| For a long time,coal mine water damage has caused serious personal casualties and economic losses.The transient electromagnetic method in mines has played an important role in the exploration of water hazards.It has the advantages of convenient detection.However,this method is greatly interfered by metal anchor nets in the roadway and the detection ability of small and low-resistivity abnormal objects in the distance is weak.In order to avoid these problems,this thesis intends to study the transient electromagnetic method in the inner hole of the coal mine roadway to realize the detection of hidden disasters around the hole.In this thesis,numerical simulation,theoretical model inversion,experimental data inversion and other methods are proposed to study transient electromagnetic in the inner hole of coal mine roadway.The specific research is as follows:(1)The relationship between the input and output of the induction coil is deduced by using Kirchhoff’s law.Taking the transient electromagnetic forward modeling signal as the input signal,the numerical calculation of the transient electromagnetic forward modeling signal based on the output of the air-core coil and the matched resistor coil is realized.The transient electromagnetic forward modeling signal output by the coil in the hole is analyzed and researched(2)The calculation formula of the axial component at any position on the center line of the circular source in the whole space in the frequency domain is deduced,The Transient Electromagnetic Calculation of the Circular Loop Source in the Inner Hole of the Roadway is Realized by the Sine and Cosine Transform;The induced electromotive force signal is directly fitted to find the minimum value,and the calculation of the transient electromagnetic apparent resistivity of the roadway-hole and in-hole is realized;the goaf model is established to realize the forward modeling characteristics of the roadway-hole transient electromagnetic and the in-hole-transient electromagnetic.The research results show that the low-resistivity goaf has a greater impact on the transient electromagnetic signal,the high-resistivity goaf has less impact on the transient electromagnetic signal,and Coal-rock roadway layer has little effect on signals of roadway-hole and hole-transient-electromagnetic for low-resistivity and high-resistivity goaf.(3)Using the discontinuous Galerkin vector finite element method,the three-dimensional time domain forward modeling of transient electromagnetic in the inner hole of the coal mine roadway is realized.The parallel computing of multi-core and multi-thread is realized by utilizing the characteristics of independent update of electric field and magnetic field in sub-units.3D Forward Modeling for Arbitrary Emission Loop Directions Using Tetrahedral Meshing is realized.The synthesis of the axial component in the hole in the normal direction of the magnetic moment of the emission source is realized using the principle of decomposition and synthesis.The forward modeling of the Concealed low resistivity the goaf and collapse column model and the fault model is realized using the three-dimensional forward modeling method.The characteristics of transient electromagnetic signals at receiving point in the hole are analyzed.The results show that the transient electromagnetic method in the inner hole of the roadway can effectively identify the existence of hidden disaster sources around the hole.(4)Using Occam method,particle swarm optimization method(PSO)and genetic algorithm(GA),the inversion of transient electromagnetic in the inner hole of coal mine roadway is realized.The forward data of roadway-hole and in-hole-transient electromagnetic with Gaussian white noise added in Chapter 3 were inverted using three inversion methods.Compared with the theoretical model,the inversion effect of the three methods is verified.The 3D forward data of the airspace model was inverted,and it was verified that the transient electromagnetic inversion method of the receiving axial component in the emission hole in the roadway can effectively identify the hidden disasters around the borehole.In addition,the Occam method is used to invert the 3D forward data of the concealed low-resistivity collapse column and the goaf model in Chapter 4.It is verified that the full-space roadway-hole transient electromagnetic one-dimensional inversion method can effectively identify hidden hazards around the borehole.(5)The one-dimensional full-space inversion algorithm is applied to the experimental data received in the hole and Transmitting on the ground,and the inversion of the lithological characteristics around the hole is realized;Comparing the inversion results with the actual formation,it is proved that the comprehensive use of three full-space transient electromagnetic one-dimensional inversion methods has a certain detection effect in solving the inversion of the resistivity around the hole. |
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