JP4824441B2 - Seismic isolation structure and seismic isolation device - Google Patents

Description

  The present invention relates to a seismic isolation structure and a seismic isolation device that exhibit a seismic isolation effect by forcibly liquefying the ground.

  In landfills and alluvial river deposits, relatively loose sand often accumulates, so the ground may liquefy during an earthquake, causing ground subsidence, sand blowing, and fountain. If a foundation building is built directly on the ground where such liquefaction is possible, the support capacity of the ground will be lost due to liquefaction in the event of an earthquake, and damage such as settlement of the building or tilting of the building will occur.

  For this reason, in the past, methods have been adopted to prevent damage to buildings by improving the ground for all liquefiable formations and increasing the strength of the ground directly below the ground. .

  On the other hand, in the ground where liquefaction is possible and soft viscous ground, the ground nonlinearity appears remarkably at the time of an earthquake, so that the shear strain of the ground increases and the attenuation increases. This attenuation is the hysteresis attenuation of the ground due to repeated shearing due to the earthquake, and since the strain generated in the liquefied ground is large, the hysteresis attenuation is also increased.

  Therefore, the earthquake motion input from the deep part of the ground is not easily transmitted to the ground surface. In other words, due to the liquefaction of the ground, the ground surface is less likely to shake than the underground part.

  It has also been confirmed from the observation record of the Great Hanshin Earthquake that the vibration acceleration on the ground surface is smaller than the vibration acceleration in the ground due to the liquefaction attenuation effect of the ground.

  Therefore, seismic isolation structures using liquefaction of the ground have been proposed.

  In the ground seismic isolation structure 200 of Patent Document 1, as shown in FIG. 4, a structure 206 is provided on the soft ground 204 on the hard ground 202, and the soft ground 204 below the structure 206 is not yet formed. The ground improvement body 210 is improved so as to leave the improved portion 208.

  Therefore, when the soft ground 204 is liquefied by the earthquake, the history attenuation is caused and the seismic isolation effect can be exerted on the structure 206.

  However, since Patent Document 1 does not forcibly generate liquefaction but naturally liquefies, there is no confirmation that the liquefaction is surely caused by an earthquake. Therefore, it is difficult to design the strength of the structure assuming liquefaction.

  In the seismic isolation structure 212 of Patent Document 2, as shown in FIG. 5, a foundation pile 214 for supporting the building 216 is provided on the support ground 218, and in the ground 220 between the support ground 218 and the building 216, A saturated sandy soil layer 222 is formed. An injection pipe 230 connected to the compressed air storage tank 232 via the on-off valve 228 is piped along the foundation pile 214, and the injection port 234 of the injection pipe 230 is provided at a position in contact with the sandy soil layer 222. It has been.

  In the event of an earthquake, the control device 226 opens the on-off valve 228 in response to a signal from the seismometer 224 to inject compressed air from the injection port 234 of the injection pipe 230, and the sandy soil layer 222 saturated by this pressure is forced to be liquid. To form a liquefied layer 236.

  Therefore, this liquefied layer 236 can significantly reduce the shear rigidity of the soil, and can suppress the earthquake motion vertically upward propagating in the ground 220.

  However, since the sandy soil layer 222 of Patent Document 2 is not surrounded by a small water-permeable material, even if pressure is applied to the sandy soil layer 222, the generated excess pore water pressure is immediately dissipated. It is feared that it will end up.

In addition, since the building 216 is supported by the foundation pile 214, seismic motion transmitted from the supporting ground 218 to the foundation pile 214 or from the ground 220 other than the sandy soil layer 222 to the foundation pile 214 is propagated to the building 216. It is also possible.
JP 2003-20659 A JP-A-6-108477

  In view of such facts, the present invention has an object to provide a seismic isolation structure and a seismic isolation device that can reliably liquefy the ground and exhibit a seismic isolation effect when there is an input exceeding a predetermined seismic force. To do.

The invention according to the first aspect includes a water shielding layer surrounding the structure on the soft ground, surrounding the soft ground and reaching the hard ground or the impermeable layer, and the soft ground surrounded by the water shielding layer. And pressurizing means for increasing the water pressure inside.

