When it was completed in 1994, Kansai International Airport (KIX) in Japan was heralded as a landmark achievement in civil engineering.
Built on reclaimed land in Osaka Bay, it remains one of the most ambitious infrastructure projects of its kind. It is built entirely on two artificial islands – the first in the world – connected to the mainland by a 1.9-mile bridge.
It also boasts the longest terminal building globally and a near-flawless track record of luggage movement.
However, the airport is facing one significant challenge – it is sinking into the sea.
It has, in total, sunk about 38 feet, or nearly 12 metres. Yet it continues to serve as a hub for All Nippon Airways, Japan Airlines, and Nippon Cargo Airlines, which fly all over Asia.
Kansai’s engineers knew the airport was sinking slightly, but predicted it would settle evenly over a 50-year period. They said it would stabilise at 13 feet (four metres), the minimum elevation required to prevent flooding in case a breach develops in the encircling seawall.
However, within just six years of its launch, portions of the first of the two artificial islands already reached that threshold.
The airport is built on land that effectively acts like a wet sponge. To ensure it could support the huge weight of airport buildings and aircraft, the land needed to be transformed into a dry, dense foundation.
To achieve this, construction crews laid sand five over a metre-and-a-half deep, which helps absorb moisture from the surrounding soil. Heaps of soil were then dredged and brought into the area, compressing the ground layers to create a firmer floor.
Workers also excavated below the passenger terminal, inserting plates beneath the hydraulic jacks, and raised the columns in stages, in an effort to save the airport from the sea.
Some £117 million was spent to raise the seawall, but some engineers believe that this is too little too late.
In 2018, Typhoon Jebi hit Osaka Bay, overwhelming the seawall and flooding the runway, causing a two-week disruption. This incident prompted further upgrades, including the raising of the seawall by an additional 2.7 metres to guard against future flooding.
Some predictions believe that, by 2056, sections of the islands may well sink more than 13 feet (four metres) to sea level.
Engineers are also concerned about the fact that Kansai is not sinking evenly. The centre of the airport, for example, is thought to be sinking quicker than at the ends of the building.
This has not stopped the airport connecting Osaka, Japan’s third biggest city, with the rest of the world.
In 2023, Kansai served an incredible 25.9 million passengers, a significant increase from 2019 when it served 31.9 million passengers, according to VINCI Airports. 25 percent of all foreign visitors to Japan entered the country through KIX last year.
The airport is also currently undergoing a $740 million (£581 million) renovation, aimed at increasing capacity and further cementing its role as a key regional transport hub. It is also set to play a key role in the upcoming Osaka Expo in 2025, where it will serve as a gateway for an anticipated 28 million visitors.
The airport also claims to have not lost a single piece of luggage in its 30 years of operation, attributing this to its multilayered checking procedures and dedicated staff.