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Kansai International Airport Sinking: engineering Challenges in Osaka Bay
International airport faces ongoing subsidence problems as it sinks into Osaka Bay. Japan is taking urgent measures to address and prevent further damage."/>
OSAKA – Kansai international airport, an architectural marvel built on an artificial island in Osaka Bay, is facing important challenges due to ongoing subsidence. Japanese authorities are implementing urgent measures to combat the sinking and prevent further damage to this crucial aviation hub. Despite being recognized as the world’s best airport for luggage handling in 2024, maintaining a decade-long record of no lost luggage, the airport’s foundation is gradually succumbing to the pressures of its unique construction.
The Construction and Initial Success of Kansai Airport
Kansai International Airport, comprising two islands spanning 1,290 hectares and 2,668 hectares respectively, was built to alleviate congestion at the nearby Osaka International Airport (Osaka International Airport).Since its opening on September 4, 1994, it has become a vital hub for both domestic and international flights. In 2024, approximately 30.6 million passengers traveled through its terminals, connecting to 91 cities across 25 countries.
Did You Know? Kansai International Airport was lauded for its architectural design, efficiency, and remarkable staff, earning international accolades.
The Sinking Problem: Causes and Measurements
The airport’s gradual sinking into the soft clay beneath Osaka Bay is a major concern.Factors contributing to this include the weight of the land and infrastructure, and the construction method involving dredging and dumping millions of tons of earth and stone onto the seabed. This process did not allow the soft sediment to compact sufficiently before construction,making the island prone to settling over time.
The loose clay and sediment layer beneath the airport further exacerbate the issue.According to the airport’s service provider, the surface level of the first island is now 3.84 meters lower than when it opened in 1994. As landfill construction began, the airport has experienced an average subsidence of 13.66 meters. Data from December 2024 indicated an average subsidence of 6 cm across 17 points on the first island.The second island faces a slightly worse situation, with the ground surface having sunk by 17.47 meters since construction began, with an average subsidence of 21 cm in 2024 across 54 measurement points.
Pro Tip: Engineers installed 2.2 million vertical drainage pipes to solidify the clay and limit shrinkage, but the weight of over 200 million cubic meters of debris has caused more compression than anticipated.
Mitigation Efforts and Future Predictions
To combat the sinking, a seawall costing over US$150 million (S$193 million) was constructed around the islands. Despite these efforts,engineers predict that parts of the airport may fall below sea level within the next 30 years.
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. The typhoon led to the temporary closure of Kansai International Airport due to flooding,highlighting design flaws such as the location of critical infrastructure,including the disaster response center and power stations,underground. Approximately 5,000 people were stranded at the airport without power for over 24 hours.
Current Status and Expert Opinions
According to the service provider’s website, the airport’s subsidence rate is decreasing, and efforts are underway to monitor the airport’s foundations and collect data on the subsidence. Academic experts, such as Emeritus Professor Hiro Ishikawa from Urban Planning and Policy at Meiji University, are being consulted. Prof. Ishikawa stated that the subsidence remains at an acceptable level and serves as a valuable learning experience for similar man-made island projects.
Kansai International Airport has provided valuable lessons for the development of other airports, including Chubu Centrair International Airport, wich was also built on an artificial island off the coast of Nagoya. chubu Centrair, which opened in 2005 and covers around 1,189 hectares, was ranked the best regional airport in the world for the 11th consecutive year in 2024 by Skytrax (Chubu Centrair International Airport) and has reported fewer subsidence issues compared to Kansai.
Currently, the airport’s subsidence rate is less than 10 cm per year, and the situation is gradually improving. The airport is undertaking a major US$609 million renovation project to upgrade facilities and increase operational capacity,despite the ongoing challenges.
