China's Record-Breaking Tunnel Reaches 75m Below Yangtze

World's Longest Underwater Highway Tunnel Hits Major Milestone

Deep beneath the waters where the Yangtze River meets the sea, a massive boring machine named 'Jianghai' has just reached the deepest point of what will become the world's longest underwater highway shield tunnel. At 75 meters below the riverbed, the achievement marks a critical breakthrough in China's mega-infrastructure engineering capabilities.

The milestone, reported by CCTV on May 3, confirms that the domestically built 16.6-meter-class shield boring machine has completed 5,316 meters of excavation — setting a new depth record for ultra-large-diameter shield machines operating in underwater tunnel construction.

The Haitai Yangtze River Tunnel by the Numbers

The Haitai Yangtze River Tunnel stretches from Haimen District in Nantong to Taicang City in Suzhou, spanning a total route length of 39.07 kilometers (approximately 24.3 miles). The river-crossing tunnel section alone measures 11.185 kilometers, with the shield-bored portion extending 9,327 meters.

The project operates under extreme conditions that engineers describe with four key characteristics: 'long, large, high-pressure, and deep.' The tunnel faces maximum water pressure of 0.75 megapascals — roughly 7.5 times standard atmospheric pressure — while maintaining structural integrity at its maximum burial depth of approximately 75 meters.

For comparison, major Western underwater tunnels like the Channel Tunnel between England and France reaches depths of about 75 meters below the seabed as well, but the Haitai tunnel claims the record specifically for highway shield-tunnel construction length.

A Technological Breakthrough in Shield Tunneling

The achievement represents what Chinese engineers call a 'key breakthrough' in three simultaneous extreme conditions: ultra-large diameter, ultra-high water pressure, and ultra-deep burial depth. Operating a 16.6-meter-class shield machine — one of the largest boring machines in the world — at these depths requires precise control of tunneling parameters, advanced real-time monitoring systems, and sophisticated ground conditioning techniques.

Modern tunnel boring machines of this scale increasingly rely on sensor arrays, automated guidance systems, and data analytics to navigate geological challenges. The 'Jianghai' machine must continuously adapt to varying soil and rock conditions while maintaining millimeter-level precision in ring segment placement — a task that demands both advanced hardware engineering and intelligent control software.

Strategic Infrastructure for China's 2035 Vision

The Haitai Yangtze River Tunnel is a priority project under China's 'Yangtze River Main Line Cross-River Passage Layout Plan (2020–2035)' and is designated as a key initiative in Jiangsu Province's 14th Five-Year Plan for cross-river infrastructure. The tunnel is expected to be substantially completed by 2028.

Once operational, it will provide a critical highway link across the Yangtze River's widest section near its mouth, significantly reducing travel times between the northern and southern banks of the river delta — one of China's most economically productive regions.

Global Context

The project underscores China's growing dominance in large-scale tunneling technology, an area where European firms like Herrenknecht (Germany) have historically led. China's ability to design and deploy domestically manufactured ultra-large-diameter shield machines at record-setting depths signals intensifying competition in the global infrastructure technology market.

As nations worldwide plan ambitious underwater and underground transit projects, the engineering data and operational experience gathered from the Haitai tunnel could influence future mega-project designs across Asia, Europe, and beyond.