JP2014211073A - Ground displacement-absorbing base-isolated structure and base isolation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground displacement-absorbing base-isolated structure excellent in long-term stability, and a base isolation method.SOLUTION: In a ground displacement-absorbing base-isolated structure 100, a continuous wall-like underground wall 16 made of a clay-based material which swells when absorbing water is provided between peripheral ground 12 and a structure 14. A water storage layer 18 for storing water W with low electrolyte concentration is provided at a ground surface-side upper end 16a of the underground wall 16. In this case, preferably, a water level WL of the water storage layer 18 is set higher than a ground water level GWL of the peripheral ground 12. Thus, the ground displacement-absorbing base-isolated structure excellent in long-term stability can be provided.

Description

  The present invention relates to a ground displacement absorbing base isolation structure and a base isolation method for reducing stress on underground structures such as an open tunnel during an earthquake.

  Conventionally, as an underground seismic isolation wall for the purpose of reducing stress during earthquakes to underground structures such as open tunnels, it has been common to install continuously in the extending direction in contact with the underground structure If it is this installation position, it can be constructed simultaneously with the construction of the underground structure. For example, Patent Document 1 proposes a ground displacement absorbing method in which polymer improved soil is cast as an underground seismic isolation wall for the purpose of reducing stress on underground structures during an earthquake.

  On the other hand, Non-Patent Document 1, for example, discloses an underground seismic isolation wall for an underground structure such as an open-cut tunnel that is not continuously installed in the extending direction of the underground structure. In this nonpatent literature 1, the vertical cylinder-shaped polymer improvement soil is intermittently arrange | positioned in the ground along the underground structure.

However, the above conventional underground seismic isolation wall has the following problems.
That is, in the construction method for placing the polymer improved soil as disclosed in Patent Document 1, the polymer seismic isolation material is greatly compressed and deformed due to the influence of normal earth pressure and the like. Therefore, the wall thickness of the predetermined underground seismic isolation wall set at the time of construction cannot maintain the initial wall thickness for a long time, and there is a concern that the seismic isolation wall may be crushed in some cases. Such a change in the thickness of the base isolation wall is caused by a decrease in the displacement absorption performance of the polymer base isolation wall, and the effect of absorbing the ground displacement by the underground base isolation wall is not fully exhibited. There was a problem that the reduction effect was reduced.

  As a countermeasure, Non-Patent Document 1 is considered in which the underground seismic isolation wall is intermittently arranged so as to avoid the continuous arrangement along underground structures such as open tunnels. However, in the seismic isolation walls that are not arranged continuously, the surrounding ground and the structure are connected by soil, so that the seismic isolation effect of sufficiently absorbing the original displacement is significantly reduced. there were.

  Moreover, since the polymer material is dissolved in water in the ground where the groundwater level exists, there is a problem that the construction is not easy. Furthermore, although a predetermined reinforcing agent must be added to the polymer seismic isolation material, there is a problem that an expensive reinforcing agent is required for environmental considerations and costs are increased.

  In this way, when an underground seismic isolation wall is provided along an underground structure such as an open-cut tunnel, it can sufficiently resist the earth pressure acting on the underground isolation wall and ensure long-term stability. On the other hand, in order to exert the seismic isolation effect, it is desirable that the material has low rigidity, and there is a need for an underground seismic isolation wall that provides a good balance between the two. There was room for.

  As a structure for solving such a problem, the present inventor has already provided the ground displacement absorption isolation structure of Patent Document 2. This structure can ensure the long-term stability of the underground seismic isolation wall and can reduce the stress on underground structures such as open tunnels during an earthquake. (1) to (4) ).

(1) As shown in FIG. 8, a wall-shaped underground seismic isolation wall 3 (underground wall) continuous with a water-absorbing swelling clay-based material is installed between the surrounding ground 1 and the underground structure 2. .
(2) The underground wall is made of a mixture of bentonite and water, or a mixture of bentonite and aggregates (soil materials such as gravel or artificial materials that are difficult to change for a long time such as glass beads) and water.
(3) The area | region filled with the material which consists of a mixture of the bentonite and water in the clay earth material which comprises an underground wall is 300-1200 kg / m < ³ > in a bentonite dry density.
(4) In a material composed of a mixture of bentonite, aggregate, and water in the viscous earth-based material constituting the underground wall, an area filled with bentonite and water (the bentonite filling the area excluding the aggregate area and The water mixture) is 300-1200 kg / m ³ in terms of bentonite dry density.

JP 2006-112182 A JP 2012-031662 A

Tsuyoshi Murono, Masaru Tateyama, Fumi Kiryu, Shosuke Kobayashi, “Reinforcement of existing excavated tunnels with polymer seismic isolation walls”, Foundation work, 2007.3, P69-71

  In the ground displacement absorption seismic isolation structure described in Patent Document 2 described above, water-absorbing expansive clay (for example, bentonite) that exhibits a swelling pressure (water-absorbing expansion pressure) that can resist soil pressure is used while being a continuous underground wall. Thus, there was a feature in maintaining the structural form of the underground wall.

As a specific example, the above Patent Document 2 shows the following example. That is, since the area filled with bentonite and water is in the range of 300 to 1200 kg / m ³ in terms of the bentonite effective dry density, the density range shown in FIG. As shown in 9), the water absorption swelling pressure is 0.03 to 0.3 MPa. Therefore, assuming that the underwater mass of the ground is about 1 g / cm ³ and the lateral earth pressure is 1 times the earth covering pressure, it can withstand earth pressure up to a depth of 30 m. It can be made more effective by constructing by adjusting the density of the material appropriately according to the installation depth of the underground seismic isolation wall.

Here, groundwater exists in the gap between the ground around the underground wall. In Japan, the groundwater level usually exists up to the surface of the ground, and the quality of groundwater is generally freshwater. There is little need to consider the impact on the structural stability of clay.
However, depending on groundwater conditions, the following problems may be a concern.

(Groundwater condition 1)
If the surrounding ground is not completely dry, the water retention ability of bentonite is maintained, so that the thickness and material density of the underground wall can be maintained for a long time. However, if the groundwater level is significantly lower than the ground surface and the clay that makes up the underground wall may dry and shrink, the underground wall will dry and shrink, the thickness will decrease, and the rigidity of the underground wall will be reduced. Increases the displacement absorption capacity, resulting in a decrease in seismic isolation performance.

(Groundwater condition 2)
When the electrolyte concentration of the groundwater quality is high, for example, when the water quality is close to seawater, such as a landfill near the coast, the water absorption expansion pressure decreases as shown in FIG. As a result, the water absorption expansion pressure that can resist the earth pressure acting on the underground wall cannot be exerted, the underground wall is deformed by the earth pressure, the thickness is reduced, and the pore water is drained to remove the underground wall. The density of the constituent clay increases and the rigidity increases. When such a phenomenon occurs, the capacity for absorbing the displacement of the underground wall decreases, and the seismic isolation performance decreases.

