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

A large-diameter tunnel boring machine (TBM) with a record-breaking excavation diameter of 16.64 meters rolled off the production line in Changsha, Central China's Hunan Province on Thursday. It will be used in the construction of the world's longest underwater highway project — the Haitai Yangtze River Tunnel in East China's Jiangsu Province.

Independently developed by China to date, the machine with the name of "Jianghai," marks a breakthrough in the industrialization of domestically produced large-diameter TBMs, according to a CCTV report.

The TBM was jointly developed by China Railway Construction Heavy Industry Corp and China Railway 14th Bureau Group Corp. It measures 145 meters in length and weighs about 5,000 tons. 

Song Huan, a senior engineer on the Haitai Yangtze River Tunnel project who works for China Railway 14th Bureau, told CCTV that the TBM is set to undertake a lengthy, uninterrupted excavation beneath the Yangtze River.  

Song noted that the project faces significant challenges, especially in maintaining ground settlement within a 1-centimeter margin while crossing the river and embankments on both banks, and the limited scope of geological surveys in the riverbed means there are many unknown or uncontrollable factors, Song said.

The TBM has made key technology advancements, such as an increased cutter head opening ratio, a high-pressure central flushing system, as well as a cutter head mud-cake monitoring system enabling "Jianghai" to tackle the demanding 9,315-meter continuous excavation beneath the riverbed. Altogether, the TBM guarantees an effective and safe construction process.

TBMs with diameters of 14 meters or above are generally classified as ultra-large diameter machines. 

The development of "Jianghai" represents a milestone for Chinese enterprises in both the design and deployment of ultra-large TBMs, demonstrating China's capability for full industrialization amid the production chain of ultra-large diameter TBMs, Chinese media outlets reported.

Global Times