JP7270905B2 - Soil improvement body construction device, ground improvement method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soil improvement body construction device used to form a cylindrical (substantially ring-shaped cross section) soil improvement body, and a ground improvement construction method using this device.

As a countermeasure for supporting, stabilizing, and suppressing deformation of embankments and structures on soft ground, a cement slurry type deep mixing method is used. In the deep mixing method, a slurry injection material consisting of a cement-based solidification material and water is discharged from a stirring blade at the tip of a boring rod penetrated into the ground, and the soft ground is directly stirred and mixed to create a cylindrical ground improvement body. It is a construction method to create

When constructing an embankment on soft ground, there is a concern that the embankment will deform laterally near the toe of the slope due to subsidence or sliding failure of the soft ground. In that case, for the purpose of suppressing deformation of surrounding houses and structures, by creating multiple rows of columnar improvement bodies in the soft ground near the toe of the embankment, the soil pressure acting laterally from the soft ground under the embankment will be applied. It has a structure that resists In addition, it is common to create a cylindrical improvement body over the entire surface as a measure to secure the bearing capacity of embankments and structures and to stabilize them.

However, when creating multiple rows of cylindrical improved bodies or when creating a cylindrical improved body over the entire surface, there are problems such as a longer construction period depending on the number of improved bodies to be created, and a higher construction cost. was there. Therefore, there has been a demand for a solution capable of reducing the number of constructions and shortening the construction period without sacrificing the functions of the improved body.

In view of the problems of the conventional technology described above, the purpose of the present invention is to reduce the construction area to a cylindrical shape instead of a cylindrical shape while maintaining the functions of the improved body, so that the number of construction works can be reduced and the construction period can be shortened. It is to provide a technique for creating a ground improvement body that is

The shape of the improvement body created by the ground improvement method is a flat ring, and the shape is a cylindrical improvement body (see the right side of Fig. 1) in which no solidification material is injected into the hollow part. To efficiently create a cylindrical improved body with an improved inner diameter of about 4 to 1/8 of the improved outer diameter, which is the ring thickness that can reduce the body cross-sectional area to the maximum. As a method for forming a cylindrical improved body, a combined method of mechanical stirring and jetting is used in order to form a reliable improved body.

And the above purpose is
A device that injects injection material into the ground to be improved and creates a soil improvement body as a cylindrical improvement body, and the ring thickness obtained by subtracting the improvement inner diameter from the improvement outer diameter of the cylindrical improvement body is the size of the improvement outer diameter In the device for creating a cylindrical improved body set to about 4 to 1/8,
A plurality of upper stirring blades having a blade diameter smaller than the improved inner diameter of the improved body to be created;
It is achieved by a soil improvement body construction device having a plurality of lower stirring blades having a blade diameter smaller than the outer diameter of the improvement body to be constructed, which is equipped with a flow path for injection material and an injection nozzle.
In this soil improvement body construction device, the lower stirring blade is
a downward injection nozzle capable of injecting the injection material downward;
an obliquely downward injection nozzle capable of injecting an injection material outward and obliquely downward;
Either or both of

The soil improvement body construction device may have a plurality of stages of stirring blades.

Further, in the above soil improvement body construction device, the lower stirring blade has, for example, two obliquely downward injection nozzles and at least one downward injection nozzle.
In this case, the outer area corresponding to approximately two-thirds of the area of the ring thickness portion to be formed is formed with the injection material injected from the two obliquely downward injection nozzles, and the remainder of the ring thickness portion to be formed is approximately An inner area corresponding to one-third of the area is formed by injection material injected from the downward injection nozzle provided in the center of the ring thickness.

In addition, the soil improvement body construction device may further have an injection nozzle for feeding the liquid to the inner region of the improvement body.

In addition, the above-mentioned object is a ground improvement method for creating a cylindrical improvement body using the above-mentioned soil improvement body creation device,
A penetration step of penetrating the soil improvement body construction device into the ground while rotating the stirring blade forward,
A pulling-up step of pulling up the soil improvement body construction device from the ground while rotating the stirring blade in reverse;
This is achieved by ground improvement methods including
In this ground improvement method, in the penetration process, the injection material is injected into the ground through the injection nozzle during the penetration process. Inject 3/4. Further, in the lifting process, the injection material is injected into the ground through the injection nozzle in the process of pulling up, and at that time, the remaining approximately one-fourth of the predetermined injection amount is injected, and approximately half of the injection amount is injected. Pull up the soil improvement body construction device from the ground at a speed of 1 to 4 times.

