Study Of Transient Electromagnetic Perspective Technology On Ultra-wide Working Surface

To find out the geological structure in the ultra-wide working surface is an urgent problem to be solved in the modern mine in China in order to ensure safe and efficient production,and the current commonly used wireless electromagnetic wave perspective technology has the disadvantage of short transmission distance,the construction of the slot wave seismic exploration technology is inefficient,the economic cost is high,the water-bearing structure can not be accurately detected.Therefore,on the basis of drawing lessons from the idea of ground-tunnel transient electromagnetic technology,this paper puts forward the transient electromagnetic perspective technology of ultra-wide working face based on the theory of electromagnetic field diffusion propagation,i.e.a rectangular loop with step wave current is arranged in one tunnel of the working face to emit a pulse magnetic field to the working face,and a coil is used in the other tunnel to receive the secondary induced eddy current field caused by the medium of the working face,so as to effectively detect geological anomalies in the working face.In this paper,the geophysical model of transient electromagnetic perspective in ultra-wide coal mining face is established,and the response characteristics of transient electromagnetic perspective signal from long rectangular loop source are studied by using vector finite element numerical simulation technology:(1)Firstly,the theoretical equation of transient electromagnetic field diffusion and the theoretical basis of vector finite element numerical calculation are expounded;(2)Based on the full-space model,the full-space diffusion and propagation law of long rectangular loop source transient electromagnetic field is studied,and the distribution range of uniform background field is summarized,which provides a theoretical basis for the design of underground observation system of transient electromagnetic perspective technology.(3)Based on the full-space layered medium model,the influence law of coal seam electrical property difference and coal seam thickness on transient electromagnetic field transmission signal is studied.It is considered that the full-space layered medium can be treated as a uniform background field to simplify the calculation when the thickness and resistivity of coal seam change little on the receiving side signal.(4)Based on the three-dimensional geological structure anomaly model in the whole space,the transient electromagnetic field transmission signal response characteristics under different geometric shapes,different spatial occurrence orientations and different sizes of geological structures such as collapse columns and faults are studied.The results show that the transient electromagnetic perspective technology has obvious response signals to collapse column anomalies in the working face when the working face is wide,and the specific position and direction of the anomalies can be delineated according to the extreme points and slopes of the signals,and the transient electromagnetic perspective technology has higher horizontal resolution to low-resistance anomalies,which proves the effectiveness and feasibility of the transient electromagnetic perspective technology.There are 49 pictures,3 tables and 85 references in this paper.