Shaft connection structure and connection method for ground improvement device

Abstract

This invention provides a connection structure and method for the shaft of a ground improvement device that connects the upper and lower parts of a double-walled pipe. [Solution] The shaft of a ground improvement device is configured in a double-tube shape with an outer shaft 20 and an inner shaft 21, which are rotated in opposite directions, and multiple outer shafts and inner shafts are connected vertically to form a shaft 90. The outer shaft has an outer shaft male part 30a at its upper end and an outer shaft female part 30b at its lower end, and an inner shaft fall prevention bolt screw hole 85 and an outer shaft fall prevention rib 71 on the upper end side, forming an outer shaft connection part 30 when the outer shafts are connected. The inner shaft has an inner shaft male part 40a inside the outer shaft male part, an inner shaft female part 40b below the outer shaft female part, and an inner shaft fall prevention rib 82 and an inner shaft protection plate 83 below the inner shaft male part, forming an inner shaft connection part 40 when the inner shafts are connected. When the inner shaft connection part is released, an inner shaft fall prevention bolt 81 is screwed into the inner shaft fall prevention bolt screw hole, and the pressing force from the screwing acts on the inner shaft protection plate, preventing the inner shaft from falling.

Description

Technical Field

[0001] The present invention relates to a connecting structure and a connecting method for a shaft of a ground improvement device, which is configured as a double tube with an outer shaft and an inner shaft, and the outer shaft and the inner shaft are relatively rotated in opposite directions by a rotation driving device, and a plurality of outer shafts and inner shafts are vertically connected to form a shaft, and a stirring and mixing part is provided at the lower end of the shaft. And it belongs to the deep mixing treatment method.

Background Art

[0002] In a ground improvement device in which a drilling shaft is formed as a double tube with an inner and outer shaft, the inner shaft is accommodated inside the outer shaft. Therefore, when extending the double tube of the inner and outer shafts, while holding the lower inner shaft structure and the lower outer shaft structure whose connection to the rotation driving device has been released, the upper inner shaft structure and the upper outer shaft structure to be connected are connected at the connection part, which is a complicated operation. For this reason, those related to the release and connection of the lower inner shaft structure and the lower outer shaft structure, and those related to the connection part, etc. have been developed.

[0003] In Patent Document 1, the drilling shaft 9 (lower shaft 90B) and the rotation drive device connection shaft 8 (upper shaft 90A) include a tubular outer shaft 20 and a tubular inner shaft 21 rotatably and vertically movable disposed inside the outer shaft 20. When separating the lower shaft 90B and the upper shaft 90A, after preventing the fall of the outer shaft 20 of the lower shaft 90B, the outer shaft connection part 30 between the outer shaft of the lower shaft 90B and the outer shaft of the upper shaft 90A is released, and the inner shaft connection part 40 between the inner shaft 21 of the lower shaft 90B and the inner shaft of the upper shaft 90A is connected and raised by a predetermined distance S3. An inner shaft fall prevention fitting plate is inserted into the gap Sa between the lower end of the inner shaft fall prevention rib 81 of the lower shaft 90B and the upper end of the outer shaft male part 30a of the outer shaft 20, and then lowered so that the inner shaft 21 of the lower shaft 90B is supported by the upper end of the outer shaft male part 30a and the fall is prevented. After that, the inner shaft connection part 40 is released, and the separation of the inner shaft 21 of the upper shaft 90A from the inner shaft 21 of the lower shaft 90B is completed. When connecting the pile driving drilling shaft 9M to the drilling shaft 9 (lower shaft 90B), it is described that it is performed in the reverse procedure of separation.

[0004] Patent Document 2 describes a ground improvement device 1 in which the excavation shaft 13 is formed as a double-pipe structure of inner and outer shafts 15 and 16. When the excavation shaft 13 is detached, a support plate 55 is interposed between the flange 52 of the outer shaft component 36 embedded in the ground and the ground 54 to fix the outer shaft component 36, exposing the insertion hole 48 and through hole 49 of the outer shaft component 36. A connecting jig 53 is inserted through the through hole 49, and the locking groove 42 of the inner shaft component 35 and the through hole 49 of the outer shaft component 36 are locked together by the connecting jig 53. The inner and outer shaft components 35 and 36 can be separated vertically by removing the connecting pin 47 from the connecting hole 46 of the outer shaft component 36 and removing the connecting pin 41 of the inner shaft component 35 from the insertion hole 48 of the outer shaft component 36. Since the inner shaft component 35 is connected to the outer shaft component 36 which is fixed to the ground 54, it is possible to prevent the inner shaft component 35 from falling due to its own weight. When connecting the excavation shaft 13, the procedure is to be the reverse of the separation procedure described above.

[0005] Patent Document 3 describes how the excavation depth of the ground is increased 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 stirring shaft 8, the outer shaft drive device 9 is pulled up, the upper end of the upper shaft 8a is retracted into the support cylinder portion 10b of the inner shaft drive device 4, the lower shaft 8b descends due to its own weight, the outer shaft side stopper piece 27 engages with the inner shaft side stopper piece 28 (Figure 5), the connecting ends of the upper shaft 8a and the lower shaft 8b of the stirring shaft 8 are separated (space S), and the connecting portion of the excavation thread 6 connected by the detachable pin 15 is exposed, and in this state The procedure involves removing the attachment pin 15 of the drilling shaft 6, releasing the connection between the upper shaft 6a and the lower shaft 6b, raising the upper shaft 6a of the drilling shaft 6 and the upper shaft 8a of the stirring shaft 8, which are integrated with the inner shaft drive unit 4 and the outer shaft drive unit 9, to the required height, inserting and positioning a shaft for extending the drilling shaft between the upper shaft 6a and the lower shaft 6b of the drilling shaft 6 while holding it with a wire or the like, and connecting them with an attachment pin, and inserting and connecting a shaft for extending the drilling shaft between the upper shaft 8a and the lower shaft 8b of the stirring shaft 8 in the same manner as described above, and then further excavating the ground.

[0006] Patent Document 4 describes an excavation shaft member fixing device 51 having an excavation shaft member holding part 55 that holds the upper ends of the excavation shaft members 13 and 15 whose lower parts have entered the hole due to excavation of the ground, the upper ends that protrude from the upper surface of the ground, a ground surface contact part 57 that contacts the ground, and a positioning part 59 (composed of a cylindrical part 63, a wedge 65, and a bolt 67) that positions the upper ends of the excavation shaft members 13 and 15, and the excavation shaft member fixing device 51 is located between the rotary drive device 11 and the stirring blade 23 in the vertical direction, and the excavation shaft member fixing device 51 is suspended by a wire 81, and excavation The description states that the drilling shaft member 15 is rotated and lowered to excavate a hole H1, the drilling shaft member fixing device 51 is lowered to a position slightly above the ground level (GL), and at the positioning section 59, a wedge 65 is inserted into the gap to position the upper ends of the drilling shaft members 13 and 15 relative to the cylindrical section 63, and the positioning state is maintained by radially arranged bolts 67, and then the drilling shaft member 15 is detached from the rotary drive device 11, and the drilling shaft member fixing device 51 and the drilling shaft member 15 are lowered slightly to position and install the drilling shaft member fixing device 51 at the ground level (GL). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 7385788 [Patent Document 2] Japanese Patent Publication No. 2009-249921 [Patent Document 3] Official Gazette No. 3-79331 [Patent Document 4] Japanese Patent Publication No. 2017-166134 [Overview of the project] [Problems that the invention aims to solve]

[0008] Conventionally, the invention described in Patent Document 1 requires raising the inner shaft connecting portion 40 by a predetermined distance S3 while it is connected, inserting the inner shaft fall prevention fitting plate into the gap Sa between the lower end of the inner shaft fall prevention rib 81 of the lower shaft 90B and the upper end of the outer shaft male portion 30a, and then lowering it to support the inner shaft 21 of the lower shaft 90B on the upper end of the outer shaft male portion 30a. This requires raising and lowering by a predetermined distance, making the connection work time-consuming. The invention described in Patent Document 2 requires inserting a connecting jig 53 through the outer through hole 49 of the outer shaft component 36, locking the locking groove 42 of the inner shaft component 35 with the through hole 49 of the outer shaft component 36, and connecting the inner shaft component 35 and the outer shaft component 36 to restrict vertical movement. This requires a complex and precise operation, making the connection work difficult. The invention described in Patent Document 3 involves a complex process of raising the outer shaft drive unit 9, retracting the upper end of the upper shaft 8a, allowing the lower shaft 8b to descend under its own weight and engage with the stopper pieces 27 and 28, separating the connecting ends of the upper shaft 8a and lower shaft 8b of the stirring shaft 8, removing the attachment / detachment pin 15 of the drilling shaft 6, releasing the connection between the upper shaft 6a and lower shaft 6b, raising the inner shaft drive unit 4 and outer shaft drive unit 9 to the required height, and individually inserting and connecting the drilling shaft 6 and stirring shaft 8. This process requires the separate inner shaft drive unit 4 and outer shaft drive unit 9, resulting in a large device. The invention described in Patent Document 4 relates to a single-axis drilling member fixing device 51. When adding a single-axis rotating member, a complex work procedure was required in which the positioning state was maintained by a cylindrical part 63, a wedge 65, and a bolt 67 while the device was slightly above the ground level (GL), and the drilling shaft member fixing device 51 and the drilling shaft member 15 were slightly lowered to position and install them at the ground level.

[0009] The present invention has been made in view of the above problems, and aims to provide a shaft connection structure and connection method for a ground improvement device that allows connection and disconnection of shafts configured as a double tube by an outer shaft and an inner shaft with a simple configuration, without requiring operation of the inner shaft from the outside of the outer shaft by a complex and sophisticated mechanism, and without requiring any special equipment. [Means for solving the problem]

[0010] The invention according to claim 1 of this application is a shaft connection structure for a ground improvement device, wherein the shaft is configured in a double-tubular shape with an outer shaft and an inner shaft, the outer shaft and the inner shaft are rotated in relatively opposite directions by a rotary drive device, and a plurality of the outer shafts and inner shafts are connected vertically to form a shaft, and the shaft is driven into the ground, wherein the outer shaft has an outer shaft male part at the upper end and an outer shaft female part at the lower end, and below the outer shaft male part there is an inner shaft fall prevention bolt screw hole and an outer shaft fall prevention rib, and when a plurality of the outer shafts are connected vertically, the outer shaft male part and the outer shaft female part are connected to form an outer shaft connection part between the upper shaft and the lower shaft, the inner shaft has an inner shaft male part inside the outer shaft male part and an inner shaft female part below the outer shaft female part, and below the inner shaft male part there is an inner shaft protection plate protruding from the inner shaft surface and the inner shaft protection plate Between the male part of the inner shaft, The shaft connection structure for a ground improvement device is characterized by having an inner shaft fall prevention rib that protrudes outward from the inner shaft protection plate, and when multiple inner shafts are connected vertically, the male part of the inner shaft and the female part of the inner shaft are connected to form an inner shaft connection part between the upper shaft and the lower shaft, and when the inner shaft connection part is released, an inner shaft fall prevention bolt is screwed into the inner shaft fall prevention bolt screw hole of the outer shaft which is prevented from falling, the tip of the inner shaft fall prevention bolt comes into contact with the surface of the inner shaft protection plate, and the pressing force caused by the screwing of the inner shaft fall prevention bolt with the outer shaft as a reaction force acts on the inner shaft protection plate, thereby preventing the inner shaft from falling.

