Excavation and mixing equipment

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

[Technical Field]

[0001] The present invention relates to an excavating and stirring device in which an excavating blade and an stirring shaft rotate together with a rotary shaft, and a pair of anti-co-rotation blades are provided so as to be rotatable relative to the rotary shaft. [Background technology]

[0002] A conventional excavation and mixing device is used in a ground improvement method known as deep mixing. This type of device generally includes a rotating shaft with a soil conditioner discharge port, a drilling blade protruding from the outer periphery of the rotating shaft at the lower end, and a mixing blade protruding from the outer periphery of the rotating shaft above the drilling blade. This device discharges soil conditioner from the discharge port, and the excavation and mixing blades rotate together with the rotating shaft while the device is lowered. While the drilling blade excavates the ground, the mixing blade mixes and mixes the soil and soil conditioner in the excavated hole, creating a columnar ground improvement structure known as a column.

[0003] However, with the above-mentioned conventional excavation and mixing apparatus, the soil in the borehole rotates together with the drilling and mixing blades, which causes a problem of making it impossible to mix the soil and soil conditioner uniformly. Patent Document 1 therefore discloses an excavation and mixing apparatus in which a pair of anti-rotation blades 100, 100 are provided between the drilling and mixing blades so as to be rotatable relative to a rotating shaft 101 (FIG. 7). In the apparatus of Patent Document 1, the pair of anti-rotation blades 100, 100 are made longer than the drilling and mixing blades, and the pair of anti-rotation blades 100, 100 are thrust into the wall W of the borehole H in order to prevent the soil S from rotating together with the drilling and mixing blades. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Utility Model Registration No. 3215453 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the excavation and mixing device of Patent Document 1, the pair of anti-rotation blades 100, 100 have the same length. For this reason, the excavation and mixing device of Patent Document 1 is not suitable for simultaneously reducing the risk of the anti-rotation blades 100, 100 protruding from the site boundary B and increasing the effect of preventing the soil and sand S from rotating together (the site boundary B is the boundary between the area where construction is permitted and the area where construction is not permitted).

[0006] In other words, if the length of the anti-rotation vanes 100, 100 is shortened as shown in Figure 7(A) in order to prevent the anti-rotation vanes 100, 100 from protruding from the site boundary B, the length by which the anti-rotation vanes 100, 100 penetrate into the hole wall W of the borehole H will be shortened. As a result, the anti-rotation vanes 100, 100 will be more likely to rotate due to the force received from the co-rotating soil and sand S, and the effect of preventing the co-rotation of the soil and sand S will not be improved.

[0007] Furthermore, if the pair of anti-rotation wings 100, 100 are lengthened as shown in Figure 7(B) in order to enhance the effect of preventing co-rotation of the soil and sand S, the allowable rotation angle of the anti-rotation wings 100, 100 becomes smaller, and the risk of the anti-rotation wings 100, 100 protruding from the site boundary B increases (the above-mentioned allowable rotation angle is the rotation angle of the anti-rotation wings from their initial position until they reach a position where they protrude from the site boundary B).

[0008] The present invention has been made in consideration of the above-mentioned matters, and its purpose is to provide an excavation and mixing device that is suitable for both reducing the risk of the anti-rotation blades protruding from the site boundary and increasing the effectiveness of the anti-rotation blades in preventing the soil and sand from rotating together. [Means for solving the problem]

[0009] To achieve the above object, the present invention includes the following subject matter.

[0010] Item 1. A rotating shaft having a soil conditioner discharge port and extending in the vertical direction; An excavation blade provided at a lower end of the rotary shaft so as to protrude from the outer periphery of the rotary shaft and rotate together with the rotary shaft; a co-rotation prevention mechanism attached to the rotating shaft above the excavating blade; a stirring blade provided above the co-rotation prevention mechanism so as to protrude from the outer periphery of the rotating shaft and rotate together with the rotating shaft; the co-rotation prevention mechanism includes a cylindrical body through which the rotation shaft passes and a pair of co-rotation prevention blades protruding in opposite directions from an outer periphery of the cylindrical body, and is rotatable relative to the rotation shaft; a first length from the axis of the rotating shaft to the tip of the excavating blade in the radial direction of the rotating shaft is equal to or greater than a second length from the axis of the rotating shaft to the tip of the stirring blade in the radial direction; a third length from the axis center to a tip of one of the anti-rotation vanes in the radial direction and a fourth length from the axis center to a tip of the other anti-rotation vane in the radial direction are each greater than the first length, The excavating and stirring device, wherein the third length is greater than the fourth length.

