Site improvement equipment

Abstract

The objective is to provide a ground improvement device that can construct an enlarged diameter section without using complex enlarged wings. [Solution] The system consists of an anti-rotation wing 102 attached to the outer shaft 10, a guide portion 103 formed on a part of the outer shaft 10, an excavation wing 201 and a guided portion 203 attached to the inner shaft 20, and a protruding portion 202 attached to the excavation wing 201. When the guided portion 203 is in the region on the upper end side of the guide portion 103, a part of the protruding portion 202 is located within the rotational region of the anti-rotation wing 102, and when the guided portion 203 is in the region on the lower end side of the guide portion 103, the upper end of the protruding portion 202 is located below the rotational region of the anti-rotation wing 102.

Description

Technical Field

[0005]

[0001] The present invention relates to a ground improvement device that performs ground improvement by mixing and stirring excavated soil and an improvement material while excavating the ground.

Background Art

[0002] As a ground strengthening method when constructing structures such as houses on soft ground, there is a method of constructing columnar improvement bodies in the ground by discharging a solidifying material such as cement milk simultaneously with excavation and mixing and stirring the excavated soil and the solidifying material to cause consolidation. Generally, in the device used for this method, a rotary shaft that can be raised and lowered by a rotary drive device such as an earth auger is provided with excavation blades, anti-rotation blades, and stirring blades at predetermined intervals.

[0003] As a method for increasing the supporting force of the ground compared to the columnar improvement bodies constructed by such a general ground improvement device, there is a method of constructing a diameter-expanded portion in which a part is expanded in the width direction. Generally, the ground improvement device used for this method uses expanding blades with a complicated structure. However, the applicant of the present application previously invented a ground improvement device that does not rely on such a complicated structure (Patent Document 1). This invention forms a diameter-expanded portion by rotating the anti-rotation blade in the reverse rotation direction (rotation in the direction opposite to the rotation direction during excavation).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the ground improvement device for constructing this diameter-expanded portion, since the swing arm 63 swings as the rotating portion 62 rotates, the rotating portion 62 may malfunction due to rust, wear, etc., and there was a problem in terms of durability.

[0006] Therefore, the present invention aims to provide a ground improvement device that can construct an enlarged diameter section without requiring such an operating device. [Means for solving the problem]

[0007] The ground improvement device according to claim 1 comprises a cylindrical outer shaft extending in the axial direction, an inner shaft inserted from an opening at the lower end of the outer shaft and movable within the internal space of the outer shaft, a drilling blade extending radially outward from the outer circumferential surface at the lower end of the inner shaft and rotating together with the rotation of the inner shaft, and a co-rotation prevention blade extending radially outward from the outer circumferential surface at the lower end of the outer shaft to a length longer than the drilling blade and rotatably attached to the outer shaft, wherein the outer shaft has guide portions extending in the axial and axial directions, respectively, which penetrate a portion of the circumferential wall. The invention is formed by the above, wherein a guided portion is attached to the outer circumferential surface of the inner shaft, with a part of the inner shaft inserted into the internal space of the outer shaft, and a projection extending upward is attached to the drilling blade, wherein when the guided portion is in the region on the upper end side of the guide portion, a part of the projection is located within the rotation region of the anti-rotation blade, and when the guided portion is in the region on the lower end side of the guide portion, the upper end of the projection is located below the rotation region of the anti-rotation blade.

[0008] The ground improvement device according to claim 2 is the ground improvement device according to claim 1, characterized in that the guide portion is formed by chamfering the corner edge of the peripheral wall that bends 90 degrees from the axial direction to the axial direction.

[0009] The ground improvement device according to claim 3 is the ground improvement device according to claim 1, wherein the guide portion is formed by chamfering the corner edge of the peripheral wall that bends 90 degrees from the axial direction to the axial direction, and the guided portion has a substantially rectangular parallelepiped or substantially cubic shape extending radially outward, and two of the four sides along the radially outward direction that are diagonally opposite to each other are chamfered.

