Study On Law Of Fracture Development Around Borehole In Soft Coal Seam

In this paper,the coal briquettes with different water content in a soft coal seam are used to prepare the briquette with different water content.The simulation experiment,theoretical analysis,numerical simulation and field test are used to study the stress and strain of the single axis of water content,the distribution of the cracks around the borehole and the development law.In order to prepare the briquette and carry out the simulation experiment of the coal seam drilling,combined with the numerical simulation experiment,the development of the cracks around the borehole in the drilling process is simulated,and the distribution of the cracks and the law of the development in the drilling process are analyzed.Finally,the suitable sealing method is verified through the field gas measurement.In order to improve the accuracy of gas pressure measurement and reduce the occurrence of gas dynamic disasters.The main research results are as follows:（1）According to the theory analysis and experiment,the molding coal mould is designed and prepared.On the basis of the experience of preparing the briquette by the predecessors,through the laboratory experiment,the molding pressure,the binder and the particle size ratio of the different water content briquette are obtained.（2）Using YAD-2000 type micro electro-hydraulic rock pressure test system,the mechanical properties of briquette were tested,and the mechanical properties of briquette were obtained.（3）Similar simulation experiments on coal seam drilling of different water content briquettes are carried out,and RSM-SY5 geotechnical instruments are used to test the sound waves of briquettes before and after drilling and after grouting,and the fracture development of different water content briquettes is obtained.（4）The distribution of the fracture is observed by extracting the surrounding fracture of the borehole and analyzing the distribution law of the crack.The length of cracks around boreholes is mainly within 5mm.The number of cracks around the hole increases first and then decreases with drilling.（5）Using the FLAC^3D numerical simulation software,the process of the surrounding rock of the hole in the drilling process is destroyed and the fracture process is simulated.The software is more accurate to reflect the distribution of the crack in the borehole section in the simulation experiment;the numerical simulation is more accurate to simulate the distribution of the crack in the coal body around the borehole;and the numerical simulation experiment is carried out.The fracture around borehole varies with water content of coal,and the water content is 6%.The development of fractures around the coal body is weak,and the fracture development of coal with 12%moisture content is strong.