English：

Aiming at the problems of difficult alignment, difficult control of deformation and difficultunification of connection safety in the underwater docking of the final closure section of super⁃largediameter HDPE submarine pipe, based on the JIGCC water intake and drainage project in Gizan, SaudiArabia, an underwater connection installation method of moderately lengthening the closure section andreverse arcing is proposed. The mechanical analysis model under end constraints is established to studythe relationship between growth, arc shape, nozzle displacement and internal force response, and tocheck the bearing capacity of flange ring. The results show that the reserved growth is mainly transformedinto the displacement of the nozzle, and the elongation consumption of the pipe section is small. Thedouble arc shape formed by the pulling effect can achieve displacement coordination, and the structuralresponse is mainly overall bending. Under various working conditions, the strength of the pipe sectionand the flange connection meet the requirements. Finally, the closure can be transformed from empiricalunderwater adjustment into a flexible deformation coordination process with controllable parameters.