Cross-delta bridge soon to see light at end of tunnel

The final phase of construction of the Hong Kong-Zhuhai-Macao Bridge IHZMB) is almost at hand. China Communications Construction Co Ltd (CCCC) is about to install the 26th of 33 tube couplings, according to Lin Ming, general manager of the island-tunnel project. Lin added that complete installation of the immersed tunnel is the linchpin of the whole endeavor.

At present, 25 tube couplings have been installed for the Pearl River Delta crossing. “The most difficult challenge afterward will be the installation of curve immersed tubes and the final connection of the tunnel’s separate parts,” said Lin of this decisive stage.

To date, 85 percent of island-tunnel engineering work has been completed and 4,365 m of the immersed tunnel has been embedded for the world’s longest cross-sea structure. The fourth phase, to be conducted over the next year, will involve engineering work inside the tunnel, as well as further construction work on the artificial islands.                                          

Hong Kong-Zhuhai-Macao Bridge [Photo / Xinhua]

With a total length of 55 km, the bridge is a gigantic engineering undertaking integrating spans, islands and tunnels. It includes the 6.7 km subsea tunnel, which both is the world’s first deep-buried immersed tunnel and the largest marine bridge-tunnel. 

The immersed tunnel has 33 tube couplings in total, each weighing about 80,000 tons – roughly the mass of a middle-sized aircraft carrier. “The pre-casting of the gigantic concrete tunnel segments, their towing and immersion under complicated sea conditions, the connection of tunnel segments under high water pressure, and the water-tightness and durability of the segment joints all call for the highest world standards,” according to CCCC.

The project’s chief designer, Liu Xiaodong, said the greatest difficulty lies in the joining of 180 m long immersed tubes in 40 m of water. Its degree of difficulty is similar to that of space docking. However, he reported, the 200-plus joints of the immersed tunnel have been coupled impermeably -- at an advanced international level.

The construction team has independently developed and implemented many new structures, techniques and pieces of equipment. It has carried out over a hundred experimental research tests, solved more than ten world-level technical problems such as the rapid formation of man-made islands, and secured at least 400 patents.

Only a few countries worldwide have the capability to build offshore immersed tubes. The bridge is the first such operation in China, according to Lin.

Li Ying, Chinese representative and project manager of Tunnel Engineering Consultants, a Dutch company specializing in immersed tunnel design, construction and project management, said that China has full potential to become a world leader in immersed tunnel projects. HKMB will be a good reference for the construction of the Fehmarn Belt Fixed Link (a planned immersed tunnel to connect the Danish island of Lolland with the German island of Fehmarn) and the Shenzhen-Zhonshan Crossing immersed tunnel project (to be the world’s first immersed tunnel with two-way eight lanes).