English：

In view of the design requirements and potential risks of shield tail lengthening in theconstruction of synchronous shield tunnels, a three⁃dimensional finite element model of the shield shell isconstructed to study the mechanical response of the shield shell structure under water and soil load basedon a shield tunnel section project of the Shanghai Metro. The influence of shield tail length andoverburden thickness on the stress and deformation of the shield shell is mainly discussed. The resultsindicate that the shield shell structure has sufficient strength and deformation margin under a designoverburden thickness of 25m and a shield tail length of 3. 65m. The maximum deformation and stress ofthe shield shell increase linearly with the length of the shield tail and increase nonlinearly with the depthof the overburden soil and are significantly affected by the initial geometric defects. To ensure that themaximum deformation of the shield tail is less than the minimum shield tail clearance under the shieldpitching excavation, the design should comprehensively consider the buried depth change and thegeometric initial defect, and the shield tail lengthening design should be carried out in a targeted manner.