In the first aspect of the invention, the water shielding layer surrounding the structure on the soft ground and surrounding the soft ground reaches the hard ground or the impermeable layer. And the water pressure in the soft ground surrounded by the water shielding layer is raised by the pressurizing means.

  As a result, the soft ground supporting the structure can be liquefied reliably when there is an input exceeding the specified seismic force, and the seismic isolation effect can be exerted to reduce the seismic input to the structure. Can do.

  Also, regardless of the magnitude of the seismic force, the soft ground can be liquefied forcibly when necessary to reduce the seismic input to the structure, enabling design with reduced structure strength and reducing construction costs. it can.

  Moreover, since the soft ground is surrounded by the structure, the water-impervious layer, and the hard ground or impermeable layer, it is possible to prevent the excess pore water pressure generated during liquefaction from being immediately dissipated. . Therefore, it can liquefy more reliably and can further accelerate liquefaction.

According to a second aspect of the present invention, in the first aspect, the underground portion of the structure or the structure is formed such that the soft ground layer is left between the structure and the hard ground or the impermeable layer. It is characterized by the fact that there is a foundation part.

In the invention of the second aspect , the structure is provided with an underground part or a foundation part. However, the underground part or the foundation part of the structure is provided so as to leave a soft ground layer between the structure and the hard ground or impermeable layer.

  Thereby, compared with the case where an underground part or a foundation part is not provided, the thickness of the layer of the soft ground which supports a structure becomes small. Therefore, it is possible to prevent the structure from sinking more than necessary when the water pressure of the raised soft ground is restored after the earthquake stops and the excess pore water pressure in the soft ground is dissipated.

According to a third aspect of the present invention, in the first aspect, a ground improvement layer of the soft ground is provided so as to leave the soft ground layer between the structure and the hard ground or the impermeable layer. It is characterized by that.

In the invention of the third aspect , the ground improvement layer of the soft ground is provided. However, this ground improvement layer is provided so as to leave a soft ground layer between the structure and the hard ground or impermeable layer.

  Thereby, the thickness of the layer of the soft ground which supports a structure becomes small compared with the case where a ground improvement layer is not provided. Therefore, it is possible to prevent the structure from sinking more than necessary when the water pressure of the raised soft ground is restored after the earthquake stops and the excess pore water pressure in the soft ground is dissipated.

Invention of the fourth aspect, in the third embodiment, the structure is mounted, and a support portion having a projecting portion projecting to the outside of the structure, between the ground improvement layer and the overhanging portion And a damper that absorbs vertical vibration, and the damper is replaceable with a jack that expands and contracts in the vertical direction.

In the invention of the fourth aspect , the structure is placed on the support portion. And the overhang | projection part with which this support part was equipped overhangs out of the structure. Moreover, the damper which absorbs a vertical vibration is provided between the ground improvement layer and overhang | projection part of the soft ground. Further, the damper can be replaced with a jack that can be expanded and contracted in the vertical direction.

  Thereby, the rocking | rocking of the structure on the liquefied soft ground which generate | occur | produces by an earthquake motion is reduced by a damper. When the structure is inclined, the inclination of the structure can be corrected by replacing the jack with a jack and jacking up the structure.

In the fifth aspect of the invention, a seismometer is provided in the seismic isolation structure of any one of the first to fourth aspects , and the seismometer is surrounded by the impermeable layer when it detects a P wave during an earthquake. The water pressure in the soft ground is raised by the pressurizing means.

In the fifth aspect of the invention, the seismometer is provided in the seismic isolation structure of any of the first to fourth aspects . And when a seismometer detects the P wave at the time of an earthquake, a pressurizing means is operated and the water pressure in the soft ground surrounded by the water shielding layer is raised.

  This makes it possible to reliably liquefy the ground when the S wave of the main motion arrives.

  Since this invention set it as the said structure, when there exists an input exceeding predetermined | prescribed seismic force, the ground can be liquefied reliably and the seismic isolation effect can be exhibited.

  A seismic isolation structure and a seismic isolation device according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, an example of an RC apartment house will be described, but it can be applied to any building.

  First, the seismic isolation structure 10 and the seismic isolation device 11 according to the first embodiment of the present invention will be described. FIG. 1 shows a seismic isolation structure 10 and a seismic isolation device 11 according to this embodiment.

