The world's largest-diameter shield machine for constructing high-speed railway tunnels, independently developed by China, marked its 10,000-meter tunneling milestone under the Yangtze River on Tuesday, achieving a giant stride for a project that aims to develop a faster transportation channel between Shanghai and Jiangsu province.

With only 1,000 meters remaining to the southern bank of the Yangtze, the boring operation is expected to conclude in late 2026, paving the way for the completion of a 14.25-kilometer vital link connecting Shanghai's Chongming district with the city of Taicang in Jiangsu.

Upon completion, the Chongming-Taicang tunnel will allow high-speed trains to cross the river at 350 km per hour, which will significantly shorten the travel time between cities in the Yangtze River Delta region, including Nanjing in Jiangsu and Hefei in Anhui province, and is expected to better support the high-quality development of the Yangtze River Economic Belt.

Purpose-built for the high-speed railway tunnel project, the shield machine — named Linghang — features the world's largest cutting wheel with a diameter of 15.4 meters. The machine is 148 meters long and weighs about 4,000 metric tons.

"This is the first time globally that a 15-meter-diameter shield machine has achieved continuous tunneling exceeding 10,000 meters in a single drive," said Li Bin, chief engineer of the project.

According to China Railway Tunnel Group Co, the project's contractor, the single-tunnel double-track structure has established multiple records.

In addition to marking the longest single-drive tunneling distance of 11.32 km, the project has achieved the highest global design speed for an underwater tunnel at 350 km per hour and the greatest depth for a Yangtze River tunnel at 89 meters.

"The machine incorporates an advanced tunneling system, which enables autonomous operation through intelligent analysis and decision-making," said Wang Yi, deputy equipment manager of the project.

"Drawing from hundreds of historical datasets and machine-learning models, the system's capabilities enable efficient manned supervision along with unmanned operation," he said.

Wang added that the implementation of nine intelligent systems across sensing, design, construction and management areas has enabled normalized unmanned intelligent boring with algorithmic control.

Engineers have overcome several technical challenges, particularly the complex geology of the Yangtze riverbed, to advance the project.

Li, the chief engineer, said they have addressed obstacles including "the superlarge diameter and long boring distance, navigation through different sediment layers with gas emissions, and simultaneous construction of multiple tunnel components".

The project team has maintained and will continue to maintain strict environmental protection measures, given the tunnel's winding route through residential areas, embankments, anchorage zones and protected aquatic breeding grounds, Li said.

As the project enters its final phase of underwater boring, the focus is on maintaining safety and quality standards, he said, adding that the team is conducting thorough equipment inspections and maintenance while fully utilizing the intelligent construction system to ensure successful completion of the work.

The Shanghai-Nanjing-Hefei high-speed railway represents a crucial section of China's national high-speed railway network. When operational, it will strengthen connectivity between the Shanghai, Nanjing and Hefei metropolitan areas, further advancing the integration of the Yangtze River Delta region.

zhengzheng@chinadaily.com.cn