Analytic study of stress and displacement for shallow twin tunnels subjected to surcharge loads

•Solution for in-service shallow-buried twin tunnels subjected to surcharge loads is presented.•The Flamant solution and the complex variable method are iteratively combined.•Twin tunnels of arbitrary geometry and surcharge loads of different form are considered. This paper presents an analytical solution for the stress and displacement for shallow twin tunnels subjected to surcharge loads. Multi-interactions, including the interaction between liners and geomaterial, the interaction between twin tunnels, and the interaction between surcharge loads and twin tunnels, are considered in the proposed solution. The solution is elaborated using an iterative three-step procedure based on the Schwarz alternating method. The complex variable method and the Flamant solution and its modification are employed in the derivation. Verification of the analytical solution is obtained through comparisons to a corresponding numerical solution and an existing case study. The close correspondence indicates the accuracy and generality of the proposed solution. A parametric investigation is performed to investigate the influence of surcharge load (including load position, range and distribution), elastic parameters of geomaterial, and liner geometry (including tunnel radius and liner thickness). Based on the parametric investigation, several advices for surcharge loads and liners are provided to help tunnel designers to avoid possible damages for shallow twin tunnels.