Connecting structure and connecting method for shaft of ground improvement device

Abstract

To provide a connecting structure and a connecting method for a shaft of a ground improvement device that connects the top and bottom of a double pipe.SOLUTION: In a connecting structure and a connecting method for a shaft of a ground improvement device, a shaft 90 is formed in a double tube shape by an outer shaft 20 and an inner shaft 21, rotated in opposite directions, and connected vertically with multiple outer shafts and inner shafts. The outer shaft has an outer shaft male part 30a at an upper end and an outer shaft female part 30b at a lower end, and further has an outer shaft drop prevention rib 71. When the outer shafts are connected vertically, the outer shaft male part and the outer shaft female part form an outer shaft connecting part 30. The inner shaft has an inner shaft male part 40a inside the outer shaft male part and an inner shaft female part 40b inside the outer shaft female part, and further has an inner shaft drop prevention rib 81 below the inner shaft male part. When the inner shafts are connected vertically, the inner shaft male part and the inner shaft female part form an inner shaft connecting part 40. The inner shaft is supported on the upper end of the outer shaft male part, which is prevented from falling, via the inner shaft drop prevention rib and an inner shaft drop prevention fitting plate 82, and is configured so as to be allowed to rise.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a connection structure and a connection method for the shafts of a ground improvement device, which is configured with an outer shaft and an inner shaft in a double tube shape, rotates the outer shaft and the inner shaft in the opposite directions relative to each other by a rotary drive device, connects a plurality of outer shafts and inner shafts vertically to form a shaft, and has a stirring and mixing part at the lower end of the shaft. The present invention belongs to a deep layer mixing treatment method. [Background technology]

[0002] In a ground improvement device in which the excavation shaft is formed into a double tube shape with an inner and outer shaft, the inner shaft is accommodated inside the outer shaft, so when extending the double tube of the inner and outer shafts, it is a complicated task to connect the upper inner shaft constituent and the upper outer shaft constituent to be connected with the connecting part while holding the lower inner shaft constituent and the lower outer shaft constituent that have been released from the rotary drive device. For this reason, devices related to the release and holding of the lower inner shaft constituent and the lower outer shaft constituent, devices related to the connecting part, etc. have been developed.

[0003] Patent Document 1 discloses a ground improvement device 1 in which an excavation shaft 13 is formed into a double-tube structure of inner and outer shafts 15 and 16. When the excavation shaft 13 is to be separated, a support plate 55 is interposed between a flange body 52 of an outer shaft constituent body 36 buried in the ground and the ground surface 54 to fix the outer shaft constituent body 36, an insertion hole 48 and a through hole 49 of the outer shaft constituent body 36 are exposed, a connecting jig 53 is inserted from the through hole 49, and the locking groove 42 of the inner shaft constituent body 35 and the through hole 49 of the outer shaft constituent body 36 are locked by the connecting jig 53. and its vertical movement is restricted; next, the connection pin 47 is removed from the connection hole 46 of the outer shaft constituent 36, and the connection pin 41 of the inner shaft constituent 35 is removed from the insertion hole 48 of the outer shaft constituent 36, so that the inner and outer shaft constituents 35, 36 can be separated into upper and lower parts; since the inner shaft constituent 35 is connected to the outer shaft constituent 36 fixed to the ground 54, it is possible to prevent the inner shaft constituent 35 from falling under its own weight; and when connecting the drilling shaft 13, the procedure for disconnecting described above is reversed.

[0004] Patent Document 2 discloses a ground improvement device A in which an excavation shaft body 6 is formed into an inner and outer double shaft structure, and the inner and outer shafts 10 and 11 each have a stepped convex male end 10a and 11a at one end and a stepped concave female end 10b and 11b at the other end to enable countersunk engagement, and the countersunk engagement parts 20 and 21 are formed with a connection pin insertion hole 22 (inner shaft) and a connection pin insertion hole 23 (outer shaft) through which a connection pin 24 (inner shaft) and a connection pin 25 (outer shaft) are inserted so as to be freely inserted and removed, and the connection pin formed on the outer shaft 11 is inserted into the countersunk engagement parts 20 and 21. It is described that a connection pin 24 is removably inserted through the insertion holes 26, 26 to enable connection of multiple inner shafts 10, the connection pin insertion holes 26, 26 are closed by closure bodies 27, 27 to allow for free opening and closing, the connection pin 24 is fixed by a connection pin anti-slip bolt 30, the connection pin anti-slip bolt 30 is inserted removably through anti-slip bolt insertion holes 32, 32 formed in the outer shaft 11, and the anti-slip bolt insertion holes 32, 32 are closed by closure bodies 33, 33 to allow for free opening and closing.

[0005] In Patent Document 3, the ground is excavated to the limit of the leader 2, the detachable pin 20 is removed to release the connection between the upper shaft 8a and the lower shaft 8b of the agitator shaft 8, the outer shaft drive unit 9 is pulled up, the upper end of the upper shaft 8a is pulled into the support cylinder portion 10b of the inner shaft drive unit 4, the lower shaft 8b descends under its own weight, the outer shaft side stopper piece 27 engages with the inner shaft side stomper piece 28 (FIG. 5), the connecting ends of the upper shaft 8a and the lower shaft 8b of the agitator shaft 8 are separated (space portion S), and the connecting portion of the excavator shaft 6 connected by the detachable pin 15 is exposed. In this state, the detachable pin 15 of the drilling shaft 6 is removed, the connection between the upper shaft 6a and the lower shaft 6b is released, the upper shaft 6a of the drilling shaft 6, which is integral with the inner shaft drive unit 4 and the outer shaft drive unit 9, and the upper shaft 8a of the agitation shaft 8 are raised to the required height, a shaft for extending the drilling shaft is inserted between the upper shaft 6a and the lower shaft 6b of the drilling shaft 6 while being held by a wire or the like and these are interconnected by the detachable pin, a shaft for extending the drilling shaft is inserted and connected between the upper shaft 8a and the lower shaft 8b of the agitation shaft 8 in the same manner as above, and the ground is further excavated.

[0006] Patent Document 4 describes a method for connecting inner and outer double rotating shafts 12, 14 for stirring by a joint device (attachment) 21, which has a middle rod portion 220 and an outer rod portion 230 that connect to the inner shaft 22 at the upper end of the rotating shaft 20A, and describes that the auger 17 is lowered from the state shown in FIG. 3(A) as shown in FIG. 3(B), and the male joint 35 at the lower end of the middle rod portion 220 is connected to the female joint 36 at the upper end of the inner shaft 22 of the rotating shaft 20A by a pin or the like, and then the lifting cylinder 32 is extended, the lower side of the outer shaft rotation transmission member 24 is moved downward, and the male joint 27 of the lower connecting portion 25 of the rotation transmission member 24 is connected to the female joint 29 at the upper part of the outer shaft 23 inside the outer casing 28 of the rotating shaft 20A by a pin or the like. FIG. 5 shows an example of connecting two rotating shafts 20A and 20B, and describes that it is also possible to connect three or more shafts. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2009-249921 A [Patent Document 2] JP 2002-363969 A [Patent Document 3] Japanese Utility Model Application Publication No. 3-79331 [Patent Document 4] Japanese Patent Application Publication No. 11-21874 Summary of the Invention [Problem to be solved by the invention]

[0008] Conventionally, the invention described in Patent Document 1 required complex and precise work of inserting a connecting jig 53 from the outer through-hole 49 of the outer shaft constituent 36, engaging the locking groove 42 of the inner shaft constituent 35 with the through-hole 49 of the outer shaft constituent 36, connecting the inner shaft constituent 35 and the outer shaft constituent 36 to regulate up and down movement, making the connection work difficult. The invention described in Patent Document 2 required complex and precise work of forming connection pin insertion holes 22 and 23 in the spigot fitting portions 20 and 21, inserting the connection pins 24 and 25 so as to be freely inserted and removed, and enabling the inner shaft 10 to be connected through the outer shaft 11, making the connection work difficult, as in Patent Document 1. In the invention described in Patent Document 3, the outer shaft drive unit 9 is pulled up, the upper end of the upper shaft 8a is retracted, the lower shaft 8b is lowered by its own weight and engaged with the stopper pieces 27 and 28, the connecting ends of the upper shaft 8a and the lower shaft 8b of the agitator shaft 8 are separated, the attachment / detachment pin 15 of the drilling shaft 6 is pulled out, the connection between the upper shaft 6a and the lower shaft 6b is released, the inner shaft drive unit 4 and the outer shaft drive unit 9 are raised to the required height, and the drilling shaft 6 and the agitator shaft 8 are individually inserted and connected, which are complicated operations and require separate inner shaft drive unit 4 and outer shaft drive unit 9, resulting in a large-sized apparatus. The invention described in Patent Document 4 involves using a connecting device 21 to connect the male joint 35 of the middle rod portion 220 to the female joint 36 of the inner shaft 22 with a pin or the like, then extending the lifting cylinder 32, moving the outer shaft rotation transmission member 24 downward, and connecting the male joint 27 of the lower connecting portion 25 to the female joint 29 at the top of the outer shaft 23 with a pin or the like. However, the need for the connecting device 21 and the lifting cylinder 32 makes the device large.

