| The water-bearing structures on the top of the working face of the coal mine roadway,inside the floor or in front of the palm face are the main water inrush hazards during coal mining and tunneling.There is a clear difference between the conductivity and dielectric properties of the water-conducting structure and the complete coal-bearing formation,which provides a physical prerequisite for mine transient electromagnetic detection.The traditional multi-turn small loop transmission and receiving coils of the mine coincided with the winding method,which caused a strong mutual inductance coupling between the coils and between the coils,which in turn enhanced the shutdown effect,increased the shallow "blind zone",and achieved shallow fine Exploration is more difficult.To this end,based on the conical field source device,this paper carried out one-dimensional forward and inverse theory and application research on the whole space of the ground and roadway.The calculation formula of the coil radius of each turn in the conical field source device is derived.The one-dimensional forward calculation expression of the transient electromagnetic method of the conical field source device is analyzed based on the Maxwell equations and the superposition principle,using D.Guptasarma and B.Singh The 140-point Hankel transform method calculates the vertical magnetic field response in the frequency domain,and then uses the cosine filter algorithm to convert the frequency domain response to the time domain.The characteristics of the transient response of the conical field source to different observation parameters and changes in the resistivity and thickness of the typical electrical model are discussed.Studies have shown that the larger the top and bottom radii of the conical launcher and the smaller the uniform half-space resistivity will lead to The transient response decay becomes slower,so that the time for the transient response to enter the late decay is delayed accordingly.The late apparent resistivity curves obtained from the forward modeling of typical geoelectric models can better reflect the characteristics of the geoelectric model,and have a good layering effect,and are particularly sensitive to low-resistance bodies.The forward calculation formula of layered full-space transient electromagnetic method is introduced.Based on the superposition method,the forward calculation formula of layered full-space transient electromagnetic method of conical field source is discussed.The combination of three-layer,four-layer and typical geoelectric model is calculated.In the full-space medium model,the study found that the response time range of the low-resistance layer in the full-space layered model is slightly larger than that of the half-space model,and the response of the interface between the low-resistance layer and the lower medium is also delayed accordingly.The diffusion law of the transient electromagnetic field in the full-space layered medium is mainly in the direction of the lowest low-resistance layer,because the electromagnetic wave has the characteristic of propagating in the direction of easier diffusion.During the detection of coal mine roadway roof,the degree of influence of the low-resistance body on the observation signal in the bottom plate will depend on the magnitude of the difference in the resistivity of the low-resistance body on the top and bottom plate.If there is a low-resistance layer with lower resistivity in the top plate,the observed response will be It is mainly the low-resistance response of the top plate.If there is a low-resistance layer with low resistivity in the bottom plate,the observed response will be mainly the low-resistance response of the bottom plate.Two one-dimensional inversion methods of mine transient electromagnetic method are discussed: 1."Smoke ring" inversion.The study found that the "like" resistivity-apparent depth curve of the typical geoelectric model obtained by inversion can better reflect the morphological characteristics of the geoelectric model,and the response of the inversion to the low resistance layer is particularly sensitive.2.Improved particle swarm optimization inversion(PSO-GIS).The study found that the improved particle velocity update formula and the newly proposed inertial weight factor improvement strategy can converge to the global optimal solution faster under the test function,which improves the algorithm's global optimization ability.The proposed PSO-GIS algorithm does not depend on the setting of the initial model.The typical geoelectric model of inversion has a faster convergence speed and better calculation accuracy.The relative error of forward response of inversion results is very stable in the early stage,the average relative error is less than 1.27%,only the average relative error of K-type is 2.87%.The PSO-GIS inversion algorithm is applied to the full-space five-layer model under the influence of roadways.It is more sensitive and accurate for the inversion except for the roadway.There is a larger error in the high resistance inversion of the roadway,but the average relative error remains is 0.95%,and well divided the top and bottom plate low resistance anomalies.The research shows that the improved particle swarm optimization algorithm has a good effect in the inversion of ground and roadway theory of conical field source transient electromagnetic method.The inversion comparison of measured data from coal mines shows that the improved particle swarm optimization inversion method is more precise for the inversion of low-resistance bodies.It is feasible to apply the inversion method to the processing of measured data and improve the interpretation effect of inversion. |
PDF Full Text Request