Super Typhoon Mangkhut will test a $20 billion bridge in the South China Sea

Super Typhoon Mangkhut, one of the strongest storm systems this year, is barreling across Asia. It has already wreaked havoc in Guam, and is expected to cause major damage...


Super Typhoon Mangkhut, one of the strongest storm systems this year, is barreling across Asia. It has already wreaked havoc in Guam, and is expected to cause major damage in Luzon, the breadbasket of the Philippines, before nearing Hong Kong and Macau on Sunday (Sept. 16).

The storm, with sustained winds of nearly 130 miles an hour, equals the wind power of a Category 4 hurricane, and could be the most powerful tropical cyclone Hong Kong has experienced since the city began collecting records in 1946.

One question that Hong Kong and Macau have on their minds as the cities brace for the massive storm is this: how will the $20-billion Hong Kong-Zhuhai-Macau bridge, set to open later this year, fare under the powerful lashing of a super typhoon?

The 34-mile bridge—the world’s longest sea-crossing bridge—has been years in the making and will link Hong Kong, a former British colony, and Macau, the world’s casino capital and a former Portuguese colony, with the southern Chinese city of Zhuhai. It is part of China’s attempt to project its economic and political might to the world as it seeks to weave Hong Kong together with neighboring areas into the self-styled Greater Bay Area (paywall), a region of $67 million that would boast a trillion-dollar economy to rival San Francisco’s Bay Area as a high-tech hub.

The bridge is designed to last 120 years, withstand winds of up to 125 miles per hour, and resist the impact of a magnitude-8 earthquake and a 300,000 metric ton vessel, according to the official in charge of the project’s construction.

As of Sept. 14, gusts of 150 miles per hour have been measured at the center of the storm, but the tropical cyclone is expected to weaken by the time it passes within 200 kilometers (120 miles) of Hong Kong on Sunday morning. It’s expected to bring heavy rains and storm surges, according to the Hong Kong Observatory, which notes that the cyclone’s path can still change.

A structural and geotechnical engineer told the South China Morning Post that the super typhoon could test the limits of the bridge’s structural safety.

“Whether the bridge can withstand the destructive force of Super Typhoon Mangkhut depends on the height of the waves at the artificial island,” said Ngai Hok-yan.

Reuters

The main bridge structure of 18 miles includes two artificial islands that serve as entry and exit points for a 4-mile underwater sea tunnel west of the Hong Kong section of the bridge. In April, photos showing wave-absorbing concrete blocks apparently floating away from one of the islands were widely shared online, causing fears of erosion. The bridge authority later clarified that the interlocking concrete blocks, known as dolosse, were designed to be submerged randomly so as to limit the amount of pressure exerted on the tunnel.

“If the waves are higher than four meters [13 feet], then there is a chance these protective blocks will be washed away, and very quickly,” said Ngai. “Without the protection of the dolosse, the worst-case scenario would see the undersea tunnel detach from the artificial island and float above the sea, and also the collapse of the island,” he added.



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