JP4520913B2 - Ground improvement method and existing structure foundation reinforcement method - Google Patents

Description

  The present invention relates to a ground improvement method by high-pressure jet agitation and a method for reinforcing an existing structure foundation using the same.

The ground improvement method by high-pressure jet agitation is used in various situations as a method with relatively few restrictions on construction.
For example, if the supporting capacity of the foundation ground of an existing building decreases for some reason, or if the weight of an existing building increases due to expansion, etc., the purpose is to increase the supporting capacity of the foundation ground of the existing building. A ground improvement method using jet agitation may be employed.

  As such a ground improvement method for the purpose of increasing the bearing capacity of the foundation ground of an existing building, for example, as shown in Patent Document 1, a fistula is drilled through the side of the existing foundation or through the existing foundation. After the rod is inserted into the hole, a high-pressure jet jet containing the hardener is injected into the ground through the rod to mix with the hardener while cutting the ground around the lower end of the rod. There is a method of forming a ground improvement body having a larger plane area than the foundation below the existing foundation.

  However, the ground improvement method described above is a method of simultaneously cutting the ground and mixing the hardened material by injecting the hardened material into the ground. In some cases, the improved diameter was small. Therefore, when improving the foundation ground of the existing building, a desired ground improvement body may not be formed below the existing foundation.

In order to solve such a problem, Patent Document 2 discloses a ground improvement method that makes it possible to reliably form a ground improvement body having a desired flat area even on hard ground. This is done by drilling a predetermined depth with a rod and cutting the ground by rotating the rod up to a predetermined height while jetting a water jet of compressed air and high-pressure water in two directions from the tip of the rod in the lateral direction. When the rod reaches a predetermined height, the rod is lowered again to a predetermined depth, and a water jet is ejected from the tip of the rod, while a hard material and compressed air are ejected from the opposite direction of the water jet at the rod tip. This is a ground improvement method in which a hardened material and the ground are mixed by stirring while being rotated up to a height to form a ground improvement body having a predetermined shape.
JP-A-6-146258 ([0010]-[0012], FIGS. 1-2) JP-A-7-18658 ([0011]-[0018], FIGS. 1-5)

However, the conventional ground improvement method requires high-pressure water, compressed air, and a hardened material to be injected into the ground at the same time, resulting in large-scale equipment and a large work space for arranging these equipment. I needed it. For this reason, there is a problem in that the places where construction is possible are limited. In addition, in order to simultaneously inject high-pressure water, compressed air, and a hardened material, a triple pipe must be used as a rod, and handling of the rod becomes complicated due to its diameter and weight, resulting in poor workability. Also had a point.
Further, the conventional ground improvement method has a large discharge amount in each step of ground cutting by jetting water jets in two directions and agitation and mixing by jetting water jets and hardeners. There was also a problem that the amount increased and the processing cost increased.

  The present invention has been made in order to solve the above-mentioned problems, and uses a ground improvement method and a ground improvement method that are excellent in workability, less limited by construction conditions, and excellent in economic efficiency. The problem is to propose a method for reinforcing existing foundations.

  In order to solve the above-mentioned problems, the present invention is a ground improvement method in which a ground improvement target area is divided into a plurality of small areas that are continuous in the height direction, and the ground is improved in order from the bottom small area. In each small region, a cutting step of pulling up a predetermined height while rotating the rod while injecting high-pressure water and compressed air in the lateral direction from the tip of the rod inserted to a predetermined depth, and the cutting step A rod lowering step in which the rod pulled up by the rod is lowered by the amount raised, and a predetermined amount while rotating the rod while injecting a hardening material and compressed air laterally from the tip of the rod lowered by the rod lowering step. And a jet stirring step of raising the height.

  In this ground improvement method, after the ground is loosened by the cutting process, the hardened material and the ground are stirred and mixed by the jet stirring process. It is possible to build. Moreover, since the injection of high-pressure water and the curing material is performed in separate processes, construction by a double pipe is possible, the handling of the pipe material is easy, and the workability is excellent. In addition, since the equipment required for construction is simplified, construction in a relatively narrow work space is possible, and the application range is relatively wide. Furthermore, since the amount of mud discharged in the jet stirring step can be reduced by separating the amount of the hardened material by dividing it from the cutting step, the amount of discharged mud is smaller than in the past, which is excellent in terms of economy and environment.

