Three-dimensional inversion of controlled-source electromagnetic data for surveying the Jiutianshan high-speed railway Tunnel, China

Abstract

Controlled-source electromagnetic surveying was conducted to identify underground faults and potential water hazards that could affect the construction of the Jiutianshan High-speed Railway Tunnel in the Qinling Mountains, western China. The transmitter length was 978 m, and the receivers were positioned along five profiles that were located about 9.5 km from the transmitter. The observation parameter, the electric-field amplitude |Ex|, was inverted using a finite-memory quasi-Newton method in three-dimensional mode. The resultant model is divided into horizontal blocks and vertical layers. The vertical cross-section along the tunnel shows a pattern of alternating high- and low-resistivity layers. The electrical resistivity pattern is divided into two vertical layers, with a clear boundary between the high- and low-resistivity zones. Combined with the results from previous exploration, geological survey, and drilling data, the inversion results identify the strata and faults along the planned route, and four risk areas are delineated. Our results highlight the power of employing geophysical investigations for risk assessments along tunnels.