  The RC apartment house 14 as a structure is directly supported by the foundation on the soft ground 12 in the upper layer of the hard ground 18. In addition, a ground improvement layer 16 that prevents liquefaction is formed immediately below the housing complex 14. Between the ground improvement layer 16 and the hard ground 18, the soft ground 12A is left as an unimproved layer.

  An RC continuous wall 26 as a water shielding layer is constructed so as to surround the apartment house 14, and the lower end portion of the RC continuous wall 26 reaches the hard ground 18. The soft ground 12 is surrounded by the RC continuous wall 26. In addition, the soft ground 12 between the RC continuous wall 26 and the ground improvement layer 16 located near the groundwater level is improved to a water-impermeable layer 28 having a water shielding property by a chemical injection method. Therefore, the soft ground 12 is surrounded by the RC continuous wall 26, the hard ground 18, the impermeable layer 28, and the ground improvement layer 16, and is separated from the soft ground 32 outside the RC continuous wall 26 in a generally sealed state. Yes.

  Further, the stand pipe 20 is piped substantially vertically from the ground toward the unimproved soft ground 12A layer. At the lower end of the stand pipe 20, a spout 20 </ b> A is provided at a position in contact with the unimproved soft ground 12 </ b> A layer. The upper end of the stand pipe 20 is connected to a pump 22, and by operating the pump 22, water in a water storage tank 23 provided on the roof of the apartment house 14 is injected into the stand pipe 20 under pressure. Then, the water pressure in the stand pipe 20 is raised, and the pressurized water is ejected from the spout 20A provided at the tip of the stand pipe 20. Further, a three-pronged opening / closing valve 25 is provided between the pump 22 and the upper end of the stand pipe 20, and by switching the opening / closing valve 25, connection between the pump 22 and the stand pipe 20, disconnection, An opening operation can be performed. During the shut-off operation of the on-off valve 25, the connection between the stand pipe 20 and the outside air on the ground is also cut off, so that the pressure in the soft ground 12 surrounded by the RC continuous wall 26 can be kept constant. it can. Further, when the opening / closing valve 25 is opened, the water injected into the soft ground 12 can be discharged to the drain tank 29 provided outside via the discharge pipe 27 connected to the opening / closing valve 25. A filter (not shown) is attached to the upper end portion of the stand pipe 20 to prevent the earth and sand from being discharged together with water.

  A seismometer 30 for detecting a P wave at the time of an earthquake is placed on the ground surface of the soft ground 32. The seismometer 30 is connected to the control device 24, and the control device 24 determines whether or not to operate the pump 22 from the P wave data sent from the seismometer 30, and turns the pump 22 on and off. To control.

  Next, the operation and effect of the seismic isolation structure 10 and the seismic isolation device 11 according to the first embodiment of the present invention will be described.

  As shown in FIG. 1, when an earthquake occurs and the seismometer 30 detects a P wave, the control device 24 determines whether or not to operate the pump 22 based on the magnitude of the P wave.

  When a P wave having a magnitude greater than a certain value is detected, the pump 22 is activated to inject water from the water storage tank 23 into the stand pipe 20 under pressure. And the water pressure in the stand pipe 20 is raised, and the pressurized water is ejected from the spout 20A provided in the lower end part of the stand pipe 20. As a result, the water pressure in the soft ground 12 surrounded by the RC continuous wall 26, that is, the pore water pressure rises, and the soft ground 12 is forcibly liquefied. After the liquefaction is completed, the pump 22 is stopped after the on-off valve 25 provided between the pump 22 and the stand pipe 20 is shut off so that the water pressure in the soft ground 12 does not decrease.

  As a result, when there is an input exceeding a predetermined seismic force, the soft ground 12 supporting the apartment house 14 is liquefied to exert a seismic isolation effect, and the earthquake input to the apartment house 14 is reduced. be able to.

  In addition, because the seismic force can be forcibly liquefied when necessary to reduce the seismic input to the apartment house 14 when necessary, it is possible to design the apartment house 14 with reduced strength and construction. Cost can be reduced.

  Moreover, the soft ground 12 is surrounded by the RC continuous wall 26, the hard ground 18, the impermeable layer 28, and the ground improvement layer 16, and is in a generally sealed state. Therefore, since it is possible to prevent the excess pore water pressure generated during liquefaction from being immediately dissipated, it is possible to liquefy more reliably and further to accelerate liquefaction.

