Record size TBM supplied for Chinese tunnel project

A new road tunnel is being driven in the Chinese city of Jinan using a tunnel boring machine (TBM) featuring a record-setting diameter. The TBM features a mixshield design and is being used to drive a two storey tunnel carrying three traffic lanes in either direction underneath the Yellow River.

The Herrenknecht TBM features a mixshield diameter of 17.63m, equalling the record setting TBM that the same firm supplied for use driving tunnels in China’s capital Beijing in 2015. The massive TBM being used in Jinan is being taken apart at present so that it can be reassembled to carry out the drive.

The special mixshield design has been designed for the extreme conditions of the geology underneath the Yellow River. The TBM has been built for the purpose by Herrenknecht subsidiary Herrenknecht Tunnelling Machinery (HTM) in China. The mixshield TBM is delivering a maximum excavation diameter of 17.505mm, featuring a cutterhead drive power of 5,600kW and a torque of 35,017kNm.

The geology is challenging and features high groundwater pressure. To provide a single tunnel tube for both directions required a large diameter of 17.5m over a stretch of 3.3km. Jinan is located around 400km south of Beijing, has a population of nine million and is the capital of the Chinese province of Shandong and an important business centre. This new road tunnel will be the second running underneath the Yellow River.

The tunnel drive is scheduled to begin in late 2024 and will help to improve the connection between the two sides to the north and south of the Yellow River. The client for the project is Jinan Urban Construction Group Co and the work is being carried out by contractor China Railway 14th Bureau Group.

To adapt to the clay, sand and silt geology and the 7.bar groundwater pressure under the Yellow River, a mixshield TBM was selected. This technology was developed by Herrenknecht as an advance on conventional slurry technology. The support pressure in the excavation chamber is managed using an automatically controlled air cushion. This means that heterogeneous geologies and high water pressures of more than 15bars can be controlled safely, even when driving very large excavation diameters. An individual, new slurry circuit was designed especially for this TBM.

“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 15.7m diameter TBMs that are also crossing under the Yellow River just a few kilometres away from the new construction site and building the dual tube Jinan Jiluo Road North Extension.

Wang Hai is deputy general manager of the Herrenknecht office in Beijing and is advising the customer on the challenging project. He said: “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. It removes a bottleneck of traffic across the river and is calculated to absorb 7.4% of the traffic volume in one go.”