Abstract: The integration of highway and metro systems within a double-layer shield tunnel presents several challenges, including layout design, structural integrity, combined vibrations from vehicles and trains, and ventilation and smoke extraction. A case study is conducted on the Jiluo road Yangtze river-crossing tunnel in Wuhan, China, and key design technologies for double-layer shield tunnels are analyzed through comprehensive comparison and 2.5-dimensional numerical simulations. The findings include: (1) The underground space required for the highway-metro double-layer shield tunnel can be minimized by optimizing the layout of the tunnel′s plane, longitudinal and horizontal cross-sections, and implementing specialized designs for wastewater pump rooms and evacuation staircases. This approach enhances the cross-sectional utilization and allows for a reduction in the tunnel′s outer diameter. (2) The use of a semiprefabricated and semi-cast segment combined with a nonclosed lining structure improves the overall bearing capacity of the internal structure and segment lining, significantly reducing riverbed erosion and deposition. (3) The combined vibrations from automobiles and metro trains slightly affects the tunnel, and the saturated fine sand stratum at the tunnel base remains stable without liquefaction. (4) Segmented longitudinal flues in the metro tunnel effectively manage smoke extraction over long sections without requiring air shafts, facilitating evacuation and greatly reducing construction challenges. (5) The inevitable cross-influence between highway and metro operations necessitates advance study of management interfaces and investment division to aid in effective decision-making.

Key words: highway-metro integrated construction, double-layer shield tunnel, intensive design, highway-metro combined vibration effect, ventilation and smoke exhaust, disaster prevention and evacuation