Jazmin Li
The Kansai International Airport in Osaka, Japan, is sinking into the sea at an alarming rate. Built on Osaka Bay, the airport was constructed on an island made of loose clay and silt, which has compressed and settled under the weight of the infrastructure. Engineers had predicted the island would sink, but the rate of sinking has been faster and deeper than expected. In 1990, three years after construction began, the island had sunk 27 feet, 50% more than predicted. By 1999, it had sunk 8.2m (26 ft 11in), almost 50% more than the most optimistic estimate. The airport is now at risk of being below sea level by 2056.
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Kansai International Airport is sinking faster than predicted
Kansai International Airport, located in Osaka Bay, Japan, is a groundbreaking infrastructure project. It is the world's first airport built entirely on an artificial island and boasts the longest terminal building globally. However, since its opening in 1994, the airport has been sinking faster than predicted.
Engineers were aware that the airport, constructed on reclaimed land, would settle over time. This settlement is due to the composition of the seabed, which consists of loose clay and silt that compresses under the weight of the infrastructure. While this was anticipated, the rate and extent of sinking have exceeded expectations.
Initial projections estimated that the island would settle by approximately eight meters over 50 years. However, the actual subsidence has been much more rapid, with the airport sinking by more than expected within the first few years. This unexpected rate of sinking has resulted in significant additional costs, with over USD $100 million spent to maintain the island's height above sea level.
The airport operators have implemented measures to slow down the sinking and mitigate its impact. Adjustable columns and hydraulic jacks have been installed to support the terminal building and raise the foundation in stages. Additionally, the seawall surrounding the airport has been raised to protect against flooding during extreme weather events, such as Typhoon Jebi in 2018, which caused significant disruption.
Despite the ongoing efforts to keep the airport operational, the sinking remains a challenge. Experts predict that without further significant intervention, the airport's artificial islands could sink to sea level by 2056 or even earlier. The financial burden of continuously raising the runway and seawall may eventually outweigh the benefits of keeping the airport in operation. However, the airport is currently undergoing a USD $470 million renovation to increase its capacity and strengthen its role as a key regional transport hub.
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The airport was built on loose clay and silt
The Kansai International Airport in Osaka, Japan, is sinking into the sea. The airport, which opened in 1994, was constructed on an artificial island in Osaka Bay. Engineers had anticipated that the airport would sink, given the soft soils of Osaka Bay, but the rate of sinking has been faster and more severe than predicted.
The seabed beneath Kansai Airport is composed of loose clay and silt, which compresses and settles under the weight of the infrastructure. The island was formed by dredging millions of tons of soil and rock and piling it onto the seabed. This process did not fully consolidate the soft sediment, leaving it vulnerable to long-term settlement. As a result, the airport has sunk more than expected, posing significant challenges and requiring ongoing interventions to slow the sinking process.
The construction of Kansai Airport began in 1987, and by 1990, it had already sunk 27 feet, exceeding the expected rate of 19 feet. Engineers have since worked to strengthen and raise the surrounding seawall, and adjustable columns have been designed to support the terminal building. These columns can be extended by inserting thick metal plates at their bases. Despite these efforts, the airport continues to sink, and some sections are predicted to be below sea level by 2056.
The weight of the infrastructure contributes significantly to the sinking. While the terminal buildings and aircraft themselves do not cause the sinking, the 69.5 square miles of fill used to create the islands exert immense pressure on the underlying clay and silt. This weight, combined with the soft and compressible nature of the seabed, results in the gradual sinking of the airport.
The Kansai Airport project faced challenges from the beginning, with international trade friction during the bidding and construction phases. Despite these issues, the airport has become a significant hub for passenger and cargo airlines, serving over 25 million passengers in recent years. However, the ongoing sinking has led to concerns about the airport's future and the potential impact on travel and trade in the region.
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Underestimated settlement rates
Engineers underestimated the rate at which Kansai International Airport would sink in the early days of the project, and this has continued to cause problems over the years. While it was known that the airport, built on an artificial island, would settle after construction, the rate of sinking has been faster and deeper than anticipated.
The island that Kansai Airport is built on was created by dredging up millions of tons of soil and rock and piling it onto the seabed. This process did not fully consolidate the soft sediment of Osaka Bay before construction began, leaving the airport prone to long-term settlement. The seabed underneath the airport is made up of loose clay and silt, which compresses and settles under the weight of the infrastructure.
