By Rose Bell
In order to advancing a road tunnel in Jinan, China, a 17.5m diameter Herrenknecht mixshield TBM is being prepared for commissioning later this year.
Already in 2015 in Hong Kong a machine of this large diameter has been used that also was a Herrenknecht mixshield, with a 17.63m diameter.
Currently the latest TBM is being dismantled and prepared for reassembly on the construction site for the tunnel in eastern China, almost 400km south of Beijing, whereas the tunnel will have three lanes in both directions and cross beneath the Yellow River.
Being able to overcome the challenges of boring under the river in an environment with high groundwater pressure and creating only one tunnel tube for bi-directional traffic, TBM Shanhe has been manufactured by Herrenknecht subsidiary Herrenknecht Tunnelling Machinery (HTM) in China.
Additionally, for coping with the clay, sand and silt geology and the 7.5 bar groundwater pressure under the Yellow River, a large diameter 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 managed precisely using an automatically-controlled air cushion so heterogeneous geologies and 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 TBM Shanhe.
According to Herrenknecht project manager Zhao Bin: “The machine was also equipped with a telescopic camera to better monitor the tool change and face. He has supervised several projects for clients in China, including two TBMs on the Jinan Jiluo Road North Extension Tunnel project, which are crossing under the Yellow River just a few kilometres away from the new construction site. Two 15.71 diameter mixshield TBMs are excavating the twin bore tunnel.”
