Mechanical behaviours of existing tunnels due to multiple-tunnel excavations considering construction sequence

An analytical method utilizing the extended complex variable approach is presented to investigate the mechanical characteristics of pre-existing tunnels affected by the excavation of multiple tunnels. In contrast to conventional methods, this proposed approach accommodates the consideration of the construction sequence of the newly introduced multiple tunnels, the cross-sectional shapes of new tunnels, as well as different displacement and stress boundary conditions at the inner boundary. The validity of the proposed method is confirmed through numerical simulations and subsequent comparisons with other established methods. Subsequently, an in-depth analysis is performed on a project involving four shield tunnels constructed beneath existing tunnels in Shen Zhen. This analysis explores the effects of the construction sequence, the cross-sectional design of new tunnels, stress release coefficients, and deformation convergence patterns on the mechanical response of the preexisting tunnel. Additional influencing factors, such as the horizontal clearance between new tunnels and the supporting stiffness of concrete liners, are also thoroughly analysed. The results demonstrate that our proposed method exhibits exceptional applicability and universality in predicting the mechanical behaviour of existing tunnels affected by new tunnel construction.