  In addition, the ground improvement object is divided into a plurality of small areas that are continuous in the height direction, and the ground improvement body is constructed in order from the small area at the bottom, thereby improving the ground. If the body is formed, it will be possible to shorten the time from the loosening of the ground by the cutting process to the solidification of the ground by the hardened material mixed by the jet agitation process. It is possible to prevent the hole wall from collapsing by leaving it in a lowered state for a long time. Further, by leaving the ground loosened for a long time, the property of the earth and sand is prevented from changing in the ground, so that it is less likely to hinder the descent process and the jet stirring process, and is excellent in workability. Furthermore, by dividing the cutting, a large amount of earth and sand does not accumulate on the ground surface, so that the leveling of the sludge treatment can be achieved and the work efficiency can be improved.

  In addition, by injecting compressed air together with high-pressure water in the cutting step, it becomes possible to inject high-pressure water in a wider range. In addition, by jetting compressed air together with high-pressure water, this air component rises in the ground, so the lifted air action also raises the cut soil particles, and the effect of discharging soil to the ground surface is obtained. In addition, a space for arranging the curing material in the jet stirring step is formed.

  Further, if the rod pulling speed in the cutting step is made faster than the rod pulling speed in the jet stirring step according to the strength of the ground, the ground can be quickly loosened, and as a result, the ground improvement method Therefore, it is possible to shorten the entire construction time required for the process.

  Moreover, the reinforcement method of the existing structure foundation of this invention is characterized by forming a ground improvement body under the foundation of an existing structure using the said ground improvement method.

  According to such a method for reinforcing an existing structure foundation, the construction in a limited work space is often forced. The reinforcement of an existing structure can be performed with simple equipment, and the existing structure is surely secured. It is possible to build and reinforce ground improvement bodies around and below the foundation.

  By the ground improvement method of the present invention, it is excellent in workability, less limited by construction conditions, and can be improved in the ground with excellent economic efficiency. According to this, the foundation of the existing structure can be reliably reinforced.

  Preferred embodiments of the present invention will be described with reference to the drawings. In the description, the same reference numerals are used for the same elements, and duplicate descriptions are omitted.

Here, FIG. 1 is sectional drawing which shows the ground improvement method which concerns on 1st embodiment, Comprising: The construction completion status is shown. Moreover, FIG. 2 is sectional drawing which shows each construction step of the ground improvement method which concerns on 1st embodiment, (a) is a preparatory process, (b) is a fistula construction process, (c) is cutting. Each process is shown. Moreover, FIG. 3 is sectional drawing which shows the post-construction stage of each construction stage shown in FIG. 2, (a) is a jet stirring process, (b) is a 2nd cutting process, (c) is a 2nd cutting process. Each of the jet stirring steps is shown.
FIGS. 4A and 4B are diagrams showing a method for reinforcing an existing structure foundation according to the second embodiment, in which FIG. 4A is a cross-sectional view and FIG. 4B is a plan view. Moreover, FIG. 5 thru | or FIG. 7 is sectional drawing which shows the modification of the reinforcement method of the existing structure foundation based on 2nd embodiment.

<First embodiment>
In the first embodiment, as shown in FIG. 1, a ground improvement for constructing a ground improvement body 1 having a predetermined shape (substantially cylindrical shape having a predetermined height and a predetermined diameter) in the ground by a high-pressure jet stirring method. A method will be described.

  The ground improvement method according to the first embodiment is a ground improvement method in which an area to be ground improved is divided into a plurality of small areas that are continuous in the height direction, and the ground is improved in order from the lowermost area. (1) Preparatory process (see FIG. 2 (a)) for installing the construction machine M used for ground improvement, and (2) Injecting high-pressure water W downward from the tip of the double pipe (rod) 10. And cutting the fistula 11 to a predetermined depth while inserting the double pipe 10 into the ground G (see FIG. 2B), and (3) the double inserted to a predetermined depth. A cutting process (FIG. 2 (FIG. 2)) of rotating the double pipe 10 while injecting high-pressure water and compressed air (hereinafter sometimes referred to simply as “water jet”) Jw from the tip of the pipe 10 in the lateral direction. c)) and (4) the double pipe 10 pulled up by the cutting process is moved to a predetermined depth. A rod lowering step for lowering to a point, and (5) a hardening material and compressed air (hereinafter sometimes simply referred to as “hardening material jet”) Jg from the tip of the double pipe 10 lowered by the rod lowering step. The ground improvement body 1 is constructed | assembled by the injection stirring process (refer FIG. 3 (a)) which raises predetermined height, rotating the double pipe | tube 10 while making it inject.