[0010] The ground improvement device according to claim 4 is the ground improvement device according to claim 1, wherein the guide portion includes a shape that is curved from the axial direction to the axial direction, and the guided portion has a substantially cylindrical shape that extends radially outward.

[0011] The ground improvement device according to claim 5 comprises a cylindrical outer shaft extending in the axial direction, an inner shaft inserted from an opening at the lower end of the outer shaft and movable within the internal space of the outer shaft, a drilling blade extending radially outward from the outer peripheral surface at the lower end of the inner shaft and rotating together with the rotation of the inner shaft, and a co-rotation prevention blade extending radially outward from the outer peripheral surface at the lower end of the outer shaft to a length longer than the drilling blade and rotatably attached to the outer shaft, wherein the outer shaft is formed by passing through a part of the peripheral wall, and the guide portion comprises a first guide having a predetermined length along the axial direction, and a forward rotation from the region at the upper end of the first guide The device has a second guide extending in the direction of rotation and a third guide extending in the reverse direction from the region on the lower end side of the first guide, a guided portion is attached to the outer circumferential surface of the inner shaft, with a part of the inner shaft inserted into the internal space of the outer shaft, and a projection extending upward is attached to the drilling blade, and when the guided portion is in the region on the upper end side of the first guide or the second guide, a part of the projection is located within the rotation region of the anti-rotation blade, and when the guided portion is in the region on the lower end side of the first guide or the third guide, the upper end of the projection is located below the rotation region of the anti-rotation blade.

[0012] The ground improvement device according to claim 6 is the ground improvement device according to claim 5, wherein the guide portion is formed by chamfering the corner edge of a peripheral wall that bends 90 degrees from the axial direction to the axial direction, and the guided portion has a substantially rectangular parallelepiped or substantially cubic shape extending radially outward, and two of the four sides along the radially outward direction that are diagonally opposite to each other are chamfered.

[0013] The ground improvement device according to claim 7 is the ground improvement device according to claim 5, wherein the guide portion includes a shape that is curved from the axial direction to the axial direction, and the guided portion has a substantially cylindrical shape that extends radially outward.

[0014] The ground improvement device according to claim 8 is the ground improvement device according to claim 5, wherein the guide portion includes a shape that is curved from the axial direction to the axial direction, the guided portion is a substantially cylindrical shape that extends radially outward, and the inner circumferential surfaces of the ends of the second guide and the third guide are curved in an arc shape to follow the curvature of the guided portion. [Effects of the Invention]

[0015] This invention allows for the construction of an enlarged diameter section without the need for complex enlarged wings, significantly reducing manufacturing costs. Furthermore, it is unaffected by rust and wear, thus reducing the risk of failure and providing superior durability. [Brief explanation of the drawing]

[0016] [Figure 1] This is an exploded view showing an example of a ground improvement device according to the present invention. [Figure 2] This is a perspective view showing an example of a ground improvement device according to the present invention. [Figure 3] This is a perspective view showing an example of a ground improvement device according to the present invention. [Figure 4] This is a perspective view showing the construction procedure for the ground improvement device according to the present invention. [Figure 5] This is a perspective view showing an example of a guide part and a guided part. [Figure 6] This is a perspective view showing an example of a guide part and a guided part. [Modes for carrying out the invention]

[0017] The best mode for carrying out the present invention will be described with reference to the drawings.

[0018] The ground improvement device 1 according to the present invention includes an outer shaft 10, stirring blades 101 and anti-rotation blades 102 attached to the outer shaft 10, a guide portion 103 formed in a part of the outer shaft 10, an inner shaft 20 that can be inserted into the outer shaft 10, excavation blades 201 and a guided portion 203 attached to the inner shaft 20, and a protruding portion 202 attached to the excavation blades 201.

[0019] As shown in FIGS. 1 to 3, the outer shaft 10 has a hollow internal space that extends in the axial direction (longitudinal direction) by a peripheral wall that surrounds in the circumferential direction, and has a cylindrical shape with both ends of the internal space opening in the axial direction. The outer shaft 10 is arranged such that the axial direction faces the vertical direction (up and down direction). This internal space functions as a flow path for supplying a solidifying material into the ground.

