper overburden in mining field, calculating rock beamstress of13m above the11223goaf, the paper obtained that space in0~60m from the goafcenter is stress decreasing zone, the range of75~130m is the stress concentration area,different degrees of subsidence existed in the ranges of0~75m away from the goaf center.According to the theory of gas migration, the basic law of the gas transport in11223workingface was analyzed.(2)The FLAC3D numerical simulation software is used to simulate the mining process ofthe11223working face. The results show that: during the process of lower protective layermining, the upper overlying strata experienced a process of stress concentration, stressreduction, stress recovery; The obvious deformation and subsidence existed in the overlyingstrata area, along with the advancing of working face, the range and degree of subsidenceincreased gradually, especially the deformation and subsidence of the upper overlying stratain the center of mining goaf was larger, the deformation and subsidence decreased graduallyin area from central goaf to cut and working face coal wall,and the two sides of the wall; Thedistribution of stress decreasing zone and plastic zone of the upper overlying strata in the coallevel was the oval; The tensile and shear failure mainly existed respectively in center andevery side of the goaf, forming the fractured surrounding rock of "return" type in upper goaf.(3)The FLUENT numerical simulation software is used to find the gas displacement lawof gas controlling under four different conditions of the U type ventilation, U ventilation and return airway laying pipe lane type, U type ventilation and high pumping lane type, U typeventilation and high pumping Lane and return airway laying pipe lane type, and the resultsshow that: the gas emission in the working face under the condition of U type ventilation islarger, the gas concentration in the upper corner is higher, therefore the gas drainage measuresmust be increased; More gas can be gathered in the return air side with the pumping flowunder the condition of U type ventilation and return air lane laying pipe, which will result ingas emission in working face and the gas concentration at the upper corner increasing.Under the condition of U type ventilation and high pumping, the gas emission in the workingface is decreased to a certain degree, but because of the location of the high pumping Lane,the high concentration of gas gathered in lower goaf adjacent return air lane side cannot beeffectively extracted, so the problem of gas emission of the working face and gas overrun atthe upper corner still cannot be solved effectively. Under the condition of U type ventilationand high pumping Lane and return airway laying pipe lane, high gas emitted from overlyingstrata adjacent coal seam and lower gas gathered in lower goaf can be effectively extracted,thus the better effect of gas control was obtained.(4)In view of lower protective layer mining in the close distance coal seam group, themigration and collection characteristics of pressure relief gas was discussed, the reasonablemethod of pressure relief gas extraction was summarized. According to the actual situation oflower protective layer mining in Jinjia mine, the gas control method under the condition of Utype ventilation and high pumping Lane and return airway laying pipe lane was established,and field measurements showed that gas treatment has obtained good effect.