Soil improvement device

Abstract

To provide a soil improvement device capable of excavating a desired area by surely enlarging a diameter in spite of a simple structure.SOLUTION: A main body portion 10 or a main shaft portion 20 connected to a rotary drive device and configured to rotate, a pair of support portions provided on the main shaft portion 20 so as to face each other in a radial direction, an enlarged head portion 50 rotatably attached to the support portions, and a pair of enlarged bars 60 provided on the main shaft portion 20 or the main body portion 10 and configured to engage with the enlarged head portion 50, An enlarged bar 60 is engaged with the enlarged head part 50 to rotate the tip of the enlarged head part 50.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a ground improvement device that excavates and mixes ground, and in particular to a ground improvement device that can expand the excavation area when it reaches a predetermined depth. [Background technology]

[0002] Soil improvement, which involves excavating and improving the ground, has been widely practiced in the past. This ground improvement is essential for improving the stability of the ground when building foundations or constructing roads.

[0003] In such ground improvement work, the so-called expanded foot consolidation method is used, in which the ground is excavated in the supporting layer using the core excavation method or pre-boring method, and a foot consolidation bulb is created by injecting a foot consolidation liquid (cement milk) into this expanded excavation, thereby increasing the tip bearing capacity of the prefabricated pile.

[0004] In such an expansion foot protection method, an expansion excavation device is used, which is a type in which the expansion blades are switched from a reduced diameter state to an expanded diameter state by earth pressure when the drilling rod is rotated in the reverse direction, or a type in which the expansion blades are switched between a reduced diameter state and an expanded diameter state by a fluid pressure cylinder such as hydraulic or water pressure.

[0005] In such a device, the expansion blades are kept in a contracted state until the predetermined depth is reached, and then expanded when the predetermined depth is reached, thereby preventing unnecessary excavation over a wide area up to the predetermined depth, and expanding the excavation area when the predetermined depth is reached, thereby enabling work to be carried out efficiently. For ground improvement under such conditions, a ground improvement excavator as described in Patent Document 1, for example, has been developed.

[0006] The ground improvement excavator described in Patent Document 1 has expandable and contractible excavation stirring blades attached to a drilling rod. The stirring blades are attached to a pair of brackets arranged opposite to each other in the axial direction of the drilling rod, and swing toward the drilling rod when the drilling rod rotates forward, and swing away from each other due to earth pressure when the drilling rod rotates reversely.

[0007] The mixing blade is composed of an arc-shaped reinforcing plate, a shaft, a tip bit, and multiple bits. It fits inside the drilling head when the drilling rod rotates forward, and when the rod rotates reversely, the distance between the bits is more than twice the distance between the tips of the brackets.

[0008] With this ground improvement device, the diameter of the improvement body can be made larger for the same pilot hole diameter, which reduces the number of holes required to improve the same area of ​​ground.In addition, the device is simpler than devices that use fluid pressure cylinders such as hydraulic or water pressure to switch the expansion blades between a reduced diameter state and an expanded diameter state. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-301453 Summary of the Invention [Problem to be solved by the invention]

[0010] However, although the ground improvement device described in Patent Document 1 is simple because it does not use a cylinder or the like, it relies on the expectation that the mixing blades will expand due to earth pressure when the excavation rod is reversed, and there have been cases where the mixing blades do not expand. If the mixing blades do not expand, it is not possible to excavate the specified area, which can cause major problems in that it hinders construction work after excavation.

[0011] The present invention has been proposed to solve the above problems, and has an object to provide a soil improvement device with a simple structure, while reliably enlarging the diameter and excavating a desired area. [Means for solving the problem]

[0012] (1) A ground improvement device includes a rotating main body or main shaft connected to a rotary drive device, a drilling bit provided at the tip of the main shaft, a pair of support sections provided on the main shaft radially opposite the base end of the drilling bit section, an enlarged head section rotatably attached to the support sections, and a pair of expansion bars provided on the main shaft or the main body and engageable with the enlarged head sections, wherein when the rotary drive device rotates forward, the main body and the main shaft rotate forward and the tip of the enlarged head section rotates so that the tip of the enlarged head section is aligned with the circumferential direction of the main shaft section, and when the rotary drive device rotates reversely, the main body and the main shaft rotate reversely and the tip of the enlarged head section rotates so that the tip of the enlarged head section is aligned with the radial direction of the main shaft section, and the expansion bars engage with the enlarged head section, rotating the tip of the enlarged head section.