[0009] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a connecting structure and a connecting method for the shafts of a ground improvement device, which enables connecting and disconnecting a shaft configured in a double tube shape from the outer shaft and the inner shaft with a simple configuration, without operating the inner shaft from outside the outer shaft with a complex and sophisticated mechanism, and without requiring any special equipment. [Means for solving the problem]

[0010] The invention according to claim 1 of the present application is a shaft connection structure of a ground improvement device, in which an outer shaft and an inner shaft are configured into a double tube shape, the outer shaft and the inner shaft are rotated relatively in opposite directions by a rotary drive device, and a shaft is formed by connecting a plurality of the outer shafts and the inner shafts vertically, and the shaft is inserted into the ground, the outer shaft has an outer shaft male part at an upper end and an outer shaft female part at a lower end, and an outer shaft drop prevention rib is provided below the outer shaft male part, and when the plurality of outer shafts are connected vertically, the outer shaft male part and the outer shaft female part are connected to each other, thereby forming an outer shaft connection between the upper shaft and the lower shaft. a connecting structure for the shafts of a ground improvement device, characterized in that the inner shaft comprises an inner shaft male part inside the outer shaft male part and an inner shaft female part inside the outer shaft female part, and has an inner shaft anti-drop rib below the inner shaft male part, and when multiple inner shafts are connected vertically, the inner shaft male part and the inner shaft female part are connected to form an inner shaft connecting part for the upper shaft and the lower shaft, and the inner shaft is supported on the upper end of the outer shaft male part, which is prevented from falling, via the inner shaft anti-drop rib and the inner shaft anti-drop fitting plate, and is allowed to rise.

[0011] The invention of claim 2 of the present application is a connecting structure of the shaft of the ground improvement device described in claim 1, characterized in that the lower end of the shaft is provided with a stirring and mixing section, which has a lower stage stirring blade at the lower end of the outer shaft and an auxiliary stirring blade at the lower end of the inner shaft, the maximum allowable lift distance of the inner shaft is the distance between the lower end of the lower stage stirring blade and the upper end of the lower horizontal blade that constitutes the auxiliary stirring blade, and the distance between the lower end of the inner shaft fall prevention rib and the upper end of the outer shaft male part does not exceed the maximum allowable lift distance.

[0012] The invention of claim 3 of the present application is a connecting structure of the shaft of the ground improvement device described in claim 1, characterized in that an outer shaft anti-fall rib is provided below the outer shaft anti-fall rib, and is fitted into the groove of the fall prevention workbench via an outer shaft anti-fall and anti-rise fitting plate, thereby preventing the outer shaft from rising together with the rise of the inner shaft.

[0013] The invention according to claim 4 of the present application is a method for connecting shafts of a ground improvement device, comprising: configuring an outer shaft and an inner shaft into a double tube shape; rotating the outer shaft and the inner shaft in relatively opposite directions using a rotary drive device; connecting a plurality of the outer shafts and the inner shafts vertically to form a shaft; and penetrating the shaft into the ground, wherein the outer shaft has an outer shaft male part at an upper end and an outer shaft female part at a lower end, and has an outer shaft drop prevention rib below the outer shaft male part; when the plurality of outer shafts are connected vertically, the outer shaft male part and the outer shaft female part are connected to form an outer shaft connecting part of an upper shaft and a lower shaft; and the inner shaft has an inner shaft male part inside the outer shaft male part and an inner shaft female part inside the outer shaft female part, and has an inner shaft drop prevention rib below the inner shaft male part; when the plurality of inner shafts are connected vertically, the inner shaft male part and the inner shaft female part are connected to form an outer shaft connecting part of an upper shaft and a lower shaft. a step of separating the lower shaft connected to the upper shaft and leaving the lower shaft in the ground using a shaft connecting structure of the ground improvement device in which the inner shaft is supported on the upper end of the outer shaft male part, the drop of which is prevented, via the inner shaft drop prevention rib and the inner shaft drop prevention fitting plate and the rise of the shaft is permitted, the step of preventing the outer shaft of the lower shaft from falling, releasing the connection of the outer shaft connecting part between the upper shaft and the lower shaft, raising the inner shaft of the upper shaft to expose the inner shaft connecting part between the lower shaft and the upper shaft, and inserting the inner shaft drop prevention fitting plate between the inner shaft drop prevention rib of the lower shaft and the upper end of the outer shaft male part, the drop of which is prevented, by the rise of the inner shaft of the upper shaft.

[0014] The invention according to claim 5 of the present application is a method for connecting shafts of a ground improvement device, comprising: configuring an outer shaft and an inner shaft into a double tube shape; rotating the outer shaft and the inner shaft in relatively opposite directions using a rotary drive device; connecting a plurality of the outer shafts and the inner shafts vertically to form a shaft; and penetrating the shaft into the ground, wherein the outer shaft has an outer shaft male part at an upper end and an outer shaft female part at a lower end, and has an outer shaft drop prevention rib below the outer shaft male part; when the plurality of outer shafts are connected vertically, the outer shaft male part and the outer shaft female part are connected to form an outer shaft connecting part of an upper shaft and a lower shaft; the inner shaft has an inner shaft male part inside the outer shaft male part and an inner shaft female part inside the outer shaft female part, and has an inner shaft drop prevention rib below the inner shaft male part; when the plurality of inner shafts are connected vertically, the inner shaft male part and the inner shaft female part are connected to a step of connecting the upper shaft to the lower shaft, which has been left in the ground and both the outer shaft and the inner shaft prevented from falling, using a shaft connecting structure of the ground improvement device in which the inner shaft is supported on the upper end of the outer shaft male part, which has been prevented from falling, via the inner shaft drop prevention rib and the inner shaft drop prevention fitting plate, and which is allowed to rise, comprising at least a step of lowering the upper shaft and connecting the inner shaft female part of the upper shaft to the inner shaft male part of the lower shaft to form the inner shaft connecting part, and a step of raising the inner shaft of the upper shaft and removing the inner shaft drop prevention fitting plate from between the inner shaft drop prevention rib of the lower shaft and the upper end of the outer shaft male part, which has been prevented from falling. Effect of the Invention

[0015] According to the present invention, when connecting and disconnecting the outer shaft of the upper shaft and the lower shaft, the outer shaft of the lower shaft can be prevented from falling by the outer shaft drop prevention rib, and the connecting part of the outer shaft can be safely connected and disconnected. Also, the inner shaft has an inner shaft drop prevention rib below the inner shaft male part, and is supported by the inner shaft drop prevention rib and the inner shaft drop prevention fitting plate at the upper end of the outer shaft male part that is prevented from falling, and is allowed to rise, so that the inner shaft of the upper shaft and the lower shaft can be easily connected and disconnected. In addition, the invention described in Patent Document 1 restricts the up-down movement by connecting the inner shaft constituent body 35 (corresponding to the inner shaft connecting part of the present application) and the outer shaft constituent body 36 (corresponding to the outer shaft connecting part of the present application), and the lower inner shaft 15 (corresponding to the inner shaft of the present application) cannot be raised, and is clearly different from the present invention. In addition, the invention described in Patent Document 3 includes an excavation shaft 6 (corresponding to the inner shaft of the present application) and an excavation shaft 8 (corresponding to the outer shaft of the present application), and when the upper shaft 8a and the lower shaft 8b of the agitation shaft 8 are released from the connection, the lower shaft 8b (corresponding to the outer shaft of the lower shaft of the present application) descends by its own weight, and the outer shaft side stopper piece 27 (corresponding to the outer shaft drop prevention rib of the present application) is engaged with the inner shaft side stomper piece 28, and further, the connection between the upper shaft 6a and the lower shaft 6b of the excavation shaft 6 is released, and the excavation shaft 6 cannot be raised, and is clearly different from the present invention. The inventions described in Patent Documents 2 and 4 are described in paragraphs 4 to 6 and 8, and therefore the differences between the present invention and the invention are clear, and therefore a comparison of the individual invention-specific matters will be omitted.

[0016] In addition, the distance between the lower end of the inner shaft anti-fall rib and the upper end of the male part of the outer shaft is set so as not to exceed the maximum allowable lift distance between the lower stage agitator blade at the lower end of the outer shaft and the upper end of the lower horizontal blade that constitutes the auxiliary agitator blade at the lower end of the inner shaft, thereby allowing the inner shaft to be lifted safely.

[0017] In addition, by providing the outer shaft drop prevention ribs and the outer shaft rise prevention ribs at two levels, one above the other, it is possible to prevent the outer shaft from falling and also to prevent the outer shaft from rising together with the inner shaft when it rises.

[0018] In addition, in the process of separating the lower shaft connected to the upper shaft and leaving the lower shaft in the ground, the outer shaft of the lower shaft is prevented from falling, the upper shaft and the lower shaft are separated, the upper shaft is raised to expose the inner shaft connection part between the lower shaft and the upper shaft, and the inner shaft drop prevention fitting plate can be easily inserted between the inner shaft drop prevention rib of the lower shaft and the upper end of the outer shaft male part that has been prevented from falling. Thus, the lower shaft can be left in the ground in a state where both the inner shaft and the outer shaft are prevented from falling.

