JP2000199236A - Earthquake resistant reinforcing method for existence pile foundation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent piles or a foundation slab from being destroyed or sunk unequally by constructing improvers reaching the bottom surface of the foundation slab by its end from the outer circumference of a foundation slab through the stirring and mixing operation of original ground soil and a solidifying agent. SOLUTION: Improvers 4 are constructed to be inclined with respect to perpendicularity in a manner not giving rise to collision with piles 2 so that its end comes to a foundation slab 1 or the bottom surface of the ground therearound through the stirring and mixing of ground soil and a solidifying agent from the ground at the outer periphery of the foundation slab 1. In this instance, an outer peripheral slab 5 being connected with each apex of the improvers 4 is constructed in contiguity with the foundation slab, and the improvers 4 are indirectly connected to the foundation slab. As such, inasmuch as the improvers 4 are caused to bear a part of the vertical load of an upper part structure and horizontal force exerting the foundation slab during earthquake, vertical upward reaction exerting the piles with the horizontal force, compression force and horizontal force being borne by the piles can be reduced. Therefore, this prevents the destruction and sinking of piles caused along with an effect of horizontal force can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for increasing the horizontal strength of an existing pile foundation and preventing the pile from being damaged by an earthquake.

[0002]

2. Description of the Related Art When an earthquake force acts on an existing pile foundation in which a foundation slab is supported by a pile, a horizontal force P input to the foundation slab as shown in FIG.
The pile exerts a bending moment and a shearing force on the pile, but the pile bears all of the horizontal force P. If the horizontal strength of the pile is insufficient against the excessive horizontal force P, the pile can be broken by the horizontal force P. There is. This is remarkable in the case of soft ground where the restraint of the pile is weak.

In addition, the pile attempts to resist the vertical force acting on the foundation slab by the vertical upward reaction force,
The reaction force increases the compressive force borne by the vertical load W of the upper structure 7 on the foundation slab in normal times, so the compressive force borne by the pile during an earthquake becomes excessive, and the vertical load capacity of the pile decreases. This may lead to uneven settlement of the foundation slab.

In view of the above background, the present invention proposes a seismic reinforcement method for preventing pile breakage and uneven settlement of a foundation slab due to seismic force acting on an existing pile foundation.

[0005]

According to the present invention, an improved body is constructed in which the tip reaches the bottom of the base slab or its surrounding ground from the outer periphery of the base slab by stirring and mixing the original ground soil and the solidified material. At the same time, the existing pile foundation is seismically reinforced by constructing an outer peripheral slab connected to the top of the foundation slab and the improved body on the outer periphery of the foundation slab. The improved body is constructed to be inclined with respect to the vertical from the outer periphery of the base slab to the bottom side of the base slab.

[0006] The improved body is constructed obliquely below the base slab while being connected at the top to an outer peripheral slab connected to the base slab, so that the vertical load W of the upper structure 7 on the base slab and the base slab during an earthquake are reduced. Of the horizontal force P acting on the pile, and the compressive force and the horizontal force that the pile bears are reduced accordingly.

[0007] The improved body also bears part of the vertical upward reaction force additionally generated on the pile due to the horizontal force acting on the foundation slab, and reduces the increase in the compressive force of the pile due to the action of the horizontal force. I do.

[0008] By reducing the horizontal force and compressive force that the pile bears during an earthquake, the pile is prevented from breaking and subsidence due to the action of the horizontal force, and the pile foundation is kept healthy even against excessive horizontal force. It becomes possible.

According to the second aspect of the present invention, when the improved body is arranged so as to surround the base slab on both sides of the base slab on a plane and in two directions, the ground is restrained by a set of improved bodies. Because of the effect, the improved body also functions to prevent liquefaction of the ground that may be liquefied.

[0010] If a core material having a tensile resistance is inserted in the axial direction of the improved body as described in claim 3, the improved body also has a resistance to tensile force, so that the improved body sandwiches the base slab. When constructed from both sides, one improvement sandwiching the foundation slab bears the compressive force against the horizontal force, the other improvement bears the tensile force, and both improvements on both sides resist the horizontal force. Therefore, the compressive force and the horizontal force to be borne by the pile are further reduced, and the safety against breakage and settlement of the pile is improved.

According to a fourth aspect of the present invention, when a tension is applied to the core material in the third aspect, a prestress is introduced into the improved body, whereby the bending strength and the shear strength of the improved body itself are increased.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a method for reinforcing an existing pile foundation 3 in which a foundation slab 1 is supported by piles 2 by means of an improved body 4.

As shown in FIG. 1 and FIG. 2, the improved body 4 is formed by stirring and mixing the original ground soil and the solidified material from the ground around the foundation slab 1 so that the tip of the improved body 4 is below the bottom of the foundation slab 1 or the surrounding ground. And is constructed so that collision with the pile 2 does not occur.

On the outer periphery of the base slab 1, an outer peripheral slab 5 to which the top of the improved body 4 is connected is constructed by connecting to the base slab 1, and the improved body 4 is indirectly connected to the base slab 1. The improved body 4 is formed in a columnar shape as shown in FIG. 1 or on the outer periphery of the cutter post by a stirring and mixing processing method of excavating the ground and stirring and mixing with the solidified material by rotating a drilling bit having a drilling bit and a stirring blade. A ground improvement machine on which an endless chain having cutting agitating wings is stretched is horizontally moved with the discharge of the solidified material while circulating through the endless chain, thereby forming a wall shape as shown in FIG. In the former case, the excavation rod is used, and in the latter case, the cutter post is used with the cutter inclined.

