JP2023176278A - Underfloor reinforcement method and underfloor reinforcement structure - Google Patents

Abstract

To provide an underfloor reinforcement method or the like increased in strength in a reinforced place.SOLUTION: The underfloor reinforcement method for reinforcing an underfloor by filling a cavity 3 between a ground 2 and a floor 1 comprises: a step of forming a through-hole 4 connected to the cavity 3 in the floor 1; a step of inserting a rod-like drill from the through-hole 4 into the cavity 3 side to dig in the ground 2, and forming a longitudinal hole extending down from the cavity 3 directly below the through-hole 4; a step of supplying a liquid ground reinforcement 5 from the through-hole 4 into the cavity 3 and the longitudinal hole; a step of inserting the drill from the through-hole 4 into the longitudinal hole and stirring the ground reinforcement 5 in the longitudinal hole to permeate the ground reinforcement 5 through soil around the longitudinal hole, and retaining the shape of the longitudinal hole through curing action of the ground reinforcement 5; a step of supplying a foaming resin from the through-hole 4 to fill the cavity 3 and the longitudinal hole; and a step of closing the through-hole 4 after the cavity 3 and the longitudinal hole have been filled with the foaming resin.SELECTED DRAWING: Figure 6

Description

Application for application of Article 30, Paragraph 2 of the Patent Act has been filed (1) Publication address (top page) https://reiwa-corp. net/ (invention publication page) https://reiwa-corp. net/construction. html Posted on July 1, 2021

The present invention relates to an underfloor reinforcing method and an underfloor reinforcing structure.

Floors of factories, warehouses, etc. are generally made of cement-based materials such as concrete and mortar. This type of floor is usually formed into a layer (plate shape) having a predetermined thickness so as to cover the ground. Such floors are widely used because they have excellent strength and load resistance.

By the way, it is known that cavities are formed under this type of floor over time. Cavities are mainly caused by vibrations generated by various mechanical devices installed on the floor (e.g. machine tools) or moving objects moving on the floor (e.g. forklifts) being transmitted to the ground, causing the ground to loosen. It is thought that it is formed due to subsidence. Since such a cavity is formed between the floor and the ground, the part of the floor where the cavity is formed is separated from the ground and appears to be floating in the air. In other words, the floor in the area where the cavity is formed is not supported by the ground, so it supports the load solely by its own strength. If a floor in such a state is left unattended, damage such as cracks may occur in the floor, and in some cases, the floor may cave in.

Furthermore, since moisture (moisture) tends to accumulate inside the cavity, if cracks or the like occur in the floor, moisture may enter through the cracks or the like into the interior of the floor. Generally, reinforcing bars are buried inside the floor for reinforcement purposes, so if moisture comes into contact with such reinforcing bars, the reinforcing bars will rust over time and the volume of the reinforcing bars will decrease. will expand. As a result, cracks and the like will grow further and the floor will be destroyed.

Conventionally, before the floor is destroyed due to such cavities, work has been carried out to fill the cavities and reinforce the underfloor.

For example, in Patent Document 1, a through hole of 0.5 cm to 1.0 cm is formed in the concrete floor in the area where the cavity is formed, and water is injected into the cavity through the through hole to inject water into the ground. It is described that after infiltration, a predetermined resin is injected through the cotton with cotton stuffed in the through hole. The resin injected in this manner foams and expands, thereby filling the cavity with the resin. Note that the through hole will eventually be covered with concrete. Such an underfloor reinforcement method has attracted attention in recent years because it does not require replacing the floor, is easy to construct, and is advantageous in terms of cost.

Patent No. 6885641

Conventional underfloor reinforcement methods have room for improvement. For example, over time, due to the influence of vibrations and the like, the resin in the part that filled the cavity becomes misaligned with respect to the floor or ground, and there is a risk that a new cavity will be formed again at the reinforced location. Therefore, in this type of underfloor reinforcement method, it has been desired to further improve the strength of the repaired area.

An object of the present invention is to provide an underfloor reinforcing method and the like in which the strength of reinforced areas is improved.