[0020] On the outer shaft 10, in a region on the lower end (tip) side, a pair of anti-rotation blades 102 that extend in opposite directions radially outward (horizontal direction) from the outer peripheral surface of the peripheral wall are rotatably attached to the outer shaft 10. Further, a plurality of stirring blades 101 are fixedly attached to the outer shaft 10 at a position above the position where the anti-rotation blades 102 are attached. In a general ground improvement device, excavation blades 201 are attached to the outer shaft 10, but in the ground improvement device 1 according to the present invention, the excavation blades 20 are attached to the inner shaft 20 instead of the outer shaft 10.

[0021] The outer shaft 10 receives a rotational force from a rotational drive device (not shown) and rotates in either the forward or reverse direction around the axis with the axis extending in the axial direction (vertical direction) as the center of rotation.

[0022] The inner shaft 20 has an outer diameter slightly smaller than the inner diameter of the outer shaft 10 and has a hollow cylindrical shape extending in the same axial direction as the outer shaft 10. The inner shaft 20 is inserted into the internal space of the outer shaft 10 from the opening on the lower end side of the outer shaft 10 (see the arrow in FIG. 1). The inner shaft 20 arranged with the same axial direction as the outer shaft 10 in this way can rotate around the axis of the internal space of the outer shaft 10 or move in the axial direction along the inner peripheral surface of the peripheral wall of the outer shaft 10.

[0023] The hollow portion of the inner shaft 20 functions as a flow path for the solidifying material supplied from the opening at the upper end of the outer shaft 10, while the opening at the lower end (tip) serves as the discharge port for the solidifying material. Therefore, it is desirable to minimize the gap between the outer shaft 10 and the inner shaft 20 as much as possible to prevent the solidifying material from entering the gap. In other words, it is desirable that the outer diameter of the inner shaft 20 be as close as possible to the inner diameter of the outer shaft 10, within a range that allows for smooth rotation in the circumferential direction and movement in the axial direction.

[0024] A pair of drilling blades 201 are integrally attached to the outer circumferential surface of the lower end (tip) of the inner shaft 20, extending radially (in the direction perpendicular to the axial direction) outward in opposite directions. The drilling blades 201 are plate-shaped and arranged at an inclination with respect to the axial direction. Multiple drilling bits 201a are also attached to the drilling blades 201 at an inclination with respect to the axial direction. Since the drilling blades 201 and drilling bits 201a rotate around the axis as the inner shaft 20 rotates, the ground can be drilled when the inner shaft 20 rotates.

[0025] The anti-rotation wing 102 is composed of a substantially rectangular plate-like body with a predetermined thickness, extending radially outward (in a direction perpendicular to the axial direction). The anti-rotation wing 102 extends radially outward beyond the excavation wing 201. It is installed in a state where it is oriented vertically, with the shorter side of the main surface of the plate-like body parallel to the axial direction, so that it can receive earth pressure on the main surface (the surface that makes up the plate-like body and has a larger area than the other surfaces).

[0026] On the outer shaft 10, guide portions 103 are formed at predetermined positions, excluding the upper and lower ends, by hollowing out a part of the peripheral wall, and extending from the outer peripheral surface to the inner peripheral surface in the thickness direction. The guide portion 103 has a first guide 103a that extends in the axial direction and has a predetermined length, a second guide 103b that extends from the upper end region of the first guide 103a, bent 90 degrees toward the forward rotation direction, and a third guide 103c that extends from the lower end region of the first guide 103a, bent 90 degrees toward the reverse rotation direction. These first guide 103a, second guide 103b, and third guide 103c are formed continuously with the same width. That is, the guide portion 103 is formed with the first guide 103a in between, with the second guide 103b and third guide 103c formed continuously with a predetermined width at separate locations in the vertical direction (up and down direction), each facing in opposite directions. Therefore, when the inner shaft 20 is inserted into the outer shaft 10, a portion of the inner shaft 20 becomes visible from the guide portion 103. Note that multiple guide portions 103 may be installed.

