| We often encounter problems of coal mine water hazards in mine extracting, and how to ascertain or position flood anomalies is an important part of the prevention and treatment of water disasters. One of the commonly used detection methods is mine transient electromagnetic method(MTEM), and a large number of practical exploration practices have shown that this method can achieve good results. However, there are some problems, the main problem is that the lateral resolution of the method is higher but the longitudinal resolution is relatively poor, the anomalous body is shown as an amplified low value area in the apparent resistivity section, the boundary of the abnormal body cannot be located accurately, detection depth is relatively shallow. Besides, when using MTEM to detect iron mine water damage, the polarity reversal problem of transient response is often encountered. Generally, the data of this polarity reversal is treated as interference data.Make simple associations of a branch of the transient electromagnetic method—borehole transient electromagnetic method or drilling transient electromagnetic method, source is set on the surface, the receiver is made into an elongated cylindrical shape, and put it in the drill hole, carry on observation in turn from top to bottom or from bottom to top, a large number of practical detection results show that the drillhole transient electromagnetic method obviously better than the traditional ground transient electromagnetic on the vertical resolution and the boundary of the anomaly body.Combined with the urgent needs of water hazard detection and the advantage of the drillhole transient electromagnetic method, in this paper, we studied the ground—drill hole transient electromagnetic in coal mine underground roadway. The source laid in the roadway, and the receiving probe is placed in the hole of the tunnel, then which can improve the vertical resolution and boundary location in mine flood anomaly detection.Therefore, this paper based on the induced electromotive force in mine tunnel hole TEM response characteristics and the induction electromotive force response polarity reversal phenomenon in whole space TEM. By the means of theoretical analysis, derivation, integral equation method of numerical simulation and cole-cole model theory as the study of methods / tools. Numerical simulation prepared using procedures mine tunnel hole in full space transient electromagnetic induction electromotive force response characteristics. And the main research results are as follows:1.The electromagnetic response formula of the magnetic dipole source and horizontal circular loop source in the whole space 1D horizontal layered medium was derived.For the Y horizontal magnetic dipole source in the 1D horizontal layered medium, the vector potential function in frequency domain is used, including the horizontal vector potential and the vertical vector potential, which indicate the electromagnetic field in each layer to reduce the degree of freedom. The interface layer cut to the electric field and magnetic field of the continuous equation and the vector potential function and the electric field E and magnetic field H differential equation of vector potential function to satisfy the continuity equation, boundary conditions, using boundary conditions derived above and beneath the source in each layer of the horizontal vector potential function and vertical vector potential function in a constant proportional relationship. The boundary conditions of the top and bottom of the source are applied to calculate the horizontal vector potential coefficient and the vertical vector potential. The vector potential function boundary condition is used to derive the horizontal vector potential and the vertical vector potential. Then the integral expressions of E and magnetic field H in each layer are derived. For the X horizontal magnetic dipole source in the whole space 1D horizontal layered medium, the electromagnetic response of the X to the magnetic dipole source is derived by using the transformation relationship between the electromagnetic field response of the X to the magnetic dipole source and the electromagnetic response of the y to the magnetic dipole source.For horizontal circular loop source, the vertical magnetic hertz frequency domain was used to represent the potential function within each electromagnetic field, which is used to reduce the degree of freedom. Cut to the electric and magnetic boundary conditions and Hertz potential and E and h of differential equation of Hertz potential satisfies the boundary conditions using layer at the interface, and then export the source interface(the source interface, if the source is not in the actual interface, insert a virtual interface) upper and lower layers of Hector hereby potential constant coefficient ratio. According to the boundary conditions at the source interface, the Hertz potential coefficient of the upper layer of the source interface is derived and the downward propagation of the lower layer of the source interface. The electromagnetic field expression in each layer is obtained. The electromagnetic response formula of vertical magnetic dipole source is derived by using the limit relation between horizontal circular loop source and vertical magnetic dipole source, which is the vertical magnetic dipole source when the horizontal circle line source radius is 0. In the end, the electromagnetic field response of the magnetic dipole source in any direction is given by using the vector superposition method.And compared with the magnetic dipole source electromagnetic field response formula in whole space 1D layered by predecessors, the formula derived in response to this article, the export process is simple, easy to understand, for programming, good numerical stability.2.The electromagnetic response program of the magnetic dipole source and horizontal circular loop source and the integral equation of the whole space electromagnetic method are developed in the whole space 1D horizontal layered medium.3.Whole space borehole 1D transient response characteristics of electromagnetic induction electromotive force and its variation.According coal mine actual geological conditions, there are total 6 geoelectric models for the establishment of full space 1D geoelectric model.Its transient response characterized by:(1)Attenuation curve from shallow to deep Vz each measuring point in response to a turning point in the corresponding time gradually increases; drilling on the cross section, in response to the rapid decay of the early Vz increases with depth, curved, middle and late change attenuation slow, it was nearly linear.