World’s best luggage handling airport in Japan is sinking. Here’s why

Once seen as a unique feat of engineering, Japan’s Kansai International Airport (KIX) is now slowly sinking.

The airport stands on two man-made islands in Osaka Bay.

In 2024, it was named the world’s best airport for luggage handling, having gone over ten years without losing a single bag.

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But the ground beneath the first island has dropped by around 3.84 metres (12.6 feet) since the airport opened in 1994. This means that the sinking has not stopped and continues each year.

Why is this happening? And what steps is Japan taking to stop it?

Here’s what we know:

Why Japan’s Kansai Airport is sinking

The airport, once praised for its design, smooth operations, and accurate baggage handling, is now dealing with a tough challenge: its battle with nature.

It is built on a large artificial island in Osaka Bay. This man-made structure is slowly sinking into the soft clay below.

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Opened in 1994, the airport was planned to ease congestion at Osaka’s older airport.

Since then, it has grown into a busy global hub, connecting over 30 million travellers to 91 cities across 25 countries, according to the South China Morning Post.

It now handles a mix of domestic and international flights and plays an important role in the country’s air travel network.

But over the years, the airport has sunk further into the clay foundation than experts first expected. And it’s still sinking.

What is behind this slow sinking?

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Several factors are responsible. These include the heavy weight of the airport structures and the method used to create the island, by dumping millions of tonnes of soil and stone onto the seabed.

This approach did not allow the soft ground beneath to fully settle before building began. As a result, the land has continued to sink over time, according to The Straits Times.

Another reason is the layer of loose clay and sediment under the island, which gets compressed under pressure.

Because of this, the ground has been sinking faster than engineers had planned for.

According to a report by the airport’s operator, the surface of the first island is now 3.84 metres lower than it was when the airport opened in 1994.

Since the landfill work began, the airport has sunk by an average of 13.66 metres.

In the most recent data from December 2024, the average drop recorded at 17 different points on the island was 6cm.

Things are slightly worse on the second island. There, the surface has gone down by 17.47 metres since construction started. Measurements taken at 54 points on the island in 2024 showed an average drop of 21cm.

The islands were built on a thick 20-metre layer of clay and sediment, which acts like a sponge.

To control the sinking, engineers installed 2.2 million vertical drainage pipes to help firm up the clay and reduce shrinkage.

But the huge weight of the landfill, which is more than 200 million cubic metres of material, has pressed down on the clay more than expected.

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What happens now?

To deal with the sinking issue, a seawall worth over US$150 million (over Rs 1,280 crore) was built around the islands.

As mentioned on the service provider’s website, teams are closely watching the airport’s foundations and collecting information to track the sinking.

Still, engineers believe that parts of the airport could drop below sea level over the next 30 years.

Back in September 2018, Typhoon Jebi, the strongest storm to hit Japan in 25 years, caused US$13 billion in damage and killed 21 people across the Pacific.

Kansai International Airport had to shut down temporarily because of flooding.

The typhoon also exposed major design problems.

Key infrastructure like the disaster response centre and power stations, which are essential for keeping the airport running, were placed underground and ended up completely flooded.

Around 5,000 people were stuck at the airport with no power for over 24 hours.

Emeritus Professor Hiro Ishikawa, who teaches Urban Planning and Policy at Meiji University, told This Week in Asia that while the island is still sinking, the rate is manageable.

He added that it has become an important case study for future projects on artificial islands.

Right now, the airport is going through a major renovation worth US$609 million. This work is focused on improving the facilities and handling more flights, even as the airport continues to sink further into Osaka Bay, according to reports.