|Liquefaction map illustrated liquefaction degree of risk distribution of 3 earthquakes that damage assumption intended for in "Yokohama-shi earthquake damage assumption investigation" that we announced in October, 2012.|
"Instructions when you see liquefaction map"
We used PL level for judgment of liquefaction degree of risk. PL level is value to express degree of risk of liquefaction at the point.
Like Minato Mirai 21 district of Nishi Ward, wide range excludes place where liquefaction measures are performed by ground improvement from liquefaction judgment beforehand.
Because we liquefy based on representative ground bowling data around 50 meters of mesh, and it is determined, the ground which is hard to take place of liquefaction may be included in the mesh.
We improve the ground which is easy to already liquefy, and there is conducted place, but, in area that liquefaction degree of risk is high in, liquefaction measures recommend that they have you have you carry out ground investigation individually in future about points of building plan and perform examination of measures to done place or building for soil products from the earth.
|Genroku era type Kanto earthquake
||Earthquake in northern Tokyo Bay
||Nankai Trough giant earthquake
|◆Q&A about liquefaction
Does Q1" liquefaction "mean that what happens?
It turned out that was the ground which land where was going to build Q2" building was easy to liquefy, what should do?
Place that the Q3" ground has bad is told to be all right if we make raft, is it true?
On the ground which is easy to liquefy of Q4" reclaimed land, is high-rise building all right in apartments?
In Q5" detached residence, what kind of measures should we take?
As the ground liquefies Q6" reclaimed land at the time of earthquake, it should be dangerous and hears, in the reclaimed land of Yokohama, what kind of measures are taken for earthquake?
■Structure of liquefaction
Liquefaction is phenomenon that the ground becomes like liquid by earthquake temporarily. We let you let building on the ground incline by phenomenon to occur on the ground of sabulosity which included a lot of moisture including reclaimed land and the river mouth and set.
This phenomenon attracted attention by damage such as collapse of collapse of apartment and new bridge having appeared one after another by Niigata earthquake of 1964. Port Island and Rokko Island were damaged, and even South Hyogo earthquake of 1995 (the Great Hanshin-Awaji Earthquake) attracted attention recently.
When it is groundwater keeping constant balance, and the sand layer in saturated state is shaken by (state of ), strong earthquake, water in gap of sand and sand comes pressure, and fighting each other between sand comes. And coming together of particle of sand comes off at last, and particle of sand is in a condition to have loosened in water. (state of ) the surface of the earth is filled with pushed water with sand afterwards. (state of ) call phenomenon that the ground becomes like liquid in this way "liquefaction".
Power to support building when the ground liquefies disappears, and the following damage might occur because building or ground itself sinks heterogeneously.
■Liquefaction measures of my home
We avoid the ground which is easy to liquefy
The following place is place where liquefaction is easy to occur. When you must build buildings on such ground, we can reduce damage by taking measures.
・Place that water level under the ground is high in on the ground of sabulosity
・Place that it was river, and filled up place where there were rice field, marsh, the shore, and prepared land in old days
We strengthen the ground
Liquefaction measures become method that ground improvement is effective. When there is stratum which does not liquefy from the ground to depth of around 2m from damage experience of past earthquake, there is findings that damage decreases. Thus, we tighten the ground to this depth and harden, and ground improvement such as rearranging in soil which it is hard to liquefy is said to be the most effective method of liquefaction measures.
We make building resisting liquefaction
With form of house as simple form (rectangle) that is strong for earthquake, it is effective measure to reinforce foundations of building.