CHINA Rail Construction Group (CRCG) presented its newly constructed super-size tunnel boring machine (TBM) for high-speed rail construction on January 16.

Built jointly by CRCG’s 11th Bureau and China Railway Construction Heavy Industry in Changsa, in south central China, the TBM is 14.6m wide, weighs 4350 tonnes, some 700% heavier than standard TBMs, and is approximately 11km long. It is understood to be the world's widest and longest marine TBM.

Named Dinghaihao, the TBM will be used to bore the 16.2km Jintang marine tunnel on the 77km Ningbo - Zhoushan high speed line currently under construction. When complete, the Jintang tunnel will be China’s first and longest marine tunnel on a high-speed line, with a maximum depth of 76m. To reach the tunnelling site the machine will be dismantled at the factory in Changsha and moved 1000km before it starts work.

The oversize dimensions of the TBM are necessary to overcome the complex geology and busy maritime traffic above. Around 90% of the Ningbo - Zhoushan high-speed line in China’s eastern province of Zhejiang will run either elevated on 36 bridges or underground in 17 tunnels. The new line is due to open in 2026.

CRCG says its engineers have employed innovative technical advances in the new TBM, including advanced geological forecasting, saturated pressure tool changing, TBM tail synchronous dual liquid slurry, a double-layer shell, segment floating monitoring and wall back grouting, which should ensure safe, green, efficient and high-quality tunnel construction.

The Ningbo - Zhoushan line will offer a journey time of 26 minutes when completed. This compares with the current journey time of 90 minutes and will achieve Zhejiang Province's goal of a one-hour radius journey time by high-speed rail for all major centres in the province. It will also help to accelerate integration of Zhoushan and Ningbo into China’s national Belt and Road economic development strategy, as well as the Yangtze River Economic Belt.