  In the above-mentioned Patent Document 2, FIG. 2 shows the relationship between the bentonite effective dry density and the swelling pressure. This relationship is a characteristic when the pore water is pure water. FIG. 9 shows FIG. 2 described in Patent Document 2. On the other hand, FIG. 10 shows the relationship between the effective clay density (dry density) and the water absorption expansion pressure (swelling pressure) of bentonite, which is a water-absorbing clay, when the pore water is pure water and when the NaCl concentration is 1 wt%. It is a comparison. The swelling property of bentonite is due to the osmotic action of the surroundings by the presence of cations that are taken in by electric force between the layered structure of clay mineral called montmorillonite, which is the main component of bentonite. It is exhibited by water absorption and expansion due to the characteristic of absorbing water molecules from the gaps into the clay mineral crystal layer. Therefore, when the electrolyte concentration of the groundwater in the ground around the underground wall is high, the electrolyte concentration of the pore water of the clay constituting the underground wall also gradually increases, and eventually indicated by arrows in FIG. Thus, the expansion pressure in a pure water environment is reduced to the expansion pressure in an environment with a high electrolyte concentration.

  For this reason, in the conventional ground displacement absorption seismic isolation structure, ensuring long-term stability was calculated | required.

  This invention is made | formed in view of the above, Comprising: It aims at providing the ground displacement absorption seismic isolation structure and seismic isolation method excellent in long-term stability.

  In order to solve the above-described problems and achieve the object, the ground displacement absorption isolation structure according to the present invention is a continuous wall-like structure made of a clay-based material having water absorption and swelling between the surrounding ground and the structure. In the ground displacement absorbing base-isolated structure provided with the underground wall, a water storage layer for storing water having a low electrolyte concentration is provided at the upper surface side of the underground wall.

  In addition, another ground displacement absorbing base isolation structure according to the present invention is characterized in that, in the above-described invention, the water level of the reservoir is made higher than the groundwater level of the surrounding ground.

  In addition, in the above-described invention, another ground displacement absorption seismic isolation structure according to the present invention is in addition to the boundary surface between the underground wall and the surrounding ground, or the boundary surface between the underground wall and the surrounding ground. By providing a planar water-impervious member at the boundary surface between the underground wall and the structure, drying of the underground wall is suppressed, and pore water in the underground wall due to infiltration of groundwater in the surrounding ground To suppress the increase in electrolyte concentration of the clay, to maintain a constant swelling pressure of the clay-based material saturated with water, to suppress changes in the thickness and density of the underground wall, and to maintain the rigidity of the underground wall It is characterized by doing.

  In addition, in the above-described invention, the ground displacement absorbing base isolation structure according to the present invention is the ground wall in addition to the peripheral ground side in the underground wall or the peripheral ground side in the underground wall. By providing a planar water-impervious member on the inside of the structure, it is possible to suppress drying of the underground wall and to increase the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground. Suppressing and maintaining a constant swelling pressure of the clay-based material saturated with water, suppressing changes in the thickness and density of the underground wall, and maintaining the rigidity of the underground wall .

  Further, another ground displacement absorption isolation structure according to the present invention is characterized in that, in the above-described invention, a plurality of perforated pipes extending from the reservoir to the inside of the underground wall are arranged.

  Further, the seismic isolation method according to the present invention is a seismic isolation method for the structure by providing a continuous wall-shaped underground wall made of a clay-based material having water absorption swelling between the surrounding ground and the structure. In addition, a reservoir for storing low electrolyte concentration water is provided at the upper surface of the underground wall, and the electrolyte concentration is always low from above through the reservoir in the clay-based material constituting the underground wall. By supplying water, drying of the clay-based material is suppressed, and the rigidity of the clay-based material saturated with water is maintained.

  In another seismic isolation method according to the present invention, the structure is isolated by providing a continuous wall-shaped underground wall made of a clay-based material having water absorption swelling between the surrounding ground and the structure. In the method, a water reservoir for storing water having an electrolyte concentration lower than that of ground water in the surrounding ground is provided at an upper end on the ground surface side of the underground wall, and the reservoir is formed on the clay-based material constituting the underground wall. The clay-based material saturated with water while suppressing an increase in the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground by always supplying water having a low electrolyte concentration from above through The swelling pressure is kept constant, the change in thickness and density of the underground wall is suppressed, and the rigidity of the underground wall is maintained.

  Another seismic isolation method according to the present invention is the above-described invention, wherein a plurality of perforated pipes extending from the reservoir to the inside of the underground wall are arranged from the reservoir, and the reservoir from the reservoir through the perforated pipe. Water having a low electrolyte concentration is supplied to the clay-based material constituting the underground wall.

  Another seismic isolation method according to the present invention is the above-described invention, in the invention described above, in addition to the boundary surface between the underground wall and the surrounding ground, or the boundary surface between the underground wall and the surrounding ground. By providing a planar water-impervious member at the boundary surface between the wall and the structure, it is possible to suppress the drying of the underground wall, and the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground The swelling pressure of the clay-based material saturated with water is kept constant, the change in thickness and density of the underground wall is suppressed, and the rigidity of the underground wall is maintained. Features.

  Another seismic isolation method according to the present invention is the above-described invention, in the above-described invention, in addition to the surrounding ground side inside the underground wall, or the surrounding ground side inside the underground wall in addition to the inside of the underground wall. By providing a planar water-impervious member on the structure side, the drying of the underground wall is suppressed, and an increase in the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground is suppressed, The swelling pressure of the clay-based material saturated with water is maintained constant, changes in thickness and density of the underground wall are suppressed, and rigidity of the underground wall is maintained.

  According to the ground displacement absorption isolation structure according to the present invention, a ground displacement absorption isolation structure having a continuous wall-shaped underground wall made of a clay-based material having water absorption and swelling between the surrounding ground and the structure. In the ground wall, a water reservoir for storing low electrolyte concentration water is provided at the top surface side of the ground surface, so that it can resist the normal earth pressure received from the surrounding ground by the underground wall, such as an open tunnel during an earthquake. In addition to having the basic effect as a seismic isolation structure that can reduce the stress on underground structures, it is always from the reservoir layer at the top of the underground wall to the underground wall. By supplying water, the water retention ability of the water-absorbing and swelling clay-based material constituting the underground wall is maintained, so that the thickness of the underground wall and its constituent material density can be maintained constant for a long period of time. For this reason, there exists an effect that the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided.

  In addition, according to another ground displacement absorption seismic isolation structure according to the present invention, since the water level of the reservoir is higher than the groundwater level of the surrounding ground, water having a low electrolyte concentration is always supplied from the upper end of the underground wall. By supplying, it can suppress that the electrolyte density | concentration of the pore water of the clay-type material which comprises an underground wall rises. Therefore, for example, when a clay-based material is composed of a mixture of bentonite and water or a mixture of bentonite, aggregate and water, this material exhibits a predetermined swelling pressure. It is possible to resist the normal earth pressure received from the water, and by constantly supplying water with a low electrolyte concentration, changes in the thickness of the underground wall and changes in the density of the constituent materials are suppressed. For this reason, there exists an effect that the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided.

  In addition, according to another ground displacement absorption seismic isolation structure according to the present invention, a plurality of perforated pipes extending from the reservoir to the inside of the underground wall are disposed, so that the concentration of electrolyte stored in the reservoir is low. Water can be more reliably supplied to the entire underground wall through the porous tube, and the quality of the pore water of the clay-based material constituting the underground wall can be more stably maintained.

  Moreover, according to another ground displacement absorption isolation structure according to the present invention, in addition to the boundary surface between the underground wall and the surrounding ground, or the boundary surface between the underground wall and the surrounding ground, the underground By providing a planar water-impervious member at the boundary surface between the wall and the structure, it is possible to suppress the drying of the underground wall, and the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground The rise of the water is suppressed, the swelling pressure of the clay-based material saturated with water is kept constant, the change in thickness and density of the underground wall is suppressed, and the rigidity of the underground wall is maintained. The water shielding member can more effectively prevent the drying of the underground wall and the increase in the electrolyte concentration of pore water. For this reason, there exists an effect that the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided.

