为经济合理地解决甬舟铁路金塘海底隧道盾构段衬砌选型难题，结合隧道盾构段超高水压、超长距离、复杂海域环境及防灾疏散救援难度大等特点，围绕结构横断面受力变形分析和隧址海域条件特殊工况分析、衬砌纵向地震响应及风险处置等方面进行单双层衬砌比选研究，论述设置双层衬砌的必要性、可行性及经济性。其中，为实现全环叠合式双层衬砌，从有效净空面积和轨下结构型式等方面对双层衬砌结构断面进行优化。研究结果表明： 1）静力荷载工况下，双层衬砌方案结构变形相对较小，对轨道平顺性更有利，但总体上和单层衬砌方案差别不大； 进一步考虑海域段复杂的建设环境，从长久安全考虑，宜预留二次衬砌空间。2）纵向地震工况下，叠合式衬砌结构二次衬砌与管片连接性能较强并共同承载，能够显著降低管片峰值变形和应力，土层段拱顶最大降幅为20.58%，并通过减震措施解决二次衬砌易受拉损伤的不足。3）通过R=P×C定级法的风险评价方法进行分析，发现降低风险的投入（3.42亿元）要低于风险损失费期望值（3.47亿元），最终推荐采用双层衬砌方案。4）将轨面以上有效净空面积优化为83.79 m²，经数值计算，车体表面最大压力变化幅值和车内瞬变压力均满足相关规范要求； 相比净空面积不小于90 m²的直径14.6 m双层衬砌断面，横断面直径减小4.3%。5）依据防灾救援净空要求和断面气动效应研究结论，通过优化轨下结构型式，叠合式双层衬砌圆周范围为90.70%，基本实现全环叠合式双层衬砌，相较于直径14.3 m、全环30 cm现浇二次衬砌断面，横断面直径减小2.1%。

To rationally and economically select a feasible lining structure for the shield section of the Jintang subsea tunnel of the Ningbo-Zhoushan railway, the characteristics of the subsea shield tunnel such as ultrahigh water pressure, ultralong distance, complex sea environment, and challenges in disaster prevention, evacuation, and rescue are summarized. A comprehensive comparison of single- and double-layer lining structures is conducted in terms of structural stress and deformation, specific subsea working conditions, longitudinal seismic response, and risk mitigation. This analysis establishes the necessity, feasibility, and economic advantages of the double-layer lining structure. In addition, the double-layer lining structure section is optimized to enhance the effective clearance area and subrail structure type, enabling the realization of a full-ring superimposed double-layer lining. The findings reveal the following: (1) Under static load conditions, the structural deformation of the double-layer lining scheme is relatively small, benefiting track smoothness, though comparable to the single-layer lining scheme. Space should be reserved for secondary lining, considering the complex construction environment of the sea section and long-term safety. (2) Under longitudinal earthquake conditions, the composite lining structure, consisting of the secondary lining and segment, demonstrates stronger connection performance, jointly bearing the load. This significantly reduces the peak deformation and stress of the segment, with a maximum decrease of 20.58% at the crown. Shock absorption measures address the vulnerability of the secondary lining to tensile damage. (3) Using the R=P×C grading risk assessment method, the risk reduction cost (RMB 342 million) is lower than the expected risk loss cost (RMB 347 million), indicating the superiority of the double-layer lining structure. (4) The effective above-rail net clearance area is optimized to 83.79 m², resulting in a reasonable change in the maximum stress on the train surface and transient pressure. The net clearance area is 4.3% less than the double-layer lining with a net clearance area of no less than 90 m² and a cross-sectional diameter of 14.6 m. (5) Based on disaster prevention, evacuation, and rescue requirements, as well as the aerodynamic effects of the cross-section, the subrail structure type is optimized. The circle range of the full-ring superimposed double-layer lining achieves 90.70%, with the cross-section diameter reduced by 2.1% compared to the full-ring 30 m cast-in-place secondary lining, which has a cross-section diameter of 14.3 m.