Japan’s $20B Kansai Airport in Osaka sinking at an alarming rate: experts

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When Japan’s Kansai International Airport (KIX) opened in 1994, it was considered an engineering marvel. It is one of the world’s floating airports and cost roughly $20 billion to construct.

30 years on, it remains an important hub in Japan. In 2022, Statista named KIX the third busiest airport in the country, after Narita International Airport (NRT) and Tokyo Haneda Airport (HND). The airport serves as a hub for major airlines including All Nippon Airways, Japan Airlines, Nippon Cargo Airlines and even Japan’s low-cost airline, Peach. 

However, some experts believe that KIX airport may be completely submerged by 2056. To get to the bottom of this, it’s necessary to know the airport’s background.

Why is Kansai Airport in the middle of the sea?

Kansai Airport was built to relieve overcrowding at the first airport in Osaka: Itami Airport (ITM). 

Its initial location was slated for near Japan’s Kobe region, but city officials and locals protested against the plan. This resulted in the decision to build the new airport in a unique location – in the middle of the sea, where operations can take place 24 hours without disturbing locals.

To build an airport in the middle of the sea, engineers drained millions of liters of water out of the 20-meter deep soft clay that lies beneath the airport’s current location, before constructing a seawall.

The reclaimed land resembled a wet sponge and was transformed into a dry and dense foundation before supporting the weight of the airport buildings. 

Construction crews laid sand five feet deep atop the clay seabed and installed 2.2 million vertical pipes, each nearly 16 inches in diameter. These pipes were then pounded into the clay and filled with sand and soil to create a more stable base.

Construction of KIX airport began in 1987 and took seven years to complete. 

Why is Kansai Airport sinking?

Throughout its 30 years, the floating airport withstood a major earthquake in 1995, the great Hanshin earthquake which reached a magnitude of 7.2 and claimed more than 6,000 lives. In 1998, the airport also survived typhoon Stella which triggered over 70 landslides.

However, the airport is sinking faster than anticipated. Owing to its foundation being similar to a wet sponge experts have calculated that the airport would sink by 5.7 meters in 1990. Instead, it had gone down 8.2 meters

In a Smithsonian Magazine interview in 2018, Yukako Handa, a representative of Kansai Airports was quoted as saying: “When the Kansai airport was constructed, the amount of soil to reclaim the land was determined based on necessary ground level and subsidence estimation over 50 years after the construction.”

By 2018, the airport had sunk 38 feet since its construction, 25% more than what experts anticipated.

Despite the sinking predictions, the outlook remains positive and the airport has continued to expand. In December 2023, a new international departure area was opened, with future expansions set to be completed by 2025.

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