Assessment of hydraulic conductivity ahead of tunnel face using hydrogeologic data under full-decay induced polarization constraints

Abstract With the rapid development of underground engineering, tunnel construction faces the challenge of increasingly complex geological conditions. Geological hazards, such as water inrush, frequently occur during tunnel construction. Specifically, water inrush is primarily governed by hydraulic conductivity. Therefore, accurately assessing the distribution of hydraulic conductivity ahead of the tunnel face is vital. However, applying hydraulic tomography (HT) as a routine method during tunnel construction is difficult because of its time-consuming implementation and limited data availability, which can significantly affect the construction schedule. Therefore, an inversion method using hydrogeologic data under full-decay induced polarization (FDIP) constraints is proposed to assess hydraulic conductivity distribution in front of the tunnel face. The proposed method combines the complementary advantages of HT and FDIP by constructing a spatial gradient function from the relaxation time to constrain the conventional HT inversion, thereby improving the accuracy of hydraulic conductivity inversion. The constrained inversion method is tested on synthetic model, and the results are compared with the individual HT. The results indicate that the proposed approach can more accurately delineate zones of high hydraulic conductivity. Additionally, the constrained inversion method is more robust because the constructed spatial gradient constraint function preserves the high-resolution gradient information from FDIP. Hence, the proposed method is applied to a diversion tunnel project in southwestern China, and the results demonstrate its ability to accurately assess the hydraulic conductivity ahead of the tunnel face. The proposed method is efficient and cost-effective and has potential for engineering applications, providing a feasible approach for accurately assessing areas with anomalous hydraulic conductivity ahead of the tunnel face.