巷道电性源瞬变电磁响应三维数值模拟

Three-dimensional numerical simulation of grounded-source transient electromagneticresponses in roadways

近年来地面电性源得到成功应用,巷道电性源瞬变电磁探测将成为热点。本文采用三维时域有限差分法,对巷道底板以及巷道与巷道之间异常体的电性源瞬变电磁响应进行了模拟。模拟结果表明:对于巷道底板异常体,受异常体表面电荷影响,电场水平分量和垂直分量在异常体表面剧烈变化,水平电场对低阻体的分辨能力较强,对高阻体的分辨能力较弱,低阻体与高阻体的垂直电场响应的符号相反;低阻体和高阻体的∂B_(y)/∂t响应在早、晚期的符号相反,低阻体响应在早期的符号为负,晚期为正,而高阻体响应在早期的符号为正,晚期为负。对于巷道与巷道之间的异常体,水平电场对低阻体的分辨能力较强,对高阻体的分辨能力较弱;高阻体模型的∂B_(z)/∂t响应曲线高于背景曲线,低阻体模型的响应曲线低于背景曲线,说明磁场∂B_(z)/∂t响应对高阻体和低阻体均有分辨能力。

Owing to the successful application of grounded-source in recent years,roadway detection using the grounded-source transient electromagnetic(TEM)method has attracted significant academic interest.Using the three-dimensional finite-difference time-domain(FDTD)method,this study simulated the grounded-source TEM responses of the anomalies in the roadway floors and between roadways.The simulation results are as follows:(1)For anomalies in the roadway floors,their surfaces show violent changes in the horizontal and vertical components of the electric field subjected to the surface charge of anomalies.The horizontal electric field exhibits a strong ability to discriminate low-resistivity bodies but a weak ability to discriminate high-resistivity bodies.The vertical electric field displays opposite response signs from the low-and high-resistivity bodies.The low-and high-resistivity bodies correspond to opposite∂B_(y)/∂t responses in the early and late stages.Specifically,the response signs are negative in the early stage and positive in the late stage for low-resistivity bodies,whereas the results are contrary for high-resistivity bodies;(2)For anomalies between roadways,the horizontal electric field also exhibits a strong ability to discriminate low-resistivity bodies but a weak ability to discriminate high-resistivity bodies.The∂B_(z)/∂t response curves are above the background curves in the model of high-resistivity bodies but below the background curves in the model of low-resistivity bodies,suggesting the discrimination ability of the∂B_(z)/∂t response for both low-and high-resistivity bodies.