  In addition, since the pump 22 is activated when the P wave (initial motion) is detected and liquefaction can be started before the S wave (main motion) arrives, liquefaction of the soft ground 12 is delayed. Can be prevented.

  After the earthquake has stopped, when the on-off valve 25 provided between the pump 22 and the stand pipe 20 is opened, the water injected by the pump 22 is naturally drained by the increased pressure in the soft ground 12. 29, the excess pore water pressure is dissipated and the soft ground 12 returns to its original state.

  Thus, since the water injected by the pump 22 is discharged, the ground does not sink after the excess pore water pressure has been dissipated, but if the water injected by the pump 22 is larger than the amount of water injected Even if it has been discharged, since the thickness of the soft ground 12A is reduced by providing the ground improvement layer 16, the apartment house 14 can be prevented from sinking more than necessary.

  The ground improvement layer 16 may be a soil cement-based improvement body, sand compacted by a sand compaction pile method, or the like, but is not limited thereto, and may be any ground improvement material that can prevent liquefaction.

  Moreover, although the RC continuous wall 26 was shown as a water-impervious layer surrounding the soft ground 12, a soil cement wall, a steel sheet pile wall, a steel pipe sheet pile wall, etc. may be used as long as it has a water-impervious property.

  In addition, the impermeable layer 28 formed near the groundwater level prevents the pressure from escaping when the water pressure in the soft ground 12 surrounded by the RC continuous wall 26 rises, and improves the sealing performance of the soft ground 12 and is effective. Although the water pressure is increased, liquefaction can be reliably generated without the impermeable layer 28.

  Next, the seismic isolation structure 34 and the seismic isolation device 35 of the 2nd Embodiment of this invention are demonstrated.

  In the second embodiment, an impermeable layer is formed at the position of the lower end portion of the RC continuous wall 26 in the first embodiment. Therefore, in the following description, the same components as those in the first embodiment are denoted by the same reference numerals and are appropriately omitted.

  FIG. 2 shows the seismic isolation structure 34 and the seismic isolation device 35 of this embodiment. An RC continuous wall 26 as a water shielding layer is constructed so as to surround the apartment house 14, and the lower end portion of the RC continuous wall 26 reaches the impermeable layer 36. The soft ground 12 is surrounded by the RC continuous wall 26. The impermeable layer 36 is formed by improving the soft ground 12 by injecting a chemical solution from the ground through an injection hole 38 piped substantially vertically so as to reach the impermeable layer 36 from the ground. Further, the soft ground 12 between the RC continuous wall 26 and the ground improvement layer 16 located near the groundwater level is also improved to a water-impermeable layer 28 having a water-impervious property by a chemical solution injection method. Therefore, the soft ground 12 is surrounded by the RC continuous wall 26, the impermeable layer 36, the impermeable layer 28, and the ground improvement layer 16, and is separated from the soft ground 32 outside the RC continuous wall 26 in a generally sealed state. ing.

  Next, operations and effects of the seismic isolation structure 34 and the seismic isolation device 35 according to the second embodiment of the present invention will be described.

  In the second embodiment, the same effect as in the first embodiment can be obtained, and as shown in FIG. 2, the hard ground 18 is formed at a deep position, and the soft ground layer below the apartment house 14 is formed. Even when it is thick, by forming the water-impermeable layer 36, the layer thickness of the soft ground 12A to be liquefied can be reduced without increasing the thickness of the ground improvement layer 16.

  Thus, after the earthquake has stopped, the water-impermeable layer 36 and the ground improvement layer 16 are provided even if a larger amount of water than the amount of water injected by the pump 22 is discharged. As a result, the thickness of the soft ground 12A layer is reduced, so that the apartment house 14 can be prevented from sinking more than necessary.

  Next, the seismic isolation structure 40 and the seismic isolation apparatus 41 of the 3rd Embodiment of this invention are demonstrated.

  In the third embodiment, a support portion on which the apartment house 14 is placed is provided in the first embodiment. Therefore, in the following description, the same components as those in the first embodiment are denoted by the same reference numerals and are appropriately omitted.