[0011] The invention according to claim 2 of this application is a shaft connection structure for a ground improvement device according to claim 1, characterized in that the inner shaft further comprises an inner shaft rise prevention rib disposed below the inner shaft protection plate and protruding outward from the inner shaft protection plate.

[0012] The invention according to claim 3 of this application is provided with a stirring and mixing section at the lower end of the shaft of the rotary drive device, the stirring and mixing section having an outer shaft stirring blade at the lower end of the outer shaft and an inner shaft stirring blade at the lower end of the inner shaft, the inner shaft having a permissible travel distance that allows the inner shaft stirring blade to move up and down relative to the outer shaft stirring blade, and being supported by a wire connected to the rotary drive device so as to be able to move up and down within the range of the permissible travel distance. When the inner shaft connecting portion begins to make contact with the outer shaft connecting portion due to the upward movement within the range of the allowable travel distance, connection is possible without interference with the outer shaft connecting portion.The inner shaft was moved upward to the upper limit of the allowable travel distance. Later, when the internal shaft connection is released, the fall is prevented. The shaft connection structure of the ground improvement device according to feature 1.

[0013] The invention according to claim 4 of this application is a shaft connection structure for a ground improvement device according to claim 1, characterized in that it is equipped with an inner shaft helical blade and / or a compressed air discharge mechanism for preventing fluidized mixed soil from entering the gap between the inner shaft and the outer shaft.

[0014] The invention according to claim 5 of this application is a method for connecting the shaft connection structure of a ground improvement device, wherein the shaft is configured in a double-tubular shape with an outer shaft and an inner shaft, the outer shaft and the inner shaft are rotated in relatively opposite directions by a rotary drive device, and a plurality of the outer shafts and inner shafts are connected vertically to form a shaft, and the shaft is driven into the ground, wherein the outer shaft has an outer shaft male part at its upper end and an outer shaft female part at its lower end, and below the outer shaft male part there is an inner shaft fall prevention bolt screw hole and an outer shaft fall prevention rib, and when a plurality of the outer shafts are connected vertically, the outer shaft male part and the outer shaft female part are connected to form an outer shaft connection part between the upper shaft and the lower shaft, the inner shaft has an inner shaft male part inside the outer shaft male part and an inner shaft female part below the outer shaft female part, and below the inner shaft male part there is an inner shaft protection plate protruding from the inner shaft surface and the inner shaft protection plate Between the male part of the inner shaft,The inner shaft has an inner shaft fall prevention rib that protrudes outward from the inner shaft protection plate, and when multiple inner shafts are connected vertically, the male and female parts of the inner shaft are connected to form an inner shaft connection part between the upper shaft and the lower shaft, and when the inner shaft connection part is released, the inner shaft fall prevention bolt is screwed into the inner shaft fall prevention bolt screw hole of the outer shaft which is prevented from falling, the tip of the inner shaft fall prevention bolt comes into contact with the surface of the inner shaft protection plate, and the pressing force from the screwing of the inner shaft fall prevention bolt, with the outer shaft as the reaction force, acts on the inner shaft protection plate, thereby preventing it from falling, and the upper shaft is connected The method for connecting the shaft connection structure of a ground improvement device is characterized in that the step of separating the connected lower shaft and leaving the lower shaft in the ground includes at least the steps of preventing the outer shaft of the lower shaft from falling, releasing the connection of the outer shaft connection portion between the upper shaft and the lower shaft, and screwing the inner shaft fall prevention bolt into the inner shaft fall prevention bolt screw hole of the outer shaft from which the fall has been prevented, bringing the tip of the inner shaft fall prevention bolt into contact with the surface of the inner shaft protection plate, and using the outer shaft as a reaction force, the pressing force caused by screwing the inner shaft fall prevention bolt onto the inner shaft protection plate to prevent the inner shaft from falling.

[0015] The invention according to claim 6 of this application relates to a shaft connection structure of the ground improvement device, wherein the shaft is provided with a stirring and mixing section at the lower end, the stirring and mixing section has an outer shaft stirring blade at the lower end of the outer shaft and an inner shaft stirring blade at the lower end of the inner shaft, and the inner shaft has a permissible travel distance that allows the inner shaft stirring blade to move up and down relative to the outer shaft stirring blade. When the inner shaft connecting portion begins to make contact with the outer shaft connecting portion due to the upward movement within the range of the allowable travel distance, connection is possible without interference with the outer shaft connecting portion. The method for connecting the shaft connection structure of a ground improvement device according to claim 5 is characterized in that the step of separating the lower shaft connected to the upper shaft and leaving the lower shaft in the ground further includes the step of raising the inner shaft to the upper limit of the allowable movement distance.

[0016] The invention according to claim 7 of this application is a method for connecting the shaft connection structure of a ground improvement device, wherein the shaft is configured in a double-tubular shape with an outer shaft and an inner shaft, the outer shaft and the inner shaft are rotated in relatively opposite directions by a rotary drive device, and a plurality of the outer shafts and inner shafts are connected vertically to form a shaft, and the shaft is driven into the ground, wherein the outer shaft has an outer shaft male part at its upper end and an outer shaft female part at its lower end, and below the outer shaft male part there is an inner shaft fall prevention bolt screw hole and an outer shaft fall prevention rib, and when a plurality of the outer shafts are connected vertically, the outer shaft male part and the outer shaft female part are connected to form an outer shaft connection part between the upper shaft and the lower shaft, the inner shaft has an inner shaft male part inside the outer shaft male part and an inner shaft female part below the outer shaft female part, and below the inner shaft male part there is an inner shaft protection plate protruding from the inner shaft surface and the inner shaft protection plate Between the male part of the inner shaft, The inner shaft has an inner shaft fall prevention rib that protrudes outward from the inner shaft protection plate, and when multiple inner shafts are connected vertically, the male and female parts of the inner shaft are connected to form an inner shaft connection between the upper and lower shafts, and when the inner shaft connection is released, the inner shaft fall prevention bolt is screwed into the inner shaft fall prevention bolt screw hole of the outer shaft which is prevented from falling, the tip of the inner shaft fall prevention bolt abuts against the surface of the inner shaft protection plate, and the pressing force from screwing in the inner shaft fall prevention bolt with the outer shaft as a reaction force protects the inner shaft The method for connecting the shaft connection structure of a ground improvement device is characterized in that, by acting on the plate, the falling is prevented, and the upper shaft is connected to the lower shaft which is left in the ground with both the outer shaft and the inner shaft prevented from falling, and the steps of lowering the upper shaft and connecting the female inner shaft portion of the upper shaft to the male inner shaft portion of the lower shaft to form the inner shaft connection portion, and unscrewing the inner shaft fall prevention bolt that prevents the inner shaft from falling from the inner shaft fall prevention bolt screw hole of the lower shaft. [Effects of the Invention]

[0017] According to the present invention, when connecting and disconnecting the outer shafts of the upper and lower shafts, the outer shaft of the lower shaft can be easily prevented from falling by the outer shaft fall prevention rib. Furthermore, the inner shaft fall prevention bolt, which is screwed into the inner shaft fall prevention bolt helical hole provided on the outer shaft whose fall prevention is prevented, can be screwed into and pressed against the inner shaft protection plate directly below the inner shaft fall prevention rib, thereby easily preventing the inner shaft from falling. Even if the tip position of the inner shaft fall prevention bolt is misaligned, the inner shaft fall prevention rib can prevent it from falling. Furthermore, the invention described in Patent Document 1 is a structure in which, when separating the lower shaft 90B and the upper shaft 90A, the inner shaft 21 is raised by a predetermined distance S3 while still connected, and an inner shaft fall prevention fitting plate is inserted into the lower end of the inner shaft fall prevention rib 81 and supported on the upper end of the outer shaft male part 30a. It does not include an inner shaft fall prevention bolt, an inner shaft protection plate, or an inner shaft fall prevention rib, and is clearly different from the present invention. The invention described in Patent Document 2 is a structure in which a connecting jig 53 (corresponding to the inner shaft fall prevention bolt of the present invention) is inserted through the outer through hole 49 of the outer shaft component 36 (corresponding to the outer shaft connecting part of the present invention), and the locking groove 42 of the inner shaft component 35 (corresponding to the inner shaft connecting part of the present invention) is locked with the through hole 49 of the outer shaft component 36, thereby connecting the inner shaft component 35 and the outer shaft component 36 and restricting vertical movement. It does not include an inner shaft fall prevention bolt, an inner shaft protection plate, or an inner shaft fall prevention rib, and is clearly different from the present invention. As described in paragraph 5, the differences between the invention described in Patent Document 3 and the present invention are clear, so a comparison of the specific features of the invention will be omitted. The invention described in Patent Document 4 relates to a positioning part 59 at the upper end of a single-axis drilling shaft member 13, 15 (corresponding to the inner shaft). The positioning part 59 of the drilling shaft member fixing device 51 is suspended by a wire 81 and, while slightly above the ground level (GL), maintains a position relative to the cylindrical part 63 (corresponding to the outer shaft) by a wedge 65 and a bolt 67 (corresponding to the inner shaft fall prevention bolt), and is then lowered and installed on the ground level. The purpose and problem is to position the drilling shaft members 13, 15, not to prevent them from falling, and the solution is the combined use of "wedge 65 and bolt 67". Since the drilling shaft members 13, 15 are single-axis, there is no outer shaft, and the drilling shaft members 13, 15 do not have an inner shaft protection plate or an inner shaft fall prevention rib. Therefore, the purpose, problem and solution are clearly different from the present invention.

[0018] In addition, an anti-ascending rib of the inner shaft disposed directly below the inner shaft protection plate prevents the inner shaft from ascending.

[0019] In addition, the stirring and mixing unit includes an outer shaft stirring blade and an inner shaft stirring blade, and the inner shaft raised to the upper limit of the allowable movement distance is fixed by an inner shaft falling prevention bolt. Therefore, when connecting the upper shaft and the lower shaft, the end of the inner shaft male part raised by the allowable movement distance of the lower shaft first contacts the end of the inner shaft female part of the upper shaft with respect to the end of the outer shaft female part and the end of the inner shaft female part of the upper shaft. At this time, the end of the outer shaft female part of the upper shaft and the end of the outer shaft male part of the lower shaft are separated by the allowable movement distance. For this reason, the inner shaft female part of the upper shaft can be easily and accurately connected to the inner shaft male part of the lower shaft without being affected by the outer shaft connection part.

