JP2015200071A - temporary support method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temporary support method capable of efficiently and surely base-isolating an existing building, while burdening stress caused in a foundation of the existing building.SOLUTION: A temporary support method is a method for temporarily supporting an existing building 1 from below. The temporary support method comprises a step S4 of providing a frozen soil wall 40 by freezing moisture of at least a part of a ground 5 under the existing building 1, a step S5 of forming an excavation space 21a by excavating the ground 5 while temporarily supporting the existing building 1 by the frozen soil wall 40 and a step S6 of temporarily supporting the existing building 1 by a timbering 50 by providing the timbering 50 in the excavation space 21a.

Description

  The present invention relates to a temporary support method for temporarily supporting a structure when the structure is subjected to seismic isolation, for example.

Conventionally, there has been known a base-isolated retrofit construction for making an existing building base-isolated under the foundation (see Patent Document 1).
When an existing building having a foundation without piles is to be seismically isolated by this foundation seismic isolation retrofit construction, for example, construction is performed according to the following procedure.

First, the ground just under the pillars and pressure plates other than the pillars is excavated, and a support is built in the excavated space to temporarily support the foundation.
Next, the ground directly under the pillar is excavated, and a seismic isolation device such as laminated rubber is attached to the excavated space, and then the jack is removed. Thereby, the base is supported by the seismic isolation device, and the existing building is seismically isolated (see Patent Document 1).

JP 2003-253911 A

  However, since the vertical load of the upper layer of the building is transmitted mainly to the lower layer through the pillar, the portion of the foundation of the existing building located immediately below the pillar is subjected to a larger vertical load than the remaining part. Therefore, when temporarily supporting the foundation of an existing building, if a portion away from the pillar, such as a foundation beam or a pressure plate, is supported, a large load is applied to the supported portion. Therefore, when the foundation beam and the pressure plate have low rigidity against the vertical load acting on the column, there is a problem that the foundation cracks or sinks.

  It is an object of the present invention to provide a temporary support method for a foundation that can efficiently and reliably perform seismic isolation even in an existing building having low rigidity of a foundation beam or a pressure plate.

  The temporary support method according to claim 1 is a temporary support method for temporarily supporting a structure (for example, an existing building 1 to be described later) from below, and a ground (for example, a ground 5 to be described later) under the structure. A step of freezing water in at least a part of the soil to provide a frozen soil portion (for example, a frozen soil wall 40 described later) and a temporary support of the structure in the frozen soil portion, A step (for example, step S5 described later) for excavating the ground to form a drilling space (for example, a later-described excavation space 21a), and a support (for example, a later-described support 50 for the later-described) are provided in the excavation space A step of temporarily supporting the structure by the support (for example, step S6 described later).

  The temporary support method according to claim 2 is characterized in that the frozen soil portion is provided immediately below a pillar (for example, a pillar 4 described later) of the structure.

  The temporary support method according to claim 3, wherein the frozen soil portion is formed around a freezing pipe (for example, a freezing pipe 41 described later) disposed in the soil along the core of the pillar of the structure. It is characterized by that.

According to the present invention, the frozen soil portion is provided on the ground below the foundation and directly below the pillar. Therefore, the vertical load applied to the pillars of the existing building can be temporarily supported by this frozen soil part, so that even if the existing building has a low rigidity of the foundation beam or pressure plate, it is prevented from cracking or sinking in the foundation. It can be isolated efficiently and reliably.
Moreover, even if the ground is excavated, it is possible to prevent the excavated surface from collapsing by forming a part of the excavated surface with the frozen soil portion.
Moreover, since it is not necessary to enter the inside of an existing building, construction can be performed while using the existing building as it is.

Here, there are three methods for improving the ground: a method of injecting a solidified material at a high pressure and mixing it with soil (deep mixing treatment method), a chemical solution injection method for injecting a chemical solution, and a freezing method of the present invention. The freezing method of the present invention has the following effects on the deep layer mixing method and the chemical solution injection method.
In other words, when constructing the frozen soil part, since cement-based materials are not used like the deep mixing method and chemical solution injection, it is not necessary to treat the earth and sand constituting the frozen soil part as industrial waste, and the cost is low. Become.

In addition, it is difficult to control the injection strength by controlling the injection amount in the chemical injection, but in the present invention, the strength and safety of the ground can be secured by managing the freezing temperature of the frozen soil part.
In addition, chemical injection cannot cope with rocks such as weathered rocks. However, in the present invention, the frozen soil part can be constructed only with a water content ratio regardless of the rocks, so that it is possible to cope with any rocky matter.
In addition, in the deep mixing treatment method, the solidification material is injected into the soil at a high pressure, which may cause cracks in the existing building or raise the foundation or pressure plate of the existing building. There is almost no such effect.