In addition, the above-mentioned object is a soil improvement method for creating a cylindrical improvement body using the soil improvement body creation device, and when injecting the injection material from the injection nozzle, the injection amount or injection in the injection process Accomplished by ground improvement method of varying pressure.

In the ground improvement body construction device used in the ground improvement method,
The lower stirring blade may be provided with an injection material inflow preventing plate for preventing the injection material from flowing into the inner region of the improved body, at a position substantially matching the inner diameter of the cylindrical improved body to be formed.
In this case, the inflow prevention plate is installed in a direction oblique to the direction of rotation of the stirring blade when it penetrates into the ground.

In addition, in the ground improvement body construction device used in the ground improvement method,
An inflow prevention blade may be provided between the upper stirring blade and the lower stirring blade to prevent the injection material from flowing into the improved body inner region.
In this case, the inflow prevention blade is provided with an inflow prevention plate at a position substantially matching the inner diameter of the cylindrical improved body to be produced, and is rotatably attached to the rod so as not to rotate together with the stirring blade.

In addition, in the ground improvement body construction device used in the ground improvement method,
An inflow prevention ring blade may be provided between the upper stage stirring blade and the lower stage stirring blade for preventing the injection material from flowing into the improved body inner region.
In this case, the inflow prevention ring impeller is provided with a cylindrical inflow prevention ring at a position substantially matching the inner diameter of the cylindrical improved body to be formed, and is rotatably attached to the rod so as not to rotate together with the stirring impeller. .

The product (Ep×Ap) of the cross-sectional area (Ap) and elastic modulus (Ep) of the improved body affects the amount of deformation caused by external force in the vertical direction of the improved body created in the ground. . On the other hand, the bending stiffness (Ep×Ip), which is the product of the geometrical moment of inertia (Ip) and the elastic modulus (Ep) of the improved body, is related to the deformation of the improved body due to the external force in the horizontal direction. Affect.
The cross-sectional area of the cylindrical improved body is calculated by substituting Ap=π/4×Dp ² where Dp is the improved outer diameter, and Ip=π/64×Dp ⁴ for the geometric moment of inertia. On the other hand, the cross-sectional area of the cylindrical improved body is Ap=π/4×(Dp ² −Ds ² ), where Dp is the improved outer diameter and Ds is the improved inner diameter, and the moment of inertia of the area is Ip=π/64×( Dp ⁴ -Ds ⁴ ). Fig. 2 shows the calculation results of the ring area and geometrical moment of inertia when the improved inner diameter is changed for the improved outer diameter of φ1800mm, in terms of the cylinder ratio. Furthermore, the difference between the cross-section performance ratio and the ring area ratio is defined as the stiffness cross-section reduction efficiency, and the larger this value is, the higher the cross-section reduction efficiency is compared to the decrease in cross-section performance.
The optimum shape of the cylindrical improved body is, for example, when the improved outer diameter is φ1800 mm, the improved inner diameter is 1200 mm, and the ratio of the ring thickness to the outer diameter is optimally 4 to 1/8. When this ratio is used, the cross-sectional area of the cylindrical improved body is reduced to about 50% of that of the cylindrical improved body, but about 80% of the geometrical moment of inertia can be secured.

Fig. 3 shows an example of applying the cross-sectional rigidity of a cylindrical improved body to embankment stabilization deformation countermeasures. In this example, an embankment is built on soft ground, and there are adjacent structures in the vicinity. is. In this application example, comparison is made with the improvement range of a cylindrical improved body in which the improved strength per improved body is set to the same extent. Since the cylindrical improved body has a cross-sectional area of about 50% of the cylinder, by setting the improved strength to double, the strength setting per improved body is the same, and the improved body can be made with the same amount of solidification material used. It is possible to create one. However, since about 80% of the flexural rigidity can be secured, the desired effect can be expected by creating three rows in the cylindrical improved body, while four rows are required in the cylindrical improved body.