[0020] In addition, the fluidized mixed soil is prevented from entering between the inner shaft and the outer shaft by the inner shaft spiral blade and / or the compressed air discharge mechanism.

[0021] According to the present invention, in the step of leaving the lower shaft in the ground, the fall of the outer shaft of the lower shaft is prevented, the tip of the inner shaft falling prevention bolt is abutted against the surface of the inner shaft protection plate, and a pressing force using the outer shaft as a reaction force is applied to prevent the inner shaft from falling. By this step, 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, and in a state where it is easy to connect the inner shafts of the upper shaft and the lower shaft in the next step.

[0022] In addition, the step of raising the inner shaft to the upper limit of the allowable movement distance facilitates the connection of the inner shafts in the next step. Refer to the matters described in the effect of claim 3.

[0023] According to the present invention, in the step of connecting the upper shaft to the lower shaft left in the ground in a state where both the inner shaft and the outer shaft are prevented from falling, by the step of unthreading the inner shaft falling prevention bolt that prevents the inner shaft from falling, the connection between the lower shaft left in the ground and the upper shaft can be easily completed in a short time.

Brief Description of the Drawings

[0024] [Figure 1] This is a schematic front view showing a ground improvement device according to Embodiment 1 of the present invention. [Figure 2] This figure shows the connection structure between the rotary drive device connecting shaft and the shaft according to Embodiment 1 of the present invention. (a) is a schematic diagram showing the rotary drive device connecting shaft in perspective, and (b) is a schematic diagram showing the inner shaft arranged inside the outer shaft in perspective. [Figure 3] This figure shows the outer shaft and inner shaft according to Embodiment 1 of the present invention. (a) shows the positional relationship when an inner shaft having an inner shaft male part at the upper end and an inner shaft female part at the lower end is arranged in parallel with an outer shaft having an outer shaft male part at the upper end and an outer shaft female part at the lower end. (b) shows the positional relationship when the inner shaft is arranged inside the outer shaft. [Figure 4] This figure shows the outer shaft supported on a fall prevention workbench according to Embodiment 1 of the present invention, and the outer shaft fall prevention fitting plate. (a) is a front view showing the outer shaft fall prevention fitting plate fitted into the gap between the outer shaft fall prevention rib and the fall prevention workbench. (b) is a plan view of (a) showing the shape of the outer shaft fall prevention fitting plate. (c) is an enlarged conceptual diagram of the fitting procedure. [Figure 5] This figure shows the preparation process for screwing an inner shaft fall prevention bolt into an outer shaft that has been prevented from falling, with respect to the inner shaft protection plate and inner shaft fall prevention rib (Example 1) and inner shaft rise prevention rib (Example 2) of the inner shaft according to the present invention. (a) is a transparent view of the drilling shaft connection part to which both the outer shaft and inner shaft are connected. (b) is a figure showing the state in which the inner shaft fall prevention bolt screw hole stopper cover is installed on the outer shaft with respect to the inner shaft fall prevention rib and inner shaft protection plate. (c) is a figure showing the state in which the inner shaft fall prevention bolt screw hole stopper cover is installed on the outer shaft with respect to the inner shaft fall prevention rib, inner shaft protection plate and inner shaft rise prevention rib. [Figure 6] This shows the state before and after raising the inner shaft to the upper limit of the allowable travel distance S according to Embodiment 3 of the present invention. (a) is a side view showing the positional relationship between the inner shaft fall prevention rib and inner shaft protection plate directly below the inner shaft connection part and the inner shaft fall prevention bolt screw hole stopper cover of the outer shaft before the inner shaft is raised. (b) is a side view showing the state after the inner shaft has been raised. [Figure 7]This diagram shows the connection between the upper and lower shafts according to the present invention. (a) is a diagram of the connection when the allowable movement distance of the inner shaft is zero (Example 1). (b) is a diagram of the connection when the allowable movement distance S (upward) of the inner shaft is reached (Example 3). [Figure 8] This figure shows the state in which an inner shaft fall prevention bolt is screwed into a threaded hole for an inner shaft fall prevention bolt engraved on the outer shaft according to Embodiment 1 of the present invention, with the tip in contact with the inner shaft protection plate and a pressing force applied. (a) is a side cross-sectional view, and (b) is a cross-sectional perspective view. [Figure 9] This figure shows an example of an internal shaft fall prevention bolt according to Embodiment 1 of the present invention. [Figure 10] This figure shows the construction process of a jointed pile according to Embodiment 1 of the present invention, and is a front view of the connection construction process (a) to (d) between the upper shaft and the lower shaft. [Figure 11] This figure shows the construction process of the jointed pile according to Embodiments 1 and 3 of the present invention, and is a front view of the connection construction process (e) to (h) between the upper shaft and the lower shaft. [Figure 12] This figure shows the construction process of a jointed pile according to Embodiment 1 of the present invention, and is a front view of the connection construction process (i) to (l) between the upper shaft and the lower shaft. [Figure 13] This figure shows the construction process of a jointed pile according to Embodiment 1 of the present invention, and is a front view of the connection construction process (m) to (o) between the upper shaft and the lower shaft. [Figure 14] This figure shows an internal shaft helical blade directly above the stirring and mixing section according to Embodiment 4 of the present invention. [Modes for carrying out the invention]

[0025] Preferred embodiments 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 embodiments described below. Furthermore, the materials, shapes, and dimensions of the components described below are examples of embodiments, and modifications are subject to design considerations. Additionally, it is also subject to design considerations to add devices and jigs used in known deep mixing methods to the ground improvement device of the present invention.

[0026] <Coordinate axes> The drawing shows the X, Y, and Z axes as coordinate axes. The Z-axis direction is defined as the upward direction of the leader 3 of the excavator 1, which is erected vertically to the horizontal ground, and the horizontal plane of the ground is shown as the plane XY formed by the X and Y axes.

[0027] <Definition> Up and Down: With respect to the axis (Z-axis direction) of leader 3, which is standing vertically to the ground, the side opposite the ground (positive Z-axis direction) is defined as "up," and the side facing the ground (negative Z-axis direction) is defined as "down." Connection: The process of connecting the male parts of the outer and inner shafts of one shaft with the female parts of the outer and inner shafts of another shaft, thereby forming an outer shaft connection section and an inner shaft connection section, and thus forming a single shaft. The opposite of "connection" is called "disconnection."

[0028] <Soil improvement equipment> Figure 1 shows a ground improvement device 1 according to Embodiment 1 of the present invention, which is used in the so-called deep mixing method. The ground improvement device 1 has a leader 3 erected in the Z-axis direction at the front end of an excavator 2 installed on the 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 able to move up and down in the Z-axis direction.

[0029] In Figure 1, below the rotary drive unit connecting shaft 8, which is located directly below the rotary drive unit 7, the basic drilling shaft 9X and the drilling shaft 9M (M=1) for connecting piles are connected via a connecting shaft coupling part 50, as an example. Below the drilling shaft 91 for connecting piles, the drilling shaft 9 is connected via a drilling shaft coupling part 60. Below the drilling shaft 9, the mixing and stirring section 10 is connected via a mixing and stirring section coupling part 65. The rotary drive unit connecting shaft 8, the basic drilling shaft 9X, the drilling shaft 91 for connecting piles, and the drilling shaft 9 are connected vertically in the Z-axis direction to form a shaft 90, which is driven into the ground. The upper of the two vertically connected shafts 90 will be referred to as the upper shaft 90A, and the lower as the lower shaft 90B. For example, Figure 1 shows the relationship between the basic drilling shaft 9X (upper shaft 90A) and the joint drilling shaft 91 (lower shaft 90B) connected to the rotary drive unit connecting shaft 8, and the relationship between the joint drilling shaft 91 (upper shaft 90A) and the drilling shaft 9 (lower shaft 90B). The number of joint drilling shafts 9M (M=1~N) is arbitrary, and N is determined by the design improvement length (also called the design depth).

[0030] The rotary drive unit 7 is configured with a reduction gear (not shown) that allows the tubular outer shaft 20, which constitutes the rotary drive unit connecting shaft 8, the basic drilling shaft 9X, the drilling shaft 91 for the extended pile, the drilling shaft 9, and the agitation and mixing section 10, and the tubular inner shaft 21, which is rotatably disposed inside the outer shaft 20, to rotate in opposite directions on both axes. Multiple outer shafts 20 and inner shafts 21 are connected vertically to form a shaft 90. Therefore, the rotary drive unit connecting shaft 8, the drilling shaft 9M1 for the extended pile, the drilling shaft 9, and the agitation and mixing section 10, which are composed of the outer shaft 20 and inner shaft 21, are also connected vertically to form a shaft 90. As an example, an outer shaft helical blade 20a is provided on the outer circumference of the outer shaft 20.

[0031] <Agitation and mixing unit connected to the drilling shaft> The lower end of the shaft 90 of the rotary drive unit 7 is equipped with a stirring and mixing section 10. The stirring and mixing section 10 consists of an outer shaft stirring blade fixed to the lower end of the outer shaft 20 and an inner shaft stirring blade fixed to the lower end of the inner shaft 21. For example, the outer shaft stirring blade consists of an upper stirring blade 22 and a lower stirring blade 23. The inner shaft stirring blade consists of an auxiliary stirring blade 24 and a drilling blade 25. For example, the auxiliary stirring blade 24 consists of an upper horizontal blade 24a, a lower horizontal blade 24b and vertical blades 24c on both sides. It should be noted that employing a known stirring and mixing mechanism in the stirring and mixing section 10 is a design consideration.

[0032] The outer shaft 20 and the inner shaft 21 rotate in opposite directions. Therefore, the upper and lower stirring blades 22 and 23, and the auxiliary stirring blades 24 and drilling blades 25 rotate in opposite directions and mix in three dimensions. Consequently, uniform mixing is achieved.

[0033] The inner shaft 21 has a permissible movement distance S that allows the inner shaft stirring blade to move up and down relative to the outer shaft stirring blade, and is supported by a wire 6 connected to the rotary drive device 7 so that it can move up and down within the range of the permissible movement distance S. The permissible movement distance S is set to 50 mm as an example. Thus, the inner shaft 21 is arranged to be rotatable inside the outer shaft 20 and to move within the range of the above permissible movement distance S. The upward movement of the inner shaft 21 is performed as needed when releasing the upper and lower shafts. In Embodiment 1, the upward movement of the inner shaft 21 within the range of the permissible movement distance S is not performed.

[0034] The drilling shaft 9, the basic drilling shaft 9X, and the drilling shaft 9M for connecting piles are supported via a vibration-damping device 4 that is mounted on the leader 3 so as to be able to move up and down. The vibration-damping device 4 also functions as a work platform to prevent the lower shaft 90B from falling during the process of connecting or disconnecting the lower shaft 90B and the upper shaft 90A.

