Now You can Land Airplanes in the Sea – Kansai International Airport Japan

Japan, the land
of rising sun was advancing with technology at a fast rate after World War II,
Its economy was on the verge of stabilization. But here the question arises
where do you put a plane in a space that run out of space? The Japanese have
found its answer you can make the airplane to as well as it flies. In Japan at
that time the largest international airport was in Tokyo; the middle of the
island. Business owners had to ship their goods hundreds of miles so they could
be exported out of the country. This was both costly and time – consuming.
Osaka was the
ancient capital of Japan and the former playground for the last samurai. The
home of 3 millions Japanese, a new energy in Osaka has propelled this place to
become the commercial and industrial center of western Japan. But in order to
compete with their big sister Tokyo – Osaka needed to find a way to bring in
more people with a Yen for Big business. The solution that was devised “a much
bigger airport – to open up the skies”
Building an
international airport in Kansai region of Japan was developed in late 1960’s,
but the owners of the land and angry farmers were opposing the idea and thus
the idea of the project was forced to shut down. The Kansai region included the
large cities of Kobe and Osaka, advancement in these two cities forced the city
designers to find a solution as to where to put an airport. The majority of
land in Kansai region is being filled by the inhabitants and the only practical
solution to this problem was to build it on water.

SUBSURFACE INVESTIGATION

First and
foremost important step related to any geotechnical application is to gather
information about the soil as much as we can. For a task the scale of Kansai,
an extensive investigation was necessary to characterize the subsurface since
very little was known about the soil conditions below the bay,

Now You can Land Airplanes in the Sea - Kansai International Airport Japan
Fig
1 Bore Holes for Geo-tech investigation
Scientists have
used large barrages and rigs, to let engineers to be able to bore deep into the
seabed and gather information about the type of soil they would be resting
their airport on. The findings of the geotechnical investigation was as under;
the top 60 feet of the clay was soft-alluvial clay called Holocene layer which
has hardness roughly equivalent to that of toy clay, this layer had loosely
placed sediment. But that was not much problem for the engineers as they had
much experience in building on such similar deposits off the shore of the bay
and had means to control it. The problem which they had about to face was below
that alluvial clay layer was old, diluvial deposit of stiff clay,  which had never been build on before.
Now You can Land Airplanes in the Sea - Kansai International Airport Japan
Fig.
2 Subsurface profile of the Kansai Airport Foundation

Main Construction Process

Engineers have
divided the main construction into three different stages
(i)                
Remediation of the seabed
(ii)              
Placement of seawall
(iii)            
fill

Sea bed
remediation

The problem that
was faced by geo-tech engineers here was settlement, as the underlying soil was
clay. As we know that clay composed of very small soil particles having pores
in them, these pores on application of load can be re-arranged for an unknown time,
and more over this process of consolidation is very slow, but has a significant
effect on the working of the structure.
In the case of
the Kansai Airport, the upper alluvial layer was highly compressible and is
impermeable as well, thus engineers have used a technique called sand draining
method, approximately one million sand columns were inserted into the top layer
of the bay to improve drainage conditions. This allows the water to flow
horizontally to a column and then exit relatively quickly in a vertical
direction because the sand has high permeability. The sand columns not only
allows the water to drain quickly to avoid long term settlement but also
strengthens the soil during construction.
Now You can Land Airplanes in the Sea - Kansai International Airport Japan
Fig
3 : Sand Draining Technique to Increase settlement Rate of consolidating clays

Seawall

After improving
the sub-surface of the bay the scientists have to fight with the high speed
tides of the sea, because if these high velocity waves can’t let the
inhabitants to live near the sea how can these waves allow the airplanes to
live within the sea; for fighting this problem they have devised a seawall,
special “tripod” blocks were used on the seaward side to disspiate the energy
of any harsh waves. These 2 ton blocks slowly arose from the seabed creating a
ring of concrete 40 ft above sea level.
Now You can Land Airplanes in the Sea - Kansai International Airport Japan
Fig
4: typical cross-section of the seawall
Now You can Land Airplanes in the Sea - Kansai International Airport Japan
Fig
5 : Complete seawall

Fill:

Once the seawall
was completed, workers started on the body of the island, The source of their
fill material, which consists of different grades of sand, gravel and rock, was
from three nearby mountains. Trucks transported from the borrow site to the
nearby ships which shipped it three miles to the site. It almost took four
years to fill such a land and it took 750 million cubic feet of fill, three
mountaintops had disappeared.
To tackle with
the problem of settlement, the first question that was put forward to the
scientists was How much the island would ultimately settle. By using their
knowledge of soil mechanics they have calculated the ultimate settlement of the
soil to be between 19 and 25 feet. Interestingly enough, the airport was
designed for an island that would settle only 19 feet. By the time the island
was completed in 1990, it had already settled 27 feet and was continuing at a
rate of 2 inches per month. This prompted designers to put an extra ten feet of
fill on top to compensate for the difference, adding even more stress to the
seabed.
The deep clay
layer was not a uniform or homogeneous layer, it has sand layers within its
mass and engineers believed that these sand layers will allow the water to
drain quickly themselves but care full study shows that among these continuous
sand layers there are a few discontinuous sand layers which doesn’t allow the
water to drain and thus there comes the problem of differential settlement.
To encounter the
differential settlement between island and the terminal, engineers have lined
the basement of the terminal with a quarter of a million tons of iron ore.
Without iron ore, the terminal weight would be less and the remaining island
would sink and settles thus the terminal might fail thus the additional weight
of the iron ore beneath the terminal allows the terminal to settle at
approximately the same rate as the rest of the island.
The runways were
paved specifically with asphalt and not the concrete reason being that if some
patch holes appears they could be paved easily with asphalt and concrete could
fail in this case easily. The terminal was build on 900 columns, the height of
these columns was controlled by a hydraulic jack and the settlement of these
columns was computer monitored thus if some differential settlement might be
observed the hydraulic jacks come in place to counter that settlement. Once the
jacks were removed steel plates were slid under the columns.

Earthquakes and other Natural Disasters:

Engineers have
used rocks when they were filling within the seawalls as a fill, inclusion of
these rocks had some objective and that was to absorb any earthquake shaking
activity and that was proved fruitful in the 1995 earthquake when after 15
years the terminal was opened an earthquake rocked the Osaka Bay area in early
morning. Kansai Airport was just 18 miles from the epicenter and the officials
were surprised to see the results of minimal damage to the island. With the exception
of a few cracks within the sidewalks the terminal was fully in perfect
condition.

References

·        
Kansai International Airport Land
Development Company, Kald Information Center: URL: < http://www.kald.co.jp/index-e.html>
·        
Takenaka Corporation, Modification
Method for Differential Settlement: URL: <
http://www.takenaka.co.jp/takenaka_e/quake_e/fudo/fudo.htm
>
·        
The Learning Channel, “Super Structures of the World: Kansai
International Airport”, Original Broadcast, 1999.
·        
Kansai International Airport “Mega
Structure” Series on National Geographic Channel.

Saad Iqbal
Hi there, I am Saad Iqbal from Pakistan. I am an enthusiastic blogger, passionate content creator, construction geek, and a creative graphic designer. Connect with me at my social channels.