[0013] (2) In the ground improvement device of (1) above, the main body is connected to the rotation drive member, and the main shaft is supported by the main body and extends in the direction of the rotation axis.

[0014] (3) In the ground improvement device of (1) above, the expansion bar is supported on the main shaft portion, and by engaging one end with the expansion head portion and the other end with the support protrusion portion of the main body portion, it assists the expansion head portion in rotating in a direction away from the main shaft portion.

[0015] (4) In the ground improvement device described in (2) above, when the main shaft portion switches from rotating in synchronization with the forward rotation of the main body portion to rotating in reverse of the main shaft, it spins freely for a predetermined angle, and then rotates in reverse again in synchronization with the main shaft portion.

[0016] (5) In the ground improvement device of (1) above, the enlarged head portion is provided with an enlarged display portion that allows confirmation that the tip of the enlarged head portion has rotated so that the tip of the enlarged head portion is aligned radially with the main shaft portion.

[0017] (6) In the ground improvement device of (1) above, the expansion bar is provided with the other end fixed to the main body portion, and by engaging one end with the expansion head portion, the tip of the expansion head portion is rotated.

[0018] (7) The ground improvement system of the present invention comprises a rotary drive device capable of switching between forward and reverse rotation, a main body or main shaft connected to the rotary drive device and rotating, a drilling bit provided at the tip of the main shaft, a pair of support sections provided on the main shaft radially opposite the base end of the drilling bit section, an enlarged head section rotatably attached to the support sections, and a pair of expansion bars provided on the main shaft or the main body and engageable with the enlarged head sections, wherein when the rotary drive device rotates forward, the main body and the main shaft rotate forward and the tip of the enlarged head section rotates so that the tip of the enlarged head section is aligned with the circumferential direction of the main shaft, and when the rotary drive device rotates reversely, the main body and the main shaft rotate backward and the tip of the enlarged head section rotates so that the tip of the enlarged head section is aligned with the radial direction of the main shaft, and the expansion bars engage with the enlarged head section, rotating the tip of the enlarged head section.

[0019] (8) A method for expanding an improvement area of ​​a ground improvement device includes rotating a rotary drive device in the forward direction, rotating a main body and a main shaft in the forward direction in synchronization with the rotary drive device, rotating the rotary drive device in the reverse direction, rotating one of the main body or the main shaft in the reverse direction in synchronization with the rotary drive device, allowing the other of the main body or the main shaft to spin freely for a predetermined angle, and then rotating it in the reverse direction again in synchronization with one of the main body or the main shaft, and the reverse rotation of one of the main body or the main shaft causes the expansion bar to engage with the expansion head and rotate the tip of the expansion head. [Effects of the Invention]

[0020] According to the present invention, the soil improvement device can be made to have a simple structure while being reliably in an expanded diameter state to excavate a desired area. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a side view showing a ground improvement system according to an embodiment of the present invention. [Figure 2] 2 is a side view showing the soil improvement device of the soil improvement system shown in FIG. 1 in an expanded diameter state. [Figure 3] 2 is a front view showing the soil improvement device of the soil improvement system shown in FIG. 1 in an expanded diameter state. [Figure 4] 1A and 1B are bottom cross-sectional views for explaining the expanded and contracted states of a rotary bit of a ground improvement device according to an embodiment of the present invention, where FIG. 1A shows the expanded state and FIG. 1B shows the contracted state. [Figure 5] A front cross-sectional view showing the main body, main shaft, and enlarged head of the soil improvement device according to the embodiment of the present invention. [Figure 6] FIG. 2 is a top cross-sectional view showing the engagement relationship between the main body and the main shaft of the ground improvement device according to the embodiment of the present invention. [Figure 7] This is a front view to explain the operation of the expansion bar of the ground improvement device of an embodiment of the present invention, where (A) shows the state in which the expansion bar is in a free position, and (B) shows the state in which the expansion bar is in a position along the rotation axis direction. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, a ground improvement system S according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, the left-right direction in Fig. 1 is referred to as a first direction X, the up-down direction in Fig. 1 is referred to as a second direction Y, and the direction perpendicular to the paper surface in Fig. 1 is referred to as a third direction Z.

