Japan's Kansai International Airport is sinking, but how fast?
Japan's Kansai International Airport is sinking, but how fast?
Japan's Kansai International Airport (KIX), an award-winning airport for its architectural design, efficiency, staff, and baggage delivery, is sinking.
Built on a man-made island in Osaka Bay to alleviate overcrowding at the nearby Osaka International Airport, KIX has become a major hub for domestic and international flights since its opening in September 1994.
Since then, Kansai International Airport has seen remarkable growth, connecting 91 cities across 25 countries with around 30.6 million passengers in 2024.
Airport's growth and concerns about sinking
However, it has sunk into the clay layers beneath the bay more than engineers had initially expected, continuing to inch lower every year.
The airport's first island is now about 3.84 meters lower than when it opened, and since landfill began for its construction, it has sunk an average of 13.66 meters.
Despite these concerns, the operator Kansai Airports emphasized that some "settling" was always expected.
Sea walls have been raised around KIX
Kansai Airports reported that the average subsidence was 6 cm across 17 points last year.
To mitigate the effects of subsidence, more than $150 million has been spent on raising sea walls around KIX.
The islands were constructed atop a 20-meter (65.6-foot) thick layer of alluvial clay, which acted like a sponge.
How island was created; challenges
But even after installing 2.2 million vertical pipe drains designed to strengthen the clay and reduce contraction, the weight of the landfill, which includes over 200 million cubic meters (7.6 billion cubic feet) of debris and 48,000 tetrapods, has compressed the clay more than expected.
In September 2018, the challenges posed to the airport became evident when Typhoon Jebi struck.
The airport had to be entirely shut down after being flooded by storm surges.
KIX inundated after typhoon
The flooding exposed a significant design flaw: essential infrastructure, such as the disaster response center and an electric substation necessary for powering the facility, was situated at the basement level and was inundated.
As a result, approximately 5,000 people were stranded at the airport without power for over 24 hours.
Subsidence rate lesser than before
However, according to a statement on the operator's website, the rate of subsidence is decreasing.
They continue to monitor the airport's foundations by gathering data on subsidence and consulting with academic experts.
Hiroo Ichikawa, a professor emeritus of urban planning and policy at Meiji University, stated that the sinking of the islands has remained within acceptable limits.
He also noted that the entire project has provided valuable lessons for other similar man-made island initiatives.