Experimental Study On Mechanical Seepage Characteristics And Acoustic Emission Characteristics Of Gas Bearing Coal Under The Influence Of Mining

Coal has always been the largest part of China’s energy production.In recent years,with the increase of the demand for coal resources in the national economic construction,and the distribution characteristics of China’s coal resource reserves are more in the West than in the East,In the future,the northwest region will become an important place for coal mining,especially in Xinjiang.In recent years,with the increase of coal mining intensity and depth in Xinjiang,the phenomenon of gas,coal and rock dynamic disasters in the working face is increasingly prominent.Due to the influence of mining,the stress distribution of coal and rock mass is redistributed,and the mechanical and gas permeability characteristics of coal and rock mass are changed.In this paper,the micro structure of coal sample is studied firstly by experimental method,and the pore connectivity of experimental coal sample is mastered;secondly,the experimental system of gas bearing coal seepage and acoustic emission is composed of triaxial creep seepage adsorption desorption experimental device and acoustic emission monitoring device.According to the stress path of coal under the influence of mining stress,Under the condition of closed pressure,different initial axial pressure is applied.The axial pressure is first increased and then the closed pressure is released.At the same time add axial pressure and release confining pressure under different initial axial pressure,at the same time add axial pressure and release confining pressure,under the condition of different gas pressure,the mechanical characteristics,seepage characteristics and acoustic emission characteristics of gas bearing coal are tested and studied.The main results of this paper are as follows:(1)Through SEM observation,it can be seen that there is a small amount of mineral filling on the surface of the coal sample in mining area,and some holes and fractures are connected with each other;through NMR experiment,it can be seen that the average porosity of the three coal samples is 1.41%,the average movable fluid saturation is 56.65%,and the connectivity between the holes is good,which is easy to flow and transport gas in the coal body,and the overall permeability of the coal sample is relatively good ok.(2)The compressive strength and deformation of gas bearing coal are related to the loading and unloading conditions as follows: under different initial confining pressure conditions,the compressive strength of coal sample increases with the increase of initial confining pressure;under different gas pressure conditions,the compressive strength of coal sample decreases with the increase of gas pressure;when the pressure of Watts increases from 1MPa to 2MPa and 4MPa,the compressive strength of coal sample decreases from 46.15 Mpa to 45.87 Mpa.44.62 Mpa indicates that the larger the adsorbed gas pressure is,the more serious the expansion deformation of the coal sample will be after the adsorption saturation,which will increase the brittleness of the coal sample and reduce the compressive strength;at the same time,under the condition of adding axial pressure and releasing confining pressure,the radial direction of the test coal sample at the time of instability and failure should change greatly,which indicates that the failure of the coal sample is more severe and the internal damage is more serious under this path.(3)Under certain gas pressure,the permeability of coal sample decreases exponentially with the increase of initial axial pressure and confining pressure.In the unstable process,the minimum permeability decreases exponentially with the increase of initial axial pressure and confining pressure;The lowest permeability of coal sample under constant axial pressure and confining pressure relief occurs at the unloading point;at the same time,the lowest permeability of coal sample under axial pressure and confining pressure relief occurs In the yield stage of the stress-strain curve,the larger the initial axial confining pressure is,the smaller the lowest value of permeability is when the coal sample is damaged;when the initial axial confining pressure is 16 MPa and the gas pressure is 1MPa,2MPa and 4MPa respectively,there is no obvious Klinkenberg effect.At the same time,the permeability of the coal sample with axial pressure and the lowest value of permeability in the process of instability and failure are all with the gas pressure the increase is in the form of quadratic polynomial function.(4)Comprehensive analysis of the characteristics of acoustic emission in the process of gas bearing coal failure under different loading and unloading experimental paths shows that the precursory information point of coal failure is roughly between85.5% and 92.6% of compressive strength,which can be used as the precursory information to predict the instability of coal failure in advance.