On July 30, the world's largest diameter high-speed rail shield machine, the "Leading Arrow," independently developed by China, successfully reached the No. 2 shaft on the south bank of the Yangtze River, marking the completion of the river-crossing section of the Chongtai Yangtze River Tunnel. This achievement set a new world record for a 15-meter-class large-diameter shield machine, continuously excavating 11.325 kilometers without intermediate stops.

This is also the world's first instance of a horizontal shield machine achieving an "intersection reception" with a shaft underground, providing a "Chinese solution" for the construction of ultra-large diameter shield tunnels worldwide. The Chongtai Yangtze River Tunnel is a critical control project of the national "Two Priorities" initiative, the Shanghai-Nanjing section of the Huyichang High-Speed Railway. It connects Shanghai's Chongming Island with Jiangsu's Taicang, spanning a total length of 14.25 kilometers and featuring three shafts.

The shield tunnel section from the No. 3 shaft on the north bank to the No. 2 shaft on the south bank measures 11.325 kilometers. With a maximum burial depth of 89 meters beneath the riverbed, an ultra-high water pressure of 0.9 MPa, and a design speed of 350 km/h, it is currently China's highest-standard and most technically challenging high-speed rail river-crossing tunnel. The project is managed by Shanghai Guotie Construction Management Company and constructed by China Railway Tunnel Group.

The "Leading Arrow" shield machine used for the Chongtai tunnel has a cutterhead diameter of 15.4 meters, a total length of 148 meters, and weighs approximately 4,000 tons. It is equipped with the "smartest brain" for shield control, the I-TBM system, along with high-water pressure sealing systems, long-life main bearings, and wear-resistant cutterheads. It features intelligent functions such as pressure self-adaptation within the chamber, data self-decision-making for cloud predictions, self-cruising for excavation posture, and self-adjustment for ring-flow slag discharge, enabling unmanned intelligent excavation under full system algorithm control. For the first time underwater in the Yangtze River, it achieved over 11 kilometers of continuous excavation, completing an unprecedented "ultra-long-distance run" beneath the riverbed.

The No. 2 shaft on the south bank was constructed for the reception, maintenance, and second launch of the "Leading Arrow" shield machine. The construction team custom-designed the world's largest diameter vertical shaft boring machine, the "Dawn," with a diameter of 24 meters, a maximum excavation depth of 75 meters, and the ability to withstand 8 bar water pressure. Equipped with multiple innovative technologies, it achieves integrated "excavation, support, and transport" operations, solving construction challenges like "invisibility and measurement inaccuracy," and setting records of 4 meters daily and 56.08 meters monthly for shaft excavation, ensuring precise reception of the "Leading Arrow."

The geological conditions at the Yangtze River estuary are complex, described as a "geological museum, hydrological pressure cooker, and ecological sensitive zone." The project required reaching depths of 89 meters beneath the riverbed while maintaining an ultra-long, high-pressure excavation of over 11 kilometers, demanding high technical standards and presenting significant difficulties. Shanghai Guotie and China Railway Tunnel Group adhered to a "risk-first, systematic planning" approach, establishing an expert committee and releasing the "Blue Paper on Intelligent Construction of Chinese Shield/TBM Tunnels." They routinely applied a nine-major intelligent construction technology system, including intelligent sensing, intelligent prefabrication, intelligent excavation, and intelligent control, building a three-in-one multi-layer protection system of "sealing, grouting, and intelligent monitoring." This system enabled data collection and intelligent early warning for processes like shield excavation, shaft construction, segment production, and liner installation, controlling tunnel alignment accuracy to millimeter levels, and successfully crossing the Yangtze River embankment, main shipping channel, and national-level aquatic germplasm resource protection areas for the Chinese noodlefish.

The construction team strengthened safety through penetration management, implementing a "factory-based thinking + standardized execution" model. Using Work Breakdown Structure (WBS) project decomposition and grid management, they broke down processes like shield excavation, segment assembly, and box culvert installation into standardized, assembly-line operations. They established a closed-loop control mechanism of "first-piece system + SOP + factory-based operation" to ensure safe and orderly progress of the 10-kilometer river-crossing project. For ecological and environmental protection, the entire project promoted green construction with "no slurry on the ground, no slag on the ground," employing a fully enclosed integrated mud-water separation circulation system and multi-stage water hammer pressure relief devices to achieve zero ground contact and resource recycling of slag and mud. Low-disturbance intelligent pressure-holding excavation technology was used to minimize deformation of the riverbed soil layer and impact on the aquatic ecology, safeguarding the Yangtze River ecosystem and the environment of Chongming Island, a world-class ecological island.

According to the construction schedule, after the "Leading Arrow" undergoes thorough maintenance at the No. 2 shaft, the project team will organize its second launch to complete the "final 1.8 kilometers" of excavation from the No. 2 shaft to the No. 1 shaft, with full tunnel completion expected by the end of 2026. Once operational, the Chongtai Yangtze River Tunnel will significantly reduce travel time between Shanghai and Jiangsu, enabling high-speed rail to cross the river without decelerating for the first time. It will also end the era without high-speed rail access to China's third-largest island, Chongming Island, playing a vital role in building a "rail-based Yangtze River Delta" and serving the high-quality development of the Yangtze River Economic Belt and regional integration.