Abstract: Conventional analytical methods for tunnel seepage fields－such as the mirror method, well-flow theory, and conformal transformation－are limited to single-layer geological structures. To overcome this limitation, the tunnel seepage field in stratified rock masses is decomposed into three components: the vertical unidirectional seepage field of the rock strata, the radial seepage field in the surrounding rock, and the radial seepage field in the tunnel lining. Based on groundwater dynamics and the complex potential function theory, the governing equations for each component are independently solved. Subsequently, the analytical solution for the overall seepage field under stratified rock mass conditions is derived using appropriate boundary conditions. The validity of the analytical solution is confirmed through numerical simulation of a representative engineering case. The analytical solution is further used to investigate the influence of layer thickness and permeability coefficients on tunnel seepage flow and the external water pressure acting on the tunnel lining in stratified rock environments. The results indicate that in tunnels overlain by strata with high permeability in the upper layers and low permeability in the lower layers, the thickness and permeability of the weakly permeable layer in which the tunnel is embedded critically control both the seepage flow and external water pressure. This phenomenon arises because the low-permeability layer acts as a relatively impermeable barrier within the stratified rock mass. Variations in its thickness and permeability significantly impact tunnel seepage behavior and lining water pressure.

Key words: tunnel, seepage field, characteristic stratification of rock mass, external water pressure, seepage flow, analytical solution