(2) Attenuation curve, essentially coincident y each measuring point to the induced electromotive force Vy; on the drilling sectional, Vy response was nearly linear for a typical North China coal field six whole space model and vertical drilling.(3) Compared with the half-space, small space when the whole back line source simulated frequency range should be appropriate to extend to higher frequencies for two low clip a high level in the whole space of the three-tier model.4.Response characteristics and variation law of 3D transient electromagnetic induction electromotive force in the hole of full space tunnel.According to the practical geological conditions of coal mine, there are total 54 geoelectrical models for the establishment of typical full 3D geoelectric model, the circular loop radius change model, model in the mine tunnel, the top floor material and geometry parameters of the model, properties of abnormal body and geometry parameters of the model, borehole geometry parameters of the model, source and abnormal body and drilling relative position change model, two models of anomalous body such as typical geoelectric model, numerical simulations are carried out, the transient response characteristics are as follows:(1) The small radius loop source can be used as the excitation source of the transient electromagnetic method in the whole space of the mine when the effective coupling of the abnormal body is ensured.(2)Mine roadway side help coal body influence on the tunnel bottom hole transient response is strong early and shallow, advanced deep and weak; and strong influence on the axial induction electromotive force VR, while the vertical to the induction electromotive force VZ effect weak.(3)With the decrease of the resistivity of the top and bottom plate media, the electromagnetic response of the whole space layered medium(background response) will gradually suppress the abnormal response. This effect on the Vz and Vy in the hole 3 and the Vz in the hole 1 has a strong effect on the Vy and Vz in the hole 3 and the Vr in the hole.(4)The change of the height of the roadway has a weaker effect on the Vz of the three kinds of holes, but the early and shallow part of the Vy has a relatively strong influence on the three kinds of holes, and the influence on the medium and late stage and the deep part is weak.(5)With the decrease of the resistivity of the anomalous body, the increase of the anomalous body thickness and the buried depth of the anomalous body, the abnormal response becomes stronger.(6)When the hole 1 and hole 2 are inclined to the abnormal body, the abnormal response is enhanced, and the hole 3 is inclined to the Vy curve when the Vz curve is inclined to the source direction and the abnormal response is strong. The tendency of borehole is influenced by Vz, but the influence on Vr is relatively small.(7)When the source is located at the top of the anomalous body, the anomalous response becomes stronger due to the coupling between the source and the anomalous body.5.The response characteristics and variation law of transient electromagnetic induction electromotive force in 1D and mine roadway 3D in the presence of polarization or polarization anomalies.According to the actual geological conditions of coal mines, build surface layer containing clay polarization whole space 1D model, with the polarization of aqueous anomalous body(polarized conductive bodies) typically electric model and other models, and the development of theoretical models cole-cole program to simulate transient response characteristics are as follows, there are total 20 geoelectrical models:(1)Effect of polarization by excitation of surface polarization layer of clay, with decreasing radius of the loop, the whole space under the central loop Vz with time decay curves appear on the polarity inversion point, a small change in the time in which they appear; Vz response amplitude attenuation curve decreases, the curvature point before polarity inversion of the curve becomes smaller Vz, Vz the same slope of the curve after the polarity reversal point.(2)The response of the side wall of the coal roadway containing sulfide has great influence on the shallow part of the Vz response, and the influence of the deep part is small.(3)With the increase of the resistivity of the direct roof, the time of the polarity reversal points on the Vz attenuation curve appears to be significantly reduced, and then the change is small.(4)(1) With the decrease polarization anomaly depth, increasing polarization, the frequency increases with increasing time constant factor, Vz decay time of polarity inversion point appears on the curve decreases, polarity inversion point before Vz curvature curve gradually increases.(2) With the polarization anomaly body size increases, the time point of the polarity inversion occurs slowly reduced, polarity inversion point is responding to negative response before and after the inflection point extremum were increased. With the increasing polarization resistivity anomaly, after the time-response curve Vz polarity reversals occur decreases and then increases, the polarity inversion point before Vz amplitude of the response curve of inflection and a negative response to extremes gradually decreases.(5)Affected by abnormal excitation polarization effect of the body, through the drilling of the anomaly in Vz response, abnormal response manifested as a polar opposite field polarity arc background curve; and the borehole Vy response, abnormal response from the early to the late performance from shallow to deep polarity inversion, that is generated from the performance of both the temporal and spatial characteristics of polarity reversal.Comprehensive analysis of the above results we can see that the whole space in the mine, when conditions permit, as far as possible the use of large loop means, if space constraints, you can use a small loop hole transient electromagnetic detection of emission source, subject to the source and abnormal body has a good coupling. Conducting mine tunnel drill hole transient electromagnetic detection, it is necessary to receive the vertical axis and the induced voltage. When the whole space or a layer with low resistivity anomalies having polarization properties, from the mine tunnel hole transient response profiles can clearly distinguish the induced polarization effects. |
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