Effect of Excavation Sequence on Uplift Deformation of Underlying Existing Metro Tunnel

Abstract

Although an appropriate excavation sequence contributes to minimizing the excavation-induced impact on the underlying existing tunnel, few studies have focused on the comparison of the excavation sequence for engineering projects in practice. In this paper, the numerical simulations based on FLAC3D were carried out to discuss the excavation-induced impact on the underlying existing tunnel, and the numerical results were analyzed in combination with the field data through a case history. The influence of different excavation sequences on the underlying tunnel was interpreted in comparison with the practical construction process. The results show that the excavation directly above the existing tunnel is the main cause of the uplift deformation of the underlying tunnel and that the soil above both sides of the tunnel should be excavated preferentially. The timely application of the foundation pit floor structure, together with the uplift piles and isolated piles, forms a door-frame structure that can effectively suppress the uplift deformation of the underlying tunnel after the excavation directly above the tunnel.