(1) Preparatory process As shown in FIG. 2 (a), the preparatory process is a construction machine M and other various devices required for construction above the construction site where the ground improvement body 1 (see FIG. 1) is formed in the ground. Install equipment (not shown). At this time, the pit 12 is formed on the ground surface of the construction site, and the mud 1c (see FIG. 1) flowing out from the borehole 11 to the ground surface is temporarily associated with the borehole construction process, the cutting process, and the jet stirring process. Configure for deposition. A gantry S is installed on the upper surface of the pit 12 so that the construction machine M can be installed. Here, the pit 12 may be constructed as necessary, and may be omitted when it is difficult to construct the pit 12 due to the existence of an existing structure. Moreover, what is necessary is just to arrange | position the equipment similar to the equipment used in the well-known high-pressure jet stirring method, and detailed description is abbreviate | omitted.

(2) Fistula construction process As shown in FIG. 2 (b), the fistula construction process is performed by using a construction machine M from the downward injection port 10b formed at the tip of the double pipe 10 to the bottom. In this process, the tip bit 10a is rotated while the high-pressure water W is jetted in the direction to drill the hole. At this time, the rotation speed and stroke speed of the double pipe 10 are set according to the geology and strength of the ground G. Further, the double pipe 10 is lifted by the crane C via a double pipe swivel 13. The crane C is used to install the double pipe 10 on the construction machine M and hold the direction (angle) of the double pipe 10.

  In addition, prior to drilling with the double pipe 10, in order to ensure drilling accuracy, prevent displacement, and prevent jamming, a prior drilling with a drilling diameter of 140 mm or more is performed in advance, and the top end of the planned ground improvement body 1 is prepared. You may arrange | position the guide pipe | tube 11a (refer FIG. 1) to the vicinity.

In the first embodiment, the fistula 11 is constructed by jetting high-pressure water W. However, if the ground G can be cut by the tip bit 10a formed at the tip portion of the double pipe 10, the high-pressure water is not necessarily used. It is not necessary to inject W, and the water pressure may be appropriately reduced. Thus, the construction method of the fistula 11 may be selected from known means according to the geology and strength of the ground G. Moreover, the waste mud 1c accumulated in the pits 12 with the cutting of the hole 11 is appropriately carried out by a sand pump (not shown) or the like.
In the first embodiment, the crane C is used to install the double pipe 10 and adjust the angle. However, for example, it is difficult to place the crane C inside or near the existing structure. Needless to say, the crane C is not necessarily used.

(3) Cutting process As shown in FIG.2 (c), a cutting process is carried out from the front-end | tip part of the double pipe 10, rotating while rotating the double pipe 10 inserted in the fistula 11 at a predetermined speed, In this step, the ground G is loosened in a predetermined range by spraying the water jet Jw in the lateral direction to form a loose ground body (first loose ground body 1a ′) having a predetermined shape. Here, the double pipe 10 used in the first embodiment is individually separated in the double pipe 10 from the lateral injection port 10c at the tip, similarly to the double pipe used in the known high-pressure jet stirring method. The high-pressure water and the compressed air that have been pumped into the tank can be jetted simultaneously. That is, by closing the downward injection port 10b formed at the lower end of the double tube 10 and opening the lateral injection port 10c formed on the side surface of the double tube 10, the water jet Jw Is configured to be jetted in the lateral direction. At this time, the high-pressure pump is connected to the water tank in the same manner as in the fistula construction step, and supplies high-pressure water to the double pipe 10.

Here, the double pipe 10 used in the first embodiment has the same configuration as the double pipe used in the known high-pressure jet agitation method, and is an air passage that pumps compressed air inside the pipe (rod). And a pumping path for pumping high-pressure water or a hardener. And the compressed air pumped by this air path and the high-pressure water or hardened material pumped by the pump path are jetted simultaneously from the jet port 10b or jet port 10c formed at the lower end of the double pipe 10, thereby It is configured to be jetted to the ground G as a jet Jw or a hardened material jet Jg. Moreover, when the depth of the ground improvement body 1 is deep, the double pipe 10 is inserted to a predetermined depth by adding a rod at any time.
An air compressor (not shown) is connected to the upper end of the air passage, and a high pressure pump (not shown) is connected to the upper end of the pressure feeding passage. In the shaft construction process, water stored in a water tank (not shown) is pumped to the double pipe 10 via a high-pressure pump.