Means for solving the above problem are as follows. That is,
<1> An underfloor reinforcement method for reinforcing the underfloor by filling a cavity formed between the ground and a floor having a predetermined thickness constructed on the ground, the method comprising penetrating the floor in the thickness direction. a through-hole forming step of forming a through-hole connected to the cavity, and inserting a rod-shaped drill from the through-hole into the cavity side and digging into the ground with the drill, thereby forming the cavity directly below the through-hole. a vertical hole forming step of forming a vertical hole extending downward from the through hole, a first supply step of supplying a liquid ground strengthening agent from the through hole to the cavity and the vertical hole, and inserting the drill from the through hole into the vertical hole. By stirring the ground strengthening agent in the vertical hole with the drill, the soil strengthening agent is infiltrated into the soil around the vertical hole, and the shape of the vertical hole is maintained by the hardening action of the soil strengthening agent. a vertical hole shape retaining step, and a second supply step of supplying a foamable resin from the through hole to fill the cavity and the vertical hole after the vertical hole shape retaining step; A method for reinforcing an underfloor, comprising a step of closing the through hole after the through hole is filled with resin.

<2> In the second supply step, a nozzle for supplying the foamable resin is inserted into the through hole, and a gap formed between the through hole and the nozzle is filled with water containing liquid. The underfloor reinforcing method according to <1> above, in which the underfloor reinforcement method is covered with a rubber sheet.

<3> In the closing step, the water-retaining sheet used in the second supplying step is packed into the through-hole, and the through-hole is closed with a cement-based material so as to cover the packed water-retaining sheet. The underfloor reinforcement method described in <2>.

<4> An underfloor reinforcement structure that fills a cavity formed between the ground and a floor having a predetermined thickness constructed on the ground, the structure being formed in the floor and penetrating the cavity in the thickness direction. a through hole connected to the through hole, a vertical hole formed directly below the through hole, extending downward from the cavity and retaining its shape due to the hardening action of a soil strengthening agent that has permeated into the surrounding soil, and the cavity and the vertical hole. An underfloor reinforcing structure comprising a foamed resin made of a foamable resin that fills the through hole, and a plug that closes the through hole.

According to the present invention, it is possible to provide an underfloor reinforcing method and the like in which the strength of the reinforced portion is improved.

Explanatory diagram showing an example of a floor constructed on the ground Explanatory diagram showing a state in which a cavity is formed between the floor and the ground Explanatory diagram showing the through hole forming process Explanatory diagram showing the vertical hole forming process An explanatory diagram showing a vertical hole formed by digging into the ground during the vertical hole formation process Explanatory diagram showing the first supply process Explanatory diagram showing the vertical hole shape retention process Explanatory diagram showing a vertical hole with the surrounding mixture hardened and retaining its shape Explanatory diagram showing the second supply process Explanatory diagram showing the occlusion process Enlarged cross-sectional view of the plug that closes the through hole

[Embodiment 1]
The underfloor reinforcing method according to Embodiment 1 of the present invention will be described below with reference to FIGS. 1 to 11. FIG. 1 is an explanatory diagram showing an example of a floor 1 constructed on a ground 2. As shown in FIG. First, the floor 1 to which the underfloor reinforcing method of this embodiment is applied will be briefly described. The floor 1 is a layered (plate-shaped) member having a predetermined thickness and made of a cement-based material such as concrete or mortar as a main material (base material). Examples of such a floor 1 include a concrete floor, a mortar floor, and the like. Furthermore, reinforcing members such as reinforcing bars may be provided inside the floor 1. Floor 1 is the floor of a building such as a factory, warehouse, or store.

In addition, in other embodiments, the present invention may be applied to floors of civil engineering buildings formed on the ground, and road surfaces such as roads and runways, in addition to building floors, as long as the purpose of the present invention is not impaired. A method of reinforcing the underfloor may be applied. FIG. 1 shows a state in which a floor 1 is constructed directly on the surface 2a of the ground 2. In addition, in other embodiments, another layer (for example, a crushed stone layer) for the purpose of strengthening the ground may be formed on the surface 2a of the ground 2, as long as the object of the present invention is not impaired.

As shown in FIG. 1, when the floor 1 is initially constructed on the ground 2, there is no cavity between the ground 2 and the floor 1. In the following description, it is assumed that the floor 1 is a "concrete floor" having a predetermined thickness (0.5 mm to 20 mm).

