Kansai International Airport, the world’s first airport built entirely on an artificial island, sank more than 12 meters in the first 8 years.
Kansai International Airport on Osaka Bay, Japan. Image: B1M
Kansai International Airport, a remarkable achievement in the field of civil engineering, has just entered its 31st year of operation. Located on an artificial island in Osaka Bay, it is one of the most ambitious infrastructure projects belongs to this category. Kansai opened in 1994 and was the first airport in the world built entirely on an artificial island. The airport also has the longest terminal in the world and has almost never lost a passenger’s luggage for decades.
The idea of building an airport on the sea comes from essential needs. By the late 1960s, Osaka, Japan’s second largest city, had grown beyond what its domestic airport could handle. There was no more space to expand in this city surrounded by mountains. The only feasible but also extremely bold and untested solution is to build an offshore airport.
Construction began in 1987, after 20 years of planning. This was a huge and expensive project, with a total cost of up to $14 billion at the time – equivalent to nearly $40 billion today. The project requires the creation of a completely new island, protected by an 11 km seawall, connected to the mainland by a bridge costing $1 billion to build. Kansai’s success paved the way for later floating airports.
Despite achieving many breakthrough achievements, the project is facing a big challenge – sinking into the sea faster than expected. Engineers initially predicted that the island would sink about 8 meters within 50 years. In fact, the rate of subsidence is much faster, up to more than 12 m in the first 8 years.
The main problem lies in the clay layers below the artificial island. Although the engineering team took steps to strengthen the top layer, the deeper clay layer, filled with sand pockets, was less predictable. This subsidence significantly increased costs: More than $100 million was spent to keep the island above sea level.
Despite its subsidence problems, Kansai’s design is a testament to ingenious engineering. The station was designed by famous architect Renzo Piano to be able to withstand natural disasters, including earthquakes. In 1995, when the Kobe earthquake devastated surrounding areas, Kansai airport remained intact and operated normally.
The airport’s design also allows for continuous adjustments. The station sits on 900 support columns that can be raised or lowered to overcome the problem of uneven subsidence. Even runways – built with flexible asphalt instead of concrete – can absorb vibrations without cracking.
In recent years, airports have faced a number of new challenges. In 2018, Typhoon Jebi hit Osaka Bay, breaching the seawall and flooding the runway, disrupting operations for two weeks. This incident prompted further upgrades, including raising the seawall by 2.7 m to protect against future flooding.
So how long can these measures keep Kansai International Airport open? Experts predict that without significant intervention, the airport’s artificial island could sink to sea level by 2067. Someday, the financial burden of continually raising the runway will and seawalls may exceed the benefits of keeping the airport open.