JP7326684B2 - Vertical dynamic seismic isolation method for structures - Google Patents

Description

The present invention relates to a vertical dynamic seismic isolation method for a structure.

During an earthquake, both horizontal motion (horizontal vibration) and vertical motion (vertical vibration) are input to structures. In particular, when the structure is a large-span building, a production facility in a factory, or the like, the effect of vertical movement during an earthquake becomes large.

Here, conventionally, various three-dimensional seismic isolation devices have been proposed that exhibit seismic isolation effects against both horizontal and vertical motions that are input to structures during an earthquake. However, since existing three-dimensional seismic isolation devices are expensive, they are rarely applied to existing structures.

On the other hand, it is known that the velocity of P-waves propagating in the ground decreases when the saturation of the ground is decreased. For example, Patent Literature 1 discloses a method of estimating the degree of saturation of the ground by measuring the velocity of P waves propagating in the ground.

JP-A-2-125013

The invention disclosed in Patent Document 1 prevents liquefaction of the ground by forming an unsaturated region in the ground where the velocity of the P wave is reduced. That is, the technique of forming an unsaturated region in the ground has been applied to countermeasures against liquefaction of the ground, and there has been no example of applying the technique of forming an unsaturated region in the ground to countermeasures against earthquakes in structures.

SUMMARY OF THE INVENTION In view of the above facts, it is an object of the present invention to provide a vertical dynamic seismic isolation method for a structure capable of avoiding resonance between the structure and the ground by forming an unsaturated region in the ground.

The vertical motion seismic isolation method for a structure according to claim 1, wherein the unsaturated region is formed in the ground immediately below the structure by adjusting the range of air injection into the groundwater in the ground. By adjusting the range of and adjusting the range of the unsaturated region, the dominant period of the vertical movement of the ground during an earthquake is adjusted, and the vertical movement of the ground is adjusted to the natural period of the vertical movement of the structure shift the dominant period of

According to the above configuration, it is possible to adjust the range of the unsaturated region formed in the ground by adjusting the range of air injection into the groundwater in the ground. In addition, by adjusting the range of the unsaturated region formed in the ground, it is possible to adjust the range in which the velocity of the P wave is reduced, and to adjust the degree of lengthening of the predominant period of the vertical movement of the ground.

As a result, by adjusting the range of air injection into the groundwater in the ground, it is possible to shift the predominant period of the vertical movement of the ground from the natural period of the vertical movement of the structure. can be avoided.

The vertical motion seismic isolation method for a structure according to claim 2 is the vertical motion seismic isolation method for a structure according to claim 1, comprising: an air injection step of injecting the air into the groundwater; a region specifying step of specifying the range of the unsaturated region by specifying the distribution range of the air bubbles; and a vibration measuring step of measuring the speed of vibration propagating in the ground; and the vibration velocity obtained in the vibration measurement step, the range of the air injection into the groundwater is adjusted in the air injection step.

According to the above configuration, by specifying the range of the unsaturated region in the region specifying step and measuring the speed of vibration in the vibration measurement step, it is possible to measure the degree of decrease in the speed of the P wave with respect to the range of the unsaturated region. can. By adjusting the range of air injection into the groundwater based on the degree of P-wave velocity reduction with respect to the range of this unsaturated region, it is possible to adjust the range in which the P-wave velocity is reduced, and the predominant period of the ground can be adjusted to the desired period.

The vertical motion seismic isolation method for a structure according to claim 3 is the vertical motion seismic isolation method for a structure according to claim 2, wherein, based on the speed of the vibration obtained in the vibration measurement step, estimating the dominant period of the vertical movement of the ground, and injecting the air into the groundwater in the air injection step so that the dominant period of the vertical movement of the ground is shifted from the natural period of the vertical movement of the structure; to adjust.

According to the above configuration, the structure and the ground are controlled by adjusting the range of air injection into the groundwater in the air injection process so that the dominant period of the vertical motion of the ground is shifted from the natural period of the vertical motion of the structure. resonance can be avoided, and vertical movement of the structure can be suppressed.

