Disaster Prevention for Housing Land

Unprecedented ground liquefaction damage were caused by the Great East Japan Earthquake in 2011. Recurrence prevention measures are desired in affected areas, however, there are little practical examples of antiliquefaction to area with existing buildings. In cooperation with the MLIT City Bureau, we are developing technologies to assist affected municipal governments to whom urgent support is necessary. For example, "Analysis Tool on Soil Liquefaction Potential for Housing Land" can be downloaded from our homepage.

Software Development to Support the Creation of Liquefaction Hazard Maps

The Division has developed housing land liquefaction hazard map technology to help regional public bodies provide liquefaction information. The software can be obtained by applying to the NILIM web site.

In response to damage to housing and public infrastructure by wide-spread liquefaction phenomena caused by the Great East Japan Earthquake of March 2011, the National Government has revised liquefaction damage possibility estimate methods in the gTechnical Guidance for Estimating Liquefaction Potential of Housing Landsh (April 2012). To be able to easily perform liquefaction estimates based on the technical guidance, the NILIM has developed an Excel-based calculation sheet and provided it on the NILIM Housing Land Disaster Prevention web site where it is downloadable.
Housing Land Liquefaction Map
Figure: Sample Display of a Housing Land Liquefaction Map
NILIM has developed software that applies this calculation sheet to create housing land liquefaction maps based on judgments under the above technical guidance. This software displays the possibility of liquefaction damage on a map in three ranks in mesh units 250m or 500m as determined by judgments of the possibility of liquefaction damage at survey points obtained by entering past boring survey results to the calculation sheet. It can also be used to update wide area and high survey density liquefaction maps of object areas by adding new boring survey results.
An application to obtain this software can be submitted through the NILIM Housing Land Disaster Prevention web site. The use of this software is counted on to further advance the creation of housing land liquefaction maps by regional public bodies and expand the provision of information concerning the possibility of liquefaction damage to residents etc. and to advance countermeasures to protect housing land from liquefaction.

Liquefaction Countermeasure by the Grid-form Underground Wall for Reclaimed Housing Areas

To provide applicable re-liquefaction countermeasures for housing areas damaged by the Great East Japan Earthquake, NILIM performed experiments to test the grid-form underground wall method.

Soil liquefaction countermeasures are usually taken on vacant land without buildings, but there has been no applicable method that can be implemented in residential districts already occupied by detached houses. However, since the Great East Japan Earthquake, urgent technical research to develop a practical method has been required. The research revealed two countermeasure methods: the ground water level reduction method and the grid-form underground wall method. Of these, the latter method is counted on to be used on reclaimed land around Tokyo Bay, where there is a lower clay layer at high risk of consolidation settlement. But it has never been applied to detached housing land so there is little technical information that local governments or residents can use as a reference to find out how to apply it and how effective it will be.
(Top) without countermeasure without countermeasure
(Bottom) grid-form underground wall method executed grid-form underground wall method executed
Figure: Excess Pore Water Pressure Ratio Contour Obtained by the Test
NILIM developed a software program for the simple evaluation of the effectiveness of the grid-form underground wall method, and placed it on its web site as a free download in January 2013, in order to allow local governments as well as residents to judge whether the countermeasure can be effective or not by inputting the proper test data for soil conditions at the site. Then, NILIM performed seismic experiments followed by the preparation of a ground model that can simulate ground conditions in reclaimed land along Tokyo Bay using a centrifugal device by varying conditions such as the intervals between the underground walls. The results have shown that if the grid size of an underground wall encloses a lot of about 50 tsubo (165 sq. meters), it can be counted on to mitigate damage caused by earthquake motion equal to that of the Great East Japan Earthquake, and that if this is combined with an embankment of about 1m or with ground water level reduction, it appears sure to mitigate liquefaction to a great degree.
The figure shows the results of the seismic test with and without the countermeasure, with the red part indicating liquefaction. It is possible to view an animation of liquefaction on our web site (mp4, avi).

Experiment for Anti Soil Liquefaction of Housing Sites

In order to find practical anti soil liquefaction technology for developed housing areas where detached houses are built and located, research projects including seismic tests and simulations are underway.

Photo: Large Scaled Specimen of Sand Ground for the Seismic Liquefaction Test
Soil liquefaction hit housing areas with unprecedentedly huge scale during the Great East Japan Earthquake Most of the areas severely damaged are detached housing districts. The MLIT established a new subsidy system in the third supplementary budget of 2011 to support the area wide anti land liquefaction project which includes both alley roads and housing lots. However, the technologies usable to build up housing areas have not been developed because there is no practical example, though the technologies for vacant land are already established, so that the research for technology development has, in practice, to be conducted simultaneously with planning and implementation of the restoration projects in damaged districts.

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Research Results