In the first embodiment, the lifting height of the double pipe 10 in the cutting process is set to about 1 m, and the planned ground improvement body 1 is divided into a plurality of small regions continuous in the height direction. Moreover, although the pulling-up speed of the double pipe in the cutting process is appropriately set according to the situation of the natural ground, in this embodiment, it is set to about 5 to 10 min / m, and during the jet stirring in the jet stirring process described later. The double pipe 10 is pulled up at a speed of about 3 to 4 times the pulling speed.
Moreover, although the injection pressure of high pressure water and compressed air is not limited, in 1st embodiment, the injection pressure of high pressure water is 20-30 Mpa, and the injection pressure of compressed air is 0.7 Mpa.

  Here, the sludge 1c that has risen up the fist hole 11 and accumulated in the pits 12 with the cutting of the ground G is appropriately carried out by a sand pump (not shown) or the like.

(4) Rod lowering step The rod lowering step is a step of lowering the double pipe 10 pulled up in the cutting step (about 1 m) and returning it to the position before cutting. At this time, since the strength of the first loose ground body 1a ′ is reduced by the cutting process, the double pipe 10 can be lowered by lowering the double pipe swivel 13 by the crane C. Depending on the situation of the first loose ground body 1a ′, the double pipe 10 may be lowered by applying a rotational force and a thrust by the construction machine M as necessary.
Here, the length by which the double pipe 10 is lowered in the rod lowering process may be equal to the length raised in the cutting process, and may be slightly increased or decreased.

(5) Injecting and stirring step As shown in FIG. 3A, the injecting and stirring step is performed from the distal end portion of the double tube 10 to the first loosened ground body 1a ′ formed by cutting the ground G in the cutting step. The hardened material is mixed and stirred in the first loose ground body 1a ′ by rotating the double pipe 10 while rotating the jetting hard material jet Jg in the lateral direction, and the first mixed body 1a (small region) is stirred. It is a process of forming.

  At this time, the high-pressure pump connected to the double pipe 10 is connected to a grout tank (not shown), and the grout, which is a hardening material, is injected into the ground through the pressure feed path. In the first embodiment, the connection between the high-pressure pump and the water tank in the cutting process and the connection between the high-pressure pump and the grout tank in the jet stirring process are performed via known switching means. It is good also as a structure which switches piping by, and the switching method is not limited.

  The pulling-up speed of the double pipe 10 at the time of jetting agitation may be determined according to the condition of the natural ground, and is not limited, but is set to about 15 to 40 min / m in this embodiment. Moreover, although the injection pressure of a hardening material and compressed air is not limited, in 1st embodiment, the injection pressure of hardening material is 20-30 Mpa, and the injection pressure of compressed air is 0.7 Mpa.

  Here, the relationship between the pulling speed of the double pipe 10 at the time of cutting the ground and the pulling speed of the double pipe 10 at the time of jet stirring is not limited and may be the same, but the hardening material at the time of jet stirring The jet Jg injection also has an element that cuts the ground G together with the mixing and stirring of the hardened material and the ground G. Therefore, the cutting of the ground G in the cutting process may be to loosen the ground G and shorten the construction time. From this point of view, it is preferable to raise the pulling speed of the double tube 10 at the time of cutting faster than the pulling speed at the time of jet stirring. Further, the range in which the hardener jet Jg is sprayed in the jet stirring step may be performed in a slightly wider range than the range loosened in the cutting step.

