JP3677700B2 - Ground seismic isolation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ground seismic isolation method suitable for use in building various structures such as buildings on soft ground.
[0002]
[Prior art]
As is well known, various structures such as buildings are damaged during an earthquake because a large stress is generated in the structure due to seismic waves input from the ground and the structure is destroyed.
[0003]
Conventionally, in order to avoid such damage during earthquakes, seismic isolation devices such as laminated rubber with low rigidity against shear deformation have been installed on the foundations of structures, etc., and this seismic isolation device absorbs seismic waves from the ground. Seismic isolation methods are used to prevent this from reaching the structure.
[0004]
By the way, in the 1995 Hyogoken-Nanbu Earthquake, in areas where land such as landfills was liquefied, there was less structural damage to buildings compared to areas where liquefaction did not occur. It is said that This is because when the ground liquefies due to an earthquake, the rigidity of the ground significantly decreases, and this liquefied ground functions in the same way as the seismic isolation device, reducing the seismic waves input from the ground to the structure. It is.
[0005]
However, if the ground becomes liquefied due to an earthquake, the support capacity of the structure by the ground is lost, so the entire structure may be tilted or toppled, and if lateral flow of the ground occurs due to liquefaction, Foundation piles may also be damaged. Therefore, at present, as shown in FIG. 6, in the ground G where the occurrence of liquefaction is predicted at the time of an earthquake, in order to prevent liquefaction, a countermeasure method such as ground improvement is provided in the area S below the structure 1. Has been given.
[0006]
[Problems to be solved by the invention]
However, in the conventional technology as described above, since the ground G in the improved range S has high shear rigidity, seismic waves are easily transmitted to the structure 1 and the seismic force input to the structure 1 is increased. . For this reason, in order to avoid damage to the structure 1, not only the ground G is improved, but also the seismic isolation device as described above must be installed. However, seismic isolation devices such as laminated rubber are extremely expensive, and in order to obtain an effective seismic isolation effect, there is a problem that enormous costs and construction work are required.
[0007]
The present invention has been made in consideration of the above points, and an object of the present invention is to provide a ground seismic isolation method capable of easily obtaining an effective seismic isolation effect at low cost.
[0008]
[Means for Solving the Problems]
The invention according to claim 1 is a ground seismic isolation method when the ground supporting the structure is a liquefied ground where liquefaction is expected to occur during an earthquake, and the liquefied ground below the structure In the range from the lower surface of the structure to a defined depth below the structure , a dilute chemical solution is used so that the rigidity is always maintained and the rigidity is reduced during an earthquake. The ground is improved by pouring, and the ground is improved so that the shear rigidity is increased in a range below the predetermined depth .
[0009]
The invention according to claim 2 is the ground seismic isolation method according to claim 1, wherein the dilute chemical solution is diluted 3 to 5 times with a normal chemical solution of 8 to 10 kilograms in silica concentration in 100 liters of the chemical solution. It is characterized by using the thing.
The invention according to claim 3 is the ground seismic isolation method according to claim 1 or 2 , wherein a foundation pile is constructed in the liquefied ground as a foundation of a structure.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the ground seismic isolation method according to the present invention will be described with reference to FIGS. 1 to 4.
[0011]
As shown in FIG. 1, the structure 10 is constructed | assembled on the ground (liquefaction ground) G by which generation | occurrence | production of liquefaction is estimated at the time of an earthquake, The foundation 11 is provided with the foundation piles 12, 12, ... Yes. And the ground G of the range S below the structure 10 is ground-improved as follows.
[0012]
That is, among the ground G in the range S below the structure 10, the same ground improvement method, for example, a sand compaction method, a gravel drain, is used in a range S 1 below the predetermined depth from the lower surface 10 a of the structure 10. Use the construction method, cement solidification method, chemical solution injection method, etc. to sufficiently improve the ground.
[0013]
And in the range S2 from the lower surface 10a of the structure 10 to the predetermined depth, the diluted chemical solution L is injected to improve the ground.
As this dilute chemical solution L, for example, a chemical solution similar to that conventionally used in the chemical solution injection method or the like is used, but its concentration is changed to a conventional normal concentration (for example, silica (Si-O in 100 liters of chemical solution). ₂ ) For example, a dilute one diluted 3 to 5 times with respect to 8 to 10 kg) is used.
[0014]
Here, the result of the indoor liquefaction test of the sand (corresponding to the range S2 of the ground G) into which the diluted chemical liquid L is injected is shown. Here, as the diluted chemical solution L, one having a concentration of about 1/4 with respect to the normal chemical solution concentration was used.
