Enhanced Analytical Method for Evaluating the Existing Tunnel Response Caused by Tunneling Underlying

In order to figure out the response of existing tunnel induced by shield tunneling underneath, an enhanced analytical method for estimating the interaction between existing tunnels and surrounding soil is proposed. The Loganathan solution is employed to obtain the free displacement field of the surrounding soil induced by the shield tunneling. Subsequently, the existing tunnel is simplified as a Euler–Bernoulli beam placed on a Vlasov foundation, considering the lateral soil effect on both sides of the existing tunnel. By utilizing the boundary conditions of the existing tunnel and expanding in terms of the Maclaurin’s series, an enhanced analytical solution for the tunnel deformation response can be derived. Comparing the results with measured data from Shanghai engineering, it can be found that the results given by this method closely match the measured data, demonstrating its reliability. When compared to the degenerate analytical solution, our method’s results better align with the measured data. Then a series of parameter analysis is conducted. The parameter study reveals that as the vertical clearance between two tunnels increases, the influence of shield tunnel excavation on the existing tunnel gradually diminishes. Increasing the ground loss ratio leads to a linear increase in the displacement and flexural moment of the existing tunnel. Additionally, enhancing the existing tunnel’s flexural stiffness significantly reduces the impact of shield tunnel excavation on the stress and deformation response of the existing tunnel.