Abstract: River-crossing tunnels in urban core areas are constrained by limited construction sites, complex geological conditions, and sensitive surrounding environments, resulting in a complex coupling of design parameters and formidable overall design challenges. A case study is conducted on the Shayuzhou Tunnel in Guangzhou, China, and engineering analogy and scheme comparison methods are adopted to investigate key technical issues of the Shayuzhou Tunnel, including technical standards, overall alignment, cross-sectional layout, construction methods, island-landing schemes, and shallow-overburden treatment measures, based on road network planning, traffic volume prediction, and restrictive construction conditions. The primary conclusions are summarized as follows: (1) For river-crossing tunnels in urban core areas, the overall design should prioritize planning conformity, the rationality of technical standards, and the integrity of traffic functions, and special thematic assessments can be conducted for locally constrained sections. (2) It is unnecessary to deepen the entire alignment of large-diameter shield tunnels to accommodate localized shallow-overburden areas. Local ballast reinforcement can be adopted in ultra-shallow-overburden zones to satisfy the antifloating and safe tunneling requirements of shield machines, which provide a feasible reference for optimizing tunnel alignment length and controlling project investment. (3) When the main tunnel passes through Grade Ⅳ or higher surrounding rock at a suitable buried depth, a combined construction method using the mining method for the main tunnel and the shield method for the ramps is applicable to the island connection section. This approach avoids the adverse effects of open-cut-based elevation adjustment of the main tunnel on the overall longitudinal profile and driving comfort, offering a novel solution for the island-landing design of shield tunnels.

Key words: cross-river tunnel, super-large-diameter shield, overall design, ultra-shallow overburden, technical standards, construction method comparison and selection, island-landing scheme