| Radium and uranium nuclides are naturally stored in coal bodies,and radon is generated by decaying under the action of jet gas.The study of radon precipitation law during coal sample rupture is of great significance for early warning of coal and gas protrusion and other dynamic disasters.In this paper,the expressions of radon concentration distribution under multi-physical fields were obtained through theoretical analysis,determining the negative exponential decay characteristics of radon concentration with water absorption rate,porosity and pressure gradient.On the basis of analyzing the damage patterns of coal samples containing fissures under different stress paths,the radon precipitation test of coal samples under different loading and unloading stress paths and affecting factors was carried out,which revealed the precipitation law of radon and the sensitivity of each factor during the damage of coal samples with the changes of loading path,water absorption rate,porosity,gas pressure,temperature,etc.A mining integrated radon meter was developed,which can realize the simultaneous detection of radon concentration,gas concentration and temperature in the underground,and applies it in the underground,acquiring the characteristics of radon concentration distribution in different locations of the two lanes of the working face and in different retrieval processes of the working face.The correlation coefficients of radon concentration,gas concentration and temperature were acquired by using gray system theory.The following main research conclusions were obtained:(1)The distribution model of radon concentration in multi-physics field was established and analyzed,and the expressions of radon concentration with porosity,water absorption rate and pressure gradient were obtained.The results showed that: the increase of porosity provided a convenient channel for radon precipitation,and the distance to reach radon equilibrium concentration was farther;the increase of water absorption increased the resistance encountered by radon in the migration process,decreased the distance to reach equilibrium concentration,and decreased the radon precipitation rate;the pressure gradient could make radon reach equilibrium concentration from radon source quickly.The larger the pressure gradient is,the faster the equilibrium will be,but it will not increase the radon migration distance.The above results laid the foundation for the subsequent setting of factors and selection of scheme for radon precipitation test in coal sample rupture process.(2)The radon precipitation tests of coal samples under uniaxial compression,triaxial compression and different loading and unloading paths were carried out to determine the segmental response mechanism of axial stress-strain and radon concentration of coal samples.During the rapture process,the radon concentration increased from the initial concentration to the compression-density stage,and decreased slightly in the elastic stage.After entering the plastic stage,the radon concentration increased rapidly and reached to the peak radon concentration near the peak of axial stress,and the radon concentration tended to stabilize after the destruction of coal samples.(3)Under the triaxial compression stress path,with the increasing circumferential pressure,the radon concentration changes of characteristic point A and characteristic point E appeared monotonic,and the radon concentration at characteristic point A gradually increased with the increase of circumferential pressure.The radon concentration at the characteristic point A gradually increases with the increase of the surrounding pressure.The characteristic point B gradually decreased with the increase of the surrounding pressure,due to the more developed cracks inside the coal sample under the low surrounding pressure.The high surrounding pressure prevented the development,expansion and penetration of the cracks,thus affecting the formation of radon precipitation channels.There is a "jump" in radon concentration before and after the unloading point,and the degree of "jump" would increase with the increase of surrounding pressure.The reason for this phenomenon was that the larger the surrounding pressure was,the more elastic strain energy was released during unloading,the more broken the coal sample was,the more free radon was produced by the gas injection and the precipitation channels were more favorable for radon migration.(4)The radon precipitation test under the influence of multiple factors such as different water absorption rate,pore space,gas pressure and temperature was carried out.Due to the presence of water inside the coal sample,water molecules would reduce the connection between the solid particles of the coal sample,not only reducing the compressive strength of the coal sample but also increasing the radon precipitation rate.The prefabricated holes increased the amount of free radon produced by gas injection,providing a smooth channel for radon migration,which was more favorable to radon precipitation.The effective stress effect of gas pressure on the coal sample and the dilating effect on the fissures of the sample made it more difficult to make the fissures close completely when the external load acted on the inside of the coal body.The expanded fissures provided channels for radon migration with the radon precipitation rate increasing.Due to the structural thermal stress,the damage inside the coal body formed pores,which made the radon concentration increase with the increase of temperature in the initial stage.The radon concentration at the time of coal sample destruction showed a good correlation with each influencing factor.And the sensitivity of peak radon concentration to each influencing factor was ranked as follows: axial porosity>water absorption>radial porosity>gas pressure>temperature.(5)The system hardware structure of the integrated radon meter for mining was developed,and three unit circuits of alpha energy spectrum radon measurement,laser methane measurement and infrared temperature measurement were designed.The intrinsically safe programmable controller was used to realize the integrated control of the three circuits,and the relevant operation and real-time display were carried out through the human-machine interface.(6)The radon concentration at different locations in front of the working face as well as the radon concentration,gas concentration and temperature during each process were measured underground with the developed comprehensive radon meter for mining.It showed that the developed comprehensive radon meter could meet the simultaneous measurement of radon concentration,gas concentration and temperature under the complicated conditions in the underground.Due to the effect of supporting pressure in front of the working face,the closer to the working face,the higher the radon concentration was,and the radon concentration varying with different coal mining processes reached a maximum during the coal cutting.Figure [76] Table [25] Reference [155]... |
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