Sensitivity Analysis of Geoelectric Parameters in Transient Electromagnetic Method for Tunnels
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摘要: 为探讨瞬变电磁法用于隧道超前预报时瞬变电磁场的特点,用ANSYS模拟了层状半空间和地下全空间瞬变电磁场的传播特性.通过改变低阻异常体的埋深、半径、电阻率及高阻围岩的电阻率,得到了瞬变电磁场探测结果对各参数的敏感程度,并对探测结果进行拟合,得到了相应的函数特性.结果表明:地下全空间瞬变涡流场的传播表现为"水波效应",而非层状半空间的"烟圈效应";隧道中低阻体地电参数变化将显著改变二次场的时域特性,是隧道电磁法的敏感参数;高阻围岩电导率变化对二次场时域特性的影响不大,是不敏感参数.Abstract: In order to investigate the characteristics of a transient electromagnetic field in tunnels using the transient electromagnetic method for advanced detection,the propagation characteristics of transient electromagnetic fields in an underground whole-space and in a layered half-space were respectively simulated using the ANSYS software.The sensitivity characteristics of transient electromagnetic fields were investigated by changing the depth,radius,resistivity of an anomalous body and the resistivity of surrounding rock,and the eigenfunctions of response curves for the field were obtained by fitting the data of time response spectrum.The numerical simulation results show that the propagation of the transient eddy current field in surrounding rock indicates a "water wave effect" in the whole-space other than a "smoking ring effect" in the half-space.The time-domain characteristics of the secondary field are greatly changed due to changing the geoelectric parameters of a conductive body,so the transient electromagnetic field in tunnels is sensitive to the geoelectric parameters of the conductive body.The time-domain characteristics of the secondary field are slightly changed duo to changing the geoelectric parameters of surrounding rock,so the transient electromagnetic field are lowly sensitive to the geoelectric parameters of surrounding rock.
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