According to the vertical dynamic seismic isolation method for a structure according to the present invention, resonance between the structure and the ground can be avoided by forming an unsaturated region in the ground.

1 is an overall elevational view showing a structure to be seismically isolated in a vertical motion seismic isolation method for a structure according to an embodiment; FIG. (A) is an elevation view showing an air injection step of the vertical dynamic seismic isolation method for a structure according to an example of the embodiment, and (B) is a plan view thereof. (A) is an elevation view showing a region specifying step of the vertical dynamic seismic isolation method for a structure according to an example of the embodiment, and (B) is a plan view thereof. (A) is an elevation view showing a vibration measurement process of the vertical dynamic seismic isolation method for a structure according to an example of the embodiment, and (B) is a plan view thereof. 4 is a graph showing the relationship between the saturation of the ground and the velocity of P-waves propagating in the ground; 4 is a table showing velocities of P waves propagating in the ground in the vertical dynamic seismic isolation method for a structure according to an example of the embodiment; (A) is a graph showing the natural period of the vertical motion of the structure in the vertical motion seismic isolation method for the structure according to the embodiment, and (B) is a graph showing the predominant period of the vertical motion of the ground.

A method for vertically dynamic seismic isolation of a structure according to an embodiment of the present invention will be described below with reference to FIGS. 1 to 7. FIG.

(Structure configuration)
First, the structure 10 to be seismically isolated in the vertical dynamic seismic isolation method for a structure according to the present embodiment will be described. As shown in FIG. 1, the structure 10 is, for example, a large-span building, and stands on the ground 12 . The ground 12 immediately below the structure 10 is composed of a plurality of layers (10 layers as an example), and the layers below the groundwater level HL (4th layer and deeper from the top as an example) are aquifers through which groundwater flows.

The structure 10 is supported by, for example, a plurality of foundation piles (not shown) built into the ground 12 . Also, the structure 10 has a predetermined natural period. In this embodiment, as shown in the graph of FIG. 7A, as an example, the natural period of the structure 10 is approximately 0.05 (s).

(Vertical dynamic seismic isolation method for structures)
Next, the vertical dynamic seismic isolation method for a structure according to this embodiment will be described. In this embodiment, the range of the unsaturated region M (see FIG. 2A) formed in the ground 12 is adjusted by adjusting the range of air injection into the groundwater in the ground 12 immediately below the structure 10. , the dominant period of the vertical movement of the ground 12 during an earthquake is adjusted, and the vertical movement of the structure 10 is suppressed.

Specifically, the vertical motion seismic isolation method for a structure mainly includes an air injection process, an area identification process, and a vibration measurement process. In this embodiment, each step of the air injection step, the area identification step, and the vibration measurement step is repeated until the predominant period of the ground 12 reaches a desired period.

(Air injection process)
In the air injection step, an unsaturated region M is formed in the ground 12 by injecting air into groundwater in the ground 12 immediately below the structure 10 . That is, the saturation degree Sr (%) of the ground 12 is lowered (the ground 12 is desaturated). The saturation degree Sr of the ground 12 is obtained by dividing the volume Vw of water contained in the soil by the sum of the volume Va of air and the volume Vw of water and multiplying by 100 (Sr=(Vw/(Va+Vw))). × 100).

Specifically, as shown in FIGS. 2A and 2B, a plurality of excavation holes 14 are formed in the ground 12 . The drilled holes 14 are composed of a plurality of first drilled holes 14A formed on one side of the structure 10 and a plurality of second drilled holes 14B formed on the other side. The first excavation hole 14A and the second excavation hole 14B may be boring holes formed for investigation of the ground 12, or may be formed by excavating the ground 12 newly.

A pump 16 is installed on the ground 12 . One end of a plurality of pumping pipes 18 is connected to the pump 16, and the other ends of the plurality of pumping pipes 18 are inserted into the respective first excavation holes 14A. Further, as shown in FIG. 2(B), the other end of the pumping pipe 18 inserted into the first excavation hole 14A is formed with a plurality of pumping ports 18A for pumping up the groundwater in the ground 12 onto the ground 12. It is

Furthermore, one end of a plurality of water injection pipes 20 is connected to the pump 16, and the other ends of the plurality of water injection pipes 20 are inserted into the respective second excavation holes 14B. A plurality of water injection ports 20A for injecting the pumped groundwater into the ground 12 are formed at the other end of the water injection pipe 20 inserted into the second excavation hole 14B.