FIG. 2 is an explanatory diagram showing a state in which a cavity 3 is formed between the floor 1 and the ground 2. As time passes, the ground 2 under the floor 1 may loosen and sink due to the influence of vibrations from vibration sources (machine tools, forklifts, etc.) installed on the floor 1. FIG. 2 shows a state in which the ground 2 has loosened in this way and a cavity 3 of a predetermined depth is formed between the lower surface 1b of the floor 1 and the surface 2a of the ground 2. The underfloor reinforcing method of this embodiment is for reinforcing the underfloor 1 by filling the cavity 3 etc. formed under the floor 1 with a predetermined resin (cured foamable resin).

The underfloor reinforcing method of this embodiment mainly includes a through hole forming step, a vertical hole forming step, a first supply step, a vertical hole shape maintaining step, a second supply step, and a closing step.

The through-hole forming step is a step of forming a through-hole 4 in the floor 1 in the thickness direction and connected to the cavity 3. FIG. 3 is an explanatory diagram showing a through hole forming step. In this through-hole forming step, a drill D is used to drill a hole in a portion of the floor 1 that vertically overlaps with the cavity 3 to form a hole with a predetermined diameter (for example, A through hole 4 having a diameter of approximately 10 mm to 15 mm is formed. The through hole 4 is connected to the cavity 3 while passing through the floor 1 in the thickness direction (vertical direction). The through hole 4 is provided in the floor 1 so as to overlap the cavity 3 when the floor 1 is viewed from the top surface 1a side. Usually, the size of the through hole 4 is very small compared to the cavity 3. Only one or two or more such through holes 4 may be formed in each cavity 3 under the floor 1. Note that, from the viewpoint of further improving the strength at the reinforced portion, it is preferable that a plurality of through holes 4 be formed in one cavity 3. Further, when a plurality of through holes 4 are formed in the floor 1, it is preferable to set the interval between adjacent through holes 4 to a predetermined size (for example, in the range of 50 cm to 100 cm). Further, as the drill D used in the through-hole forming step, for example, a commercially available concrete drill can be mentioned. After the through holes 4 are formed in the floor 1 in the through hole forming step, a vertical hole forming step is performed.

In the vertical hole forming process, a rod-shaped drill D is inserted into the cavity 3 side from the through hole 4 and the ground 2 is dug with the drill D, thereby forming a vertical hole 31 extending downward from the cavity 3 directly below the through hole 4. It is a process. FIG. 4 is an explanatory diagram showing the vertical hole forming process.

In the vertical hole forming step, a vertical hole 31 connected to the cavity 3 is formed directly below the through hole 4 . The drill D used in the vertical hole forming process is a drill D that is longer than the depth of the cavity 3 when inserted into the through hole 4, and is drilled into the ground 2 to a predetermined depth (length) below the cavity 3. There is no particular restriction as long as the vertical hole 31 can be formed. Therefore, normally, the drill D used in the above-described through hole forming step is used as is in the vertical hole forming step. In addition, in other embodiments, a drill prepared separately from the drill used in the through hole forming step may be used in the vertical hole forming step. FIG. 4 shows a drill D used in the through hole forming step.

In the vertical hole forming step, a rod-shaped drill D having a predetermined length is inserted into the through hole 4 provided in the floor 1 from the upper surface 1a side of the floor 1 toward the lower surface 1b side. By pressing the tip of the drill D inserted into the through hole 4 against the bottom of the cavity 3 (that is, the surface 2a of the ground 2) located directly below the through hole 4, and rotating the drill D in this state, the ground 2 is dug with a drill D, and a vertical hole 31 connected to the cavity 3 is formed. The vertical hole 31 has an overall cylindrical shape with a bottom that is open upward. The depth (length in the vertical direction) of the vertical hole 31 is not particularly limited as long as it does not impair the purpose of the present invention, but for example, it may be twice the depth (length in the vertical direction) of the cavity 3. It is preferable to set the depth to about 5 times. The depth of the vertical hole 31 is preferably, for example, 10 cm to 30 cm. Note that the inner diameter of the vertical hole 31 is approximately the same as the diameter of the through hole 4 provided in the floor 1.

FIG. 5 is an explanatory diagram showing a vertical hole 31 formed by digging into the ground 2 in the vertical hole forming process. The vertical hole 31 is located directly below the through hole 4 and is connected to the cavity 3. After the vertical hole 31 is formed in this manner, a first supply step is performed.

