The reflected radio wave method for detecting coal seam faults in mining face

Mine radio wave exploration can be used for coal seam geological structure exploration. With its advantages of portability and good effect, it has become a conventional and necessary means for coal seam geological structure exploration. At present, the energy attenuation of radio wave signal in coal seam is fast, and the transmission radio wave detection of working face is restricted in large width coal seam. On this basis, the radio wave reflection exploration method of coal seam working face is proposed. Firstly, the electric model of two-dimensional coal measure strata is constructed by numerical simulation to analyze the field strength value of radio wave H_x component signal. The experimental results show that the attenuation of the H_x component signal in the normal coal seam roadway is approximately linear with the propagation distance, which lays a theoretical foundation for the radio wave reflection imaging algorithm. Secondly, fault anomaly areas are set at 5, 10, 15, 20, 25 and 30 m away from roadway in the model. Compared with the normal coal seam, the H_x component field strength value has a mutation at the fault. The field strength value increases first and then decreases, and the over all reflected field strength value decreases with the increase of the distance between the fault and the roadway. When the fault is 25 m away from the roadway, the field strength value change is not obvious. Finally, the field experiment was carried out in a coal mine working face. The experiment uses the frequency of 0.965 MHz to detect the radio wave reflection of the whole roadway. In the detection results, the field strength value of radio wave near the geological anomaly is abnormally high, showing an obvious superposition of direct wave and reflection wave. The abnormal field value agrees well with the fault position from the actual mining verification data, and the experiment has achieved good results. In summary, the attenuation of field strength value of radio wave in normal coal seam roadway is approximately linear with the propagation distance. When there is any geological structural anomaly in the working face, the superposition of direct wave and reflected wave will occur, and the field value will jump up. It is feasible and effective to detect geological anomalies by reflection radio wave method, which provides a new method and idea for geological structure exploration in coal seam working face.