A compressor 22 is installed on the ground 12 . The compressor 22 is connected to the water injection pipe 20 on the ground 12 , and the air compressed by the compressor 22 is injected into the groundwater flowing inside the water injection pipe 20 .

In the air injection process, the groundwater in the ground 12 is pumped up to the ground by the pump 16 from the water pumping port 18A formed in the water pumping pipe 18 inserted into the first excavation hole 14A. Then, the air compressed by the compressor 22 is injected into the pumped-up groundwater, and the air-injected groundwater is returned into the ground 12 through the water injection port 20A formed in the water injection pipe 20 inserted into the second excavation hole 14B. , circulates the groundwater and injects air into the groundwater in the ground 12 . In this embodiment, as an example, air is injected into three layers from the fourth layer to the sixth layer of the ground 12 to desaturate the fourth layer to the sixth layer.

(Region identification step)
After the air injection step, in the region specifying step, the range (for example, layer thickness) of the unsaturated region M is specified by specifying the distribution range of the air bubbles K in the groundwater. That is, the range (layer thickness) of the region where the ground 12 is desaturated by air injection in the air injection process is confirmed. In addition, in FIGS. 2 to 4, the bubble K is drawn larger than its actual size for ease of explanation.

Specifically, as shown in FIGS. 3A and 3B, as an example, the underwater speaker 24 and the receiver 26 are used to identify the distribution range of the air bubbles K in the groundwater. An underwater speaker 24 is inserted into one of the plurality of first boreholes 14A and is connected to an acoustic amplifier 28 placed on the ground 12. As shown in FIG. On the other hand, the receiver 26 is inserted into one of the plurality of second boreholes 14B and connected to the recorder 30 installed on the ground 12 .

In the region identification process, the sound wave amplified by the acoustic amplifier 28 is transmitted from the underwater speaker 24, and the sound wave propagating through the ground 12 directly below the structure 10 is received by the receiver 26 and recorded in the recorder 30. By analyzing the speed and attenuation of the sound waves recorded by the recording device 30, the distribution range of the air bubbles K in the groundwater is specified. Further, by specifying the distribution range of the bubbles K, the range (layer thickness) of the unsaturated region M, that is, the range (layer thickness) of the region where the ground 12 is desaturated by injecting air is specified.

(Vibration measurement process)
After the region specifying step, the vibration measuring step measures the velocity of vibration (elastic wave) propagating through the ground 12 . Specifically, as shown in FIGS. 4(A) and 4(B), as an example, a PS logging sonde 32 is used to measure the velocity of vibration.

A PS logging sonde 32 is inserted into one of the plurality of first boreholes 14A and is connected to a recorder 34 installed on the ground 12 . A vibration source 36 is installed near the PS logging sonde 32 on the ground 12 . The vibration source 36 includes a striking member (not shown) such as a hammer that strikes the ground 12 to vibrate the ground 12 .

In the vibration measurement process, the ground 12 is struck by a striking member (not shown) of the vibration source 36 to vibrate the ground 12, and the elastic wave propagating through the ground 12 is measured by the PS logging sonde 32 and recorded in the recorder 34. do. Also, from the waveforms of the elastic waves (P waves and S waves) recorded in the recorder 34, the propagation time until the elastic wave generated by the vibration source 36 propagates through the ground 12 and reaches the PS logging sonde 32 By reading, the velocity of the elastic waves (P wave and S wave) propagating in the ground 12 is obtained. Among the elastic waves propagating through the ground 12, the velocity Vp (m/s) of the P wave is extracted, and the predominant period of the vertical movement of the ground 12 is calculated from the velocity Vp of the P wave.

After the above-described air injection process, region identification process, and vibration measurement process are executed, the natural period of the vertical motion of the structure 10 is compared with the calculated predominant period of the vertical motion of the ground 12 . Then, when the dominant period of the vertical motion of the ground 12 deviates from the natural period of the vertical motion of the structure 10 by a predetermined value or more, the above process is finished.

