Abstract: One of the key aspects of the construction of underwater shield tunnels lies in the design of the overburden thickness. A substantially small thickness of the overburden layer increases the instability tendency of surrounding rocks under construction disturbance, causing disasters such as collapse and water inrush. By contrast, an excessively large thickness will necessitate higher requirements for the project budget and construction period. The authors, supplemented with a comprehensive review of literature and insights from real world underwater tunnel engineering cases, systematically study and review the current rational design and calculation methodologies for overburden thickness. The content is crucial in ensuring the safety and stability of the underwater shield tunnel structure and smooth progress of the project, which can provide a reference for follow-up research and engineering practice. Several key findings are as follows: (1) Theoretical analysis and numerical simulation methods are included in the design methodologies for underwater shield tunnels. (2) Theoretical analysis methods are divided based on the focus of stability analysis, differentiating between those accounting for antifloating and tunnel face stability. (3) Current design methodologies for reasonable overburden thickness in underwater shield tunnels primarily rely on numerical simulation and theoretical analysis. However, these approaches oversimply actual engineering conditions, disregarding the nuanced influence of complex building environments, construction technology, and the intrinsic structural characteristics of the tunnel. Consequently, the research depth of overburden thickness and the applicability of design methodologies can be improved by conducting further research. (4) Currently available research on the minimum overburden thickness of shield tunnels in water-rich environments has been abundant, but its integration with the actual engineering is difficult. Overall, the aspects of construction economy, construction process, complex environmental impact, structural life, and intelligent construction platform should be further considered in future research.

Key words: underwater shield tunnel; reasonable overburden thickness, antifloating stability, tunnel face stability; design methods