In order to detect the distribution, development scale and shape of mining area in tunnel hidden coal measure strata, and provide intuitive and reliable geological basis for later design and construction, geological mapping combined with audio frequency magnetotelluric method was used for exploration. In this paper, firstly, the characteristics of tunnel hidden goaf and the basic principle of audio frequency magnetotelluric (AMT) method are briefly described; secondly, the key technologies of scientific acquisition and data processing flow of the method are analyzed; secondly, the geological characteristics of goaf under different conditions are analyzed, and the geological models are established for forward modeling; finally, the method is applied in yuchanshan tunnel of Ronglu expressway The results of electromagnetic imaging directly and accurately reflect the distribution position and scale of goaf, and provide reliable basic data for later design. Through theoretical analysis and practical application, the results show that audio frequency magnetotelluric method combined with geological mapping can play an important role in the investigation of tunnel hidden goaf, and can directly reflect the location, shape and other basic elements of goaf, providing more reliable basic data for subsequent investigation and design.
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