Research On Response Law Of ULF Electromagnetic Radiation Monitoring Coal Seam With Impact Proneness

With mining depth increased, coal and rock dynamic disaster frequencyincreasing year by year, it is necessary to have an early warning before disasteroccurred. Conventional electromagnetic radiation technology has been widely usedin monitoring coal and rock dynamic disaster. But there are limitations in itsmonitoring distance and anti-electromagnetic interference. The ultra-low-frequency(ULF) electromagnetic radiation with long propagation distance and stronganti-interference ability can make up for the deficiencies of conventionalelectromagnetic radiation. Through theoretical analysis and field testing, papersresearched ULF electromagnetic signals response to the mine rock stress duringexcavation, studied the coal and rock stress concentration in time and spatialdistribution characteristics, analyzed the ULF electromagnetic radiation responsecharacteristics of stress relief measures, revealed the ULF electromagnetic radiationprecursory law before the occurrence of strong stress relief. These all has importantpractical significance in ULF electromagnetic radiation applying to forecast the coaland rock burst in instability coal seam with impact tendency.Main findings:(1) ULF electromagnetic radiation has good response to stress distribution ofcoal roadway during mining. Coal and rock stress in different regions can bereflected by ULF response characteristics in space and the stress trend of some areasvaried from time (mining progress) can be also reflected by ULF responsecharacteristics in time. Compared with conventional electromagnetic radiation, ULFhas a certain advance in response to coal stress concentration.(2) ULF electromagnetic radiation has certain response characteristics aroundwater injection and pressure relief measures carried in impact coal seam, which canreduce the coal stress concentration. With the implement of coal water injection, theintensity of ULF showed a decreasing trend, and it has a positive correlation withthe index changes of drill cuttings. The intensity of ULF fluctuates at a high levelbefore blasting, then a sudden decrease and stabilize a period, sudden growth, thenslow down to a lower intensity and stabilize for a long time. The coal-gun occurredwhen relief measures are not completely reducing the stress concentration; theintensity of ULF will show a sudden increase in trend.(3) The intensity of on-line ULF electromagnetic will present obvious precursor law, the performance of “up-down” and “up-down-up” trend, before a sudden stressrelief occurring in coal and rock.(4) Compared with conventional electromagnetic radiation, ULFelectromagnetic radiation has a better anti-interference ability. Their intensityresponse to the electromagnetic interference in mine roadway shows a decreasingtrend with increasing test distance, but the ULF can avoid mechanical and electricalinterference in a relatively close range, in particular, can better avoid the effects ofhigh frequency electromagnetic interference waves. The main frequency response ofULF and conventional electromagnetic radiation to cables and running injectionpumps respectively concentrate in3kHz,1.3kHz and45kHz,5kHz.