[0015]
FIG. 2 shows changes in the generation of strain when repeated loading corresponding to seismic waves is applied. FIG. 2 (a) shows the case of sand not containing a chemical solution (state without ground improvement), FIG. (B) is a case of sand mixed with a dilute chemical L. As is clear from this figure, in the sand not containing the chemical solution shown in FIG. 2 (a), the strain rapidly increases due to repeated loading due to the earthquake, thereby causing the ground G to liquefy. On the other hand, the sand (range S2) mixed with the dilute chemical liquid L shown in FIG. 2 (b) does not have a huge strain even when repeated loading due to an earthquake is applied, and liquefaction is prevented. It can be seen that there is no lateral flow or enormous settlement.
[0016]
In addition, it has been clarified in the previous studies that the ground subsidence (volume strain) due to liquefaction is determined by the magnitude of the shear strain generated during the earthquake. The relationship of the volume strain after liquefaction is shown. In the experimental result shown in FIG. 2 (b), since the shear strain is about 2% in the sand (range S2) mixed with the diluted chemical liquid L, the structure 10 is obtained from the relationship shown in FIG. It can be seen that the actual subsidence amount of the ground G below (see FIG. 1) is limited to about 0.8% of the thickness of the range S2 improved by the diluted chemical L.
[0017]
Further, FIG. 4 shows a stress-strain curve at the time of the indoor liquefaction test. As shown in FIG. 4 (a), it is repeatedly loaded in sand not containing chemicals (in a state where the ground is not improved). When it receives, the rigidity decreases, and the strain increases with this. On the other hand, as shown in FIG. 4B, in the sand (range S2) mixed with the diluted chemical liquid L, the rigidity starts to decrease when it is repeatedly loaded. Does not grow. This is because the soil G in this range S2 always maintains rigidity by mixing the dilute chemical L, but if it receives seismic force, the rigidity decreases and it becomes difficult to transmit the seismic wave, and it is enormous. It has the property that no displacement occurs. In addition, the stress-strain hysteresis loop is thicker than liquefied sand (see FIG. 4 (a)), and the attenuation of sand (range S2) mixed with dilute chemical liquid L is large. It shows that the energy absorption effect is high.
[0018]
In this way, the ground G to which the ground improvement shown in FIG. 1 is applied is improved in the shear rigidity and the liquefaction is prevented in the range S1 where the normal ground improvement construction method is applied. Lateral flow is also prevented. In the range S2 into which the dilute chemical solution L is injected, the rigidity is always maintained, and when subjected to seismic force, the rigidity is lowered and the damper function is prevented to prevent the seismic wave from being transmitted to the structure 10, and Liquefaction is prevented without causing enormous displacement.
[0019]
In the ground seismic isolation method described above, the ground G that supports the structure 10 is ground improved by the thin chemical L in the range S2 from the lower surface 10a of the structure 10 to the predetermined depth, and the range S1 below the range S1 is normal. The ground is improved by the ground improvement method. Thereby, in any of the range S1 in which the normal ground improvement has been performed and the S2 in which the ground improvement by the dilute chemical liquid L has been performed, the liquefaction of the ground G and the lateral flow caused thereby can be prevented. It is possible to avoid damages such as tilting or overturning of the structure 10 and damage to the foundation pile 12. In addition, in the range S <b> 2 in which the ground improvement by the dilute chemical solution L is performed immediately below the structure 10, the rigidity is reduced when the seismic force is applied, and a damper function that prevents the seismic wave from being transmitted to the structure 10 is exhibited. As a result, it is possible to prevent the ground structure G from being damaged due to the seismic isolation effect of the ground G.
[0020]
And since the chemical | medical solution L with a low viscosity becomes low compared with the chemical | medical solution used conventionally, it can inject | pour in a wide range from one injection hole, and can perform injection | pouring operation | work easily and efficiently.
[0021]
Moreover, if the chemical solution injection method is applied also to the range S1 where the normal ground improvement is performed, the construction can be performed by changing the concentration of the chemical solution in this range S1 and the range S2 where the ground improvement by the diluted chemical solution L is performed. This also makes it possible to further facilitate the construction.
[0022]
In this way, according to the above-mentioned ground seismic isolation method, the ground G having an effective seismic isolation effect can be easily obtained at low cost by simply performing ground improvement and without using an expensive seismic isolation device. Can be formed.
