JP2024013278A - Excavation and agitation device - Google Patents

Abstract

To provide an excavation and agitation device suitable for both reducing a risk of co-rotation prevention blades protruding from site boundaries and increasing an effect of co-rotation prevention blades on preventing earth and sand from co-rotating.SOLUTION: An excavation and agitation device 2 comprises a rotation shaft 20, an excavation blade 21, a co-rotation prevention mechanism 22, an agitation blade 23, and a pair of co-rotation prevention blades 41A and 41B. The excavation blade 21 and the agitation blade 23 rotate together with the rotation shaft 20. The pair of co-rotation prevention blades 41A and 41B are rotatable relative to the rotation shaft 20. A first length L1 from a shaft center C of the rotation shaft 20 to a tip of the excavation blade 21 is the same as a second length L2 from the shaft center C to a tip of the agitation blade 23. A third length L3 from the shaft center C to a tip of one co-rotation prevention blade 41A and a fourth length L4 from the shaft center C to a tip of the other co-rotation prevention blade 41B are longer than the first length L1. The third length L3 is larger than the fourth length L4.SELECTED DRAWING: Figure 2

Description

Application for application of Article 30, Paragraph 2 of the Patent Act (Part 1) Submission date: February 15, 2022 Testing agency: Architectural Research Institute of Japan

The present invention relates to an excavation agitation device in which an excavation blade and an agitation shaft rotate together with the rotation shaft, and a pair of co-rotation prevention blades are provided so as to be rotatable relative to the rotation shaft.

Conventionally, an excavation stirring device used in a ground improvement method called deep mixing treatment has been used. This type of general device consists of a rotating shaft having a soil conditioner discharge port, a digging blade that protrudes from the outer periphery of the rotating shaft at the lower end of the rotating shaft, and a cutting blade that protrudes from the outer periphery of the rotating shaft above the digging blade. It is equipped with a stirring blade. According to this device, the soil conditioner is discharged from the discharge port, and the device is lowered while rotating the excavating blades and stirring blades together with the rotary shaft, so that while the excavating blades excavate the ground, the stirring blades excavate the excavated hole. The soil and soil improver are stirred and mixed to construct a columnar ground improvement body called a column.

However, in the above-mentioned conventional general excavation agitation device, the earth and sand in the excavation hole co-rotate with the excavation blade and the agitation blade, resulting in a problem that the earth and sand and the soil conditioner cannot be homogeneously mixed. Therefore, Patent Document 1 discloses an excavation stirring device in which a pair of co-rotation prevention blades 100, 100 are provided so as to be relatively rotatable on a rotating shaft 101 between the above-mentioned excavation blades and stirring blades (Fig. 7 ). In the device of Patent Document 1, in order to restrict the co-rotation of the earth and sand S by the pair of co-rotation prevention blades 100, 100, the pair of co-rotation prevention blades 100, 100 are made longer than the excavation blade and the stirring blade. The co-rotation prevention blades 100, 100 of are stuck into the hole wall W of the excavated hole H.

Utility model registration No. 3215453

By the way, in the excavation stirring device of Patent Document 1, the lengths of the pair of co-rotation prevention blades 100, 100 are the same. Therefore, the excavation agitation device of Patent Document 1 is not suitable for both reducing the risk of the co-rotation prevention blades 100, 100 protruding from the site boundary B and increasing the effect of preventing the co-rotation of the earth and sand S. (The above site boundary B is the boundary between the area where construction is permitted and the area where construction is not permitted).

In other words, in order to prevent the co-rotation prevention blades 100, 100 from protruding from the site boundary B, when the length of the co-rotation prevention blades 100, 100 is shortened as shown in FIG. 100, 100 penetrates into the hole wall W of the excavated hole H becomes shorter. For this reason, the co-rotation prevention blades 100, 100 tend to rotate due to the force received from the co-rotating earth and sand S, and the effect of preventing the co-rotation of the earth and sand S cannot be enhanced.

In addition, in order to increase the effect of preventing the co-rotation of the earth and sand S, when the pair of co-rotation prevention blades 100, 100 is lengthened as shown in FIG. 7(B), the allowable rotation angle of the co-rotation prevention blades 100, 100 is small This increases the risk that the co-rotation prevention blades 100, 100 will protrude from the site boundary B (the above allowable rotation angle is the rotation angle of the co-rotation prevention blades from the initial position to the position where they protrude from the site boundary B. rotation angle).

