JP3689840B2 - Seismic reinforcement method for existing structure foundation - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a seismic reinforcement method for enhancing the seismic resistance of foundations of existing structures such as piers and buildings.
[0002]
[Prior art]
When performing seismic reinforcement of foundations of existing structures, increasing the proof strength (supporting force) of the foundation and preventing liquefaction of the ground are important issues, and various methods for solving these two issues have hitherto been proposed. Has been developed. That is, as a method of increasing the proof stress, for example, an additional pile is constructed by placing an additional pile around the pile foundation and integrating the additional pile with the existing footing. There are methods such as adding steel pipe sheet pile foundations and integrating these with existing footings. In addition, as a method of preventing liquefaction, for example, a method of suppressing the shear deformation of the ground that occurs during an earthquake by surrounding the foundation ground with concrete walls, sheet pile walls, etc., a high-pressure jet stirring method from the bottom of the footing to the support layer There is a solidification method that improves the foundation ground by applying a solidification method such as the above.
[0003]
[Problems to be solved by the invention]
However, each of the above-mentioned construction methods has a large construction, and requires not only a wide construction space, but also has a problem that extension of construction period and increase in construction cost are inevitable.
In addition, each of the above-mentioned construction methods is effective only for either increasing the yield strength of the foundation or preventing liquefaction of the ground, and there is another problem that it is not reliable in terms of seismic reinforcement. there were.
Recently, as an additional pile of the above-described additional pile method, a method using a micropile that is easy to construct has also been developed (see, for example, Japanese Patent Laid-Open No. 10-140583). Inability to prevent this is no different from the conventional additional pile method.
[0004]
The present invention was made in order to solve the above-mentioned conventional problems, and the object of the present invention is to provide an existing structure that is easy to construct, capable of simultaneously increasing the yield strength of the foundation and preventing liquefaction of the ground. The purpose is to provide a seismic reinforcement method for building foundations.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present invention creates a modified column in the ground around a foundation under a footing of an existing structure by a high-pressure jet stirring method, and uses a steel pipe as a core material in the modified column. A pile is placed, and the construction of the improved pillar and the placement of the micropile are continuously performed so that the improved pillars wrap each other, and a continuous wall surrounding the foundation is constructed. The footing is added so as to wrap the pile pile head.
[0006]
In the seismic retrofitting method for existing structure foundations, the high-pressure injection stirrer method can be used to create large-diameter improved columns, and these improved columns are continuously wrapped together. Thus, a continuous wall surrounding the foundation under the footing can be easily constructed. And the presence of this continuous wall suppresses the shear deformation of the ground under the footing during an earthquake and prevents the ground from becoming liquefied.
In addition, a micropile with a steel pipe as the core material is placed in each improved pillar that constitutes this continuous wall, and the pile head of each micropile is wrapped in an additional part of the footing and integrated with the footing. , The support of the foundation itself will be sufficient.
[0007]
In the present invention, it is desirable to form the improved column in such a form as to embed the outer peripheral edge of the footing, whereby the footing and the improved column are brought into close contact with each other, and the load transmission from the footing to the improved column is ensured. .
In the present invention, it is also desirable to add a footing after connecting the pile heads of each micropile to each other, which makes the integration of the pile head and the footing of the micropile more reliable, Yield strength is further improved.
In the present invention, a reinforcing member such as an H-shaped steel, a steel pipe, or a steel bar may be inserted into the steel pipe of the micropile, thereby increasing the horizontal resistance force (bending rigidity) of the micropile itself and increasing the size. As a seismic reinforcement of existing structures, the reliability is significantly improved.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
[0009]
1 and 2 show one embodiment of the seismic reinforcement method according to the present invention. The present embodiment is intended for the foundation of an pier 1 as an existing structure. The pier 1 is formed on a plurality of piles 4 in which footings 2 provided integrally at the bottom of the pier 1 are placed in the ground 3. Installed and fixed in the mounted state. Each pile 4 is driven into the ground 3 until the tip of each pile reaches the support ground 5, and a plurality of the piles together constitute one pile foundation 6 and exhibit a predetermined proof strength (supporting force). It is like that. Thus, an annular continuous wall 10 is constructed around the pile foundation 6. On the other hand, on the ground surface side of the ground 3, the upper end of the continuous wall 10 and the footing of the pier 1 (existing footing). An extension footing 11 that connects and integrates 2 and 2 is constructed.
