The Tuen Mun-Chek Lap Kok Link (TM-CLKL) is a strategic sub-sea road transport link, constructed to alleviate traffic congestion and shorten the journey between Hong Kong’s Northwest New Territories and the Hong Kong International Airport via a 4.1 km dual, two-lane subsea tunnel.
At 55 m below sea level, this is the deepest, longest, and largest sub-sea road tunnel ever built in Hong Kong. It was constructed using the world’s largest tunnel boring machine (TBM) with a diameter of 17.6 m, as well as two 14 m diameter TBMs and a mini TMB for constructing the 57 connecting cross passages.
Over the four-year project, WSP* provided specialist geotechnical services for the ‘Southern Landfall’ area of the project, overcoming the significant challenges posed by complex geotechnical conditions and high ground water pressure. Ground conditions at the southern landfall area included reclaimed land and soft compressible marine and alluvium deposits, with the potential to settle or ‘creep’, presenting a risk of unacceptable deformation of the structures.
The team combined its deep expertise in geotechnical risk mitigation and analytical skills with the use of digital engineering tools including Bentley’s gINT, HoleBASE (Keynetix), MicroStation and PLAXIS to model and analyse the complex interactions between the ground conditions, design of the tunnels and geo-structures, and the construction processes.
To mitigate risks of potential long-term tunnel ovalisation (deformation of the tunnel rings, with impacts on stability and serviceability) due to dissipation of excess pore pressure and long-term creep of the alluvial clay at the newly reclaimed ground, barrette panels were constructed adjacent to both sides of the tunnels to stiffen the ground and tunnel lining response.
Using PLAXIS 3D, WSP* optimised the design for the tunnel-stabilising barrettes, both in relation to the quantity and the physical dimensions. The original design required 158 barrettes of 19.2 m in length; however, WSP* was able to safely reduce this requirement to 106 barrettes, of which 46 were shortened by almost 3 m. This saved approximately USD 16 million in costs, two months of construction time and avoided 1500 tonnes of carbon dioxide emissions.
In addition, WSP*’s involvement was critical in the successful design of the ‘plug’ to secure watertightness when the TBM began and ended its tunnelling ‘drive’ through the Southern Landfall, breaking into and out of the cut-and-cover tunnel and southern ventilation shaft structures. WSP* also determined the appropriate slurry pressure (or face support pressure) needed to maintain stability during tunnelling through the Southern Landfall.
Complex geotechnical risks were identified early in the project as the ground conditions were investigated and understood. Proactive mitigation measures were successfully applied, enabling successful delivery of the project within the anticipated schedule and budget.
The design of this project had environmental advantages over traditional road projects, including reduced disturbance to the public during construction, reduced use of formwork and falsework, and the avoidance of dredging and pollution of seawater (due to the effective transport of slurry through pipes to the surface).
The safe, cost-effective, and timely development of this large transportation project is expected to bring social, economic, and environmental benefits to Hong Kong, reducing the travelling distance and time to the airport as well as avoiding the emissions generated by traffic congestion.
The TM-CLKL tunnel won the International Tunnelling and Underground Space Association (ITA) Major Project of the Year (over €500M) Award 2019.
WSP* was a winner at the Bentley Systems Year in Infrastructure 2020 Awards in the Geotechnical Engineering category for our work on the Tuen Mun-Chek Lap Kok Link Tunnel, Southern Landfall project.
* This work was performed by Golder professionals who joined WSP in an acquisition completed in 2021.