The present invention has been made in view of the above-mentioned matters, and its purpose is to reduce the risk of the co-rotation prevention blade protruding from the site boundary, and to increase the effect of the co-rotation prevention blade in preventing earth and sand from co-rotating. An object of the present invention is to provide an excavation agitation device suitable for achieving both of the following.

To achieve the above object, the present invention includes the subject matter described in the following sections.

Item 1. a rotating shaft having a soil conditioner discharge port and arranged to extend in the vertical direction;
an excavating blade that is provided at a lower end of the rotating shaft to protrude from the outer periphery of the rotating shaft and rotates together with the rotating shaft;
a co-rotation prevention mechanism attached to the rotation shaft above the excavation blade;
a stirring blade that is provided to protrude from the outer periphery of the rotating shaft above the co-rotation prevention mechanism and rotates together with the rotating shaft,
The co-rotation prevention mechanism includes a cylindrical body through which the rotating shaft is passed, and a pair of co-rotation prevention wings protruding in opposite directions from the outer periphery of the cylindrical body, and prevents relative rotation with respect to the rotary shaft. It is possible and
The first length from the axial center of the rotating shaft to the tip of the excavating blade in the radial direction of the rotating shaft is the same as the second length from the axial center to the tip of the stirring blade in the radial direction, or greater than the second length;
A third length from the axis in the radial direction to the tip of one co-rotation prevention blade, and a fourth length from the axis in the radial direction to the tip of the other co-rotation prevention blade, respectively, greater than the first length;
The excavation stirring device wherein the third length is greater than the fourth length.

Item 2. The pair of co-rotation prevention wings each include an arm portion protruding from the outer periphery of the cylindrical body, and a tip portion provided at the tip of the arm portion,
Item 2. The excavation stirring device according to Item 1, wherein the tip portion extends parallel to the axial direction of the rotating shaft.

Item 3. Item 3. The excavation stirring device according to item 1 or 2, wherein the third length is 1.04 times or more the first length, and the fourth length is 1.35 times or less the first length.

Item 4. The first length is 250 mm or more and 1250 mm or less,
Item 4. The excavation agitation device according to item 3, wherein the value obtained by subtracting the first length from the third length is 60 mm or more, and the value obtained by subtracting the first length from the fourth length is 150 mm or less.

The excavation stirring device of the present invention is suitable for both reducing the risk of the co-rotation prevention blade protruding from the site boundary and increasing the effect of the co-rotation prevention blade on preventing earth and sand from co-rotating.

1 is a perspective view of a ground improvement system including an excavation stirring device according to an embodiment of the present invention. (A) is a side view of the excavation agitation device, and (B) is a front view of the tip portion of the excavation agitation device. FIG. 2 is a side view showing the excavation stirring device in use. It is a top view which shows the state of the co-rotation prevention mechanism at the time of use of an excavation stirring device. FIG. 3 is a side view showing a state in which the co-rotation prevention mechanism is removed from the rotating shaft. FIG. 3 is a plan view showing the procedure for attaching the co-rotation prevention mechanism to the rotating shaft, in which (A) shows the state immediately before the co-rotation prevention mechanism is attached to the rotating shaft, and (B) shows the state after the co-rotation prevention mechanism is attached to the rotating shaft. Indicates the status of It is a top view which shows the state of the co-rotation prevention blade at the time of use of the conventional excavation stirring device, (A) shows the case where the co-rotation prevention blade is long. (B) shows the case where the co-rotation prevention blades are short.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a perspective view of a ground improvement system 1 including an excavation stirring device according to an embodiment of the present invention.

The ground improvement system 1 is used to construct a columnar ground improvement body called a column. The ground improvement system 1 includes a self-propelled cart 3 equipped with an excavation agitation device 2 according to the present embodiment, an improvement agent generation means 4 for generating a soil improvement agent, and soil generated by the improvement agent generation means 4. and an improving agent supply means 5 for supplying the improving agent to the excavation stirring device 2.

In this embodiment, the soil conditioner is cement milk. The improver generating means 4 includes a silo 6 for storing cement, a tank 7 for storing water, and a mixing plant that mixes the cement supplied from the silo 6 and the water supplied from the tank 7 to produce cement milk. 8.

