Kansai Airport Faces Submersion Threat: Unraveling the Issues Behind Its Sinking

Osaka, Japan - Kansai International Airport, built on two artificial islands, is increasingly at risk of submerging into the sea. This ambitious infrastructure project, inaugurated in 1994, serves approximately 30 million passengers annually. However, the airport's precarious foundation on soft seabed has resulted in a significant decline in its elevation, raising alarms about its future viability.

Since its opening, Kansai Airport has experienced a remarkable subsidence of 11.5 meters, a stark contrast to the initial forecast of just 6.5 meters over a 50-year period. The situation was critical even at the time of its launch, with the airport having already sunk by 8 meters.

The decision to construct an airport offshore stemmed from a lack of available land in the coastal region. Consequently, planners opted for a site about five kilometers from the coast of Osaka Bay, creating a facility measuring four kilometers in length and 2.5 kilometers in width. This unique airport stands as a testament to engineering innovation, yet it is now facing severe challenges.

Geological assessments revealed that beneath the surface lies a thick layer of soft clay, measuring up to 20 meters deep, followed by 140 meters of additional layers of clay, sand, and gravel. Only at depths exceeding 160 meters does stable rock material become accessible.

The construction process, which began in 1987, involved solidifying the clay layers by adding a sand layer over the seabed. Additionally, a million boreholes were drilled into the ground to inject sand, aimed at expelling water from the clay soil and hastening its consolidation. Ultimately, 430 million cubic meters of clay were deposited to form the island, which was expected to harden over time.

Despite these efforts, experts have noted that seawater may have intruded into the subsurface over the years, preventing the material from achieving the desired firmness akin to concrete. The total investment in this expansive project reached approximately $20 billion.

During the planning phase, some subsidence was anticipated, yet the actual settling exceeded expectations, causing the airport to sink even during its construction phase. Flights continue to operate daily at Kansai Airport, but ongoing subsidence poses a serious risk of eventual submersion.

The terminal, designed by renowned architect Renzo Piano, stretches 1,700 meters and is supported by 900 adjustable steel pillars. Maintenance teams must continually recalibrate these pillars to ensure the terminal remains level, although only ten pillars can be adjusted per work shift.

Since its inception, Kansai Airport has required costly repairs due to structural issues, exacerbated by ongoing expansions that increase pressure on the underlying seabed. Experts have warned that without intervention, the airport faces a grim future, with the potential for complete submersion if current trends continue.