[0023] Furthermore, in the ground improvement system S according to this embodiment, the rotation drive device 2 rotates around an axis extending in the second direction Y, and therefore the second direction Y is also referred to as the rotational axis direction Y or simply the axial direction Y. The rotational direction relative to the rotational axis direction is also referred to as the rotational circumferential direction, and the direction perpendicular to the rotational circumferential direction is also referred to as the rotational radial direction. Furthermore, the downward direction in the rotational axis direction is also referred to as the tip side or tip side, and the upward direction is also referred to as the base side or base direction. In this embodiment, clockwise rotation when viewed from above and below in the second direction Y is described as forward rotation, and counterclockwise rotation is described as reverse rotation.

[0024] In addition, in this embodiment, unless otherwise specified, the joining, coupling and connection of each member and each part are performed by general appropriate means such as welding, screws, bolts B and lock pins. <Configuration of Ground Improvement System S> As shown in Figure 1, the ground improvement system S comprises a large base machine 1 such as a pile driver, a rotary drive device 2 such as an auger device attached to the tip of the leader of the base machine 1, and a ground improvement device 3 attached to the rotary drive device 2. According to the ground improvement system S of the present invention, the ground improvement device 3 excavates the ground underground. The rotary drive device 2 rotates around the vertical direction (rotation axis direction Y).

[0025] As shown in Figures 2 to 6, the ground improvement device 3 is attached to the tip of the rotational axis direction Y of the rotary drive device 2. The ground improvement device 3 is formed with a flow path R for injecting a foot-hardening liquid (cement milk) or the like into the soil during ground improvement (see Figure 5).

[0026] The ground improvement device 3 comprises a main body 10 attached to the rotary drive device 2, a main shaft 20 extending from the main body 10 in the axial direction Y, a drilling bit 30 provided at the tip of the main shaft 20, a pair of expansion head support parts 40 provided on the main shaft 20 at the base end side of the drilling bit part 30, an expansion head part 50 rotatably supported on each expansion head support part 40, and a pair of expansion bars 60 rotatably provided on the main shaft 20 at the base end side of the expansion head support part 40.

[0027] The main body 10 is attached to the tip of the rotary drive device 2 and includes a main body connecting part 11 extending in the direction of the rotation axis Y, a cylindrical main body support part 12 provided below the main body connecting part 11 and supporting the main shaft part 20, and a plate-shaped screw part 13 provided in a spiral shape around the main body support part 12. The main body 10 is connected to the rotary drive device 2 by the main body connecting part 11, and the rotational force of the rotary drive device 2 is transmitted from the main body connecting part 11, causing each part of the main body 10 to rotate forward or backward integrally.

[0028] The main body support part 12 is provided with a pair of rotational engagement parts 14 having opposing rotational engagement parts 14a, 14b on its cylindrical inner circumferential surface, a first sliding member 15, and a second sliding member 16 (see FIG. 5). The pair of rotational engagement parts 14 are arranged to face each other at a distance in the circumferential direction. Each rotational engagement part 14 is formed in a roughly fan shape that opens at an angle of 30° (see FIG. 6). The first sliding member 15 is provided in a portion that contacts a first cylindrical part 22a (described later), and the second sliding member 16 is provided in a portion that contacts a third cylindrical part 22c.

[0029] Main shaft portion 20 includes a cylindrical shaft portion 21 that extends in the direction of the rotation axis, and a generally cylindrical shaft support portion 22 that is connected to shaft portion 21 and extends in the direction of the rotation axis (see FIG. 5). Therefore, main shaft portion 20 extends in the direction of the rotation axis.