The improving agent supply means 5 includes a pipe line 10 that connects the mixing plant 8 and the excavation agitation device 2, and pumps cement milk (soil improvement agent) produced in the mixing plant 8 to the excavation agitation device 2 via the pipe line 10. A pump 11 is provided for this purpose. The downstream end of the pipe line 10 is constituted by a pipe body 12 supported by the self-propelled truck 3. The tube body 12 is supported so as to extend in the vertical direction, and can be vertically moved and rotated by driving a drive device 13 provided on the self-propelled trolley 3.

Note that the present invention does not limit the soil conditioner to cement milk. The configuration of the improver producing means 4 and the improver supplying means 5 may be changed as appropriate depending on the type of soil improver.

FIG. 2(A) is a side view of the excavation stirring device 2. FIG. 2(B) is a front view of the tip portion 44 of the excavation stirring device 2. FIG. 3 is a side view showing the excavation stirring device 2 in use. FIG. 4 is a plan view showing the state of the co-rotation prevention mechanism 22 when the excavation stirring device 2 is in use.

The excavation stirring device 2 includes a rotating shaft 20 arranged to extend in the vertical direction, an excavating blade 21 provided so as to protrude from the outer periphery of the rotating shaft 20 at the lower end of the rotating shaft 20, and an excavating blade 21 located above the excavating blade 21. A co-rotation prevention mechanism 22 that is attached to the rotation shaft 20 in the rotation shaft 20 and a stirring blade 23 that is provided so as to protrude from the outer periphery of the rotation shaft 20 above the co-rotation prevention mechanism 22 are provided.

The rotating shaft 20 is constituted by a tubular body having a discharge port 24 for the soil conditioner, and is made of metal such as S45C carbon steel for machine structures, SS400 rolled steel for general structures, or the like. The rotating shaft 20 is connected to the lower end of the tubular body 12, so that it moves up and down and rotates together with the tubular body 12. The inside of the rotating shaft 20 communicates with the inside of the pipe body 12, and the soil conditioner that has passed through the pipe line 10 by driving the pump 11 is supplied to the inside of the rotating shaft 20 and is discharged from the discharge port 24. . In the illustrated example, the discharge port 24 is formed at the lower end of the rotating shaft 20, but it may be formed at any position on the rotating shaft 20.

The excavating blade 21 includes an excavating plate 30 extending from the outer periphery of the rotating shaft 20 and a plurality of excavating claws 31 extending downward from the excavating plate 30. The excavating plate 30 and each excavating claw 31 are made of metal. As the metal for forming the excavation plate 30, for example, SS400 rolled steel for general structure or S45C carbon steel for machine structure can be used, and as the metal for forming the excavation claw 31, for example, S45C carbon steel for machine structure can be used. Steel materials, tungsten cemented carbide, and diamond powder can be used. The excavating blade 21 moves up and down and rotates together with the rotating shaft 20 because the excavating plate 30 is provided integrally with the rotating shaft 20 . Note that the present invention does not limit the number of excavation blades 21 and excavation claws 31 or the direction in which the excavation wings 21 and excavation claws 31 extend, and the above-mentioned numbers and directions can be set arbitrarily.

The stirring blade 23 is constituted by a plate material extending from the outer periphery of the rotating shaft 20, and is formed using metal such as SS400 general structural rolled steel material. The stirring blade 23 is provided integrally with the rotating shaft 20, so that it moves up and down and rotates together with the rotating shaft 20. A first length L1 from the axis C of the rotating shaft 20 in the radial direction of the rotating shaft 20 to the tip of the excavating blade 21, and from the axis C of the rotating shaft 20 in the radial direction of the rotating shaft 20 to the tip of the stirring blade 23. It is preferable that the second length L2 is the same as the second length L2. In this way, the earth and sand S and the soil conditioner can be stirred and mixed by the stirring blades 23 over the entire diameter of the hole H excavated by the digging blades 21. Note that the first length L1 may be larger than the second length L2 in order to allow the excavation wing 21 to descend smoothly within the excavation hole H.

