Inside the $20bn international airport that's 'slowly sinking' into the sea

Kansai International Airport in Japan , despite sinking 38 feet since it opened 30 years ago, continues to function daily. The airport, which was constructed at a whopping cost of $19.6 billion, is slowly submerging into the sea just three decades after it first opened.

Located on two man-made islands in Osaka Bay, this isolated location serves Osaka - the third-largest city in Japan . When Kansai International welcomed its first passengers in 1994, it was greeted with immense enthusiasm by the locals.

However, ironically, the airport has been gradually distancing itself from the city, not due to physical distance, but because it's been progressively sinking into the earth beneath it . To date, Kansai has sunk 38 feet, yet it remains an essential hub for airlines like All Nippon Airways, Japan Airlines, and Nippon Cargo Airlines, operating across Asia.

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The airport's engineers knew from the beginning that some sinking would occur. They anticipated a slow settlement over a 50-year span, estimating that the airport would stabilize around 13 feet above sea level - the minimum height required to prevent flooding if the seawall were breached.

However, parts of the first artificial island had already reached this critical level within just six years. An extra $153 million was spent to raise the seawall, but some experts are worried that these efforts might have been too late, reports the Express .

Current predictions indicate that by 2056, parts of Kansai's islands could be submerged more than 13 feet below sea level. Kansai International is built on reclaimed land, which reacts much like a saturated sponge under pressure.

To ready this unstable ground for the massive weight of airport structures, construction teams lay five feet of sand on the cay seabed. These pipes were filled with sand to extract moisture from the surrounding soil and underlying layers.

Extra soil was dredged from nearby areas and compacted into the ground to form a firmer base. Once the seabed was stabilized, the seawall was built, and the rock foundation was strengthened to bear the future airport's weight.

To keep Kansai International above water, workers dug underneath the passenger terminal, placed plates beneath hydraulic jacks, and systematically raised the supporting columns. Despite these extensive efforts, the airport continues to sink, and engineers now face the dual challenge of both the rate of subsidence and its uneven nature.

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The unsettling truth is that different parts of the airport are sinking at varying speeds. For example, the central section of the airport is believed to be sinking faster than the outer edges of the terminal.