  Further, according to another ground displacement absorption seismic isolation structure according to the present invention, in addition to the surrounding ground side inside the underground wall or the surrounding ground side inside the underground wall, the inside of the underground wall By providing a planar water-impervious member on the structure side, the drying of the underground wall is suppressed, and an increase in the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground is suppressed, Since the swelling pressure of the clay-based material saturated with water is kept constant, the change in thickness and density of the underground wall is suppressed, and the rigidity of the underground wall is maintained. It is possible to more effectively prevent wall drying and increase in electrolyte concentration of pore water. For this reason, there exists an effect that the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided. Moreover, since the water-impervious member is provided inside the underground wall, there is an effect that the water-impervious member can be easily constructed.

  Further, according to the seismic isolation method according to the present invention, the structure is isolated by providing a continuous wall-shaped underground wall made of a clay-based material having water absorption swelling between the surrounding ground and the structure. In this method, a water reservoir for storing water having a low electrolyte concentration is provided at the upper surface of the underground wall, and the electrolyte concentration is always applied to the clay-based material constituting the underground wall from above via the reservoir. By supplying low water, the drying of the clay-based material is suppressed, and the rigidity of the clay-based material saturated with water is maintained. For this reason, even if the groundwater level of the surrounding ground is remarkably low from the ground surface and the clay-based material constituting the underground wall is likely to dry and shrink, the supply of water with a low electrolyte concentration from above Since the drying shrinkage of the underground wall is suppressed and the thickness is kept constant, the rigidity of the underground wall is kept small. Therefore, there is an effect that the required seismic isolation performance can be exhibited stably for a long period of time.

  Further, according to another seismic isolation method according to the present invention, the structure can be obtained by providing a continuous wall-like underground wall made of a clay-based material having water absorption swelling between the surrounding ground and the structure. In the seismic isolation method, a water storage layer for storing water having an electrolyte concentration lower than ground water of the surrounding ground is provided at an upper end on the surface side of the underground wall, and the water storage is performed on the clay-based material constituting the underground wall. By constantly supplying water with a low electrolyte concentration from above through a layer, an increase in the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground is suppressed, and the clay saturated with water The swelling pressure of the system material is kept constant, the change in thickness and density of the underground wall is suppressed, and the rigidity of the underground wall is maintained. For this reason, even if the electrolyte concentration of the groundwater in the surrounding ground is relatively high, such as seawater, the underground wall stiffness is kept small by supplying water with a low electrolyte concentration from above the underground wall. Is done. Therefore, there is an effect that the required seismic isolation performance can be exhibited stably for a long period of time.

  Further, according to another seismic isolation method according to the present invention, a plurality of perforated pipes extending from the reservoir to the inside of the underground wall are arranged, and the electrolyte concentration from the reservoir is measured via the perforated pipe. Since low water is supplied to the clay-based material constituting the underground wall, water having a low electrolyte concentration can be supplied to the entire underground wall more reliably, and the pore water of the clay-based material constituting the underground wall can be supplied. The water quality can be maintained more stably.

  Further, according to another seismic isolation method according to the present invention, in addition to the boundary surface between the underground wall and the surrounding ground, or the boundary surface between the underground wall and the surrounding ground, the underground wall and the By providing a planar water-impervious member on the boundary surface with the structure, it is possible to suppress drying of the underground wall, and to increase the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground. Inhibiting and maintaining a constant swelling pressure of the clay-based material saturated with water, suppressing changes in the thickness and density of the underground wall, and maintaining the rigidity of the underground wall, Thus, it is possible to more effectively prevent the drying of the underground wall and the increase in the electrolyte concentration of pore water. For this reason, there exists an effect that the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided.

  Further, according to another seismic isolation method according to the present invention, in addition to the surrounding ground side inside the underground wall, or the structure side inside the underground wall in addition to the surrounding ground side inside the underground wall By providing a planar water-impervious member, the underground wall is prevented from drying, and the electrolyte concentration in the underground wall due to infiltration of groundwater in the surrounding ground is suppressed, and saturated with water. Since the swelling pressure of the clay-based material is kept constant, the change in thickness and density of the underground wall is suppressed, and the rigidity of the underground wall is maintained. In addition, an increase in the electrolyte concentration of pore water can be prevented more effectively. For this reason, there exists an effect that the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided. Moreover, since the water-impervious member is provided inside the underground wall, there is an effect that the water-impervious member can be easily constructed.

FIG. 1 is a front sectional view showing a first embodiment of a ground displacement absorbing base isolation structure according to the present invention. FIG. 2 is a partially enlarged view of the reservoir of FIG. FIG. 3-1 is a diagram illustrating an image of drying shrinkage of the underground wall when the groundwater level of the surrounding ground is low. FIG. 3-2 is a diagram illustrating an image in which water having a low electrolyte concentration penetrates from the reservoir to the underground wall when the groundwater level of the surrounding ground is low. FIG. 3-3 is a diagram illustrating an image in which the underground wall is always saturated with water due to water having a low electrolyte concentration penetrating from the reservoir when the groundwater level of the surrounding ground is low. FIG. 4-1 is a diagram in the case where the electrolyte concentration of the groundwater quality in the surrounding ground is high, and is a diagram illustrating an image of the shape change of the underground wall accompanying the increase in the electrolyte concentration of pore water in the underground wall. FIG. 4-2 is a diagram illustrating an image in which pore water in the underground wall is always maintained with water having a low electrolyte concentration by water having a low electrolyte concentration penetrating from the reservoir. FIG. 5-1 is a schematic perspective view showing a second example of the ground displacement absorption seismic isolation structure according to the present invention. FIG. 5-2 is a partially enlarged view of the reservoir of FIG. 5-1. FIG. 5-3 is a diagram illustrating an image in which water having a low electrolyte concentration permeates the underground wall in FIG. 5-2. FIG. 6A is a schematic perspective view showing Example 3 of the ground displacement absorption seismic isolation structure according to the present invention. FIG. 6B is a partially enlarged view of the upper end portion of the underground wall in FIG. 6A. FIG. 6-3 is a diagram illustrating an image in which water having a low electrolyte concentration permeates the underground wall in FIG. 6-2. FIG. 7-1 is a schematic perspective view showing a fourth embodiment of the ground displacement absorption seismic isolation structure according to the present invention. FIG. 7-2 is a partially enlarged view of the reservoir of FIG. 7-1. 7-3 is the elements on larger scale of the water reservoir of the modification of Example 4 of the ground displacement absorption seismic isolation structure which concerns on this invention. FIG. 8 is a schematic perspective view showing a conventional ground displacement absorbing base isolation structure. FIG. 9 is a diagram showing the relationship between the bentonite effective dry density and the swelling pressure described in FIG. FIG. 10 is a diagram comparing the relationship between the bentonite effective dry density and the swelling pressure when the pore water is pure water and when the NaCl concentration is 1 wt%.

  Hereinafter, embodiments of a ground displacement absorbing base isolation structure and a base isolation method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

First, the basic configuration of the ground displacement absorbing base isolation structure and the base isolation method according to the present invention will be described.
As shown in FIG. 1, a ground displacement absorbing seismic isolation structure 100 according to the present invention is for reducing stress during an earthquake acting on an underground structure 14 such as an open tunnel provided on a surrounding ground 12. . The underground structure 14 is a reinforced concrete structure such as a box culvert, and is constructed to extend in a predetermined direction (a direction perpendicular to the paper surface of FIG. 1) while being embedded in the upper ground 12A. The upper layer ground 12A in which the underground structure 14 is embedded is a soft ground having an elastic wave velocity Vs of, for example, 100 to 200 m / s, and exists on the lower layer ground 12B having an elastic wave velocity Vs of, for example, 300 to 500 m / s. ing.

