高分辨电磁法在B隧道勘查中的应用

本文介绍了在B隧道勘查中应用高分辨电磁成像技术探测隐伏构造的一个成功实例。数据采集采用高频电磁成像系统（STRATAGEM EH4，频率范围从1Hz到90kHz）。野外采集正交的电磁场分量，从地磁成像剖面中提取目标体有关电磁学信息。为获取高质量的采集数据，野外采用包含天然场源和全张量可控源的混合场源。B隧道坐落在位于中国中部的湖北省的西部，隧道埋深不到200m，但区域地质作用导致它的地质机构十分复杂。第一次勘查过程中，勘探人员误把一个脱落体的露头当成基岩面，施工过程中出现了冒顶。第二次勘探时采用高分辨电磁法和折射地震法，这次勘探找到了隐伏的基岩面和一个隐伏断裂。勘探结果与后来隧道挖掘揭示的构造吻合。

Application of the high-resolution EM method in the investigation of B Tunnel

A successful case history of exploring for concealed structure using the high-resolution EM method in the investigation of the West-East Gas Pipeline Project’s B Tunnel is presented in this paper. The high frequency electromagnetic image system named STRATAGEM EH4, operating at frequencies ranging from 90 KHz to lHz, was used for data acquisition. The orthogonal components of the electromagnetic field were measured during the field acquisition and the relevant electromagnetic attributes of the object body were extracted from the electromagnetic data. Hybrid sources, consisting of natural and full tensor-controlled sources, were utilized to produce high-quality electromagnetic field data. B Tunnel lies in the western part of Hubei province, at depths of less than 200 m. The geologic setting of B tunnel is very complex. Following an initial geologic investigation, an outcrop considered to be a bedrock interface by investigators, collapsed during tunneling operations. A second investigation applied high-resolution EM and seismic refraction methods to reveal a more complex geologic structure along the tunnel route. The predicted rock classes and fault were encountered during the subsequent tunneling operations. The work is sponsored by National Natural Science Foundation of China (No. 40074036). First Author He Lanfang, Geophysicist, BGP, China National Petroleum Corp. graduated and received a B.S. in Applied Geophysics from Central South University inl996, and received a M.S. in Solid geophysics from Chengdu University of Technology in 2002. He work in BGP, China National Petroleum Corp from 1996.