[0019] In addition, in the process of connecting the upper shaft to the lower shaft left in the ground with both the inner shaft and the outer shaft prevented from falling, the upper shaft can be lowered to connect the inner shaft female part of the upper shaft to the inner shaft male part of the lower shaft to easily form the inner shaft connecting part. As a result, the inner shafts of the upper shaft and the lower shaft are connected, and the inner shaft drop prevention fitting plate can be easily removed from between the inner shaft drop prevention rib and the upper end of the outer shaft male part by raising the upper shaft. Therefore, the upper shaft can be easily connected to the lower shaft left in the ground with both the inner shaft and the outer shaft prevented from falling. [Brief description of the drawings]

[0020] [Figure 1] 1 is an overall front view showing a schematic diagram of a ground improvement device according to a first embodiment of the present invention. [Diagram 2] FIG. 11 is a diagram showing the connection state between the rotary drive unit connecting shaft and the excavation shaft / joint pile excavation shaft in accordance with the second embodiment of the present invention; (a) is a schematic diagram showing the rotary drive unit connecting shaft in a see-through manner; (b) is a schematic diagram showing the excavation shaft / joint pile excavation shaft in a see-through manner, with the inner shaft arranged inside the outer shaft; and (c) is a schematic diagram showing the inner shaft male part protruding from the upper end of the outer shaft male part when the inner shaft in (b) is raised a predetermined amount. [Diagram 3] FIG. 3 is a diagram showing the drilling shaft and stirring / mixing section according to the third embodiment of the present invention; (a) is a drilling shaft connected to the tip of the stirring / mixing section, and (b) is a schematic diagram showing that when the inner shaft of (a) is raised a predetermined amount, the auxiliary stirring blade of the stirring / mixing section rises and the male part of the inner shaft protrudes from the upper end of the male part of the outer shaft. [Figure 4] FIG. 11 is a diagram showing an outer shaft male part and an inner shaft male part according to a second embodiment of the present invention, (a) being an enlarged view showing the positional relationship between the inner shaft male part and the inner shaft fall prevention rib, and the outer shaft male part and the outer shaft fall prevention rib, and (b) being an enlarged view showing the positional relationship when the inner shaft is disposed within the outer shaft. [Diagram 5] FIG. 13 is a diagram showing a jig and a process for supporting an outer shaft on a fall prevention worktable in accordance with Example 4 of the present invention, in which (a) is a front view in which an outer shaft fall prevention fitting plate is fitted into the gap between the outer shaft fall prevention rib and the fall prevention worktable, (b) is a plan view of (a), and (c) is a front view in which the outer shaft is lowered and supported on the fall prevention worktable by the outer shaft fall prevention rib and the outer shaft fall prevention fitting plate. [Figure 6] 13A to 13C are diagrams showing a jig and a process for supporting the outer shaft according to the fifth embodiment of the present invention on a fall prevention work bench by the outer shaft fall prevention rib and the outer shaft co-rise prevention rib. [Figure 7] FIG. 13 is a diagram showing a jig and a process for supporting the inner shaft drop prevention rib of the inner shaft on the upper end of the outer shaft male part in accordance with Example 7 of the present invention, (a) is a front view with the inner shaft drop prevention fitting plate fitted into the gap between the upper end of the outer shaft male part and the inner shaft drop prevention rib, (b) is a plan view of (a), (c) is a front view with the inner shaft drop prevention rib of the inner shaft supported on the upper end of the outer shaft male part via the inner shaft drop prevention fitting plate, and (d) is a front view with the inner shaft connecting jig of the inner shaft removed and the upper shaft raised. [Figure 8] FIG. 13 is a diagram showing the construction process of the joint pile according to Example 8 of the present invention, and is a front view of the connection construction process (a) to (d) of the upper shaft and the lower shaft. [Figure 9] FIG. 13 is a diagram showing the construction process of the joint pile according to Example 8 of the present invention, and is a front view of the connection construction steps (e) to (h) of the upper shaft and the lower shaft. [Figure 10] FIG. 13 is a diagram showing the construction process of the joint pile according to Example 8 of the present invention, and is a front view of the connecting construction steps (i) to (l) of the upper shaft and the lower shaft. [Figure 11] FIG. 13 is a diagram showing the construction process of the joint pile according to Example 8 of the present invention, and is a front view of the connection construction steps (m) to (p) of the upper shaft and the lower shaft. [Figure 12] FIG. 13 is a diagram showing the construction process of the joint pile according to Example 8 of the present invention, and is a front view of the connection construction steps (q) to (t) of the upper shaft and the lower shaft. [Figure 13] FIG. 13 is a diagram showing the construction process of the joint pile according to Example 8 of the present invention, and is a front view of the connection construction process (u) to (v) of the upper shaft and the lower shaft. [Figure 14] 13 is a front view of a shaft in which a pile drilling shaft according to Example 9 of the present invention is connected to multiple drilling shafts. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] A preferred embodiment of the present invention will be described in detail below with reference to the drawings. It goes without saying that the present invention is not limited to the embodiment described below. In addition, the materials, shapes and dimensions of each member described below are examples, and changes are a design matter. Furthermore, adding devices and jigs used in a known deep mixing treatment method to the ground improvement device of the present invention is also a design matter.

[0022] <Coordinate axis> In the drawings, the X-axis, Y-axis, and Z-axis are shown as coordinate axes. The Z-axis direction is the upward direction of the leader 3 of the excavator 1 that stands vertically on the ground, which is a horizontal plane, and the horizontal plane of the ground is shown as the plane XY formed by the X-axis and Y-axis.

[0023] <Definition> Top and bottom: With respect to the axis of the leader 3 which stands vertically to the ground (Z-axis direction), the side opposite the ground (positive Z-axis direction) is considered "top" and the side facing the ground (negative Z-axis direction) is considered "bottom." Connection: The male part of the outer shaft and the inner shaft of one shaft are fitted and connected to the female part of the outer shaft and the inner shaft of another shaft to form the outer shaft connecting part and the inner shaft connecting part, thereby forming one shaft. Note that the opposite of "connecting" is called "releasing."

[0024] <Soil improvement equipment> Fig. 1 shows a ground improvement device 1 according to an embodiment of the present invention (Example 1), which is used for a so-called deep mixing treatment method. The ground improvement device 1 has a leader 3 standing in the Z-axis direction at the front end of an excavator 2 installed on ground 5. A rotary drive device 7 is suspended from the upper end of the leader 3 by a wire 6 so as to be freely raised and lowered in the Z-axis direction.

[0025] In FIG. 1, two pile drilling shafts 9M (M=1, 2) are connected to the lower side of the rotary drive device connection shaft 8 provided directly below the rotary drive device 7 via the connection shaft connecting part 50. The drilling shaft 9 is connected to the lower side of the pile drilling shaft 9M (M=1, 2) via the drilling shaft connecting part 60. The mixing and mixing part 10 is connected to the lower side of the drilling shaft 9 via the mixing and mixing part connecting part 65. The rotary drive device connection shaft 8, the pile drilling shafts 9M (M=1, 2), the drilling shafts 9 and the mixing and mixing part 10 are connected vertically in the Z-axis direction to form a shaft 90, which is penetrated into the ground. The upper side of the two shafts 90 connected vertically is referred to as the upper shaft 90A, and the lower side is referred to as the lower shaft 90B. For example, it represents the relationship between the rotary drive unit connection shaft 8 (upper shaft 90A) and the joint pile drilling shaft 92 (lower shaft 90B) shown in Figure 1, and the relationship between the joint pile drilling shaft 91 (upper shaft 90A) and the drilling shaft 9 (lower shaft 90B).

[0026] The tubular outer shaft 20 and the tubular inner shaft 21 rotatably arranged inside the outer shaft 20 rotate in opposite directions by a reduction gear (not shown) that constitutes the rotary drive device 7. The outer shaft 20 and the inner shaft 21 are connected vertically to each other to form a shaft 90. The rotary drive device connection shaft 8, the joint pile drilling shaft 9M (M = 1, 2), the drilling shaft 9, and the stirring and mixing section 10, which are made up of the outer shaft 20 and the inner shaft 21, are also connected vertically to form the shaft 90. As an example, an outer shaft helical blade 20a is provided on the outer periphery of the outer shaft 20.

[0027] The stirring and mixing section 10 is composed of, for example, an upper stirring blade 22, a lower stirring blade 23, an auxiliary stirring blade 24, and a digging blade 25. The auxiliary stirring blade 24 is further composed of, for example, an upper horizontal blade 24a, a lower horizontal blade 24b, and both side vertical blades 24c. The distance between the lower end of the lower stirring blade 23 fixed to the outer shaft 20 and the upper end of the lower horizontal blade 24b constituting the auxiliary stirring blade 24 fixed to the inner shaft 21 is S0. In this sense, it can be said that the maximum allowable lift distance of the inner shaft is the distance S0. The adoption of a known stirring and mixing mechanism in the stirring and mixing section 10 is a design matter.

[0028] The upper stirring blade 22 and the lower stirring blade 23 are fixed to the outer shaft 20. The auxiliary stirring blade 24 and the digging blade 25 are fixed to the inner shaft 21. Therefore, since the outer shaft 20 and the inner shaft 21 rotate in opposite directions, the upper stirring blade 22 and the lower stirring blade 23, and the auxiliary stirring blade 24 and the digging blade 25 rotate in opposite directions and are mixed and stirred three-dimensionally, thereby achieving uniform mixing.

[0029] The inner shaft 21 is arranged inside the outer shaft 20 so as to be rotatable and to be able to rise and fall. Therefore, the auxiliary mixing blade 24 and the excavation blade 25 fixed to the inner shaft 21 are also rotatable and able to rise and fall. The movement of the inner shaft 21 to rise and fall is mainly for connecting and disconnecting the upper shaft and the lower shaft. The upper shaft 90A connected to the rotary drive device 7 is raised and lowered in the Z-axis direction by the wire 6, whereby the inner shaft 21, which is integrated with the upper shaft 90A and the upper shaft 90A, is raised and lowered. Furthermore, when a lumpy clay has entered between the lower mixing blade 23 and the auxiliary mixing blade 24 in a co-rotating state, or when a boulder or the like has become caught, the raising and lowering of the auxiliary mixing blade 24 and the excavation blade 25 by the raising and lowering of the inner shaft 21 is an effective measure. The inner shaft 21 returns to its original position in FIG. 1 by lowering after rising.

