Fast inversion for advanced detection using induced polarization in tunnel

Geological hazards such as water inrush have become one of the bottleneck problem s for tunnel construction. It’s very common that there are many water-bearing structures in front of tunnel face. And advanced detection of many water-bearing structures is a hard problem to be solved. Chargeability as one parameter of induced polarization (IP) is sensitive to water. And IP is introduced into the advanced detection of water-bearing structures in tunnels. IP on the advanced detection is deeply studied from the aspects of forward theory, inversion interpretation, physical simulation and application. Firstly, a theoretical formula for detecting many water-bearing structures is derived. And apparently chargeability data are calculated using the equivalent resistivity method, laying a solid foundation for fast inversion. Secondly, the traditional damping least squares inversion method controls two changing factors using one damping factor, which causes a contradiction. And the idea that two damping factors are used to control step length and search direction is put forward. The improved damping least squares inversion method with little dependence, fast convergence rate and high accuracy is put forward based on theoretical formula. Apparent resistivity and IP data are inversed at the same time. And many models for the water-bearing structures are inversed successfully. Finally, the physical model tests and engineering applications show that IP fast inversion method is efficient in detecting water-bearing structures. And it provides a feasible approach to solving the problem of advanced detection of many water-bearing structures.