Numerical Simulation Study Of Static Expansion Agent Cracking Low Permeability Outburst Coal Seam

At present,coal is still the main energy source in my country,and coal mining continues to extend to the depths.In the face of low-permeability outburst gas-containing coal seams,gas disaster prevention has become a governance problem.Gas drainage is one of the main measures for gas prevention,but traditional gas drainage Caving technology has poor effect on outburst coal seams with low permeability.Therefore,research on a new type of anti-reflection technology is carried out on the traditional anti-reflection technology.According to the application principles of static expansion agents in stone mining,open-pit slopes,buildings,etc.,a new idea of using static expansion agents to crack low-permeability outburst coal seams is proposed.The thesis adopts a combination of theoretical analysis,experimental research and numerical simulation.Based on the theory of static expansion agent action mechanism and fracture mechanics of fractured holes,the paper systematically studies the crack change rules under different hole layout methods,and establishes the The experimental models under different hole spacing and row spacing,and the particle flow discrete element software is used for numerical simulation research.The main research results are as follows:(1)Combining the rock-breaking mechanism of static expansion agent,elastoplastic mechanics and fracture drilling to conduct mechanical analysis of fracture development.Theoretical analysis shows that: the single-hole fractured cracks extend along the direction of the minimum resistance surface,generating 3-4 main cracks.When the multiple holes are broken,the expansion pressure generated by each hole interacts,and the expansion pressure is superimposed on the line of the hole axis.(2)A physical experiment platform with internal dimensions of 1500 mm×1500 mm×1500 mm was established,and different schemes were designed to analyze the crack development law of static expansion agent cracked coal by free surface,borehole diameter and hole spacing.The experimental results show that the more free surfaces in the coal,the larger the pore size,the smaller the hole spacing,the more the number of cracks,the shorter the cracking time of the expansion agent,and the more penetrating cracks;the control holes are controlled on the basis of one expansion.Expansion agent is injected to expand the coal sample for a second time,and finally a large number of cross-fracture networks are formed between the boreholes.(3)Based on the results of physical experiments,with the help of discrete element theory and PFC2 D for numerical simulation,the dual-hole expansion model and the short-term blasting model were established,and the influence of the hole spacing in the double-hole expansion on the development of cracks and the stress changes around the borehole were analyzed;Based on the millisecond blasting model,different schemes are designed to study the influence of hole arrangement and diameter on the cracking effect.The results show that the stress around the borehole is consistent with the generation and attenuation of the swelling pressure,and the closer to the borehole position,the greater the stress peak;the larger the hole diameter,the more conducive to the development,expansion and penetration of cracks.Under the same aperture,the cracking effect of scheme three is the best.The short-distance blasting verified that the implementation of secondary expansion in the physical experiment is beneficial to the expansion and penetration of the cracks,improves the cracking effect of the coal body,and increases the permeability of the coal seam.