Research On Evolution Rule Of Fracture Field And Application In Close Distance And Inclined Coal Seam Mining

Close distance coal seams are widely distributed and rich in resources in China.However,due to the small spacing between the coal seams at close distances and the comprehensive mechanization of the coal seam working face,the propulsion speed is accelerated.Whether it is single mining or repeated mining,some damage will be caused to the surrounding rock to form the mining fracture field.the fracture not only have an impact on the stability of roadway surrounding rock,but also a channel for groundwater and gas migration.In particular,the majority of coal seams in Guizhou Province,coal mine geological factors,coal seam occurrence and characteristics are more complex,roof accidents,water seepage accidents and gas outbursts or gas explosions and other disasters occur.Therefore,this paper combines the actual geological profile of a coal mine in Tongzi of Guizhou Province and the 20701 mining face,through the combination of mining engineering,rock mechanics,numerical simulation and other multidisciplinary theories,using field investigation,theoretical analysis,numerical simulation.The combined method is used to study the fracture field of coal seam mining to analyze the failure mechanism of surrounding rock of the roadway.According to its failure mechanism,it puts forward reasonable suggestions for the surrounding rock control of the roadway and strengthens the stability of surrounding rock of the roadway.The details are as follows:(1)After the mining face of the close distance and inclined coal seam is mined,the stress concentration zone appears on both sides of the coal seam working face,but the vertical stress in the lower part of the working face is much larger than the working face of the coal seam;With the continuous propulsion of mining work,due to the different physical and mechanical parameters of each rock layer,the overburden began to appear to be bent and sinked until the advancing distance exceeded the ultimate strength of the overburden,the overlying strata were reached when the ultimate gradient of the rock was reached.At the same time,the fallen overburden lost its continuity.The overburden rock on the side of the coal wall and the coal pillar in the gob was respectively forced to form a cantilever beam structure,thus on the side of the coal pillar and the gob.Form a triangular-like spatial structure--"triangular closed" structure.(2)On the one hand,the monitoring results of the roadway section indicate that the mining roadway of the semi-coal-rock mining in the inclined coal seam is affected by multiple factors,the roadway located in the lower part of the working face is severely deformed in the “triangular closed” structure.Under the condition of the original support scheme,the deformation of the surrounding rock violently reflects three characteristics: the deformation and destruction of the roadway lasts for a long time,the excavation of the section of the mining roadway has undergone many renovations and has adopted various renovation and support methods,but the effect is not obvious;the deformation of the top and bottom plates is serious and the surrounding rock on the roadway surface is broken,which is characterized by the sinking of the roof,the bottom heave and the internal squeezing of the two gangs;A large number of failures occurred in the components: the bolts and anchor cables were broken,the trays were separated from the anchor rods,the joints between the steel mesh and the tray were cut.On the other hand,under the existing mining technology conditions,the surrounding rock of the roadway is severely deformed and difficult to control effectively.It is urgent to find an effective roadway surrounding rock control technology.(3)The numerical simulation of the optimization scheme of mining roadway support is carried out,the effect of anchor spray and advanced grouting+anchor-spray composite support is compared and analyzed.advanced grouting+anchor-spray composite support structure effectively reduces the deformation and displacement of the roadway.The grouting is used to reinforce the crushed surrounding rock to improve its own carrying capacity,provide a stable foundation for the anchor,finally the anchor spray zone and grouting area forms a strong bearing-arch together,the weak bearing-arch is formed by the anchor cable zone,which can effectively control the surrounding rock deformation of the roadway.