Herrenknecht Mixshields are in their element when it comes to the biggest challenges in mechanized tunnelling. Such as in the construction of a gigantic twin-tube road tunnel in Hong Kong. With a length of around 5 kilometers, in future the Tuen Mun – Chek Lap Kok Link will connect the international airport and the new Hong Kong-Zhuhai-Macau Bridge, inaugurated in October 2018, with the mainland to the north, crossing under a branch of the Pearl River Delta at depths of up to 50 meters.
Herrenknecht’s commitment and leadership have played an essential role in our decision-making to procure this TBM and implement such a technique.
Seved Robin, Project Director Dragages-Bouygues Joint Venture
For the construction of the two parallel tubes the tunnelling joint venture of specialists Dragages and Bouygues ordered three Mixshields from Herrenknecht. The star of the trio is the S-880 – with a shield diameter of 17.6 meters the world's largest tunnel boring machine dwarfs anything ever seen before. The concept of the project provided for a clever division of labor to the benefit of both budget and scheduling: from the northern launch shaft the Mixshield giant first drove an approximately 650 meter long section where a larger diameter was required. The TBM was then scaled down to a diameter of 14 meters for the rest of the tunnelling distance toward the airport. Core components and the three-story back-up were taken from the larger machine. Then followed the drive under the estuary. The second 14-meter Mixshield drove the parallel tunnel from the launch shaft in one go.
In an official launching ceremony the 17.6 m TBM was sent on its underwater mission.
November 3, 2015: after 646 m of tunnelling came the successful breakthrough of the supersize giant. As soon as the water was pumped out of the intermediate shaft, conversion began – to a machine of 14 m with the same drive and back-up system.
The assembly of the 4,850 tonne and 120 meter long supersize TBM at the Herrenknecht site in Nansha meant that after factory acceptance in October 2014 the machine could be quickly transported to the launch shaft. In May 2015 already the site crew began the drive and reached the target shaft exactly to plan on November 3, 2015. In March 2016 the converted machine then continued on its way parallel to its sister TBM. The latter began its 5 kilometer long drive in June 2015.
The unloading of the up to 23 m long machine and back-up segments took place at the jobsite’s own dock directly adjacent to the launch shaft.
Another highlight of the project was the final double breakthrough of the Herrenknecht Mixshields on February 27, 2019. Almost simultaneously, the sister TBMs successfully broke through into the target shaft. By the end of the mission they had achieved daily best performances of 30.8 meters and weekly peak performances of 167.2 meters. Together, all three TBMs have built around 10 kilometers of new, state-of-the-art tunnel shells.
In addition to the three large diameter machines, Herrenknecht's scope of supply for the Tuen Mun – Chek Lap Kok Link also included two AVN3000 microtunnelling machines. Using the pipe jacking method, in a very tight time frame they built 46 cross passages between the two main tubes.
For this purpose a special start-up structure was developed. It allowed for pipe jacking directly from one of the large tunnel tubes while all logistic processes for the large diameter TBM could continue in parallel – another innovation in mechanized tunnelling. Because of the surrounding groundwater pressure of 5.5 bar, a special launch and breakthrough process was developed: a special launch seal including an emergency seal was installed at the starting point of each borehole. A receiving bell ensured a safe breakthrough into the target tunnel. A jacking trailer with a mobile gantry crane was used to quickly reposition the equipment and machine for construction of the next connecting tunnel. On average, a cross passage was created within 20 days. In January 2019 all connecting tunnels were successfully completed.
|Soft ground, heterogeneous ground:
Completely Decomposed Granite (CDG), alluvium, granite, marine deposits
|Highways Department, Hong Kong Government
|Dragages - Bouygues Joint Venture
Diameter: 17,630 mm
Lining method: Segmental lining
Cutterhead power: 5,600 kW
Torque: 27,722 kNm
Diameter: 13,950 mm
Lining method: Segmental lining
Cutterhead power: 4,900 kW
Torque: 24,256 kNm
2x AVN Machine:
Diameter: 3,605 mm
Lining method: Pipe jacking
Cutterhead power: 400 kW
Torque: 800 kNm
We are ready!