TBMs launched for world’s longest subsea high-speed railway tunnel

Two super-large diameter slurry tunnel boring machines (TBMs), developed by China Railway Construction Heavy Industry Corporation Limited (CRCHI), have been launched from opposite directions in Ningbo and Zhousha in China for the Jintang subsea tunnel of the newly-built Ningbo-Zhoushan Railway.

TBM The TBMs, named ‘Dinghai’ and ‘Yongzhou’, have a total length of 135m and a maximum excavation diameter of 14.57m

The simultaneous rotation of the cutterheads of the two TBMs marks the start of the TBM advance phase for what is said to be the world’s longest subsea high-speed railway tunnel.

The Jintang subsea tunnel of the Ningbo-Zhoushan Railway stretches from Yinzhou District in Ningbo City in the west to Jintang Town in Zhoushan City in the east, spanning a total length of 16.18km, of which the TBM section is 11.2km long, with a maximum buried depth of 78m.

The TBMs, named ‘Dinghai’ and ‘Yongzhou’, have a total length of 135m and a maximum excavation diameter of 14.57m.

The tunnel undercrosses the 100,000-ton Jintang main navigation channel. The two TBMs have started excavation towards each other from Ningbo and Zhoushan respectively, ultimately docking at the bottom of the sea with an accuracy requirement of an error not exceeding 20mm.

This will be the world’s first case of subsea docking and disassembly of super-large diameter shield machines.

In view of the complex construction characteristics of subsea tunnels, the R&D team of CRCHI has implemented several  designs for the shield machine, such as the heavy pressurised cutterhead design, 70 disc cutters, and more than 100 tons of weight added compared to the conventional cutterhead. There is a reduction in cutter spacing, and an increased number of disc cutters.

The disc cutters have an intelligent monitoring system that are said to enhance the cutterhead’s wear resistance and rock-breaking ability, ensuring complete tunnelling efficiency. The shield machine also uses a guidance system with high control precision and advanced technology acting as the ‘eyes’ for the tunnelling equipment and is equipped with special features such as advanced geological forecasting and probe grouting reinforcement.

The Ningbo-Zhoushan Railway project spans about 77km and has a design speed of 250 km/h.

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