[0011] Item 2. The pair of anti-corotation 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 excavating and stirring device according to item 1, wherein the tip portion extends parallel to the axial direction of the rotating shaft.

[0012] Item 3. The excavating and 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.

[0013] Item 4. The first length is 250 mm or more and 1250 mm or less; Item 4. The excavating and stirring 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. [Effects of the Invention]

[0014] The excavation and mixing device of the present invention is suitable for achieving both reducing the risk of the anti-rotation blades protruding from the site boundary and increasing the effectiveness of the anti-rotation blades in preventing the soil and sand from rotating together. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a perspective view of a ground improvement system equipped with an excavation and stirring device according to an embodiment of the present invention. [Figure 2] FIG. 1A is a side view of the excavating and stirring apparatus, and FIG. 1B is a front view of the tip end portion of the excavating and stirring apparatus. [Figure 3] FIG. 2 is a side view showing the excavation and stirring device in use. [Figure 4] 10 is a plan view showing the state of the co-rotation prevention mechanism when the excavating and stirring device is in use. FIG. [Figure 5] FIG. 10 is a side view showing a state in which the co-rotation prevention mechanism is removed from the rotating shaft. [Figure 6] 1A and 1B are plan views showing the procedure for attaching the co-rotation prevention mechanism to the rotating shaft, in which (A) shows the state immediately before attaching the co-rotation prevention mechanism to the rotating shaft, and (B) shows the state after attaching the co-rotation prevention mechanism to the rotating shaft. [Figure 7] 1A and 1B are plan views showing the state of the anti-rotation blades when a conventional excavation and mixing device is in use, where (A) shows the case where the anti-rotation blades are long, and (B) shows the case where the anti-rotation blades are short. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a perspective view of a ground improvement system 1 equipped with an excavating and stirring device according to an embodiment of the present invention.

[0017] The ground improvement system 1 is used to construct a pillar-shaped ground improvement body called a column. The ground improvement system 1 includes a self-propelled carriage 3 on which the excavating and mixing device 2 according to this embodiment is mounted, an improvement agent generating means 4 for generating a soil improvement agent, and an improvement agent supplying means 5 for supplying the soil improvement agent generated by the improvement agent generating means 4 to the excavating and mixing device 2.

[0018] In this embodiment, the soil conditioner is cement milk. The conditioner producing means 4 includes a silo 6 for storing cement, a tank 7 for storing water, and a mixing plant 8 for mixing the cement supplied from the silo 6 with the water supplied from the tank 7 to produce cement milk.

[0019] The conditioner supply means 5 includes a pipeline 10 connecting the mixing plant 8 and the excavation and mixing device 2, and a pump 11 for pressure-feeding the cement milk (soil conditioner) produced in the mixing plant 8 to the excavation and mixing device 2 via the pipeline 10. The downstream end of the pipeline 10 is formed by a pipe body 12 supported by the self-propelled carriage 3. The pipe body 12 is supported so as to extend in the vertical direction, and can move up and down and rotate by being driven by a drive device 13 provided on the self-propelled carriage 3.

[0020] In the present invention, the soil conditioner is not limited to cement milk. The configurations of the conditioner generating means 4 and the conditioner supplying means 5 can be changed appropriately depending on the type of soil conditioner, etc.

[0021] Fig. 2(A) is a side view of the excavating and stirring apparatus 2. Fig. 2(B) is a front view of the tip 44 provided on the excavating and stirring apparatus 2. Fig. 3 is a side view showing the state of the excavating and stirring apparatus 2 when in use. Fig. 4 is a plan view showing the state of the co-rotation prevention mechanism 22 when the excavating and stirring apparatus 2 is in use.

[0022] The drilling and stirring device 2 comprises a rotating shaft 20 arranged to extend in the vertical direction, a drilling blade 21 arranged at the lower end of the rotating shaft 20 so as to protrude from the outer periphery of the rotating shaft 20, a co-rotation prevention mechanism 22 attached to the rotating shaft 20 above the drilling blade 21, and a stirring blade 23 arranged so as to protrude from the outer periphery of the rotating shaft 20 above the co-rotation prevention mechanism 22.

[0023] The rotating shaft 20 is configured as a pipe having a soil conditioner discharge port 24, and is made of metal such as S45C carbon steel for mechanical structures or SS400 rolled steel for general structures. The rotating shaft 20 is connected to the lower end of the pipe 12, and moves up and down and rotates together with the pipe 12. The interior of the rotating shaft 20 is in communication with the interior of the pipe 12, and the soil conditioner that has passed through the pipeline 10 by the drive of the pump 11 is supplied to the interior of the rotating shaft 20 and 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.

