Mechanism Of Pre-Splitting Blasting To Increase Lump Coal Rate In Hard Coal Fully Mechanized Mining Face

In order to improve the lump coal rate of the fully mechanized mining face in hard coal seams,with the Liangshuijing 42110 working face as the engineering background,the formation mechanism of lump coal in the fully mechanized mining face was studied through theoretical analysis,mechanical test,numerical simulation,and field measurement.The cutting fragmentation distribution law,the influence of advanced pre-blasting on lump coal rate,the optimized advanced pre-blasting parameters,and the following research results:(1)A simulation method for cutting the coal wall by a drum shearer is proposed.Use mechanical tests to determine the macro-mechanical parameters of the coal in the working face,use trial and error to calibrate the simulated meso-parameters,establish a numerical model of initial coal wall cutting;analyze the formation mechanism of lump coal under the action of drum cutting,and monitor the coal mining process According to the distribution law of the cutting force of the drum,a monitoring method for lump coal under simulated conditions is proposed.(2)The influence of advanced blasting and pre-splitting of working face on the distribution of cutting fragments is analyzed.Using the infinite medium theory,the relationship between the respective ranges of the cavity,broken zone,fracture development zone,and elastic zone after blasting and the blasting energy,the characteristics of energy dissipation,frequency,and vibration amplitude of the shock wave in each zone,and the impact of blasting in the coal body are analyzed.The relationship between the range and the lateral pressure coefficient;the influence of the advanced abutment pressure on the secondary expansion of the fracture after blasting is analyzed,and the correlation between the increase in the lump coal rate and the development range of the fracture is finally obtained.(3)The evolution of fractures in the working face under the combined action of advanced blasting stress and abutment pressure was studied,and the characteristics of the smaller the explosion power required for the less boundary conditions to produce penetrating fractures;the establishment of different filling amounts and different blasthole spacing The multi-hole blasting scheme of the blasting method obtained the change in the number of fractures in each scheme;it was concluded that the change in the action time of the leading support pressure had little effect on the increase in the number of prefabricated fractures.It is concluded that the number of generated fissures is gradually decreasing,and the new fissures mainly exist between the two blastholes.(4)The parameters of advanced pre-splitting blasting were optimized,and it was concluded that after the coal blasting pre-splitting,the change of the cutting force of the drum became smaller and the frequency increased;after the drum was cut,the proportion of 30～80 mm lump coal increased with The blast hole spacing becomes larger,first increases and then decreases;the reduction of coal content larger than 80 mm gradually decreases with the increase in blast hole spacing;the optimal solution is determined to be 1.2 kg explosive charge and 3.5 m gun Hole spacing plan: The consumption of drum picks after blasting is significantly reduced after field practice statistics.The paper has 68 figures,13 tables,and 102 references.