[0010]
The continuous wall 10 includes a large-diameter improved column 12 formed in the ground 3 by a high-pressure jet stirring method described later, and a micropile 13 placed in the axial center position of the improved column 12 by a method described later. The composite 14 is a unit, and a plurality of the composites 14 are connected to each other while being wrapped together. The improved pillar 12 constituting the composite 14 is constructed so as to embrace the outer peripheral edge of the existing footing 2. Accordingly, the existing footing 2 has the lower surface of the outer peripheral edge of the improved pillar of each composite 14. 12 is supported. The micropile 13 includes a hollow core material (steel pipe) 15 and a fixing layer 16 therearound. The core material 15 is firmly fixed to the improved column 12 via the fixing layer 16. On the other hand, the pile heads 13a of each micropile 13 are embedded in the extension footing 11 in a state where they are connected to each other by connecting members (not shown) such as reinforcing bars and frames. 10 and the existing footing 2 are firmly integrated via the extension footing 11.
[0011]
In carrying out this construction method, a guide hole 20 (FIG. 3) reaching the support ground 5 is drilled in the ground 3 around the pile foundation 6 in advance using a drilling machine. Then, as shown in FIG. 3, first, an injection rod 24 having an injection nozzle 23 at the tip is inserted into a steel pipe 22 having a plurality of check valves 21 on the pipe wall, and both are supported by a processor not shown. Then, it is inserted into the guide hole 20 integrally. At this time, as shown in (1) of FIG. 3, both are positioned so that the injection nozzle 23 at the tip of the injection rod 24 protrudes from the tip of the steel tube 22, and the injection rod 24 is rotated. When the injection nozzle 23 reaches the side position S ₁ of the existing footing 2, a grout such as cement milk (water-cement ratio (W / C) of about 60 to 70%) is pumped into the rotating injection rod 24. To do. Then, the grout is sprayed from the injection nozzle 23 at the tip of the injection rod 24 onto the surrounding ground at a high pressure, and the ground around the steel pipe 22 is stirred and mixed by this grout to form a large-diameter stirring and mixing layer 25.
[0012]
The stirring and mixing layer 25 gradually expands downward in accordance with the lowering of the steel pipe 22 and the injection rod 24, and when the injection nozzle 23 reaches the bottom of the guide hole 20, as shown in (2) in FIG. It extends beyond the boundary S ₂ between the ground 3 and the supporting ground 5 until it slightly bites into the supporting ground 5. At this stage, the grout pumping to the inflow rod 24 is stopped, and the injection rod 24 is pulled out from the steel pipe 22. Instead, the injection machine (double packer) 26 is connected to the steel pipe 22 as shown in (3) in FIG. Insert inside. The injector 26 includes a pair of bulging bodies 27 that can bulge and deform. First, the injector 26 is inserted into the deepest position of the steel pipe 22, and the pair of bulging bodies 27 are expanded at the deepest position. Then, the pouring machine 25 is fixed in position, and a hardened material grout such as cement mortar (water-cement ratio (W / C) of about 40 to 50%) is pumped through the feeding pipe 28. Then, the hardened material grout is opened around the steel pipe 22 by opening the check valve 21 on the pipe wall of the steel pipe 22, mixed into the stirring and mixing layer 25, and around the steel pipe 22, the hardened material injection layer is formed. 29 is formed. The hardener injection layer 29 expands upward by repeating the above operation while pulling up the injector 26 at a predetermined pitch, and at the stage where the injector 26 is pulled up to the side position S ₁ of the existing footing 2. The injection of the grout is stopped, and the injector 26 is pulled out from the steel pipe 22 as it is.
[0013]
The stirring and mixing layer 25 and the hardened material injection layer 29 are cured after a predetermined time, and are transformed into the fixing columns 16 of the improved pillars 12 and the micropile 13, respectively, and around the pile foundation 6 as shown in FIG. In addition, one composite 14 in which the improved pillar 12 and the micropile 13 are integrated is formed. In this case, the steel pipe 22 with the check valve 21 remains as the core material 15 of the micropile 13 as it is. In the present embodiment, the formation of the composite 14 is continuously performed so that the improved pillars 12 overlap each other, and the continuous wall 10 surrounding the pile foundation 6 is constructed.