  FIG. 3 shows a seismic isolation structure 40 and a seismic isolation device 41 of the present embodiment. The apartment house 14 is placed on a first-floor beam 44 having high rigidity as a support portion. Both ends of the beam 44 are provided with an overhanging portion 42 projecting outside the apartment house 14. And the hydraulic damper 46 which absorbs a vertical vibration is provided between the overhang | projection part 42 and the ground improvement layer 16 upper surface. The hydraulic damper 46 can be replaced with a hydraulic jack (not shown) that expands and contracts in the vertical direction.

  Next, operations and effects of the seismic isolation structure 40 and the seismic isolation device 41 according to the third embodiment of the present invention will be described.

  In the third embodiment, the same effect as in the first embodiment can be obtained. Further, as shown in FIG. 3, when the apartment house 14 on the liquefied soft ground 12 is rocked due to the earthquake motion, the hydraulic damper 46 attenuates the vertical vibration, so that the locking of the apartment house 14 is reduced. can do.

  When the apartment house 14 is inclined due to liquefaction of the soft ground 12, the hydraulic damper 46 is removed and replaced with a hydraulic jack after the supporting force of the soft ground 12 is restored. The ground improvement layer 16 can be used as a reaction force to jack up the hydraulic jack, and the inclination of the apartment house 14 can be corrected.

  In addition, although the hydraulic damper 46 was shown as a damper, what is necessary is just to be able to attenuate a vertical vibration, and a metal damper, a viscoelastic damper, a vibration-proof rubber, etc. may be used.

  Moreover, although the hydraulic jack was shown as a jack, what is necessary is just to lift the apartment house 14 and to adjust height.

  In the first to third embodiments, the ground improvement layer 16 is formed directly under the apartment house 14 to reduce the thickness of the soft ground 12A layer, and the apartment house 14 sinks more than necessary. Although the example to prevent was shown, the thickness of the layer of the soft ground 12A may be adjusted according to the amount of basement or the foundation part provided in the apartment house 14, or the thickness of the soft ground 12 is originally small. In some cases, the ground improvement layer 16 may not be formed.

It is explanatory drawing which shows the seismic isolation structure and seismic isolation apparatus which concern on 1st Embodiment of this invention. It is explanatory drawing which shows the seismic isolation structure and seismic isolation apparatus which concern on 2nd Embodiment of this invention. It is explanatory drawing which shows the seismic isolation structure and seismic isolation apparatus which concern on 3rd Embodiment of this invention. It is the schematic which shows the conventional ground seismic isolation structure. It is the schematic which shows the conventional seismic isolation structure.

Explanation of symbols

10 Seismic isolation structure 11 Seismic isolation system 12 Soft ground 14 Apartment house (structure)
16 Ground improvement layer 18 Hard ground 20 Stand pipe (pressurizing means)
22 Pump (Pressurizing means)
23 Water storage tank (Pressurizing means)
26 RC continuous wall (water shielding layer)
30 seismometer 34 base isolation structure 35 base isolation device 36 impermeable layer 40 base isolation structure 41 base isolation device 42 overhang 44 beam (support)
46 Hydraulic damper (damper)

Claims (5)

A water-impervious layer surrounding the structure directly supported on the soft ground, surrounding the soft ground, and reaching the hard ground or the impermeable layer;
When an earthquake occurs, and pressurizing means for Ru is liquefying soft weak soil to raise the water pressure soft weak in soil by feeding water into the soft ground surrounded by the water shield layer,
A seismic isolation structure characterized by having The base of the structure or the base of the structure is provided so as to leave the soft ground layer between the structure and the hard ground or the impermeable layer.
The seismic isolation structure according to claim 1. A ground improvement layer of the soft ground is provided so as to leave the soft ground layer between the structure and the hard ground or the impermeable layer.
The seismic isolation structure according to claim 1. A support portion on which the structure is placed and provided with an overhanging portion projecting out of the structure;
A damper that absorbs vertical vibration, provided between the overhang portion and the ground improvement layer;
Have
The damper is replaceable with a jack that expands and contracts in the vertical direction.
The seismic isolation structure according to claim 3. A seismometer is provided in the base-isolated structure according to any one of claims 1 to 4.
When the seismometer detects a P wave during an earthquake,
The water pressure in the soft ground surrounded by the water shielding layer is raised by the pressurizing means so that the soft ground is liquefied .
A seismic isolation device characterized by that.

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