Study On The Distribution And Application Of Mine Transient Electromagnetic Field

Mine transient electromagnetic method has been gradually popularized and applied in many mining areas in recent years. The applied effect, economic performance and social benefits have been acknowledged, but the basic theory, construction technology, data processing and display technique of mine transient electromagnetic method, all that adopt the research production of transient electromagnetic method on the ground. In mining geological conditions, it is said that under the influence of the roadway space, the regularities of distribution of transient electromagnetic field in the full space has not been complete researched at the present time. It is very important that research the influence law of roadway space and metal bodies (double T-iron, rail and metal netting) to the detecting data for transient electromagnetic method data processing and data explanation. The paper made a procedure to simulate the full space transient electromagnetic field, which based on the theory of transient electromagnetic field in homogeneous medium. The main research findings as follow:1) The propagation characteristics of full-space induction field of transient electromagnetic method were researched. The results indicated that the induced current mainly distributed on the surface of the geologic body and the response of transient electromagnetic field mainly reflects the superficial information of the stratums during the early stage. But during the late stage, the high frequency component was absorbed by electrical medium, so low frequency sign was dominant. The mode of transmission of transient electromagnetic fields was mainly diffuse process which reflects the information of the deep stratums.2) The minimal and maximum detecting depth and its influence factors were researched. The results indicated that the acquisition data included not only the useful geologic signal about the aim body, but also the self-induced signal that because of the multi-turn little coils. During early stage, the self-induction signal is stronger than the useful geologic signal. It is difficult to separate the self-induction signal and the shallow stratum signal. Therefore, there is a time range, during which we cannot separate the useful signal, so before this time is the detecting blind zone for transient electromagnetic method, which is the minimal detecting depth. After the attenuation of self-induced signal, the signal is mainly induced signal for vary depths. Because of the energy attenuation, when we cannot distinguish the induced signal of deeper-stratum, which is the maximum detecting depth.3) The mathematical model of the full-space transient electromagnetic fields was established and the finite element numerical simulation method of three dimensions transient electromagnetic field was studied. The concept of area coordinates and cubage coordinates were introduced during the liner interpolation process, which made the design procedure of the mathematical model becomes easier. The memorize technology of ultra-large sparse matrix was studied, which saves the memory and the computation time. Contrasted and analysed the response characteristic of transient electromagnetic field for different models and different parameters. The results indicated that the induced signal of separate loops and overlap loops has the same attenuation laws in the homogeneous whole space, but the field value of former is smaller than the field value of later, which shows that overlap loops has a better sensitivity in the same conditions. The roadway space minished the response value of transient electromagnetic field, but did not change the attenuation trend. When there is a low resistivity body in the medium around the roadway space, the effects of the roadway space shows only in early period. This shows that the superficial layer is affected by the roadway space, and the roadway space is bigger, the effects is stronger.4) Through the physical model experiment, the paper concluded that, when transmission and reception are placed beside the aim body, the response is the strongest, and when transmission and reception are placed faraway from the aim body, the sensitivity will fall greatly. The response values become strong for the metal body (double T-iron, rail and metal netting) in roadway space, but the features keep the same for the abnormal body. The accepted induced signals mainly come from the response of terra medium near the roadway side during the survey, which is that the distance between antenna and aim body is smaller, the response is stronger.5) Base on the result of numerical simulation and physical model experiment, we designed the construction technology of mine transient electromagnetic method: If the detecting target locates in roof, and there are railway rail on the floor, the antenna should been placed near the roof. But for the target that locates under the floor, the antenna should been placed on the floor. When we cannot confirm the specific spatial location, the omni-bearing detecting technology should been applied.