Research On Optimization Of Key Parameters Of Cutting-top Relief Pre-splitting Blasting In Roadway Remaining Along Goaf

At this stage,our country's demand for coal resources is still very large.The mining of coal seams is shifting from shallow to deep.With the increase in coal seam depth,the fully mechanized mining face has increased,and the goaf roof is hard but cannot collapse in time.The emergence of these phenomena will cause a series of problems such as rock burst,large roadway deformation,gas explosion,casualties and so on.In order to solve these problems,cut-top blasting technology is used to cut off the stress transfer between the roof of the goaf and the roadway,so that the roof can collapse in time,so as to maintain the stability and safety of the roadway,improve the economic efficiency of coal mining,and avoid accidents such as casualties.The key to top-cutting blasting technology lies in the selection of blasting parameters.Reasonable blasting parameters can achieve a multiplier effect with half the effort.T herefore,based on the track along the 3307 working face of Shanxi Tang'an Coal Mine,this paper conducts detailed analysis and research on key blasting parameters through theoretical analysis,experimental analysis,and numerical simulation analysis,and finally achieved the following results:(1)Through the analysis of the pressure equivalent of the roof of the roadway in the 3307 working face of Tang'an Coal Mine,it is judged that the roof belongs to the category with strong mineral pressure,and the necessity of cutting roof pressure relief is determined;in order to achieve the purpose of cutting roof pressure relief and Determine the reasonable range of blasting parameters,analyze the results of the previous cutting-top blasting test,and conduct detailed research from the angles of top and bottom plate deformation and bottom drum deformation.Finally,it is concluded that the length of the blast hole is greater than 22m,and the length of the charge is greater than 12m.The main key layer can be completely cut off;the sealing hole length is less than 6m,and the sub-key layer can be effectively cut off and the deformation of the top and bottom plates can be reduced;the line charge density is less than 2.29kg/m,and the single hole charge is less than 13.7kg.The diameter of the hole is less than 75mm and the diameter of the charge is less than 55mm.Only in this way can the explosive resources be effectively used.Under the premise of achieving the expected blasting effect,the cost can be reduced and the economic benefit can be improved.(2)Through theoretical analysis and calculation of reasonable blasting parameters,that is,when the blast hole length is 25m,the main key layer is completely cut off,and the top coal and roof gangue completely fill the goaf,which can effectively support the overlying strata and maintain the roadway Stable and safe;when the sealing hole length is 5m and the charge length is 20m,the sub-critical layer is completely cut off,so as to meet the purpose of keeping the roadway along the goaf,cutting the roof and reducing the pressure;the line charge density is 0.45kg/m,single-hole charge When the weight is 9kg,the blasting effect is achieved and the cost is saved;when the blasthole spacing is 880mm,the perforated pre-cracked surface is formed while the surrounding rock is less damaged,which can maintain the stability and safety of the surrounding rock;due to theoretical analysis of the blasthole wall The initial pressure peak and the quasi-static pressure are much larger than the compressive strength of the rock.When the hole wall is crushed and damaged,it will cause energy loss.Therefore,the optimal blast hole spacing should be smaller than the theoretical value.(3)The numerical simulation software ANSYS/LS-DYNA is used to study and analyze the influence of the blast hole spacing on the top-cut blasting effect,and determine the optimal blast hole spacing.By simulating the blasting effect of different blasthole spacing(500mm,600mm,700mm,800mm),and then conducting detailed analysis from three aspects:the compressive stress cloud diagram,the change law of unit effective stress with time,and the development and expansion of cracks,it is finally determined When the blast hole spacing is 700mm,it is relatively close to the theoretical calculation results,which proves the reliability of the theoretical calculation parameters.At the same time,the cut-top blasting effect has reached the ideal state,that is,the crack has no effect on the supporting system,and the blasting has little damage to the surrounding rocks.The crack penetrates to form a pre-cracked surface,which realizes the purpose of cutting roof and pressure relief while saving costs,improving economic benefits,and maintaining the stability and safety of the roadway.(4)Through the analysis of the results of the field blasting test,under the premise of the optimal blasting parameters,the moving distance of the top and bottom plates is about 190mm,and the moving distance of the two sides is about 50mm.Compared with the uncut roof,the blasting parameters are selected this time.As a result,the approaching amount of the roof and floor was reduced by about 71.2%,and the approaching amount of the two sides was reduced by about 64.3%,and the effect of pre-splitting blasting along the goaf was obvious.It can be seen that this research has solved the problems of high roof pressure,strong mining pressure,rock burst,coal and gas outburst,large roadway deformation,and casualties.The research results on the optimization of key parameters of pre-splitting blasting are not only for this The mine provides technical support and also provides a certain reference value for mines under similar conditions.