In FIG. 3, in order to reduce the construction area of the outer peripheral slab 5, the length direction of the improved body 4 located on both sides of the long side of the base slab 1 is directed toward the long side of the base slab 1, The length direction of the improved bodies 4 located on both sides is directed to the short side direction of the base slab 1, but the length direction of the improved bodies 4 positioned on both sides of the long side of the base slab 1 is set to the short side of the base slab 1. In some cases, the length direction of the improved body 4 located on both sides of the short side may be directed to the long side direction of the base slab 1.

In the case of FIG. 3, in order to avoid collision with the pile 2,
Although the inclination angle of the improved body 4 with respect to the vertical cannot be increased, if the length direction of the improved body 4 located on both sides of the long side of the base slab 1 is directed to the short side direction of the base slab 1, it is shown in FIG. Even with the same inclination angle as that of the improved body 4, collision with the pile 2 can be avoided.

In the drawings, the pile foundation 3
In order to reinforce the earthquake resistance, on a plane across the foundation slab 1,
The case where the improved body 4 is constructed so as to surround the foundation slab 1 on both sides in two directions is shown, but the improved body 4 is constructed only on one side of the foundation slab 1 depending on the conditions of the site around the foundation slab 1. In some cases.

When the improved body 4 is constructed on both sides in two directions with the foundation slab 1 interposed therebetween, the two-way improved bodies 4 and 4 constructed on the plane near the corners of the foundation slab 1 do not collide with each other. The tilt angle is adjusted.

FIG. 2 shows a case where a core material 6 having a tensile resistance is inserted in the axial direction of the improved body 4. In this case, after the core 4 is applied, the core 6 is inserted into the core 4 before it is cured, and the lower end, which is the tip, is fixed in the ground. As the core material 6, a reinforcing fiber is used in addition to a steel material such as a rebar or a steel bar.

Since the core 6 functions to resist the tensile force acting on the improved body 4, it is not always necessary to apply a tension. However, in order to increase the strength of the improved body 4, The upper end may be fixed to the improved body 4 in a state where the tension is applied.

[0021]

According to the present invention, an improved body whose tip reaches the bottom of the base slab or the bottom of the base slab or the surrounding ground is constructed by stirring and mixing the original ground soil and the solidified material from the outer periphery of the base slab.
By constructing an outer slab connected to the top of the foundation slab and the improved body on the outer circumference of the foundation slab, the vertical load of the superstructure on the foundation slab and the horizontal force and horizontal force acting on the foundation slab during an earthquake on the improved body Accordingly, a part of the vertical upward reaction force acting on the pile is borne, so that the compressive force and the horizontal force borne by the pile can be reduced.

As a result, breakage and settlement of the pile due to the action of the horizontal force can be prevented, and the pile foundation can be kept healthy even with an excessive horizontal force. In claim 2, since the improved body is arranged so as to surround the base slab on both sides in two directions on a plane with the base slab interposed therebetween, an effect of restraining the ground by the assembly of the improved body is produced, and the possibility of liquefaction is generated. The liquefaction can be prevented for the ground with the ground.

According to a third aspect of the present invention, a core material having a tensile resistance is inserted in the axial direction of the improved body, and the improved body is constructed from both sides with a basic slab interposed therebetween in order to give the improved body a resistance to a tensile force. In this case, one of the improved bodies sandwiching the base slab bears the compressive force against the horizontal force, the other improved body bears the tensile force, and both improved bodies on both sides resist the horizontal force, The compressive and horizontal forces that the pile must bear are reduced,
The safety against pile breakage and settlement is improved.

According to the fourth aspect, since the tension is introduced into the core material according to the third aspect, the bending strength and the shear strength of the improved body itself are increased.

[Brief description of the drawings]

FIG. 1 is a plan view showing a relationship between an existing pile foundation and an improved body.

FIG. 2 is a longitudinal sectional view of FIG.

FIG. 3 is a plan view showing a relationship between an existing pile foundation and the improved body when the improved body is constructed in a wall shape.

FIG. 4 is a schematic diagram showing how horizontal force acts on a pile head when a horizontal force acts on an existing pile foundation.

[Explanation of symbols]

1 ... foundation slab, 2 ... pile, 3 ... existing pile foundation, 4 ...
... Improved body, 5 ... Outer peripheral slab, 6 ... Core material, 7 ... Superstructure.

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Hiromasa Huang 6-13-7 Akasaka, Minato-ku, Tokyo Tenox Co., Ltd. F-term (reference) 2D046 DA11

Claims (4)

[Claims] In an existing pile foundation in which a foundation slab is supported by piles, the tip of the foundation slab or the solidified material is agitated and mixed from the outer periphery of the foundation slab so that the tip thereof is located below the bottom surface of the foundation slab or the surrounding ground. A seismic retrofit method for an existing pile foundation that constructs an improved arriving body, connects the foundation slab to the outer periphery of the foundation slab, and constructs an outer peripheral slab to which the top of the improved slab connects. 2. The method for seismic reinforcement of an existing pile foundation according to claim 1, wherein the improved body is arranged so as to surround the foundation slab on both sides in two directions on a plane across the foundation slab. 3. The method for seismic reinforcement of an existing pile foundation according to claim 1, wherein a core material having a tensile resistance is inserted in an axial direction of the improved body. 4. The method according to claim 3, wherein a tension is introduced into the core material.