Armand van Wijck, TunnelTalk
- A design-build contract worth an equivalent of €1.15 billion (US$1.5 billion) is awarded by the Hong Kong Government to a joint venture of Dragages Hong Kong and Bouygues Travaux Publics, two subsidiaries of Bouygues Construction of France, for a new 4.2km undersea road tunnel in Hong Kong to link Tuen Mun in the New Territories on the mainland, with Hong Kong's Chek Lap Kok Airport on Lantau Island (Figs 1 and 2).
Fig 1. Aerial view of Hong Kong and its new undersea and fixed ocean link highway connections
- Within the space of a year Bouygues has won the two largest construction contracts ever awarded by the Hong Kong Government. As well as the Tuen Mun-Check Lap Kok Link (TM-CLKL), it is also constructing the first stretch of the 50km Hong Kong-Zhuhai-Macao bridge and tunnel link (HKZMB), the mega-project that will link Hong Kong with Zhuhai and Macao by means of three cable-stayed bridges, two artificial islands and a 6.7km immersed tube tunnel (Fig 1). The TM-CLKL is closely related to the HKZMB, as both involve undersea links and are connected to the Hong Kong boundary check-point facilities on Lantau Island.
- The TM-CLKL will become a 4.2km twin-tube subsea tunnel, with two traffic lanes in each 14m diameter tube. The project also includes construction of two cut-and-cover approach tunnels of 530m and 670m. The new tunnel link to Lantau Island (TM-CLKL) will connect the New Territories to the eastern end of the Hong Kong Link Road. Delivery of the civil works is scheduled for the end of 2018. More than 1,000 employees will be working on the project at peak periods.
- Compared to the current route using the Lantau Link, motorists using the TK-CLKL undersea link will enjoy a 22km reduction in travel distance between the North West New Territories and Hong Kong International Airport. The road link will also support the international airport as a regional aviation hub by providing an alternative land access to the airport.
- The new undersea highway link will be bored using two 14m diameter TBMs. The Dragages Hong Kong and Bouygues Travaux Publics JV is currently tendering for the TBM supplier. "We have consulted NFM, Herrenknecht and Hitachi," said Stephane Polycarpe, Engineering Manager of the Dragages Hong Kong-Bouygues Travaux Publics joint-venture, in an exclusive interview with TunnelTalk.
Fig 2. A closer look at the new highway tunnel route to the airport
Hyperbaric base camp
The tunnel will be bored 50m below sea level, which will require working in an environment with a high pressure of more than 5 bar. "This is a record depth for tunnel construction for us, and the depth, combined with a very low coverage of the tunnel below the seabed, will require very stringent control of the construction process," said Polycarpe. "It is a very challenging job for the JV. This tunnel is pushing forward the limits of what can be achieved by the tunnelling industry."
- Maintenance operations, particularly with respect to the TBM cutterheads and tools, will be carried out by teams of divers who will live in a hyperbaric base camp for four weeks at a time to allow them to deal with any construction issues that may arise. This will mean that divers need to decompress less frequently.
There will be a total of four hyperbaric base camps, located on the seabed surface as isolated structures. "This allows us to always keep three teams of three to five men available for saturation diving, and provide 24-hour cover for maintenance of the two TBMs, whilst one team is decompressing," said Polycarpe. Base camps consist of a living chamber and a transfer chamber. The living chambers provide sleeping and eating facilities for three to five divers, the transfer chambers provide showering, changing, toilet and storage facilities and a coupling connection to a shuttle. A hyperbaric doctor will visit each day and will be on call 24 hours a day. A hyperbaric nurse will be permanently present at the base camp. There is also a life support system that includes:
• Equipment to control all chamber compression and decompression functions
• Intercom devices (with divers)
• Communication devices
• Regulation devices for control of breathing mixtures, temperature, humidity
• Control of electrical functions
• Gas analysis measures for each compartment
• Pressure gauges for the chambers and gas storage
• Closed-circuit TV systems and all entertainment facilities
• Sanitary systems
• Fire suppression systems (high pressure deluge)
An artist's impression of the northern tunnel portal at Tuen Mun
Two control systems developed in-house by Bouygues Construction Research & Development will be used on the project to reduce the need for manual operations in hyperbaric conditions. "These systems give access to very precise data which enables control like no other system before has," said Polycarpe.
- Mobydic, a system of sensors incorporated into the disc cutters in the heads of the TBMs, will make it possible to permanently monitor their state of wear while allowing real-time geological mapping of the rock face. Snake, a remote-controlled exploration arm equipped with a high-pressure jet, will clean the TBM heads and eliminate clogging to faciltate inspection. "In addition to Snake, the cutting chamber will be equipped with a video system that provides a real-time view of the works and conditions during intervention," Polycarpe added.
- The project will pass through all the Hong Kong geological layers: from harder healthy granite to softer weakly consolidated marine deposits and from more permeable alluvial gravel to more impermeable clay meta sediments. "The complex geology is one reason why this project requires the implementation of these latest developments in TBM technology, but also because of the ground treatment methods that will need to be used for the safe construction of sub-sea cross passages," said Polycarpe.
- The two tunnel tubes will be connected every 100m by a total of 42 cross passages. Bouygues Construction will use ground freezing technology to provide a watertight environment in which these passages can be excavated. The ground will be frozen using brine that will be super-cooled to temperatures of between -30°C and -35°C. This will be circulated through a freezing plant and freezing pipes in the ground. "With one or two rows of drill holes around the cross passage the freezing action will form a thick ice wall around the excavation contour," explained Polycarpe. "An ice wall will be fully frozen in approximately 30 days." Inside each frozen wall, instrumentation to monitor temperature and pressure will be installed.
- Once the ground has been checked and the instrumentation confirms that it is completely frozen, a watertight door will be fitted before opening of the segments. The opening will be cut in the segmental lining with a diamond saw cut.
- Bouygues Construction will then excavate using electrically powered equipment to minimise diesel fumes and heat generation in the cross passage. "The cross passage will be excavated in 1m lengths installing temporary support as it advances," said Polycarpe. "When the excavation has finished and the permanent lining has been cast and cured, the freezing plant will then be switched off; the ground will then be allowed to defrost."
China's mega sea link moves forward - TunnelTalk, June 2011
Hong Kong begins massive express link to China - TunnelTalk, March 2011
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