Influence of Shallow-Buried Bias Tunnel Unloading on the Longitudinal Displacement of the Underlying Tunnel

Abstract

With the continuous development of traffic tunnels, the construction of new tunnels that intersect with existing ones has become increasingly common. The situation of tunnel bias is inevitably encountered and has a more adverse impact on the existing tunnels. This paper proposes a semianalytical method for calculating the displacement of a tunnel caused by the construction of a shallow-buried bias tunnel overlying it. In this method, the unloading load of the tunnel is orthogonally decomposed along the ground. Utilizing the Mindlin solution and mechanical stress formulas, this paper calculates the additional stress imposed on the existing tunnel by the excavation and unloading of the new tunnel, considering the ground inclination angle φ₀. This paper models the existing tunnel as an Euler–Bernoulli beam resting on a Winkler foundation to calculate the tunnel displacement. Compared with measured data from the project site, this method can better predict the uplift displacement of the existing tunnel. Furthermore, this paper investigates the influences of various factors, such as the distance between the upper and lower tunnels, the equivalent stiffness of the lower tunnel, and the ground inclination angle, on the displacement of the existing tunnel. The findings reveal that inclined ground can cause the maximum uplift position of the existing tunnel to deviate, and this offset is positively correlated with the angle. Based on these factors, practical construction recommendations are provided.