Kansai International Airport

World’s First Offshore Airport



Kansai International Airport is one of Japan’s most important international airports, situated off the coast of Senshu in Osaka Bay. It is the world’s first offshore airport constructed on an artificial island. Located on a completely man-made island about 38 km (24 mi) southwest of Osaka Station, within three municipalities, including Izumisano (north), Sennan (south), and Tajiri (central), in Osaka Prefecture, Japan, Kansai Airport terminal 1 was opened to air traffic on 4th September, 1994, to ease congestion at Osaka’s Itami Airport, which is closer to the city of Osaka and now handles only domestic flights. The airport’s construction took 38 months and involved an average of 6,000 workers (10,000 during peak construction periods).

The engineers and planners in the late 1980’s, searched for a way to revitalise the Kansai region of Japan, which was struggling to keep up with the fast-paced export trade growing in Tokyo. Further, the growing protests from local residents of the region forced the engineers to build an island as the base of the airport.

The Kansai International Airport is an architectural and engineering marvel in all its features. This magnificent accomplishment of engineering was constructed on its own island, built from three neighbouring mountains and millions of cubic metres of concrete. The 4.37 x 1.25 km artificial island, constructed over a 5 year period, is 5 km off the coast, which was specifically built to accommodate the structure.

The airport consists of two terminals: Terminal 1 and Terminal 2. The renowned Italian architect Renzo Piano, who is famous for other award-winning architectural buildings, was awarded the project for terminal 1 in 1988, following an international competition. In 2003, the airport operators started to construct a 4,000 m (13,000 ft) second runway (opened on 2 August, 2007) and terminal (opened in late 2012).

The Kansai airport is operational 24 hours a day and is one of the major transit routes for traffic to Japan, Southeast Asia and Australia. A bridge with two levels (the top level comprises a road, and the lower level contains independent railways) connects the island with the shore. The impressive bridge measures in at 3.750 km (12,300 ft) and is the longest truss bridge in the world.


The Kansai Airport Bridge



The construction work started in 1987. The site selected for the construction of the island was made up of alluvial clay seascape with the seafloor varying in depths up to 18.5 m (60 ft).  The depth of the site was a driving force as it was suitable to build the island; the water depth is 18 m on top of 20 m of soft Holocene clay which holds 70% water. The engineers also needed to overcome the extremely high risks of earthquakes and typhoons (with storm surges of up to 3 m). Thus, the clay discovered in the seafloor presented the engineers with several concerns. As a method to solve this problem, engineers utilised a newly emerging technique for sea-based foundation stabilising. They used 1.2 million sand drains, which were created with the help of tubes, and were driven, deep within the clay to inject millions of tons of sand; following this, the cylinders were removed. This successfully stabilised the sea floor to endure the weight of the planned island. The columns of sand would function as drains to the surrounding clay, maintaining the foundation from becoming soaked with moisture, consequently causing settling.



After completion of the process of seabed stabilisation, 48,000 individual concrete tetrahedrons, each weighing 200 tons, were stacked to create a firm foundation. Further, the space between the tetrahedrons was filled with 178 million cubic metres of earth obtained from three neighbouring mountains (excavated for 21 million m3 and 180 million m3, and was used to construct the island) and dispensed on the location using specific barges.

The work on the seawall and seabed was finished in a span of 3 years (1989), and thereafter, construction of the airport services began upon the island base. 10,000 workers and 10 million work hours over three years, using eighty ships, were required to complete the 30 metre layer of earth over the sea floor and inside the seawall.



View of the Machines Implementing Sand Drains into the Seafloor


The Platform

The platform symbolises a great achievement of civil engineering. It has been created upon over a million support columns, which delve 20 metres into the sea and 20 metres into a muddy layer before being driven an additional 40 metres into the rock below. The depth is because of the muddy layer, which persists to settle at an irregular rate. To identify when the mud has settled to the point that surpasses the predicted maximum acceptance of 10 mm, a series of special sensors are used.

Further, each column is equipped with a calibration system, which utilises extremely powerful hydraulic jacks; whenever a column’s location is offset, the system regulates it and locks it in its new site. This occurrence had a noteworthy effect, indeed, during the early stages, when the island settled by 50 cm from 1992 to 1996.



  Concrete Tetrahedrons before Installation    Seawall Construction of Kansai International Airport


 Airport Island Foundation                                  Diagram of the Bed below the Airport Island




The terminal building is 1.7 km long and has 42 different exits. The structure of the terminal is located upon the island like a glider. Due to the absence of any other constraints, the structure’s volumes were decided by the load and space required for the aircrafts’ exercises. The aircrafts provide form, purpose and extension to the building. The splendid glider shape is visible in the layout; the access roads form the two tail wings, while the structure’s main body and terminals signify the fuselage with its extended wings. The structure has a rising and falling, asymmetrical layout, though the noticeable beams are positioned at regular intervals. It extends over various levels, which suddenly opens onto a large central atrium.
The airport terminal’s interior arrangement is based on a functional study conducted by Paul Andeu for the Aéroports de Paris. The main structure of the building that receives the passengers is taller in the direction of the runway, 20 metres at one end and just 6 metres at the other. Further, the asymmetrical structure presents clear direction at any given point. Also, due to the structure’s significant size, a shuttle transport system is set up along the wings.


