Study On Measurement Theory And Application Of Roadside Pressure Released Zone Based On Gas Injection

The excavation of the roadway will cause the redistribution of the stress field,and pressure released zone,the stress concentration zone and the original stress zone will be formed in the surrounding rock,in which the fracture in the distressed relief zone is fully developed and the permeability is better.so as to improve the gas extraction efficiency,the depth of the hole sealing hole needs to be more than the pressure relief zone.so as to improve the ratio of gas extraction.the sealing depth of drainage boreholes needs to exceed that of the pressure released zone.Therefore,it is the premise to optimize the borehole sealing technology and improve the gas drainage efficiency by accurately measuring the width of the pressure released zone of the coal rock along the roadway.In this paper,based on the relationship among the coal seam stress,permeability and fracture development,a new pressure relief tape width test method that is drilling gas injection leakage method is proposed.Then,the feasibility of the method and the validity of the test results were verified through the combination of indoor testing,numerical simulation and field testing.The main research results are as follows:(1)The stress-strain permeability test of indoor coal samples was carried out,and the permeability model was established.The experimental results show that in the stage of compression and linear elasticity,because the coal sample is compressed and the porosity and fissure rate are reduced,which resulted in permeability continues to decline.In the stage of plastic failure and residual deformation,a large number of new fractures developed in the coal,and the permeability increased significantly.Based on the experimental results,the influence of crack generation and penetration on the permeability of the yield failure process was considered.The permeability evolution model of the coal body during the whole stress and strain process was established.The model was compared with the experimental results to verify the permeability model.Correctness.(2)Numerical simulation is carried out to study the distribution field of stress and permeability after roadway and borehole excavation.On the basis of the permeability model mentioned above,taking 3118 transport roadway in Xiadian coal mine as the research object,numerical simulation software FLAC~3DD was used to simulate the distribution field of the stress and permeability of the surrounding rock after roadway and borehole excavation.According to permeability and stress state of surrounding rock,it is divided into complete seepage area(reduced stress area),transitional seepage area(plastic enhanced area),seepage shielding area(elastic area)and original rock seepage area(primary stress area).(3)Numerical simulation is carried out to study the law of gas leakage under the condition of borehole injection and gas leakage.According to the testing principle of the borehole gas injection leakage method,and based on the previous numerical calculation model,the distribution of gas pressure and the law of gas injection gas leakage under different drilling depths were obtained by simulation.The study shows that the change of gas leakage speed can better characterize the wide band in the roadside unloading zone.It is proved that it is feasible to use the gas leakage loss method to determine the wide band of the roadside pressure relief zone.(4)A field test is carried out based on drilling gas injection leakage method of the width of the roadside pressure released zone.Taking the 3118 lane of Xia Dian coal mine as the test site,the change law of gas leakage velocity was obtained by using the method of drilling gas injection leakage.The results show that the results of field test are in good agreement with the numerical simulation.that is,with the depth of drilling,the gas leakage rate first drops sharply,then rises slightly,and finally tends to be stable.Finally,the width of the pressure released belt is investigated by drilling cuttings method.The accuracy of the borehole leak volume method is verified by the comparative analysis.