  Between the underground structure 14 and the upper ground 12 </ b> A of the surrounding ground 12, a continuous wall-shaped underground seismic isolation wall 16 (underground wall) made of a clay-based material having water absorption and swelling properties is installed. . The underground seismic isolation wall 16 has a predetermined wall width D (thickness: see FIG. 1), is disposed in contact with the left and right sides of the underground structure 14, and extends in the extending direction of the underground structure 14. It is a continuous wall-like body. The underground seismic isolation wall 16 is disposed in the upper ground 12 </ b> A, and is provided from the ground surface portion to substantially the same depth as the lower end of the underground structure 14. The underground seismic isolation wall 16 is not limited to being provided over the entire length of the underground structure 14 to be extended, and may be provided partially in the extending direction.

  As a clay-based material constituting the underground seismic isolation wall 16, a mixture of bentonite and water (hereinafter referred to as "first mixture") or a mixture of bentonite, aggregate and water (hereinafter referred to as "second mixture"). Is used. Such a clay-based material has a characteristic that when a stress is repeatedly applied during an earthquake, it absorbs the earthquake energy by hysteresis damping and plastically deforms, and returns to its original state after the earthquake ends.

The region filled with the material comprising the first mixture is 300 to 1200 kg / m ³ in terms of bentonite effective dry density. In the material composed of the second mixture, the region filled with bentonite and water is the bentonite effective dry density (in the case of a material in which bentonite and aggregate are mixed, the density of the bentonite portion that fills the aggregate gap). It is 300 to 1200 kg / m ³ in terms of dry density. The aggregate of the second mixture may be a soil material such as sand or gravel, or an artificial material that is unlikely to be altered for a long time, such as glass beads. Further, in the case of the above-mentioned first mixture material that does not contain aggregate, it is bentonite density because it is only bentonite density, but here it is used uniformly as “bentonite effective dry density”.

  Further, the wall width D of the underground seismic isolation wall 16 is preferably 0.2 to 2.5 m, and more preferably 0.25 to 1.0 m. In addition, since use of a general construction apparatus is possible, the wall width D is good also as 0.5-1.0m.

The basic action of the ground displacement absorbing base isolation structure 100 and the base isolation method having the above configuration will be described.
As shown in FIG. 1, in the ground displacement absorbing base isolation structure 100, if a clay-based material is used as the underground seismic isolation wall 16, it can be formed into a continuous wall shape. be able to. The clay-based material has, for example, 0.6 times or less rigidity compared to the surrounding upper-layer ground 12A, so that an effect of reducing the shearing force of the underground structure 14 can be obtained, and the deformation of the ground during an earthquake is alleviated. Can exhibit seismic isolation effect.

  Further, when the clay-based material of the underground seismic isolation wall 16 is a first mixture of bentonite and water, or a second mixture of bentonite, aggregate, and water, the bentonite effective dry density is adjusted to obtain a predetermined Since the swelling pressure can be exerted, it is possible to secure a reaction force that resists the normal earth pressure received from the surrounding ground.

And in the case of the 1st mixture, since the area | region filled with bentonite and water is the range of 300-1200 kg / m < ³ > by the value of a bentonite effective dry density, if it is this density range, it will be shown in FIG. Thus, the water absorption swelling pressure becomes 0.03 to 0.3 MPa. Therefore, assuming that the underwater mass of the ground (upper ground 12A) is about 1 g / cm ³ , the soil pressure up to a depth of 30 m can be withstood when the lateral earth pressure is 1 times the earth covering pressure. It can be made more effective by appropriately adjusting the material density according to the depth at which the underground seismic isolation wall 16 is installed.

  Similarly, the shear stiffness of bentonite also has different characteristics depending on the bentonite effective dry density. This is because, when the proportion of the aggregate volume in the material is 50% or less, the aggregate particles do not form a particle structure in which the aggregate particles contact each other and transmit stress to each other. This is because a bentonite gel (a mixture of bentonite and water) is interposed between them, so that the shear characteristics of the material are mainly determined by the characteristics of the bentonite gel. Therefore, by adjusting the bentonite effective dry density, the shear stiffness of the contact material can be made smaller than the surrounding ground, absorbing the ground deformation by repeated deformation at the time of earthquake, reducing the adverse effect on the frame, The effect of absorbing external force can be expected.

  Moreover, since it is characterized by fully utilizing the water absorption and expansion characteristics of bentonite, the construction is easy even in a ground environment where the groundwater level is high. That is, if the surrounding ground is not completely dry, the water retention capacity of bentonite is maintained, so that the wall width D and the material density can be maintained for a long time. Furthermore, since the clay-based material, which is an inorganic natural mineral, is used as the underground seismic isolation wall 16, there is no need to worry about the environmental impact on the surroundings.

  Here, it is known that the material of the underground seismic isolation wall 16 is considerably less rigid than the result of Toyoura sand (see, for example, FIG. 3 of Patent Document 2). Moreover, since the nonlinear characteristic of the material of the underground seismic isolation wall 16 draws a hysteresis during an earthquake (during repeated shearing), it is known to be suitable as a hysteresis damping material (damper material) by energy absorption ( For example, see FIG. 4 of Patent Document 2.) This hysteresis damping effect can be increased by mixing sand into bentonite. Therefore, the constraint pressure dependency is not as great as that of the ground material, and the bentonite effective dry density can be appropriately adjusted.

  In addition, bentonite has the property of absorbing and expanding, and even if cracking or some damage occurs, the damage can be self-repaired under the condition that groundwater penetrates. That is, there is an advantage that the wall width D of the underground seismic isolation wall 16 is not reduced by earth pressure from the surrounding ground. Further, since the clay-based material constituting the underground seismic isolation wall 16 is a natural inorganic mineral material, there is no alteration, and the water retention state is hardly changed, so that there is an effect that maintenance is unnecessary.

  Moreover, if the wall width D of the underground seismic isolation wall 16 is in the range of 0.2 to 2.5 m, the shear force reduction rate (the shear generated in the underground structure 14 when the underground isolation wall 16 is provided). The value obtained by dividing the force by the shearing force generated in the underground structure when there is no underground seismic isolation wall 16 is smaller than 1, and the shearing force of the underground structure 14 is reduced. This is because the countermeasure area (planar area where the underground seismic isolation wall 16 is arranged) is smaller than the conventional polymer construction method when the vertical cylinder-shaped polymer improved soil is disposed in the ground. A great reduction effect can be obtained, and the cost can be reduced.

  When the underground structure 14 is newly constructed, the underground seismic isolation wall 16 is constructed so as to be in contact therewith. In such a case, a construction space necessary around the underground structure 14 is constructed. Can be reduced. Moreover, although it is assumed that the underground seismic isolation wall 16 is constructed later for the underground in the vicinity of the existing underground structure 14, it is effective even if the wall width D of the underground seismic isolation wall 16 is small. Therefore, it can also be installed as a seismic isolation measure for existing structures in a narrow place where there are adjacent underground structures or inside a narrow site. Further, even in the seismic reinforcement work for the underground structure 14 that does not satisfy the earthquake resistance standard, the ground displacement absorbing seismic isolation structure 100 is used, so that the underground structure 14 that is difficult to be seismically strengthened by the existing structure is used. It can be used effectively for reinforcement.