[0024] The excavation blade 21 has a drilling plate 30 extending from the outer periphery of the rotating shaft 20 and a plurality of excavation claws 31 extending downward from the drilling plate 30. The drilling plate 30 and each of the excavation claws 31 are formed from metal. Examples of metals that can be used to form the drilling plate 30 include SS400 general structural rolled steel and S45C carbon steel for mechanical structures, and examples of metals that can be used to form the excavation claws 31 include S45C carbon steel for mechanical structures, tungsten-based cemented carbide, and diamond powder. The excavation blade 21 moves up and down and rotates together with the rotating shaft 20 because the drilling plate 30 is integral 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 blades 21 and excavation claws 31 extend, and the number and direction can be set as desired.

[0025] The agitator blade 23 is composed of a plate extending from the outer periphery of the rotating shaft 20 and is formed using a metal such as SS400 general structural rolled steel. The agitator blade 23 is integrally formed with the rotating shaft 20, allowing it to move up and down and rotate together with the rotating shaft 20. It is preferable that a first length L1, measured from the axis C of the rotating shaft 20 to the tip of the excavating blade 21 in the radial direction of the rotating shaft 20, is the same as a second length L2, measured from the axis C of the rotating shaft 20 to the tip of the agitator blade 23 in the radial direction of the rotating shaft 20. This allows the agitator blade 23 to agitate and mix the soil S and soil conditioner throughout the entire diameter of the hole H excavated by the excavating blade 21. The first length L1 may be greater than the second length L2 to allow the excavating blade 21 to smoothly descend within the borehole H.

[0026] Furthermore, in order to thoroughly mix the soil in the borehole H, it is preferable that the upper surface 23a of the mixing blade 23 be inclined downward toward the direction of rotation of the rotating shaft 20 during excavation. When the soil to be excavated is gravel, gravelly soil, sand, sandy soil, silt, clayey soil, organic soil, volcanic ash clayey soil, or highly organic soil, it is preferable that the upper surface 23a of the mixing blade 23 be inclined at an angle of 5 degrees or more and 30 degrees or less with respect to the radial plane of the rotating shaft 20. The above-mentioned "radial plane of the rotating shaft 20" refers to "a plane that extends radially of the rotating shaft 20 and is perpendicular to the axis C of the rotating shaft 20." Hereinafter, "radial direction of the rotating shaft 20" will be abbreviated as "radial direction," and "axis center C of the rotating shaft 20" will be abbreviated as "axis center C."

[0027] In the illustrated example, the excavating and stirring device 2 is provided with two pairs of agitating blades 23, 23 protruding in opposite directions from the rotating shaft 20. One set 23A of agitating blades 23, 23 is provided above the other set 23B of agitating blades 23, 23, and the extension direction of the agitating blades 23 of one set 23A is parallel to the extension direction of the drilling blade 21 (one agitating blade 23 of set 23B is not shown). The extension direction of the agitating blades 23 of the other set 23B is perpendicular to the extension direction of the agitating blades 23 and drilling blade 21 of one set 23A. Note that the present invention does not limit the number of agitating blades 23 or the direction in which the agitating blades 23 extend from the rotating shaft 20, and the number of agitating blades 23 and the extension direction of the agitating blades 23 can be set arbitrarily.

[0028] The co-rotation prevention mechanism 22 includes a cylindrical body 40 and a pair of co-rotation prevention wings 41A, 41B that protrude in opposite directions from the outer periphery of the cylindrical body 40.

[0029] The rotating shaft 20 is provided with a pair of annular spits 42, 42 for attaching the cylindrical body 40. The pair of annular spits 42, 42 each protrude from the outer periphery of the rotating shaft 20 and are provided vertically spaced apart by a distance approximately equal to the height of the cylindrical body 40. The anti-co-rotation mechanism 22 is attached to the rotating shaft 20 so as to be rotatable relative to the rotating shaft 20, with the cylindrical body 40 being placed between the pair of annular spits 42, 42 and the rotating shaft 20 passing through the inside of the cylindrical body 40.

[0030] The anti-rotation wing 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 anti-rotation wing 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, 44B each extend parallel to the axial direction of the rotation 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 of the tip portions 44A, 44B, but the shape of the tip portions 44A, 44B is not limited to the illustrated example and may be, for example, a rectangle that is long in the vertical direction when viewed from the front.

[0031] In order to restrict the rotation of the soil and sand S by inserting a pair of anti-rotation vanes 41A, 41B into the hole wall W of the borehole H, a third length L3 from the axis C in the radial direction to the tip of one of the anti-rotation vanes 41A and a fourth length L4 from the axis C in the radial direction to the tip of the other anti-rotation vane 41B are each made larger than the first length L1.

