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This study investigated the bearing capacity and failure characteristics of a shield tunnel lining structure subjected to top overload and simultaneous unloading on both sides of a tunnel, considering the presence of internal water pressure. The results show that the structural response of the shield tunnel lining is most unfavourable under the condition of a fully filled pipe, where the internal water pressure reduces the axial force of the lining ring section, compared with the conditions of an empty pipe and a partially filled pipe. When the internal water pressure increases from 0 MPa to 0.6 MPa, the convergence deformation of the lining ring under a top overload of 400 kPa increases by 23.6%, resulting from a reduction of 27.2% in the maximum axial force at the lining section. Similarly, the convergence deformation of the lining ring under simultaneous unloading of 400 kPa on both sides of the tunnel increases by 21.6% because of a reduction of 56.4% in the maximum axial force at the lining section. The shield tunnel lining rings under the action of internal water pressure when subjected to top overload or simultaneous unloading on both sides of the tunnel exhibit the same failure characteristics. As the overload or unloading value increases, the lining ring deformation gradually increases, the joint opening exceeds the waterproof design limit, and the bolt enters a plastic yield state as its stress exceeds the yield strength. Cracks occur in the concrete at the positions of the lining segments, segmental joints, and handholes because of the large strain values. Moreover, the stress of the steel bars, joint panels, and anchor bars inside the lining segments may exceed their yield strength. During the top overload, the bending moment and axial force of the lining ring section increase, whereas when unloading on both sides of the tunnel, the bending moment increases and the axial force decreases. Compared with the case with an overload value of 400 kPa, the maximum positive and negative bending moments of the lining ring under a lateral unloading value of 400 kPa decrease by 11.5% and 14.4%, respectively, whereas the maximum axial force decreases by 73.1%. This considerable decrease in axial force during lateral unloading leads to greater section eccentricity and a more adverse structural response of the lining structure than does top overload. Therefore, during the operation of shield tunnels with internal water pressure, the influence of unloading on both sides of the lining structure caused by soil stress relaxation should be taken seriously.

来源平台：INTERNATIONAL JOURNAL OF CIVIL ENGINEERING