this is Kai International Airport in Japan a true Pioneer of civil engineering that's just turned 30 years old and it has some pretty impressive achievements to its name it was the first airport ever built on reclaimed land in the ocean it has the longest terminal building in the world and it never lost a single item of luggage but it does have one rather big problem it's sinking but the story doesn't stop there because despite that it's getting a half billion dollar facelift to increase capacity and improve its status as a regional Hub so how did
they build an airport in the ocean how did it go wrong and what does the future hold for canai international nowadays building an airport on water is fairly common but none of these would have been possible without the radical design of Osaka's canai airport when construction began in 1987 it was decades ahead of its time it took 20 years to plan 7 years to build and then when it finally opened it was the most expensive civil engineering project in modern history it cost $4 billion us to construct that's nearly $40 billion in today's money the
bridge to the mainland alone cost a cool $1 billion all of this to build a miraculous City in the ocean but that all kind of begs the question why bother well after the second world war Japan experienced Decades of Staggering economic growth that made it the world's second biggest economy by 1968 and key to the country's growth was infastructure this is Osaka in the 1960s it was Japan's second largest city and this is its airport I think you can see where we're going with this the airport can't expand if it's stuck inside the city and
the city can't expand if its airport can't keep up with the m a new airport was needed but Osaka is surrounded by mountains and there just wasn't anywhere to put it so a radical solution was needed by the early 1970s four sites are being considered for the future airports three of which were out at sea but how' you build an airport in the middle of an ocean well the first thing you need to do is secure a solid foundation this is a crosssection of Osaka Bay represented here in a Lego model that my kids have
made now they only made this on the condition that I would give them a shout out in a YouTube video and help make them famous so hello kids thanks for the Lego Daddy loves you now this is representative as I said of aaka bay top bit here is water that's about 18 M deep below that is a layer of hollene clay that's also about 18 M deep underneath that is a much bigger zone of strata that includes much thicker clay and crucially some pockets of sand represented here very crudely with brown and gray Lego now
remember those pockets of sand because we're going to come back to it a bit later on fetch the sponge now that area of brown and gray clay I just showed you that's now represented by a yellow sponge stay with us is filled with lots of holes that fill with water meaning it's quite thick but also quite weak if I try and build anything on it it just deforms straight away now that's called sement and for those of you who aren't Structural Engineers just know that it's really not very good if you're trying to build an
airport so what you want to do is consolidate that layer as far as possible squeezing all the water out and compacting it as far as possible until you get a nice solid layer to build on now that all sounds really simple in theory but how on Earth do you do that on the bottom of the seabed well use something called sand drains here's how they work columns are dug into the ground and filled with sand before being capped off by another layer of sand the space above the sand mat is then filled in with rubble
which forces everything downwards under this pressure the water that's trapped inside the clay moves sideways and into the sand drains because water travels more easily through sand it shoots up to the top where it's drained away into the sea or evaporat it the land below then becomes dry Compact and crucially stable construction first began in 1987 a million sound drains were installed at the site in Osaka Bay each 40 cm wide and 20 M deep next to protect the site and give the island its shape an 11 km long seaw wall was constructed using 48,000
tetr pods then came the massive job of filling in the island with Earth over the course of more than 3 years 180 million Cub met of Earth was poured in to create the island that's about 75 times the volume of the Great Pyramid Giza over the next few years 10,000 people worked 10 million work hours to fill in the future airport site now before we go any further if these statistics make you wonder how on Earth any project like this stays on track then you might want to consider this week's video sponsor innate constructing capital
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construction industry runs deep through the entire team at in8 so you can be confident you'll get the support you need to match your workflow to find out more about how innate can transform your project management click the link below now let's get back to that airport by 1992 the Reclamation work was complete and a brand new island sat proudly in Osaka Bay the massive weight of the landfill had pushed all the water out of the clay seabeds compacting it and creating a nice solid layer to build on or so they thought Engineers always knew the
island would sink a bit as the seabeds compact it but in 1990 3 years after construction began they discovered that it was sinking much faster than expected by about 5 cm a month 100 million was spent to bulk up the Island's height and ensure it didn't sink below 4 m above sea level that's the height it has to be to avoid being flooded by rough Seas originally Engineers thought the island would sink by about 8 m over the course of 50 years but it sunk by more than that by the time the airport opened in
1994 8 years later it is sunk by 12 M but why well it all comes down to those different levels of clay we discussed earlier see I told you the Lego would be back the plan to compact the hollene clay had worked as expected but it was this different layer down here that caused the problems this layer known as Pline is made up of much thicker clay and crucially has lots of layers of sand running through it that means it's very difficult to predict how it will react when something this big is built on top
of it the fact that all of this was so unpredictable actually goes to show just how advanced this airport was even today there's an argument in academic circles about whether we need to actually rewrite some of the fundamental principles of Sor Dynamics in light of what happened at canai and before we go any further we should say that despite its foundations canai airport really is a remarkable feat of engineering take the terminal building designed by renzop piano the roof has this wav likee shape that was the result of extensive studies that found this was the
perfect shape to draw cool air through the building avoiding the need for expensive air conditioning because the terminal building is a whopping 1.7 km long 900 Jacks were fitted underneath to level out any uneven settlement under the structure these jacks are automatically measured and then adjusted every few years its lightweight design allows every part of the building to flex so it can absorb an earthquake without being damaged even the runway is paved with ashv instead of concrete which allows it to bend instead of snapping in 1995 a massive earthquake struck nearby tragically the neighboring city
of Corbet was devastated but the airport and the people inside it escaped unscathed despite all its challenges the airport was deemed so successful that in 1999 work began on a second island to increase its capacity and then in 2001 the American Society of civil engineers awarded it the Monument of the Millennium award along with the Hoover Dam and the Golden Gate Bridge the rate of settlements has almost gr to a halt from 50 cm a year in 1994 to just 7 cm a year now so that's it problem solved everyone's happy well not quite Winds
of up to 172 kmph whipped up Seas pounded the coastline and destroyed ships as typhoon jebby struck Japan in 2018 typhoon jebby hit oaka Bay and sent waves crashing over the seaw wall flooding the runway and other critical areas of the airport little could be done to keep the flood water out and hundreds of flights have been cancelled canai was closed for 3 days and didn't resume full service for almost another fortnight was a timely reminder that you can't outrun nature forever the following year another phase of remedial Works began to raise the seaw wall
and the runway to stop the works interfering with the path of the landing planes the seaw wall was initially raised by 2.2 M after this another meter was added to the runway before the wall was then raised by another 2.7 M now if you've booked a ticket to Asaka please don't worry this airport is perfectly safe to fly to despite all the struggles canai is still a thriving Regional Hub it's one of the busiest airports in Asia and the third busiest in Japan Airport bosses are so confident in the latest flood defenses that the main
terminal is getting a $470 million renovation all to increase capacity and improve passenger experience it's also a key transport hub for the upcoming Osaka 2025 Expo which is set to draw in 28 million visitors but for its long-term future well who knows the rate at which the airport sinking has been slowed massively but it's not expected to stop for sometime yet a 2015 report predicted that both Islands could have sunk to sea level by 2067 one option is to continue to raise the runway and the seaw wall but that doesn't come cheap at some point
the airport's future becomes based on economics rather than engineering what we can say is that as it reaches its 30th birthday this is a reol evolutionary airport which has served over a billion people it remains one of the most ambitious civil engineering projects ever and has pioneered airport design for decades to come we won't be saying goodbye for a very long time yet but even if we one day do it's Legacy we certainly live on this video was sponsored by innate you can learn more about that at the link below don't forget that we're inspiring
the next generation of Builders through our investment into brick borrow a fantastic Lego subscription service you can learn more and get started today over at brick.com and as always guys if you enjoyed this video and you want to get more from the definitive video channel for construction make sure you're subscribed to the b1m [Music]
