Theoretical analysis of seepage field in two supported circular tunnels within anisotropic ground

An alternative analytical solution to calculate the seepage field in two supported circular tunnels within a saturated ground is proposed, taking into account the interactions between two neighboring tunnels, rock-support, and anisotropy of permeability. The anisotropic problem is equivalent to the isotropic model using a coordinate transformation of the governing equation, and the Schwartz alternating method is employed to achieve solutions by satisfying all boundary conditions. A good agreement is observed between analytical solutions and numerical predictions, verifying the proposed analytical theory and the obtained solutions. Comprehensive parametric analyses are conducted to investigate the effect of key factors, such as anisotropy of permeability, permeability properties of support, spacings of twin tunnels, etc., on the seepage field. The results demonstrate that, as the permeability anisotropic ratio increases, the variation of water pressure with the polar angle (measured along the tunnel circumference from the horizontal direction) becomes more pronounced, leading to greater non-uniformity in both the distribution and the specific discharge of the seepage field. The proposed analytical solution provides a convenient alternative method for the preliminary design of twin-supported tunnels.