Study On The Variation Law Of Coal Sample Resistivity Under The Conditions Of Immersion,Heating And Loading

High-temperature oxidation of coal pillar not only causes serious waste of coal resources,but also threatens the personal safety of underground operators.The conventional measures to prevent high-temperature oxidation of roadway coal pillar include grouting,grouting to isolate air,spraying sealing materials,reinforcement and plugging,water injection and cooling,etc.The high-temperature oxidation of coal pillar is highly concealed and difficult to control.Conventional prevention and control methods couldn’t be applied to the automatic monitoring and prevention of hightemperature oxidation of coal pillar.This paper mainly studies the change of coal sample resistivity under water immersion,heating and loading conditions,which lays a foundation for controlling the water injection by monitoring the change of coal pillar resistivity and realizing the automatic prevention and control of coal pillar high-temperature oxidation.In order to explore the change of resistivity of coal samples under water immersion,heating and loading conditions,taking the long flame coal of Chuancaogedan coal mine and anthracite of Sangbei coal mine as the research objects,the change characteristics between resistivity and water immersion(water injection)time,temperature,load and test frequency were analyzed by means of literature review,theoretical analysis,experimental research and simulation.The distribution characteristics of resistivity under the coupling action of temperature and moisture content in coal pillar are simulated.The results show that:(1)The test frequency is one of the important factors affecting the resistivity of coal samples.With the increase of test frequency,the variation range of resistivity decreases,ρ(100Hz)>ρ(120Hz)>ρ(1k Hz)>ρ(10k Hz)>ρ(100k Hz).With the increase of water immersion temperature,the overall resistivity of long flame coal and anthracite is consistent,ρ(25℃)>ρ(40℃)>ρ(55℃)>ρ(70℃).There are great differences between long flame coal briquette and raw coal,and the regularity of resistivity change is weak under the condition of soaking and heating of raw coal sample,The resistivity of long flame coal briquette will surge or peak under the condition of high-temperature immersion and heating at 70 ℃ and 85 ℃,and the overall regularity is poor.In the immersion heating experiment,the electrical resistivity of anthracite raw coal and shaped coal shows an "L" downward trend,and its resistivity is negatively correlated with the immersion time,and its overall variation regularity is better than that of long flame coal.(2)In the process from continuous loading to coal sample crushing,the deformation of coal sample was divided into four stages.In the process,the resistivity values of unsaturated coal sample and saturated coal sample show three stages: overall sudden drop,steady decrease and sudden increase.(3)Combined with the experimental results of water immersion and heating of long flame coal,the variation characteristics of resistivity in long flame coal pillar during high temperature oxidation and water injection were simulated by COMSOL.The simulation results show that the central heating source inside the coal pillar will continue to rise and expand,and the internal resistivity will gradually increase from the center to the outside.In the process of high temperature oxidation treatment by micro pressure(0.02 MPa,0.04 MPa and 0.06 MPa)water injection,the resistivity at the water injection hole,the central heating point and the intersection of the two fields is small;Located at the edge of coal pillar floor,the resistivity is the largest;The overall resistivity of coal pillar conforms to the characteristics of high water head pressure,high water content and lower resistivity,ρ(0.02MPa)>ρ(0.04MPa)>ρ(0.06MPa).(4)By analyzing the change of resistivity of observation points in the simulated coal pillar,it is found that the change trend of resistivity conforms to the downward trend of "L" type exponential function,and the change characteristics of resistivity are consistent with the change law of electrical resistivity of long flame coal briquette and anthracite coal during the experiment.The simulation results provide guidance for the automatic control of high temperature oxidation of coal pillar by monitoring the change of coal pillar resistivity and realizing water injection.This paper has 59 figures,8 tables and 74 references.