[0035] The ground improvement device 1 uses a soil improvement agent / excavation water injection device, a compressed air discharge device, and a generator, etc., which are necessary for the deep mixing treatment method (not shown in the diagram), but their details are omitted.

[0036] <Drilling shaft or drilling shaft for connecting piles, connected to the rotary drive unit connecting shaft> Figure 2 shows a diagram in which a shaft 90 (a collective term for the drilling shaft 9, the basic drilling shaft 9X, and the drilling shaft 9M for connecting piles) is connected to a rotary drive device connecting shaft 8 according to Embodiment 1 of the present invention. Figure 2(a) shows that the rotary drive device connecting shaft 8 comprises an outer shaft 20 and an inner shaft 21 disposed inside the outer shaft 20. The lower end of the outer shaft 20 has an outer shaft female part 30b, and an inner shaft female part 40b is disposed inward and protruding from the upper end side 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.

[0037] Figure 2(b) shows the shaft 90 (collectively referred to as the drilling shaft 9, the basic drilling shaft 9X, and the drilling shaft 9M for connecting piles) connected to the rotary drive unit connecting shaft 8. The shaft 90 comprises a tubular outer shaft 20 and a tubular inner shaft 21 rotatably and vertically movable inside the outer shaft 20. One end of the outer shaft 20, the upper end (in the positive Z-axis direction), is provided with an outer shaft male part 30a and an inner shaft male part 40a located inside and spaced apart 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 of the outer shaft 20, the lower end (in the negative Z-axis direction), is provided with an outer shaft female part 30b and an inner shaft female part 40b protruding from the lower end of the outer shaft female part 30b and located inside. An outer shaft female part 30b has an outer shaft connecting hole 30c, and an inner shaft female part 40b has an inner shaft connecting hole 40c.

[0038] The outer shaft female part 30b and inner shaft female part 40b of the rotary drive device connecting shaft 8 are fitted and connected to the outer shaft male part 30a and inner shaft male part 40a at the upper end (Z-axis positive direction) of the shaft 90, for each outer shaft 20 and inner shaft 21, respectively. Then, outer shaft connecting fixtures 30d and inner shaft connecting fixtures 40d are inserted into the outer shaft connecting hole 30c and inner shaft connecting hole 40c, respectively, and connected and fixed (outer shaft connecting part 30 and inner shaft connecting part 40), forming the connecting shaft connecting part 50. The outer shaft 20 and inner shaft 21 are connected and fixed to the outer shaft connecting fixture 30d and inner shaft connecting fixture 40d using known bolts, nuts, pins, etc., so that they can rotate in opposite directions on both axes.

[0039] <Structure of the connection between the outer and inner shafts> Figure 3 shows an outer shaft 20 and an inner shaft 21 according to Embodiment 1 of the present invention. (a) is a diagram showing an inner shaft 21 having an inner shaft male part 40a at the upper end and an inner shaft female part 40b at the lower end, and an outer shaft 20 having an outer shaft male part 30a at the upper end and an outer shaft female part 30b at the lower end arranged in parallel. (b) is a diagram showing the positional relationship in which the inner shaft 21 is arranged inside the outer shaft 20. An inner shaft fall prevention rib 82 and an inner shaft protection plate 83 are arranged directly below the inner shaft male part 40a. Below the outer shaft male part 30a, an inner shaft fall prevention bolt screw hole 85, an inner shaft fall prevention bolt screw hole stopper cover 86 which is a cover, and an outer shaft fall prevention rib 71 are arranged.

[0040] <Prevention of outer shaft from falling> The ground improvement device 1 consists of a rotary drive unit connecting shaft 8, a basic excavation shaft 9X, a pile extension excavation shaft 9M, an excavation shaft 9, and a mixing unit 10, each composed of an outer shaft 20 and an inner shaft 21 positioned inside the outer shaft 20. Therefore, when connecting and disconnecting the outer shaft 20 and 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.

[0041] Figure 4 shows an example of Embodiment 1 of the present invention, in which the drilling shaft 9 (lower shaft 90B) is connected to the drilling basic shaft 9X (upper shaft 90A), and the outer shaft 20 of the lower shaft 90B, which has been pre-installed underground, is supported by the fall prevention work platform 4. The fall prevention work platform 4 is referred to as the fall prevention work platform when the anti-vibration device 4 is installed on the ground. The outer shaft 20 and inner shaft 21 of the upper shaft 90A and the outer shaft 20 and inner shaft 21 of the lower shaft 90B are connected by the drilling shaft connecting section 60 (outer shaft connecting section 30 and inner shaft connecting section 40). Figure 4(a) shows the upper shaft 90A being raised slightly (in the positive Z-axis direction, step A in Figure (c)), and the outer shaft fall prevention fitting plate 72 being inserted into the gap between the outer shaft fall prevention rib 71 below the outer shaft male part 30a of the lower shaft 90B and the fall prevention work platform 4 placed on the ground 5 (step B in Figure (c)).

[0042] As illustrated in Figure 4(b), the outer shaft fall prevention fitting plate 72 is, for example, a plate-shaped member having a handle portion and bifurcated ends on both sides. By inserting the bifurcated ends of the outer shaft fall prevention fitting plate 72 under the outer shaft fall prevention rib 71, the installation area of ​​the outer shaft fall prevention rib 71 can be increased, allowing it to be placed on the upper end of the fall prevention workbench 4.

[0043] Figure 4(c) conceptually illustrates the procedure for step C, which involves lowering the upper shaft 90A slightly (in the negative Z-axis direction) in addition to steps A and B described above, so that the weight of the outer shaft 20 of the lower shaft 90B is supported by the fall prevention workbench 4 via the outer shaft fall prevention rib 71 and the outer shaft fall prevention fitting plate 72.

[0044] Next, the outer shaft connecting jig 30d is removed from the outer shaft connecting section 30, the connection of the outer shaft connecting section 30 is released, and the outer shaft 20 of the upper shaft 90A and the outer shaft 20 of the lower shaft 90B are separated, after which 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 section 40.

[0045] By supporting the weight of the outer shaft 20 on the fall prevention work platform 4 on the ground 5 via the outer shaft fall prevention rib 71 and the outer shaft fall prevention fitting plate 72, the outer shaft 20 can be prevented from falling, and the subsequent work of releasing and connecting the inner shaft 21 can be facilitated.

[0046] <Prevention of inner shaft falling> As mentioned in the section on preventing the outer shaft from falling, when connecting and disconnecting the outer shaft 20 and 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 90B is first stably supported on the ground or the like to prevent it from falling.

[0047] Figure 5(a) shows the preparation steps for fixing the inner shaft 21 to the outer shaft 20 according to Embodiment 1 of the present invention. The outer shaft 20 of the lower shaft 90B is supported on the fall prevention work platform 4 on the ground 5 via the outer shaft fall prevention rib 71 and the outer shaft fall prevention fitting plate 72, thus preventing it from falling. The inner shaft 21 of the upper shaft 90A and the inner shaft 21 of the lower shaft 90B are connected by the inner shaft connecting portion 40. Next, the outer shaft connecting jig 30d is removed from the outer shaft connecting portion 30 of the outer shaft 20 of the upper shaft 90A, and the connection of the outer shaft connecting portion 30 is released. Furthermore, an inner shaft fall prevention bolt screw hole stopper cover 86 is installed in the inner shaft fall prevention bolt screw hole 85 screwed into the outer shaft 20.

[0048] <Plates and ribs protruding from the inner shaft surface> Figure 5(b) is a side view showing that an inner shaft protection plate 83 (for example, a steel plate 6 mm thick and 100 mm wide) is disposed below the inner shaft male portion 40a according to Embodiment 1 of the present invention, so as to protrude toward the inner surface of the outer shaft. The inner shaft protection plate 83 protects a portion of the outer surface of the inner shaft 21 by 360 degrees with a width of 100 mm. Furthermore, when the inner shaft connecting portion 40 is released, the tip of the inner shaft fall prevention bolt 81 abuts against it, and the pressing force acting due to screwing it in transmits the pressing force to the inner shaft 21. The inner shaft protection plate 83 protrudes 6 mm from the surface of the inner shaft 21. Opposite the center of the inner shaft protection plate 83, the outer shaft 20 is provided with an inner shaft fall prevention bolt screw hole 85 into which the inner shaft fall prevention bolt 81 is screwed. In Figure 5(b), the inner shaft fall prevention bolt screw hole cover 86 is installed in the inner shaft fall prevention bolt screw hole 85 to prevent the intrusion of mud, etc., and the hole is shown covered.

[0049] Figure 5(b) is a side view showing that an inner shaft fall prevention rib 82 (for example, 9 mm thick and 30 mm wide) is provided, positioned above the inner shaft protection plate 83 according to Embodiment 1 of the present invention, and protruding from the inner shaft side of the outer shaft from the inner shaft protection plate 83. The inner shaft fall prevention rib 82 surrounds a portion of the outer surface of the inner shaft 21 with a width of 30 mm for 360 degrees. The inner shaft fall prevention rib 82 protrudes 3 mm from the surface of the inner shaft protection plate 83 at the upper part of the inner shaft protection plate 83. Furthermore, if the contact position due to the pressing force of the tip of the inner shaft fall prevention bolt 81 shifts upward (the inner shaft 21 falls), the inner shaft fall prevention rib 82 supports the tip of the inner shaft fall prevention bolt 81, and has the function of preventing the inner shaft 21 from falling.

[0050] Figure 5(c) is a side view showing that, in addition to the inner shaft protection plate 83 and inner shaft fall prevention rib 82 according to Embodiment 1 of the present invention, an inner shaft rise prevention rib 84 (for example, 9 mm thick and 30 mm wide) according to Embodiment 2 of the present invention is also provided, positioned below the inner shaft protection plate 83 and protruding from the inner shaft side of the outer shaft. The inner shaft rise prevention rib 84 protects a portion of the outer surface of the inner shaft 21 with a width of 30 mm for 360 degrees. The inner shaft rise prevention rib 84 protrudes 3 mm from the surface of the inner shaft protection plate 83 at the lower part of the inner shaft protection plate 83. Furthermore, if the contact position due to the pressing force of the tip of the inner shaft fall prevention bolt 81 shifts downward (the inner shaft 21 rises), the inner shaft rise prevention rib 84 supports the tip of the inner shaft fall prevention bolt 81, and has the function of preventing the inner shaft 21 from rising.

[0051] The inner shaft fall prevention bolt screw hole stopper cover 86, which is disposed on the outer shaft 20, is located opposite the center of the inner shaft protection plate 83. Therefore, the inner shaft fall prevention bolt 81 is disposed in the center of the inner shaft protection plate 83, sandwiching the inner shaft fall prevention rib 82 and the inner shaft rise prevention rib 84. The tip of the inner shaft fall prevention bolt 81 has the inner shaft fall prevention rib 82 in the upward direction and the inner shaft rise prevention rib 84 in the downward direction, so that even if the contact position due to the pressing force of the tip of the inner shaft fall prevention bolt 81 shifts downward or upward, the inner shaft 21 can be prevented from falling or rising.

