JPH11323993A - Disaster-suffering preventive structure of and disaster-suffering preventive method of foundation structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a disaster-suffering preventive structure of and a disaster- suffering preventive method of a foundation structure excellent in cost and easily applicable to an existing structure. SOLUTION: A part of the ground G around pile footings 7 is improved, and foundation improving bodies 15 are formed so that the upper end parts 15a and the lower end parts 15b are respectively positioned in an upper nonliquefied layer 5 and a lower nonliquefied layer 3 and the central parts 15c are positioned in a liquefied layer 4. When an earthquake occurs, at least a part of horizontal force acting in the ground G is shared with the foundation improving bodies 15, and horizontal directional relative displacement between the upper/lower nonliquefied layers 5, 3 is regulated by the foundation improving bodies 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for preventing damage to a foundation structure provided in the ground when the ground liquefies during an earthquake, and a method for preventing damage to the foundation structure. It is about.

[0002]

2. Description of the Related Art As is well known, it has been reported that when a huge earthquake occurs, liquefaction of the ground causes great damage to foundation structures, especially piles. Such damage is particularly noticeable at the boundary between the non-liquefied layer near the ground surface and the liquefied layer below it, or at the boundary between the liquefied layer and the non-liquefied layer below it. It is known to

The reason can be explained as follows. For example, as shown in FIG. 5, it has a support layer 1 and a surface layer 2 located thereabove, and the surface layer 2 is composed of a lower non-liquefied layer 3, a liquefied layer 4, and an upper non-liquefied layer 5. It is assumed that the pile foundation 7 is cast in the ground G that is located so as to reach the support layer 1 from the ground surface Gs. In this case, when the support layer 1 vibrates due to the earthquake,
Since the lower non-liquefied layer 3 is in direct contact with the support layer 1,
It shows the same behavior as the seismic motion, and displaces quickly with a small amplitude as shown by the arrow p in the figure. The lower non-liquefied layer 3 is
Due to the high rigidity, the displacement is relatively small even if the acceleration acting due to the earthquake is large. In this case, the horizontal force acting on the pile foundation 7 increases almost linearly from the tip of the pile foundation 7 to the boundary between the lower non-liquefied layer 3 and the liquefied layer 4 ( (See arrow A in the figure)

On the other hand, the liquefied layer 4 located above the lower non-liquefied layer 3 undergoes large shear deformation as shown in FIG.
Therefore, the amplitude there, as shown by the arrow q in the figure,
It is larger than that in the lower non-liquefied layer 3. However, since this layer has low rigidity, the horizontal force acting on the pile foundation 7 is smaller than that of the lower non-liquefied layer 3 as shown by the arrow B in the figure.

Since the upper non-liquefied layer 5 is located on the liquefied layer 4 which undergoes large shear deformation, the upper non-liquefied layer 5 moves with a large amplitude and slowly as shown by an arrow r in the figure. In this case, since the rigidity of the upper non-liquefied layer 5 is larger than that of the liquefied layer 4, a large horizontal force acts on the pile foundation 7 as shown by an arrow C in the figure.

As described above, there is a great difference in the horizontal force acting on the pile foundation 7 between the lower non-liquefied layer 3 and the liquefied layer 4 and between the liquefied layer 4 and the upper non-liquefied layer 5. This causes the difference in these forces to be
It is considered that this acts as a shearing force on the pile, causing breakage of the pile foundation 7.

[0007] Also, in general consideration, the groundwater level is usually several meters from the ground surface, and the groundwater level shallower than the groundwater level does not liquefy irrespective of the nature of the ground. It is considered that there are many cases where the pile foundation is damaged in the case.

In order to prevent damage to foundation structures such as pile foundations as described above, it is most effective to prevent liquefaction of the ground. For this reason, compaction, injection of chemicals,
Alternatively, a construction method of improving the ground by means such as cement mixing, or a construction method of surrounding the structure with an underground continuous wall or the like and restraining shear deformation of the ground below the structure is adopted.

[0009]

However, the method of improving the ground has a problem that it is difficult to apply it to existing structures. In addition, it is difficult to solidify the ground to prevent liquefaction. In order to increase the transmitted acceleration,
Even if the basic structure could be protected, there was a concern that the upper structure would be damaged. In addition, the construction method of surrounding the structure with walls has problems in terms of cost and construction period. SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has a structure for preventing damage to a foundation structure, which is excellent in cost and can be easily applied to existing structures. It is an object to provide a method.

[0010]

In order to solve the above problems, the present invention employs the following means. That is, the damage prevention structure for a substructure according to claim 1 has a support layer and a surface layer located on the support layer, and the surface layer is formed on the lower non-liquefied layer and the lower non-liquefied layer. Applied to the substructure provided in the ground consisting of a liquefied layer located on the ground and an upper non-liquefied layer located on the liquefied layer to prevent damage when the ground is liquefied An underground structure is provided on at least a part of the ground around the substructure, and the underground structure has an upper non-liquefaction layer and an upper end and a lower end. It is characterized in that it is located in the lower non-liquefied layer, and a central portion located between the upper end and the lower end is located in the liquefied layer.

