A Theoretical Study of Underground Magnetic Resonance Sounding for the Advanced Detection of Water Influxes in Tunnels

Based on surface magnetic resonance sounding (MRS), a relationship is proposed to express the MRS response signal with a vertical coil for the MRS method for a whole underground space model. Firstly, the declination and inclination characteristics of the Earth's magnetic field and the coil normal angle are studied by deriving the angle rotation matrix. Surprisingly, the results indicate that the MRS signal can be effectively improved by changing the normal direction of the coil perpendicular to that of the Earth's magnetic field. The advanced detection distance of the underground MRS method is closely related to the exciting pulse moment and the receiving sensitivity. Hence, a larger pulse moment and high receiving sensitivity correspond to a longer advanced detection distance. However, the limited transmitting moment will reduce the advanced detection distance. In the research coincident loop with the coil 2 m by 2 m square is employed. In order to overcome the noises with 1 nV and 100 nV level, the turns of loop should be 100 turns and 400 turns, respectively. Finally, the numerical simulation results verify the feasibility of underground whole MRS theory and resolution analysis method for the advanced detection of water-inrush disasters in mines and tunnels.