[0030] The drilling shaft 9 and the joint pile drilling shaft 9M are supported via a vibration control device 4 that is movably mounted on the leader 3. The vibration control device 4 also functions as a work platform to prevent the drilling shaft 9 (lower shaft 90B) from falling during the process of connecting the joint pile drilling shaft 9M (upper shaft 90A) used for subsequent construction to the drilling shaft 9 (lower shaft 90B) used for preceding construction.

[0031] The ground improvement device 1 uses an improvement agent / drilling water injection device and a generator, etc., not shown, which are necessary for the deep mixing treatment method, but their description is omitted.

[0032] <Drilling shaft for pile connection or drilling shaft connected to the rotary drive device connection shaft> Fig. 2 shows a specific embodiment (Example 2) in which a pile drilling shaft 9M or a drilling shaft 9 is connected to a rotary drive device connecting shaft 8. Fig. 2(a) shows that the rotary drive device connecting shaft 8 is equipped with an outer shaft 20 and an inner shaft 21 arranged inside the outer shaft 20. The outer shaft 20 has an outer shaft female part 30b at its lower end, and an inner shaft female part 40b arranged and protruding inside a range of a distance S1 = 530 mm from the upper end side of the outer shaft female part 30b, for example. An outer shaft connecting hole 30c is formed in the outer shaft female part 30b, and an inner shaft connecting hole 40c is formed in the inner shaft female part 40b.

[0033] 2(b) shows the drilling shaft 9 and the joint pile drilling shaft 9M connected to the rotary drive device connection shaft 8. The drilling shaft 9 and the joint pile drilling shaft 9M are provided with a tubular outer shaft 20 and a tubular inner shaft 21 arranged inside the outer shaft 20 so as to be rotatable and movable up and down. The upper end (positive direction of the Z axis) of the outer shaft 20 is provided with an outer shaft male part 30a and an inner shaft male part 40a arranged inside a range of a distance S1 = 530 m, for example, from the upper end of the outer shaft male part 30a. An outer shaft connecting hole 30c is formed in the outer shaft male part 30a, and an inner shaft connecting hole 40c is formed in the inner shaft male part 40a. The other end, that is, the lower end (negative direction of the Z axis), of the outer shaft 20 is provided with an outer shaft female part 30b and an inner shaft female part 40b disposed inwardly and protruding within a range of a distance S1 = 530 mm, for example, from the upper end of the outer shaft female part 30b. An outer shaft connecting hole 30c is formed in the outer shaft female part 30b, and an inner shaft connecting hole 40c is formed in the inner shaft female part 40b. In addition, an outer shaft drop prevention rib 71 is formed on the outer shaft male part 30a, and an inner shaft drop prevention rib 81 is formed on the male part 40a of the inner shaft 21. The distance from the upper end of the outer shaft male part 30a to the lower end of the inner shaft drop prevention rib 81 is, for example, a distance S2 = 650 mm.

[0034] The outer shaft female part 30b and the inner shaft female part 40b of the rotary drive device connection shaft 8 are fitted and connected to the outer shaft male part 30a and the inner shaft male part 40a at the upper end (Z-axis positive direction) of the joint pile drilling shaft 9M or the drilling shaft 9 for the outer shaft and the inner shaft, respectively. Then, the outer shaft connecting jig 30d and the inner shaft connecting jig 40d are inserted into the outer shaft connecting hole 30c and the inner shaft connecting hole 40c, respectively, and connected and fixed (the outer shaft connecting part 30 and the inner shaft connecting part 40), thereby forming the connection shaft connecting part 50. The outer shaft 20 and the inner shaft 21 are connected and fixed to the outer shaft connecting jig 30d and the inner shaft connecting jig 40d using known bolts, nuts, pins, etc., so that they can rotate counter-rotatably on two axes.

[0035] <Excavation shaft for pile joint or excavation shaft connected to the lower end of the excavation shaft for pile joint> In Fig. 2(b), the outer shaft female part 30b and the inner shaft female part 40b at the lower end (Z-axis minus direction) of the joint pile drilling shaft 9M are fitted and connected to the outer shaft male part 30a and the inner shaft male part 40a at the upper end of the joint pile drilling shaft 9M or the drilling shaft 9 for the outer shaft 20 and the inner shaft 21, respectively. Then, the outer shaft connecting jig 30d and the inner shaft connecting jig 40d are inserted into the outer shaft connecting hole 30c and the inner shaft connecting hole 40c, respectively, and connected and fixed (the outer shaft connecting part 30 and the inner shaft connecting part 40), forming the drilling shaft connecting part 60, and the outer shaft 20 and the inner shaft 21 are capable of biaxial counter-rotation.

[0036] FIG. 2(c) shows the protruding state when the joint pile drilling shaft 91 or the inner shaft male part 40a of the drilling shaft 9 rises alone in the positive direction of the Z axis.

[0037] <Agitation and mixing section connected to the drilling shaft> In FIG. 3(a), as an example, the stirring and mixing unit 10 illustrated in Example 1 is connected to the tip of the drilling shaft 9 via a stirring and mixing unit connection part 65 (Example 3). The upper stirring blade 22 and the lower stirring blade 23 are fixed to the outer shaft 20, and the auxiliary stirring blade 24 and the drilling blade 25 are fixed to the inner shaft 21. The inner shaft 21 is arranged inside the outer shaft 20 so as to be rotatable and to be able to rise and fall. Therefore, the auxiliary stirring blade 24 and the drilling blade 25 fixed to the inner shaft 21 are also rotatable and able to be raised and lowered. The separation distance S0 between the lower end of the lower stirring blade 23 fixed to the outer shaft 20 and the upper end of the lower horizontal blade 24b constituting the auxiliary stirring blade 24 fixed to the inner shaft 21 is the maximum allowable rise distance of the inner shaft, and as an example, S0=800 mm.

[0038] The inner shaft male part 40a is disposed inside the outer shaft 20 within a range in the negative Z-axis direction of, for example, a distance S1 = 530 mm from the upper end of the outer shaft male part 30a (see FIG. 2(b)). When the inner shaft female part 40b (upper shaft 90A) and the inner shaft male part 40a (lower shaft 90A) are connected to form the inner shaft connecting part 40, the inner shaft 21 of the upper shaft 90A and the lower shaft 90B becomes a single shaft. It is assumed that the outer shaft 20 is supported on the ground in a state in which it is prevented from falling. The inner shaft 21 alone is raised in the positive Z-axis direction by, for example, a distance S2 = 650 mm from the upper end of the outer shaft male part 30a to the lower end of the inner shaft drop prevention rib 81. Then, the inner shaft male part 40a of the inner shaft connecting part 40 protrudes in the positive Z-axis direction from the upper end of the outer shaft male part 30a, including the lower end of the inner shaft drop prevention rib 81. At that time, there is a sufficient distance between the lower end of the lower-stage agitating blade 23 and the upper end of the lower horizontal blade 24b constituting the auxiliary agitating blade 24, so it can be said that the inner shaft 20 can be raised safely and with a margin. See Figure 3(b).

[0039] <Outer shaft male part and inner shaft male part at the top end of the excavation shaft or the excavation shaft for pile joints> Fig. 4(a) is an enlarged view of the outer shaft male part 30a and the inner shaft male part 40a which constitute the upper end, which is one end of the drilling shaft 9 or the joint pile drilling shaft 91 shown in Fig. 2(b) of Example 2. An outer shaft drop prevention rib 71 is provided on the outer periphery of the outer shaft male part 30a. Also, the lower end of the inner shaft drop prevention rib 81 is disposed at a position on the outer periphery of the inner shaft male part 40a at a distance S2 of, for example, 650 mm from the upper end of the outer shaft male part 30a.

[0040] Fig. 4(b) is an enlarged view of the inner shaft male part 40a shown in Fig. 4(a) disposed inside the outer shaft male part 30a. The outer shaft drop prevention rib 71 is disposed on the upper end side (positive direction of the Z axis) of the outer shaft male part 30a from the position of the inner shaft drop prevention rib 81. Therefore, by optimizing the rising distance of the inner shaft 21, the inner shaft drop prevention rib 81 can be reliably disposed to rise and protrude in the positive direction of the Z axis from the upper end of the outer shaft male part 30a.

[0041] <Outer shaft support> The rotary drive unit connection shaft 8, the joint pile drilling shaft 9M, the drilling shaft 9, and the stirring and mixing section 10 that constitute the ground improvement device 1 are composed of an outer shaft 20 and an inner shaft 21 disposed inside the outer shaft 20. For this reason, when connecting the outer shaft 20 and the inner shaft 21 of the upper shaft 90A and the lower shaft 90B, it is necessary to first stably support the outer shaft 20 of the lower shaft 90B on the ground or the like to prevent it from falling.

