Kansai airport

Year:1994

Duration:7 years

Cost:$14bn (£31bn today)

Country: Japan

What did this project achieve?

Build a landmark international airport

Kansai International Airport is built on an artificial island in Osaka Bay, 5km off the coast of Honshu - the largest and most populated island of Japan.

Opened in September 1994, it was intended to relieve pressure on the busy Osaka International Airport nearby.

More than 25m passengers used Kansai in 2016, making it the third busiest airport in Japan, and the 30th busiest in Asia. It handled over 802,000 tonnes of freight in the same year – most of it international.

The airport cost an initial $14bn to construct. By 2008, the price tag had risen to $20bn. This included land reclamation, two runways – a second 4,000m runway was added in 2007 – and terminal buildings.

Many of the additional costs were due to the island sinking – this was expected, because of the soft soils in Osaka Bay. The sink rate fell from 50cm a year in 1994 to 7cm a year in 2008.

The scheme is known for the striking Terminal 1 building designed by Italian architect Renzo Piano. Piano’s other designs include the Shard in London and the Pompidou Centre in Paris.

After 20 years of planning, seven years of construction and $15bn investment from the US government, the project was, at the time, the most expensive civil works project in modern history.

The airport was one of 10 structures given the ‘Civil Engineering Monument of the Millennium’ award in 2001 by the American Society of Civil Engineers.

Difference the project has made

Kansai relieved pressure on Osaka airport, which was struggling to cope with passenger numbers. Osaka now only handles domestic flights.

Many of the lessons learned about building an artificial island went into the designs for Japan’s Kobe and New Kitakyushu airports, as well as Hong Kong International Airport.

Kansai is a major local employer. The airport’s brought more tourists to the area – boosting the region’s economy.

How the work was done

One of the main challenges that engineers faced on the Kansai scheme was the construction of the artificial island in Osaka bay. Although it wasn’t the first to be built in the bay, it would be in water more than 18m deep.

The seabed in the bay is alluvial clay – loose clay made up of several materials. As weight was added to the sea bed – by building the island - water would be squeezed out of the clay. This meant the clay would shrink - and the island would sink as a result.

Engineers installed sand drains measuring nearly 1m in the bay to speed up the shrinking process. A sand drain is a deep hole drilled into the seabed and filled with sand. A heavy weight – often more sand – is placed on top of the drain. This compacts the clay by forcing moisture outward along the sand columns.

Despite the sand drains, the clay hadn’t completely settled when engineers began work on building the island. Continued shrinkage since construction has brought criticism that this part of the scheme wasn’t well planned.

"​‌

‘It's fabulous… when you see [it] you'll know why we went through the trouble

Zenjiro Ogawa

managing director of the Kansai International Airport Company, on the terminal building, New York Times, 16 December 1993

Fascinating facts

As Japan is in a major earthquake zone, Kansai airport was constructed to survive them.

In January 1995, Japan was hit by the Kobe earthquake - killing over 6,300 people on Honshu island, just 5km from Kansai. The airport survived - mainly because of the sliding joints in many of its structures.

The airport was also largely undamaged by a typhoon in 1998. The storm saw winds of up to 200km/h.

People who made it happen

  • Architect: Renzo Piano
  • Consulting engineers: Peter Rice, Ove Arup and Partners

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