[0052] <Increase in the allowable travel distance S of the inner shaft: Example 3> The inner shaft 21 has a permissible movement distance S that allows the inner shaft stirring blade to move up and down relative to the outer shaft stirring blade, and is supported by a wire 6 connected to the rotary drive device 7 so that it can move up and down within the range of the permissible movement distance S. The permissible movement distance S is set to 50 mm as an example. Thus, the inner shaft 21 is arranged to be rotatable inside the outer shaft 20 and to move within the range of the above permissible movement distance S. The upward movement of the inner shaft 21 is performed as needed when the upper shaft 90A and lower shaft 90B are released. In Embodiment 3, the inner shaft 21 is moved upward to the upper limit of the permissible movement distance S. The only difference from Embodiment 1 is that the inner shaft 21 is moved upward by the permissible movement distance S; all other aspects are the same as in Embodiment 1.

[0053] When the outer shaft connecting portion 30 of the upper shaft 90A and the lower shaft 90B is released, the inner shaft 21 is supported by a wire 6 connected to the rotary drive device 7 and can move up and down within the range of the allowable travel distance S. In Embodiment 3, the upper shaft 90A connected to the rotary drive device 7 is raised in the Z-axis direction by the wire 6, thereby moving the upper shaft 90A and the inner shaft 21 integrated with the upper shaft 90A up to the upper limit of the allowable travel distance S.

[0054] Figure 6 shows the state before and after raising the inner shaft 21 by an allowable travel distance S according to Embodiment 3 of the present invention. Figure 6(a) is a side view showing the positional relationship between the inner shaft fall prevention rib 82, the inner shaft protection plate 83, and the inner shaft fall prevention bolt screw hole stopper cover 86 directly below the inner shaft connecting portion 40 before the inner shaft 21 is raised. The inner shaft fall prevention bolt screw hole stopper cover 86, which is a cover for the inner shaft fall prevention bolt screw hole 85 disposed on the outer shaft 22, is located above the center of the inner shaft protection plate 83 disposed on the inner shaft 21. Furthermore, the inner shaft connecting hole stopper cover 40e is also located above the inner shaft connecting jig 40d of the inner shaft connecting portion 40. In this state, the outer shaft connecting jig 30d of the outer shaft 20 of the upper shaft 90A is released, but the inner shaft 21 remains connected at the inner shaft connecting portion 40.

[0055] Figure 6(b) shows the state in which the outer shaft connecting jig 30d of the outer shaft 20 of the upper shaft 90A is released, and the upper shaft 90A is raised upward by the allowable travel distance S. Since the inner shaft 21 is connected by the inner shaft connecting part 40, the inner shaft 21 is raised by the allowable travel distance S (for example, set to 50 mm). In this state, the inner shaft connecting hole stop cover 40e is in a position that coincides with the inner shaft connecting jig 40d of the inner shaft male part 40a. Also, the inner shaft fall prevention bolt screw hole stop cover 86 is positioned opposite the center of the inner shaft protection plate 83.

[0056] <Effect of the allowable movement distance S of the inner shaft> Figure 7 illustrates the connection between the upper shaft 90A and the lower shaft 90B. Figure 7(a) shows the case where the allowable travel distance S is zero (Example 1). Figure 7(b) shows the case where the allowable travel distance S is set to a rise of 50 mm as an example (Example 3).

[0057] When the allowable travel distance S is zero (Example 1) (Figure 7(a1)), when the upper shaft 90A and the lower shaft 90B are connected, the end 30bp of the outer shaft female part 30b and the end 40bp of the inner shaft female part 40b of the upper shaft 90A begin to make contact simultaneously with the end 30ap of the outer shaft male part 30a and the end 40ap of the inner shaft male part 40a of the lower shaft 90B. See Figure 7(a2). However, in Example 3, the inner shaft 21 of the lower shaft 90B is held in a state raised by the allowable travel distance S (for example, set to 50 mm). See Figure 7(b1). Therefore, when connecting the upper shaft 90A and the lower shaft 90B, the end 40ap of the inner shaft male part 40a of the lower shaft 90B, which has been raised by the allowable travel distance S (for example, set to 50 mm), first contacts the end 40bp of the inner shaft female part 40b of the upper shaft 90A with respect to the end 30bp of the outer shaft female part 30b and the end 40bp of the inner shaft female part 40b of the upper shaft 90A. At this point, the end 30bp of the outer shaft female part 30b of the upper shaft 90A and the end 30ap of the outer shaft male part 30a of the lower shaft 90B are separated by S = 50 mm. As a result, the inner shaft female part 40b of the upper shaft 90A can be easily and accurately connected to the inner shaft male part 40a of the lower shaft 90B without being affected by the outer shaft connection part 30.

[0058] By raising the inner shaft 21 of the lower shaft 90B by an allowable travel distance S (for example, set to 50 mm), the connection of the inner shaft connection part 40 can be performed without being affected by the outer shaft connection part 30 when connecting the upper shaft 90A and the lower shaft 90B in the next process. This improves the connection accuracy of the inner shaft connection part 40, and as a result, the connection work of the outer shaft connection part 30 also becomes easier.

[0059] <Prevention of the inner shaft from falling using an inner shaft fall prevention bolt> Figure 8(a) is a side cross-sectional view showing the state in which the inner shaft 21 of the inner shaft 21 is prevented from falling when the inner shaft connecting portion 40 of the inner shaft 21 according to Embodiment 1 of the present invention is released, and the inner shaft fall prevention bolt 81 is used to prevent it from falling. The outer shaft 20 of the lower shaft is supported on the fall prevention workbench 4 via the outer shaft fall prevention rib 71 and the outer shaft fall prevention fitting plate 72, and is prevented from falling. The inner shaft 21 of the upper shaft and the inner shaft 21 of the lower shaft are connected by the inner shaft connecting portion 40. The inner shaft fall prevention bolt 81 is screwed into the inner shaft fall prevention bolt screw hole 85 threaded in the outer shaft 20. Figure 8(b) is a cross-sectional perspective view showing the state in which the inner shaft connecting portion 40 of the inner shaft 21 is released, and the inner shaft 21 of the lower shaft is prevented from falling by the inner shaft fall prevention bolt 81 screwed into the inner shaft fall prevention bolt screw hole 85 of the outer shaft 20.

[0060] The threaded holes 85 for the inner shaft fall prevention bolts, provided on the outer shaft 20, are evenly arranged in four directions on the outer circumference of the outer shaft 20, for example. An inner shaft fall prevention bolt 81 (for example, an M30 bolt, 112 mm in length) is screwed into the inner shaft fall prevention bolt threaded hole 85, and the tip of the inner shaft fall prevention bolt 81 is evenly in contact with the inner shaft protection plate 83, which is provided directly below the inner shaft fall prevention rib 82, and is in a pressed state. Thus, when the inner shaft connecting part 40 is released, the inner shaft fall prevention bolt 81 is screwed into the threaded holes 85 of the outer shaft 20, which is prevented from falling, and the tip of the inner shaft fall prevention bolt 81 comes into contact with the surface of the inner shaft protection plate 83. The pressing force from the screwing of the inner shaft fall prevention bolt 81, with the outer shaft 20 as the reaction force, acts on the inner shaft protection plate 83, thereby preventing the inner shaft 21 from falling.

[0061] Figure 9 shows an internal shaft fall prevention bolt 81 according to Embodiment 1 of the present invention. As an example, the internal shaft fall prevention bolt 81 is provided with symmetrical arms (Lb=100mm) on the nut head of an M30 bolt (La=112mm). The internal shaft fall prevention bolt 81 can be easily screwed into the internal shaft fall prevention bolt spiral hole 85 provided on the outer shaft 20 by rotating the symmetrical arms on the nut head of the internal shaft fall prevention bolt 81, and can be easily unscrewed by simply rotating the symmetrical arms on the nut head in the opposite direction. Furthermore, the screwing of the internal shaft fall prevention bolt 81 can be performed as appropriate by manually rotating the symmetrical arms on the nut head, or by using an electric rotating jig or the like on the nut head.

[0062] <Mechanism for preventing the internal shaft from falling off the bolt> The fall prevention mechanism for the inner shaft fall prevention bolt 81 works by screwing the inner shaft fall prevention bolt 81 into the inner shaft fall prevention bolt helical hole 85 located on the outer shaft 20, thereby applying a pressing force Q to the inner shaft 21, and preventing the inner shaft 21 from falling due to its own weight W by the frictional force F generated between the inner shaft 21 and the outer shaft 20. The frictional force F must be greater than or equal to the weight W, and considering the safety factor s, it is given by the following formula. F≧s×W (Formula 1)

[0063] The frictional force F is given by the following formula, taking into account the friction coefficient μ and the pressing force Q generated by the internal shaft fall prevention bolt 81. F=Q×μ...(Formula 2) Therefore, the equation that satisfies the requirement to prevent the inner shaft 21 from falling is, from equation 1 and equation 2, the following equation. Q≧s×W / μ···(Formula 3)

[0064] Assuming that the internal shaft fall prevention bolts 81 of number n bear the pressing force evenly, the required pressing force Qa per bolt is given by the following formula. Qa≧s×W / μ / n (Formula 4)

[0065] The required specifications for the internal shaft fall prevention bolt 81 shall be determined by considering known required strength, strength class, contact conditions, friction fastening conditions, etc.

[0066] <Specifications of the internal shaft fall prevention bolt> For example, if the internal shaft 21 has a self-weight W = 15 tons (147 kN), and the above conditions are set, and four M30 bolts are used as an example, the required pressing force per bolt will be Qa = 294 kN.

[0067] <Tightening torque for the internal shaft fall prevention bolt> The tightening torque T per bolt is given by the following formula, where Qa is the required pressing force, k is the torque coefficient, and d is the bolt diameter. T=Qa×k×d...(Formula 5) For example, if the required pressing force Qa = 294 KN per bolt is calculated, the tightening torque T = 1324 N·m per bolt is obtained.

[0068] With regard to the internal shaft fall prevention bolt 81, safety has been confirmed by checking the shear force on the internal shaft fall prevention bolt 81 and the internal shaft fall prevention rib 82, taking into consideration the case where the required pressing force Qa on the internal shaft 21 decreases due to a decrease in friction force F, etc.