[0042] FIG. 5 is a diagram showing a jig and a process for supporting the outer shaft 20 of the lower shaft 90B on the fall prevention work platform 4. When the vibration prevention device 4 is installed on the ground, it is called a fall prevention work platform 4. As a specific embodiment (embodiment 4), the jig and process for supporting the outer shaft 20 of the drilling shaft 9 (lower shaft 90B) that has been previously installed in the ground by connecting the drilling shaft 9 (lower shaft 90B) to the rotation drive device connection shaft 8 (upper shaft 90A) on the fall prevention work platform 4 are shown. The outer shaft 20 / inner shaft 21 of the rotation drive device connection shaft 8 (upper shaft 90A) and the outer shaft 20 / inner shaft 21 of the drilling shaft 9 (lower shaft 90B) are connected by the connection shaft connecting part 50 (outer shaft connecting part 30 / inner shaft connecting part 40). Hereinafter, the upper shaft 90A and the lower shaft 90B will be described. FIG. 5(a) illustrates that the upper shaft 90A is slightly raised (Z-axis positive direction) and the outer shaft drop prevention fitting plate 72 is inserted into the gap between the outer shaft drop prevention rib 71 near the outer shaft male part 30a of the lower shaft 90B and the drop prevention workbench 4 arranged on the ground 5. FIG. 5(b) is a plan view. The outer shaft drop prevention fitting plate 72 is a plate-shaped member having a handle part and both sides branched into a bifurcated shape, as exemplified in FIG. 5(b). By inserting both sides branched into a bifurcated shape of the outer shaft drop prevention fitting plate 72 below the outer shaft drop prevention rib 71, the installation area of ​​the outer shaft drop prevention rib 71 can be increased and placed on the upper end of the drop prevention workbench 4.

[0043] FIG. 5(c) illustrates that the upper shaft 90A is slightly lowered (Z-axis minus direction) and the weight of the outer shaft 20 of the lower shaft 90B is supported on the fall prevention work bench 4 on the ground 5 via the outer shaft fall prevention rib 71 and the outer shaft fall prevention fitting plate 72. Next, the outer shaft connecting jig 30d of the outer shaft connecting part 30 is removed, and the outer shaft 20 of the upper shaft 90A and the outer shaft 20 of the lower shaft 90B are separated, and then the upper shaft 90A is raised. The inner shaft 21 of the upper shaft 90A and the inner shaft 21 of the lower shaft 90B are maintained connected by the inner shaft connecting part 40. Therefore, the inner shaft 21 is raised simultaneously with the upper shaft 90A, and the inner shaft connecting part 40 protrudes and is exposed from the outer shaft male part 30a of the lower shaft 90A.

[0044] By supporting the weight of the outer shaft 20 from the outer shaft drop prevention rib 71 via the outer shaft drop prevention fitting plate 72 on the drop prevention workbench 4 on the ground 5, it is possible to prevent the outer shaft 20 from falling, and this makes it easier to connect and disconnect the inner shaft 21 in the next step.

[0045] 6 is a diagram showing a jig and a process for supporting the outer shaft 20 on the fall prevention work bench 4 by the outer shaft drop prevention rib 71 and the outer shaft common rise prevention rib 73. As a specific example (Example 5), the jig and a process for supporting the outer shaft 20 of the lower shaft 90B, which is connected to the upper shaft 90A and pre-installed underground, on the fall prevention work bench 4 are shown. The outer shaft common rise prevention rib 73 is provided below the outer shaft drop prevention rib 71 in the vicinity of the outer shaft male part 30a of the lower shaft 90B, and is configured to have a function of preventing common rise in addition to preventing falling. The upper outer shaft drop prevention rib 71 and the lower outer shaft rise prevention rib 73 are fitted into the groove 4a provided in the fall prevention workbench 4 via the outer shaft drop and rise prevention fitting plate 72, and the upper outer shaft drop prevention rib 71 prevents the outer shaft 20 from falling, and the lower outer shaft rise prevention rib 73 prevents the outer shaft 20 from rising together with the rise of the inner shaft 21. The process is basically the same as in Example 4. The upper shaft 90A is slightly raised (Z-axis positive direction), and the outer shaft drop and rise prevention fitting plate 72 is fitted between the upper outer shaft drop prevention rib 71 and the lower outer shaft rise prevention rib 73 near the outer shaft male part 30a of the lower shaft 90B, and into the groove 4a provided in the fall prevention workbench 4 placed on the ground 5. In addition, the outer shaft drop and rise prevention fitting plate 72 is the same as the outer shaft drop and rise prevention fitting plate 72, and when used to prevent the outer shaft from falling and rise together as in Example 5, it is called the outer shaft drop and rise prevention fitting plate 72.

[0046] Instead of the groove 4a provided in the fall prevention workbench 4, a steel plate to which the handle of the outer shaft fall and co-rise prevention fitting plate 72 is welded can be used (Example 6, not shown). The outer shaft fall and co-rise prevention fitting plate 72 welded to the steel plate placed on the ground 5 is fitted between the outer shaft fall prevention rib 71 and the outer shaft co-rise prevention rib 73, and the outer shaft 20 can be prevented from falling by the upper outer shaft fall prevention rib 71, and the outer shaft 20 can be prevented from rising together with the inner shaft 21 by the lower outer shaft co-rise prevention rib 73.

[0047] By providing the outer shaft drop prevention rib 71 and the outer shaft rise prevention rib 73 in two upper and lower stages, it is possible to prevent the outer shaft 20 from falling and also to prevent the outer shaft 20 from rising together with the inner shaft 21 as it rises.

[0048] The process of removing the outer shaft drop (co-rise) prevention fitting plate 72 from the outer shaft drop prevention rib 71 (and the outer shaft co-rise prevention rib 73) and the drop prevention workbench 4 can be easily carried out by reversing the above construction process.

[0049] <Inner shaft support> As described in the section on supporting the outer shaft, when connecting the outer shaft 20 and the inner shaft 21 of the upper shaft 90A and the lower shaft 90B, it is a prerequisite that the outer shaft 20 of the lower shaft is first stably supported on the ground or the like to prevent it from falling. In addition, the connection of the inner shaft 21 of the lower shaft 90B to the inner shaft 21 of the upper shaft 90A must precede the connection of the outer shafts. For this reason, the inner shaft 21 of the lower shaft 90B, which is left behind, must be in a state in which it can be easily connected in advance in the next process without falling.

[0050] 7 is a diagram showing a jig and a process for supporting the inner shaft drop prevention rib 81 of the inner shaft 21 on the outer shaft male part 30a of the outer shaft 20. As a specific example (Example 7), first, the outer shaft 20 / inner shaft 21 of the rotation drive device connecting shaft 8 (upper shaft 90A) and the outer shaft 20 / inner shaft 21 of the drilling shaft 9 (lower shaft 90B) are penetrated into the ground 5 (not shown) in a state where they are connected by the connecting shaft connecting part 50 (outer shaft connecting part 30 / inner shaft connecting part 40). Next, the outer shaft 20 of the drilling shaft 9 (lower shaft 90B) is supported by the outer shaft drop prevention rib 71 via the outer shaft drop prevention fitting plate 72 on the drop prevention work bench 4 on the ground 5 to be prevented from falling (not shown). Furthermore, the outer shaft 20 of the rotary drive device connection shaft 8 (upper shaft 90A) and the outer shaft 20 of the drilling shaft 9 (lower shaft 90B) are disconnected from each other at the outer shaft connecting portion 30, and separated into the outer shaft female portion 30b (upper shaft 90A) and the outer shaft male portion 30a (lower shaft 90B). The inner shaft 21 of the upper shaft 90A and the inner shaft 21 of the lower shaft 90B are kept connected by the inner shaft connecting portion 40. Therefore, when the upper shaft 90A is raised, the inner shaft 21 is also raised at the same time. Hereinafter, the description will be given by the upper shaft 90A and the lower shaft 90B.

[0051] FIG. 7(a) shows the state in which the outer shaft female part 30b (upper shaft 90A) and the outer shaft male part 30a (lower shaft 90B) are separated, and the upper shaft 90A is raised by an elevation distance S3 of 700 mm (Z-axis positive direction) as an example. The elevation distance S3 is a distance less than the maximum allowable elevation distance S0 of the inner shaft 21 of 800 mm. The inner shafts 21 of the upper shaft 90A and the lower shaft 90B are connected by the inner shaft connecting part 40. Therefore, as the upper shaft 90A rises, the inner shaft 21 of the lower shaft 90B also rises together, and the inner shaft connecting jig 40d of the inner shaft connecting part 40 is exposed. At that time, the distance from the upper end of the outer shaft male part 30a to the lower end of the inner shaft drop prevention rib 81 is, as an example, a distance S2 of 650 mm. Furthermore, a clearance distance Sa = 50 mm is ensured between the lower end of the inner shaft drop prevention rib 81 of the lower shaft 90B and the upper end of the outer shaft male part 30a. Therefore, it can be said that the distance S2 = 650 mm between the lower end of the inner shaft drop prevention rib 81 and the upper end of the outer shaft male part 30a does not exceed the maximum allowable lift distance S0 = 800 mm. Therefore, the inner shaft drop prevention rib 81 of the inner shaft 21 can be safely lifted to the upper end of the outer shaft male part 30a.

[0052] As shown in Fig. 7(b), an inner shaft drop prevention fitting plate 82 (t = 25 mm) is inserted into the gap distance Sa = 50 mm between the lower end of the inner shaft drop prevention rib 81 and the upper end of the outer shaft male part 30a. The inner shaft drop prevention fitting plate 82 is a plate-shaped member equipped with a handle portion and both side portions branched into a bifurcated shape. By inserting both side portions branched into a bifurcated shape of the inner shaft drop prevention fitting plate 82 below the inner shaft drop prevention rib 81, the installation area of ​​the inner shaft drop prevention rib 81 can be increased and it can be placed on the upper end of the outer shaft male part 30a.

