Damage Mechanism Of Tectonic Coal And Its Role In Protrusion

As a serious underground sudden disaster,coal and gas protrusion accident has caused a large number of casualties and huge property losses.A large number of studies at home and abroad have shown that there is a close relationship between tectonic coal and coal and gas protrusion.This thesis selects tectonic coal as the main research object,takes the mechanical damage characteristics of tectonic coal as the main research content,uses the knowledge of elastoplastic mechanics,rock fragmentation,adsorption theory,pore correlation theory and other related knowledge,uses linear fitting,separation of variables and other mathematical methods,studies the microscopic pore characteristics of tectonic coal,adsorption and desorption characteristics,damage characteristics of coal particles under cyclic loading and unloading and damage characteristics under triaxial compression The relationship between tectonic coal and coal and gas protrusion was comprehensively demonstrated by combining the fracture characteristics of the protruding coal body and the influence of desorbed gas on protrusion.The main conclusions obtained are as follows:1)According to the test results of pore characteristics by low-temperature N₂adsorption method and low-pressure CO₂ adsorption method,the pore volume of tectonic coal is 67.17×10^-3cm³/g,which is about 39%higher than that of native coal;the specific surface area of tectonic coal is 136.343m²/g,which is about 27%higher than that of native coal,among which the difference of diffusion pores is the largest,and the pore volume and specific surface area of tectonic coal are about 2.75 times and6.08 times of the native coal.The fractal dimension of the tectonic coal is 2.787 and2.438,which is higher than that of the native coal 2.569 and 2.352.The destruction/pulverization during the formation of the tectonic coal has modified the microscopic pores in the coal,so that the tectonic coal has more developed microscopic pores compared with the native structural coal.2)According to the test results of 120min desorption,the gas desorption amounts of tectonic coal in the first 30s,60s and 90s under different gas pressure are higher than that of the native coal,in which the first 30s tectonic coal is 4.4-5.7 times of the native coal,the first 60s tectonic coal is 4.6-6.4 times of the native coal,and the first 90s tectonic coal is 3.1-4.1 times of the native coal.The corresponding gas desorption rate is much larger than that of the native coal,in which the average gas desorption rate in the first 30s at 1 MPa is 6.84 times higher than that of the native coal.The initial gas desorption ability of the tectonic coal is much stronger than that of the primary coal,which makes the tectonic coal can release a large amount of gas in a short time and promote the development of the protrusion process.3)According to the fitting results of strength and elastic modulus parameters of coal particles,the strength and elastic modulus of tectonic coal particles under the same particle size are much smaller than those of primary coal.According to the results of the determination of the crushing specific work of coal particles,the crushing specific work of primary coal is 1075.26J/m²,which is about 19.7 times of that of the construction coal.According to the settlement results of protrusion accident data,the upper limit of crushing specific work for protrusion occurs is 9.44-299.99J/m²,and only the crushing specific work of tectonic coal meets this range.Under the same external force conditions,the deformation and damage of the tectonic coal are more likely to occur.The crushing ratio work of the structure coal is much smaller than that of the primary coal,and the energy consumed by the crushing of the structure coal is less,and it is more likely to be crushed or pulverized,and only the crushing ratio work of the structure coal meets the conditions of coal and gas protrusion.4)According to the results of mechanical characteristics analysis under triaxial loading,the peak strength of primary coal is much larger than that of tectonic coal,which is about 2.3-7.6 times of that of tectonic coal under the same circumferential pressure.The cohesive force of the native coal is 4.307MPa,which is about 11.5 times of that of the tectonic coal,and the internal friction angle of the native coal is 44.58°,which is about 33.4%higher than that of the tectonic coal.The modulus of elasticity of primary coal is about 6.8 to 18.8 times higher than that of tectonic coal under the same circumferential pressure.Compared with about primary coal,tectonic coal reflects the characteristics of low strength and weak bonding,and the resistance to deformation of tectonic coal is weaker,which is more prone to damage and destruction under triaxial conditions and provides favorable conditions for the development of protrusion.There are 54 figures,28 tables and 126 references in this thesis.