JPH02132218A - Earthquake-proof area structure - Google Patents

Abstract

PURPOSE:To prevent the liquidizing phenomenon of the ground and to reduce a quake at the time of an earthquake by separating the underground with underground walls formed by an impermeable elastic body layer and draining in this area through drainage wells to keep an underground water level at a low water level. CONSTITUTION:An earthquake-proof area 5 has a impermeable elastic body layer in a tub shape consisting of an annular continuous underground wall 6 and a bottom board 7 in a landfill layer 4 and the landfill layer 4 is thereby separated. Drainage wells 9 are provided at predetermined intervals in this area to drain eternally for keeping a underground water level at a low level. The elastic body layer 8 is formed by pouring e.g., isocyanate group prepolymer composition into the landfill layer 4 and by impermeable elastic body mainly made of the mixture of polyurethane resin and circumferential soil. Consequently, there is no danger of liquidizing due to low underground water level and a quake can be reduced by the buffer function of the elastic body layer 8 at the time of an earthquake.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is useful for seismic isolation in areas that are made up of reclaimed land, sand layers, clay layers, etc., where the groundwater level is high, there is a risk of liquefaction during an earthquake, and the area is prone to large tremors. Concerning the structure of the area.

[Problem to be solved by the invention]

In the case of coastal reclaimed land, for example, in the case of the Tokyo Bay coast, the soft layer is thick and the supporting layer is as deep as 60 to 70 m, and the reclaimed layer mainly made of sand formed on the soft layer has a tendency to be amplified by the soft layer during an earthquake. Seismic waves enter and liquefaction phenomena are likely to occur. In addition, in reclaimed land with deep soft layers, subsidence is likely to occur, and earthquake shaking tends to be large, increasing damage.

In a ground with alternating sand and clay layers and a high groundwater level, the clay layer tends to consolidate and settle, and the sand layer has a high risk of liquefaction during an earthquake.

This invention has been made in view of the above-mentioned problems. The purpose is to propose a structure for a seismic isolation area that does not cause ground liquefaction, has small shaking during earthquakes, and can control ground subsidence.

[Means and Examples for Solving the Problems] The structure of the seismic isolation area according to the present invention is a seismic isolation area that divides the inside of the ground by providing an annular continuous underground wall that reaches a predetermined depth from the ground surface. The underground wall is formed of a water-impermeable elastic layer,
The underground water level in the area is maintained at a low level by draining water from a drainage well.

The following will explain the embodiments shown in the drawings.

Figure 1 shows a seismic isolation area established on a coastal reclaimed land. The reclaimed land 1 consists of a supporting layer 2 with a depth of 60 to 70 m, a soft layer 3, and a reclaimed layer 4 mainly made of sand above it. has been done. The seismic isolation area 5 is an impermeable elastic area with a thickness of 1.5 to 2.0 m, which is in the shape of a tub consisting of a continuous annular underground wall 6 reaching a depth of 10 m from the ground surface and a bottom plate 7 within the reclaimed layer 4. A body layer 8 is formed and partitioned. Drainage wells 9 are provided within this seismic isolation area at desired intervals to permanently drain water and maintain the groundwater level lO at a low level.

The water-impermeable elastic layer is formed by injecting an isocyanate-based brevolimer composition that reacts with water and bonds with urethane into the reclaimed layer 4 to form a water-impermeable elastic layer that is mainly composed of a mixture of polyurethane resin and surrounding soil. form.

The seismic isolation area 5 with this configuration is surrounded by a tub-shaped impermeable elastic layer 8, and the groundwater level 10 is maintained at a low level, so consolidation easily progresses and further subsidence does not occur. do not have. In the event of an earthquake, since the groundwater level is low, there is no risk of liquefaction, and the buffering action of the surrounding impermeable elastic layer 8 reduces shaking.

If the soft layer 3 below this seismic isolation area 5 has already reached a normal consolidation state, there is no fear of new consolidation subsidence due to the creation of this seismic isolation area. Moreover, this area 5
, a weight commensurate with the amount of drainage of groundwater and a buoyant force equivalent to the weight of excavated soil act on the structure, so when structure 11 is constructed, consolidation settlement will not occur if the weight is less than the buoyant force, and if the weight is greater than that, In this case, a corresponding consolidation settlement will occur.

Figure 2 shows a seismic isolation area 5 constructed on ground with alternating layers of sand 12 and clay 13 and a high groundwater level IO. This seismic isolation area 5 has a thickness of 1.5 mm where the tip penetrates into the underlying clay layer 13.
~2. A connecting underground wall 6 is formed and separated by a water-impermeable elastic layer 8 of 0 m. Drainage wells 9 are provided at predetermined intervals within this area 5 to permanently drain water and maintain the groundwater level 10 at a low level.

In the seismic isolation area 5 having this configuration, the consolidation settlement rapidly progresses and the seismic isolation area 5 having this configuration becomes stable, and at the same time, the entire area receives buoyancy from the surrounding ground. In the event of an earthquake, since the groundwater level 10 is at a low level, there is no risk of liquefaction, and the surrounding impermeable elastic layer acts as a damper, providing a damping effect.

Pore water pressure corresponding to the groundwater level of the surrounding ground is distributed in the ground below this seismic isolation area 5.

Therefore, if there is an increase in the weight of the structure 11 that exceeds the amount of drainage of groundwater in the area 5 and the weight of the excavated soil, the corresponding consolidation settlement will occur, but no further settlement will occur.

It should be noted that at the time of initial drainage, the seismic isolation area 5 temporarily dried and shrunk.
The amount of contraction will not all appear as ground subsidence, but will instead appear as inward contraction.

Inward shrinkage appears as subsidence of the surrounding ground, so it is necessary to take this into account during construction when draining water.

[Action and effect of the invention]

The structure of this seismic isolation area consists of the above-mentioned structure; it is surrounded by an impermeable elastic material, and the groundwater level is maintained at a low level, so the ground is consolidated, there is no risk of liquefaction, and there is no risk of earthquakes. The fluctuations of time will also become smaller. Furthermore, when a constructed structure exceeds a certain level, it will sink by an amount corresponding to its weight, but the amount of sinking can be calculated and is stable after sinking, so this is not a problem. This structure does not cover a wide area such as the entire reclaimed land, but rather covers a fairly large area surrounded by roads, etc. Therefore, it is possible to create a seismic isolation area in a focused manner, and there is no risk of lowering the groundwater level outside the area or causing ground subsidence outside the area.

[Brief explanation of drawings]

The drawing is a longitudinal sectional view showing the structure of the base isolation area of the example,
Figure 1 shows the reclaimed land, and Figure 2 shows the seismic isolation area constructed on alternating layers of sand and clay. ■...Landfill, 2...Support layer, 3...
...Soft layer, 4...Reclaimed layer, 5...
・Seismic isolation area, 6... Continuous underground wall, 7...
・Bottom plate, 8... Impermeable elastic body, 9...
・Drainage well, 10... Groundwater level, 11...
・Structure, 2...Sand layer, ...Clay layer.

Claims (1)

[Claims] (1) A seismic isolation area in which the ground is divided by a continuous annular underground wall reaching a predetermined depth from the ground surface, the underground wall being formed of an impermeable elastic layer, and The structure of the seismic isolation area is characterized by the fact that the groundwater level is maintained at a low level by draining water from a drainage well.