Mechanical responses of existing tunnel due to new tunnelling below without clearance

With the development of urban subway, there are more projects of new subway construction below existing subway. The project is more challenging if the new subway is excavated below the existing subway with no pillar in between. In this research, we propose an analytical solution to investigate the mechanical responses of the existing tunnel due to new tunnel construction below without clearance. We put forward a superposition method based on the Winkler model to simulate the absence of the springs under the existing tunnel at the intersection of the new and existing tunnel. The proposed solution is successfully validated by FEM simulation. The influences of the input parameters of the model, including the range of deleted springs, the coefficient of subgrade reaction, and the equivalent bending stiffness, on the deflection and the bending moment of the existing tunnel, are studied. The research can serve as a reference to ensure both the safety and the serviceability of existing tunnels in case of new tunnelling below existing tunnel without clearance.