[0023]
In addition, in the said embodiment, although it was set as the structure which constructs the foundation piles 12, 12, ... in the foundation 11 of the structure 10, a foundation form is not limited to this. As shown in FIG. 2 and FIG. 3, the sand (range S2) subjected to ground improvement with the dilute chemical solution L has a shear strain of about 2% at most, and the subsidence amount is also the range S2 improved with the dilute chemical solution L. Since, for example, as shown in FIG. 5, when the structure 10 ′ is a middle-low layer, a solid foundation 13 that does not construct the foundation pile 12 (see FIG. 1), etc. It is also good. Of course, other basic forms can be applied.
[0024]
In addition, the flat area and thickness of the range S2 into which the dilute chemical solution L is injected, the concentration of the dilute chemical solution L, and the like are appropriately set according to the geology of the ground G, the load by the structure 10, the type of the foundation 11, and the like. However, the present invention is not limited to the numerical values given in the above embodiment.
[0025]
In addition to this, any configuration may be adopted as long as it does not depart from the gist of the ground seismic isolation method according to the present invention.
[0026]
【The invention's effect】
As described above, according to the ground seismic isolation method according to claim 1, the liquefied ground below the structure is improved by the ground improvement means, and the depth defined below from the lower surface of the structure is determined. About the range up to this point, the rigidity is always maintained and the ground is improved by injecting a thin chemical solution so that the rigidity decreases in the event of an earthquake , and the shear rigidity is increased in the range below the specified depth. In this way, the ground is improved . And according to the ground seismic isolation method according to claim 2, it is configured to use a dilute chemical solution obtained by diluting a normal chemical solution of 8 to 10 kilograms 3 to 5 times in terms of silica concentration in 100 liters of chemical solution. . And according to the ground seismic isolation method which concerns on Claim 3 , it has the structure by which the foundation pile was constructed | assembled as a foundation of a structure. By improving the ground below the structure in this way, liquefaction of the ground and lateral flow caused by it can be prevented, and damage such as tilting and overturning of the structure and damage to the foundation pile can be prevented. Can be avoided. In addition, in areas where the ground has been improved with dilute chemicals, the rigidity decreases when subjected to seismic forces, and a damper function that prevents the seismic waves from being transmitted to the structure can be demonstrated. It has an effect and can prevent damage such as damage to the structure. In addition, since a diluted chemical solution has a lower viscosity than a conventionally used chemical solution, the injection operation can be performed easily and efficiently. Furthermore, if the chemical solution injection method is applied to the ground improvement in the range below the specified depth (the portion below the range where the diluted chemical solution is injected) , the range where the ground improvement by the diluted chemical solution is applied, Construction can be carried out only by changing the chemical concentration in the lower range, and further construction can be facilitated from this point. In this way, according to the above-mentioned ground seismic isolation method, it is possible to easily form a ground with an effective seismic isolation effect at low cost by simply performing ground improvement without the need for expensive seismic isolation devices. can do.
[Brief description of the drawings]
FIG. 1 is a vertical sectional view showing an example of a structure constructed by applying a ground seismic isolation method according to the present invention.
FIG. 2 shows test results for confirming the ground improvement effect by a dilute chemical solution in the ground seismic isolation method, showing changes in liquefaction characteristics when repeatedly loaded; (a) It is a figure which shows the result in the ground which inject | poured the result in the ground which has not inject | poured, (b) the thin chemical | medical solution.
FIG. 3 is a graph showing the relationship between the shear strain during liquefaction and the volume strain during liquefaction.
FIG. 4 shows changes in the stress-strain relationship when repeatedly loaded, (a) results in the ground not injected with chemicals, and (b) results in the ground injected with dilute chemicals. It is.
FIG. 5 is an elevational sectional view showing another example of a structure to which the ground seismic isolation method according to the present invention is applied.
FIG. 6 is an elevational sectional view showing an example of a structure to which a conventional ground improvement is applied.
[Explanation of symbols]
10, 10 'structure 10a lower surface 11 foundation 12 foundation pile G ground L dilute chemical

Claims (3)

A ground isolation method when the ground supporting the structure is a liquefied ground where liquefaction is expected to occur during an earthquake, wherein the liquefied ground below the structure is improved by ground improvement means. In the range from the lower surface of the structure to a predetermined depth below the structure, the rigidity is constantly maintained, and the ground is improved by injecting a diluted chemical solution so that the rigidity decreases during an earthquake , A ground-isolated construction method characterized by improving the ground so that the shear rigidity is enhanced in the range below the specified depth . 2. The ground seismic isolation method according to claim 1, wherein the dilute chemical solution is obtained by diluting 8 to 10 kilograms of a normal chemical solution 3 to 5 times in a silica concentration of 100 liters of the chemical solution. The ground seismic isolation method. The ground seismic isolation method according to claim 1 or 2 , wherein a foundation pile is constructed in the liquefied ground as a foundation of the structure.

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