[0027] The width of the guide section 103 only needs to be slightly larger in diameter than the width of the guided section 203 so that the guided section 203 can move within the guide section 103. Also, the length of the first guide 103a extending in the forward rotation direction and the length of the third guide 103c extending in the reverse rotation direction should be sufficient to accommodate the guided section 203.

[0028] The inner shaft 20 has a guided portion 203 attached to its outer surface. This guided portion extends radially outward (horizontally) from the outer surface of the inner shaft 20, passing through the guide portion 103 of the outer shaft 10, and moves while being guided by the guide portion 103. The guided portion 203 is fixed to the outer surface of the inner shaft 20 by welding, screwing, or other methods. Since the guided portion 203 protrudes radially outward (horizontally) from the outer wall of the outer shaft 10, the inner shaft 20 is supported by the guide portion 103, preventing it from falling into the drilled hole. Furthermore, the inner shaft 20 can reciprocate while being guided by the guide portion 103 in conjunction with the rotation, pushing, and pulling movements of the outer shaft 10. The range of reciprocal movement of the guided portion 203 is from the end of the second guide 103b (the tip on the forward rotation side) to the end of the third guide 103c (the tip on the reverse rotation side). It is desirable that the guided portion 203 protrudes radially outward (horizontally) beyond the position of the peripheral wall of the outer shaft 10, but it is sufficient if it extends to the position of the peripheral wall of the outer shaft 10. If multiple guide portions 103 are installed, the same number of guided portions 203 will be installed.

[0029] The guided portion 203 moves axially and around the axis relative to the guide portion 103, guided by the guide portion 103. Specifically, when the outer shaft 10 is pushed downward while the guided portion 203 is positioned on the first guide 103a, the guided portion 203 moves to the upper end of the first guide 103a. Conversely, when the outer shaft 10 is pulled upward, the guided portion 203 moves to the lower end of the first guide 103a. Furthermore, when the outer shaft 10 is rotated in the reverse direction while the guided portion 203 is positioned on the upper end of the first guide 103a, the guided portion 203 moves to the second guide 103b. In addition, when the outer shaft 10 is rotated in the forward direction while the guided portion 203 is positioned on the lower end of the first guide 103a, the guided portion 203 moves to the second guide 103c.

[0030] Then, when the outer shaft 10 is rotated with the guided portion 203 positioned at the end of either the second guide 103b or the third guide 103c, the inner shaft 20 rotates along with the rotation of the outer shaft. Specifically, when the outer shaft 10 is rotated in the forward direction with the guided portion 203 positioned at the end of the second guide 103b, the inner shaft 20 also rotates in the forward direction. Furthermore, when the outer shaft 10 is rotated in the reverse direction with the guided portion 203 positioned at the end of the third guide 103c, the inner shaft 20 also rotates in the reverse direction.

[0031] A projection 202 is attached to the drilling blade 201, extending vertically upward from a portion of the upper end of the drilling blade 201. The projection 202 may be attached to either one of the drilling blades 201, or it may be attached to both drilling blades 201. The vertical length of the projection 202 is determined such that when the guided portion 203 is in the upper end region of the guide portion 103, a portion of the projection 202 is located inside the rotation region (rotating region) of the anti-rotation blade 102, and when the guided portion 203 is in the lower end region of the guide portion 103, the upper end of the projection 202 is located below the rotation region of the anti-rotation blade 102. In other words, when the guided portion 203 is at the upper end of the first guide 103a or the second guide 103b, the upper end of the protruding portion 202 is positioned above the rotational region in which the lower edge of the anti-rotation wing 102 rotates, and when the guided portion 203 is at the lower end of the first guide 103a or the third guide 103c, the upper end of the protruding portion 202 is positioned below the rotational region in which the lower edge of the anti-rotation wing 102 rotates. In this way, as the guided portion 203 moves up and down on the first guide 103a, the protruding portion 202 moves between a position in which it can contact the anti-rotation wing 102 and a position in which it does not contact it.

