Waterproof concrete extends life span of tunnel

The Hong Kong-Zhuhai-Macao Bridge, one of the most massive infrastructure projects ever undertaken, is being hailed as a remarkable achievement in cutting-edge civil engineering. International tunnel expert Tommy Olsen, from COWI, a leading infrastructure consulting company in Denmark, said its immersed tunnel sets a standard that may be copied in other projects around the world.

One concept that Olsen's team brought to the Chinese project was watertight concrete, keeping the concrete tunnel safe from high hydraulic pressure without the need for waterproofing membranes.

Such membranes cannot be guaranteed to last as long as 120 years, the designed life span of the bridge, Olsen said, but good quality concrete can.

Olsen, who led a consulting team working with Chinese designers on the project, said the concept has been used for immersed tunnels in Europe and Korea, but the HZMB established new standards.

"This project is unique and what has been learned from this project could be applied to other long immersed tunnels worldwide in the coming years - like some of the concepts my team brought to this project," he said.

Before joining the HZMB team, Olsen's company helped design the Busan-Geoje Fixed Link in South Korea and the Oresund Bridge linking Denmark and Sweden - two of the world's leading bridge-tunnel projects.

After visiting the bridge site in February, after the principal sections were completed, Olsen told China Daily: "I am very impressed when I see the quality of the job. I am quite impressed by what I have seen today.

"When it is constructed in this way and with high quality, there is much greater likelihood that the tunnel will not leak water for the next 120 years, which is a very long time span for a project."

The intended 120-year life span of the bridge embraced talents supplied by the governments of Hong Kong, Macao and Guangdong province. The achievement is considered a high watermark of positive exchanges in civil engineering among the three jurisdictions.

Lau Ching-kwong, a bridge expert in Hong Kong, credits this cooperation with ensuring the high quality of the bridge.

Lau, a fellow of the Hong Kong Academy of Engineering Sciences, led the construction in the 1990s of the Tsing Ma Bridge in Hong Kong, the world's longest suspension bridge accommodating both rail and road traffic.

He was also a member of the expert group advising on key technologies for the HZMB.

The designed life span of a bridge on the Chinese mainland is normally 100 years, Lau said, but in Hong Kong it is 120 years. That was the standard set for the HZMB, which meant better materials were demanded.

The same principle was applied to the standards for earthquake resistance, wind shear and every other index that defines a solid engineering structure, Lau said.

It was a challenge for engineers in the three places, but Lau said, "You can see that it worked out great."