[0069] <Threading of the internal shaft fall prevention bolt> The internal shaft fall prevention bolt threaded holes 85, which are provided in the outer shaft 20 and threaded, are evenly arranged in four directions on the outer circumference of the outer shaft 20. The internal shaft fall prevention bolt threaded holes 85 are covered with internal shaft fall prevention bolt threaded hole covers 86 (φ50 mm for example) to prevent the inflow of mud. First, the internal shaft fall prevention bolt threaded hole covers 86 are unscrewed and removed. Next, four internal shaft fall prevention bolts 81 (M30 bolts, 112 mm in length for example) are screwed into the internal shaft fall prevention bolt threaded holes 85, which are evenly arranged in four directions, and the four bolts are screwed in evenly. Furthermore, the internal shaft fall prevention bolts 81 are screwed in and pressed using the outer shaft 20 as a reaction force. Then, the tips of the four internal shaft fall prevention bolts 81 are evenly brought into contact with the internal shaft protection plate 83, which is provided directly below the internal shaft fall prevention rib 82. Then, by screwing in the four bolts evenly, the inner shaft protection plate 83 is subjected to equal pressure from four directions, resulting in a uniform pressure state. As a result, the pressure exerted by screwing in the inner shaft fall prevention bolts 81, with the outer shaft 20 acting as a reaction force, acts on the inner shaft protection plate 83, preventing the inner shaft 21 from falling.

[0070] Subsequently, the inner shaft connecting hole retaining cover 40e provided on the outer circumference of the outer shaft 20 is removed, and the inner shaft connecting jig 40d is removed to release the inner shaft connecting portion 40. The inner shaft connecting hole retaining cover 40e (for example, φ100 mm) is provided larger than the inner shaft connecting jig 40d (for example, a φ30 mm fall prevention pin), allowing the inner shaft connecting jig 40d to be easily removed from the outer circumference of the outer shaft 20. As a result, the outer shaft 20 and inner shaft 21 of the upper shaft 90A are separated from the outer shaft 20 and inner shaft 21 of the lower shaft 90B, and the outer shaft 20 and inner shaft 21 of the lower shaft 90B are left in their current positions.

[0071] The inner shaft 21 is provided with an inner shaft protection plate 83 that protrudes from the surface of the inner shaft 21 below the inner shaft male portion 40a, and the upper part of the inner shaft protection plate 83 has an inner shaft fall prevention rib 82 that protrudes outward. By simply screwing the inner shaft fall prevention bolt 81 into the inner shaft fall prevention bolt screw hole 85 of the outer shaft, the inner shaft protection plate 83 can be easily pressed, preventing the inner shaft 21 from falling relative to the outer shaft 20. Even if the frictional force of the inner shaft fall prevention bolt 81 decreases and the inner shaft 21 sinks, the inner shaft fall prevention rib 82 prevents further sinking. Thus, the connection and disconnection of the inner shafts 21 of the upper shaft 90A and the lower shaft 90B is easy and safe.

[0072] In Example 3, raising the position of the inner shaft connecting portion 40 by an allowable movement distance S makes it easier to connect the inner shaft 21 of the upper shaft 90A of the joint pile excavation shaft 9M to the lower shaft 90B in the next step. Specifically, when the inner shaft female portion 40b of the inner shaft 21 of the upper shaft 90A begins to make connection contact with the inner shaft male portion 40a of the inner shaft 21 of the lower shaft 90B, a separation distance of allowable movement distance S = 50 mm is secured with respect to the outer shaft connecting portion 30. Therefore, the connection work of the inner shaft connecting portion 40 can be carried out in advance without interference with the outer shaft connecting portion 30, and the connection can be made while adjusting the connection accuracy of the upper shaft 90A and the lower shaft 90B.

[0073] When connecting the outer shaft 20 and inner shaft 21 of the upper shaft 90A of the joint pile excavation shaft 9M to the outer shaft 20 and inner shaft 21 of the lower shaft 90B that remain in place as described above, the procedure is carried out in the reverse order of the above.

[0074] <Experiment to confirm the prevention of internal shaft drop using internal shaft drop prevention bolts> Field experiments were conducted to connect the drilling shaft 9 via the drilling shaft connecting section 60. As an example, four internal shaft fall prevention bolts 81 (M30 bolts) were screwed into four internal shaft fall prevention bolt screw holes 85 evenly arranged on the outer circumference of the outer shaft 20. Next, the bolts were screwed into the internal shaft protection plate 83 of the internal shaft 21 (self-weight = 15 tons) while checking the length evenly by hand. Furthermore, a torque wrench was used to set the final predetermined tightening torque T = 1.3 KN·m on the nut heads of the internal shaft fall prevention bolts 81, and the bolts were screwed in evenly to complete the fixing. It was then confirmed that the internal shaft 21 (self-weight = 15 tons) would not fall. Furthermore, the internal shaft 21 was raised by the maximum allowable movement distance S of 50 mm, and the internal shaft fall prevention bolts 81 were screwed in and fixed according to the same procedure as above, and it was confirmed that the internal shaft 21 would not fall.

[0075] <Construction process for jointed piles> If the improved length of the drilling shaft 9 is insufficient to meet the design improved length (design depth), it is necessary to connect a number of drilling shafts 9M (M=1~N) for connecting piles to the drilling shaft 9 to satisfy the insufficient improved length (hereinafter referred to as "connecting piles"). The construction process for connecting piles according to Embodiments 1 and 3 of this application consists of the following intermediate steps (A) to (D). Embodiment 3 adds only the step of raising the inner shaft 21 by the allowable movement amount S in step e of intermediate step B to Embodiment 1.

[0076] (A) The penetration and mixing process for the pre-construction work consists of the following steps: (a) connecting the basic drilling shaft 9X to the pre-construction drilling shaft 9, (b) penetrating and mixing the shaft to the improved length of the drilling shaft 9, (c) stopping the rotation and penetration at the depth of the pre-construction work, and (d) fixing the outer shaft of the drilling shaft 9. (Figure 10(a)~(d))

[0077] (B) In Example 1, the outer shaft connection part 30 is released: step (e). In Example 3, the outer shaft connection part 30 is released, and the inner shaft 21, which is integrated with the inner shaft connection part 40, is raised by the allowable movement amount S: step (e). The outer shaft connection part 30 is released, and the inner shaft 21, which is integrated with the inner shaft connection part 40, is fixed to the outer shaft 20 with the inner shaft fall prevention bolt 81: step (f). The lower excavation shaft 90B is left in place: step (g). The upper excavation shaft 90A is moved to the joint pile 91: step (h). This is the excavation shaft retention process for the preliminary construction. (Figure 11(e)~(h))

[0078] (C) The process of withdrawing and moving a joint pile for subsequent construction consists of the following steps: (i) forming an inner shaft connection part 40 between the excavation shaft 91 for joint piles to be constructed later and the lower end of the moved basic excavation shaft 9X, and unscrewing the inner shaft fall prevention bolt 81; (j) forming an outer shaft connection part 30; (k) withdrawing the excavation shaft 91 for joint piles connected to the basic excavation shaft 9X and leaving the excavation head 9MH in place; and (l) moving to the lower excavation shaft 90B left in place from the previously constructed joint pile. (Figure 12(i)~(l))

[0079] (D) A pile splicing process consisting of: (m) constructing the inner shaft connection part 40 between the drilling shaft 9 and the drilling shaft 91 for splicing piles; (n) constructing the outer shaft connection part 30; and (o) improving the pile to the designed improved length. (Figure 13(m)~(o))

[0080] <(A) Penetration and stirring process of the preliminary construction (a)~(d), see Figure 10> (a) The ground improvement device 1 is used to prepare for the insertion of the pre-constructed drilling shaft 9 (lower shaft 90B) into the ground. The ground improvement device 1 used consists of a leader 3 erected in the Z-axis direction at the front end of the drilling machine 2 installed on the ground 5, and a rotary drive device 7 suspended from the upper end of the leader 3 by a wire 6 so as to be able to move up and down in the Z-axis direction. Furthermore, the basic drilling shaft 9X (upper shaft 90A) is connected to the lower part of the rotary drive device connecting shaft 8 via a connecting shaft coupling part 50. Furthermore, the drilling shaft 9 (lower shaft 90B) is connected to the lower part of the basic drilling shaft 9X via a drilling shaft coupling part 60. Below the drilling shaft 9, the mixing unit 10 is connected via a mixing unit coupling part 65. The drilling shaft 9 is supported by a vibration damping device 4 that is provided on the leader 3 so as to be able to move up and down. Next, the drilling machine 2 is moved to the construction position and installed. The selection of various known ground improvement agents, water, and compressed air to be used during penetration is a design consideration.

[0081] (b) The vibration damping device 4 is installed on the ground 5 and penetrated into the ground and mixed up to the improved length of the previously constructed excavation shaft 9 (lower shaft 90B). When the vibration damping device 4 is installed on the ground, it is called 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).

[0082] (c) Penetrate and agitate to a depth where the previously constructed drilling shaft 9 (lower shaft 90B) is separated, then stop rotation and penetration.

[0083] (d) The outer shaft fall prevention fitting plate 72 is inserted into the gap 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 work platform 4. Then, the drilling shaft 9 (lower shaft 90B) is driven in to eliminate the gap, thereby fixing and supporting the outer shaft 20 of the drilling shaft 9 (lower shaft 90B) to the fall prevention work platform 4 and preventing the outer shaft 20 from falling. (Lower shaft outer shaft fall prevention process)

[0084] <(B) Remaining excavation shafts from the preceding construction (e)~(h), see Figure 11> (e) In Embodiment 1 of the present invention, the outer shaft connecting jig 30d is removed from the outer shaft connecting hole 30c of the outer shaft connecting section 30, which connects the outer shaft 20 of the drilling shaft 9 (lower shaft 90B) to the outer shaft 20 of the basic drilling shaft 9X (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 basic drilling shaft 9X (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 basic drilling shaft 9X (upper shaft 90A) are connected by the inner shaft connecting section 40. Note that in Embodiment 1, the allowable travel distance S is not increased. (Step of releasing the connection between the outer shaft connecting section of the upper shaft and the lower shaft)

[0085] (e) In Embodiment 3 of the present invention, the outer shaft connecting jig 30d is removed from the outer shaft connecting hole 30c of the outer shaft connecting section 30, which connects the outer shaft 20 of the drilling shaft 9 (lower shaft 90B) to the outer shaft 20 of the basic drilling shaft 9X (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 basic drilling shaft 9X (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 basic drilling shaft 9X (upper shaft 90A) are connected by the inner shaft connecting section 40. (Step to release the connection between the outer shaft connecting section of the upper shaft and the lower shaft)

[0086] Next, in Embodiment 3(e) of the present invention, the rotary drive device 7 is wound up with a wire (in the positive Z-axis direction) to raise the drilling base shaft 9X (upper shaft 90A) to the upper limit of the allowable movement distance S of the inner shaft stirring blade relative to the outer shaft stirring blade, for example, S = 50 mm (in the positive Z-axis direction). The inner shaft 21 of the drilling shaft 9 (lower shaft 90B) and the inner shaft 21 of the base drilling shaft 9X (upper shaft 90A) are connected by an inner shaft connecting part 40. Therefore, the inner shaft 21 of the drilling shaft 9 (lower shaft 90B) can be raised to the upper limit of the allowable movement distance S, for example, 50 mm. This is a characteristic of Embodiment 3. Raising the position of the inner shaft connecting part 40 by the allowable movement distance S has the effect of making it easier to connect the inner shaft 21 of the upper shaft 90A of the joint pile drilling shaft 91 to the lower shaft 90B. (Step of raising the inner shaft to the upper limit of the allowable movement distance)