[0032] Therefore, the axial length of the first guide 103a is determined such that it includes the region in which a part of the projection 202 rotates with the anti-rotation wing 102, and the region in which the upper end of the projection 202 is below the rotation region of the anti-rotation wing 102. In other words, the axial length of the first guide 103a is determined such that it includes both the position above the rotation region in which the lower end edge of the anti-rotation wing 102 rotates, and the position below the rotation region in which the lower end edge of the anti-rotation wing 102 rotates. Furthermore, the axial length of the inner shaft 20 is determined such that, when inserted into the internal space of the outer shaft 10, the upper end edge of the inner shaft 20 is positioned above the upper end of the guide portion 103.

[0033] The procedure for improving soft ground using the ground improvement device 1 configured in this way will now be explained. Here, the direction of rotation when excavating the ground is called the "forward rotation direction," and the direction of rotation opposite to the direction of rotation during excavation is called the "reverse rotation direction." For forward rotation, this will be described as left rotation (clockwise), and reverse rotation, this will be described as right rotation (counterclockwise). Note that the stirring blade 101 is omitted from the illustration in Figure 4 for the sake of explanation.

[0034] First, as shown in Figure 4(a), the guided portion 203 is positioned in contact with the third guide 103c. In this state, when the outer shaft 10 is rotated in the forward direction, the end of the third guide 103c continues to push the guided portion 203 in the forward direction, causing the guided portion 203 to also rotate in the forward direction. As the guided portion 203 rotates in the forward direction, the inner shaft 20 also rotates in the forward direction, causing the excavation blade 201 to rotate as well, allowing the excavation to progress. At this time, the protruding portion 202 does not come into contact with the anti-rotation blade 102, so the anti-rotation blade 102 remains embedded in the ground outside the excavation hole and does not rotate. Then, the excavation progresses while rotating the outer shaft 10 in the forward direction until the design depth is reached. At this time, the solidifying agent is discharged from the discharge port of the inner shaft 20 and mixed with the excavated soil.

[0035] Next, after reaching the design depth, when the outer shaft 10 is rotated in the reverse direction, the guided portion 203 moves towards the lower end of the first guide 103a (Figure 4(b)). The arrow shown in Figure 4(b) indicates that the outer shaft is rotated slightly in the reverse direction.

[0036] Next, when the outer shaft 10 is pushed downward (advanced), the guided portion 203 moves to a state where it is in contact with the upper end of the first guide 103a (Figure 4(c)). The arrow shown in Figure 4(c) indicates pushing the outer shaft downward.

[0037] Subsequently, by rotating the outer shaft 10 in the reverse direction, the guided portion 203 moves to a position where it contacts the inner circumferential surface of the end of the second guide 103b. At this time, the guided portion 203 has reached a position where it can contact the anti-rotation wing 102, so when the outer shaft 10 is rotated in the reverse direction, the end of the second guide 103b continues to push the guided portion 203 in the reverse direction, causing the guided portion 203 to rotate in the reverse direction as well. When the guided portion 203 rotates in the reverse direction while in a position where it can contact the anti-rotation wing 102, the anti-rotation wing 102 also rotates in the reverse direction, allowing the tip of the anti-rotation wing 102 to excavate the ground outside the excavation hole (Figure 4(d)).

[0038] As a result, it becomes possible to form an enlarged borehole with a larger diameter than other parts at any point in the excavation hole. Then, by mixing and stirring the excavated soil with the solidifying agent and allowing it to solidify, an enlarged diameter section can be constructed in which a part of the columnar improved body is widened in the width direction.

