Japan’s Kansai Airport sinking due to subsidence issues
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Japan's Kansai Airport, which is located near Osaka, has also won international accolades for its architectural design, efficiency and staff.
PHOTO: BLOOMBERG
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OSAKA – Kansai International Airport faces ongoing subsidence problems as it sinks into Osaka Bay, prompting urgent measures by Japan to address and prevent further damage.
Kansai International Airport in Japan was recognised as the world’s best airport for luggage handling in 2024, maintaining a flawless record of no lost luggage for more than a decade.
It has also won international accolades for its architectural design, efficiency and staff. However, this acclaimed airport is now “sinking”.
Built on an artificial island in Osaka Bay, Kansai International Airport is one of Japan’s largest construction and engineering projects.
The airport consists of two islands, with one covering 1,290ha and the other spanning 2,668ha.
It was constructed to alleviate congestion at the nearby Osaka International Airport and opened its doors on Sept 4, 1994.
Since then, the airport has increasingly served both domestic and international flights, becoming a vital aviation hub.
In 2024, approximately 30.6 million passengers passed through its terminals, travelling to 91 cities across 25 countries.
While these figures are impressive, it is hard to ignore the fact that the airport has sunk deeper into the soft clay beneath Osaka Bay than engineers had initially predicted and is continuing to sink every year.
Several factors contribute to the gradual sinking of the airport.
These include the weight of the land and infrastructure, as well as the method used to construct the island by dredging millions of tonnes of earth and stone and dumping them onto the seabed.
This process did not allow the soft sediment to compact sufficiently before construction began, making the island prone to settling over time.
A further major cause is the loose clay and sediment layer beneath the airport, which sinks under weight. As a result, the airport has been subsiding faster than engineers originally calculated.
According to a report from the airport’s service provider, the surface level of the airport’s first island is now 3.84m lower than when it opened in 1994.
Since the commencement of landfill construction, the airport has experienced an average subsidence of 13.66m.
The latest data released in December 2024 indicated that the average subsidence measured at 17 points on the artificial island was only 6cm.
However, the situation on the second island is slightly worse, with the ground surface having sunk by 17.47m since construction began. The average subsidence across 54 measurement points on this island in 2024 was 21cm.
These islands were built on a 20m thick layer of clay and sediment that functions like a sponge.
Despite the installation of 2.2 million vertical drainage pipes to solidify the clay and limit shrinkage, the weight of the landfill, including more than 200 million cubic m of debris, has caused the clay to compress more than anticipated.
To address this issue, a seawall costing more than US$150 million (S$193 million) was constructed around the islands. Nonetheless, engineers still predict that, in the next 30 years, parts of the airport may fall below sea level.
In September 2018, Typhoon Jebi, the most powerful typhoon to strike Japan in 25 years, caused US$13 billion in damage and claimed 21 lives across the Pacific.
The typhoon led to the temporary closure of Kansai International Airport due to flooding.
This event highlighted significant design flaws, as critical infrastructure, including the disaster response centre and power stations essential for supplying electricity to the facilities, was located underground and completely flooded.
About 5,000 people were stranded at the airport without power for more than 24 hours.
According to a statement on the service provider’s website, the airport’s subsidence rate is currently decreasing, and efforts are being made to monitor the airport’s foundations while collecting data on the subsidence.
Academic experts have also been consulted for advice.
Emeritus Professor Hiro Ishikawa from Urban Planning and Policy at Meiji University, said the subsidence of the island remains at an acceptable level and is considered a valuable learning experience for similar man-made island projects.
Prof Ishikawa told This Week in Asia: “When we needed to build a second airport for Osaka, we had to decide to build offshore because there were few viable options. Land space on the mainland was very limited for large construction projects, and residents in nearby areas might be affected by noise and night flights.”
Kansai International Airport has provided valuable lessons for the development of other airports, including Chubu Centrair International Airport, which was also built on an artificial island off the coast of Nagoya.
Chubu Centrair, which opened in 2005 and is smaller than the Kansai airport, covering around 1,189ha, was ranked the best regional airport in the world for the 11th consecutive year in 2024 by the Skytrax industry organisation. It has reported fewer subsidence issues compared with Kansai.
Prof Ishikawa explained the engineering principles behind the Kansai airport: “We knew from the start that the airport would subside, and we considered the various impacts in the design. However, there were still mistakes, such as placing emergency facilities in underground areas prone to flooding.”
Currently, the airport’s subsidence rate is less than 10cm per year, but the situation is gradually improving and manageable. Subsidence in urban areas is not a new phenomenon and occurs worldwide, such as in Venice and Manhattan, due to the weight of buildings.
At present, the airport is undertaking a major US$609 million renovation project aimed at upgrading facilities and increasing operational capacity, despite the ongoing challenge of sinking deeper into Osaka Bay. THE NATION/ASIA NEWS NETWORK
