Numerical Simulation on Deformation and Damage Mechanism of Existing Underground Structures Induced by Adjacent Construction of Super-Large-Diameter Tunnels

The development of urban underground spaces has led to an increasing number of projects involving super-large-diameter shield tunnels, making research on their impact on existing structures particularly significant. This paper investigated the numerical simulation on deformation and damage mechanism of existing underground structures induced by adjacent construction of super-large-diameter tunnels. A 3D finite element model using ABAQUS (version 2022) software incorporating the Concrete Damaged Plasticity (CDP) constitutive model was established, and this paper was used to systematically analyze the deformation, internal force response, and damage evolution of existing tunnels. The results showed the following: (1) The double-line tunnel excavation intensified settlement superposition, increasing the maximum settlement from −19.70 mm (single-line) to −24.51 mm (double-line) and transforming the settlement trough from a V shape to a W shape. (2) The vertical bending moment evolved from a single peak to double peaks being the dominant loading mode, with the maximum horizontal moment only about 1/8 of the vertical value. (3) During the construction, the peak tensile stress at the tunnel bottom reached 2.655 MPa, exceeding the C50 concrete tensile strength, but later decreased to 2.097 MPa. Damage was primarily caused by bending-induced tension. (4) Tunnel damage was triggered by the historical peak stress and accumulated irreversibly, resulting in a final state of low-stress and high-damage, with a maximum tensile damage of 92.4%. This research can provide a theoretical basis for safety control in similar adjacent engineering projects.