[0032] Furthermore, in order to simultaneously reduce the risk of the anti-rotation wings 41A, 41B protruding from the site boundary B (Figure 4) and increase the effect of preventing the soil and sand S from rotating together, the third length L3 is made longer than the fourth length L4.

[0033] 5 is a side view showing the state in which the co-rotation prevention mechanism 22 has been removed from the rotating shaft 20. FIGS. 6(A) and 6(B) are plan views showing the procedure for attaching the co-rotation prevention mechanism 22 to the rotating shaft 20.

[0034] In this embodiment, the anti-rotation 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 of the anti-rotation blades 41A. The divided member 50B includes a second plate portion 51B, a second boss portion 52B, and the other of the anti-rotation blades 41B. The first and second boss portions 52A and 52B form the cylindrical body 40 and are semicircular 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 anti-rotation 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 anti-rotation blade 41B extends from the other end 56 of the second boss portion 52B. A through hole 61 for passing a bolt 60 therethrough is formed on the base end side of each of the first plate portion 51A, the second plate portion 51B, and the arm portions 43A and 43B.

[0035] 6(B), the first and second boss portions 52A, 52B are disposed between the annular protrusions 42, 42 so that the first plate portion 51A butts against the base end side of the arm portion 43B and the second plate portion 51B butts against the base end side of the arm portion 43A, thereby sandwiching the rotating shaft 20 between the first and second boss portions 52A, 52B. Then, bolts 60 are passed through the through holes 61, 61 of the first plate portion 51A and the arm portion 43B, and through the through holes 61, 61 of the second plate portion 51B and the arm portion 43A, and nuts 62 are fastened to the bolts 60. By performing the above steps, the cylindrical body 40 formed by the first and second boss portions 52A, 52B is positioned between the annular spit portions 42, 42, and the rotating shaft 20 is passed through the inside of the cylindrical body 40 (i.e., the co-rotation prevention mechanism 22 is attached to the rotating shaft 20).

[0036] When the excavating and mixing apparatus 2 is in use, the pump 11 is driven to discharge soil conditioner (not shown) from the discharge port 24, while the drive unit 13 is driven to rotate the excavating blade 21 and the mixing blade 23 together with the rotary shaft 20, thereby lowering the apparatus 2. As a result, the excavating blade 21 excavates the ground, while the mixing blade 23 mixes and mixes the soil S and soil conditioner in the borehole H, thereby constructing a columnar ground improvement body. Furthermore, the anti-rotation blades 41A and 41B penetrate the hole wall W of the borehole H and become difficult to rotate, thereby preventing the soil S in the borehole H from rotating together with the rotation, and the soil S and soil conditioner are mixed homogeneously.

[0037] According to the excavating and stirring apparatus 2 of this embodiment, the third length L3 is large, thereby ensuring a large length by which the rotation prevention vanes 41A penetrate into the hole wall W. This allows the rotation prevention mechanism 22 to increase its resistance to rotation, thereby improving the effect of the rotation prevention vanes 41A, 41B in preventing rotation of the soil S. Furthermore, the fourth length L4 is shorter than the third length L3, thereby increasing the allowable rotation angle of the rotation prevention vanes 41A, 41B and reducing the risk of the rotation prevention vanes 41A, 41B protruding from the site boundary B.

[0038] Furthermore, according to the drilling and stirring device 2 of this embodiment, the tip 44 of each of the anti-rotation blades 41A, 41B extends parallel to the axial direction of the rotating shaft 20, so that these tip portions 44 penetrate into the hole wall W, thereby strongly increasing the force resisting rotation of the anti-rotation mechanism.

[0039] The present invention provides a structure for an excavating and mixing apparatus 2 that is suitable for both reducing the risk of the anti-rotation blades protruding from the site boundary B and increasing the effectiveness of the anti-rotation blades in preventing the soil S from rotating together with the soil. The specific dimensions of the excavating and mixing apparatus 2 are determined appropriately depending on the soil to be excavated and the shortest distance D between the borehole H and the adjacent boundary B. For example, if the soil to be excavated is gravel, gravelly soil, sand, sandy soil, silt, clayey soil, organic soil, volcanic ash clayey soil, or highly organic soil, in order to achieve the above-mentioned effect, it is preferable to set the third length L3 to 1.04 times or more the first length L1 and the fourth length L4 to 1.35 times or less the first length L1. For example, when the first length L1 is set to 250 mm or more and 1250 mm or less, it is preferable that the third and fourth lengths L3, L4 be set so that the value P1 obtained by subtracting the first length L1 from the third length L3 is 60 mm or more, the value P2 obtained by subtracting the first length L1 from the fourth length L4 is 150 mm or less (see Table 1 described later), and the third length L3 is 1.04 times or more the first length L1 and the fourth length L4 is 1.35 times or less the first length L1. Furthermore, in order to prevent the allowable rotation angle of the rotation prevention vanes 41A, 41B from being limited by at least the rotation prevention vane 41A, it is preferable that the value P2 obtained by subtracting the first length L1 from the fourth length L4 is equal to or less than the shortest distance D between the borehole H and the site boundary B.