It is sectional drawing of the foundation part of the existing building with which the temporary support method of the foundation which concerns on one Embodiment of this invention is applied. It is sectional drawing which shows the state by which the existing building which concerns on the said embodiment was seismically isolated. It is a flowchart of the procedure which seismically isolates the existing building which concerns on the said embodiment. It is sectional drawing (the 1) for demonstrating the procedure which makes the existing building which concerns on the said embodiment seismic isolation. It is a top view for demonstrating the procedure to make the existing building based on the said embodiment seismic isolation. It is AA sectional drawing of FIG. It is BB sectional drawing of FIG. It is sectional drawing (the 2) for demonstrating the procedure which makes the existing building which concerns on the said embodiment seismic isolation. It is sectional drawing (the 3) for demonstrating the procedure which makes the existing building which concerns on the said embodiment seismic isolation.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of a foundation portion of an existing building 1 as a structure to which a temporary support method according to an embodiment of the present invention is applied.
The existing building 1 has an underground frame 2, and the underground frame 2 includes a foundation 3 and a plurality of pillars 4 extending upward from the foundation 3.

The foundation 3 is a solid foundation without piles constructed on the ground 5, and the foundation 3 includes a footing 10 and a pressure plate 11 that connects the footings 10 to each other.
Each column 4 extends upward from the center of the footing 10.

  As shown in FIG. 2, the existing building 1 is seismically isolated by supporting the foundation 3 from below with a seismic isolation device 20.

Specifically, an installation space 21 for installing the seismic isolation device 20 is formed under the foundation 3 of the existing building 1. On the bottom surface of the installation space 21, a mat slab 22 as a reinforced concrete base is constructed over the entire surface. In the upper surface of the mat slab 22, a base isolation base 23 made of reinforced concrete is provided at a position directly below the pillar 4, and the base isolation device 20 is provided on the base isolation base 23.
The seismic isolation device 20 takes a reaction force against the seismic isolation base 23 and the mat slab 22 to support the portion located immediately below the pillar 4 of the base 3 from below, while the base 3 is movable in the horizontal direction. keeping.

  A surrounding space 30 is formed around the underground building 2 of the existing building 1, and the surrounding space 30 is surrounded by a retaining wall 31. The lower end of the retaining wall 31 is joined to the mat slab 22. A retaining wall 32 is provided outside the retaining wall 31.

FIG. 3 is a flowchart showing a procedure for isolating the foundation 3 of the existing building 1.
In step S1, primary excavation is performed as shown in FIG.
That is, the retaining wall 32 is constructed around the existing building 1, and the ground 5 between the existing building 1 and the retaining wall 32 is excavated to the depth of the lower end of the foundation 3. The space formed by this excavation becomes a part of the surrounding space 30.

In step S2, as shown in FIG. 4, a leading frame is constructed in the part that has been primarily excavated.
That is, a part of the retaining wall 31 is constructed in advance inside the mountain retaining wall 32, and a temporary beam 33 that connects the retaining wall 31 and the underground frame 2 of the existing building 1 is constructed. This temporary beam 33 functions as a mountain retaining work such as a cut beam that supports earth pressure and horizontally restrains it.
Here, the ground 5 is composed of a stratum M1 directly below the foundation 3 of the existing building 1 and a stratum M2 below the stratum M1. For example, the formation M1 is a pumice tuff layer, the formation M2 is a tuff silt formation, and is a more stable ground than the formation M1.

In step S3, secondary excavation is performed as shown in FIGS.
That is, the ground 5 between the existing building 1 and the mountain retaining wall 32 is excavated to a depth that becomes the lower end of the mat slab 22 to complete the surrounding space 30.
By this secondary excavation, the slope 5A of the ground 5 is exposed under the foundation 3, so that the surface of the slope 5A is sprayed to protect it.

In step S4, as shown in FIGS. 5-7, the frozen soil wall 40 as a frozen soil part is constructed in the ground 5 under the foundation 3 of the existing building 1. FIG.
The frozen earth wall 40 is formed by a freezing method. Specifically, first, a plurality of freezing tubes 41 are driven substantially horizontally along the core of the pillar 4 from the slope 5A protected by the mortar toward the ground 5 below the foundation 3. Thereby, the freezing pipe 41 is disposed in the soil. Then, by circulating a cooling liquid through the freezing tube 41, the periphery of the freezing tube 41 is cooled to freeze moisture in the soil. Thereby, the frozen earth wall 40 centering on these freezing pipes 41 is formed.
The height of these frozen earth walls 40 extends from the boundary between the formation M1 and the formation M2 to the lower surface of the foundation 3.

  In step S5, as shown in FIG. 8, the ground 5 under the foundation 3 of the existing building 1 is excavated while the foundation 3 is supported by the frozen earth wall 40. The excavation space 21 a formed by this excavation becomes a part of the installation space 21.

In step S6, as shown in FIG. 8, the support 50 is installed in the bottom part of the excavation space 21a, and the foundation 3 is temporarily supported. This support work 50 is installed directly under the pillar 4 as much as possible. Specifically, the support work 50 is installed in the vicinity of the frozen soil wall 40 and directly below the footing 10.
The support 50 includes a reinforced concrete base 51 that is a part of the mat slab 22, and a column 52 that extends upward from the base 51 and incorporates a jack.