The first supply step is a step of supplying the liquid ground strengthening agent 5 from the through hole 4 to the cavity 3 and the vertical hole 31. FIG. 6 is an explanatory diagram showing the first supply step. The ground strengthening agent 5 is in a liquid state, penetrates into the soil 2b constituting the ground 2 from the surface 2a of the ground 2, etc., and hardens the ground 2 in the permeated portion. As shown in FIG. 6, since a vertical hole 31 is formed in the ground 2, the soil strengthening agent 5 is also supplied into the vertical hole 31. In this embodiment, a type of ground strengthening agent 5 that hardens by reacting with moisture contained in the soil 2b and the like is used. Examples of such a ground strengthening agent 5 include isocyanate-based ground strengthening agents (eg, polymethylene polyphenyl polyisocyanate). In addition, the ground reinforcement agent 5 may contain a solvent etc. suitably.

In the first supply step, the ground strengthening agent 5 is supplied using, for example, a supply device (for example, an electric mini pump, maximum discharge pressure: 1.4 MPa) equipped with a predetermined discharge nozzle 6. In this case, the tip of the elongated discharge nozzle 6 is inserted into the cavity 3 through the through hole 4, and the liquid ground strengthening agent 5 is discharged from the discharge nozzle 6 in this state. Note that the method for supplying the ground strengthening agent 5 into the cavity 3 is not limited to this, and may be selected as appropriate depending on the purpose. The supply amount of the soil strengthening agent 5 is appropriately set according to the condition of the soil 2 (for example, the type of soil 2b, the moisture content, etc.).

After the ground strengthening agent 5 is supplied into the cavity 3 and the vertical hole 31 in the first supply step, the discharge nozzle 6 is appropriately extracted from the through hole 4, and the next vertical hole shape holding step is performed.

In the vertical hole shape holding step, a drill D is inserted into the vertical hole 31 from the through hole 4, and the ground strengthening agent 5 in the vertical hole 31 is stirred by the drill D. ) is infiltrated into the soil, and the shape of the vertical hole 31 is maintained by the hardening action of the soil strengthening agent 5. FIG. 7 is an explanatory diagram showing the vertical hole shape holding step.

After the first supply step, the liquid ground strengthening agent 5 is accommodated in the vertical hole 31. When a drill D is inserted into such a vertical hole 31 and the soil strengthening agent 5 in the vertical hole 31 is stirred by the rotation of the drill D, the soil strengthening agent 5 mixes with the soil 2b constituting the ground 2 and is mixed with the soil 2b constituting the ground 2. 31 (surrounding surface and bottom surface) will be forcibly penetrated into the soil. At this time, the soil strengthening agent 5 efficiently permeates from the circumferential surface of the vertical hole 31 so as to spread outward.

A mixture M in which the ground reinforcement agent 5 and the soil 2b are mixed exists around the drill D that has been inserted into the vertical hole 31 and rotated. Such a mixture M forms the circumferential surface and bottom surface of the vertical hole 31. In such a state, when the mixture M hardens due to the hardening action of the soil strengthening agent 5, a vertical hole 31 whose shape is maintained is obtained in the soil 2. FIG. 8 is an explanatory diagram showing the vertical hole 31 in a state where the surrounding mixture M is hardened and the shape is maintained.

The drill D used in the vertical hole shape holding process may be the same as that used in the vertical hole forming process and the through hole forming process described above, or another separately prepared drill may be used. In addition, from the viewpoint of improving work efficiency, it is preferable to use the same drill D used in the vertical hole forming process and the through hole forming process in the vertical hole shape holding process.

After the first supply step, the liquid soil strengthening agent 5 accommodated in the vertical hole 31 will permeate into the soil existing around the vertical hole 31 even without stirring with the drill D. However, if the agitation by the drill D is not performed, the soil existing on the bottom side of the cavity 3 may flow into the vertical hole 31, or the shape of the vertical hole 31 may collapse, and a sufficient size of the vertical hole 31 cannot be secured. There is. Moreover, if stirring by the drill D is not performed, the penetration of the soil strengthening agent 5 tends to be uneven, and the shape of the vertical hole 31 may be difficult to maintain. Therefore, the vertical hole shape holding step needs to be performed after the first supply step and before the soil strengthening agent 5 in the vertical hole 31 permeates into the soil.

The second supply step is a step of supplying the foamable resin 8 from the through hole 4 so as to fill the cavity 3 and the vertical hole 31 after the vertical hole shape holding step. FIG. 9 is an explanatory diagram showing the second supply step. The foamable resin 8 is liquid in an uncured state. When such uncured foamable resin 8 expands in volume due to foaming and is cured, it becomes a solid resin (foamed resin 80 to be described later).

