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The Hong Kong government started to plan the Tuen Mun – Chek Lap Kok Link (TM-CLKL) early in 2007 to serve as an ancillary project of the Hong Kong-Zhuhai-Maco Bridge (HZMB) project. Not only the TM-CLKL is beneficial to the residents living in the north and west of the New Territories to travel back and forth between the Hong Kong International Airport (HKIA) and New Territories, the TM-CLKL is also an integral link to improve the transportation network of the area near the HKIA and the HZMB.

Overview of the Tuen Mun – Chek Lap Kok Link

The design of the TM-CLKL is very complicated and the nine-km link is divided into two parts: The Southern Connection and the Northern Connection. The Southern Connection is a 1.6-km viaduct that links North Lantau and HZMB Hong Kong Port together while the Northern Connection is a five-km sub-sea road tunnel i.e. the Tuen Mun - Chek Lap Kok Tunnel (Northern Connection tunnel) that links Pillar Point in Tuen Mun South and HZMB Hong Kong Port together.

Being an enormous construction project, the TM-CLKL was plagued by significant delay, the two Connections were completed and put into service in stages: in 2018, the South Connection has already been put into service, while the awaited North Connection was finally opened to traffic in late December, 2020. The construction works of the Northern Connection has also shattered a few new records.


The TM-CLKL is a new strategic road to Hong Kong, followed by its commencement, the link provides a more convenient and direct route for citizens to travel back and forth between New Territories West and North to the HKIA and its adjacent transportation network. The link also effectively reduces the journey time: only ten minutes is need to travel between Tuen Mun South and the HKIA, compared with the original route, the journey time reduces by approximately 20 minutes.

Moreover, the TM-CLKL serves as an alternative route of the Lantau Link to connect HKIA and the urban area in Hong Kong. Theoretically, it can also re-distribute the traffic flow of the Lantau area and the HKIA area so as to alleviate the burden of the North Lantau Highway, Lantau Link and Tuen Mun Road, leading a smoother traffic situation.

Overview: Northern Connection

The Northern Connection of the TM-CLKL has received a lot of attention in recent years as the design of the project itself is enormous and complicated.

With a total width of 5.5 kilometres, there is a five-km sub-sea road tunnel connecting Tuen Mun South and the HZMB Hong Kong Port, i.e. Tuen Mun – Chek Lap Kok Tunnel is opened for traffic in late 2020 with a cost of HK$44.8 billion. It was originally expected to be completed in 2016, however, a four-year delay was resulted due to different reasons. Before the commencement of this colossal tunnel, a 16.5-hectare reclamation work was carried out at the northern entrance. Also, at the southern entrance, a 500-metre cut-and-cover tunnel was constructed.


After seven years of hard work, the Northern Connection tunnel has gained a lot of attention as it was a pioneering project that overcame a lot of challenges and shattered several records in the tunnel construction history in Hong Kong. The tunnel is now the longest and deepest road tunnel in Hong Kong, as most of the construction works were carried out under the sea surface, the working team had to work under the huge pressure brought by the compressed environment under the sea. The team had to strictly follow the limitations related to environmental protection of the surrounding area as well. They have to fulfil high standard requirements regarding the protection of marine ecology, noise, sewage treatment and water quality management.

The working team introduced several innovative technologies to the project, they dived into the seabed where it is 60 metres under the sea surface to carry out construction works, including the largest tunnel boring machine in the world, “Qin Liangyu”.

Pressure in: Construction Process

Even though there are experiences of adopting the immersed tube method to construct three sub-sea road tunnels in Hong Kong, the alignment of the Northern Connection walks across the hustling Urmston Road and there are crucial electricity supply facilities under the seabed, therefore, the construction team decided to build the sub-sea tunnel by adopting shield tunnelling method to reduce the impact posted to surrounding areas and the marine ecology. It is also the first time in Hong Kong to use such method to build a tunnel.

Saturation Diving Technique

The tunnel boring machine (TBM) “Qin Liangyu” has a diameter of 17.6 metres, which is approximately equal to the height of a 6-storey building. While excavating the tunnel, more than 200 blades or cutter heads had to cut solid rocks (for example: granites) that lead to abrasion, therefore, regular checking and replacement of cutter heads were often need. Nonetheless, the construction were performed 60 metres under the sea surface, for normal practice, professional divers will have to pressurise their bodies before diving in the sea and decompress after finishing their work. However, this regular process may increase the risk for suffering from decompression sickness; in the mean time, the actual working hours will only be at most two hours, which would be a potential factor to delay the working time. To protect the health of the team members working under the sea and enhance the working efficiency, the working team had introduced the saturation diving technique as a new working mode, moving all the daily routines, which include sleeping, eating and working etc., of the well-trained professional technicians into the seabed.

Technicians would be working as a team of four in a 28-day working cycle, they would be living in a pressurised living chamber and transported to a working chamber by a high pressure shuttle every day, after 25 days of work, the technicians had to stay in the decompression chamber for three days to carry out the decompression process and re-acclimate to normal pressure. After 18 saturated diving working cycles, the team had kept their high standard working efficiency and replace more than 1,400 TBM cutter heads safely while the Northern Connection works were underway.

Modular Integrated Construction (MiC) and Building Information Modelling (BIM)

To further boost the working efficiency, the working team has widely adopted the method of MiC in line with BIM. Facilities inside the tunnel including the slabs of the ventilation shaft, service gallery and parapets were mostly made by MiC precast modules, which effectively reduced the temporary supporting devices and concrete templates, the MiC could also prevent safety hazards and delay due to weather and other unstable factors.

Service Galley

In the meantime, for a more convenient and better management of the tunnel in later times, this is also the first time in Hong Kong to set up a service galley under a road tunnel. The service galley also serves as a storage space for electrical and mechanical facilities, fire service equipment and bi-directional electric vehicles etc. If maintenance and repairing works are needed, the works can be carried out in daytime without affecting normal traffic; maintenance schedule will therefore become more flexible and convenient.

Other Innovative Techniques

The working team also employed a wide variety of innovative techniques and ideas during the construction of the Northern Connection. Among all, one of the most outstanding techniques was adopting a 15-cell caterpillar shaped cofferdam to provide a bigger and safer working space for the cut-and-cover tunnel located at the southern exit of the shield tunnelling section. By taking advantage of the arching effect produced by the caterpillar shaped cofferdam, the ability to stand up the pressure of the soils of the two sides will be increased; also, it effectively reduced the number of horizontal supports.


To cater to the opening of the TM-CLKL, the government has waived the tolls of the Lantau Link and the TM-CLKL since the 27 December 2020 to facilitate the utilisation of different traffic options to ease the traffic burden in particular areas and relive the burden of the citizens, public transport operators and transportation industry on transport fares.

The entire construction project has utilised innovative construction techniques and strategies, the Northern Connection tunnel can be considered as one of the pioneer projects, which is in line with the innovative direction that the construction industry is advocating right now. Under a challenging working environment, the team has overcome every challenge and complete the project with excellent team work and innovation spirit. It is hoped that in the future, the construction industry will let this spirit continue and complete more meaningful projects which are beneficial to the general public in Hong Kong.

Complimentary copies available to members of the following associations:

The Hong Kong Construction Association
Macau Coustruction Association
Hong Kong General Building Contractors Association
Hong Kong Institute of Utility Specialists
China Hongkong Society for Trenchless Technology Association
Hong Kong Construction Materials Association Limited
Contractor's Authorised Signatory Association
Hong Kong Construction Machinery Association