  Next, a characteristic configuration of the ground displacement absorbing base isolation structure and the base isolation method according to the present invention will be described.

Example 1
First, Example 1 of the present invention will be described.
As shown in FIG. 1, the ground displacement absorption seismic isolation structure 100 according to the first embodiment of the present invention stores water W having a low electrolyte concentration on the top surface 16 a on the surface GL side of the underground seismic isolation wall 16. The water reservoir 18 is further provided.

  As shown in FIG. 2, the reservoir 18 has a U-shaped groove formed by two vertical walls 18a and a bottom plate 18b connecting the lower ends thereof, and the top end portion is covered with a lid plate 18c. Yes. The bottom plate 18b has a water permeable structure, and water W having a low electrolyte concentration stored in the reservoir 18 can penetrate the bottom plate 18b and penetrate the upper end portion 16a of the underground seismic isolation wall 16 below the bottom plate 18b. Yes. The water level WL of the low-electrolyte water W in the reservoir 18 is set to be higher than the groundwater level GWL (not shown) of the surrounding ground 12, and the groundwater of the surrounding ground 12 flows into the reservoir 18. It is supposed not to. The width E of the bottom plate 18b is set to be larger than the wall width D of the underground seismic isolation wall 16, and the range covered by the permeate flow of water W having a low electrolyte concentration from the bottom plate 18b is the underground isolation. The entire upper surface of the upper end portion 16a of the wall 16 is covered.

The operation and action of the above configuration will be described.
First, the operation and action when the groundwater level GWL of the surrounding ground 12 is extremely low will be described.

  3-1 to 3-3 are diagrams in the case where the groundwater level GWL of the surrounding ground 12 is extremely low. Fig. 3-1 shows an image of drying shrinkage of the underground seismic isolation wall 16 when there is no penetration of water W having a low electrolyte concentration, and Fig. 3-2 shows the electrolyte concentration from the reservoir 18 to the underground isolation wall 16 An image of low water W penetrating, FIG. 3-3 shows an image in which the underground seismic isolation wall 16 is always saturated with water by the water W having a low electrolyte concentration penetrating from the reservoir 18.

  As shown in FIG. 3-1, when the groundwater level GWL of the surrounding ground 12 is remarkably low and there is no penetration of water W having a low electrolyte concentration, the underground seismic isolation wall 16 above the groundwater level GWL is configured. Since the clay-based material is dried and shrunk, the upper part of the underground seismic isolation wall 16 is dried and shrunk to reduce the wall width D and increase the rigidity. Therefore, the lateral earth pressure acting on the underground seismic isolation wall 16 is reduced. As a result, the seismic isolation performance declines.

  On the other hand, as shown in FIGS. 3-2 and 3-3, water W having a low electrolyte concentration is always supplied to the upper end portion 16a of the underground seismic isolation wall 16 by the downward osmotic flow from the reservoir 18. In this case, since the water-absorbing and swelling clay-based material constituting the underground seismic isolation wall 16 is always saturated with water and the water retention capability is maintained, the underground seismic isolation wall 16 does not shrink and dry. The wall width D of the base isolation wall 16 and its constituent material density can be maintained constant for a long period of time, and the rigidity of the underground base isolation wall 16 can be kept small. As a result, since the displacement absorption capacity of the underground seismic isolation wall 16 is maintained, there is no possibility that the seismic isolation performance is deteriorated. Therefore, according to Example 1 of this invention, the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided.

Next, the operation and action when the electrolyte concentration of the groundwater quality in the surrounding ground 12 is high will be described.
FIGS. 4-1 and FIGS. 4-2 are figures when the electrolyte concentration of the groundwater quality of the surrounding ground 12 is high. FIG. 4A is an image of a morphological change accompanying an increase in the electrolyte concentration of pore water in the underground seismic isolation wall 16 when there is no penetration of water W having a low electrolyte concentration, and FIG. 4B penetrates from the reservoir 18. It shows an image in which the pore water in the underground seismic isolation wall 16 is always maintained by water having a low electrolyte concentration by the water W having a low electrolyte concentration.

  As shown in FIG. 4-1, when the electrolyte concentration of the groundwater quality of the surrounding ground 12 is high (for example, when the water quality is close to seawater like a landfill near the coast), the underground seismic isolation wall 16 is configured. The electrolyte concentration of pore water in the clay-based material increases, and the water absorption expansion pressure decreases (see FIG. 10). As a result, the water absorption expansion pressure that can resist the lateral earth pressure acting on the underground seismic isolation wall 16 cannot be exhibited, the underground seismic isolation wall 16 is deformed by the earth pressure, the wall width D is reduced, and the gap is reduced. As the water is drained, the density of the constituent materials increases and the rigidity increases. In this case, since the displacement absorption capacity of the underground seismic isolation wall 16 is reduced, the seismic isolation performance is lowered as a result. Furthermore, the ground around the underground wall is deformed to the side, and there is a concern that ground surface settlement may occur.

  On the other hand, as shown in FIG. 4B, the water W having a lower electrolyte concentration due to the downward seepage flow from the reservoir 18 is always present at the upper end 16a of the underground seismic isolation wall 16 (the electrolyte is lower than the groundwater of the surrounding ground 12). When there is a supply of low-concentration water), the pore water of the clay-based material constituting the underground seismic isolation wall 16 is always saturated with water having a low electrolyte concentration, and the underground isolation due to the infiltration of groundwater in the surrounding ground 12 An increase in the electrolyte concentration of pore water in the seismic wall 16 is suppressed. Since the swelling pressure of the clay-based material saturated with water having a low electrolyte concentration is kept constant, the change in the wall width D of the underground seismic isolation wall 16 and the density of its constituent materials is suppressed, and the underground isolation wall The rigidity of 16 can be kept small. As a result, since the displacement absorption capacity of the underground seismic isolation wall 16 is maintained, there is no possibility that the seismic isolation performance is deteriorated. In addition, ground deformation and ground subsidence around the underground wall do not occur. For this reason, even if it is a case where the electrolyte concentration of the groundwater of the surrounding ground 12 is comparatively high like seawater, long-term stable and seismic isolation performance can be exhibited.

(Example 2)
Next, a second embodiment of the present invention will be described.
As shown in FIGS. 5A and 5B, the ground displacement absorbing base isolation structure 200 according to the second embodiment of the present invention is the same structure as the ground displacement absorbing base isolation structure 100 according to the first embodiment. A water reservoir 20 for storing water W having a low electrolyte concentration is provided on the upper end portion 16a on the ground surface GL side of the underground seismic isolation wall 16, and a porous tube 22 is disposed below the water reservoir 20 It is.

  The water reservoir 20 has a structure similar to that of the water reservoir 18 of the first embodiment, and as shown in FIG. 5B, a U plate composed of two vertical walls 20a and a bottom plate 20b connecting the lower ends thereof. It has a groove shape, and its top end portion is covered with a cover plate 20c. An opening 24 communicating with the porous tube 22 is provided at the center in the width direction of the bottom plate 20b.

