3D multi-scale resistivity inversion method applied in the tunnel face to borehole observations for tunnel-ahead prospecting

Abstract

Many adverse geological structures, such as karst caves and faults, may exist in front of the tunnel face. If adverse geological structures ahead of the tunnel face cannot be detected clearly, geological hazards (i.e., the inrush of clay and water) may occur during excavation. In this study, a new ahead prospecting scheme was proposed to detect adverse geological structures during tunnel construction using probe holes. First, a new array was proposed: the potential electrodes were placed at the tunnel face, and the current electrodes were placed in the hole. The potential data were collected and used for inversion. Furthermore, a 3D resistivity multi-scale inversion method was proposed to locate and describe boundaries of geological structures with high accuracy. In this method, the 3D convolutional wavelet transform is used to extract wavelet parameter information from the resistivity model. On this basis, the inverted solution space is transformed from the spatial domain to the wavelet domain. The solution in the wavelet domain can be obtained using the inversion equation. Then, the solution in the spatial domain can be obtained from the wavelet domain using the 3D deconvolution transform. Finally, the effectiveness of the new ahead prospecting scheme was verified by numerical inversion tests. Furthermore, this paper describes the successful application of the new scheme to detect water-bearing structures in tunnel of the project “transfer water from Hongyan river to Shitou river”.