It is a perspective view (perspective view) showing a ground improvement body (cylindrical improvement body) created by a conventional technique and a ground improvement body (cylindrical improvement body) created by the present invention. It is a graph which shows the cross-sectional performance of a cylindrical improved body. It is a figure which shows the application example to the embankment stabilization deformation countermeasure work of the cylindrical improved body. It is a figure which shows the construction outline (construction equipment used by a ground improvement construction method) of a cylindrical improvement body. It is a top view which shows the stirring blade which a soil improvement body construction apparatus has. It is a cross-sectional view showing a stirring blade provided in the soil improvement body construction device. It is a perspective view which shows an example of a soil improvement body construction apparatus. It is a perspective view which shows another example of a soil improvement body construction apparatus. It is a perspective view which shows another example of a soil improvement body construction apparatus.

(Glossary)
First, the main terms used in this application will be explained.

"Cylindrical improvement body" means a cylindrical soil improvement body. The term "cylindrical" as used herein includes those having a cylindrical appearance (substantially cylindrical).

"Injection material" is a soil improvement material used to create a cylindrical improvement body. The cylindrical improvement body is formed by mixing the injection material (soil improvement material) injected into the ground to be improved and chemically solidifying the ground. A specific example of the injection material is a slurry injection material composed of a cement-based solidifying material and water.

The "injection nozzle" mainly plays the role of injecting the injection material into the ground of the ground to be improved. The injection material to be injected is pressure-fed through the flow path of the rod and the stirring blade, and is injected from the injection nozzle.

"Improved outer diameter" means the outer diameter (diameter of the outer peripheral surface) of the cylindrical improved body to be constructed. See FIG.

"Improved inner diameter" means the inner diameter (diameter of the inner peripheral surface) of the cylindrical improved body to be constructed. See FIG.

The "improved body inner region" means a region inside the inner diameter (inner peripheral surface) of the cylindrical improved body to be created.

By "ring thickness" is meant the thickness between the outer and inner surfaces of the cylindrical refinement. Since the thickness between the outer peripheral surface and the inner peripheral surface of the cylindrical improved body looks ring-shaped in plan view (or in cross section), this application describes this thickness (when the cylindrical improved body is viewed in plan or cross section). The thickness of the ring) is called the ring thickness. The ring thickness can be expressed by subtracting the improved inner diameter from the improved outer diameter of the cylindrical improved body.

"Ring thickness outer region" or "outer region" refers to the outer portion of the ring thickness. In FIGS. 5A and 5B, the ring thickness outer region is shown with cross hatching. In the embodiments described later, the portion of the outer region corresponding to approximately two-thirds of the area of the thick ring portion to be formed (approximately two-thirds of the outer side of the thick ring portion) is referred to as the “thickness outer region of the ring”. is called

"Ring thickness inner region" or "inner region" refers to the inner portion of the ring thickness. In FIGS. 5A and 5B, the ring thickness inner region is shown with hatching. In the embodiments described later, the portion of the inner region corresponding to approximately one-third of the area of the thick ring portion to be formed (approximately one-third of the inner side of the thick ring portion) is referred to as the “thickness inner region of the ring”. is called

The "ring thickness central portion" means a portion located between the ring thickness outer region and the ring thickness inner region. In FIGS. 5A and 5B, the central portion of the ring thickness is located between the hatched portion and the cross-hatched portion.

(Equipment necessary for construction of ground improvement method)
As shown in Fig. 4, a cement silo, a mixing plant, a grout pump, and a deep mixing machine are used for the outline of construction of the cylindrical improved body. The soil improvement body construction device provided in the deep mixing machine has a boring rod. A special stirring blade is attached to the tip of this boring rod (hereinafter simply referred to as "rod"). In this application, the special stirring blade is simply referred to as "stirring blade" as necessary.

(Specific configuration of soil improvement body construction device)
The soil improvement body construction device of this embodiment has a rod and a special stirring blade provided at the tip of the rod. The rod and the special stirring blade are provided with a flow path for pumping the injection material, and the special stirring blade is provided with an injection nozzle for spraying the injection material pumped through the flow path. It is

Hereinafter, based on FIG. 5A and FIG. 5B, the configuration of the special stirring blade provided in the soil improvement body construction device will be specifically described.

The special stirring blades employed in this embodiment have a three-bladed upper and lower two-stage structure.

