Kansai Airport in Osaka is sinking faster than expected – the soft seabed is to blame. Engineers are using high-tech solutions to combat the slow sinking.

It was once a symbol of technological progress: Kansai International Airport, built on an artificial island in Osaka Bay. But the ambitious construction project has been struggling with a massive problem for decades: the island is sinking faster than originally calculated.

Sinking during the construction phase

As reported in Smithsonian magazine, the first island began to sink much faster than expected during the construction phase in the late 1980s. Instead of the predicted 5.8 meters, the subsidence in 1990 was already 8.2 meters – and by the time the airport opened in 1994, the island had sunk by around 12 meters. According to the Smithsonian, engineers on site are now openly talking about the fact that they “never expected” the island to sink at this rate.

Marine clay as the cause

The reason lies in the subsoil: the artificial island was built on a thick layer of soft marine clay. The weight of the materials used to build the island is gradually compressing this clay – a process that is well known, but the speed of which was apparently underestimated. On their website (kansai-airports.co.jp), the operators of Kansai International Airport state that they started using so-called sand drainage early on to drain the water in the soil more quickly and control the subsidence – but the effect was limited.

Measures taken

Over the years, extensive measures have been taken to ensure the safety of the airport. These include, among other things, hydraulic jacking devices installed under the terminal to lift it if necessary – an elaborate but effective solution, as an Smithsonian analysis emphasizes.

Problems in the past, too

The situation became particularly dramatic when Typhoon Jebi passed through in 2018, when strong waves flooded parts of the runways and the terminal. The airport was unable to function for several days – a serious setback that attracted international attention. According to Wikipedia, the protective walls had to be raised and the flood protection massively strengthened as a result.

It is being invested in

Despite these challenges, Kansai remains an important international hub for Japan. The operators continue to invest in new technologies and structural adjustments to keep the airport above water in the long term – literally.

Image:
Ankou1192, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons