Analytical investigation of tunnel deformation caused by circular foundation pit excavation

With the continuous progress of urbanization, excavation works near tunnel engineering projects are increasing. The stress relief caused by the excavation inevitably affects the deformation of a tunnel. Therefore, it is of great theoretical and practical significance to correctly evaluate the tunnel’s transverse and longitudinal deformation to ensure its safe and normal operation. Many studies have been conducted on the effect of quadrangle excavation on the deformation of adjacent subway tunnels. However, the influence of circular excavation on tunnel deformation is still not fully understood, and remains the main technical barrier toward optimal engineering design and construction. Based on Mindlin’s displacement solutions, an analytical model of tunnel deformation resulting from a circular excavation was developed, and the reliability of the solution was verified by comparison with existing centrifuge model test results and an analytical solution for a square excavation. On this basis, the influence of the basement geometry, relative position of the tunnel and basement, and soil’s Young’s modulus on tunnel deformation resulting from a circular excavation were analyzed. The results revealed that the analytical solutions proposed in this paper can better predict the maximum tunnel heave resulting from a circular excavation. Moreover, the maximum tunnel heave increased linearly as the diameter and depth of the circular basement excavation increased. However, the non-linearity decreased with the tunnel cover depth. The results obtained by this study can provide a simple calculation method to predict the maximum tunnel heave caused by a circular excavation, and can also be used to confirm the rationality of a numerical simulation.