Zhuhai City, Guangdong Province, south China - April 10, 2017
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1. Various of aerials of Hong Kong-Zhuhai-Macao Bridge

2. Workers celebrating completion of Gongbei tunnel
3. SOUNDBITE (Chinese) Liu Zhigang, Engineering Management Department Manager, Hong Kong-Zhuhai-Macao Bridge Zhuhai connecting project:
"We are so excited that although there is a major challenge in the future, the tunnel's completion is really a great encouragement for us."
4. Various of Gongbei tunnel
5. SOUNDBITE (English) Hans De Wit, CEO, Tunnel Engineering Consultants:
"(The project adopted the) combination of jacking and freezing. So I think this is actually stretching the limits of this technique and it will be used as a reference in future projects all over the world."
6. Various of animation of Hong Kong-Zhuhai-Macao Bridge
7. Map showing project outline
8. Tunnel
9. Map showing different segments of Gongbei tunnel
10. Animation showing linking of Gongbei tunnel
11. Trucks inside tunnel
12. Workers welding
13. Pillars of tunnel
14. Various of tunnel
15. Various of workers welding
16. Various of border defense soldiers patrolling

The Hong Kong-Zhuhai-Macao Bridge in Zhuhai City of south China's Guangdong Province has marked another milestone towards its completion on Monday morning by completing a main tunnel segment linking Zhuhai and Macao.

"We are so excited that although there is a major challenge in the future, the tunnel's completion is really a great encouragement for us," said Liu Zhigang, Engineering Management Department Manager of the Hong Kong-Zhuhai-Macao Bridge Zhuhai connecting project.

Gongbei tunnel, the main tunnel, is a western part of the Hong Kong-Zhuhai-Macao Bridge. It's only 2.7 kilometers long, but what makes it special is that it passes right beneath a customs clearance point at the Gongbei border crossing linking Zhuhai and Macao. And that made its construction a lot more difficult as it wanted to avoid disrupting the running of the customs which clears nearly 300,000 passengers a day.

For this, a special pipe roofing was created for digging the tunnel. Engineers used dozens of curved steel pipes to form a huge outline of the tunnel, a very difficult process to install the pipes due to complicated geological conditions.

The tunnel is one of the most challenging subsea projects in the world. It has a large cross-section, roughly the size of a basketball court. So workers separated the section into a number of smaller parts while digging. The tunnel is designed to have two stories, each with three lanes going the same direction.

Workers had to use a strong brine circulation to freeze the soil and mud outside the tunnel to make it solid enough for safety and to prevent water leakage.

"The project adopted the combination of jacking and freezing. So I think this is actually stretching the limits of this technique and it will be used as a reference in future projects all over the world," said Hans De Wit, CEO of Tunnel Engineering Consultants.

The tunnel, together with the bridge is on target to be fully operational by the end of 2017. It will become the world's longest cross-sea bridge. It consists of 23 kilometers of bridges, seven kilometers of tunnels, and a number of artificial islands.