In step S7, the frozen soil wall 40 is removed while the foundation 3 is temporarily supported by the support 50 as shown in FIG.
That is, the jack of the support 50 is driven, and the foundation 3 is temporarily supported by the support 50 from below. Next, freezing by the freezing tube 41 is released, and this freezing tube 41 is removed. Thereafter, the remaining ground 5 under the foundation 3 of the existing building 1 is excavated to complete the installation space 21.

In step S8, as shown in FIG. 9, the bar is placed at the bottom of the installation space 21 and concrete is laid to construct the mat slab 22. At this time, the base 51 of the support 50 becomes a part of the mat slab 22.
Moreover, the lower part of the retaining wall 31 is constructed and the retaining wall 31 and the mat slab 22 are integrated.

  In step S9, the base isolation base 23 is constructed on the mat slab 22, the base isolation device 20 is installed on the base isolation base 23, and the part located directly below the pillar 4 of the base 3 with the base isolation device 20 Support.

  In step S10, the temporary support by the support work 50 is released, and the support work 50 is removed.

According to this embodiment, there are the following effects.
(1) A frozen soil wall 40 was provided at a position on the ground 5 below the foundation 3 and immediately below the pillar 4. Therefore, since the vertical load applied to the pillar 4 of the existing building 1 can be temporarily supported by the frozen wall 40, even if the existing building 1 has low rigidity of the foundation beam or the pressure plate, the foundation 3 is cracked or sinks. It is possible to prevent seismic isolation and ensure seismic isolation.
Even if the ground 5 is excavated, the excavated surface can be prevented from collapsing by forming a part of the excavated surface with the frozen soil wall 40.
Moreover, since it is not necessary to enter the inside of the existing building 1, it can construct while using the existing building 1 as it is.

  When constructing the frozen soil wall 40, cement-based materials are not used, such as deep mixing method and chemical injection, so it is not necessary to treat the earth and sand that constitutes the frozen soil wall 40 as industrial waste. In addition to reducing the impact, the cost is low.

In addition, in the chemical injection, it is difficult to control the injection amount and manage the strength of the ground, but in the present invention, the freezing temperature of the frozen soil wall 40 is managed to ensure the strength and safety of the ground.
In addition, chemical injection cannot cope with rocks such as weathered rocks. However, according to the present invention, the frozen soil wall 40 can be constructed only with the water content regardless of the rocks, so that it is possible to cope with any rocks.
In addition, in the deep mixing treatment method, since the solidification material is injected into the soil at a high pressure, there is a possibility that the existing building 1 may be cracked or the foundation or pressure plate of the existing building may be lifted. There is almost no such effect.

It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.
For example, in the present embodiment, the height of the frozen soil wall 40 is set from the boundary portion between the formation M1 and the formation M2 to the lower surface of the foundation 3. However, the present invention is not limited to this, and the height of the frozen soil wall is the lower end of the mat slab 22 It is good also from the vicinity to the lower surface of the foundation 3.

  In the present embodiment, the support 50 is installed at the bottom of the excavation space 21a, and the base 51 of the support 50 is a part of the mat slab 22. However, the present invention is not limited to this, and the support 50 is installed. Alternatively, a part of the mat slab 22 may be constructed, and a support work may be provided on the constructed mat slab.

  Further, in this embodiment, excavation is started from the surrounding space 30 outside the existing building 1, but when there is not enough room on the site, an opening is provided in the pressure-resistant plate 11 of the existing building 1, and excavation is performed from this opening. You may start.

  Moreover, in this embodiment, although the wall-shaped frozen earth wall 40 was formed in a part of the ground 5 directly under the foundation 3, you may freeze the whole ground 5 directly under the foundation 3 not only in this.

Moreover, in this embodiment, although this invention was applied to the solid foundation without a pile, it is not restricted to this, It can also apply to the pile foundation which has a pile, and the lack of pile yield strength at the time of excavation can also be compensated.
Moreover, in each above-mentioned embodiment, although this invention was applied to the existing building 1, it can apply not only to this but to structures, such as a retaining wall.

M1, M2 ... Geologic layer 1 ... Existing building (structure)
2 ... underground structure 3 ... foundation 4 ... pillar 5 ... ground 5A ... slope 10 ... footing 11 ... pressure resistant plate 20 ... seismic isolation device 21 ... installation space 21a ... excavation space 22 ... mat slab 23 ... base isolation base 30 ... surrounding space 31 ... Retaining wall 32 ... Mountain retaining wall 33 ... Temporary beam 40 ... Frozen earth wall (frozen earth part)
41 ... Freezing pipe 50 ... Supporting work 51 ... Base 52 ... Post

Claims (3)

A temporary support method for temporarily supporting a structure from below,
Freezing the moisture in the soil of at least part of the ground under the structure to provide a frozen soil part;
A step of excavating the ground to form an excavation space while temporarily supporting the structure in the frozen soil portion;
Providing a supporting work in the excavation space, and temporarily supporting the structure by the supporting work.   The temporary support method according to claim 1, wherein the frozen soil portion is provided directly below a pillar of the structure.   The temporary support method according to claim 1, wherein the frozen soil portion is formed around a freezing pipe disposed in the soil along a core of a pillar of the structure.

Images