Analytical Study of Transient Seepage Effects on Soil Responses Surrounding Deep Diversion Tunnels

High hydraulic gradients induced by initial water filling in diversion tunnels with permeable linings or sudden fluctuations in total head inside the tunnels trigger transient seepage in the surrounding soils. Although this transient flow helps relieve excess pore pressure, it also leads to significant ground deformation, variations in in‐situ stress, and expansions of the plastic zone around the tunnel. This effect is especially produced in deep tunnels embedded in low‐permeability soils, where the transient flow process may be prolonged and have a substantial impact on the local stress‐strain environment. This study presents an analytical solution for characterizing transient seepage around deep tunnels by employing the superposition principle and the method of separation of variables. A seepage stress potential function is introduced to analyze the variations in soil responses and plastic stress evolution under high in‐situ stress conditions based on the Mohr–Coulomb failure criterion. The results show that stress, strain, and displacement within the soil are proportionally related to the total head difference between the tunnel interior and the surrounding ground. Specifically, rheological soil behaviors accelerate the transient seepage process. The plastic zone, influenced jointly by transient seepage and in‐situ stress, undergoes significant development before stabilization. The proposal analytical solution provides a rigorous and highly efficient tool for evaluating the operational environment of diversion tunnels and supports their safe and effective designs and maintenance.