As the foamable resin 8, a general resin used in this type of method for filling the cavity 3 can be used. As the foamable resin 8, for example, a urethane-based foamable resin composed of a base resin and a catalyst can be mentioned. The main ingredient of the urethane foamable resin includes, for example, methylene bis(4,1-phenylene) diisocyanate. The catalyst for the urethane foamable resin includes, for example, dimethylmyristylamine. The urethane-based foamable resin is composed of a liquid composition containing such a main ingredient and a catalyst in predetermined proportions. Note that the foamable resin 8 such as urethane-based foamable resin may contain a solvent or the like as appropriate.

In the second supply step, the foamable resin 8 is supplied using, for example, a supply device equipped with a predetermined discharge nozzle 6A. As this supply device, for example, a device similar to that used in the first supply step described above (equipped with a similar discharge pressure) can be used. As shown in FIG. 9, the tip of the elongated discharge nozzle 6A is inserted into the cavity 3 through the through hole 4, and from the discharge nozzle 6A in this state, a predetermined amount of liquid foaming resin 8 is ejected. is discharged. Note that the method of supplying the foamable resin 8 into the cavity 3 is not limited to this, and may be selected as appropriate depending on the purpose.

When the foamable resin 8 is supplied using the discharge nozzle 6A in this manner, the vertical hole 31 and the cavity 3 are filled with the foamable resin 8. After a predetermined amount of foamable resin 8 is supplied to the cavity 3 or the vertical hole 3, the discharge nozzle 6A is removed from the through hole 4 as appropriate. The foamable resin 8 supplied to the cavity 3 or the vertical hole 3 undergoes a chemical reaction accompanied by foaming over time, and hardens while expanding in volume.

In the second supply step, when the foamable resin 8 is supplied from the through hole 4 into the cavity 3 and the vertical hole 31, the foamable resin 8 is prevented from overflowing from the through hole 4 to the outside (to the upper surface 1a side of the floor 1). may be treated as appropriate. For example, when supplying the foamable resin 8 by inserting the discharge nozzle 6A into the through hole 4, the gap created between the through hole 4 and the discharge nozzle 6A is filled with a water-retentive sheet (waste paper) of a predetermined size. The foamable resin 8 may be prevented from overflowing to the outside from the through-hole 4 by blocking it with an outflow prevention material 7 made of a liquid such as water, etc.) impregnated with a liquid such as moisture. The outflow prevention material 7 is preferably formed of a water-retaining sheet containing liquid in an annular shape so as to surround the through hole 4 .

The closing process is a process of closing the through hole 4 after the cavity 3 and the vertical hole 31 are filled with the foamable resin 8. FIG. 10 is an explanatory diagram showing the closing step, and FIG. 11 is an enlarged sectional view of the stopper 9 that closes the through hole 4. In this closing step, the through hole 4 is closed with a plug 9 made of at least a cement material such as mortar. In addition, as shown in FIG. 11, in the closing step, first, the lower part of the through hole 4 is filled with rolled up outflow prevention material 7 (water-retaining sheet) used in the second supply step described above. is preferred. Next, it is preferable that a porous member 10 made of a plastic sponge or the like be layered on top of the rolled outflow prevention material 7, and filled into the through hole 4. Then, the plug 9 made of the above-mentioned cement material is formed on top of the porous member 10 in an overlapping manner. By blocking the through hole 4 with the stopper 9 in this manner, the airtightness and watertightness of the floor 1 in the area where the through hole 4 is formed is maintained.

By going through the through hole forming step, vertical hole forming step, first supply step, vertical hole shape holding step, second supply step and closing step as described above, the cavity 3 and the vertical hole 31 formed under the floor 1 are The area under the floor 1 is reinforced by filling it with foamed resin 80, which is a cured product of foamable resin 8. Therefore, the foamed resin 80 reinforces the ground 2 below the floor 1, and the reinforced ground 2 supports the floor 1 from below, thereby reinforcing the floor 1.

