Abstract: The high water head at the onshore final joint of the immersed tunnel of the dry dock of the Yuliangzhou section on the EastWest axis in Xiangyang, China has led to a complex secondary cofferdam structure of the dock door and a difficult water stop. To address these issues, a steel shell sandwich wall concrete cofferdam waterretaining structure and a triple waterproof structure at the bottom of the immersed tube (i.e., rubber water stop + mold bag concrete + underwater grouting) are proposed. The strength and the deformation of the cofferdam retaining structure are simulated using the finite element method. The compression sealing performance of the rubber water stop is examined using the laboratory test method. The grouting technology and the water stop feasibility of mold bag concrete are also investigated. The adopted technologies guarantee high efficiency, rapid construction of the secondary cofferdam structure, and good waterstop effect. The successful application of the recommended technologies shows that a new structure of the steel shell sandwich wall concrete cofferdam can be used in a secondary cofferdam waterretaining design. Furthermore, the triple waterproof structure achieves a reliable waterstop effect when the clearance range between the immersed tube and the force transfer plate foundation is within 100 mm.

Key words: immersed tunnel, axis dry dock, final joint, secondary cofferdam, steel shell sandwich wall concrete, triple waterproof structure