On December 30, inside the Qingdao Port terminal, as the cutterhead of the "Haitian" shield machine slowly rotated, the main-line tunnel of the south line of the Qingdao Jiaozhou Bay Second Tunnel—invested in and built by Qingdao Conson Group and constructed by China Railway 14th Bureau Group—began shield tunneling. This marks the official start of the shield-driven undersea operation for the main body of the world's largest and longest subsea road tunnel.

The tunnel connects Qingdao's main urban area with the Qingdao West Coast New Area of *** New Area, with a design speed of 80 km/h. The project has a total length of 17.48 km, and the main tunnel is 14.37 km long, of which 9.95 km is the undersea section. This shield tunneling drive covers a distance of 3,255 meters, tunneling westward from inside the Qingdao Port terminal toward the West Coast, where it will connect with the drill-and-blast tunnel section, and the shield machine will be received and dismantled in an undersea chamber.

The undersea geological conditions of Jiaozhou Bay are complex. The "Haitian" shield machine enters the sea immediately upon launch and must traverse long distances through complex, variable, soft-hard uneven and fault-zone strata. At the same time, the maximum burial depth of this tunnel section is 95 meters, and the water and soil pressure is enormous—equivalent to bearing nearly 100 kilograms of weight on an area the size of a fist. To this end, the builders adopted a super-large-diameter slurry balance shield machine with an excavation diameter of 15.63 meters, designed to withstand a maximum pressure of 12 bar, optimized equipment selection and material application, and equipped it with intelligent systems such as a telescopic main drive and excavation chamber monitoring to improve tunneling efficiency and safety assurance.

It is reported that the Jiaozhou Bay Second Tunnel takes the form of a main tunnel plus an intermediate service tunnel, and also functions as a cross-sea passage for both passenger and freight vehicles. The total excavated earth and rock volume exceeds 6 million cubic meters, surpassing Japan's Seikan Undersea Tunnel and the Channel Tunnel between Britain and France, among others. It is also the undersea tunnel with the largest cross-section connecting the drill-and-blast method with the shield method.

After the tunnel opens to traffic, Qingdao will enter the "dual-tunnel era," which is of major strategic significance for alleviating cross-bay traffic pressure, promoting the integrated development around Jiaozhou Bay, building a global ocean city, and creating a bridgehead for opening up.