Optimization And Practice Of Key Parameters For Pressure Relief In Gob Side Entry Driving Of Thick Coal Seam

Thick coal seam,as the main coal seam in China's coal mining,the recovery rate of coal resources is low during the mining process and has higher requirements for mining and roadway maintenance technology.Although the technology of driving along the goaf can effectively improve the coal recovery rate and shorten the maintenance time of the tunnel,it is often faced with problems such as large impact of dynamic pressure,high concentration of stress in the surrounding rock and coal pillar of the tunnel,and serious development of joint fissures.However,presplitting blasting is an effective way to solve this problem.As a technology of presplitting in advance of the roadway roof,presplitting blasting has outstanding advantages in shortening the cantilever beam length of the roof,reducing the stress concentration of the surrounding rock and coal pillar of the roadway,and the rationality of the selection of the key technical parameters of the presplitting blasting has an important impact on the effect of presplitting and top unloading.Therefore,by means of numerical simulation,laboratory test,similarity test,theoretical analysis and field industrial test,the key technical parameters of roof fracturing and pressure relief for pre splitting blasting are systematically studied from the aspects of the law of rock caving deformation,the characteristics of underground pressure and the effect of pressure relief.The following results are obtained:(1)The physical and mechanical parameters of uniaxial compressive strength,tensile strength,material density,cohesive force and internal friction angle of coal samples are obtained through laboratory tests;(2)The numerical simulation calculation model of different cutting angle and height is established,the stress concentration degree of surrounding rock and the law of roof collapse in goaf are analyzed,and the reasonable range of cutting design parameters is determined;(3)A similar simulation test model for roof cutting and pressure releasing along goaf was established,and the influence rule of roof cutting height and angle on roof overburden collapse,roof stress distribution and stress concentration of coal pillar was analyzed.The principle of presplitting blasting and the mechanism of crack forming are studied,and the range of crack expanding area in directional blasting is given.Combined with similar simulation test and stress wave monitoring,the change of stress wave in directional and undirected presplitting blasting is analyzed,and the optimum range of blasting hole spacing is determined;(4)The principle of pre-splitting blasting and the mechanism of crack formation are studied,and the scope of the area of directional crack propagation is presented.The amplitude range of stress wave is analyzed according to similar simulation test and stress wave monitoring,and the best scope of blasting hole spacing is determined;(5)Based on the theoretical analysis,numerical simulation and similar test,the reasonable range of the key technical parameters of roof cutting and pressure relief is studied.Combined with the geological conditions of the test section,the roof cutting and pressure relief scheme of the gob side entry in thick coal seam is designed,and the field engineering practice is carried out.Through drilling peep and roadway displacement and deformation monitoring,it is concluded that the selection of key technical parameters for roof cutting and pressure relief is reasonable and the implementation effect of the scheme is significant,which further verifies the reliability of the research results in this paper.There are 51 papers,7 tables and 81 references.