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A large-diameter tunnel boring machine (TBM) with a record-breaking excavation diameter of 16.64 meters rolls off the production line in Changsha, Central China's Hunan Province on October 31, 2024. Photo: VCG

China's largest shield tunneling machine cutter head, with a record-breaking diameter of 16.64 meters, descended at the construction site of the Haitai Yangtze River Tunnel in East China's Jiangsu Province on Wednesday, signaling the start of its initial testing phase. 
 
The machine, named "Jianghaihao," was independently designed and developed by China Railway Construction Heavy Industry Corp in collaboration with China Railway 14th Bureau Group Corp. Measuring 145 meters in length and weighing about 5,000 tons, the machine represents a significant engineering achievement. 

The cutter head, measuring 16.64 meters in diameter and weighing 460 tons, was precisely lowered into place at the site, highlighting one of the most intricate and challenging stages of the shield tunneling machine 's assembly, according to a CCTV report.

This machine will be used to construct the Haitai Yangtze River Tunnel, a critical part of the world's longest underwater highway tunnel project. The machine is designed to tackle the extraordinary challenge of excavating a tunnel with a maximum diameter of 16.64 meters, Chen Jian, deputy chief engineer at China Railway 14th Bureau Group Corp, told the Global Times on Wednesday.

The machine's excavation work is expected to begin in late March, and the total tunneling distance is more than 9 kilometers, a significant feat that presents unique challenges. The massive cutter head will face immense soil and water pressure considering the combination of the ultra-large diameter and extended tunneling distance at site, Chen said. 

In terms of design, this machine represents a significant leap in shield tunneling technology. The machine's main driving system, designed for ultra-long-distance tunneling, faces stringent performance and durability tests, which have already been successfully tackled by Chinese engineers, according to Chen.

The Haitai Yangtze River Tunnel, a key component of the world's longest underwater highway tunnel, will stretch 39.07 kilometers, including an 11.185-kilometer underwater section. The tunnel will feature a six-lane design, utilizing the shield tunneling machine to navigate challenging geological conditions, including high water pressure and intricate operational demands.

The project is expected to progress rapidly, as more than 200 workers will remain on-site during the coming Spring Festival holidays to assemble the components of the machine and finalize adjustments, CCTV News reported on Wednesday. By the end of March, the machine is set to begin tunneling work, setting the stage for the tunnel's eventual groundbreaking excavation.