Transient electromagnetic and high-density inversion are used to make geological analysis and prediction within 50 meters below the surface. The distance between TEM measuring points is 2 meters, with 131 measuring points in total. The emission current is 42A and the sampling interval is 0.8us. The comparison and analysis are made with the high-density data made by the project department. See the figure for details.

  (a) Inversion map of high-density resistivity method of the Project Department; (b) Inversion diagram of transient electromagnetic apparent resistivity

Transient electromagnetic inversion corresponds to high density on the whole. There is a collapse area between 21540-21560, where there is low resistance response and the high resistance response of the tunnel can be shown. On the top of mileage 21700, there is a high resistance response, and there is a low resistance area below the high resistance response, which is completely consistent with the high-density data.