Further, in order to sufficiently stir the earth and sand in the excavation hole H, it is preferable that the upper surface 23a of the agitation blade 23 is inclined downward in the direction of rotation of the rotary shaft 20 during excavation. When the soil to be excavated is gravel, gravelly soil, sand, sandy soil, silt, clay soil, organic soil, volcanic ash clay, or highly organic soil, the upper surface 23a of the stirring blade 23 is connected to the rotating shaft 20. It is preferable to incline at an angle of 5 degrees or more and 30 degrees or less with respect to the radial plane. The above-mentioned "radial plane of the rotating shaft 20" is "a plane extending in the radial direction of the rotating shaft 20 and perpendicular to the axis C of the rotating shaft 20." Hereinafter, "the radial direction of the rotating shaft 20" will be abbreviated as "radial direction", and "the axial center C of the rotating shaft 20" will be abbreviated as "the axial center C".

In the illustrated example of the excavation stirring device 2, two sets of a pair of stirring blades 23, 23 are provided that protrude from the rotating shaft 20 in opposite directions. One set 23A of stirring blades 23, 23 is provided above the other set 23B of stirring blades 23, 23, and the direction in which the stirring blades 23 of one set 23A extend is the direction in which the excavation blades 21 extend. (one stirring blade 23 of the set 23B is not shown). The direction in which the stirring blades 23 of the other set 23B extend is perpendicular to the direction in which the stirring blades 23 and the digging blades 21 of the one set 23A extend. Note that the present invention does not limit the number of stirring blades 23 or the direction in which the stirring blades 23 extend from the rotating shaft 20, and the number of stirring blades 23 and the direction in which the stirring blades 23 extend can be set arbitrarily.

The co-rotation prevention mechanism 22 includes a cylindrical body 40 and a pair of co-rotation prevention wings 41A and 41B protruding from the outer periphery of the cylindrical body 40 in opposite directions.

The rotating shaft 20 is provided with a pair of annular portions 42, 42 for attaching the cylindrical body 40. The pair of annular saliva parts 42, 42 each protrude from the outer periphery of the rotating shaft 20, and are vertically provided with an interval equal to the height of the cylindrical body 40. The co-rotation prevention mechanism 22 is configured such that the cylinder body 40 is disposed between the pair of annular saliva parts 42 and 42, and the rotation shaft 20 is passed through the inside of the cylinder body 40. It is attached to the rotating shaft 20 so as to be rotatable relative to the rotating shaft 20 .

The co-rotation prevention blade 41A includes an arm portion 43A protruding from the outer periphery of the cylindrical body 40, and a tip portion 44A provided at the tip of the arm portion 43A. Similarly, the co-rotation prevention blade 41B includes an arm portion 43B protruding from the outer periphery of the cylindrical body 40, and a tip portion 44B provided at the tip of the arm portion 43B. The tip portions 44A and 44B each extend parallel to the axial direction of the rotating shaft 20. In the illustrated example, the tip portions 44A, 44B have a hexagonal shape that is long in the vertical direction when viewed from the front, but the tip portions 44A, 44B are not limited to the shape shown in the illustrated example. , for example, it may have a rectangular shape that is long in the vertical direction when viewed from the front.

A pair of co-rotation prevention blades 41A, 41B are pierced into the hole wall W of the excavation hole H to restrict the co-rotation of the earth and sand S. The third length L3 and the fourth length L4 from the axis C in the radial direction to the tip of the other co-rotation prevention blade 41B are each made larger than the first length L1.

Furthermore, in order to reduce the risk of the co-rotation prevention blades 41A, 41B protruding from the site boundary B (Fig. 4) and to increase the effect of preventing the co-rotation of earth and sand S, the third length L3 is set to the fourth length. It is made longer than length L4.

FIG. 5 is a side view showing a state in which the co-rotation prevention mechanism 22 is removed from the rotating shaft 20. FIGS. 6A and 6B are plan views showing a procedure for attaching the co-rotation prevention mechanism 22 to the rotating shaft 20.

In this embodiment, the co-rotation prevention mechanism 22 is composed of divided members 50A and 50B. The divided member 50A includes a first plate portion 51A, a first boss portion 52A, and one co-rotation prevention wing 41A. The divided member 50B includes a second plate portion 51B, a second boss portion 52B, and the other co-rotation prevention wing 41B. The first and second boss portions 52A and 52B constitute the cylindrical body 40 and have a semicircular shape in plan view. The first plate portion 51A extends from one end 53 of the first boss portion 52A. The arm portion 43A of the co-rotation prevention blade 41A extends from the other end 54 of the first boss portion 52A. The second plate portion 51B extends from one end 55 of the second boss portion 52B. The arm portion 43B of the co-rotation prevention wing 41B extends from the other end 56 of the second boss portion 52B. Through holes 61 for passing bolts 60 are formed on the base end sides of the first plate portion 51A, the second plate portion 51B, and the arm portions 43A and 43B, respectively.

