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CHINA: An 11.9 km tunnel has been completed to carry the Chongqing – Xiamen high speed rail corridor under the Yangtze River in the centre of the Chongqing conurbation.
Celebrations were held on July 24 to mark the formal completion of the Caiyuanba Yangtze River Railway Tunnel, which passes under two districts in the heart of the metropolis. According to local media, it is the first high speed line to pass under the river — all previous crossings of the Yangtze have used bridges. In this case, the mountainous geography and dense urban landscape meant that the line had to be threaded under the city, crossing below the Yuzhong Peninsula and the South Bank area.
China Railway 14th Bureau Group used a customised Herrenknecht Mixshield tunnel boring machine for most of the work. According to the manufacturer, this was designed to cope with multiple challenges including high water pressure, complex geology and surrounding buildings. The tunnel runs through a complex geological structure, including karst, a fracture zone and a coal seam gas area, as well as passing under the main channel of the Yangtze River with a minimum overburden of about 10 m, and a maximum water pressure of 9 bar. The 12.6 m diameter TBM broke through in September 2025, and the final completion of the tunnelling work will now enable the start of tracklaying.
8×8 grid nears completion
The 1 600 km Chongqing – Xiamen line is one of the ‘eight by eight’ grid of east-west and north-south high speed axes being developed across the country, and much of the route has been designed for 350 km/h operation. The 242 km section between Chongqing and Qianjiang was opened in July 2025, leaving only the 421 km Ganzhou – Changsha section to be finished by 2030.
China Railway Group reported in March that work on the grid was around 84% finished, and the government envisages that all 16 axes will be ‘substantially complete’ by 2030.
‘We will enhance the capacity and structure of our railway network over the next five years’, Wang Qiming, deputy head of the National Railway Administration, announced on July 22. As well as completing another 10 000 km of high speed line, taking the total to around 60 000 km, this would also see the development of more suburban railways and metros across the ‘major city clusters’, he said.
In recent years, China has completed several underwater tunnels as part of its high speed network. These include the 9·6 km Zhanjiang Bay undersea tunnel on the 350 km/h Guangzhou – Zhanjiang line opened last year; an 11.8 km tunnel under the Yangtze at Taicang near Shanghai, which is expected to be finished later this year; and a tunnel to carry the Shenzhen – Jiangmen line under the Pearl River, which will reportedly reach a depth of 116 m.
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