[0030] The shaft support portion 22 includes, from the distal end to the proximal end, a first cylindrical portion 22a, a second cylindrical portion 22b, a third cylindrical portion 22c, a disk-shaped base portion 22d, and a pair of rotationally engaged portions 24 having rotationally engaged portions 24a, 24b (see FIGS. 5 and 6).

[0031] Specifically, as shown in FIG. 5, the first cylindrical portion 22a has a cylindrical main body and a protruding portion that protrudes downward from the main body and has approximately the same diameter as the shaft portion 21. The protruding portion is coupled to the shaft portion 21 so as to receive the base end of the shaft portion 21. The second cylindrical portion 22b has a smaller radial dimension than the first cylindrical portion 22a so as to have a predetermined gap from the inner circumferential surface of the main body 10, and is provided with a rotationally engaged portion 24. The third cylindrical portion 22c has a smaller radial dimension than the second engaging portion. The first cylindrical portion 22a, the second cylindrical portion 22b, and the third cylindrical portion 22c are integrally formed.

[0032] Base portion 22d has an outer diameter that is approximately the same as that of first cylindrical portion 22a in the radial direction, and is joined to third cylindrical portion 22c by bolt B. As a result, shaft support portion 22 of main shaft portion 20 is formed into a shape that fits inside main body portion 10 by first cylindrical portion 22a, second cylindrical portion 22b, third cylindrical portion 22c, and base portion 22d, and is supported by main body portion 10 on main body support portion 12.

[0033] Furthermore, first sliding member 15 and second sliding member 16 reduce friction with shaft support portion 22 when main body portion 10 rotates. In this embodiment, sliding portions are provided at positions corresponding to first cylindrical portion 22a and third cylindrical portion 22c. This allows main shaft portion 20 to be rotatably supported relative to main body portion 10.

[0034] 6, the pair of rotationally engaged portions 24 are formed in a fan shape that opens at 45° along the circumference of second cylindrical portion 22b, and are arranged to face each other at a circumferential distance. Furthermore, main shaft portion 20 is fitted and covered by main body portion 10 so that each rotationally engaged portion 24 is arranged on both sides of the pair of rotationally engaging portions 14 in the circumferential direction of main body portion 10. This allows main shaft portion 20 to rotate within a predetermined angular range relative to main body portion 10.

[0035] 2, the drilling bit section 30 has a point bit 31 that protrudes in the second direction Y from the tip of the main shaft section 20, and a pair of main body bits 32 that extend in the first direction X from the tip of the main shaft section 20. The pair of main body bits 32 has a pair of bit extension sections 32a that extend in the first direction X and three bit protrusions 32b that protrude from each bit extension section 32a toward the tip.

[0036] The bit protrusions 32b are provided with a predetermined shape and angle so as to excavate the soil when the main shaft 20 rotates forward (see FIG. 3). That is, the three bit protrusions 32b provided on one bit extension 32a and the three bit protrusions 32b provided on the other bit extension 32a are formed at an angle so as to protrude in opposite directions.

[0037] The pair of enlarged head support parts 40 are disposed between the drilling bit part 30 and the main body part 10, and are provided opposite to each other with a circumferential gap between them on the shaft part 21 of the main shaft part 20. Each enlarged head support part 40 has an upper bracket 41, a lower bracket 42, and a column shaft part 43.

[0038] The upper bracket 41 and the lower bracket 42 each have a through-hole that supports the column shaft portion 43. The column shaft portion 43 has a cylindrical portion that is inserted into the through-hole of the upper bracket 41 and the through-hole of the lower bracket 42, and is fixed by engaging the upper end with the upper bracket 41 and the lower end with the lower bracket 42.

[0039] The enlarged head portion 50 includes a pivot support portion 51 that is passed through the column shaft portion 43 so as to be rotatable relative to the column shaft portion 43, a pivot bit 52 (the tip of the enlarged head portion 50) that extends from the pivot support portion 51, and an enlarged display portion 53 that confirms that the pivot bit 52 is in an expanded diameter state. The upper bracket 41 and the lower bracket 42 of the enlarged head support portion 40 have through holes with a diameter slightly larger than the diameter of the cylindrical portion of the column shaft portion 43, and the column shaft portion 43 is rotatably supported by being attached through the through holes.