When attaching the co-rotation prevention mechanism 22 to the rotating shaft 20, as shown in FIG. 6(B), the first plate part 51A and the base end side of the arm part 43B abut against each other, and the second plate part 51B and the arm part The first and second boss portions 52A, 52B are arranged between the annular saliva portions 42, 42 so that the proximal ends of the rotary shaft 20 are abutted against each other. It is said to be stuck between the two. Then, the bolts 60 are passed through the through holes 61, 61 of the first plate part 51A and the arm part 43B, and the bolts 60 are passed through the through holes 61, 61 of the second plate part 51B and the arm part 43A. will be concluded. By performing the above operations, the cylindrical body 40 constituted by the first and second boss parts 52A and 52B is arranged between the annular saliva parts 42 and 42, and the rotation shaft 20 is placed inside the cylindrical body 40. (In other words, the co-rotation prevention mechanism 22 is attached to the rotating shaft 20).

When the excavation agitation device 2 is used, the excavation blade 21 and the agitation blade 23 are rotated together with the rotary shaft 20 by the drive device 13 while discharging the soil conditioner (not shown) from the discharge port 24 by driving the pump 11. Then, the device 2 is lowered. As a result, while the ground is excavated by the excavation blades 21, the earth and sand S in the excavation hole H and the soil improvement agent are stirred and mixed by the stirring blades 23, and a columnar ground improvement body is constructed. In addition, the co-rotation prevention blades 41A, 41B stick into the hole wall W of the excavation hole H and become difficult to rotate, so that the co-rotation of the soil S in the excavation hole H is prevented, and the soil S and the soil conditioner are prevented from co-rotating. Mixed homogeneously.

According to the excavation agitation device 2 according to the present embodiment, since the third length L3 is large, it is possible to ensure a large length for the co-rotation prevention blade 41A to penetrate into the hole wall W. Therefore, the force of the co-rotation prevention mechanism 22 against rotation can be increased, so that the effect of co-rotation prevention of the earth and sand S by the co-rotation prevention blades 41A and 41B can be enhanced. In addition, since the fourth length L4 is shorter than the third length L3, the permissible rotation angle of the co-rotation prevention blades 41A, 41B is increased, and the risk of the co-rotation prevention blades 41A, 41B protruding from the site boundary B is reduced. can.

Further, according to the excavation stirring device 2 according to the present embodiment, since the tip portions 44 of each of the co-rotation prevention blades 41A and 41B extend parallel to the axial direction of the rotating shaft 20, these tip portions 44 are connected to the hole wall W. By penetrating into it, it is possible to strongly increase the force against rotation of the co-rotation prevention mechanism.

The present invention provides an excavation agitation device 2 that is suitable for both reducing the risk of the co-rotation prevention blades protruding from the site boundary B and increasing the effect of the co-rotation prevention blades on preventing soil S from co-rotation. The specific dimensions of the excavation stirring device 2 are determined as appropriate depending on the soil to be excavated, the shortest distance D between the excavation hole H and the adjacent boundary B, and the like. For example, if the soil to be excavated is gravel, gravel soil, sand, sandy soil, silt, clay soil, organic soil, volcanic ash clay soil, or highly organic soil, in order to obtain the above effects, It is preferable that the third length L3 be 1.04 times or more the first length L1, and the fourth length L4 be 1.35 times or less the first length L1. For example, when the first length L1 is 250 mm or more and 1250 mm or less, the value P1 obtained by subtracting the first length L1 from the third length L3 is 60 mm or more, and the first length is calculated from the fourth length L4. The value P2 obtained by subtracting L1 is 150 mm or less (see Table 1 below), and the third length L3 is 1.04 times or more the first length L1, and the fourth length L4 is the first length L1. It is preferable that the third and fourth lengths L3 and L4 are set to be 1.35 times or less. In addition, in order to prevent the permissible rotation angle of the co-rotation prevention blades 41A, 41B from being limited by at least the co-rotation prevention blade 41A among the co-rotation prevention blades 41A, 41B, the first length L1 is changed from the fourth length L4. It is preferable that the subtracted value P2 be equal to or less than the shortest distance D between the excavation hole H and the site boundary B.