On the other hand, when the dominant period of the vertical motion of the ground 12 does not deviate from the natural period of the vertical motion of the structure 10 by a predetermined value or more, that is, the natural period of the vertical motion of the structure 10 and the dominant period of the vertical motion of the ground 12 are overlapped, the air injection process is performed again.

Specifically, for example, air is injected into the non-saturated region (for example, the depth of the 7th layer or deeper of the ground 12) specified in the region specifying step, and the range of the unsaturated region M in the ground 12 (layer thickness ). At this time, a new range for forming the unsaturated region M is determined based on the range of the unsaturated region M obtained in the region specifying step and the velocity Vp of the P wave obtained in the vibration measurement step.

That is, by specifying the range of the unsaturated region M in the region specifying step and measuring the velocity Vp of the P wave in the vibration measuring step, the degree of decrease in the velocity Vp of the P wave with respect to the range of the unsaturated region M is measured. By adjusting the range of air injection into the groundwater in the air injection process based on the degree of reduction of the P-wave speed Vp with respect to the range of the unsaturated region M, the range of reducing the P-wave speed Vp is adjusted, Adjust the dominant period of the ground 12.

The above steps are repeated until the dominant period of the ground 12 reaches a desired period, that is, until the dominant period of the vertical motion of the ground 12 deviates from the natural period of the vertical motion of the structure 10 by a predetermined value or more. When the dominant period reaches the desired period, the above steps are terminated.

Note that the above procedure is an example, and the procedure may be different or include other procedures. For example, in the above procedure, the vibration measurement process is performed after the area identification process, but the area identification process may be performed after the vibration measurement process. Further, when it is confirmed that the dominant period of the vertical motion of the ground 12 is shifted by a predetermined value or more from the natural period of the vertical motion of the structure 10 by executing the vibration measurement process after the air injection process, it is not necessarily No region identification step need be performed.

(Effect)
Next, the effects of the vertical motion seismic isolation method for a structure according to this embodiment will be described with reference to the graphs of FIGS. 5 and 7 and the table of FIG. The figures ◯, □, and Δ in FIG. 5 represent the results of soil samples with different grain shapes.

As shown in the graph of FIG. 5, in general, when the saturation Sr of the ground 12 is in the range of 90% or more and 100% or less, when the saturation Sr of the ground 12 is decreased, the P wave propagating in the ground 12 Velocity Vp drops sharply. On the other hand, in the range where the saturation degree Sr of the ground 12 is less than 90%, even if the saturation degree Sr of the ground 12 is decreased, the velocity Vp of the P wave propagating through the ground 12 hardly decreases.

In addition, the predominant period of the vertical motion of the ground 12 is determined not only by the decrease in the velocity Vp of the P wave due to the degree of saturation Sr of the ground 12, but also by the range (thickness) of the unsaturated region M formed in the ground 12. Change. Specifically, when the range (layer thickness) of the unsaturated region M is widened, the range (layer thickness) in which the velocity Vp of the P wave is reduced is widened, and the predominant period of the vertical movement of the ground 12 is lengthened.

Before desaturation of the ground 12, the ground 12 in the layer below the groundwater level HL (fourth layer and deeper) has a saturation degree Sr of about 100%, and as shown in FIG. The velocity Vp (m/s) of is around the propagation velocity of the P wave in water (approximately 1500 m/s).

Here, in the air injection step described above, for example, when air is injected into the ground 12 from the 4th layer to the 6th layer to desaturate the ground 12, in the 3rd layer from the 4th layer to the 6th layer of the ground 12 , the velocity Vp (m/s) of the P-wave propagating through the ground 12 decreases to about 600 m/s.