After the construction of the first mixture 1a by the jet stirring step is completed, the water jet Jw is jetted in the lateral direction from the tip of the double pipe 10 while continuously rotating the double pipe 10 at a predetermined speed and rotating. The ground G is loosened within a predetermined range, and a second loose ground body 1b ′ having a predetermined shape is formed in contact with the upper end of the first mixture 1a (cutting process). Then, the double pipe 10 is lowered by the amount raised in the cutting process and the tip of the double pipe 10 is positioned at the upper end of the first mixture 1a (down process), and then the second loose ground body 1b. By mixing and stirring the hardened material to the second loose ground body 1b ′ by rotating the double pipe 10 while rotating the double pipe 10 while ejecting the hardened material jet Jg in the lateral direction from the tip of the double tube 10. Then, the second mixture 1b is formed (injection stirring step).
Furthermore, the planned ground improvement body 1 is constructed by repeating the cutting process, the descent process, and the jet stirring process in the same manner. Here, the ground improvement body is constructed by constructing the mixture (second mixture) that is constructed in the following manner in a state of being overlapped with the upper part of the mixture (first mixture) that is constructed in advance. Each small area of 1 may be constructed without a gap.

  According to the ground improvement method of the first embodiment, the ground G is loosened by the water jet Jw and then the hardened material jet Jg is jetted to mix and stir the ground G and the hardened material. Accordingly, the ground improvement body 1 having a large diameter and high quality (having a uniform strength with little variation in strength within the cross section) can be formed into a planned shape.

Further, since the formation of the ground improvement body 1 is performed by dividing it at a predetermined height, even if the planned shape of the ground improvement body 1 is large, the time of one cycle from the cutting of the ground G to the mixing of the hardener is reduced. This can be done in a short time. Therefore, in the ground G, soil particles of loosened earth and sand are settled, so that the property of the ground improvement body 1 does not change due to the depth, and the ground improvement body 1 maintaining a certain quality is formed. It becomes possible. Moreover, since one cycle is performed in a short time, there is little risk that the hole wall of the fistula 11 will collapse when the ground G is loosened.
In addition, since a large amount of waste mud is not generated at one time, the waste mud treatment is easy, and since the waste mud does not interfere with the construction due to accumulation directly above the fistula 11, the workability is improved. Are better.

Moreover, since the double pipe is used, the handling of the rod is easy and the workability is excellent.
Moreover, since the equipment is simpler than the conventional ground improvement method using a triple pipe, applicable construction sites are not limited.

  By setting the injection pressure of the hardened material at the time of jet stirring to an ultra-high pressure (20 to 30 MPa), it becomes possible to input the hardened material while cutting the ground, and the cutting time of the ground G in the cutting process can be increased. It is possible to mix the curing material uniformly even if it is loosened early.

  Since the jet pressure of high-pressure water at the time of cutting is set to an ultra-high pressure (20-30 MPa), the ground cutting ability is high, and the ground G is loosened to a desired strength even by cutting in a short time by increasing the pulling speed of the double pipe. Making it possible.

<Second Embodiment>
In 2nd embodiment, as shown in FIG. 4, the case where the foundation (existing structure foundation 20) of the existing structure 2 is reinforced is demonstrated using the ground improvement method demonstrated in 1st embodiment.
That is, by inserting the double pipe 10 to a predetermined depth through the hole 11 formed through the existing structure foundation 20, the ground G below the existing structure foundation 20 is improved and desired. The ground improvement body 1 is formed.

  In 2nd embodiment, as shown to Fig.4 (a), about the existing structure 2 which has the existing structure foundation 20 which consists of the foundation slab 21, the foundation pile 22, and the foundation beam 23, the vicinity of the existing structure foundation 20 A deep hole 11 deeper than the lower end of the foundation slab 21 is formed, and the ground improvement body 1 is formed using the deep hole 11. In the second embodiment, the six ground improvement bodies 1, 1,... Are wrapped so as to cover the periphery of the foundation slab 21 in FIG. The strength of the foundation ground (Ground G) is increased and the earthquake resistance of the existing structure 2 is improved. Here, in Fig.4 (a), the code | symbol 24 is abandoned concrete and the code | symbol 25 is a paving gravel or a chestnut stone.

  The fistula 11 has a foundation slab 21, a foundation beam 23, etc., depending on the positional relationship between the configuration of the existing structure foundation 20 and the planned placement of the ground improvement bodies 1 (number of ground improvement bodies 1, improved diameter, etc.). May be formed. Moreover, the formation method of the fistula 11 is not limited, The method of forming by inserting the double pipe 10 in the ground G, The method of forming by boring etc. in advance before inserting the double pipe 10 For example, it may be appropriately selected from known means. Moreover, in 2nd embodiment, although the existing ground foundation 20 was reinforced by forming the six ground improvement bodies 1,1, ..., it constructs in order to reinforce the existing ground foundation 20. The number of the ground improvement bodies 1 is not limited, and may be set as appropriate according to the improved diameter determined by the geology of the ground G and the scale of the existing structure foundation 20.