  The perforated tube 22 is a tube having a large number of holes in the tube body, and is provided inside the underground seismic isolation wall 16 in a manner extending vertically downward from the bottom plate 20b of the reservoir 20, and the reservoir 20 A plurality are arranged at predetermined intervals along the extending direction. Here, the water level WL of the water W having a low electrolyte concentration in the reservoir 20 is set to be higher than the groundwater level GWL (not shown) of the surrounding ground 12, and the groundwater of the surrounding ground 12 is stored in the reservoir 20. It does not flow into the interior.

  According to this configuration, water W having a low electrolyte concentration stored in the reservoir 20 can enter the perforated tube 22 through the opening 24 of the bottom plate 20b and penetrate the underground seismic isolation wall 16 around the water W. Water W having a low electrolyte concentration can be more reliably supplied to the entire interior of the underground seismic isolation wall 16 through the porous tube 22. For this reason, the quality of the pore water of the clay-based material constituting the underground seismic isolation wall 16 can be more reliably and stably maintained. Therefore, according to the second embodiment of the present invention, it is possible to provide a ground displacement absorption seismic isolation structure with better long-term stability.

Next, the operation and action when the electrolyte concentration of the groundwater quality in the surrounding ground 12 is high will be described.
FIG. 5-3 is an image in which the pore water in the underground seismic isolation wall 16 is always maintained by the low electrolyte concentration water by the low electrolyte concentration water W penetrating from the porous tube 22 below the reservoir 20. Show.

  As shown in FIG. 5-3, there is a supply of water W having a low electrolyte concentration (water having a lower electrolyte concentration than the ground water in the surrounding ground 12) due to the seepage flow from the porous tube 22 inside the underground seismic isolation wall 16. In this case, the pore water of the clay-based material constituting the underground seismic isolation wall 16 is always saturated with water having a low electrolyte concentration, and the electrolyte concentration of the pore water in the underground seismic isolation wall 16 due to the infiltration of groundwater in the surrounding ground 12. Rise is suppressed. Since the swelling pressure of the clay-based material saturated with water having a low electrolyte concentration is kept constant, the change in the wall width D of the underground seismic isolation wall 16 and the density of its constituent materials is suppressed, and the underground isolation wall The rigidity of 16 can be kept small. As a result, since the displacement absorption capacity of the underground seismic isolation wall 16 is maintained, there is no possibility that the seismic isolation performance is deteriorated. In addition, ground deformation and ground subsidence around the underground wall do not occur. Since the pore water quality of the clay-based material constituting the underground seismic isolation wall 16 can be more reliably and stably maintained, the electrolyte concentration of the groundwater in the surrounding ground 12 is relatively high like seawater. However, the required seismic isolation performance can be demonstrated stably over the long term.

Example 3
Next, Embodiment 3 of the present invention will be described.
As shown in FIGS. 6A and 6B, the ground displacement absorbing base isolation structure 300 according to the third embodiment of the present invention is similar to the ground displacement absorbing base isolation structure 200 according to the second embodiment. The upper end portion 16a of the underground seismic isolation wall 16 is provided with a supply pipe 26 for supplying the underground seismic isolation wall 16 with water W having a low electrolyte concentration for passing or storing water. The perforated tube 28 is arranged in the above.

  The supply pipe 26 basically has the same function as the water reservoir 20 of the above-described second embodiment, is embedded in the upper end portion 16 a of the underground seismic isolation wall 16, and extends along the underground seismic isolation wall 16. The pipe has a circular cross section extending in the horizontal direction. An opening 30 communicating with the porous tube 28 is provided in the lower portion of the supply tube 26. The upper end portion 16 a of the underground seismic isolation wall 16 is covered with a cover plate 32.

  The perforated tube 28 is a tube having a large number of holes in the tube body, and is provided inside the underground seismic isolation wall 16 in a manner extending vertically downward from the opening 30 of the supply tube 26. A plurality are arranged at predetermined intervals along the extending direction. Here, since the water of the supply pipe 26 is set to be maintained at a higher water pressure than the groundwater level GWL of the surrounding ground 12, the groundwater of the surrounding ground 12 does not flow into the underground seismic isolation wall 16.

  According to this configuration, water W having a low electrolyte concentration passed through or stored in the supply pipe 26 can enter the perforated pipe 28 through the opening 30 and permeate the underground seismic isolation wall 16 therearound. Water W having a low electrolyte concentration can be more reliably supplied to the entire interior of the underground seismic isolation wall 16 through the porous tube 28. For this reason, the quality of the pore water of the clay-based material constituting the underground seismic isolation wall 16 can be more reliably and stably maintained. Therefore, according to the third embodiment of the present invention, it is possible to provide a ground displacement absorption seismic isolation structure with better long-term stability.

Next, the operation and action when the electrolyte concentration of the groundwater quality in the surrounding ground 12 is high will be described.
FIG. 6-3 is an image in which the pore water of the underground seismic isolation wall 16 is always maintained by water having a low electrolyte concentration by the water W having a low electrolyte concentration penetrating from the porous pipe 28 below the supply pipe 26. Show.

  As shown in FIG. 6-3, there is a supply of water W having a low electrolyte concentration (water having a lower electrolyte concentration than the ground water in the surrounding ground 12) due to the permeate flow from the porous tube 28 inside the underground seismic isolation wall 16. In this case, the pore water of the clay-based material constituting the underground seismic isolation wall 16 is always saturated with water having a low electrolyte concentration, and the electrolyte concentration of the pore water in the underground seismic isolation wall 16 due to the infiltration of groundwater in the surrounding ground 12. Rise is suppressed. Since the swelling pressure of the clay-based material saturated with water having a low electrolyte concentration is kept constant, the change in the wall width D of the underground seismic isolation wall 16 and the density of its constituent materials is suppressed, and the underground isolation wall The rigidity of 16 can be kept small. As a result, since the displacement absorption capacity of the underground seismic isolation wall 16 is maintained, there is no possibility that the seismic isolation performance is deteriorated. In addition, ground deformation and ground subsidence around the underground wall do not occur. Since the pore water quality of the clay-based material constituting the underground seismic isolation wall 16 can be more reliably and stably maintained, the electrolyte concentration of the groundwater in the surrounding ground 12 is relatively high like seawater. However, the required seismic isolation performance can be demonstrated stably over the long term.

Example 4
Next, a fourth embodiment of the present invention will be described.
As shown in FIGS. 7-1 and 7-2, the ground displacement absorbing base isolation structure 400 according to the fourth embodiment of the present invention is the same as the ground displacement absorbing base isolation structure 100 of the first embodiment. A planar water-impervious sheet 34 (water-impervious member) is provided on the surrounding ground 12 side inside the seismic isolation wall 16 and the structure 14 side.

  The water-impervious sheet 34 is preferably provided so as to cover the entire side surface of the underground seismic isolation wall 16, and is preferably configured using a water-impervious material such as a rubber-based or polymer-based material. As described above, the structure in which the underground seismic isolation wall 16 is sandwiched from both sides by the planar water-impervious sheet 34 allows the water W having a low electrolyte concentration from the reservoir 18 to be efficiently compared to the underground seismic isolation wall 16. Therefore, drying of the underground seismic isolation wall 16 and increase in the electrolyte concentration of pore water can be more effectively prevented. The swelling pressure of the clay-based material of the underground seismic isolation wall 16 saturated with water is kept constant, and changes in the thickness and density of the underground isolation wall 16 are suppressed, and the rigidity of the underground isolation wall 16 is increased. Can be kept small. Therefore, it is possible to provide a ground displacement absorption seismic isolation structure with excellent long-term stability. In addition, as a construction method of the water shielding sheet 34, for example, a method described in Japanese Patent No. 4405936 or Japanese Patent No. 4771157 may be applied. By using such a method, construction of the water shielding sheet 34 can be performed relatively easily.

