The Researches Of The Improvement Of The Mine Transient Electromagnetic Device And Its Application

Shanxi is rich in coal mine in CHINA. The yearly coal output of the Shanxiprovince occupied one in every four of the whole country. For a long time in thefuture,the coal mine would always be the pillar industry in Shanxi.However,with the great amount of the wealth, the mine accident occurredfrequently. So the early warning system for coal-mine security can influence thesafe production of the coal mine seriously. The water hazard has been thebiggest potential hazard next to gas explosion among all kinds of accidents. Insummary, coal mine water early warning system is very important to theproduction of mine industry and the life of coal-miners.At present, a series of techniques has been applied to detect the water thatis harmful for the work under the mine, like the High-density electrical, thetransient electromagnetic method, the seismic reflection method, the radarmethod, TSP advanced prediction method etc. Above all, the coal-minetransient electromagnetic method which developed from the half-space transientelectromagnetic method has been regarded as the best technique to detect lowresistance water. The characteristic of this technique is high resolution, depth ofinvestigation, convenient construction. It was used to make sure the safe of the roof and floor both sides and heading face of Mine tunnel.First of all, we show the rationale basis of the transient electromagnetic andthe difference between the half-space theory and full-space theory. Thehalf-space theory is applied on the ground and the full-space theory is appliedunder coal mine. The mathematical model and the full-spaceresistivity formula and time-depth formula of the full-space theory were allcalculated on the basis of the half-space theory. We calculated thedistribution of the electromagnetic field on the vertical dipole on the surface ofthe boundary of the Two conductors half space and obtained the calculationformula of apparent resistivity that applied in the mine TEM detection.Finally,we got the mine TEM depth estimation formula and depth of offull-space TEM was1~1.5times of half-space.Secondly, we summarized the defects of the transientelectromagnetic devices like the long trailing edge of the pulse and the strongmutual inductance of the transmitter and receiving coils. We designed thecontrol-circuit and the drive circuit and the transmitter circuit to improve thetransmitting device to overcome the defects mentioned above. On the other hand,we selected the induction probe as the receiving sensor to replace the coil toenhance the signal receiving. We introduced the sampling gate of the receivingdevice and the amplitude-frequency characteristic of the probe.Finally, we summarized the hydrogeological condition of the Sitai Mineand designed a series of experiments of geophysical prospecting on some driving faces with water burst risk. We test the system of the mine transientelectromagnetic device and compare the performance of the coil and the probeunder coal mine. The results of experiments show that the improved system canreach the purpose of detecting low resistance water hazard.