Research And Application Of CSAMT In Deep And Long Tunnel Exploration

Geological engineering detection of deep, large, long tunnel is the world's major research projects urgent to solve. Controlled Source Audio-frequency MagnetoTellurics (CSAMT) is widely used in the tunnel survey due to deep exploration depth; topographic impact on small, low resistivity is very sensitive and effective shield to avoid high resistance and strong resolution, high efficiency characteristics. According to the practical problems in A tunnel and combined with engineering geological investigation the paper has researched survey and application of Controlled Source Audio-frequency MagnetoTellurics in the long and deep tunnel.Firstly, the paper made some elaboration on the Controlled Source Audio-frequency MagnetoTellurics of application background and research. Then it introduced the theoretical basis and field work methods of Controlled Source Audio-frequency MagnetoTellurics. Next it made some research of the problems in the work they may encounter by using Controlled Source Audio-frequency MagnetoTellurics, The paper analyzed and summarized the cause and correction method of the static effect and the near field effect, while also given some elaboration of the field source effect and the false extreme effects also with a preliminary study of resolution in Controlled Source Audio-frequency MagnetoTellurics.Finally, with combination of analysis of A tunnel engineering survey examples the paper studied how to proven geological structures, the location of fault zone and karsts and the depth and size of fracture zone, soft zone and water-rich zone by using Controlled Source Audio-frequency MagnetoTellurics. Also it made the rock classification combined with the speed data.By analyzing and summarizing the application of Controlled Source Audio-frequency MagnetoTellurics in A tunnel. We can draw the following conclusions:1. The bad geological such as the fault rupture zone, karsts, weak zone and water-rich zone showed features that the low resistance with the sheet, massive and banded shape in resistivity section.2. CSAMT can detect the abnormal formation of deep karsts or not is depended on diameter-depth ratio and the size of the resistivity difference.3. We can sub-interpretation faults according to the following two in CSAMT data:First, low resistance was banded or beaded in the resistivity section, and second, resistivity in sounding curves is obvious decrease or the overall resistivity is lower.In addition, under width and orientation of low-resistivity anomalies the width and orientation of fault zone can be inferred roughly.