Research Trends and Results

NILIM Supports Local Governments on Anti
Liquefaction of Housing Areas for Recovery from theGreat East Japan Earthquake Disaster
AKASHI Tatsuo (Ph.D.), HeadOHASHI Masamiki, Senior Researcher
Urban Planning Division, Urban Planning Department
ARAI Hiroshi (Ph.D.), Senior Researcher
Structural Standards Division, Building Department(Key words)

Land Liquefaction, Disaster Prevention on Housing Area, Great East Japan Earthquake

1. Anti-liquefaction Method implementable toHousing Areas
The Great East Japan Earthquake caused not onlytsunami disaster but also caused very extensive landliquefaction including in housing areas. Method ofanti-liquefaction which should be implemented to areas
with roads and houses has been a big problem on theprocess of recovery because there are very seldom
precedent cases other than in plain ground with nobuilding. Another big problem is construction costs
which should be affordable for ordinary house owners.
Established methodology has yet to be conceived.
In order to support the local government as well as
residents in the struck areas, the City Bureau of MLIT
introduced new financial subsidy to the local
governments in order to implement district wide
treatment with both roads and housing lots integrally,
which will is expected to reduce allotted payment for
housing owners indirectly. Then, NILIM has taken
charge of technical support to the local governments
mainly for adequate selection of unprecedented method.
One example will now be introduced.
2. Development of the Simple Calculation Softwarefor Lowering Groundwater Levels Method
Firstly, we focused on Lowering Groundwater Levels
Method. An advantage of this method is that construction
is needed only within the area of roads but its effect willreach into the surrounding housing lots. Running cost canbe reduced if the depth of groundwater lowered is lessthan 3 meters from the surface. However, there are anegative sub effect of potential land subsidence whichcaused by compaction of deeper clay layers. These
positive and negative effects can be estimated but only
through complicated formula. It was a kind of abottleneck of investigation making consensus building
and decision making difficult.
In order to break the bottleneck, a simple software tool
based on Microsoft Excel sheets was urgently developed.
As figure shows, what depth zone has liquefaction risk by
FL value graph as well as easily calculate potential
ground sinkage both by liquefaction and clay layercompaction can easily be seen. The output is frequently
updated according to the input on scale of earthquakes
and groundwater levels.
NILIM offered the calculation software for freethrough its homepage, which has been contributed to
local decision making in the struck areas.
3. Development of Second Software for Grillwork
Underground Walls Method
Next, NILIM developed second simple calculation
software on Grillwork Underground Walls Method which
is an alternative for the ground where unsuited fordowning groundwater level. It also use Excel sheets, but
its output is calculated by high speed computer inadvance with approximately 18,000 ways of equivalentlinearization analysis, which is hard to do for local
governments by themselves. This is also able todownload free from NILIM homepage.

Figure: Image of Calculation Software for Anti
Liquefaction Effect (NILIM Liquefaction Sheets)[Sources]1) NILIM homepage
http://www.nilim.go.jp/lab/jbg/takuti/takuti.html