[0087] (f) With the connection between the outer shaft 20 of the drilling shaft 9 (lower shaft 90B) and the outer shaft 20 of the basic drilling shaft 9X (upper shaft 90A) released, the positions of the inner shaft fall prevention rib 82 and the inner shaft protection plate 83 coincide with the position of the inner shaft fall prevention bolt screw hole stopper 86 provided on the outer shaft 20. The screw holes 85 for the inner shaft fall prevention bolts, which are provided on the outer shaft 20 and are threaded to prevent falling, are arranged evenly in four directions on the outer circumference of the outer shaft 20 as an example. The inner shaft fall prevention bolt screw holes 85 are covered with the inner shaft fall prevention bolt screw hole stopper 86 to prevent the inflow of mud. First, unscrew and remove the inner shaft fall prevention bolt screw hole stopper 86. Next, screw the four inner shaft fall prevention bolts 81 into the inner shaft fall prevention bolt screw holes 85 which are arranged evenly in four directions, and proceed to screw all four bolts evenly. Furthermore, the internal shaft fall prevention bolts 81 are screwed in and pressed using the outer shaft 20 as a reaction force. The tips of the four internal shaft fall prevention bolts 81 then evenly contact the internal shaft protection plate 83, which is located directly below the internal shaft fall prevention rib 82. By screwing in the four bolts evenly, an equal pressing force is applied to the internal shaft protection plate 83 from four directions, resulting in a uniform pressing state. The internal shaft fall prevention bolts 81 are screwed in using the outer shaft 20 as a reaction force, and the pressing force acts on the internal shaft protection plate 83, preventing the internal shaft 21 from falling. (This process involves screwing the internal shaft fall prevention bolts into the internal shaft fall prevention bolt screw holes of the outer shaft, which has been prevented from falling, bringing the tips of the internal shaft fall prevention bolts into contact with the surface of the internal shaft protection plate, and using the outer shaft as a reaction force to apply the pressing force from screwing in the internal shaft fall prevention bolts to the internal shaft protection plate, thereby preventing the internal shaft from falling.)

[0088] (g) Remove the inner shaft connecting hole cover 40e provided on the outer circumference of the outer shaft 20, remove the inner shaft connecting jig 40d, and release the inner shaft connection. The inner shaft connecting hole cover 40e is provided larger than the inner shaft connecting hole 40c where the inner shaft connecting jig 40d is located, so that the inner shaft connecting jig 40d can be easily removed from the outer circumference of the outer shaft. As a result, the outer shaft 20 and inner shaft 21 of the upper shaft 90A are separated from the outer shaft 20 and inner shaft 21 of the lower shaft 90B. Then, the rotary drive device 7 is wound up with a wire to raise the drilling shaft 9X (upper shaft 90A), and the drilling shaft 9 (lower shaft 90B) that was previously constructed and separated is left in the ground. (Step of separating the lower shaft connected to the upper shaft and leaving the lower shaft in the ground)

[0089] (h) The detached drilling shaft 9X (upper shaft 90A) is moved to the position of the drilling shaft 91 for the subsequent pile construction. The drilling shaft 91 for the subsequent pile construction has a drilling head MH attached to its tip and is installed in the ground beforehand. That is, the configuration and construction process are the same as those described in the preceding drilling shaft retention process (a) to (g), except that the drilling head MH is attached to the drilling shaft 91 for the subsequent pile instead of the mixing unit 10 and is installed in the ground. An outer shaft fall prevention fitting plate 72 is inserted between the outer shaft fall prevention rib 71 of the outer shaft 20 of the drilling shaft 91 for the subsequent pile (lower shaft 90B) and the fall prevention work platform 4, and the outer shaft 20 of the drilling shaft 91 for the subsequent pile (lower shaft 90B) is supported by the fall prevention work platform 4. Furthermore, the inner shaft 21 of the excavation shaft 91 for the joint pile (lower shaft 90B) is prevented from falling by screwing an inner shaft fall prevention bolt 81 into the inner shaft fall prevention bolt screw hole 85 of the outer shaft, and pressing the tip of the inner shaft fall prevention bolt 81 against the inner shaft protection plate 83 provided directly below the inner shaft fall prevention rib.

[0090] The excavation shaft 9 (lower shaft 90B) constructed in advance is left in place with both the outer shaft 20 and the inner shaft 21 in a state where they are prevented from falling. In addition, in Embodiment 3, the inner shaft 21 of the lower shaft 90B is left in a state raised by 50 mm. Therefore, the inner shaft male part 40a of the lower shaft 90B and the inner shaft female part 40b of the lower shaft 90A, which has descended, can be easily connected to form the inner shaft connecting part 40, making the subsequent pile extraction and movement process easier.

[0091] <(C)(Subsequent construction process of pulling out and moving the jointed piles (i)~(l), see Figure 12)> (i) The lower end of the rotary drive unit 7 of the excavator 2 is lowered (in the negative Z-axis direction) to the upper end of the later-constructed excavation shaft 91 (lower shaft 90B) for the joint pile, which is already installed in the ground. Then, the inner shaft female part 40b protruding from the outer shaft female part 30b of the basic excavation shaft 9X (upper shaft 90A) and the inner shaft male part 40a inside the outer shaft male part 30a of the joint pile excavation shaft (lower shaft 90B) are connected by an inner shaft connecting jig 40d to form an inner shaft connecting part 40.

[0092] (j) The internal shaft fall prevention bolt 81 is unscrewed from the internal shaft fall prevention bolt screw hole 85 which is screwed into the outer shaft 20 of the excavation shaft 91 (lower shaft 90B) for the joint pile, which is installed in the ground, and the internal shaft fall prevention bolt screw hole stopper cover 86 is screwed into the internal shaft fall prevention bolt screw hole 85. Then, the outer shaft connecting jig 30d is inserted into the outer shaft connecting hole 30c of the outer shaft 20 of the basic excavation shaft 9X (upper shaft 90A) and the excavation shaft for the joint pile (lower shaft 90B) to form the outer shaft connecting section 30 and complete the connection.

[0093] (k) The wire 6 is used to wind up the basic drilling shaft 9X (upper shaft 90A) slightly, and the outer shaft fall prevention fitting plate 72 between the outer shaft fall prevention rib 71 of the joint pile drilling shaft 91 (lower shaft 90B) and the fall prevention work platform 4 is removed. Next, the rotary drive device 7 is used to rotate and raise the joint pile drilling shaft 91 (lower shaft 90B), which is connected to the basic drilling shaft 9X (upper shaft 90A), to the ground. After that, the drilling head 9MH 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 mixing and stirring section connecting part 65, the drilling head 9MH is supported by the fall prevention work platform 4.

[0094] (l) The basic drilling shaft 9X, which is connected to the rotary drive unit connecting shaft 8, is connected to the drilling shaft 91 for the subsequent construction of the extension pile. Then, the drilling machine 2 is moved directly above the lower shaft 90B that was left in the ground in step (g) above. Note that from the following steps onward, the drilling shaft 91 for the extension pile becomes the upper shaft 90A.

[0095] <(D) Pile splicing process (m)~(o), see Figure 13> (m) This is the process of connecting the upper shaft 90A to the lower shaft 90B, which is left in the ground with both the outer shaft 20 and the inner shaft 21 prevented from falling. The joint pile drilling shaft 91 (upper shaft 90A) is lowered, and the inner shaft female part 40b protruding from the outer shaft female part 30b at the bottom of the joint pile drilling shaft 91 (upper shaft 90A) and the inner shaft male part 40a inside the outer shaft male part 30a at the upper end of the drilling shaft 9 (lower shaft 90B) left in place from the previous construction are connected with an inner shaft connecting jig 40d to form the inner shaft connecting part 40 (process of forming the inner shaft connecting part). Next, the inner shaft fall prevention bolt 81 is unscrewed from the inner shaft fall prevention bolt screw hole 85 which is screwed into the outer shaft 20 of the drilling shaft 9 (lower shaft 90B), and the fall prevention of the inner shaft 21 is released. Then, the inner shaft fall prevention bolt screw hole stopper 86 is screwed into the inner shaft fall prevention bolt screw hole 85. (Step to unscrew the inner shaft fall prevention bolt)

[0096] (n) The wire 6 is lowered, and the female outer shaft part 30b at the bottom of the excavation shaft 91 (upper shaft 90A) for the joint pile to be constructed later and the male outer shaft part 30a at the top of the excavation shaft 9 (lower shaft 90B) left in place from the earlier construction are connected by the outer shaft connecting jig 30d, forming the outer shaft connecting part 30. Thus, the excavation shaft 91 (upper shaft 90A) for the joint pile to be constructed later and the excavation shaft 9 (lower shaft 90B) left in place from the earlier construction are formed as a single shaft 90 by the excavation shaft connecting part 60 (outer shaft connecting part 30 and inner shaft connecting part 40).

[0097] By slightly winding up with wire 6, the outer shaft fall prevention fitting plate 72, which is left between the outer shaft fall prevention rib 71 of the outer shaft 20 of the remaining drilling shaft 9 (lower shaft 90B) and the fall prevention work platform 4, can be easily removed.

[0098] In the connection process, where the later-constructed joint pile excavation shaft 91 (upper shaft 90A) is connected as a joint pile to the previously constructed excavation shaft 9 (lower shaft 90B), which is left in a position where there is no risk of the outer shaft 20 and inner shaft 21 falling, the inner shaft connection part 40 can be easily connected to the inner shafts 21 of the upper shaft 90A and the lower shaft 90B simply by unscrewing the inner shaft fall prevention bolt 81 from the inner shaft 20. Furthermore, by lowering the upper shaft 90A, the outer shafts 20 of the upper shaft 90A and the lower shaft 90B can be easily connected at the outer shaft connection part 30. Therefore, by raising the upper shaft 90A, the outer shaft 20 also rises in conjunction, and the outer shaft fall prevention fitting plate 72 of the lower shaft 90B can be easily removed. Thus, a single excavation shaft 90 is completed by connecting the joint pile excavation shaft 91 (upper shaft 90A) as a joint pile to the previously constructed excavation shaft 9 (lower shaft 90B).

[0099] (o) Penetration is resumed using a single drilling shaft 90, which is formed by connecting a joint drilling shaft 91 (upper shaft 90A) as a joint to the previously constructed drilling shaft 9 (lower shaft 90B). Then, improved construction is carried out for the designed improved length.