  Note that a planar water-impervious sheet 36 made of the same material as the water-impervious sheet 34 may be provided on the boundary surfaces of the vertical walls 18 a and the bottom plate 18 b of the reservoir 18 and the surrounding ground 12. By doing so, direct leakage of water W from the reservoir 18 to the surrounding ground 12 is suppressed, and water W having a low electrolyte concentration is supplied from the reservoir 18 to the underground seismic isolation wall 16 more intensively. Is possible.

  Further, as in the second embodiment, the water shielding sheets 34 and 36 of the fourth embodiment are applied to a structure in which a plurality of porous tubes 22 extending vertically downward from the water reservoir 20 are disposed (see FIG. 5-2). May be applied. Similarly, the water-impervious sheet 34 according to the fourth embodiment is applied to a structure (see FIG. 6B) in which a plurality of perforated tubes 28 extending vertically downward from the supply pipe 26 are disposed as in the third embodiment. You may apply.

(Modification of Example 4)
Next, a modification of the fourth embodiment of the present invention will be described.
As shown in FIG. 7-3, the ground displacement absorbing base isolation structure 401 according to the modification of the fourth embodiment of the present invention is a planar shielding structure in the structure of the ground displacement absorbing base isolation structure 400 of the fourth embodiment. A water sheet 34 a (water-impervious member) is provided on the boundary surface between the underground seismic isolation wall 16 and the surrounding ground 12 and on the boundary surface between the underground seismic isolation wall 16 and the structure 14.

  The water shielding sheet 34a is preferably provided so as to cover the entire side surface of the underground seismic isolation wall 16 in the same manner as the water shielding sheet 34 described in Example 4 above, and is made of rubber or polymer material. It is desirable to use an aqueous material. As described above, by adopting a structure in which the underground seismic isolation wall 16 is sandwiched from both sides by the planar water-impervious sheet 34, the water W having a low electrolyte concentration from the water reservoir 18 is grounded as in the fourth embodiment. It can supply efficiently with respect to the middle seismic isolation wall 16, and can prevent the drying of the underground seismic isolation wall 16 and the electrolyte concentration rise of pore water more effectively. The swelling pressure of the clay-based material of the underground seismic isolation wall 16 saturated with water is kept constant, and changes in the thickness and density of the underground isolation wall 16 are suppressed, and the rigidity of the underground isolation wall 16 is increased. Can be kept small. Therefore, it is possible to provide a ground displacement absorption seismic isolation structure with excellent long-term stability.

  As in the fourth embodiment, the planar water-impervious sheet 36a made of the same material as the water-impervious sheet 34a with respect to the boundary surface between the vertical wall 18a and the bottom plate 18b of the reservoir 18 and the surrounding ground 12 is used. May be provided. Further, similarly to Example 4 above, the water shielding sheets 34 and 36 are applied to or supplied to a structure in which a plurality of porous tubes 22 extending vertically downward from the reservoir 20 (see FIG. 5-2) are provided. The water shielding sheet 34 may be applied to a structure (see FIG. 6B) in which a plurality of perforated tubes 28 extending vertically downward from the tube 26 are disposed.

  As described above, according to the ground displacement absorption seismic isolation structure according to the present invention, a continuous wall-shaped underground wall made of a clay-based material having water absorption swelling property is provided between the surrounding ground and the structure. In the ground displacement absorption seismic isolation structure, a water reservoir for storing water with low electrolyte concentration is provided at the top surface of the underground wall, so that it can resist the normal earth pressure received from the surrounding ground by the underground wall, Reservoir provided at the upper end of the underground wall as well as the basic effect of the seismic isolation structure that can reduce stress on underground structures such as open tunnels By constantly supplying water to the underground wall, the water retention capacity of the water-absorbing swellable clay-based material that constitutes the underground wall is maintained. Can be maintained. For this reason, the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided.

  In addition, according to another ground displacement absorption seismic isolation structure according to the present invention, since the water level of the reservoir is higher than the groundwater level of the surrounding ground, water having a low electrolyte concentration is always supplied from the upper end of the underground wall. By supplying, it can suppress that the electrolyte density | concentration of the pore water of the clay-type material which comprises an underground wall rises. Therefore, for example, when a clay-based material is composed of a mixture of bentonite and water or a mixture of bentonite, aggregate and water, this material exhibits a predetermined swelling pressure. It is possible to resist the normal earth pressure received from the water, and by constantly supplying water with a low electrolyte concentration, changes in the thickness of the underground wall and changes in the density of the constituent materials are suppressed. For this reason, the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided.

  In addition, according to another ground displacement absorption seismic isolation structure according to the present invention, a plurality of perforated pipes extending from the reservoir to the inside of the underground wall are disposed, so that the concentration of electrolyte stored in the reservoir is low. Water can be more reliably supplied to the entire underground wall through the perforated pipe, and the quality of the pore water of the clay-based material constituting the underground wall can be more stably maintained.

  Moreover, according to another ground displacement absorption isolation structure according to the present invention, in addition to the boundary surface between the underground wall and the surrounding ground, or the boundary surface between the underground wall and the surrounding ground, the underground By providing a planar water-impervious member at the boundary surface between the wall and the structure, it is possible to suppress the drying of the underground wall, and the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground The rise of the water is suppressed, the swelling pressure of the clay-based material saturated with water is kept constant, the change in thickness and density of the underground wall is suppressed, and the rigidity of the underground wall is maintained. The water shielding member can more effectively prevent the drying of the underground wall and the increase in the electrolyte concentration of pore water. For this reason, the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided.

  Further, according to another ground displacement absorption seismic isolation structure according to the present invention, in addition to the surrounding ground side inside the underground wall or the surrounding ground side inside the underground wall, the inside of the underground wall By providing a planar water-impervious member on the structure side, the drying of the underground wall is suppressed, and an increase in the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground is suppressed, Since the swelling pressure of the clay-based material saturated with water is kept constant, the change in thickness and density of the underground wall is suppressed, and the rigidity of the underground wall is maintained. It is possible to more effectively prevent wall drying and increase in electrolyte concentration of pore water. For this reason, the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided. Moreover, since the water shielding member is provided inside the underground wall, the water shielding member can be easily constructed.

  Further, according to the seismic isolation method according to the present invention, the structure is isolated by providing a continuous wall-shaped underground wall made of a clay-based material having water absorption swelling between the surrounding ground and the structure. In this method, a water reservoir for storing water having a low electrolyte concentration is provided at the upper surface of the underground wall, and the electrolyte concentration is always applied to the clay-based material constituting the underground wall from above via the reservoir. By supplying low water, the drying of the clay-based material is suppressed, and the rigidity of the clay-based material saturated with water is maintained. For this reason, even if the groundwater level of the surrounding ground is remarkably low from the ground surface and the clay-based material constituting the underground wall is likely to dry and shrink, the supply of water with a low electrolyte concentration from above Since the drying shrinkage of the underground wall is suppressed and the thickness is kept constant, the rigidity of the underground wall is kept small. Therefore, the required seismic isolation performance can be exhibited stably for a long time.