The weight of the infrastructure itself is a significant factor in the sinking. It is not the terminal buildings and aircraft that are causing the airport to sink, but the 69.5 square miles of fill that form the islands. The soft soils of Osaka Bay were anticipated by designers, but the rate of sinking has still been underestimated. By 1990, three years after construction began, the airport had sunk 27 feet, 50% more than the expected 19 feet. By 1999, the island had sunk 8.2 meters, almost 50% more than predicted.
To slow down the sinking, an additional $150 million has been spent on strengthening and raising the seawall surrounding the airport. Hydraulic jacks with iron plates have been installed, which can raise the foundation in stages. However, adjusting these every couple of years is costly and complex. While the sinking has slowed, the airport remains at risk, with some engineers predicting that sections could be below sea level as soon as 2056.
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$150 million spent on raising the seawall
Kansai International Airport, the third-largest airport in Japan, has been sinking faster than expected since its opening in 1994. The airport is located on two man-made islands in Osaka Bay and was constructed at a cost of $19.6 billion, making it the most expensive civil works project in modern history.
Engineers were aware from the beginning that some sinking would occur due to the soft soils of Osaka Bay. However, the rate of sinking has been faster and deeper than anticipated. By 1999, the island had sunk 8.2 meters, exceeding the original estimates by 2.4 meters. To slow down the sinking process, $150 million has been spent on strengthening and raising the seawall surrounding the airport.
The seawall, made of 48,000 concrete blocks and anchored in steel chambers, was initially built to protect the airport from flooding. However, as the sinking continued, the seawall had to be raised to prevent the airport from sinking below sea level. Hydraulic jacks and iron plates were installed beneath the passenger terminal to raise the columns supporting the building in stages.
While these measures have helped slow the sinking, the airport remains at risk. Engineers predict that by 2056, sections of the airport could be submerged more than 13 feet below sea level. The ongoing maintenance and repairs to adjust the hydraulic jacks every two years have also significantly increased costs.
The sinking of Kansai International Airport highlights the challenges of building infrastructure on reclaimed land and the importance of addressing critical issues such as sinking rates in the design and construction phases. Despite the efforts to raise the seawall and slow the sinking process, the airport's future remains uncertain.
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The airport is Japan's third busiest
The Kansai International Airport in Osaka, Japan, is the country's third busiest airport. It is built on an artificial island in Osaka Bay and serves as a hub for several major airlines and cargo carriers, including All Nippon Airways, Japan Airlines, and Nippon Cargo Airlines. In 2019, the airport handled 31.9 million passengers, with a freight volume of 802,162 tonnes. The airport has two runways and terminals, and its total cost, including land reclamation and facilities, amounted to $20 billion as of 2008.
Kansai Airport was constructed to relieve overcrowding at Osaka's first airport, Itami Airport. With no available land for expansion, the new airport was built offshore, aiming to avoid disturbing local residents. However, the soft soils of Osaka Bay have caused the airport to sink faster and deeper than anticipated. Engineers had predicted a maximum sink rate of 18 feet, but by 1999, the island had sunk by 26 feet, almost 50% more than projected.
The sinking rate has slowed down over the years, decreasing from 19 inches per year in 1994 to 2.8 inches annually by 2008. To mitigate the issue, adjustable columns support the terminal building, and a further $150 million was spent on strengthening and raising the seawall. Despite these measures, the airport remains at risk, with sections potentially falling below sea level by 2056.
Kansai International Airport has received recognition for its operations and services. In 2020, Skytrax ranked it as the tenth-best airport globally and awarded it the titles of Best Airport Staff in Asia, World's Best Airport Staff, and World's Best Airport for Baggage Delivery. The airport has established itself as an Asian hub, offering numerous weekly flights to various regions, including Asia, Australasia, Europe, the Middle East, and North America.
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Frequently asked questions
Kansai International Airport in Osaka Bay, Japan, has sunk 8.2 meters since its construction in 1987.
The airport was built on a seabed made of loose clay and silt, which compresses and settles under the weight of the infrastructure.
To slow down the sinking process, $150 million has been spent on strengthening and raising the seawall surrounding the airport. Hydraulic jacks with iron plates have also been installed to raise the foundation in stages.