[0040] The rotary bit 52 is configured so that its tip faces the opposite direction of rotation during forward rotation, making it less susceptible to resistance from the soil due to rotation, and is oriented along the circumferential direction of the shaft portion 21 (reduced diameter state) as shown in FIG. 4(B). The rotary bit 52 is configured so that its tip faces the direction of rotation during reverse rotation, making it less susceptible to resistance from the soil due to rotation, and is oriented so that its tip extends along the radial direction of rotation (expanded diameter state) as shown in FIG. 4(A). The rotary bit 52 is formed into a shape that allows it to excavate.

[0041] The enlarged display portion 53 allows confirmation that the enlarged head has been expanded underground when the ground improvement device 3 is raised to the ground surface. In this embodiment, the enlarged display portion 53 includes a cylindrical portion extending in the axial direction Y provided on the upper bracket 41 of the enlarged head support portion 40, and a rod-shaped member (not shown) passing through and fixed toward the tip of the cylindrical portion. The cylindrical portion is provided at a position where the rod-shaped member will collide with the rotary bit 52 and break when the rotary bit 52 is in an expanded diameter state. Whether the enlarged head portion 50 has been expanded in diameter can be confirmed by visually checking whether the rod-shaped member of the enlarged display portion 53 raised to the ground surface has been broken.

[0042] The expansion bar 60 is formed in a rod shape with roughly rectangular sides, and its center is rotatably supported by the main shaft 20. The expansion bar 60 has a length that allows it to engage with both the expansion head 50 and the support protrusion 17 of the main body 10 when extending along the rotation axis direction Y.

[0043] The support protrusion 17 of the main body 10 is provided on the same side as the side with which the expansion head 50 engages when the expansion bar 60 is aligned along the axial direction Y. When the expansion head 50 engages with the expansion bar 60, the expansion bar 60 engages with the support protrusion 17, so that the expansion bar 60 maintains its position extending along the axial direction Y.

[0044] <Operation of the magnifying head> In the ground improvement device 3, the main body 10 rotates forward when the rotary drive device 2 rotates forward, and rotates backward when the rotary drive device 2 rotates backward. In other words, the main body 10 is connected to the rotary drive device 2 and rotates in synchronization with the rotary drive device 2.

[0045] 6, when the main body 10 rotates forward, one rotationally engaged portion 24a of the main body 10 engages with one rotationally engaging portion 14a of the main body 10, and the other rotationally engaged portion 24b of the main body 10 engages with the other rotationally engaging portion 14b of the main body 10, thereby rotating forward. On the other hand, when the main body 10 rotates backward, one rotationally engaged portion 24a of the main body 10 engages with the other rotationally engaging portion 14b of the main body 10, and the other rotationally engaged portion 24b of the main body 10 engages with one rotationally engaging portion 14a of the main body 10, thereby rotating backward.

[0046] Furthermore, when the rotation of main body 10 switches from forward rotation to reverse rotation, one rotation engaging portion 14a of main body 10 disengages from one rotation engaged portion 24a of main shaft 20 and moves toward and engages with the other rotation engaged portion 24b of main shaft 20. At the same time, the other rotation engaging portion 14b of main body 10 disengages from the other rotation engaged portion 24b of main shaft 20 and moves toward and engages with one rotation engaged portion 24a of main shaft 20. During this period, that is, while rotation engaging portion 14 moves from disengaging with rotation engaged portion 24 to newly engaging with rotation engaged portion 24, main shaft 20 does not rotate, and only main body 10 rotates in the reverse direction.