[0039] Here, as shown in Figure 5, it is desirable that the guide portion 103 is formed by bends of the peripheral wall of the outer shaft 10 surrounding the guide portion 103 at a 90-degree angle from the axial direction to the axial direction (the direction in which the outer shaft 10 rotates), and that the two corner edges C1 and C2 extending in the thickness direction are chamfered. Specifically, it is desirable that the corner edge C1 of the peripheral wall of the outer shaft 10, which is the lower end edge of the boundary between the first guide 103a and the second guide 103b, be chamfered. Similarly, it is desirable that the corner edge C2 of the peripheral wall of the outer shaft 10, which is the upper end edge of the boundary between the first guide 103a and the third guide 103c, be chamfered. Because the guide portion 103 bends at a right angle from the axial direction to the axial direction, the corner edges C1 and C2 of the bent peripheral wall have a pointed shape. Therefore, when the guided portion 203 moves, it may get caught on the corner edges C1 and C2, preventing it from moving from the first guide 103a to the second guide 103b or the third guide 103c. Also, if excavated soil enters the guide portion 103, it may prevent the guided portion 203 from moving from the first guide 103a to the second guide 103b or the third guide 103c. Therefore, by chamfering the corner edges C1 and C2 of the peripheral wall, the guided portion 203 can move smoothly within the guide portion 103. The chamfering can be C-shaped or R-shaped, or any shape that allows the guided portion 203 to move smoothly.

[0040] Furthermore, the guided portion 203 has a roughly rectangular parallelepiped or roughly cubic shape extending radially outward, and it is desirable that two of the four radially outward-extending sides, S1 and S2, which contact the two corner edges C1 and C2 of the chamfered peripheral wall when the guided portion 203 moves from the axial direction to the axial direction, are chamfered. These two sides may only have chamfered portions (parts of the sides) that contact the two corner edges C1 and C2 of the chamfered peripheral wall. The chamfering can be C-shaped or R-shaped, or any shape that allows the guided portion 203 to move smoothly. By chamfering the guided portion 203 in this way, the guided portion 203 can move more smoothly within the guide portion 103, and furthermore, deterioration of the peripheral wall due to impact can be prevented.

[0041] Furthermore, as shown in Figure 5, the guided portion 203 has a roughly rectangular parallelepiped or roughly cubic shape extending radially outward, and it is desirable that two of the four radially outward-extending sides, S1 and S2, which contact the two corners of the chamfered peripheral wall when the guided portion 203 moves from the axial direction to the axial direction, are chamfered. These two sides may only have chamfered portions (parts of the sides) that contact the two corners of the chamfered peripheral wall. The chamfering can be C-shaped or R-shaped, or any shape that allows the guided portion 203 to move smoothly. By chamfering the guided portion 203 in this way, the guided portion 203 can move more smoothly within the guide portion 103, and furthermore, deterioration of the peripheral wall due to impact can be prevented.

[0042] Furthermore, as shown in Figure 6, it is desirable that the guided portion 203 extends radially outward (horizontally) from the outer circumferential surface of the inner shaft 20 and has a substantially cylindrical shape with curved side surfaces. By rounding the corners of the guide portion 103 and the guided portion 203, the guided portion 203 can move more smoothly within the guide portion 103, and deterioration of the peripheral wall due to impact can be prevented.

[0043] Furthermore, as shown in Figure 6, it is desirable that the inner circumferential surfaces 103E at the ends of the second guide 103b and the third guide 103c are curved in an arc shape to follow the curvature of the guided portion 203. By forming the side surface of the guided portion 203 in an arc shape approximately the same as the radius of curvature of the guided portion 203, the entire inner circumferential surface 103E at the end of the second guide 103b can continue to push the guided portion 203 in the reverse direction even when the outer shaft 10 is rotated in the reverse direction. As a result, it becomes possible to rotate the inner shaft 20 with a relatively small rotational force, and furthermore, deterioration of the circumferential wall and the guided portion 203 can be prevented. The same applies to the third guide 103c. [Explanation of symbols]

[0044] 1 Ground improvement equipment 10 Outer shaft 102 Anti-rotation wing 20 Inner shaft 201 Drilling blade 202 Protrusion 203 Guided part