[0040] When the soil to be excavated is gravel, gravelly soil, sand, sandy soil, silt, clayey soil, organic soil, volcanic ash clayey soil, or highly organic soil, the dimensions of the excavating and mixing equipment 2 have the relationship shown in Table 1 below, for example. Note that the present invention does not limit the dimensions of the excavating and mixing equipment 2 to the dimensions shown in Table 1 below.

[0041] [Table 1]

[0042] The present invention is not limited to the above-described embodiment, and various modifications can be made.

[0043] For example, the structure of the divided members 50A, 50B that make up the anti-co-rotation mechanism 22 is not limited to the structure shown in Figures 5 and 6. Although not shown, for example, the divided members 50A, 50B may have a pair of first plate portions 51A extending from both ends of the first boss portion 52A, and the arm portion 43 of one of the anti-co-rotation wings 41A, 41B extending from the center of the width of the first boss portion 52A, and the divided members 50A, 50B may have a pair of second plate portions 51B extending from both ends of the second boss portion 52B, and the arm portion 43 of the other anti-co-rotation wings 41A, 41B extending from the center of the width of the second boss portion 52B. In this case, the first and second boss portions 52A, 52B are inserted between the annular salient portions 42, 42 so that one first plate portion 51A and one second plate portion 51B abut against each other and the other first plate portion 51A and the other second plate portion 51B abut against each other, thereby sandwiching the rotating shaft 20 between the first and second boss portions 52A, 52B. Then, by passing bolts 60 through the through holes 61 of the abutted first and second plates and fastening nuts 62 to the bolts 60, the cylindrical body 40 formed by the first and second boss portions 52A, 52B is disposed between the annular salient portions 42, 42, and the rotating shaft 20 is passed through the inside of the cylindrical body 40 (i.e., the co-rotation prevention mechanism 22 is attached to the rotating shaft 20).

[0044] Also, instead of disposing the cylindrical body 40 between the annular protrusions 42, 42, the cylindrical body 40 may be disposed in a recess formed on the outer periphery of the rotating shaft 20.

[0045] Furthermore, the tip portions 44 of the anti-corotation blades 41A and 41B are not necessarily required and may be omitted. [Explanation of symbols]

[0046] 2. Excavation and mixing equipment 20 Rotation axis 21 Drilling Wing 22 Co-rotation prevention mechanism 23 Stirring blade 24 Outlet 40 Cylinder 41A, 41B Anti-corotation blades 43 Arm section 44 Tip L1 First length L2 Second length L3 Third length L4 Fourth length P1: Third length minus first length P2: Fourth length minus first length

Claims

1. a rotating shaft having a discharge port for the soil conditioner and extending in the vertical direction; An excavation blade provided at a lower end of the rotary shaft so as to protrude from the outer periphery of the rotary shaft and rotate together with the rotary shaft; a co-rotation prevention mechanism attached to the rotating shaft above the excavating blade; a stirring blade provided above the co-rotation prevention mechanism so as to protrude from the outer periphery of the rotating shaft and rotate together with the rotating shaft; the co-rotation prevention mechanism includes a cylindrical body through which the rotation shaft passes and a pair of co-rotation prevention blades protruding in opposite directions from an outer periphery of the cylindrical body, and is rotatable relative to the rotation shaft; a first length from the axis of the rotating shaft to the tip of the excavating blade in the radial direction of the rotating shaft is equal to or greater than a second length from the axis of the rotating shaft to the tip of the stirring blade in the radial direction; a third length from the axis center to a tip of one of the anti-rotation vanes in the radial direction and a fourth length from the axis center to a tip of the other anti-rotation vane in the radial direction are each greater than the first length, The excavating and stirring device, wherein the third length is greater than the fourth length.

2. each of the pair of anti-corotation wings includes an arm portion protruding from an outer periphery of the cylindrical body and a tip portion provided at a tip of the arm portion; The excavating and stirring device according to claim 1 , wherein the tip portion extends parallel to the axial direction of the rotating shaft.

3. The excavating and 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.

4. the first length is equal to or greater than 250 mm and equal to or less than 1250 mm, The excavating and 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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