A file photo of the Hong Kong-Zhuhai-Macau Bridge during its construction. Photo: Xinhua
A file photo of the Hong Kong-Zhuhai-Macau Bridge during its construction. Photo: Xinhua

As super typhoon Mangkhut bears down on southern China, bringing some of the strongest winds for half a century, concerns are growing over the stability of the unopened Hong Kong-Zhuhai-Macau Bridge.

Residents in Hong Kong and Macau have sealed windows and cleared  supermarket shelves of rice, bottled water and cup noodles as they brace for the impact. However, many eyes are on the 55-kilometer Hong Kong-Zhuhai-Macau Bridge, which faces its first major test.

Wriggling through the Pearl River estuary, the bridge was designed to withstand gales of up to 2ookm/h, equivalent to a category 16 typhoon on the Beaufort wind-force scale. Yet Mangkhut has already been recorded at 285 kilometers per hour, according to Philippine authorities, with sustained winds of up to 240km/h near the center.

An aerial view of the main pylons supporting the bridge. Photo: Xinhua

While it is assumed that the three cable-stayed bridges, linked by two artificial islands, can exceed their design capacity, there are greater concerns over the structural integrity of an underwater tunnel that lies on the estuary seabed, stretching for 6.7 kilometers.

In the worst-case scenario the islands, created from reclaimed land at each end of the tunnel, could be submerged by high seas, which might threaten the tunnel as flash-flooding pumps in a torrent of seawater.

One of the two artificial islands. Photo: Hong Kong-Zhuhai-Macau Bridge Authority
A computer-generated image of flooding on one of the islands. Photo: Internet

Images taken recently from drones revealed that seawalls and tetrapods meant to protect these islands are collapsing and drifting away into the sea. Mainland officials vehemently denied there were any construction flaws or negligence, saying that the scattered blocks were part of the original design and posed no safety hazard.

Hong Kong’s Highways Department insisted in a media response that the bridge was designed to withstand typhoons and storms in a region with an annual active typhoon season. But just in case, it noted that all work other than the installation of feeder lines in Hong Kong waters had been handled by mainland Chinese contractors.

A storm gathers above the bridge in the Pearl River estuary. Photo: Xinhua
Forecast rainband and circulation range of Mangkhut. Photo: Hong Kong Observatory

Chief Executive Carrie Lam Cheng Yuet-ngor said after the drone photos emerged last month that the project was “world-class” and there were no safety issues. “The stability of construction works is a scientifically proven thing, so I hope the press and commentators can read the experts’ explanations before making comments,” she said.

However, it was revealed last year that strength tests on concrete had been falsified and that some re-testing had been ordered. A consortium that built the tunnel and artificial islands was headed by the privately-owned China Communications Construction Company Limited. 

According to tracking by the Hong Kong Observatory, Mangkhut will move across the northern part of Luzon in the Philippines into the South China Sea Saturday while maintaining its strength as a super typhoon. The storm may even ramp up more destructive power when it crosses vast expanse of water in the sea, before making landfall along the western portion of the Guangdong coastline.

Read more: China’s road to nowhere on a bridge over troubled waters

Tetrapods protecting bridge project ‘collapsing, drifting’

Opening of mega bridge held back by delays at HK end

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