[0053] 7(c), the upper shaft 90A is slightly lowered (in the negative Z-axis direction) so as to eliminate the gap distance Sa, and the inner shaft 21 is also lowered in conjunction with it, so that the weight of the inner shaft 21 can be easily supported by the upper end of the outer shaft male part 30a of the outer shaft 20, which is prevented from falling, via the inner shaft drop prevention rib 81 and the inner shaft drop prevention fitting plate 82. Thus, the inner shaft 21 of the lower shaft 90B is prevented from falling.

[0054] 7(d), the inner shaft connecting jig 40d of the inner shaft connecting portion 40 is removed, and the inner shaft female portion 40b of the upper shaft 90A and the inner shaft male portion 40a of the lower shaft 90B are separated. Then, by lifting the upper shaft 90A, the lower shaft 90B is left in a state in which the inner shaft male portion 40a protrudes from the upper end of the outer shaft male portion 30a of the lower shaft 90B so that the inner shaft 21 can be easily connected prior to the outer shaft 20.

[0055] The process of removing the inner shaft drop-prevention fitting plate 82 from the lower end of the inner shaft drop-prevention rib 81 and the upper end of the outer shaft male part 30a can be easily performed by the reverse construction process to that described above (lowering the upper shaft 90A relative to the lower shaft 90B -> forming the inner shaft connecting part 40 of the upper shaft 90A and the lower shaft 90B -> raising the inner shaft 21 in conjunction with the raising of the upper shaft 90A -> removing the inner shaft drop-prevention fitting plate 82 from the gap between the inner shaft drop-prevention rib 81 of the lower shaft 90B and the outer shaft male part 30a).

[0056] The inner shaft 21 of the lower shaft 90B is raised within the range of the maximum allowable rise distance S0 so that the inner shaft drop prevention fitting plate 82 can fit between the lower end of the inner shaft drop prevention rib 81 and the upper end of the outer shaft male part 30a. After the inner shaft drop prevention fitting plate 82 is fitted, the inner shaft 21 is supported by the upper end of the outer shaft male part 30a of the outer shaft 20, which is prevented from falling, via the inner shaft drop prevention rib 81 and the inner shaft drop prevention fitting plate 82 (the inner shaft is supported by the upper end of the outer shaft male part, which is prevented from falling, via the inner shaft drop prevention rib and the inner shaft drop prevention fitting plate), and the inner shaft 21 of the lower shaft 90B is prevented from falling and is left in a state in which it does not descend. In the next step of connecting the upper shaft 90A of the joint pile to the remaining lower shaft 90B, the exposed inner shaft male part 40a of the lower shaft 90B and the inner shaft female part 40b of the lowered upper shaft 90A can be easily connected in a visual state to form the inner shaft connecting part 40. As a result, the inner shaft 21 of the upper shaft 90A and the lower shaft 90B form a single shaft and moves in conjunction with the upper shaft 90A. As the upper shaft 90A rises, the inner shaft 21 also rises (rising is permitted), and the inner shaft drop prevention fitting plate 82 can be easily removed. Therefore, it can be said that the inner shaft 21 is supported by the upper end of the outer shaft male part 30a, which is prevented from falling, via the inner shaft drop prevention rib 81 and the inner shaft drop prevention fitting plate 82, and its rising is permitted.

[0057] <Pile construction process> When the improvement length of the excavation axis 9 is insufficient to meet the design improvement length, it is necessary to connect a number of excavation axes 9M (M=1 to N) for joint piles (hereinafter referred to as joint piles) to the excavation axis 9 to satisfy the insufficient improvement length. The construction process for joint piles in Example 8 is composed of the following intermediate processes (A) to (D). (A) Excavation shaft leaving process (a) to (i) in which the excavation shaft 9 from the preceding construction penetrates to the improvement length and is left in place. (B) Step (j) of preparing the drilling shaft for the subsequent pile construction, in which the drilling shaft 9M (M=1) for the pile construction is prepared underground. (C) The joint pile connection process (k) to (u) for connecting the excavation shaft 9 of the preceding construction and the excavation shaft 9M (M = 1) for the joint pile to be constructed subsequently. (D) Restarting the penetration, a penetration restart step (v). Figure 8 shows sub-processes (a) to (d), Figure 9 shows sub-processes (e) to (h), Figure 10 shows sub-processes (i) to (l), Figure 11 shows sub-processes (m) to (p), Figure 12 shows sub-processes (q) to (t), and Figure 13 shows sub-processes (u) to (v).

[0058] <(A) Excavation shaft leaving process (a) to (i), see Figures 8 to 10> (a) The ground improvement device 1 prepares to penetrate the excavation shaft 9 (lower shaft 90B) of the preceding construction into the ground. The ground improvement device 1 used has a leader 3 standing in the Z-axis direction at the front end of an excavator 2 installed on the ground 5, and a rotary drive unit 7 suspended from the upper end of the leader 3 by a wire 6 so that it can rise and fall in the Z-axis direction. The excavation shaft 9 (lower shaft 90B) is connected to the lower part of the rotary drive unit connection shaft 8 (upper shaft 90A) via a connection shaft connecting part 50, and the stirring and mixing part 10 is connected to the lower part of the excavation shaft 9 via a stirring and mixing part connecting part 65. The excavation shaft 9 is supported by a vibration prevention device 4 provided on the leader 3 so that it can rise and fall freely. The selection of various known ground improvement agents and water to be used during penetration is a design matter. (The following is a process of separating the lower shaft connected to the upper shaft and leaving the lower shaft in the ground.)

[0059] (b) The vibration prevention device 4 is installed on the ground 5, and the preceding excavation shaft 9 (lower shaft 90B) is inserted into the ground. When the vibration prevention device 4 is installed on the ground, it is hereinafter referred to as a fall prevention work platform 4, and functions as a fall prevention work platform 4 that supports the outer shaft 20 of the excavation shaft 9 (lower shaft 90B).

[0060] (c) A gap is provided between the outer shaft fall prevention rib 71 of the outer shaft 20 of the drilling shaft 9 (lower shaft 90B) and the fall prevention workbench 4 to insert the outer shaft fall prevention fitting plate 72, thereby stopping the penetration of the previously constructed drilling shaft 9 (lower shaft 90B).

[0061] (d) The outer shaft drop prevention fitting plate 72 is inserted between the outer shaft drop prevention rib 71 of the outer shaft 20 of the drilling shaft 9 (lower shaft 90B) and the drop prevention workbench 4, and then the drilling shaft 9 (lower shaft 90B) is inserted to eliminate the gap, and the outer shaft 20 of the drilling shaft 9 (lower shaft 90B) is supported on the drop prevention workbench 4 to prevent the outer shaft 20 from falling (this is the process of preventing the outer shaft of the lower shaft from falling).

[0062] (e) The outer shaft connecting jig 30d is removed from the outer shaft connecting hole 30c of the outer shaft connecting part 30 that connects the outer shaft 20 of the drilling shaft 9 (lower shaft 90B) to the outer shaft 20 of the rotation drive unit connecting shaft 8 (upper shaft 90A). As a result, the connection between the outer shaft 20 of the drilling shaft 9 (lower shaft 90B) and the outer shaft 20 of the rotation drive unit connecting shaft 8 (upper shaft 90A) is released. In this state, the inner shaft 21 of the drilling shaft 9 (lower shaft 90B) and the inner shaft 21 of the rotation drive unit connecting shaft 8 (upper shaft 90A) are connected by the inner shaft connecting part 40. Therefore, the inner shaft 21 of the upper shaft 90A and the lower shaft 90B constitute a single shaft, and moves in conjunction with the rise and fall of the upper shaft 90A. (This is a process of releasing the connection of the outer shaft connecting part between the upper shaft and the lower shaft.)

[0063] (f) The rotary drive device 7 is wound up with a wire (in the Z-axis positive direction), and the rotary drive device connection shaft 8 (upper shaft 90A) is raised (in the Z-axis positive direction) by, for example, a distance S3 = 700 mm. As a result, the inner shaft 21 of the lower shaft 90B is also raised, and the inner shaft connecting jig 40d of the inner shaft connecting portion 40 between the inner shaft 21 of the lower shaft 90B and the inner shaft 21 of the upper shaft 90A is exposed. In addition, the distance from the upper end of the outer shaft male part 30a to the lower end of the inner shaft drop prevention rib 81 is, for example, a distance S2 = 650 mm. Therefore, a gap distance Sa = 50 mm is secured between the lower end of the inner shaft drop prevention rib 81 of the lower shaft 90B and the upper end of the outer shaft male part 30a. (This is a process of raising the inner shaft of the upper shaft to expose the inner shaft connecting portion between the lower shaft and the upper shaft.)

[0064] (g) Insert the inner shaft drop prevention fitting plate 82 (t = 25 mm) into the gap Sa = 50 mm between the lower end of the inner shaft drop prevention rib 81 of the drilling shaft 9 (lower shaft 90B) and the upper end of the outer shaft male part 30a. (This is the process of inserting the inner shaft drop prevention fitting plate between the inner shaft drop prevention rib of the lower shaft and the upper end of the outer shaft male part that has been prevented from falling by the rise of the inner shaft of the upper shaft.)

[0065] (h) The rotation drive device 7 is lowered slightly (Sb = 25 mm) (in the negative Z-axis direction) to eliminate the gap. The inner shaft 21 of the drilling shaft 9 (lower shaft 90B) is supported on the upper end of the outer shaft male part 30a, preventing the inner shaft 21 of the drilling shaft 9 (lower shaft 90B) from falling. Then, the inner shaft connecting jig 40d is removed from the outer shaft connecting hole 40c of the inner shaft connecting part 40 that connects the inner shaft 21 of the drilling shaft 9 (lower shaft 90B) and the inner shaft 21 of the rotation drive device connection shaft 8 (upper shaft 90A).

