Abstract: The existing terminal joint construction of an immersed tunnel is challenging due to multiple underwater operation procedures, complex construction technology, and difficult quality detection of underwater antithrust structure. To address these issues, a case study is conducted on the Hanjiang river immersed tunnel in Xiangyang, China, and a novel immersed tunnel terminal joint construction technique is proposed based on the concept of friction antithrust. This technique exploits the friction force between the tunnel elements and the surrounding stratum as well as the tension force of the temporary finish rolled steel bar installed at the element joints to compensate for the water pressure dissipated at the end of the final tunnel element, guaranteeing the safety and stability of the tunnel elements. Furthermore, the calculation methods for the total antithrust and thrust forces of the tunnel element are established. The research results reveal the following: (1) When the top of the tunnel elements is backfilled, the connection measure of setting up temporary finish rolled steel bars at the E1/E2 and E2/E3 joints is adopted, effectively exploiting the friction force between the tunnel elements and the surrounding sandgravel strata, and preventing the compressed Gina waterstop from bouncing back; thus, the safety and stability of tunnel elements can be ensured and a separate antithrust structure need not be set at the end of the immersed tunnel. (2) During dry dock pumping and castinplace tunnel construction, monitoring data of the opening and closing amount of tunnel element joints and the axial force of the temporary finish rolled steel bars are relatively stable and consistent with the calculation results; furthermore, the feasibility of the proposed terminal joint construction technique for the immersed tunnels based on friction antithrust is validated.

Key words: immersed tunnel, terminal joint, friction antithrust, temporary finish rolled steel bars