Numerical Simulation of Audio-Frequency Magnetotelluric Method for Goaf Under Transmission Towers

Underground goaf areas beneath transmission towers, prone to water accumulation and collapse, pose significant threats to power line safety and stability, necessitating accurate detection of their distribution. Conventional methods are challenged by the trade-off between equipment portability and sufficient penetration depth, particularly in complex terrains. The Audio-frequency Magnetotelluric (AMT) method, offering advantages of lightweight equipment and significant exploration depth, is well-established in mineral and hydrocarbon exploration. However, detecting goaf areas under transmission towers imposes more stringent requirements on the mining depth-to-thickness ratio than traditional resource exploration. Addressing the Depth-to-Thickness Ratio (DTR) of 30, this study constructs a geoelectric model of a transmission tower goaf and synthesizes the AMT apparent resistivity response via finite element simulation. The reconstructed resistivity image effectively distinguishes water-saturated goafs and air-filled goafs from the background stratigraphy. These findings confirm the feasibility of AMT for goaf detection beneath transmission towers.