[0066] (i) The rotary drive unit 7 is wound up with a wire, the rotary drive unit connection shaft 8 (upper shaft 90A) is raised, and the previously constructed excavation shaft 9 (lower shaft 90B) that has been disconnected and separated is left in the ground.

[0067] The outer shaft 20 of the lower shaft 90B is supported by the fall prevention workbench 4 with the outer shaft fall prevention rib 71 and the outer shaft fall prevention fitting plate. The inner shaft 21 of the lower shaft 90B is supported by the outer shaft male part 30a of the outer shaft 20, the inner shaft fall prevention rib 81, and the inner shaft fall prevention fitting plate 82. Therefore, the preceding excavation shaft 9 (lower shaft 90B) is left in a state where there is no risk of the outer shaft 20 and the inner shaft 21 falling. In addition, the inner shaft male part 40a of the lower shaft 90B is in an exposed state. Therefore, the inner shaft connecting part 40 can be easily connected in a visual state between the inner shaft male part 40a of the lower shaft 90B and the inner shaft female part 40b of the upper shaft 90A that has descended, and the next step of the pile joint connecting step is easy.

[0068] <(B) Preparation of excavation shaft for pile joints (j), see Figure 10> (j) The drilling shaft 91 (M=1) for the subsequent construction is previously connected to the tip of the drilling shaft 91 for the subsequent construction and is inserted into the ground by connecting the drilling head 91H (M=1) of the drilling shaft for the subsequent construction. That is, the drilling head 91H is connected to the drilling shaft 91 for the subsequent construction instead of the mixing and mixing unit 10, and is inserted into the ground. The construction and construction process are the same as those described in the drilling shaft leaving process (a) to (i) for the preceding construction. The outer shaft drop prevention fitting plate 72 is inserted between the outer shaft drop prevention rib 71 of the outer shaft 20 of the drilling shaft 91 for the subsequent construction (lower shaft 90B) and the drop prevention workbench 4, and the outer shaft 20 of the drilling shaft 91 for the subsequent construction (lower shaft 90B) is supported by the drop prevention workbench 4. Between the inner shaft drop prevention rib 81 of the inner shaft 21 of the joint pile drilling shaft 91 (lower shaft 90B) and the upper end of the outer shaft male part 30a, an inner shaft drop prevention fitting plate 82 is inserted, and the inner shaft 21 is supported by the upper end of the outer shaft male part 30a to prevent it from falling. (The following is a process in which the upper shaft is connected to the lower shaft that has been left in the ground and has been prevented from falling, with both the outer shaft and the inner shaft prevented from falling.)

[0069] <(C) Pile connection process (k)~(u), see Figures 10~13> (k) With the rotary drive unit connection shaft 8 (upper shaft 90A) attached to the lower end of the rotary drive unit 7 of the excavator 2, it is moved directly above the joint pile excavation shaft 91 (lower shaft 90B) for subsequent construction that is installed in the ground. Next, the rotary drive unit connection shaft 8 (upper shaft 90A) is lowered (Z-axis minus direction). Then, the inner shaft female part 40b protruding downward from the outer shaft female part 30b of the rotary drive unit connection shaft 8 (upper shaft 90A) and the inner shaft male part 40a protruding upward from the outer shaft male part 30a of the joint pile excavation shaft (lower shaft 90B) are connected by the inner shaft connecting jig 40d to form the inner shaft connecting part 40. As a result, the rotary drive unit connection shaft 8 (upper shaft 90A) and the inner shaft 21 of the joint pile excavation shaft 91 (lower shaft 90B) for subsequent construction can be easily connected by the inner shaft connecting part 40. Therefore, the inner shaft 21 of the upper shaft 90A and the lower shaft 90B constitute a single shaft, which moves in conjunction with the upward and downward movement of the upper shaft 90A. (This is the process of lowering the upper shaft and connecting the inner shaft female part of the upper shaft and the inner shaft male part of the lower shaft to form the inner shaft connecting part.)

[0070] (l) The rotary drive unit 7 is wound up with the wire 6 (in the positive direction of the Z axis), and the rotary drive unit connection shaft 8 (upper shaft 90A) is raised slightly. This causes the inner shaft 21 of the joint pile drilling shaft 91 (lower shaft 90B) to rise in tandem. A gap is formed between the upper end of the outer shaft male part 30a and the lower end of the inner shaft drop prevention rib 81, and the inner shaft drop prevention fitting plate 82 can be easily removed from between the upper end of the outer shaft male part 30a and the lower end of the inner shaft drop prevention rib 81. (This is the process of raising the inner shaft of the upper shaft and removing the inner shaft drop prevention fitting plate from between the inner shaft drop prevention rib of the lower shaft and the upper end of the outer shaft male part that has been prevented from falling.)

[0071] (m) The wire 6 is wound down to lower the rotary drive unit 7 (upper shaft 90A) a predetermined distance. The outer shaft female part 30b of the rotary drive unit connection shaft 8 (upper shaft 90A) and the outer shaft male part 30a of the joint pile drilling shaft 91 (lower shaft 90B) are connected with the outer shaft connecting jig 30d to form the outer shaft connecting part 30.

[0072] (n) By winding up the wire 6, the rotary drive unit connection shaft 8 (upper shaft 90A) can be slightly raised, and the outer shaft drop prevention fitting plate 72 between the outer shaft drop prevention rib 71 of the joint pile drilling shaft 91 (lower shaft 90B) and the drop prevention workbench 4 can be easily removed.

[0073] (o) The rotary drive unit 7 rotates and raises the joint pile drilling shaft 91 (lower shaft 90B) connected to the rotary drive unit connection shaft 8 (upper shaft 90A) to the ground. After that, the drilling head 91H of the joint pile drilling shaft at the tip of the joint pile drilling shaft 91 (lower shaft 90B) is removed. At that time, before removing the inner shaft connecting jig 40d of the inner shaft connecting part 40 of the stirring and mixing unit connecting part 65, the inner shaft drop prevention fitting plate 82 is inserted between the drilling head 91H and the fall prevention workbench 4, and the drilling head 91H is supported by the fall prevention workbench 4.

[0074] In the case of the following pile drilling shaft 91 (lower shaft 90B), the inner shaft 21 can be easily constructed into a single shaft by connecting the upper shaft 90A and the lower shaft 90B with the inner shaft connecting jig 40. Therefore, the inner shaft drop prevention fitting plate 82 and the outer shaft drop prevention fitting plate can be removed by the upward and downward movement of the upper shaft 90A, and the pile drilling shaft 91 can be easily connected to the rotary drive device connecting shaft 8.

[0075] (p) The excavator 2 is moved with the joint pile drilling shaft 91 for subsequent construction connected to the rotary drive device connection shaft 8. Note that from the following process onwards, the joint pile drilling shaft 91 becomes the upper shaft 90A.

[0076] (q) With the pile drilling shaft 91 (upper shaft 90A) connected to the rotary drive device connection shaft 8, it is moved to a position directly above the remaining drilling shaft 9 (lower shaft 90B). (The following is a process in which the upper shaft is connected to the lower shaft that was left in the ground and both the outer shaft and the inner shaft were prevented from falling.)

[0077] (r) The wire 6 is lowered, and the inner shaft female part 40b protruding from the outer shaft female part 30b at the bottom of the joint pile excavation shaft 91 (upper shaft 90A) is connected with the inner shaft connecting jig 40d to the inner shaft male part 40a protruding from the outer shaft male part 30a at the top of the excavation shaft 9 (lower shaft 90B) left behind in the previous construction, thereby forming the inner shaft connecting part 40. Thus, the inner shafts 21 of the upper shaft 90A and the lower shaft 90B form a single shaft, which moves in conjunction with the rise and fall of the upper shaft 90A. (This is the process of lowering the upper shaft and connecting the inner shaft female part of the upper shaft to the inner shaft male part of the lower shaft to form the inner shaft connecting part.)

[0078] (s) The wire 6 is wound up to slightly raise the pile drilling shaft 91 (upper shaft 90A). As a result, the inner shaft 21 of the drilling shaft 9 (lower shaft 90B) also rises, forming a gap between the inner shaft drop prevention rib 81 and the upper end of the outer shaft male part 30a, and the inner shaft drop prevention fitting plate 82 between the upper end of the outer shaft male part 30a and the lower end of the inner shaft drop prevention rib 81 can be easily removed. (This is the process of raising the inner shaft of the upper shaft and removing the inner shaft drop prevention fitting plate from between the inner shaft drop prevention rib of the lower shaft and the upper end of the outer shaft male part that has been prevented from falling.)

[0079] (t) The wire 6 is lowered, and the outer shaft female part 30b at the bottom of the drilling shaft 91 (upper shaft 90A) for the following pile to be constructed and the outer shaft male part 30a at the top of the drilling shaft 9 (lower shaft 90B) left behind in the preceding construction are connected by the outer shaft connecting jig 30d to form the outer shaft connecting part 30. Thus, the drilling shaft 91 (upper shaft 90A) for the following pile to be constructed and the drilling shaft 9 (lower shaft 90B) left behind in the preceding construction are configured as a single shaft 90 by the drilling shaft connecting part 60 (outer shaft connecting part 30 / inner shaft connecting part 40).