Kansai Airport’s Runway


Terminal’s Roof

The form of the terminal’s roof is inspired from an extensive study on the dynamic air flow inside the building. Further, the roof’s cross-section has the shape of an irregular arc (which is a series of arcs of different radii); it was given this shape to direct the air from the passenger side to the runway side, without necessitating the use of congested conduits. Also, blade-like deflectors direct the air flow down the ceiling and mirror the light from above. Hence, all the elements that would have concealed the sight of the construction have been eliminated.

The mammoth three-dimensional beams that carry the roof are over 80 metres long. The asymmetrical profile of the beams is planned based on the same calculations that have allowed for the invisible air flow to be appropriately channelled.


The Kansai System – Air Flow


Consequently, Kansai airport’s 82,000 stainless steel panels are completely identical, which is also due to the structure’s general size, which lets the curves be engaged with low tolerances. Also, building’s ‘wings’ are curved and defined according to toroidal geometry, due to the application of a strict law.

The wings represent the upper segment of a 16,800 metre ring, with a radius slanting at 68° with respect to the horizon, which passes through the earth and emerges over the island. Although this curving is nearly indiscernible, it was necessary to ensure the control tower’s lateral line of vision.


  Kansai International Airport’s Roof


Problems For Kansai Airport

The engineers optimistically estimated that with a strong foundation design, the island would sink a maximum of 5.7 m (19 ft). The island has however, sunk 13.05 m (42 ft) at a rate of 50 cm/yr subsequent to construction, as the weight of the material used for construction compressed the seabed silts. Through the employment of steadying techniques, engineers have reduced that to a recurrently dropping rate of 6 cm/yr. Currently, engineers are believed to have control on this former troublesome dropping rate, and improvements to airport services are underway.


Kansai Airport Flooded by Typhoon Jebi


 Earthquake And Typhoon

Japan was struck by the Kobe earthquake in 1995, the epicentre of which was about 20 km (12 mi) away from the Kansai airport and killed 6,434 people on Japan’s main island of Honshu. Due to its earthquake engineering and utilisation of sliding joints, the airport remained unscathed. Even the glass in the windows remained intact. Further, in 1998, the airport survived a typhoon with wind speeds of up to 200 km/h (120 mph).

Smart Island Project

SF Solar Power, with the contribution of Solar Frontier and Development Bank of Japan Inc., has reached an agreement with the New Kansai International Airport Company Ltd. (company formed to unify the management of the Kansai and Osaka Airport), for the construction of a solar project KIX Megasolar, with a total capacity of 11.6 MW at the Kansai International Airport.

New Kansai International Airport Company Ltd. is working as a part of its Smart Island Project (Project for intelligent island) to use clean energy sources, including solar energy and hydrogen to realise an environmentally advanced airport. It is expected that KIX Megasolar, as a part of this initiative, will be the largest solar installation at an Asian airport.

Further, the project will include the setting up of 72,000 CIS modules beside the airport runway B (96,700 sq. m) and on the top of the cargo warehouse (23,000 sq. m). It is estimated that the yearly production of the two installations will be 12,000,000 kWh, which is equivalent to the electricity used by 4,100 homes; the installations will allow a decrease the annual CO2 emissions by 4,000 tons.



Kansai Airport Today

The airport currently averages over 3 million flights in a year. Functioning as a present-day hub for 6 major airlines, the airport is living up to design expectations. Kansai Airport is continuously cited as one of the greatest engineering achievements of the 20th century. This over two decade old structure persists to maintain its ground against newer engineering marvels, making much more remarkable. In 2001, the American Society of Civil Engineers (ASCE) selected the Kansai International Airport as one of the ten civil engineering achievements with the greatest positive impact on life in the 20th century. The airport was one of ten structures presented with the ‘Civil Engineering Monument of the Millennium’ award. As of 2008, the total cost of Kansai Airport is $20 billion; this includes land reclamation, two runways, terminal and facilities. Most supplementary costs were primarily due to the island sinking, expected due to the soft soils of Osaka Bay.


  1. https://en.wikipedia.org/wiki/Kansai_International_Airport
  2. https://earth.esa.int/web/earth-watching/historical-views/content/-/article/kansai-and-kobe-international-airport-osaka-bay-japan-
  3. https://journey-of-japan.com/article/107/en
  4. http://www.kansai-airports.co.jp/en/company-profile/about-airports/kix.html


Amrita Batra 
Associate Editor
Civil Engineering and Construction Review