Abstract
Karst cavity mapping is now experiencing great interest from engineering geologists as karst cavities have been considered as one the most dangerous geo‐hazards in engineering construction in south‐west China. Given the major electrical resistivity contrast between karst cavities and host rocks, geo‐electrical methods are widely used for mapping karst cavities. A successful case history of mapping karst cavities in the planed railway route using CSAMT is presented in this paper. Scalar CSAMT, with the frequency ranging from 8192 Hz to 0.5 Hz, is used in the field data acquisition. Bostick conversion with EMAP filtering is used for data processing. G Tunnel is one the key tunnel of Gui‐Guang high speed railway. The initial geophysical and engineering geological result considered the bed rocks of the survey section as sand rock, and no karst cavity was expected in the engineering design in this section. An initial CSAMT survey indicated the presence of a resistivity anomaly along the tunnel route and it was interpreted that a karst cavity was developed on the predicted path of the tunnel. A borehole drilled on this anomaly confirmed the presence of a karst cavity as the drilling result agreed closely with the geophysical anomaly. A second CSAMT survey confirmed the response of the karst cavity and helped in its location.
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