Impact of Pile–Beam–Arch Tunnel Enlargement Method on Ground Movements and Building Damage

Metro station construction in densely built urban areas often faces challenges due to limited space on the ground surface for conventional open-cut methods. In such situations, enlarging the driven shield tunnel proves to be a more viable alternative. This paper assesses the effectiveness of the Pile–Beam–Arch method for constructing metro stations by enlarging shield tunnels in areas where conventional methods are impractical. The process of tunnel enlargement involves the destruction of the existing lining and additional excavation around the tunnel, resulting in alterations to in-situ stresses and ground stability. The induced ground movements during this process can have significant impacts on nearby buildings, particularly in densely populated areas. To address this concern, our research focuses on analyzing the ground movements resulting from tunnel enlargement and evaluating their effects on adjacent buildings. Using a three-dimensional numerical analysis based on finite-difference FLAC 3D, we conducted a comprehensive study to assess the safety of the Pile–Beam–Arch tunnel enlargement method concerning adjacent structures in urban areas. The study revealed that the maximum horizontal displacement on the ground surface occurs at a distance of 1.6 times the diameter of the tunnel. This amount of displacement can potentially cause tension cracks in buildings within this vicinity. This indicates that the primary mode of damage in this location is the lateral displacement of the ground transmitted to the foundation and structure. In accordance with Boscardin and Cording diagrams, this critical distance emerges as a pivotal consideration for the safety and stability of urban buildings during the tunnel enlargement process.