基于1 Hz~100 kHz天然电磁场深埋长隧道勘察  

Detection of deeply buried long tunnel with 1 Hz~100 kHz magnetotelluric method

作　　者：郭涛 席振铢[1] 王鹤[1] 韦洪兰 刘威 杨晓敏 黄晓帝 GUO Tao;XI Zhenzhu;WANG He;WEI Honglan;LIU Wei;YANG Xiaomin;HUANG Xiaodi(School of Geosciences and Info-physics,Central South University,Changsha 410012,China;Hunan 5D Geophyson Company Limited,Changsha 410025,China)

机构地区：[1]中南大学地球科学与信息物理学院,湖南长沙410012 [2]湖南五维地质科技有限公司,湖南长沙410025

出　　处：《铁道科学与工程学报》2023年第11期4107-4116,共10页Journal of Railway Science and Engineering

基　　金：国家重点研发计划课题(2022YFC2903404)。

摘　　要：随着深埋长大隧道洞身埋深的增加,目前常用的10~8192 Hz频带音频大地电磁法满足不了隧道勘察中浅层高分辨率探测和深部数千米深度探测的需求。为了提高浅层分辨率和深埋洞身探测能力,将频率范围扩展至1 Hz~100 kHz进行研究。首先建立复杂地形深埋长大隧道与不良地质体的电性模型结构,利用非结构化网格剖分有限元二维正演计算频率1 Hz~100 kHz宽频天然电磁场的电阻率和相位响应。研究结果显示:TM极化模式对地形、断层及浅部异常体的横向分辨力更强,但受静态效应影响导致纵向分辨率较差;TE极化模式横向分辨力较TM极化模式稍差但不受静态效应影响拥有较高纵向分辨能力,理论上论证1 Hz~100 kHz的频带范围可满足0~2000 m范围内复杂地形深埋长隧道探测需求。随后,基于MPMT-18系统,一次性完整采集了重庆市武隆区高速公路谭家隧道1 Hz~100 kHz的天然场电磁信号,计算了电阻率和相位响应并反演了谭家隧道的电性结构得到电阻率剖面图,以不同岩性电性特征为物性依据进行综合解释:精细划分了地表第四系覆盖层的厚度,推断了土石界面;分辨了洞身二叠系下统的灰岩、泥岩以及志留系页岩不同岩性围岩,为隧道施工提供了依据;根据电阻率特征在灰岩、泥灰岩地层中划分出3个异常区,经SZK02和SD 33钻孔揭示异常区存在3~4 m大小的岩溶,验证了资料解释的可靠性。As the buried depth of long tunnel increases,the conventional AMT method covering 10~8192 Hz band cannot meet the demand for shallow high-resolution detection and deep detection of thousands of meters.To improve the shallow resolution and the detection capability of deep-buried tunnels,the conventional measurement frequency band was intended to be extended to 1 Hz~100 kHz.Firstly,two geoelectric models of deep-buried long tunnels with complex terrain and bad geological bodies at different depths were established.The corresponding apparent resistivity and phase responses were calculated using finite element forwarding method with unstructured grid.The results show that the MT in TM polarization mode has a higher lateral resolution for the terrain,fault and shallow anomaly,but behaves moderately worse in vertical resolution due to the static effect.The AMT in TE polarization mode has a slightly worse lateral resolution,but behaves better in vertical resolution free from the static effect.It is theoretically demonstrated that the proposed AMT of 1 Hz~100 kHz band can meet the detection demand for deep-buried long tunnels within the depth of 0~2000 m with complex terrain.Then,a MT survey is conducted on the Tanjia tunnel in Wulong District,Chongqing.The measurement collection of 1 Hz~100 kHz band is implemented using MPMT-18 system.The resistivity distribution profile of the tunnel is obtained by inverting the apparent resistivity and phase derived from the MT measurements.Based on the inversion results and the geoelectric properties of different lithologies,this work accurately delineates the thickness of the Quaternary overburden on the surface and infers the soil-rock interface,and distinguishes the different lithologies of the Permian Lower Permian tuffs,mudstones and Silurian shales in the vicinity of the cave,which provides a basis for the tunnel construction.Three anomalous zones are delineated in the tuff and marl strata,and the boreholes SZK02 and SD33 confirm a karst of about 3~4 m size in the delineated an

关 键 词：宽频大地电磁法 TE与TM极化 深埋长隧道 非结构化网格剖分 隧道勘察 

分 类 号：P631.3[天文地球—地质矿产勘探]