KANSAI INTERNATIONAL AIRPORT in Japan, a landmark achievement in civil engineering, has just celebrated its 30th anniversary. Built on reclaimed land in Osaka Bay, it remains one of the most ambitious infrastructure projects of its kind. However, despite its groundbreaking achievements, the airport faces a serious problem – it is sinking. The large airport is sinking into the sea at an average rate of more than 30 cm per year. The $18 billion hub was built on two artificial islands in Osaka, which are now moving further and further away from the metropolis. Completed in 1994, Kansai was the first airport in the world to be built entirely on an artificial island. It also boasts the longest terminal building in the world and a virtually impeccable reputation for baggage management. The idea of ​​building an airport on the sea was born out of necessity. By the late 1960s, Osaka, Japan’s second-largest city, had outgrown its landlocked airport. The city simply didn’t have room to expand because it was surrounded by mountains. The only viable solution was a bold, untested move: build an airport on the sea. Construction began in 1987 after 20 years of planning. It was a colossal and expensive undertaking, with a total cost of US$14 billion at the time – equivalent to nearly US$40 billion today. The project called for the creation of an entirely new island, protected by an 11-kilometer seawall and connected to the mainland by a bridge that itself cost US$1 billion. Radical as the plan may seem, Kansai’s success paved the way for future airports built on water. To offset the enormous construction costs, the government increased rents and landing fees. At one point, the airport had the highest landing fees of any airport in the world. For example, the airport charged about $7,500 to land a Boeing 747, compared to $2,500 at New York’s Kennedy Airport. Some even suggested that a cup of coffee would have to cost more than ten dollars to cover the airport’s costs. Despite all of its achievements, the airport had to face an unexpected problem: the island beneath the airport was settling faster than expected. Engineers initially predicted that the island would settle by about eight meters in 50 years. Instead, the subsidence occurred much faster, sinking more than 12 meters in the first eight years. In order for such an artificial structure to support such a huge weight as an airport building, the land on which it will be built is made dry and compact. This makes it a suitable foundation. To do this, construction crews laid sand five feet above the seabed and then installed 2.2 million vertical pipes about 2 feet in diameter. The pipes were anchored in clay and filled with sand, which absorbs moisture from the surrounding soil and the layers beneath it. Then the bottom was reinforced with an additional layer of earth and a seawall was built. By 1990, when the first island had sunk 8 meters instead of the predicted 5, engineers became alarmed. To save the airport from the sea, workers dug a pit under the passenger terminal, inserted iron plates under hydraulic jacks and raised the columns in stages. Even with these corrective measures, the airport will likely continue to subside, perhaps for centuries, but at a much slower rate. The main problem lies in the clay layers beneath the artificial island. While engineers have taken steps to consolidate the top layer, the deeper clay layers, riddled with pockets of sand, have proven more unpredictable. This subsidence has led to significant additional costs, with more than US$100 million spent maintaining the island's elevation above sea level. Music: bensound-summer