On January 11, the "Haihong" shield machine, independently developed by China Railway Engineering Equipment Group, successfully completed the subsea tunnel on the section from the Railway Station to the South Suoyuwan Station of Dalian Metro Line 5. This marks China's successful conquest of the "world-class challenge" of a large-diameter shield tunneling beneath karst geology under the sea, accumulating valuable experience for subsea karst strata and long-distance hard-rock large-diameter shield construction in "river-crossing and sea-crossing" tunnels worldwide.

It is understood that Dalian Metro Line 5 has a total length of 24.484 kilometers and 18 stations. The large-diameter shield section from the Railway Station to the South Suoyuwan Station, a controlling project of the entire line, is 2,882 meters long, of which 2,310 meters run beneath the waters of Dalian's Suoyuwan Bay.

China Railway Engineering Equipment Group actively implemented General Secretary Xi Jinping's important instruction on the "Three Transformations," vigorously explored the adaptability of shield machine construction under new working conditions, and made every effort to overcome the "world-class challenge" of long, deep underwater tunnels. It developed the "Haihong," the world's most functionally complete and technologically advanced shield machine (a 12.26-meter-diameter air-cushion slurry pressure-balance shield machine), for the sea-crossing construction, and pursued technological and management innovation, building an intelligent information management system to guide on-site construction in real time.

The "Haihong" was launched on January 18, 2019. In the sea-crossing construction, it faced four major difficulties—"long, large, high, and risky"—which brought unpredictable challenges to construction and were characterized by industry experts as an unprecedented "world-class challenge." "Long" refers to the long excavation distance in high-strength hard-rock strata; the shield machine had to continuously tunnel through 2,882 meters of hard rock. "Large" refers to the high environmental risk: the large-diameter shield passes beneath navigation channels, wharves, and other important structures and traffic facilities, through weathered troughs, fault zones, and heterogeneous strata, with limestone, diabase, and calcareous slate widely distributed. The rock compressive strength is high, with a maximum of 118 MPa, posing great safety risks. "High" refers to the great tunnel burial depth and high water pressure, with a maximum water head pressure of 0.5 MPa, equivalent to the pressure of three people standing on an area the size of an egg. "Risky" refers to the tunnel passing through 1,538 meters of a strongly developed karst area, where exploration found more than 1,000 karst caves of various sizes, with the largest cave 29.8 meters high. Detecting and treating the karst caves is extremely difficult and risky, and shield tunneling had to proceed as cautiously as "mine clearance."

The "Haihong" successfully completed the subsea tunnel breakthrough on the Huosuo section of Dalian Metro Line 5. Once the metro is completed, it will form a north-south urban express corridor, shortening the travel time between Suoyuwan and the Railway Station from more than 30 minutes to less than 3 minutes, effectively alleviating pressure on surface traffic and building a new coastal urban pattern of "one bay, two shores."