Mitigating surcharge‐induced column‐head cracking in double‐deck shield tunnels using hyperelastic bearing joints

Abstract Double‐deck shield tunnels in urban areas may suffer severe cracking at beam–column joints of internal frames when subjected to surface surcharge, because lining ovalization imposes incompatible deformation demands on rigid internal connections. Motivated by field observations from a river‐crossing tunnel in Jiangsu, China, where diagonal cracks developed at column heads and the crack width exceeded 1 cm during temporary soil stockpiling, this study proposes a practical mitigation measure by inserting hyperelastic bearings (natural rubber, NR; polyurethane, PU) at beam–column joints to provide a “vertically stiff–horizontally compliant” connection. A staged three‐dimensional nonlinear soil–structure interaction (SSI) model is established, in which segmental lining joints are represented by calibrated multi‐directional connector elements and concrete damage is explicitly captured. The flexible joint releases part of the imposed displacement through shear deformation of the hyperelastic layer, thereby reducing column‐head shear/bending demand and redirecting surcharge‐induced load sharing toward stiffer slabs and the base. Compared with rigid joints, the proposed measure increases the ultimate surcharge resistance by about 54% (NR) and 58% (PU), while allowing larger convergence increments exceeding 0.07% of the segment inner diameter before severe damage. Practical implications for construction feasibility, inspection, and replacement of bearings, and risk mitigation measures are discussed. The proposed strategy provides a feasible and maintainable solution to enhance the serviceability and safety of double‐deck shield tunnels exposed to operational surcharge and imposed deformation.