Herrenknecht has built a mixshield tunnel boring machine (TBM), featuring a large diameter of 17.5 m, for the construction of a two-storey road tunnel with three lanes in both directions in the eastern Chinese city of Jinan. This mixshield technology is designed for the extreme conditions of the upcoming undercrossing of the Yellow River.

A machine of this diameter has only been used twice before in the history of tunnelling, revealed Herrenknecht. The largest one was in Hong Kong in 2015, also a Herrenknecht mixshield with a diameter of 17.63 m.

In this latest project, which was awarded to the Herrenknecht subsidiary, Herrenknecht Tunnelling Machinery (HTM) in China, the order was for a machine to cross under the Yellow River, in a geological environment with high groundwater pressure and to create just one tunnel tube for both directions of travel. Thus a large diameter was required: 17.5 m over a section of 3.3 km.

The mixshield TBM, named ‘Shanhe’, is scheduled to begin tunnelling in late 2024. The project aims to improve the connection between the two sides to the north and south of the river.

Adapting to the geology

To adapt to the clay, sand and silt geology and the 7.5 bar groundwater pressure under the Yellow River, a mixshield TBM was selected. The mixshield technology, developed by Herrenknecht, is an advance on conventional slurry technology. The support pressure in the excavation chamber is precisely managed using an automatically controlled air cushion. This means that heterogeneous geologies and high water pressures of more than 15 bar can be controlled safely, even with very large excavation diameters. An individual, new slurry circuit was designed especially for the TBM Shanhe.

“We have also equipped the machine with our special telescopic camera in order to better monitor the tool change and the face,” said Herrenknecht project manager Zhao Bin, who has already supervised several projects for clients in China. Most recently, he supervised the two TBMs that are also crossing under the Yellow River just a few kilometres away from the new construction site and building a road tunnel with two tubes (the shield diameter of these two mixshields for the Jinan Jiluo Road North Extension Tunnel project is 15.71 m).

“Thanks to its efficiency, the new single-tube tunnel supports the national strategy of ecological protection and high-quality development of the Yellow River basin,” said Wang Hai, deputy general manager of the Herrenknecht office in Beijing. “It removes a bottleneck of traffic across the river and is calculated to absorb 7.4% of the traffic volume in one go.”