| Coal body gas pressure,ground stress and mining stress are the key factors affecting the safety and stability of deep mining.In order to systematically study the evolution characteristics of coal body physical field under gas pressure and stress conditions,taking a coal mine in Pingxiang City of Jiangxi Province as the research background,laboratory physical simulation tests were carried out.Combined with the physical and chemical properties of coal,similar material physical simulation,similar physical model,Origin data processing and multiple linear regression analysis,MATLAB numerical analysis and processing and other means,a large true triaxial physical simulation test platform was used to carry out physical simulation tests on the influence of cyclic stress on coal seam parameters under different initial gas pressure conditions.The evolution characteristics of gas pressure,coal seam strain with the number of cycles and gas pressure are studied.(1)According to the stress distribution law in front of mining face under caving coal mining and the empirical formula that the stress changes with the buried depth,the physical similarity ratio is obtained.The true triaxial physical simulation test equipment is used to carry out tests on the evolution characteristics of coal parameters and the law of coal seam gas migration under cyclic stress.(2)Through the cyclic loading and unloading test,the gas pressure change process of each position in coal body under the initial gas pressure condition of 1MPa was studied.The results show that the gas pressure of coal seam decreases under the action of stress.In the loading stage,the strain and gas pressure of coal seam increase with the increase of stress.In the unloading stage,the strain and gas pressure of coal seam decrease gradually.During the whole cycle process,the migration and enrichment law of gas molecules is as follows: from the stress variation zone to the original stress zone and stress concentration zone.(3)The change rate of gas pressure on the measuring point,section line,main layer and main vertical plane was analyzed.It was concluded that the change rate of gas pressure was the largest in the first loading stage,then the change rate of gas pressure first decreased and then increased,and finally the change rate of gas pressure gradually stabilized.In the longitudinal section line,the change rate of gas pressure increases first and then decreases,while in the transverse section line,the change rate of gas pressure decreases first and then increases.In the unloading stage,the change rate of gas pressure decreases from left to right on the main longitudinal plane and main plane.The change rate of coal gas pressure at each measuring point first decreases and then increases with the increase of the number of cycles.On the main level,the change rate of gas changes from "convex" shape to "concave" shape with the change of the number of cycles.(4)By comparing the gas pressure evolution law of 0.5MPa,0.75 MPa and 1MPa initial gas pressure,it is concluded that the greater the initial gas pressure is,the greater the increase of gas pressure in the loading process.At the same time,the reduction of gas pressure in unloading process is larger.In the loading stage,under the initial gas pressure condition of0.75 MPa,the change rate of gas pressure is the highest,while that of 0.5MPa is the minimum and has a negative growth.(5)The multiple linear fitting formula of the number of cycles and the change of gas pressure is obtained,and the distribution of gas pressure in each section,plane and longitudinal plane is obtained by MATLAB numerical analysis. |
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