The rod is provided with three upper stirring blades 21, 22 and 23 at equal angular intervals. The upper stage stirring blades 21, 22, 23 have a blade diameter (diameter of the rotation trajectory of the tip of the stirring blade) smaller than the improved inner diameter to be created. That is, the three upper stirring blades 21, 22, and 23 are set to have dimensions that can be accommodated inside the improved inner diameter of the cylindrical improved body to be created (improved body inner region). By providing the upper stirring blades 21, 22, 23 with a blade diameter smaller than the improved inner diameter in this way, it is possible to separate the upper soil mass by rotating the upper stirring blade, increasing the lifting capacity of the soil improvement body construction device. can be done. Further, by setting the blade diameters of the upper stirring blades 21, 22, 23 smaller than the improvement inner diameter, it becomes possible to form the soil improvement body into a cylindrical shape more reliably.

In addition, the rod is provided with three lower stirring blades 41, 42, and 43 at equal angular intervals below the upper stirring blade. The lower stage stirring blades 41, 42, 43 have a blade diameter (diameter of the rotation locus of the tip of the stirring blade) smaller than the improved outer diameter to be created. That is, the three lower-stage stirring blades 41, 42, 43 are set to have a size that fits inside the improved outer diameter of the cylindrical improved body to be formed, and a size that protrudes outside the improved inner diameter. The three lower stirring blades 41, 42, 43 are provided with flow paths and injection nozzles A, B, C, respectively. The injection nozzles A and B and the injection nozzle C have different roles. Details are given below.

Of the three lower stirring blades, the lower stirring blades 41 and 42 are provided with obliquely downward injection nozzles A and B for injecting the injection material obliquely downward and outward (outward direction). The injection directions of the obliquely downward injection nozzles A and B are provided near the tips of the lower stirring blades 41 and 42 . As shown in FIG. 5B, the injection directions of the obliquely downward injection nozzles A and B are inclined 10° to 30° in the outer peripheral direction with respect to the vertical direction (a line parallel to the central axis of the rod). The obliquely downward injection nozzles A and B provided in the lower stage stirring blades 41 and 42 have an outer region portion corresponding to approximately two-thirds of the area of the ring thickness portion to be formed (the portion indicated by cross hatching in FIGS. 5A and 5B). It plays the role of injecting the injection material for creating the

Of the three lower stirring blades, the lower stirring blade 43 has a downward injection nozzle C for downward injection of the injection material. This downward injection nozzle C is provided at a position corresponding to the vicinity of the central portion of the thickness of the ring to be formed. The obliquely downward injection nozzle C provided in the lower stirring blade 43 creates an inner region portion (the hatched portion in FIGS. 5A and 5B) corresponding to the remaining one-third area of the ring thickness portion to be created. It plays the role of injecting the injection material for.

Since the obliquely downward injection nozzles A and B make it possible to create an improved outer diameter that is larger than the diameter of the stirring blade, it is possible to create an improved diameter that is larger than the working capacity of the deep mixing processor.
Further, by injecting the injection material to the outside through the oblique downward injection nozzles A and B, it is possible to prevent the original ground outside the improved outer diameter from entering the improved outer diameter.
In addition, by forming the outer region and the inner region of the thick ring portion to be formed with injection materials from different injection nozzles, it is possible to form a cylindrical improved body with no bias between the outer side and the inner side of the thick ring portion. .

In addition, the lower stage stirring blades 41, 42, 43 are provided with an inflow prevention plate 45 for preventing the injection material from flowing into the improved body inner region. This inflow prevention plate 45 is provided at a position substantially matching the inner diameter of the cylindrical improved body to be constructed. Further, as shown in FIG. 5A, the inflow prevention plate 45 is installed in a direction that forms an oblique angle of approximately 10° to 30° with respect to the rotating direction of the stirring blade when penetrating into the ground.

In addition, although illustration is omitted in this embodiment, any one or more of the lower stirring impeller blades 41, 42, 43 of the soil improvement body construction device, separately from the injection nozzles A, B, C described above , another injection nozzle may be added for sending liquid to the inner region of the improved body. The liquid delivered to the inner region of the improved body may be, for example, water for reducing penetration resistance, or a liquid for inhibiting hardening of the injection material. By sending water through such an injection nozzle, for example, at the time of penetration of the soil improvement body construction device, the penetration resistance can be reduced by the injection effect. Further, by feeding a liquid that inhibits hardening of the injection material, a cylindrical improved body can be formed more reliably. In addition, the liquid injection from the injection nozzle can be performed in either one or both of the penetration step and the pulling-up step, which will be described later.