At this time, the predominant period of the vertical movement of the ground 12 becomes longer as the velocity Vp of the P wave decreases. Specifically, as shown in the graph of FIG. 7(B), the dominant period of the ground 12 whose period was about 0.05 (s) before desaturation changed to about 0.05 (s) after desaturation. 1(s). That is, as shown in FIGS. 7A and 7B, before desaturation, the natural period of the vertical motion of the structure 10 and the dominant period of the vertical motion of the ground 12 overlapped. , after the desaturation, the dominant period of the vertical motion of the ground 12 shifts from the natural period of the vertical motion of the structure 10 .

According to this embodiment, the range (layer thickness) of the unsaturated region M formed in the ground 12 can be adjusted by adjusting the range of air injection into the groundwater in the ground 12 . In addition, by adjusting the range of the unsaturated region M formed in the ground 12, the range in which the velocity Vp of the P wave propagating in the ground 12 during an earthquake can be reduced can be adjusted, and the predominant period of the vertical movement of the ground 12 can be adjusted. The degree of period lengthening can be adjusted.

By adjusting the range of air injection into the groundwater in the ground 12 in this way, the predominant period of the vertical motion of the ground 12 can be shifted from the natural period of the vertical motion of the structure 10 . and the ground 12 can be avoided.

In particular, according to the present embodiment, in the air injection step, groundwater is pumped up from the first drilled hole 14A formed on one side of the structure 10, and groundwater is pumped from the second drilled hole 14B formed on the other side. It is returned to the ground 12. By circulating the groundwater in this way, groundwater flow can be created between the first drilled hole 14A and the second drilled hole 14B in the ground 12 immediately below the structure 10, and the air is uniformly distributed in the ground 12. can be diffused into

Further, in the present embodiment, the range of the unsaturated region M is specified in the region specifying step, and the vibration velocity Vp is measured in the vibration measurement step, whereby the degree of decrease in the velocity Vp of the P wave with respect to the range of the unsaturated region M to measure. Then, based on the degree of decrease in the velocity Vp of the P wave with respect to the range of the unsaturated region M, the range of air injection into the groundwater is adjusted. As a result, it is possible to adjust the range of air injection into the groundwater in the ground 12 while confirming the degree of decrease in the speed Vp of the P wave and the range in which the P wave is decreased, and the dominant period of the ground 12 can be adjusted to the desired period. can be adjusted to

Specifically, by adjusting the range of air injection into the groundwater in the air injection process, the structure 10 is and the ground 12 can be avoided, and the vertical movement of the structure 10 can be suppressed.

(Other embodiments)
Although one example of an embodiment of the present invention has been described above, the present invention is not limited to such an embodiment, and various other embodiments are possible within the scope of the present invention.

For example, in the above embodiment, the structure 10 erected on the ground 12 was a large-span building as an example, but the structure 10 is not limited to a building, and may be a production facility or the like. The equipment may be installed together.

In the above embodiment, the air compressed by the compressor 22 is directly injected into the ground 12 in the air injection process. good too. In this case, the foaming agent chemically reacts in the ground 12 to generate air bubbles K, which can be diffused in the ground 12 .

10 structure 12 ground K bubble M unsaturated region

Claims (3)

Adjusting the range of the unsaturated region formed in the ground by adjusting the range of air injection into the groundwater in the ground in the ground immediately below the structure,
Adjusting the predominant period of the vertical movement of the ground during an earthquake by adjusting the range of the unsaturated region,
Shifting the predominant period of the vertical motion of the ground with respect to the natural period of the vertical motion of the structure;
Vertical dynamic seismic isolation method for structures. an air injection step of injecting the air into the groundwater;
a region identifying step of identifying the range of the unsaturated region by identifying the distribution range of bubbles in the groundwater;
a vibration measuring step of measuring the speed of vibration propagating through the ground;
has
Adjusting the injection range of the air into the groundwater in the air injection step based on the range of the unsaturated region obtained in the region identification step and the speed of the vibration obtained in the vibration measurement step. do,
The vertical movement seismic isolation method for a structure according to claim 1. estimating the predominant period of the vertical movement of the ground based on the speed of the vibration obtained in the vibration measurement step;
adjusting the injection range of the air into the groundwater in the air injection step so that the dominant period of the vertical movement of the ground is shifted from the natural period of the vertical movement of the structure;
The vertical movement seismic isolation method for a structure according to claim 2.