[0080] (u) By slightly winding up the wire 6, the outer shaft drop prevention fitting plate 72 that was left between the outer shaft drop prevention rib 71 of the outer shaft 20 of the remaining drilling shaft 9 (lower shaft 90B) and the drop prevention workbench 4 can be easily removed.

[0081] In the connecting process of connecting the following pile drilling shaft 91 (upper shaft 90A) to the preceding drilling shaft 9 (lower shaft 90B) left in a state where there is no risk of the outer shaft 20 and the inner shaft 21 falling, the inner shaft 21 of the upper shaft 90A and the lower shaft 90B are easily connected by the inner shaft connecting part 40, and then the inner shaft 21 is raised in conjunction with the upper shaft 90A, so that the inner shaft drop prevention fitting plate 82 of the lower shaft 90B can be easily removed. Furthermore, by lowering the upper shaft 90A, the outer shaft 20 of the upper shaft 90A and the lower shaft 90B can be easily connected by the outer shaft connecting part 30. Therefore, the outer shaft 20 is raised in conjunction with the upper shaft 90A, so that the outer shaft drop prevention fitting plate 72 of the lower shaft 90B can be easily removed. Then, a single excavation shaft 90 is completed by connecting the joint pile excavation shaft 91 (upper shaft 90A) to the previously constructed excavation shaft 9 (lower shaft 90B) as a joint pile.

[0082] <(D) Penetration restart process (v), see Figure 13> (v) Penetration is resumed using a single excavation shaft 90 in which a joint excavation shaft 91 (upper shaft 90A) is connected as a joint pile to the excavation shaft 9 (lower shaft 90B) of the previously constructed excavation shaft 9.

[0083] <When pulling out the piles> When pulling out the pile, the drilling shaft 9M (M=1 to N) for the joint pile that was connected during penetration can be easily removed by following the reverse procedure.

[0084] Fig. 14 shows a ground improvement device 1 (Example 9) configured with a shaft 90 in which M = 3 drilling shafts M for joint piles are connected to an excavation shaft 9, as an example, using the connection structure and connection method of the shaft 90 of the ground improvement device 1 described above. When the improvement length of the excavation shaft 9 of the preceding construction is insufficient to meet the designed improvement length, the number of drilling shafts 9M for joint piles (M = 1 to N) of the succeeding construction that meet the insufficient improvement length can be connected, and improvement construction to the designed improvement length can be easily performed. [Explanation of symbols]

[0085] 1 Ground improvement equipment 2. Excavator 3. Leader 4 Anti-vibration device (when installed on the ground: fall prevention workbench) 4a Groove 5 Ground 6 Wire 7 Rotational drive unit 8 Rotation drive unit connection shaft 9 Drilling axis 9M Drilling shaft for connecting pile (M=1~N) 9MH Drilling head for pile drilling shaft (M=1~N) 90 Axis 90A upper shaft 90B lower shaft 10 Stirring and mixing section 20 Outer shaft 20a external helical wing 21 Inner shaft 22 Upper mixing blade 23 Lower mixing blade 24 Auxiliary mixing blade 24a upper horizontal wing 24b lower horizontal wing 24c Double vertical wings 25 Digging blade 30 Outer shaft connection part 30a Outer shaft male part 30b Outer shaft female part 30c Outer shaft connection hole 30d Outer shaft connection jig 40 Inner shaft connection part 40a Inner shaft male part 40b Inner shaft female part 40c Inner shaft connection hole 40d Inner shaft connection jig 50 Connection shaft joint 60 Drilling shaft connection part 65 Stirring and mixing section connection 70 Outer shaft drop (co-rise) prevention device 71 Outer shaft drop prevention rib 72 Outer shaft drop (together rise) prevention fitting plate 73 Outer shaft anti-lift rib 80 Inner shaft drop prevention device 81 Inner shaft drop prevention rib 82 Inner shaft drop prevention fitting plate

Claims

1. A connection structure of the shaft of a ground improvement device, in which an outer shaft and an inner shaft are configured in a double tube shape, the outer shaft and the inner shaft are rotated in relatively opposite directions by a rotary drive device, and a shaft is formed by connecting a plurality of the outer shafts and the inner shafts vertically, and the shaft is inserted into the ground. The outer shaft has an outer shaft male part at an upper end and an outer shaft female part at a lower end, and has an outer shaft drop prevention rib below the outer shaft male part, When the outer shafts are connected vertically, the outer shaft male portion and the outer shaft female portion are connected to each other to form an outer shaft connecting portion of an upper shaft and a lower shaft, the inner shaft includes an inner shaft male portion inside the outer shaft male portion and an inner shaft female portion inside the outer shaft female portion, and has an inner shaft drop prevention rib below the inner shaft male portion, When the plurality of inner shafts are vertically connected, the inner shaft male portion and the inner shaft female portion are connected to each other to form an inner shaft connecting portion between the upper shaft and the lower shaft, A shaft connecting structure for a ground improvement device, characterized in that the inner shaft is supported on the upper end of the outer shaft male part, which is prevented from falling, via the inner shaft fall prevention rib and the inner shaft fall prevention fitting plate, and is allowed to rise.

2. The lower end of the shaft is provided with a stirring and mixing section, The stirring and mixing section is provided with a lower stage stirring blade at the lower end of the outer shaft and an auxiliary stirring blade at the lower end of the inner shaft, the maximum allowable lift distance of the inner shaft is the distance between the lower end of the lower stage stirring blade and the upper end of the lower horizontal blade that constitutes the auxiliary stirring blade, and the distance between the lower end of the inner shaft fall prevention rib and the upper end of the outer shaft male part does not exceed the maximum allowable lift distance.

3. The shaft connecting structure of a ground improvement device described in claim 1, characterized in that an outer shaft anti-fall rib is provided below the outer shaft anti-fall rib, and is fitted into a groove of a fall prevention work table via an outer shaft anti-fall and anti-rise fitting plate, thereby preventing the outer shaft from rising together with the rise of the inner shaft.

4. A method for connecting the shafts of a ground improvement device, comprising: configuring an outer shaft and an inner shaft into a double tube shape; rotating the outer shaft and the inner shaft in relatively opposite directions using a rotary drive device; connecting a plurality of the outer shafts and the inner shafts vertically to form a shaft; and penetrating the shaft into the ground; The outer shaft has an outer shaft male part at an upper end and an outer shaft female part at a lower end, and has an outer shaft drop prevention rib below the outer shaft male part, When the outer shafts are connected vertically, the outer shaft male portion and the outer shaft female portion are connected to each other to form an outer shaft connecting portion of an upper shaft and a lower shaft, the inner shaft includes an inner shaft male portion inside the outer shaft male portion and an inner shaft female portion inside the outer shaft female portion, and has an inner shaft drop prevention rib below the inner shaft male portion, When the plurality of inner shafts are vertically connected, the inner shaft male portion and the inner shaft female portion are connected to each other to form an inner shaft connecting portion between the upper shaft and the lower shaft, The inner shaft is supported on the upper end of the outer shaft male part, which is prevented from falling, via the inner shaft drop prevention rib and the inner shaft drop prevention fitting plate, and is allowed to rise. Using the shaft connection structure of the ground improvement device, The step of separating the lower shaft connected to the upper shaft and leaving the lower shaft in the ground includes: a step of preventing the outer shaft from dropping from the lower shaft; releasing the connection of the outer shaft connecting portion between the upper shaft and the lower shaft; lifting the inner shaft of the upper shaft to expose the inner shaft connection portion between the lower shaft and the upper shaft; A method for connecting shafts of a ground improvement device, comprising at least a step of inserting the inner shaft drop prevention fitting plate between the inner shaft drop prevention rib of the lower shaft and the upper end of the outer shaft male part that has been prevented from falling, by raising the inner shaft of the upper shaft.

5. A method for connecting the shafts of a ground improvement device, comprising: configuring an outer shaft and an inner shaft into a double tube shape; rotating the outer shaft and the inner shaft in relatively opposite directions using a rotary drive device; connecting a plurality of the outer shafts and the inner shafts vertically to form a shaft; and penetrating the shaft into the ground; The outer shaft has an outer shaft male part at an upper end and an outer shaft female part at a lower end, and has an outer shaft drop prevention rib below the outer shaft male part, When the outer shafts are connected vertically, the outer shaft male portion and the outer shaft female portion are connected to each other to form an outer shaft connecting portion of an upper shaft and a lower shaft, the inner shaft includes an inner shaft male portion inside the outer shaft male portion and an inner shaft female portion inside the outer shaft female portion, and has an inner shaft drop prevention rib below the inner shaft male portion, When the plurality of inner shafts are vertically connected, the inner shaft male portion and the inner shaft female portion are connected to each other to form an inner shaft connecting portion between the upper shaft and the lower shaft, The inner shaft is supported on the upper end of the outer shaft male part, which is prevented from falling, via the inner shaft drop prevention rib and the inner shaft drop prevention fitting plate, and is allowed to rise. Using the shaft connection structure of the ground improvement device, The step of connecting the upper shaft to the lower shaft, which is left in the ground while preventing the outer shaft and the inner shaft from falling, includes: a step of lowering the upper shaft and connecting the inner shaft female portion of the upper shaft and the inner shaft male portion of the lower shaft to form the inner shaft connecting portion; A method for connecting shafts of a ground improvement device, comprising at least a step of raising the inner shaft of the upper shaft and removing the inner shaft drop prevention fitting plate from between the inner shaft drop prevention rib of the lower shaft and the upper end of the outer shaft male part that has been prevented from falling.

Images