In particular, in the case of this embodiment, the foamed resin 80 is filled not only in the cavity 3 formed under the floor 1 but also in the vertical hole 31 extending downward from the cavity 3. Therefore, the main body portion 81, which is the portion of the foamed resin 80 that is filled in the cavity 3, is supported from below by the column portion 82, which is the portion that is filled in the vertical hole 31. As described above, the vertical hole 31 has its shape maintained by the hardening effect of the soil strengthening agent 5 that has permeated into the surrounding soil 2b (that is, the shape of the vertical hole 31 is maintained due to the hardening action of the soil strengthening agent 5 that has penetrated into the surrounding soil 2b (that is, the mixture M of the soil 2b and the soil strengthening agent 5 forming the ground 2 A column 82 is housed inside such a vertical hole 31. The column portion 82 has a generally cylindrical shape extending in the vertical direction. Since the main body part 81 is supported from below by the pillar part 82 in such a state, it has a structure that is difficult to shift or sink with the ground 2, and can be said to be highly effective in supporting the floor 1. According to such an underfloor reinforcement method, the strength of the reinforced portion is improved compared to conventional methods.

Note that if a gap (such as a crack) is formed that opens on the lower surface 1b side of the floor 1, the foamable resin 8 filled in the cavity 3 or the like can also enter such a gap. Therefore, according to the underfloor reinforcing method of this embodiment, such gaps can be repaired at the same time.

In addition, the structure under the floor 1 reinforced by the underfloor reinforcement method of this embodiment is called the underfloor reinforcement structure 100. The underfloor reinforcement structure 100 is a structure that fills a cavity 2 formed between a ground 2 and a floor 1 constructed on the ground 2 and having a predetermined thickness. Such an underfloor reinforcing structure 100 is formed in the floor 1 and includes a through hole 4 that extends in the thickness direction and connects to the cavity 3, and is formed directly below the through hole 4, extending downward from the cavity 3 and connecting the ground 2. A vertical hole 31 whose shape is maintained by a mixture M of the soil 2b and a soil strengthening agent 5, a foamed resin 80 made of a foamable resin that fills the cavity 3 and the vertical hole 31, and a plug 9 that closes the through hole 4. Be prepared.

1... Floor, 2... Ground, 3... Cavity, 4... Through hole, 5... Ground reinforcement agent, 6, 6A... Discharge nozzle, 7... Outflow prevention material, 8... Foaming resin, 80... Foamed resin, 81... Main body part, 82... Pillar part, 9... Plug, 100... Underfloor reinforcement structure, D... Drill

Claims (4)

An underfloor reinforcement method for reinforcing the underfloor by filling a cavity formed between the ground and a floor having a predetermined thickness constructed on the ground, the method comprising:
a through-hole forming step of forming a through-hole in the floor that extends in the thickness direction and connects to the cavity;
A vertical hole forming step of inserting a rod-shaped drill into the cavity side from the through hole and digging into the ground with the drill to form a vertical hole extending downward from the cavity directly below the through hole;
a first supply step of supplying a liquid ground strengthening agent from the through hole to the cavity and the vertical hole;
By inserting the drill into the vertical hole from the through hole and stirring the ground strengthening agent in the vertical hole with the drill, the soil strengthening agent is infiltrated into the soil around the vertical hole, and the ground strengthening agent is infiltrated into the soil around the vertical hole. a vertical hole shape retaining step of retaining the shape of the vertical hole through a hardening action;
After the vertical hole shape holding step, a second supply step of supplying a foamable resin from the through hole so as to fill the cavity and the vertical hole;
An underfloor reinforcing method comprising: filling the cavity and the vertical hole with the foamable resin, and then closing the through hole. In the second supply step, a nozzle for supplying the foamable resin is inserted into the through hole, and a gap formed between the through hole and the nozzle is filled with a water-retentive sheet impregnated with liquid. The underfloor reinforcing method according to claim 1, wherein the underfloor reinforcing method is closed. 3. In the closing step, the water-retaining sheet used in the second supplying step is packed into the through-hole, and the through-hole is closed with a cement-based material so as to cover the packed water-retaining sheet. The underfloor reinforcement method described. An underfloor reinforcement structure that fills a cavity formed between the ground and a floor having a predetermined thickness constructed on the ground,
a through hole formed in the floor and connected to the cavity while penetrating in the thickness direction;
a vertical hole that is formed directly below the through hole, extends downward from the cavity, and maintains its shape due to the hardening effect of a soil strengthening agent that has permeated into the surrounding soil;
a foamed resin made of a foamable resin that fills the cavity and the vertical hole;
An underfloor reinforcement structure comprising: a plug that closes the through hole.

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