In addition, in the present embodiment, the stirring blades are arranged in two stages, upper and lower, but the number of stages of the stirring blades is not limited to this, and three or more stages may be provided. Further, the stirring blades provided with injection nozzles are not limited to one stage (the lowest stage stirring blades), and the injection nozzles may be provided in two or more stages of stirring blades.

In the present embodiment, the lower stirring blade is provided with two types of injection nozzles, namely, obliquely downward injection nozzles and downward injection nozzles, but only one of these injection nozzles may be provided in the lower stirring blade. In addition, in the present embodiment, one injection nozzle is provided for one lower stirring blade, but both an obliquely downward injection nozzle and a downward injection nozzle may be provided for one lower stirring blade. A plurality of injection nozzles for either one may be provided on the stirring blade.

(Ground improvement method)
Next, a ground improvement method for creating a cylindrical improvement body using the soil improvement body creation device having the above configuration will be described.

The construction method of the ground improvement method is mainly
・ A penetration step of penetrating the soil improvement body construction device into the ground while rotating the stirring blade forward,
・ A lifting step of lifting the soil improvement body construction device from the ground while rotating the stirring blade in the opposite direction (rotating in the opposite direction to the rotation direction at the time of penetration),
It consists of two steps.

In the penetration process, the injection material is injected into the ground through the injection nozzles A, B, and C, and at that time, a predetermined injection amount (predetermined amount required to create one cylindrical improvement body) Inject approximately three-fourths of the injection volume). That is, in the penetration process, a larger amount of the injection material is injected into the ground than in the uplift process.

In the lifting process, the injection material is injected into the ground via the injection nozzles A, B, C, with approximately the remaining quarter of the predetermined injection amount being injected. That is, in the uplift process, less of the injection material is injected into the ground than in the penetration process. In the pulling process, a cylindrical improved body is formed by reverse rotation stirring while pulling at a speed about 2 to 4 times that of the penetration.

As a result, the cylindrical improved body is formed mainly by positive rotation stirring during penetration, and the inflow prevention plate 45 installed at an oblique angle to the rotation direction prevents the injection material from moving around the rod due to stirring. It is possible to suppress it, and a homogeneous cylindrical improved body can be created.

Since the injection material is jetted downward or obliquely downward from the lower stirring blades 41, 42, 43 at a high pressure of approximately 5 MPa to 20 MPa, it assists the ability of the stirring blades to penetrate into the ground and enhances adaptability to any type of ground. .
Furthermore, in the lifting process where the effect of injection on construction performance cannot be expected, the rotation of the upper stage stirring blades 21, 22, and 23, which have a blade diameter smaller than the improved inner diameter to be created, pushes through the upper soil mass, thereby increasing the lifting performance. It has a structure that allows
In addition, by stirring only with the lower stirring blades 41, 42, and 43 without stirring the ring thickness portions with the upper stirring blades 21, 22, and 23, the material is intensively injected and stirred in the ring thickness portions, and homogeneous. A cylindrical improvement can be created.

In either or both of the penetration process and the lifting process, when the injection material is injected from the injection nozzles A, B, and C, the injection amount (L / min) or injection pressure (MPa) is changed during the injection process. You can change it. That is, the injection material may be injected from the injection nozzles A, B, and C while changing the injection amount or the injection pressure. As a result, for example, the improved outer diameter can be arbitrarily set, and the improved strength can be arbitrarily changed so that the strength gradually changes from low strength to high strength toward the improved outer diameter from the center of the improved inner diameter of the cylindrical improved body. can be set. In addition, the strength and outer diameter of the cylindrical improved body to be constructed can be changed in the depth direction.

In addition, in this embodiment, it is assumed that the injection material is injected into the ground from the same injection nozzle in the penetration process and the pulling process, but the injection material is injected into the ground from different injection nozzles in the penetration process and the pulling process. You can inject inside.
For example, when the soil improvement body construction device is penetrated into the ground while rotating the stirring blade forward, the flow path in the stirring blade leading to the injection nozzle A is closed with a valve, and the injection material is injected from the other injection nozzle B. When injecting into the ground and pulling up the soil improvement body construction device from the ground while rotating the stirring blade in the reverse direction, the flow path in the stirring blade leading to the injection nozzle B is closed with a valve, The injection material may be injected into the ground from the injection nozzle A of .
Further, for example, when the rotation direction of the stirring blade is changed from normal rotation to reverse rotation, a valve that opens and closes the flow path may be operated in conjunction with the reversal of the rotation direction.

