Flexible joint is an important part of concrete immersed tunnel as it must be sufficiently flexible and resilient, as well as waterproof. The element tube at the joint is weakened in section to make space for joint construction. This weakened part, called extended shell, is a structural weak area, although it only transmits limited axial and vertical load between elements. This paper is based on an actual project, and investigates the structural performance of extended shell under external load, and its influence on adjacent tunnel structure. For the investigation, a model of tunnel segment at element end is established and analyzed with FEM software ANSYS. From the results, conclusions are drawn that the extended shell is structurally reliable, and does have a certain influence on the stress and deformation of adjacent tunnel structure, which is not considered yet by now. This should be paid more attention in further research and design.
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