When the target soil for excavation is gravel, gravelly soil, sand, sandy soil, silt, clay soil, organic soil, volcanic ash clay soil, or highly organic soil, the dimensions of the excavation stirring device 2 are, for example, as shown in the table below. The relationship shown in 1 is assumed. Note that the present invention does not limit the dimensions of the excavation stirring device 2 to those shown in Table 1 below.

The present invention is not limited to the above embodiments, and can be modified in various ways.

For example, the structure of the divided members 50A and 50B that constitute the co-rotation prevention mechanism 22 is not limited to the structure shown in FIGS. 5 and 6. Although not shown, for example, in the divided members 50A and 50B, a pair of first plate portions 51A extend from both ends of a first boss portion 52A, and an arm portion 43 of one co-rotation prevention wing 41A and 41B extends from the first boss portion 52A. The pair of second plate portions 51B extend from both ends of the second boss portion 52B, and the arm portions 43 of the other co-rotation prevention blades 41A, 41B extend from the center of the width of the split members 50A, 50B. It may extend from the width center of the two boss portions 52B. In this case, the annular saliva portion 42, The first and second boss portions 52A and 52B are inserted between the first and second boss portions 42, and the rotating shaft 20 is sandwiched between the first and second boss portions 52A and 52B. Then, by passing the bolts 60 through the through holes 61 of the butted first and second plates and fastening nuts 62 to each bolt 60, the cylindrical body 40 constituted by the first and second boss portions 52A and 52B is shaped into an annular shape. It is arranged between the spit parts 42, 42, and the rotating shaft 20 is passed through the inside of the cylinder 40 (that is, the co-rotation prevention mechanism 22 is attached to the rotating shaft 20).

Moreover, instead of arranging the cylindrical body 40 between the annular saliva parts 42, 42, the cylindrical body 40 may be disposed in a recess formed on the outer periphery of the rotating shaft 20.

Further, the tip portions 44 of the co-rotation prevention blades 41A, 41B are not necessarily required and may be omitted.

2 Excavation stirring device 20 Rotating shaft 21 Excavation blade 22 Co-rotation prevention mechanism 23 Stirring blade 24 Discharge port 40 Cylindrical body 41A, 41B Co-rotation prevention blade 43 Arm portion 44 Tip portion L1 First length L2 Second length L3 Third Length L4 Fourth length P1 Value obtained by subtracting the first length from the third length P2 Value obtained by subtracting the first length from the fourth length

Claims (4)

a rotating shaft having a soil conditioner discharge port and arranged to extend in the vertical direction;
an excavating blade that is provided at a lower end of the rotating shaft to protrude from the outer periphery of the rotating shaft and rotates together with the rotating shaft;
a co-rotation prevention mechanism attached to the rotation shaft above the excavation blade;
a stirring blade that is provided to protrude from the outer periphery of the rotating shaft above the co-rotation prevention mechanism and rotates together with the rotating shaft,
The co-rotation prevention mechanism includes a cylindrical body through which the rotary shaft passes inside, and a pair of co-rotation prevention wings protruding in opposite directions from the outer periphery of the cylindrical body, and prevents relative rotation with respect to the rotary shaft. It is possible and
The first length from the axial center of the rotating shaft to the tip of the excavating blade in the radial direction of the rotating shaft is the same as the second length from the axial center to the tip of the stirring blade in the radial direction, or greater than the second length;
A third length from the axis in the radial direction to the tip of one of the co-rotation prevention blades, and a fourth length from the axis to the tip of the other co-rotation prevention blade in the radial direction are, respectively, greater than the first length;
The excavation stirring device wherein the third length is greater than the fourth length. The pair of co-rotation prevention wings each include an arm portion protruding from the outer periphery of the cylindrical body, and a tip portion provided at the tip of the arm portion,
The excavation stirring device according to claim 1, wherein the tip portion extends parallel to the axial direction of the rotating shaft. The excavation stirring device according to claim 1 or 2, wherein the third length is 1.04 times or more the first length, and the fourth length is 1.35 times or less the first length. . The first length is 250 mm or more and 1250 mm or less,
The excavation stirring device according to claim 3, wherein the value obtained by subtracting the first length from the third length is 60 mm or more, and the value obtained by subtracting the first length from the fourth length is 150 mm or less. .

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