[0047] As shown in Figure 7, in the ground improvement device 3, when the rotary drive device 2 shifts from forward rotation to reverse rotation, only the main body 10 rotates in the reverse direction, the support protrusion 17 of the main body 10 engages with the other end of the expansion bar 60, and one end of the expansion bar 60 rotates toward the expansion head 50. As a result, one end of the expansion bar 60 engages with the expansion head 50, and the expansion head 50 enters an expanded state. As the expansion head 50 enters an expanded state, the main shaft 20 also begins to rotate in the reverse direction, and the expansion head 50 is reliably expanded under soil pressure. The position of the expansion bar 60 is free to change due to soil pressure during forward rotation.

[0048] <Variations> In the present embodiment, the soil improvement device 3 is described as being connected to and rotated by the rotary drive device 2. However, the soil improvement device 3 may also be provided with the rotary drive device 2.

[0049] In this embodiment, the ground improvement device 3 has been described as rotating the main body 10 connected to the rotary drive device 2, and rotating the main shaft 20 through the rotation of the main body 10. However, the ground improvement device 3 may also be configured to rotate the main shaft 20 through the rotary drive device 2, and rotate the main body 10 through the rotation of the main shaft 20.

[0050] In the present embodiment, the main body portion 10 has been described as including the main body connecting portion 11, the main body supporting portion 12, and the screw portion 13. However, the main body portion 10 may have other configurations as long as it supports the main shaft portion 20 and rotates the main shaft portion 20 in synchronization under predetermined conditions.

[0051] In the present embodiment, the main shaft portion 20 has been described as including the shaft portion 21 and the shaft support portion 22. However, the main shaft portion 20 may have another configuration as long as it has a cutting bit attached thereto, receives the rotational force of a rotary drive device, and rotates to perform cutting.

[0052] In this embodiment, the drilling bit unit 30 has been described as including a point bit 31 and a main bit 32 consisting of a bit extension 32a and three bit protrusions 32b. However, the drilling bit unit 30 may have other configurations as long as it can perform drilling during forward rotation.

[0053] In the present embodiment, the enlarged head support part 40 includes an upper bracket 41, a lower bracket 42, and a column shaft part 43, and is provided on the shaft part 21 of the main shaft part 20 so as to face each other with a circumferential gap therebetween. However, the enlarged head support part 40 may have another configuration as long as it can rotatably support the enlarged head part 50.

[0054] In the present embodiment, the expanding head portion 50 has been described as including a rotation support portion 51 that is passed through the column shaft portion 43 so as to be rotatable relative to the column shaft portion 43, and a rotation bit 52 (the tip of the expanding head portion) that extends from the rotation support portion 51. However, the expanding head portion 50 may have another configuration as long as the rotation bit can be rotated from a reduced diameter state to an expanded diameter state.

[0055] In this embodiment, the expansion bar 60 is described as being pivotally supported on the main shaft. However, as long as the expansion bar has the function of expanding the diameter of the expansion head when the rotation drive device 2 switches from forward rotation to reverse rotation, the expansion bar may be attached to the main body, or may be fixedly attached rather than pivotally supported.

[0056] In this embodiment, the enlarged display portion has been described as having an axially extending cylindrical upper portion on the upper bracket 41 of the enlarged head support portion 40, and a rod-shaped member (not shown) is passed through the cylindrical portion toward the distal end and fixed thereto. However, the enlarged display portion 53 may have a different configuration as long as it can be confirmed that the enlarged head has been enlarged.

[0057] The above describes the ground improvement system S according to the embodiment of the present invention. However, the ground improvement system S is not limited to the above embodiment, and other configurations are possible within the scope of achieving the object of the invention. [Industrial Applicability]

[0058] The present invention can be used in civil engineering works such as ground improvement works. [Explanation of symbols]

[0059] 1: Base machine 2: Rotation drive unit 3: Ground improvement equipment 10: Main body 11: Main body connection part 12: Main body support part 13: Screw section 14: Rotational engagement part 14a: Rotational engagement part 14b: Rotational engagement part 15: First sliding member 16: Second sliding member 17: Support protrusion 20: Main shaft part 21: Shaft section 22: Shaft support part 22a: First cylindrical section 22b: Second cylindrical section 22c: Third cylindrical section 22d: Base 24: Rotating engaged part 24a: Rotation engaged part 24b: Rotation engaged part 30: Drilling bit part 31: Pointed bit 32: Body bit 32a: Bit extension 32b: Bit protrusion 40: Enlarged head support part 41: Upper bracket 42: Lower bracket 43:Column shaft part 50: Enlarged head 51: Rotation support part 52: Rotating bit 53: Enlarged sign area 60: Expanding bar B: Bolt R: Flow path S: Ground improvement system