(Structure for preventing inflow of injection material into inner region of improved body)
An overall view of the special stirring blade is shown in FIG.
The inflow prevention plate 45 installed at the improved inner diameter of the lower stirring blade is also effective for edge cutting between the cylindrical improved body and the inner soil due to the horizontal rotation of the stirring blade, contributing to the creation of a reliable cylindrical shape.

The structure shown in FIGS. 7 and 8, which provides the same effect as the inflow prevention plate 45, can also be applied.

The soil improvement body construction apparatus shown in FIG. 7 is provided with an inflow prevention blade 51 for preventing the inflow of the injection material into the inner region of the improvement body at an intermediate portion between the upper stage stirring blade and the lower stage stirring blade.
The inflow prevention wing 51 has an inflow prevention plate 55 at a position substantially matching the inner diameter of the cylindrical improved body to be constructed.
Also, the inflow prevention blade 51 is rotatably attached to the rod so as not to rotate together with the upper and lower stirring blades.
In this way, by attaching the inflow prevention blade 51 to the rod so that it does not rotate in the same manner as the stirring blade, rotation resistance in the ground does not occur, and an edge cutting effect with the improved inner diameter portion is expected. can.

FIG. 8 has anti-flow ring vanes 61 that match the modified inner diameter in place of the anti-flow plate.

That is, the soil improvement body construction device shown in FIG. 8 is provided with an inflow prevention ring blade 61 for preventing the inflow of the injection material into the inner region of the improvement body at the intermediate portion between the upper stage stirring blade and the lower stage stirring blade.
The inflow prevention ring wing 61 is provided with a cylindrical inflow prevention ring 65 at a position substantially matching the inner diameter of the cylindrical improved body to be produced.
Also, the inflow prevention ring blade 61 is rotatably attached to the rod so as not to rotate together with the upper and lower stirring blades.
In this way, by attaching the inflow prevention ring blade 61 to the rod so as not to rotate in the same manner as the stirring blade, rotation resistance in the ground does not occur, and the edge cutting effect with the improved inner diameter portion is obtained. I can expect it.

21, 22, 23 Upper stirring blades 41, 42, 43 Lower stirring blade 45 Inflow prevention plate 51 Inflow prevention blade 55 Inflow prevention plate 61 Inflow prevention ring blade 65 Inflow prevention ring

Claims (5)

A device for creating a soil improvement body as a cylindrical improvement body,
In an apparatus for forming a cylindrical improved body in which the ring thickness obtained by subtracting the improved inner diameter from the improved outer diameter of the cylindrical improved body is set to approximately 4 to 1/8 of the improved outer diameter,
A plurality of upper stirring blades having a blade diameter smaller than the improved inner diameter to be created and provided so as to fit inside the improved inner diameter ;
It has a plurality of lower stirring blades having a blade diameter smaller than the improved outer diameter to be created, which is equipped with an injection material flow path and an injection nozzle,
The lower stage stirring blade,
a downward injection nozzle capable of injecting the injection material downward;
an obliquely downward injection nozzle capable of injecting an injection material outward and obliquely downward;
and
The lower stirring blade has two obliquely downward injection nozzles and at least one downward injection nozzle,
forming an outer area corresponding to an area of approximately two-thirds of the thickness of the ring to be formed with injection material injected from the two obliquely downward injection nozzles;
forming an inner region portion corresponding to the remaining one-third area of the ring thickness portion to be formed with the injection material injected from the downward injection nozzle;
A soil improvement body construction device characterized by: 2. The apparatus of claim 1, wherein
A soil improvement body construction device characterized by comprising a plurality of stages of stirring blades. A device according to claim 1 or claim 2, wherein
A soil improvement body construction device characterized by having an injection nozzle for sending a liquid to an inner region of the improvement body. A ground improvement method for creating a cylindrical improvement body using the device according to claim 1 or claim 2,
A ground improvement method, characterized in that the injection amount or the injection pressure is changed when the injection material is injected from the injection nozzle. A device according to claim 1 or claim 2, wherein
The lower stirring blade has an injection material inflow prevention plate for preventing the injection material from flowing into the inner region of the improved body, at a position substantially matching the inner diameter of the cylindrical improved body to be created,
A soil improvement body construction device, wherein the inflow prevention plate is installed in a direction oblique to a rotating direction of the stirring blade when penetrating into the ground.

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