& Tornado Alley
In the mid-1980's Osaka's Itami Airport was woefully inadequate for the needs of the Kansai region of Japan. The Kansai region includes not only Osaka, the second largest city of Japan and a major commercial center, but also the major cities of Kyoto and Kobe. The old airport was hemmed in by urban development in more ways than one. The urban development prevented any spatial expansion, but it also restricted the hours of use because of the aircraft noise in the late hours of the night would disturb the sleep of the residents in the vicinity of the airport.
The limitation of the old airport was forcing the exporters of the Kansai region to ship their aircargo to Tokyo for shipment abroad. This inconvenience was probably limiting those exports.
The airport authorities considered finding a land site for a new airport, but they looked at the experience of Tokyo in building the Narita Airport. The protests of the farmers to the forced sale of their land mobilized a movement that delayed the completion of the airport for years. It is little appreciated outside of Japan that there is a substantial group of violent radical activists in Japan who will flock to any public protest movement and turn it into vicious showdown of force. In the Narita Airport construction these radicals fire bombed the heavy earth-moving equipment and endangered the lives of the equipment operators. There were several deaths in the Narita Airport protests and three thousand radical activists were arrested.
It is quite possible that the radical activists could prevent a new, land-based airport for the Kansai region from ever being built. That motivated the consideration of a water-based airport. An airport operating from an island in Osaka Bay could operate 24 hours per day. Radical activists could be prevented from getting access to the construction site.
Since there is no island in Osaka Bay where the airport is needed, one would have to be built. That would be costly be not impossible. There are several factors that have to be considered. The Kansai region is subject to severe earthquakes and earthquakes can liquify the sort of land-fill that might be used to construct such an island. Also Japan is subject to typhoons (hurricanes in the Pacific). A typhoon in 1934 created a surge that raised water levels ten feet in the Osaka area for several hours. An island airport would have to be high enough to withstand severe typhoon water surges.
When serious design work started on the island airport the authorities headed off a potential protest from Osaka Bay fishermen who would have their livelihood disturbed by the construction. A generous payment was offered by the airport authorities and accepted by the fishermen.
The designers envisioned an airport 2.5 miles long and 4000 feet wide. The site selected was three miles from land and there the water depth was 60 feet. The water depth was not a serious impediment. The problem was the condition of the soil under the water. Soil immediately under the water was a soft clay called alluvial clay. This alluvial clay went down 100 meters. Japanese engineers had solved the problem of building in this soil. They would drive down pipes which would be then packed with sand. The pipes would then be pulled up leaving columns of sand in place to absorb the moisture in the alluvial clay. The uncertainty for the construction came from the layer of clay lying below the alluvial clay. This clay was called dialluvial clay and extended about one thousand feet down. The compressibility of this clay was uncertain and because of its depth nothing could be done to modify that compressibility.
The airport authorities had a number of experts estimate how much the airport island would sink as a result of the weight of its weight. The estimates ranged from 19 feet to 25 feet.
The official looked at the estimates of the degree of sinking and did what now seems to have been the worse possible thing. They accepted the smallest estimate, 19 feet, in what appears to have been wishful thinking. The design of the airport was then based upon a sinking of 19 feet.
The construction started in 1987. The alluvial clay was stabilized with sand columns as described above. The perimeter of the island was defined by means of 69 steel chambers which were sunk to the bay floor. These chambers were 75 feet in height and 75 feet in diameter. They weighed 200 tons each. The spaces between the chambers were filled with 48,000 specially shaped concrete blocks. Irregular stones weighing one to two tons were added to the walls.
The cavity within the walls was filled with rocks and coarse gravel to avoid the danger of liquification of earth-fill during an earthquake. The fill came two mountains which were leveled in the process.
The radicals, not to be denied their opportunity to commit violence, attached the quarries where the fill material for the island was being escavated. Altogether there were about two dozen attacks.
The island airport had to be linked to the land. That part of the project was started in 1987 and by March of 1990 the bridge link was completed, at a cost of $1 billion. The trussed bridge framework carried a railway on its lower level and a motor vehicle highway of the upper level.
By 1990 the island and its link to the land had been completed. Ten thousand people had worked on the project. The trouble was that the airport island was sinking more than the design provided for. The maximum estimate was 25 feet. The airport authorities took the minimum estimate of 19 feet. The actual sinkage by 1990 was 27 feet and the island was still sinking at a rate of about per feet per year at that time.
The authorities added another 11.5 feet of fill at a cost of $150 million. The runway was covered with asphalt rather than concrete to avoid cracking. The terminal facilities were yet to be constructed.
(To be continued.)
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