| In this paper,based on the study of fracture evolution of cumulative sand-carrying blasting,the test prototype is 5 coal of xinjiliuzhuang coal mine of China coal,aiming at the poor permeability of coal seam and the difficulty of gas extraction,the experimental study on anti-reflection technology of cumulative sand-carrying blasting is carried out in order to improve the extraction efficiency.The anti-reflection mechanism of cumulative blasting was studied by theoretical analysis method,and a similar simulation test platform was built in the laboratory to carry out the sand cumulative blasting test.The feasibility and excellence of applying the pressure relief and permeability improvement technology of sand-carrying cumulative blasting to the coal seam with low permeability and high gas outburst are established through comparative analysis.The following conclusions have been reached.Firstly,the anti-reflection mechanism of sand-carrying cumulative blasting is theoretically analyzed by summarizing the research status at home and abroad as well as the classical theories.The factors affecting the generation of fractures include blast wave and stress wave,shaped charge structure,and the effects of blasting gas in different stages of the process of blasting crack propagation.The mechanism of directional fissure induced by cumulative energy-carrying sand blasting is obtained,and the blocking effect of supporting particles on the closure of cracks in cumulative energy-carrying sand blasting is analyzed.Secondly,based on the similarity theory,explosion mechanics and fracture mechanics,a similarity simulation test system was built in the laboratory by investigating the geological conditions of coal seam 5 in liuzhuang coal mine,and the simulation materials and similar ratio were determined according to the strength of coal and rock mass.The ratio of simulated roof is:sand;Cement:gypsum:water=6.3:1.0:0.7:1.1.The ratio of simulated coal seam material is:sand;Cement:gypsum:pulverized coal:water=3.2:0.3:0.9:1.6:1.1.Cement:gypsum:water=6.3:0.9:0.3:1.1.Finally,by using the ratio of the similar material for casting model after curing 28 d blasting experiment was carried out,using the network parallel electrical method meter test before and after blasting internal resistivity model before and after blasting,can draw together with sand blasting is produced by ordinary blasting fracture is more focused on shaped the direction,the direction of the shaped the resistivity changes little;High speed photography can be used to see the evolution process of surface fractures.The fractures generated in the explosion process will become smaller due to the action of dead weight and loading.In addition,cumulative sand-carrying blasting produces a series of main fractures concentrated in the direction of cumulative energy.The strain rate peak value in the direction of cumulative energy was 1.16-1.2 times of that in the direction of non-cumulative energy,which indicated that there were more cracks in the block in the direction of cumulative energy.These three monitoring methods jointly confirm that the cracks generated by cumulative sand-carrying blasting are concentrated in a range of areas in the direction of cumulative energy,which can protect the integrity of the roof and floor while achieving the purpose of anti-reflection,and improve the utilization rate of explosives,thus providing reference for practical engineering application.Figure[59]table[12]reference[94]... |
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