Airport Engineering Marvel: Built On Water

The idea of an airport built on water has been around since the 1930s, but the world's first airport built on water, Kansai International Airport in Osaka Bay, Japan, was completed in 1994. The airport is built on two artificial islands and is an engineering marvel, but it has been sinking into the sea at an alarming rate. Several other floating airport projects have been proposed, but none have been realised due to high costs and other concerns.

Japan's Kansai International Airport

The construction of the airport began in 1987 and was completed in 1994. It was a challenging task as the airport was built on a clay seabed 60 feet deep. To fortify the seabed, a five-foot layer of sand was laid down, and 2.2 million vertical pipes, each 16 inches in diameter, were inserted. These pipes were then filled with sand, and soil was used to create a denser foundation. The total cost of the airport was $20 billion, including land reclamation, two runways, terminals, and facilities.

Kansai International Airport is a large airport, occupying two artificial islands in Osaka Bay. The first island covers approximately 510 hectares (1,260 acres), and the second covers 545 hectares (1,347 acres), for a total area of 2,607 acres. The airport was designed to be a state-of-the-art, fully functioning international airport that was both spectacular and resilient enough to withstand natural disasters.

However, the airport has faced some challenges. In 1999, reports showed that the island had sunk 26 feet, almost 50% more than predicted. As of 2024, the airport has sunk more than 38 feet, and engineers predict that sections of the artificial islands may sink to sea level by 2056. Despite this, Kansai International Airport remains a busy hub, with 31.9 million passengers using the airport in 2019, making it the third busiest in Japan. The airport has also received several awards, including being ranked the tenth-best airport in the world by Skytrax in 2020.

Building on unstable land

The construction of Kansai International Airport began in the late 1980s and was completed in 1994. One of the primary challenges was creating a stable foundation for the airport on the clay seabed. To address this, construction crews laid sand up to five feet deep and installed vertical pipes, which were then filled with sand. This process helped transform the wet and spongy reclaimed land into a dry and dense foundation capable of supporting the weight of the airport buildings.

However, despite these efforts, the airport has continued to sink at an alarming rate. Reports indicate that the structure had sunk almost 30 feet within the first three years of its construction and continued to sink at a rate of two inches per month. This prompted architects and engineers to find solutions to keep the island above water. One solution was to rapidly add 11 feet of soil, which was then compressed by a two-tonne weight. Additionally, a quarter of a million tonnes of iron ore was poured into the building's foundation to act as ballast and counteract the inevitable cracking and separation caused by the building's weight.

The sinking of Kansai International Airport highlights the complexities and challenges of building on unstable land. While it is possible to transform unstable land into a usable foundation, it requires careful planning, innovative engineering solutions, and ongoing maintenance. In the case of Kansai Airport, the continuous sinking has led to concerns about its long-term viability, with experts apprehensive that it may sink completely one day.

The role of sand

Japan's Kansai International Airport, built on water in Osaka Bay, is a spectacular feat of engineering. The airport, constructed between 1987 and 1994, is made up of two artificial islands and is the world's first airport built entirely on water.

The construction of the airport was a challenging task due to the geological location and the deep ocean floor. The project began by fortifying the seabed with a five-foot layer of sand and inserting sand drains. This process involved laying sand atop the clay seabed and installing vertical pipes, which were then pounded into the clay and filled with sand. This technique helped absorb water from the clay, causing it to harden and creating a stable foundation for the airport buildings.

Additionally, sand was used in the construction of the sea wall surrounding the airport. The sea wall, made up of steel chambers, huge stones, and tetrapods, provided protection against natural disasters such as typhoons and tsunamis, which are common in Japan. The sand, along with the strategically placed rocks, helped to stabilize the structure and ensure its resilience against the forces of nature.

While the airport is considered a marvel of engineering, it has faced challenges over the years. Reports have indicated that the airport is sinking at an alarming rate, with experts expressing concern about its long-term future. This issue highlights the complexities of building such structures on water and the ongoing efforts required to maintain their stability.

The role of clay

The construction of Kansai International Airport, the world's first airport built on water, posed several challenges for engineers. One of the most significant challenges was dealing with the clay seabed, which was composed of two distinct layers. The first layer, an alluvial clay layer about 100 meters deep, was relatively manageable and could be reinforced with the insertion of sand drains. However, the second layer, a diluviual clay layer approximately 1,000 meters deep, presented a more complex problem as it had never been built on before and was out of reach for sand drains.

To address this issue, engineers started by laying down a five-foot layer of sand over the clay seabed. They then installed an extensive network of vertical pipes, each about 16 inches in diameter. These pipes were driven deep into the clay and filled with sand. This process was crucial in stabilising the clay and preventing it from shifting or liquefying, a common issue in landfill sites affected by natural disasters. The sand drains acted like anchors, providing stability and absorbing water from the clay, causing it to harden over time.

Additionally, the construction process involved the strategic placement of rock and soil. Soil was added and compressed to keep the island above water, and excavations from three mountains were carefully positioned within the perimeter to enhance stability. The varying types and sizes of rock used were specifically chosen to withstand the instability caused by natural disasters, such as earthquakes, typhoons, and tsunamis, which are common in Japan due to its geological location and climate.

While the airport is considered a stunning feat of engineering, it has faced challenges over the years. Reports indicate that the airport has sunk significantly and continues to sink at a rate of two inches per month. This issue has prompted concerns about the airport's long-term stability and has led to ongoing efforts to address and mitigate the sinking. Despite these challenges, Kansai International Airport remains a testament to the innovative use of clay stabilisation techniques and the resilience of structures built on water.

The future of floating airports

The idea of floating airports is not new. The first discussion of a floating airport was for transatlantic flights, proposed in a 1930 issue of Popular Mechanics. The article suggested that airports on long columns could span the Atlantic Ocean at 400-mile (643-kilometer) intervals. However, the concept has never come to fruition, despite air traffic continuing to increase and urban development sprawling.

In 1995, the Japanese Technological Research Association of Mega-Float, supported by the government, aimed to design and test a floating airport concept in Tokyo Bay. A model with a 1,000-metre-long runway was built, and tests proved that the Mega-Float was suitable for aircraft operations. However, the project was dismantled, and the idea was seemingly abandoned.

In recent years, the idea of floating airports has received renewed interest, particularly in densely populated areas with limited space for traditional airports, such as San Diego, London, and Tokyo. For example, in 2014, architecture firm Gensler and Thames Estuary Research and Development (Testrad) proposed the London Britannia Airport, a six-runway floating airport to be built on an artificial island in the Thames Estuary. This proposal was rejected by the UK Airports Commission in 2014 due to its high cost and other concerns.

Despite these setbacks, some believe that floating airports could still have a future in aviation. As the world's population increases and land becomes more scarce and expensive, very large floating structures (VLFS) such as floating airports could help solve issues related to land use, pollution, and aircraft noise. Floating airports are also theorized to have less environmental impact than traditional airports, as they do not require dredging, mountain removal, or clearing of green space. Additionally, the floating structure can provide a reef-like environment that promotes marine life.

Furthermore, with advancements in technology, it may be possible to address some of the challenges that have hindered floating airport projects in the past, such as security concerns, transportation of fuel and other resources, and high costs. While there are no floating airports in operation today, it is possible that with continued innovation and a growing need for aviation infrastructure, we may see floating airports become a reality in the future.

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