A Chinese tunnel boring machine named Linghang has set a record by completing a continuous 11.325-kilometre excavation beneath the Yangtze River from a single launch point, without opening intermediate shafts or additional excavation fronts, according to Global Times.
The machine took 27 months to complete the drive. China is presenting the run as the longest achieved beneath a river by a large-diameter tunnel boring machine in the 15-metre class.
Linghang was built by China Railway Engineering Equipment Group for the Chongtai tunnel. It left the production line on 27 January 2024, finished assembly in March and began excavating on 29 April of that year. The cutting head measures 15.4 metres in diameter, the machine reaches 148 metres in length and weighs around 4,000 tonnes.
The machine incorporates the I-TBM intelligent system, which monitors chamber pressure, trajectory and the removal of excavated material. It also features waterproofing systems rated for high water pressure, a long-life main bearing and a cutting head designed to resist wear from the silts and sands of the riverbed.
One of the main challenges of the project is pressure. Linghang has worked at 89 metres below the bed of the Yangtze, withstanding up to 0.9 megapascals. The resulting tunnel has an outer diameter of 14.8 metres and will carry two tracks in a single bore.
That size is partly driven by the speed planned for the trains. A train travelling at 350 km/h pushes a large mass of air ahead of it, and a wider tunnel cross-section reduces the piston effect and allows trains to maintain that speed through the crossing without slowing before entry.
Linghang is the largest boring machine built for a high-speed rail tunnel, but not the largest in absolute terms. The Guinness-recognised record belongs to the Herrenknecht Mixshield S-880, used in 2015 to bore a road tunnel in Hong Kong, which had a shield of 17.63 metres, measured 120 metres in length and weighed 4,850 tonnes.
The Chongtai tunnel will measure 14.25 kilometres in total and forms part of the high-speed corridor linking Shanghai, Chongqing and Chengdu. After a review at an intermediate shaft, Linghang will resume excavation of the remaining 1.8 kilometres, with the full bore expected to be completed before the end of 2026. Once the line enters service, trains will be able to cross beneath the Yangtze at 350 km/h, cutting the 63-kilometre journey between Chongming and Shanghai Baoshan station to around 17 minutes.