In this structure for preventing damage to the substructure, the underground structure reduces the shearing force borne by the substructure and suppresses the movement of the upper non-liquefied layer with respect to the lower non-liquefied layer. Act like so.

The structure for preventing damage to a foundation structure according to claim 2 is the structure for preventing damage to a foundation structure according to claim 1, wherein the foundation structure is a pile foundation. The damage prevention structure for the substructure according to claim 3 is:
The disaster prevention structure for a substructure according to claim 1 or 2, wherein the underground structure is a ground improvement body obtained by improving the ground.

According to a fourth aspect of the present invention, there is provided a method for preventing damage to a substructure, comprising a support layer and a surface layer located on the support layer, wherein the surface layer comprises a lower non-liquefied layer and a lower non-liquefied layer. Applied to a substructure provided in the ground consisting of a liquefied layer located above and an upper non-liquefied layer positioned above the liquefied layer, the base structure when the ground is liquefied A method for preventing damage to an object, wherein a part of the ground around the substructure is improved to form a ground improvement body, the upper end and the lower end of which are the upper non-liquefied layer and the lower part. So that each is located in the non-liquefied layer, and
A central portion located between the upper end and the lower end is formed so as to be located in the liquefaction layer, and when the earthquake occurs, at least a horizontal force acting in the liquefaction layer. It is characterized in that part of the burden is placed on the ground improvement body, and that the ground improvement body controls horizontal relative displacement between the upper and lower non-liquefaction layers.

In this method for preventing damage to a substructure, ground improvement can be performed mainly on the liquefied layer as much as required in terms of strength, so that the cost does not increase. In addition, since it is not necessary to strengthen the entire ground, it is possible to prevent the seismic force input to the foundation structure from being increased.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, the same components as those of the above-described conventional technology are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, reference numeral 11 denotes a structure provided on the ground G. The structure 11 includes an upper structure 12 located above the ground surface Gs and a pile foundation (base structure) that is provided so that the lower end thereof reaches the support layer 1 and supports the upper structure 12 at the upper end. ) Are provided.

As shown in the figure, the pile foundations 7, 7,
On the side of…, when the liquefied layer 4 liquefies, the pile foundation 7,
A disaster prevention structure 14 is provided to prevent the .7 from being damaged. This damage prevention structure 14 is a ground improvement body (underground structure) 15, 15, formed by consolidating a part of the ground G by means such as injection of a chemical solution.
… Consisting of The ground improvement body 15 has an upper end 15
a and the lower end 15b are respectively provided in the upper non-liquefied layer 5
And a central portion 15 c located between the upper end portion 15 a and the lower end portion 15 b is located in the liquefied layer 4.

FIG. 2 shows the structure 11 and the damage prevention structure 1.
FIG. 4 is a diagram showing 4 in a plan view. As shown in the figure, the disaster prevention structure 14 has a configuration in which a plurality of ground improvement bodies 15, 15,... Are arranged so as to surround the pile foundations 7, 7,.

In order to obtain such a disaster prevention structure 14,
For example, several places around the structure 11 are drilled, and the ground G in the range of the installation target depth of the ground improvement body 15 is mixed and stirred using a stirring blade or the like, and a stabilizing material such as lime or cement is injected. . Thus, the ground G is consolidated to form the ground improvement bodies 15, 15,....

Next, the operation of the disaster prevention structure 14 configured as described above will be described. 3 and 4 are views showing the behavior of the structure 11 and the ground G when subjected to seismic force. FIG. 3 shows the case where the ground improvement bodies 15,. This is an example in which it is assumed that the ground improvement body 15,... Is not provided.

When these are compared, in the case shown in FIG. 4, since no structure is provided for regulating the relative displacement between the upper and lower non-liquefied layers 3 and 5 and the shear deformation of the liquefied layer 4, A large inertial force as shown by an arrow D in the figure acts on the pile foundations 7,. In contrast, FIG.
In the case shown in (1), the ground improvement body 15,... Is provided such that the upper end 15a and the lower end 15b are located in the upper and lower non-liquefied layers 5, 3, respectively. 15,... Suppress the shear deformation of the liquefied layer 4 and the upper and lower non-liquefied layers 5,
It acts to regulate the horizontal relative displacement between the three.

Therefore, the inertial force acting on the pile foundations 7, 7,... Is smaller than that shown in FIG. Thus, in the case shown in FIG. 4, there is a possibility that the pile foundations 7, 7,... May be damaged as shown in the figure, whereas in the case shown in FIG. Will be protected. Also,
In particular, in the case shown in FIG. 3, since the ground improvement body 15 bears the inertial force that acts on the pile foundations 7 in cooperation with each other, the force acting on the pile foundations 7 is further reduced. Is done.