Claims

1. A cylindrical outer shaft extending in the axial direction, An inner shaft is inserted from the opening at the lower end of the outer shaft and is movable within the internal space of the outer shaft, A drilling blade extending radially outward from the outer circumferential surface at the lower end of the inner shaft and rotating together with the rotation of the inner shaft, A co-rotation prevention blade extends radially outward from the outer circumferential surface of the lower end of the outer shaft, and is longer than the drilling blade, and is rotatably mounted on the outer shaft, Equipped with, Guide portions extending along the axial direction and the direction around the axis are formed on the outer shaft by penetrating a portion of the peripheral wall. A guided portion is attached to the outer circumferential surface of the inner shaft, with a portion of the inner shaft inserted into the internal space of the outer shaft, and guided by the guide portion. The aforementioned drilling blade is fitted with an upwardly extending projection, A ground improvement device characterized in that when the guided portion is in the region on the upper end side of the guide portion, a part of the protruding portion is located within the rotational region of the anti-rotation wing, and when the guided portion is in the region on the lower end side of the guide portion, the upper end of the protruding portion is located below the rotational region of the anti-rotation wing.

2. The ground improvement device according to claim 1, characterized in that the guide portion is formed by chamfering the corner edge of the peripheral wall that bends 90 degrees from the axial direction to the direction around the axis.

3. The guide portion is formed by chamfering the corner edge of the peripheral wall that bends 90 degrees from the axial direction to the direction around the axis. The ground improvement device according to claim 1, characterized in that the guided portion has a substantially rectangular parallelepiped or substantially cubic shape extending radially outward, and two of the four sides along the radially outward direction that are diagonally opposite each other are chamfered.

4. The guide portion includes a shape that is curved from the axial direction to the direction around the axis, The ground improvement device according to claim 1, characterized in that the guided portion has a substantially cylindrical shape extending radially outward.

5. A cylindrical outer shaft extending in the axial direction, An inner shaft is inserted from the opening at the lower end of the outer shaft and is movable within the internal space of the outer shaft, A drilling blade extending radially outward from the outer circumferential surface at the lower end of the inner shaft and rotating together with the rotation of the inner shaft, A co-rotation prevention blade extends radially outward from the outer circumferential surface of the lower end of the outer shaft, and is longer than the drilling blade, and is rotatably mounted on the outer shaft, Equipped with, Guide portions extending along the axial direction and the direction around the axis are formed on the outer shaft by penetrating a portion of the peripheral wall. The guide portion comprises a first guide having a predetermined length along the axial direction, a second guide extending in the forward rotation direction from the upper end region of the first guide, and a third guide extending in the reverse rotation direction from the lower end region of the first guide. A guided portion is attached to the outer circumferential surface of the inner shaft, with a portion of the inner shaft inserted into the internal space of the outer shaft, and guided by the guide portion. The aforementioned drilling blade is fitted with an upwardly extending projection, A ground improvement device characterized in that when the guided portion is in the region on the upper end side of the first guide or the second guide, a part of the protruding portion is located within the rotation region of the anti-rotation wing, and when the guided portion is in the region on the lower end side of the first guide or the third guide, the upper end of the protruding portion is located below the rotation region of the anti-rotation wing.

6. The guide portion is formed by chamfering the corner edge of the peripheral wall that bends 90 degrees from the axial direction to the direction around the axis. The ground improvement device according to claim 5, characterized in that the guided portion has a substantially rectangular parallelepiped or substantially cubic shape extending radially outward, and two of the four sides along the radially outward direction that are diagonally opposite each other are chamfered.

7. The guide portion includes a shape that is curved from the axial direction to the direction around the axis, The ground improvement device according to claim 5, characterized in that the guided portion has a substantially cylindrical shape extending radially outward.

8. The guide portion includes a shape that is curved from the axial direction to the direction around the axis, The guided portion has a substantially cylindrical shape that extends radially outward, The ground improvement device according to claim 5, characterized in that the inner circumferential surfaces of the respective ends of the second guide and the third guide are curved in an arc shape to conform to the curvature of the guided portion.

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