JPH07103544B2 - Structure of seismic isolation area - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] This invention is a seismic isolation system for landfills or areas with sand layers, clay layers, etc. Regarding the structure of the area.

[Problems to be Solved by the Invention]

For example, in the case of Tokyo Bay, the coastal landfill has a thick soft layer and a deep support layer of 60 to 70 m. The landfill layer mainly composed of sand formed on the soft layer was amplified by the soft layer during an earthquake. Liquefaction phenomenon easily occurs due to seismic waves entering. In addition, subsidence is likely to occur in landfills where the soft layer is deep, and the shaking of the earthquake is large, and damage tends to increase.

Clay layers tended to consolidate on the ground where sand layers and clay layers were alternating and the groundwater level was high, and the sand layers had a high risk of liquefaction during an earthquake.

The present invention has been made in view of the above problems. The purpose is to propose the structure of the seismic isolation area where the ground liquefaction phenomenon does not occur, the shaking during the earthquake is small, and the ground subsidence can be controlled.

[Means and Examples for Solving the Problems]

The structure of the seismic isolation area according to the present invention is a seismic isolation area in which a continuous underground wall that reaches a predetermined depth from the surface of the earth is provided to divide the inside of the ground, and the underground wall substantially contains bubbles. It is formed of an impermeable elastic layer that does not contain, and the groundwater level in the area is characterized by being drained from a drainage well and maintained at a low water level.

Hereinafter, description will be made with reference to the illustrated embodiment.

Figure 1 shows the seismic isolation area provided on the coastal landfill site. The landfill site 1 is composed of a support layer 2 with a depth of 60 to 70 m, a soft layer 3 and a landfill layer 4 composed mainly of sand on it. Has been done. The seismic isolation area 5 is a trough-shaped impermeable elastic layer 8 having a thickness of 1.5 to 2.0 m, which is composed of an annular continuous underground wall 6 reaching the depth of 10 m from the ground surface and a bottom plate 7 in the landfill layer 4. Are formed and separated. Within this seismic isolation area, drainage wells 9 are provided at desired intervals to permanently discharge water and maintain the groundwater level 10 at a low level.

The water-impermeable elastic layer is substantially free of air bubbles mainly composed of a mixture of a polyurethane resin and surrounding soil by injecting an isocyanate-based prepolymer composition that reacts with water to form a urethane bond into the landfill layer 4. , Forms an impermeable layer having rubber-like elasticity.

The seismic isolation area 5 of this configuration is surrounded by a trough-shaped impermeable elastic layer 8 and the groundwater level 10 is maintained at a low level, so that consolidation easily proceeds and further subsidence occurs. Absent. At the time of an earthquake, the groundwater level is low, so there is no danger of liquefaction, and the buffer action of the surrounding impermeable elastic layer 8 reduces the fluctuation.

If the soft layer 3 below the seismic isolation area 5 has already reached the normal consolidation state, there is no possibility of new consolidation settlement due to the construction of this seismic isolation area. Moreover, this area 5
Since the buoyancy corresponding to the weight of groundwater and the weight of excavated soil acts on the structure, when the structure 11 is constructed, if the weight is less than the buoyancy, consolidation settlement does not occur, and more weight is applied. In the case of, the corresponding consolidation settlement occurs.

Fig. 2 shows the seismic isolation area 5 constructed on the ground where the sand layer 12 and the clay layer 13 are alternating and the groundwater level 10 is high. This seismic isolation area 5
Is formed by forming a connecting underground wall 6 with a water impermeable elastic body layer 8 having a thickness of 1.5 to 2.0 m, the tip of which penetrates into the lower clay layer 13. In this area 5, drainage wells 9 are provided at predetermined intervals to permanently discharge water and maintain the groundwater level 10 at a low level.

In the seismic isolated area 5 having this structure, consolidation settlement rapidly progresses and is stabilized, and at the same time, the entire area receives buoyancy from the surrounding ground. At the time of an earthquake, the groundwater level 10 is low, so there is no risk of liquefaction, and the surrounding impermeable elastic layer acts as a damper to exert a damping effect.

In the lower ground of the seismic isolation area 5, pore water pressure corresponding to the groundwater level of the surrounding ground is distributed. Therefore, when the weight of the structure 11 increases beyond the drainage amount of groundwater and the weight of excavated soil in the area 5, the consolidation settlement corresponding to the increase is performed, but no further settlement occurs.

In addition, at the time of initial drainage, seismic isolation area 5 will temporarily dry and shrink,
All shrinkage does not appear as ground subsidence, but rather as inward shrinkage. Since the inward contraction appears as the subsidence of the surrounding ground, it is necessary to consider these during drainage at the time of construction.

[Operation and effect of the invention]

The structure of this seismic isolation area consists of the above-mentioned structure, the surrounding is surrounded by the impermeable elastic body, and the groundwater level is maintained at a low level, the ground is consolidated, there is no risk of liquefaction, and the earthquake The fluctuation of time also becomes smaller. Since the impermeable elastic body that constitutes the underground wall does not contain bubbles, even in deep underground where the groundwater level is high, there is no dimensional change due to collapse of bubbles or deterioration of water resistance or elasticity. Also, it is difficult for obstacles such as floating due to groundwater to occur. Further, when the constructed structure exceeds a certain level, the amount of subsidence corresponding to its weight occurs, but the amount of subsidence is a measurable amount and is stable after subsidence, which is not a problem. This structure does not cover a wide area like the entire landfill site, but rather covers a wide area surrounded by roads. Therefore, it is possible to construct the seismic isolation area with priority, reduce the groundwater level outside the area, and cause no subsidence outside the area.

[Brief description of drawings]

The drawing is a longitudinal sectional view showing the structure of the seismic isolation area of the embodiment,
Figure 1 is a reclaimed land, and Figure 2 is a seismic isolation area constructed on alternating ground of sand and clay layers. 1 ... Landfill site, 2 ... Support layer, 3 ... Soft layer, 4 ... Landfill layer, 5 ... Seismic isolation area, 6 ... Continuous underground wall, 7 ... Bottom plate, 8 ... Impermeable Elastic body, 9 ... drainage well, 10 ... groundwater level, 11 ... structure, 12 ... sand layer, 13 ... clay layer.

Claims (1)

[Claims] 1. A seismic isolation area in which a continuous underground wall that extends to a predetermined depth from the surface of the earth is provided to divide the inside of the ground, and the underground wall does not substantially contain bubbles and is impermeable and elastic. Structure of seismic isolation area characterized by being formed by body layer, and groundwater level in the area is drained from the drainage well and maintained at a low water level.