China has completed shield tunnelling on what is set to become the world's longest undersea highway tunnel beneath Jiaozhou Bay in Qingdao, Shandong Province. The Jiaozhou Bay Second Subsea Tunnel is 17.48 kilometres long, with 9.95 kilometres of the tunnel lying below the water level of the bay. As reported by People’s Daily Online , the completion of the shield tunnelling process took place on July 14. The tunnel is designed for vehicle traffic at speeds of up to 80 km/h. It will link the eastern part of Qingdao city to the Huangdao District of the western region of Jiaozhou Bay.
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A giant shield machine bored through the seabed
The tunnel was built using a huge slurry-balance shield machine, a type of tunnel boring machine designed for difficult underwater conditions. Named "Hai Tian", the machine is 15.63 metres in diameter and was made exclusively for the construction of this tunnel. The SANY Group , a firm manufacturing construction machinery, claims that the machine was created with difficult marine geology and stability during excavation in mind.
The machine's cutterhead is almost 16 metres in diameter, roughly as wide as a five-storey building is tall. Shield machines dig by cutting through soil and rock while supporting tunnel walls at the same time and inserting precast concrete segments behind them. This process helps make underground construction safer.
Constructing a tunnel under the seabed posed major engineering challenges
Building a highway tunnel under water presents engineers with high water pressure, difficult geology and limited room for repairs during excavation. According to China Communications Construction Company (CCCC), engineers involved in the construction of the Jiaozhou Bay Second Subsea Tunnel project had to use advanced monitoring equipment and special construction methods in order to tackle issues involving fault zones and changing geology underground.
As stated in the research paper titled 'Operation characteristics of the Ultra-Large Diameter Slurry Shield Machine' published in the Modern Tunnelling Technology journal, one important aspect of the project was monitoring tunnelling parameters including pressure, thrust and cutterhead performance.
The purpose of building the tunnel is to enhance connectivity in Qingdao
Once operational, the Jiaozhou Bay Second Subsea Tunnel is expected to improve transport links between Qingdao’s main districts. At present, Qingdao relies on existing roads around Jiaozhou Bay, while the new tunnel will provide an alternative crossing. As per China Communications Construction Company, the Jiaozhou Bay Second Subsea Tunnel will cut down the journey time between Qingdao and Huangdao to about 15 minutes following its establishment. The tunnel is part of Qingdao’s wider transport infrastructure programme.
China’s expanding mega underwater projects
The Jiaozhou Bay Second Subsea Tunnel joins other mega undersea projects undertaken by China.
Already, there is the Hong Kong-Zhuhai-Macao Bridge in China, which is one of the largest sea-crossing infrastructure projects in the world and comprises a 6.7-kilometre-long undersea tunnel that connects two artificial islands across the Pearl River estuary. However, the Jiaozhou Bay Second Subsea Tunnel project is unique due to its length and its use as an undersea highway tunnel.
As per China Daily reports, the project is expected to be implemented in phases, and the tunnel will start operations once the rest of the construction process is completed. For Qingdao, the tunnel is intended to ease the barrier created by Jiaozhou Bay.