  Further, according to another seismic isolation method according to the present invention, the structure can be obtained by providing a continuous wall-like underground wall made of a clay-based material having water absorption swelling between the surrounding ground and the structure. In the seismic isolation method, a water storage layer for storing water having an electrolyte concentration lower than ground water of the surrounding ground is provided at an upper end on the surface side of the underground wall, and the water storage is performed on the clay-based material constituting the underground wall. By constantly supplying water with a low electrolyte concentration from above through a layer, an increase in the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground is suppressed, and the clay saturated with water The swelling pressure of the system material is kept constant, the change in thickness and density of the underground wall is suppressed, and the rigidity of the underground wall is maintained. For this reason, even if the electrolyte concentration of the groundwater in the surrounding ground is relatively high, such as seawater, the underground wall stiffness is kept small by supplying water with a low electrolyte concentration from above the underground wall. Is done. Therefore, the required seismic isolation performance can be exhibited stably for a long period of time.

  Further, according to another seismic isolation method according to the present invention, a plurality of perforated pipes extending from the reservoir to the inside of the underground wall are arranged, and the electrolyte concentration from the reservoir is measured via the perforated pipe. Since low water is supplied to the clay-based material constituting the underground wall, water having a low electrolyte concentration can be supplied to the entire underground wall more reliably, and the pore water of the clay-based material constituting the underground wall can be supplied. The water quality can be maintained more stably.

  Further, according to another seismic isolation method according to the present invention, in addition to the boundary surface between the underground wall and the surrounding ground, or the boundary surface between the underground wall and the surrounding ground, the underground wall and the By providing a planar water-impervious member on the boundary surface with the structure, it is possible to suppress drying of the underground wall, and to increase the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground. Inhibiting and maintaining a constant swelling pressure of the clay-based material saturated with water, suppressing changes in the thickness and density of the underground wall, and maintaining the rigidity of the underground wall, Thus, it is possible to more effectively prevent the drying of the underground wall and the increase in the electrolyte concentration of pore water. For this reason, the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided.

  Further, according to another seismic isolation method according to the present invention, in addition to the surrounding ground side inside the underground wall, or the structure side inside the underground wall in addition to the surrounding ground side inside the underground wall By providing a planar water-impervious member, the underground wall is prevented from drying, and the electrolyte concentration in the underground wall due to infiltration of groundwater in the surrounding ground is suppressed, and saturated with water. Since the swelling pressure of the clay-based material is kept constant, the change in thickness and density of the underground wall is suppressed, and the rigidity of the underground wall is maintained. In addition, an increase in the electrolyte concentration of pore water can be prevented more effectively. For this reason, the ground displacement absorption seismic isolation structure excellent in long-term stability can be provided. Moreover, since the water shielding member is provided inside the underground wall, the water shielding member can be easily constructed.

  As described above, the ground displacement absorption seismic isolation structure and the seismic isolation method according to the present invention are useful for reducing stress on underground structures such as open tunnels during an earthquake. Suitable for long-term stability in seismic structures.

100 Ground displacement absorption seismic isolation structure (Example 1)
200 Ground displacement absorption seismic isolation structure (Example 2)
300 Ground displacement absorption isolation structure (Example 3)
400 Seismic displacement absorption isolation structure (Example 4)
401 Ground displacement absorbing base isolation structure (modified example of Example 4)
12 Ground around 14 Underground structure 16 Seismic isolation wall (underground wall)
16a Upper end 18, 20 Reservoir 18a, 20a Vertical wall 18b, 20b Bottom plate 18c, 20c, 32 Cover plate 22, 28 Perforated tube 24, 30 Opening 26 Supply tube 34, 34a Water shielding sheet (water shielding member)
36, 36a Water-impervious sheet W Water with low electrolyte concentration GL Surface WL Water level GWL Groundwater level

Claims (10)

In the ground displacement absorption seismic isolation structure with a continuous wall-shaped underground wall made of clay-based material having water absorption and swelling between the surrounding ground and the structure,
A ground displacement absorbing seismic isolation structure characterized in that a water reservoir for storing water having a low electrolyte concentration is provided at the upper surface of the underground wall on the surface side.   The ground displacement absorbing seismic isolation structure according to claim 1, wherein the water level of the reservoir is higher than the groundwater level of the surrounding ground.   The ground displacement absorbing seismic isolation structure according to claim 1 or 2, wherein a plurality of perforated pipes extending from the reservoir to the inside of the underground wall are disposed.   In addition to the boundary surface between the underground wall and the surrounding ground, or the boundary surface between the underground wall and the surrounding ground, a planar water-impervious member is provided on the boundary surface between the underground wall and the structure. This suppresses drying of the underground wall, suppresses an increase in the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground, and reduces the swelling pressure of the clay-based material saturated with water. The ground displacement according to any one of claims 1 to 3, wherein the rigidity of the underground wall is maintained by maintaining constant and suppressing changes in thickness and density of the underground wall. Absorption seismic isolation structure.   By providing a planar water-impervious member on the peripheral ground side inside the underground wall, or on the structure side inside the underground wall in addition to the peripheral ground side inside the underground wall, the underground Suppressing the drying of the wall, suppressing an increase in the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground, maintaining a constant swelling pressure of the clay-based material saturated with water, The ground displacement absorption seismic isolation structure according to any one of claims 1 to 3, wherein changes in thickness and density of the underground wall are suppressed to maintain the rigidity of the underground wall. A seismic isolation method for the structure by providing a continuous wall-shaped underground wall made of a clay-based material having water absorption and swelling between the surrounding ground and the structure,
A water reservoir for storing low electrolyte concentration water is provided at the upper surface of the underground wall, and water having a low electrolyte concentration is always supplied from above to the clay-based material constituting the underground wall. A seismic isolation method characterized by suppressing drying of the clay-based material and maintaining the rigidity of the clay-based material saturated with water. A seismic isolation method for the structure by providing a continuous wall-shaped underground wall made of a clay-based material having water absorption and swelling between the surrounding ground and the structure,
A water reservoir for storing water having a lower electrolyte concentration than the ground water of the surrounding ground is provided at the upper surface of the ground wall on the surface side, and the clay-based material constituting the underground wall is always placed from above through the water reservoir. By supplying water having a low electrolyte concentration, an increase in the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground is suppressed, and the swelling pressure of the clay-based material saturated with water is kept constant. And maintaining the rigidity of the underground wall by suppressing changes in thickness and density of the underground wall.   A plurality of perforated pipes extending from the reservoir to the inside of the underground wall are arranged, and the low electrolyte concentration water from the reservoir is supplied to the clay-based material constituting the underground wall through the perforated pipe. The seismic isolation method according to claim 6 or 7, characterized in that:   In addition to the boundary surface between the underground wall and the surrounding ground, or the boundary surface between the underground wall and the surrounding ground, a planar water-impervious member is provided on the boundary surface between the underground wall and the structure. This suppresses drying of the underground wall, suppresses an increase in the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground, and reduces the swelling pressure of the clay-based material saturated with water. The seismic isolation according to any one of claims 6 to 8, wherein the seismic isolation is maintained constant, and changes in thickness and density of the underground wall are suppressed to maintain rigidity of the underground wall. Method.   By providing a planar water-impervious member on the peripheral ground side inside the underground wall, or on the structure side inside the underground wall in addition to the peripheral ground side inside the underground wall, the underground Suppressing the drying of the wall, suppressing an increase in the electrolyte concentration of pore water in the underground wall due to infiltration of groundwater in the surrounding ground, maintaining a constant swelling pressure of the clay-based material saturated with water, The seismic isolation method according to any one of claims 6 to 8, wherein changes in thickness and density of the underground wall are suppressed to maintain rigidity of the underground wall.

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