Hong Kong Travel & Transport

Design docs suggest HK-Zhuhai-Macao Bridge breakwater blocks should sit above water, not below

Design documents for the HK$120 billion Hong Kong-Zhuhai-Macao Bridge show that components for a breakwater structure should be placed higher to cover the perimeter wall of an artificial island, instead of being placed randomly below water. The documents appear to contradict claims from the bridge project’s management.

Photos and videos shared this week of an artificial island for the bridge just west of Hong Kong’s border sparked concerns that breakwater components had become disconnected from the main structure. The Zhuhai-based authority managing the section, which was constructed by the mainland side, claimed that the components were deliberately designed to be placed randomly underwater.

However, in an article published in the China Harbour Engineering academic journal in 2015, the authors explained the arrangement of the reinforced concrete dolos blocks for the island should be installed in a regular form above the water level, and randomly placed at selected locations under water. They should be placed at specific angles and distance, and connected to each other in order to be effective.

Hong Kong-Zhuhai-Macao Bridge

Photo: Screenshot.

Design documents from 2009 and 2012 unearthed by Ming Pao and HK01 respectively also showed that the blocks should be placed as high as a sloped wall on the perimeter of the island in order to absorb waves.

Lau Ching-kwong, a former government director of civil engineering, told Ming Pao that there should be more blocks above the water than below, according to the design. However, he said the recent photos were not very different from the design, and that it is normal to make small changes during the construction.

Ngai Hok-yan, a civil engineer experienced in reclamation projects, said that the authority may have concerns over the weight over the cross-harbour tunnel below the blocks – each weighing five tonnes – and so reduced the number of blocks.

artificial island Hong Kong-Zhuhai-Macao Bridge

Photo: Apple Daily.

He told Apple Daily that the fact the block are sitting lower than in the design may increase the risk of the sloped wall being corroded, but it should not be difficult to fix the issue.

He added that the blocks should normally be interlocked to allow a small space to decrease the energy of waves. The arrangement of the blocks around the artificial island may not be able to perform such a task, though he noted the aim of the design may differ to those of other countries.

Hong Kong-Zhuhai-Macao Bridge

Photo: Screenshot.

Scientific examination

Chief Executive Carrie Lam responded to the incident for the first time on Friday saying that, whether an engineering project is safe depended on scientific examination, and that the media and commentators should only make comments after looking at expert opinions.

She said the government will only allow the bridge to operate once it is confirmed safe. The project is set to open later this year.

artificial island Hong Kong-Zhuhai-Macao Bridge

Photo: Apple Daily.

She said she noticed that the authority issued a press release to clarify the issue and noted that there was no water seepage on the artificial island after typhoon Hato hit last year.

“From the design, to the completion of the bridge, many experts believe that it is a world-class project. I hope that, just because some individuals took a photo or made some comments, that people won’t immediately question the design of this engineering project,” she said.

Lam said that the Highways Department will continue communicating with the authority and will reveal further scientific information when it is available.

“The Hong Kong-Zhuhai-Macao Bridge Authority has provided a lot of diagrams as explanation. If people think they are too difficult to understand… we will follow up with the Authority to see what other information can be provided,” she said.

Design docs suggest HK-Zhuhai-Macao Bridge breakwater blocks should sit above water, not below