Analytical solution of external water pressure on deep tunnel lining in horizontally layered hydrogeological structures

Tunnel engineering worldwide frequently encounters design and construction problems related to high external water pressure, especially in deep tunnels. Nowadays, analytical solutions of external water pressure on tunnel lining usually assume that the surrounding rock mass is homogeneous. In this study, physical laboratory tests are carried to obtain seepage field in two types of horizontally layered hydrogeological structures. A new analytical solution method is investigated to compute the external water pressure accurately and fast in horizontally layered hydrogeological structures. The proposed analytical solutions are verified by numerical simulations. Results show that when the upper layer has high permeability and the lower layer has low permeability, the external water pressure is obviously governed by the permeability of the upper and lower layers, the ratio of the upper layer’s thickness and the distance between the top of a tunnel and the boundary of the upper and lower layers. When the upper layer has small permeability and the lower layer has high permeability, the external water pressure is mainly affected by the permeability of the lower layer, and the permeability of the upper layer could be ignored.