[0014]
When the creation of the continuous wall 10 is completed, first, the ground surface above this is excavated to expose the pile head 13a of the micropile 13 and the existing footing 2. Next, the pile heads 13a of each micropile 13 are connected to each other using a connecting member, and in parallel with this, the surface of the existing footing 2 is suspended, and the reinforcing bars are exposed in some cases. When a reinforcing bar is exposed, a new reinforcing bar is incorporated around the existing footing 2 in a state where the reinforcing bar is connected to a connecting member that connects the reinforcing bar and the pile head 13a, and the existing footing 2 including the pile head 13a. Put concrete around. Thereby, the extension footing 11 is constructed, and the continuous wall 10 surrounding the pile foundation 6 is firmly integrated with the existing footing 2 via the extension footing 11, and as a result, the strength of the foundation of the pier 1 as an existing structure is obtained. (Supporting force) is greatly increased and can withstand shaking during an earthquake. In the present embodiment, in particular, the grout for forming the improved column 12 has a W / C ratio of about 60 to 70%, and the grout for forming the micropile 13 has a W / C ratio of about 40 to 50%. Since it is used, the strength of the improved column 12 itself is sufficiently increased, and the bonding strength between the improved column 12 and the micropile 13 is also sufficiently increased, and the supporting force of the foundation of the pier 1 is remarkably increased.
[0015]
On the other hand, the presence of the continuous wall 10 suppresses the invasion of seismic waves into the ground below the footing 2, and the corresponding portion suppresses shear deformation of the ground, thereby preventing liquefaction of the ground. Particularly in the present embodiment, the high-strength improved column 12 is formed so as to embrace the outer peripheral edge portion of the existing footing 2, so that the adhesion between the outer peripheral edge portion of the existing footing 2 and the continuous wall 10 is established. (Joining) is sufficient, and load transmission from the existing footing 2 to the continuous wall 10 is ensured.
[0016]
In the present invention, after placing the micropile 13, the core 15 may be filled with grout. At this time, as shown in FIG. 3, for example, the H-section steel 30 ((1) ), Steel pipe 31 ({circle over (2)}), steel bar 32 ({circle over (3)}), or other types of reinforcing members such as rebar cages may be inserted into the core 15 and hardened with grout. By inserting the reinforcing members 30, 31, and 32 into the core member 15 in this way, the horizontal resistance force (bending rigidity) of the micropile 13 itself is increased, and reliability as a seismic reinforcement of a large existing structure is increased. It will be significantly improved.
[0017]
【The invention's effect】
As described above, according to the seismic reinforcement method for the existing structure foundation according to the present invention, the large-diameter improved pillar and the micropile placed inside this are integrated to reinforce the existing footing, Since the continuous wall including these improved pillars and micropile suppresses the invasion of seismic waves into the ground under the existing footing, seismic reinforcement will be made from both aspects of strengthening strength and preventing liquefaction, and the reliability is remarkably high. improves.
In addition, since the improved pillars are created using the high-pressure jet agitation method, large-scale mechanical equipment is not required for the construction, and it is possible not only to work in a small space in combination with the simple construction of the micropile. The construction period can be shortened and the construction cost can be reduced, and the utility value of the present invention is great.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing one embodiment of the present invention applied to seismic reinforcement of a bridge pier.
FIG. 2 is a plan view schematically showing a construction mode of a continuous wall according to the present invention.
FIG. 3 is a cross-sectional view schematically showing a procedure of improved column creation and micropile placement in the present invention.
FIG. 4 is a plan view showing types of reinforcing members to be inserted into the micropile and insertion states thereof.
[Explanation of symbols]
1 Pier (existing structure)
2 Existing Footing 3 Ground 4 Existing Pile 5 Support Ground 6 Pile Foundation 10 Continuous Wall 11 Additional Footing 12 Improved Pillar 13 Micropile 13a Micropile Pile Head 15 Steel Pipe 16 Fixing Layer 30, 31, 32 Reinforcing Member

Claims (4)

In the ground around the foundation under the footing of the existing structure, an improved column is created by a high-pressure jet stirring method, and a micropile with a steel pipe as a core material is placed in the improved column, Constructing and placing the micropile continuously so that the improved pillars wrap each other to build a continuous wall surrounding the foundation, and then the footing to wrap the pile head of the micropile Seismic reinforcement method for existing structural foundations, characterized by the expansion. The seismic reinforcement method according to claim 1, wherein the improved column is formed in such a manner as to embrace the outer peripheral edge of the footing. The seismic reinforcement method according to claim 1 or 2 , wherein a footing is added after the pile heads of each micropile are connected to each other. The seismic reinforcement method according to any one of claims 1 to 3 , wherein a reinforcing member is inserted into the steel pipe of the micropile.

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