Analytical Solution of Seepage Response Around an Underwater Tunnel With Grouting Ring Under Water Level Fluctuations

ABSTRACT Underwater tunnels are sensitive to load variations induced by external water level fluctuations, making accurate prediction of pore pressure on tunnel linings essential for structural safety. Existing analytical studies on transient seepage often neglect the backfill grouting layer, leading to overestimated pore pressures and potentially unsafe design assessments. To address this limitation, this study investigates the transient seepage field within a composite “soil‐grouting ring‐lining” system under two scenarios: surface water level fluctuations (SWF) and groundwater level fluctuations (GWF). Based on the decoupled Biot's consolidation theory and the principle of superposition, a rigorous analytical solution is derived. The accuracy and engineering applicability of the proposed method are strictly validated against numerical simulations and field monitoring data from the Qingchun Road Tunnel in Hangzhou, China. Parametric analyses show that increasing grouting ring permeability reduces pore pressure and improves its distribution uniformity. With increasing soil permeability, pore pressure exhibits a three‐stage nonlinear evolution: rapid rise, gradual increase, and decay to zero. Increasing grouting ring thickness effectively decreases pore pressure, and when the grout‐to‐lining thickness ratio is below 0.5, tunnel diameter has negligible influence. Mechanical properties also play a key role: higher grouting stiffness increases pore pressure but stabilizes beyond a modulus ratio of 0.002, while greater soil shear modulus reduces pore pressure. These findings provide a theoretical basis for improved design of underwater tunnels considering grouting effects.