  In addition, about the said existing structure 2, when improving vertical support performance, as shown in FIG. 5, the front-end | tip of the foundation pile 22 is utilized using the hole 11 formed deeper than the front-end | tip of the foundation pile 22. As shown in FIG. It is performed by forming the ground improvement body 1 in the part.

  Further, in the case of improving the vertical support performance of the existing foundation type structure 2 ′, the ground improvement body 1 may be formed below the foundation slab 21 as shown in FIG. 6.

  Further, in the case of improving the seismic performance of the existing foundation structure 2 ′ of the direct foundation type, the ground improvement body 1 may be formed around the foundation slab 21 as shown in FIG. 7.

As mentioned above, although preferred embodiment was described about this invention, this invention is not limited to the said embodiment, A design change is possible suitably in the range which does not deviate from the meaning of this invention.
For example, in each of the above embodiments, the ground improvement body is divided in the height direction, and the ground improvement body is formed by dividing the ground improvement body into a plurality of times. It goes without saying that the height and the like are appropriately set according to the planned scale of the ground improvement body and the geology of the surrounding ground.

  Moreover, the ground improvement method of the present invention is not only applied to the reinforcement work for the foundation of the existing structure, but needless to say, can be applied to any ground strength reinforcement work.

  Moreover, although the said embodiment demonstrated the case where grout was used as a hardening | curing material, it cannot be overemphasized that the kind of hardening | curing material is limited, What is necessary is just to select and use a well-known hardening | curing material suitably.

  Furthermore, in the said embodiment, although the injection pressure of the high pressure water and the hardening | curing material shall be performed in the equivalent range, it cannot be overemphasized that it is not necessarily required to be equivalent. Further, the injection pressure of the high-pressure water and the hardener is not limited to the above range, and may be appropriately set according to the geological condition of the surrounding ground, the completion range, the machine capability, and the like.

It is sectional drawing which shows the ground improvement method which concerns on 1st embodiment, Comprising: The construction completion status is shown. It is sectional drawing which shows each construction step of the ground improvement method which concerns on 1st embodiment, (a) is a preparatory process, (b) is a fistula construction process, (c) has each shown the cutting process. . It is sectional drawing which shows the post-installation stage of each construction stage shown in FIG. 2, (a) shows an injection stirring process, (b) shows a 2nd cutting process, (c) shows a 2nd injection stirring process, respectively. ing. It is a figure which shows the reinforcement method of the existing structure foundation which concerns on 2nd embodiment, Comprising: (a) is sectional drawing, (b) is a top view. It is sectional drawing which shows the modification of the reinforcement method of the existing structure foundation which concerns on 2nd embodiment. It is sectional drawing which shows the other modification of the reinforcement method of the existing structure foundation which concerns on 2nd embodiment. It is sectional drawing which shows the other modification of the reinforcement method of the existing structure foundation which concerns on 2nd embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ground improvement body 1a 1st mixture 1b 2nd mixture 10 Double pipe 2 Existing structure 20 Existing structure foundation 21 Foundation slab 22 Foundation pile 23 Foundation beam G Ground Jg Hardening material jet Jw Water jet

Claims (3)

A ground improvement method that divides a target area for ground improvement into a plurality of small areas that continue in the height direction, and that improves the ground in order from the small area at the bottom,
In each subregion
A cutting step of pulling up a predetermined height while rotating the rod while injecting high-pressure water and compressed air laterally from the tip of the rod inserted to a predetermined depth;
A rod lowering step of lowering the rod pulled up by the cutting step by the amount raised;
Performing a jet stirring step of pulling up a predetermined height while rotating the rod while jetting the hardened material and compressed air in the lateral direction from the tip portion of the rod lowered by the rod lowering step, Ground improvement method.   The ground improvement method according to claim 1, wherein a rod pulling speed in the cutting step is faster than a rod pulling speed in the jet stirring step.   An existing structure foundation using the ground improvement method according to claim 1 or 2, wherein a ground improvement body is formed below the foundation of the existing structure. Reinforcement method.

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