| In this paper, the theoretical analysis, FLAC3D numerical simulation and FLUENT numerical simulation are used to study the fracture development, pressure relief effect and coal and gas production technology of the stagger position in the protection layer of the stagger position. First of all, the roadway layout of the stagger position is briefly introduced. On this basis, the failure mechanism and the failure depth of the floor of the coal mining face are studied, Calculation method of depth of floor damage, and determining the stress is one of the main factors that affect the depth of the damage.In order to get the magnitude of stress. A mechanical model of elastic thin plate is established. The calculation method of stress is combined with the key layer theory and further combined with the calculation formula of the depth of floor damage.The formula for calculating the damage depth of the bottom plate is improved:Based on the criterion of the depth of floor failure, the failure of the three cases of coal pillar, the roadway and the non coal pillar is analyzed, and the different damage of the bottom plate is obtained by the three cases.At the same time, further to stagger roadway no coal pillar lap working face floor failure depth correction, obtained without coal pillar lap wrong horizons of roadway arrangement continue working face mining caused the floor failure depth is:Analysis of the formula, stagger position roadway layout form the destruction of the two ends of the lap joint working face deep is left coal pillar mining working face at both ends of the failure depth of large and the adjacent joint working face floor there is a broken zone. The sides of the overlapping working face of the stagger position will produce a much larger rupture area than the remaining coal pillars, The unloading pressure of the protective layer is favorable to the lower layera and both sides should be used as a long-term gas drainage area.Further combined with the characteristics of the stagger position, the transverse cracks in the mining field, the first working face mining, the overlying strata collapse and fall down forming the "O" type ring and the working face mining, because of the coal pillar, the overlying rock caving zone and the first working face to form a whole, the whole mining area of the form of "O-L-O" type.Taking into account that the stagger position of roadway layout is different from the traditional coal pillar mining, therefore, the protection of different size of the coal pillar mining protection layer to the protection of the effect of the protective face, the following conclusions were obtained:(1) the coal pillar size has a direct effect on the protective face corresponding to the protective face, and the middle of the coal pillar is protected by the corresponding existence of the original rock stress zone, the stress zone, the partial discharge zone and the full unloading zone.(2) In the roadway layout mining protective face, due to the adjacent working face to achieve complete without coal pillar lap, so a plurality of adjacent working face reflects features of the work of a single surface, is protective layer in the corresponding position only full pressure relief zone and protected layer undergoes many mining influence, pressure relief more fully.On this basis, combined with the protection layer of coal pillar, the reasonable size of the coal pillar is derived from the theory of catastrophe theory, It is considered that the possibility of the occurrence of the occurrence of the coal pillar is more than 88% of the coal pillar, and the critical width of the coal pillar is to be realized: a=|25mξ/22flnfR+kt/kt[1+f/(1/ξ-1)ctgφ]|At the same time, because of the rheological properties of coal pillar, even if the load is not increased, the deformation will increase with time.When the yield region is increasing, the final system will be unstable state and the stable time of coal pillar is determined by the following formula: t=η/ElnE+λ/KdHaL=25mhξL/22flnfR+kt/kt[1+f(1/ξ-1)ctgφ]η/ElnE+λ/KdmFrom the point of view of the full release of the protective face, it is determined that the occurrence of the coal pillar has a sudden change and damage to the continuous and sufficient pressure relief of the protected seam. Reasonable size of coal pillar is given, In order to guarantee the production, the time of the coal pillar is given and the reasonable speed of the working surface is given.Because of the critical size of coal pillar,In the one hand, the impact is related to the impact of mining. On the other hand, it is related to the pressure relief effect of the protected seam. So it is optimized for the extraction scheme of the protective layer with the critical dimension, that is to use the mining model of jump. Meanwhile, the analysis of the effect of unloading is better than that of the traditional coal pillar.On this basis, the effect of the fault type of the fault in the stagger position is analyzed, That the removal of the section of the coal pillar, the first mining face of the unloading effect of the same with the other two ways,but the beginning of the working face is equivalent to increasing the length of the protective layer. At the same time to improve the recovery rate, pressure relief range is greater, the effect is better, so it should be the most favorable model.In order to further verify the results of the aforementioned studies, the effect of FLAC3D on the protection layer is simulated by using. At the same time in order to further analyze the characteristics of the 5M and the 15m of the coal pillar mining results are compared, the following conclusions are obtained:(1) Mining 8# coal seam as a protective face on the floor of the damage found, the damage range of the bottom plate increases with the increase of the working surface, but when the mining reaches a certain range, The vertical depth of the bottom plate tends to a certain value (12m), In front of the working face, the failure depth of the coal and the bottom of the bottom