Real-time detection of water-bearing structures in tunneling using the long-electrode while-drilling resistivity method

In tunnel engineering, water-related hazards such as water inrush and mud pose severe safety risks, especially in water-rich or karst environments. Traditional resistivity methods have limitations in real-time data acquisition and construction coordination. This paper proposes a long electrode source while-drilling (LEWD) resistivity method. Utilizing the drill rod as a current electrode and synchronously acquiring observation data from the tunnel face electrode array, LEWD enables continuous, automated monitoring without interrupting excavation. A 3D finite element forward model is optimized using Cholesky decomposition to improve computational efficiency, while a time-windowed iterative inversion strategy enhances the stability and accuracy of resistivity imaging. Based on this framework, numerical simulations verify the method's ability to accurately identify low-resistivity anomalies under various conditions. Furthermore, field tests in the Xianglu Mountain tunnel in China demonstrate that the LEWD method can effectively detect water-bearing structures ahead of the tunnel face. This method provides effective technical support for water hazard prevention in tunnel construction.