In the above-mentioned disaster prevention structure 14, it is not necessary to provide the ground improvement bodies 15, 15,... All over the periphery of the structure 11, and the characteristics of the ground G, the earthquake resistance of the upper structure 12, or In accordance with the horizontal strength of the pile foundations 7, 7, ..., etc., only a part of the ground G needs to be provided, which is much larger than the conventional liquefaction countermeasure structure in which the structure is surrounded by walls. The cost can be reduced. In the damage prevention structure 14, when the thickness of the liquefied layer 4 is relatively small, the ground improvement bodies 15, 1
.. Can be made smaller, so that the cost reduction effect can be made more remarkable. Also, since the ground improvement bodies 15, 15,... Are provided only in a part of the ground G, the rigidity of the entire ground G is not increased, and therefore, the input acceleration to the structure 11 does not increase. . Further, since the ground immediately below the structure 11 is not improved, the invention can be favorably applied even when the structure 11 is an existing structure. Further, the ground improvement body 15 can be easily constructed as compared with a conventional wall structure or the like, and is excellent in cost.

If the pile foundations 7, 7,... Are prevented from being damaged by liquefaction as described above, the safety of the structure 11 can be ensured effectively and at low cost.
Liquefaction countermeasures can be easily taken for existing structures.

[0025]

As described above, according to the first and second aspects of the present invention, according to the characteristics of the ground, the seismic resistance of the superstructure, or the horizontal strength of the foundation structure such as a pile foundation. ,
Since the underground structure only needs to be provided on a part of the ground, the construction cost can be greatly reduced as compared with the conventional liquefaction countermeasure structure using an underground continuous wall or the like. In addition, if the underground structure is provided only in a part of the ground as described above, the rigidity of the whole ground is increased, and the input acceleration to the structure does not increase. It is also superior in cost compared to. Also, if the thickness of the liquefied layer is relatively small,
Since the scale of the underground structure can be reduced, the effect of reducing the construction cost can be further remarkable. In addition, because it does not improve the ground immediately below the superstructure,
It can be applied well to existing structures. Further, in this case, if the underground structure is a ground improvement body formed by improving the ground, the construction can be performed more easily than a conventional underground continuous wall. It is also excellent in cost. Furthermore, according to the fourth aspect of the invention, it is possible to take effective liquefaction countermeasures at an inexpensive cost, particularly for existing structures.

[Brief description of the drawings]

FIG. 1 is a view schematically showing one embodiment of the present invention, and is an elevational sectional view of a structure and a disaster prevention structure applied thereto.

FIG. 2 is a plan sectional view of the pile foundation and the damage prevention structure shown in FIG.

FIG. 3 is a view showing the operation of the present invention, and is an elevational sectional view showing the behavior of a structure, a disaster prevention structure, and the ground on which these are provided during an earthquake.

FIG. 4 is a view showing the operation of the present invention, and is an elevational sectional view showing the behavior of the structure and the ground at the time of an earthquake when it is assumed that the damage prevention structure is not provided.

FIG. 5 is an elevational sectional view showing the force received by a pile foundation driven into the ground during an earthquake.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Support layer 2 Surface layer 3 Lower non-liquefied layer 4 Liquefied layer 5 Upper non-liquefied layer 7 Pile foundation (foundation structure) 14 Damage prevention structure 15 Ground improvement body (underground structure) 15a Upper end 15b Lower end 15c Central part G Ground

Claims (4)

[Claims] 1. A liquefaction layer comprising a support layer and a surface layer located on the support layer, wherein the surface layer comprises a lower non-liquefaction layer, a liquefaction layer located on the lower non-liquefaction layer, and the liquefaction layer. A structure for preventing damage when the ground is liquefied, being applied to a substructure provided in the ground consisting of an upper non-liquefied layer located on a layer, wherein the substructure is An underground structure is provided on at least a portion of the ground around the underground structure, and the underground structure has an upper end and a lower end located in the upper non-liquefaction layer and the lower non-liquefaction layer, respectively. A structure for preventing damage to a substructure, wherein a central portion located between the upper end portion and the lower end portion is located in the liquefied layer. 2. The structure for preventing damage to a foundation structure according to claim 1, wherein the foundation structure is a pile foundation. 3. The structure for preventing damage to a substructure according to claim 1 or 2, wherein the underground structure is a ground improvement body obtained by improving the ground. Damage prevention structure. 4. A liquefaction layer having a support layer and a surface layer located on the support layer, wherein the surface layer is a lower non-liquefaction layer, a liquefaction layer located on the lower non-liquefaction layer, and the liquefaction layer. A method for preventing damage to the substructure when the ground is liquefied, being applied to a substructure provided in the ground consisting of an upper non-liquefied layer located on a layer. The ground improvement body is obtained by improving at least a part of the ground around the substructure so that the upper end portion and the lower end portion are respectively located in the upper non-liquefaction layer and the lower non-liquefaction layer. In addition, a central portion located between the upper end portion and the lower end portion is formed so as to be located in the liquefied layer, and when the earthquake occurs, a horizontal force acting in the ground And at least part of the burden on the ground improvement body To, by 該地 Release improve body, affected method for preventing substructure, characterized in that to regulate the relative horizontal displacement of the upper and lower non liquefaction layers.