The Japanese Geotechnical Society has compiled recommendations calling on the government to implement measures to deal with liquefaction that damages single-family homes, in line with regulations applying to larger structures.
The Japanese Geotechnical Society has compiled recommendations calling on the government to implement measures to deal with liquefaction that damages single-family homes, in line with regulations applying to larger structures.
"We want to establish an objective of developing measures to deal with liquefaction that would cost about 2 million yen ($25,700) as well as inexpensive land survey methods," said Susumu Yasuda, a professor of geotechnical engineering at Tokyo Denki University, who was involved in compiling the proposal.
Liquefaction, which occurs when soil loses its strength and firmness and takes on a liquid form, was widespread after the Great East Japan Earthquake. It occurred not only in the Tohoku region that had the greatest quake damage, but also in the Kanto region hundreds of kilometers away. About 10,000 single-family homes along Tokyo Bay or built adjacent to rivers were damaged due to liquefaction, with the structures sinking into the ground or tilting.
Liquefaction is expected to occur in urban areas whenever earthquakes strike, but currently there are methods to deal with the problem only for condominiums and commercial buildings.
There are no legal restrictions for the design and construction of wooden family homes up to two stories high to prevent damage from liquefaction.
Restoring damaged homes can cost several million yen.
Among the proposals made by the Japanese Geotechnical Society are developing low-cost methods to deal with liquefaction; increasing knowledge of methods to determine if a plot of land is in danger of liquefaction should a quake hit; and improving the accuracy of hazard maps compiled by local governments that predict the areas where liquefaction may occur.
The objective of the proposals is to provide information to potential land buyers as well as to homeowners who have to choose a means of dealing with liquefaction.
Current laws only call for land surveys and methods to deal with liquefaction for residential and commercial buildings of more than two stories.
Moreover, officials of the Building Guidance Division of the Ministry of Land, Infrastructure, Transport and Tourism are cautious about strengthening restrictions to cover single-family homes.
"If we made obligatory land improvement for even small wooden homes, there is the possibility of forcing an excessive burden on residents," one official said. "We doubt whether it is realistic to say to potential homeowners that they should build their homes on the assumption that a gigantic quake like that of March 11 will strike."
The central government's basic policies for rebuilding after the March 11 disasters were decided on in late July, and they called for the consideration of measures to prevent a recurrence of liquefaction.
Because one alternative is to make repairs after the quake, land ministry officials will leave final decisions up to the builder and designer of the structures.
However, those who have to make such decisions have only the guidelines laid out by the Architectural Institute of Japan. The guidelines only list general examples for determining if liquefaction occurred as well as for dealing with liquefaction.
The development of inexpensive and new methods to deal with liquefaction as proposed by the Japanese Geotechnical Society will also not be implemented immediately.
What will be of greater relevance in the short term is making mandatory the release of land information that shows the dangers of liquefaction. If potential homeowners know the risks involved, they can make a choice between building their home in a solid land site in an inconvenient location or a convenient location with the intention of making repairs if any damage occurs due to liquefaction.
Land ministry officials are also considering whether explanations about the quality of land before a potential land transaction would be possible.
Osamu Kusakabe, a professor emeritus at Tokyo Institute of Technology who is president of the Japanese Geotechnical Society, said, "It is unfair to have a transaction without knowing about land information. In the future, efforts should be made to undertake as common practice various measures before building that would be much less expensive than any measures for (upgrading) existing homes."
Kazue Wakamatsu, a professor at Kanto Gakuin University specializing in urban environment design, has studied documents from about 1,000 earthquakes that have occurred over the past 1,600 years. According to her study, liquefaction has occurred, mainly in plains and basins, at about 16,500 locations around Japan. In 150 locations, liquefaction occurred due to several earthquakes, with one location having a series of 11 quakes. Such residential land can be found around Japan, mainly in urban areas.
Actual damage from liquefaction does not have to be extreme to inconvenience residents. For example, residents complained about losing their sense of balance when a two-meter pillar in their home tilted only about two centimeters.