Abstract: The authors present a case analysis of diseases in an operational immersed tunnel. Field investigations are conducted to assess the tunnel′s condition, and the causes of tunnel diseases are examined using diagnostic methods. Based on the findings, treatment measures are proposed to ensure the tunnel′s safe operation. The primary interventions include foundation treatment and shear key repair. For foundation treatment, the horizontal directional grouting and floor grouting methods are compared and analyzed. The shear keys are reinforced through different repair approaches, including the reinforcement of W-steel plates on the sidewall, the repair of shear key steel adhesion, and the addition of a shear frame in the middle corridor. The results indicate the following: (1) The operational immersed tunnel exhibits foundation cushion voids, pavement cracks, and shear key damage, primarily caused by uneven settlement between tunnel joints. This settlement is closely linked to factors such as river siltation, erosion, and foundation cushion loosening during operation. (2) The floor grouting method is more convenient, has minimal environmental impact, and effectively controls uneven settlement at a lower cost. (3) The W-steel plate reinforcement method significantly improves the shear strength of the middle partition wall′s concrete shear bond and is relatively simple to implement. Based on these findings, W-steel plate reinforcement and floor grouting are recommended for this case.

Key words: immersed tunnel, disease, floor grouting, shear key, W-steel plate reinforcement