Undersea Water Tunnel nearly Operational
After advancing up to 392 m (1,290 ft) per month, Robbins’ speedy Slurry TBM made a photo finish in China’s southernmost city. The 6.26 m (20.5 ft) diameter machine broke through at the end of 2012, and the pipeline was slated to become operational in March 2013. The Zhanjiang Bay Sub-Sea Tunnel runs 56 m (185 ft) below water level, and will provide fresh water to the Guangdong Steel Plant via twin pipelines.
The 2.7-km (1.6-mile) long conduit, constructed by contractor Guangdong No. 2 Hydropower Engineering Co. Ltd, required the use of a Robbins Slurry machine to excavate under 6 bars of water pressure in Zhanjiang Bay. The TBM, supplied and assembled by Robbins with key components and engineering from Mitsubishi Heavy Industries Mechatronics Systems Ltd. (MHI-MS), was launched in September 2011.
“The cutterhead design, layout of the cutters and injection ports were the most important design factors in completing this tunnel project,” said Qinghua Shi, Chief Project Engineer for the contractor.
The high-powered Robbins machine featured a smooth flow cutterhead to allow for easier removal of stones and boulders while avoiding clogging at the face. The mixed ground machine utilized interchangeable knife-edge bits that could be switched out for disc cutters in geology that included abrasive sand, gravel and silt. The “smooth flow” design approach for mixed face conditions is consistent with the Robbins design for mixed face EPB-type machines.
During tunneling, the Robbins TBM excavated up to 27 m (89 ft) per day, with no interventions needed. “Throughout the project, I felt there were no significant problems that happened on the machine. I am happy that we could operate the machine properly. There were no cutters that needed to be changed, even though this was a long tunnel excavation project. The launch and breakthrough also went very smoothly,” said Shi.
Once in operation, the Zhanjiang Bay Sub-Sea Tunnel will source water from the nearby Jianjiang River to the steel plant on Dong Hai Island. The water supply for the large company of 20,000 employees is part of a plan by the Chinese government to improve the quality and output of steel in Guangdong Province.