plate of the coal seam is the largest (16m).From the stress distribution of the bottom layer of in 8# coal seam as the upper protective seam, Stagger arrangemengt roadway layout without coal pillar mining protection layer, The pressure relief effect of the bottom plate is better, And pressure relief effect at the part of the overlap between the adjacent working surface is also achieved, To ensure the full and continuous discharge of the protective layer along the direction. While leaving coal pillar is the opposite, First of all, it affects pressure relief in the floor strata after the mining area. And below the coal pillar of retention present the stress concentration, Effecting the pressure relief effect at the base plate of the connection, The protected layer can not achieve full and continuous discharge pressure.Numerical simulation through FLAC3D, It is considered that the layout of the fault in Stagger arrangemengt roadway layout is more favorable to the full and continuous pressure relief of the protective layer. The distance between 9# and 8# is 9m, Floor damage range in 12-16m, Therefore,8# coal seam is feasible to be used as the upper protective layer of 9# coal seam.The Paper, The characteristics of gas emission, gas accumulation in 8# coal seam, and the technology of coal and gas were studied, obtaining the following conclusions:(1) After calculation, In the process of 8# coal seam mining, the gas emission in the coal seam accounts for 67.2%, the gas emission in the adjacent layer accounts for 32.8%.(2) FLUENT simulation of gas accumulation in the 8# coal seam mining area is carried out, In the process of 8# coal seam mining, the gas concentration is high, and the gas drainage measures need to be worked out. And especially high concentration of gas from the return aircourse over 30-40m should is an important area for gas drainage.(3) The characteristics of the Mined out area of 8# as protective layer and the destruction of the floor strata in the mining area, In this case, the arrangement of the first mining and continuous working face of the fault zone is arranged on the base of the ground drilling hole and the bottom layer.The paper obtains the following innovation points:(1) The calculating formula of the damage depth of the bottom plate is derived:On the basis of the criterion of judging the depth of floor failure, The destruction depth of the bottom plate in the three cases of coal pillar, Leave a roadway protection coal pillar,gob-side entrydriving and no pillar lap is analyzed, and the different damage conditions of the bottom plate of the three cases are obtained.(2) At the same time, further to Stagger arrangemengt roadway layout without coal pillar working face floor lap damage depth correction, The damage depth of the bottom plate caused by Stagger arrangemengt roadway layout without coal pillar in the mining area is the result of the failure depth of the floor:Analysis of formula discovery, Stagger arrangemengt roadway layout form the destruction of the two ends of the lap joint working face deep than leaving coal pillar mining in large damage depth of the working face ends, And the adjacent joint working face floor there is a broken zone, The sides of the overlapping working face of the fault zone will produce a greater depth of rupture zone than that of the coal pillar. The discharge pressure of the protective layer is favorable, and the two sides should be used as the area of long-term gas drainage.(3) Combined with the characteristics of Stagger arrangemengt roadway layout, For the transverse crack in the stope.During the first mining face mining, the overlying strata collapse and fall, forming the "O" type ring, During the exploitation of the next working face, the coal pillar, the overlying rock caving zone and the first working face form a whole, Along with the increase of the working face, the form of the whole mining area is "O-L-O" type.(4) The pressure relief of the protective layer on the protection layer of the coal pillar in different dimensions is studied and the corresponding partition of the coal pillar is found. On the basis of the theory of catastrophe theory, the reasonable size of coal pillar in coal pillar is derived. It is believed that the possibility of the occurrence of a sudden change in the yield of the coal pillar is more than 88% of the coal pillar. From the point of view of the full release of the protective layer, the occurrence of the coal pillar is determined to be a catastrophe and damage to the continuous and sufficient discharge pressure of the protected layer. In order to guarantee the production, the time of the coal pillar when destroyed is given, and the reasonable speed of the working surface is given, the size of the coal pillar is as follows; a=|25mξ22flnfR+kt/kt[1+f(1/ξ-1)ctgφ]|The following formula for the time of the coal pillar to remain stable: t=η/ElnE+λKdHaL=25mξL/22flnfR+kt/kt[1+f(1/ξ-1)ctgφ]η/ElnE+λ/Kdm(5)The characteristics of the collapse of 8# protective layer and the failure of the floor strata in the mining area of the fault zone,In this work,a multiple working surface is formed.which is used to solve theformation of a coal pillar without coal pillar,which is based on the layout of the ground hole and the hole in the protective layer.In this paper,the development of fracture development,unloading effect and the establishment of coal and gas production system of coal pillar and completely non coal pillar are studied.Through theoretical analysis,numerical simulation of FLAC3D and FLUENT three methods,the development characteristics of the fracture development characteristics of the bottom plate of the Stagger arrangemengt roadway layout and the effect of pressure relief are obtained.But only the gas concentration distribution in the goaf is given in FLUENT simulation,and the gas concentration distribution in the gas drainage system and the continuous working surface is not combined,which will be the focus of the next step. |
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