| China is a large country of coal consumption and production for coal is the main source in China,and it provides the basis of the energy for long-term rapid economic growth.With the dramatically increasing of mining depth and coal resources integration,many problems including serious lack of goaf data,identical difficulty of mine boundary,un-clarity of water accumulation and water filling situation,cause threats to safe production.Transient electromagnetic method is sensitive to the response of low resistivity body and is one of the most widely used methods in the detection of water-bearing goaf.However,it can only identify the approximate area and scope of water-bearing goaf,and is difficult to further judge the water content of goaf.There is insufficient understanding of transient electromagnetic response of different water-bearing goaf,which affects the identification and solution of anomalies in goaf.To solve this key problem,the transient electromagnetic response characteristics of goaf with different water content are studied by theoretical analysis,numerical simulation and physical simulation,and the application of examination of the treatment quality of filling mined-out voids using super-high-water material and water-rich detection with transient electromagnetic method was carried out.The response characteristics of goaf with different water content are verified and analyzed.The specific results are as follows:1)Based on Maxwell equation and transient electromagnetic theory,the theoretical expression of frequency domain response of horizontally layered earth surface is derived.The algorithm provides a theoretical foundation for the following research.2)The numerical model of water-bearing goaf with thickness of 20 m,depth of 100 m,200 m and 300 m respectively,water content of 0%,10%,20%,……100% were established.The forward simulation of transient electromagnetic response in water-bearing goaf was carried out.The characteristics of transient electromagnetic response in water-bearing goaf with different depth and water content were studied and analyzed.Subsequently,the water content and induced EMF increase were analyzed by polynomial fitting method.The results indicate that the transient electromagnetic response of goaf with different water content is significant difference.The bigger the water content is,the stronger the response is,and vice versa.Under the same other conditions,the bigger the depth-thickness ratio of goaf is,the smaller the abnormal intensity is.Therefore,the transient electromagnetic method is completely feasible to analyze the water content of goaf.3)The physical models of water-bearing goaf with similarity ratio of 1:100,buried depth of 50 m,100m,150 m,200m and water content of 0%,50% and 100% were established.The physical simulation experiment of large-scale transient electromagnetic flume in water-bearing goaf was carried out.Combined with the forward results under different geo-electric parameters,the transient electromagnetic response of water-bearing goaf with different buried depth and water content was analyzed by using multi-channel profiles.The results show that with the increasing of distance between the receiving coil and the low resistance body,the response signal weakens gradually.4)The accuracy of numerical simulation and physical simulation is verified including the filling effect examination with high-water material in goaf and the application example of water-rich transient electromagnetic detection in goaf.The results show that the water content in goaf is closely related to the transient electromagnetic response.Through the analysis of the transient electromagnetic response in filling goaf with high water content materials and in hydrological reconnaissance borehole observation project,it is concluded that with the decrease of water content(filling with high water content materials in goaf and lowering of observation water level in goaf),the amplitude of induced electromotive force decreases gradually,which is consistent with the theoretical results.These conclusions can be used as the basis for evaluating water content in goaf.Then,this paper puts forward an analysis method for evaluating the water content in goaf based on normalized induction electromotive force(NIEMF)amplitude increasing through theoretical analysis,numerical simulation and physical simulation systematization.In summary,the transient electromagnetic method is closely related to the water content in goaf.The transient electromagnetic response characteristics of goaf with different water content were obtained,and the filling effect with high water material in goaf was tested.The application of water-rich transient electromagnetic detection in goaf further proved the accuracy and validity of this method.The research conclusion is helpful to improve the accuracy of identification and interpretation for water-bearing goaf,and has important practical significance for ensuring safe production during mining. |
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