Claims

1. a rotating body or spindle connected to a rotary drive; A drilling bit portion provided at the tip of the main shaft portion; A pair of support portions provided on the main shaft portion radially opposed to each other on the base end side of the drilling bit portion; an enlarged head portion rotatably attached to the support portion; a pair of expansion bars provided on the main shaft portion or the main body portion and engageable with the expansion head portion; When the rotary drive device rotates in the forward direction, the main body and the main shaft rotate in the forward direction, and the tip of the enlarged head rotates so that the tip of the enlarged head is aligned with the circumferential direction of the main shaft, A ground improvement device characterized in that, when the rotary drive device rotates in the reverse direction, the main body and the main shaft rotate in the reverse direction, and the tip of the enlarged head rotates so that the tip of the enlarged head is aligned radially with the main shaft, and the enlargement bar engages with the enlarged head, causing the tip of the enlarged head to rotate.

2. the main body is connected to the rotation drive member; The ground improvement device according to claim 1 , wherein the main shaft portion is supported by the main body portion and extends in the direction of the rotation axis.

3. the expansion bar is journalled to the main shaft portion, 2. The soil improvement device according to claim 1, wherein the tip of the enlarged head portion is rotated by engaging one end of the enlarged head portion with the other end of the enlarged head portion and engaging the support projection of the main body portion.

4. The main shaft portion is The ground improvement device according to claim 2, wherein when the main body rotates in sync with the forward rotation of the main shaft and then switches to reverse rotation of the main shaft, the main shaft spins freely for a predetermined angle, and then rotates in reverse again in sync with the main shaft.

5. The ground improvement device according to claim 1, wherein the enlarged head portion is provided with an enlarged display portion that allows confirmation that the tip of the enlarged head portion has rotated so that the tip of the enlarged head portion is aligned radially with the main shaft portion.

6. the expansion bar is provided with the other end fixed to the main body portion, The soil improvement device according to claim 1, wherein the tip of the enlarged head portion is rotated by engaging one end of the enlarged head portion.

7. a rotation drive device that can switch between forward and reverse rotation; a rotating main body or main shaft connected to the rotary drive device; A drilling bit portion provided at the tip of the main shaft portion; A pair of support portions provided on the main shaft portion radially opposed to each other on the base end side of the drilling bit portion; an enlarged head portion rotatably attached to the support portion; a pair of expansion bars provided on the main shaft portion or the main body portion and engageable with the expansion head portion; When the rotary drive device rotates in the forward direction, the main body and the main shaft rotate in the forward direction, and the tip of the enlarged head rotates so that the tip of the enlarged head is aligned with the circumferential direction of the main shaft, A ground improvement system characterized in that, when the rotary drive device rotates in the reverse direction, the main body and the main shaft rotate in the reverse direction, and the tip of the enlarged head rotates so that the tip is aligned radially with the main shaft, and the enlargement bar engages with the enlarged head and rotates the tip of the enlarged head.

8. Rotating the rotary drive device in the forward direction; rotating the main body and the main shaft forward in synchronization with the rotation drive device; rotating the rotary drive device in a reverse direction; Reversely rotating one of the main body portion and the main shaft portion in synchronization with the rotation drive device. After the other of the main body portion or the main shaft portion is rotated idle by a predetermined angle, the other is rotated in the reverse direction again in synchronization with the one of the main body portion or the main shaft portion. A method for expanding an improvement area of ​​a ground improvement device, comprising: rotating one of the main body portion or the main shaft portion in the opposite direction, thereby engaging the expansion bar with the expansion head portion and rotating the tip of the expansion head portion.

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