To alleviate problems in urban living environments, an increasing number of shield tunnels have been built that go through rivers or underwater areas. Most of these tunnels experience leakage after a long period of operation, which can impact the safety of the tunnel and induce dangerous accidents, resulting in a loss of life and property. This paper reports the leakage characteristics during operation of a double-line ultralarge-diameter underwater shield tunnel that crosses the Yangtze River. After detailed geological surveys and field inspections of the prototype tunnel, the leakage characteristics and patterns of the tunnel were summarized based on long-term monitoring data. The distribution of leak-related defects was described in-depth with sketches and field photographs. Factors influencing the leakage of the prototype tunnel (i.e., the groundwater table, longitudinal settlement, and soil conditions) were interpreted based on field measurements. The mechanisms that triggered two typical leakage accidents that occurred during tunnel operation were systematically analyzed. The leakage mechanisms of the prototype tunnel were subsequently categorized into three patterns: joint leakage, bolt hole leakage and concrete crack leakage. Four countermeasures against leakage were proposed considering the leakage-associated damage to the prototype tunnel: backfill grouting, joint grouting, installation of a bolt hole sealing cover, and caulking gasket addition. The proposed mitigation measures were validated through laboratory tests and field applications. This unique tunnel prototype engineering case can provide a reference for water leakage prevention and control in the design, construction, and operation stages of similar underwater shield tunnel projects.

来源平台：TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY