Full transcript
0:00An airport built in the middle of the
0:03sea that is still slowly sinking today .
0:06This is Kansai International Airport in
0:08Japan's Osaka Bay . It was not a natural
0:11island . It was created by humans from
0:14the sea . It cost approximately 20
0:17billion . Construction began in 1987 ,
0:20and the first phase opened on September
0:234 , 1994 . But the real story of this
0:26airport is not about the terminal or
0:28runways . The true story is hidden
0:31underground where the human eye cannot
0:33see . There was an enemy there that was
0:36very difficult to defeat . The soft sea
0:39soil that could pull everything down .
0:42If the engineers hadn't used the right
0:45method , the entire island could have
0:47collapsed . In this video , we will see
0:50how Japan turned the sea into land . An
0:53engineering story that still amazes the
0:56world today . Let's start with this
0:59unique story from beneath the sea .
1:02Engineers chose a spot in the sea 5 km
1:05away from Osaka . The water depth there
1:08was about 18 meters . The first island
1:11was to be built , spreading over 510
1:13hectares . But when engineers examined
1:16the seabed , they found a major
1:17difficulty . Beneath the sea was a thick
1:21layer of soft soil called marine clay .
1:24This soil was so soft that normal
1:27construction was not possible . If soil
1:30were dumped directly , its weight would
1:32compress the clay . Compressing it would
1:35push the water out of the clay , causing
1:37the whole island to sink . Meaning ,
1:40starting construction directly meant
1:42the entire airport would sink .
1:44Therefore , it was necessary to prepare
1:46the ground first . Before building any
1:48structures . This challenge was one of
1:51the world's most difficult marine
1:53engineering projects . Now let's see how
1:56engineers made this soft soil strong .
1:59This is a story of controlling the land
2:02from beneath the sea . First , a 1.5 -
2:05meter-thick sand blanket was laid on
2:07the seabed . This sand blanket acted as
2:11a foundational layer . Then engineers
2:14installed nearly 1 million vertical
2:16sand drains . These drains were placed
2:19in a 2.5 - meter grid . The job of these
2:22thousands of drains was to provide a
2:24path for water from within the clay . As
2:26the water was removed , the soil
2:28gradually became stronger . But sand
2:31drains alone were not enough . Engineers
2:34also used sand compaction piles , and a
2:37deep cement mixing technique was
2:39adopted . The goal of all this was to
2:42make the ground strong enough to
2:44support the seawall and the entire
2:46island's weight . After months of hard
2:50work , the seafloor was now ready for
2:52construction . Now it was time to build
2:55a wall around this land . This was the
2:58next big step in this impossible
3:01project . The ground had become stable .
3:03Now it was time to build a massive
3:06seawall around it . Construction of the
3:09seawall began in January 1987 . The
3:12design was a robust rubble-mound
3:14structure . A solid framework of stones
3:17and boulders . First , large stones were
3:20lowered onto the seabed from barges as
3:23a foundation . The size and placement of
3:27each stone were carefully planned to
3:29distribute weight . Above the foundation
3:32, stones ranging from large to small
3:34were laid layer by layer . Each layer's
3:38job was to break the force of the waves
3:40to protect the interior . On top ,
3:44special concrete armor blocks like
3:47tetrapods or interlocking blocks were
3:50used . These blocks kept the seawall in
3:55place even during stormy waves . Work
3:58continued day and night . New barges
4:00arrived every day with fresh material .
4:03Engineers constantly checked the height
4:06and alignment to ensure no deviation .
4:09In some sections , the seawall was built
4:12much higher than the sea level . For
4:14protection against storm surges and
4:17waves . Finally , in June 1989 , the 11 km
4:21long seawall was fully completed . Now ,
4:25the sea inside had become an enclosed
4:27area . The next task was to turn it into
4:30dry land . The seawall was the very
4:33foundation of the entire project . The
4:36seawall was completely ready . Now , the
4:38empty sea inside had to be turned into
4:41land . Large vessels carrying soil and
4:43sand arrived inside the seawall
4:45continuously . About 180 million cubic
4:47meters of reclamation material was
4:49needed for the first island . This
4:51material was cut from various mountains
4:53in Japan . Through special mountain
4:55cutting projects . Each ship would drop
4:58its load . Then bulldozers would spread
5:01it out evenly . Material was added layer
5:04by layer , and each layer was thoroughly
5:06compacted . Compaction was crucial to
5:10ensure the new ground was strong from
5:12the start . Slowly , the seabed began to
5:16disappear , and a new piece of land
5:18emerged . Within a few months , solid
5:21ground could be seen where there was
5:23only water . But the soft clay
5:25underneath began to sink under the new
5:28weight . This meant the new island was
5:32still gradually settling . This
5:34settlement was no accident . Engineers
5:37had included it in the design from the
5:39very beginning . The first phase of
5:42reclamation was largely finished by
5:451990 . Now the next challenge was to
5:48control this sinking land for years .
5:51Engineers began to constantly measure
5:54the island's settlement . By installing
5:56special sensors . Hydraulic jacks were
5:59installed under every structure to
6:01adjust the elevation as the ground
6:03settled . Whenever the ground sank by a
6:05few millimeters , the jacks would
6:07straighten the structure back up . This
6:10jacking system was installed under
6:12almost every major pillar of the
6:13airport . To manage this challenge , the
6:17sea walls were also raised from time to
6:18time . Brand new underground systems
6:22were also built to control groundwater
6:24and seawater . A major step was building
6:28underground water barriers that go down
6:30to 30 meters . These barriers prevent
6:33seawater from seeping inside .
6:35Especially during storm surges . By
6:38December 2025 , the island's average
6:41settlement had reached 13.72 meters . Of
6:45this , approximately 9.82 meters . Had
6:48already occurred before the airport
6:50even opened . The rest of the settlement
6:52happened over the years . But now , its
6:54pace has slowed down significantly .
6:57This is how humans kept a sinking
6:59landmass under control for years . But
7:02only the ground was ready for now . The
7:05entire airport above it was yet to be
7:07built . Both the foundation and the
7:09design were ready . Now it was time to
7:11construct the actual building . First , a
7:143,500 - meter-long runway was built on
7:16the island . Simultaneously , the
7:18taxiways also began to take shape . The
7:21terminal was designed by Renzo Piano
7:23Building Workshop , and Nikken Sekkei
7:25handled the structural design .
7:27Construction was managed by the
7:29Takenaka joint venture . The terminal's
7:31area was 291,270 . Square meters . The
7:37terminal's long curved shape was
7:38specifically chosen to facilitate
7:40passenger movement . First , steel
7:43columns were erected . Then , large steel
7:45trusses were placed on top of them . A
7:48special curved roof design , built for
7:50natural airflow , was fitted onto these
7:52trusses . After the roof was installed ,
7:55the entire building was covered with
7:56glass facets . Inside , baggage handling ,
7:59security , gates , and mechanical systems
8:01were installed . A large bridge was also
8:05built to connect the island to the
8:07mainland . The bridge had two levels .
8:09One for road traffic and the other for
8:12trains . The bridge was completed in
8:15March 1994 . In June , the terminal was
8:19also fully ready , and finally , on
8:21September 4 , 1994 , Kansai International
8:24Airport officially opened . But the
8:27story did not end there . Japan soon
8:29needed another runway . This time , the
8:32decision was made to build a second
8:35island in even deeper water . The second
8:38island spanned 545 hectares . Even
8:40further offshore than the first . The
8:43entire process was repeated again .
8:45Seabed prep , sea wall , reclamation ,
8:47monitoring . This time the water was
8:50deeper , and the clay layer was thicker
8:52than before . Therefore , the number of
8:55sand drains and compaction piles was
8:57also increased . For construction this
9:00time , 250 million cubic meters of
9:02material was used . The seawall was also
9:05designed to be longer and stronger this
9:07time . After years of hard work , a new
9:104,000 - meter runway was completed . This
9:13runway entered service in 2007 , and the
9:16airport's capacity doubled . Even today ,
9:19engineers continuously monitor this
9:22sinking land . First the land was made ,
9:24then the seawall was built , then
9:26settlement was controlled . Only then
9:28was the airport established . That is
9:30why Kansai is not just an airport , but
9:32one of the greatest marine engineering
9:34stories in the world . If you liked this
9:38story , please like the video and be
9:39sure to subscribe to the channel .