Application Of CSAMT In Surveying Long And Deep Tunnel

Long deep tunnels are ones which buried deeply,having long distance and complex geological structure.For this reason,long deep tunnel investigation has been the difficulties in the field of engineering geological investigation,which is related to the key technical problems of the tunnel route selection and construction,if the pre-rock exploration in the study of the geological structure is detailed,then the latter part of the design and construction could adapt more targeted technical measures,which can reduce the project investment and project risks consequently.General method used in the tunnel geophysical survey techniques are seismic refraction,seismic surface wave method,and high-density electrical sounding method,etc,but these methodshave shallow detection depth,slow speed,terrainimpact, low precision and other issues.Controlled source audio-frequency magnetotelluric method, referred as CSAMT method is an electromagnetic exploration method developed rapidly in recent years,which use the difference of electrical conductivity of rocks to observe the changes in EM field strength, it has many advantages: first, it used source coule controlled, measured parameters for the ratio of electric and magnetic fields - caniard resistivity, enhanced anti-jamming capability and reduce the impact of the terrain as a result; second, it use the changes in the frequency instead of changing the geometric dimensions sounding at different depths, which can launch multiple points to complete the electromagnetic sounding at one time ,resulting in improved efficiency;Third, probing depth range generally up to 1 ~ 2km; Fourth, the high lateral resolution can be Sensitive to find fault; Fifth,high resistance shielding effect is little,can penetrate the high resistance layer. Because of this, CSAMT method engineering exploration in recent years has achieved good results.This paper briefly describes the current overview research of long deep tunnel investigation and research first, and then discussed the impact by static effects caused by physical and topographical object and the correction methods, such as one-dimensional spatial filter, two-dimensional modeling method, electromagnetic array profiling, phase data correction method and so on. Finally,combined the hongchi tunnels and qingshuiling tunnel of the exploration process,we carry out the controlled source audio-frequency magnetotelluric method in long deep tunnel in the research and application , and made a successful prediction of the tunnel area lithology, geological structure and its water situation for the tunnel design and construction to provide a more scientific basis.