[0100] <When removing the extended piles> When withdrawing the pile, the drilling shaft 91 for the connecting pile, which was connected during penetration, can be easily removed by following the reverse procedure.

[0101] Using the connection structure and connection method of the shaft 90 of the ground improvement device 1, if the improvement length of the excavation shaft 9 used in the preceding construction is insufficient to meet the design improvement length, the number of subsequent excavation shafts 9M (M=1~N) for connecting piles used in the subsequent construction can be connected to satisfy the insufficient improvement length, making it easy to perform improvement work to the design improvement length.

[0102] <Internal shaft helical blade 26 and compressed air discharge mechanism 27> Figure 14 shows an internal shaft helical blade 26 disposed on the outer circumference of the internal shaft 21 directly above the stirring and mixing section 10 according to Embodiment 4 of the present invention. When the fluidized mixed soil attempts to enter between the internal shaft 21 and the external shaft 20, the rotation of the internal shaft helical blade 26 sends it back downward, preventing it from entering between the internal shaft 21 and the external shaft 20. And / or, a compressed air discharge mechanism 27 is provided at the top of the excavator 2 between the internal shaft 21 and the external shaft 20 (figure omitted) to prevent the inflow of fluidized mixed soil attempting to enter between the internal shaft 21 and the external shaft 20.

[0103] By employing the internal shaft helical blade 26 and / or the compressed air discharge mechanism 27, clogging by fluidized mixed soil can be prevented even if an internal shaft protection plate 83 protruding from the surface of the internal shaft 21, an internal shaft fall prevention rib 82 protruding outward from the internal shaft protection plate 83, and an internal shaft fall prevention bolt 81 are installed in a part of the gap between the internal shaft 21 and the external shaft 20. [Explanation of Symbols]

[0104] 1 Ground improvement equipment 2 Excavators 3 Leaders 4. Anti-vibration device (when installed on the ground: fall prevention work platform) 4a Groove 5 Ground 6 wires 7. Rotary drive device 8 Rotary drive unit connecting shaft 9. Drilling shaft 9X basic drilling axis 9M Drilling shaft for connecting pile (M=1~N) 9MH drilling head for drilling shaft for joint piles 90 shafts (a general term for drilling shafts, basic drilling shafts, and drilling shafts for joint piles) 90A upper shaft 90B lower shaft 10. Stirring and mixing section 20 Outer shaft 20a external helical wing 21 Inner shaft 22 Upper stage stirring blades 23 Lower stage stirring blades 24 Auxiliary stirring blades 24a upper horizontal wing 24b lower horizontal wing 24c Vertical wings on both sides 25 drilling blades S Allowable travel distance of the inner shaft impeller relative to the outer shaft impeller 26 Inner shaft spiral wing 27 Compressed air discharge mechanism 30 Outer shaft connection part 30a Outer shaft male part 30ap outer shaft male end 30b Outer shaft female part 30bp Outer shaft female end 30c Outer shaft connection hole 30d External shaft connecting jig 30e Outer shaft connection hole stopper cover 40 Inner shaft connection part 40a Inner shaft male part 40ap Internal shaft male end 40b Inner shaft female part 40bp inner shaft female end 40c Inner shaft connection hole 40d Internal shaft connecting jig 40e Inner shaft connecting hole stopper cover 50 Connecting shaft coupling section 60 Excavation shaft connection section 65 Stirring and mixing section connection 70 Outer shaft fall prevention device 71 Outer shaft drop prevention rib 72. Outer shaft fall prevention fitting plate 80. Inner shaft fall prevention device 81. Inner shaft fall prevention bolt 82. Inner shaft fall prevention rib 83 Inner shaft protection plate 84. Rib to prevent internal shaft rise 85 Internal shaft fall prevention bolt threaded hole 86. Inner shaft fall prevention bolt screw hole stopper cover

Claims

1. A connection structure for the shaft of a ground improvement device, comprising a double-tube structure with an outer shaft and an inner shaft, a rotary drive device that rotates the outer shaft and the inner shaft in opposite directions relative to each other, and multiple outer shafts and inner shafts connected vertically to form a shaft, the shaft being driven into the ground, The outer shaft comprises an outer shaft male portion at its upper end and an outer shaft female portion at its lower end. Below the outer shaft male portion, there is an inner shaft fall prevention bolt screw hole and an outer shaft fall prevention rib. When multiple outer shafts are connected vertically, the outer shaft male portion and the outer shaft female portion connect to form an outer shaft connecting portion between the upper and lower shafts. The inner shaft comprises an inner shaft male part inside the outer shaft male part and an inner shaft female part at the lower part of the outer shaft female part. Below the inner shaft male part is an inner shaft protection plate protruding from the inner shaft surface, and between the inner shaft protection plate and the inner shaft male part is an inner shaft fall prevention rib protruding outward from the inner shaft protection plate. 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 between the upper shaft and the lower shaft. The shaft connection structure for a ground improvement device is characterized in that, when the inner shaft connection is released, an inner shaft fall prevention bolt is screwed into the inner shaft fall prevention bolt screw hole of the outer shaft, which is prevented from falling, the tip of the inner shaft fall prevention bolt comes into contact with the surface of the inner shaft protection plate, and the pressing force caused by the screwing of the inner shaft fall prevention bolt, with the outer shaft as the reaction force, acts on the inner shaft protection plate, thereby preventing the inner shaft from falling.

2. The shaft connection structure for a ground improvement device according to claim 1, characterized in that the inner shaft further comprises an inner shaft rise prevention rib disposed below the inner shaft protection plate and protruding outward from the inner shaft protection plate.

3. The rotary drive device is provided with a stirring and mixing section at the lower end of the shaft, and the stirring and mixing section has an outer shaft stirring blade at the lower end of the outer shaft and an inner shaft stirring blade at the lower end of the inner shaft. The inner shaft has a permissible travel distance that allows the inner shaft stirring blade to move up and down relative to the outer shaft stirring blade, and is supported by a wire connected to the rotary drive device so as to be able to move up and down within the range of the permissible travel distance, and when the inner shaft connecting portion starts to make contact with the outer shaft connecting portion due to the upward movement within the range of the permissible travel distance, it is possible to connect without interference with the outer shaft connecting portion. The shaft connection structure for a ground improvement device according to claim 1, characterized in that the inner shaft is prevented from falling when the inner shaft connection is released after it has been moved upward to the upper limit of the allowable movement distance.

4. The shaft connection structure of the ground improvement device according to claim 1, characterized in that it is provided with an inner shaft helical blade and / or a compressed air discharge mechanism to prevent fluidized mixed soil from entering the gap between the inner shaft and the outer shaft.

5. A method for connecting the shafts of a ground improvement device, comprising: an outer shaft and an inner shaft forming a double-tube structure; a rotary drive device rotating the outer shaft and the inner shaft in opposite directions relative to each other; and connecting multiple outer shafts and inner shafts vertically to form a shaft, thereby penetrating the ground; The outer shaft comprises an outer shaft male portion at its upper end and an outer shaft female portion at its lower end. Below the outer shaft male portion, there is an inner shaft fall prevention bolt screw hole and an outer shaft fall prevention rib. When multiple outer shafts are connected vertically, the outer shaft male portion and the outer shaft female portion connect to form an outer shaft connecting portion between the upper and lower shafts. The inner shaft comprises an inner shaft male part inside the outer shaft male part and an inner shaft female part at the lower part of the outer shaft female part. Below the inner shaft male part is an inner shaft protective plate protruding from the inner shaft surface, and between the inner shaft protective plate and the inner shaft male part is an inner shaft fall prevention rib protruding outward from the inner shaft protective plate. 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 between the upper shaft and the lower shaft. When the inner shaft connection is released, the inner shaft is prevented from falling. An inner shaft fall prevention bolt is screwed into the inner shaft fall prevention bolt screw hole of the outer shaft, and the tip of the inner shaft fall prevention bolt contacts the surface of the inner shaft protection plate. The pressing force from the screwing of the inner shaft fall prevention bolt, with the outer shaft as the reaction force, acts on the inner shaft protection plate, thereby preventing the inner shaft from falling. The step of separating the lower shaft connected to the upper shaft and leaving the lower shaft in the ground is, A step to prevent the outer shaft of the lower shaft from falling, A step of releasing the connection between the upper shaft and the lower shaft at the outer shaft connecting portion, A method for connecting the shaft connection structure of a ground improvement device, characterized by comprising at least the steps of: screwing the inner shaft fall prevention bolt into the inner shaft fall prevention bolt helical hole of the outer shaft from which the fall has been prevented; bringing the tip of the inner shaft fall prevention bolt into contact with the surface of the inner shaft protection plate; and using the outer shaft as a reaction force, applying the pressing force caused by screwing the inner shaft fall prevention bolt to the inner shaft protection plate to prevent the inner shaft from falling.

6. The shaft connection structure of the ground improvement device is, The lower end of the shaft is provided with a stirring and mixing section, and the stirring and mixing section has an outer shaft stirring blade at the lower end of the outer shaft and an inner shaft stirring blade at the lower end of the inner shaft. The inner shaft has a permissible travel distance that allows the inner shaft stirring blade to move up and down relative to the outer shaft stirring blade, and when the inner shaft connecting portion begins to make contact with the outer shaft connecting portion due to upward movement within the range of the permissible travel distance, connection is possible without interference with the outer shaft connecting portion. The step of separating the lower shaft connected to the upper shaft and leaving the lower shaft in the ground is: A method for connecting the shaft connection structure of a ground improvement device according to claim 5, further comprising the step of raising the inner shaft to the upper limit of the allowable travel distance.

7. A method for connecting the shafts of a ground improvement device, comprising: an outer shaft and an inner shaft forming a double-tube structure; a rotary drive device rotating the outer shaft and the inner shaft in opposite directions relative to each other; and connecting multiple outer shafts and inner shafts vertically to form a shaft, thereby penetrating the ground; The outer shaft comprises an outer shaft male portion at its upper end and an outer shaft female portion at its lower end. Below the outer shaft male portion, there is an inner shaft fall prevention bolt screw hole and an outer shaft fall prevention rib. When multiple outer shafts are connected vertically, the outer shaft male portion and the outer shaft female portion connect to form an outer shaft connecting portion between the upper and lower shafts. The inner shaft comprises an inner shaft male part inside the outer shaft male part and an inner shaft female part at the lower part of the outer shaft female part. Below the inner shaft male part is an inner shaft protective plate protruding from the inner shaft surface, and between the inner shaft protective plate and the inner shaft male part is an inner shaft fall prevention rib protruding outward from the inner shaft protective plate. 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 between the upper shaft and the lower shaft. When the inner shaft connection is released, the inner shaft is prevented from falling. An inner shaft fall prevention bolt is screwed into the inner shaft fall prevention bolt screw hole of the outer shaft, which is prevented from falling. The tip of the inner shaft fall prevention bolt contacts the surface of the inner shaft protection plate, and the pressing force from the screwing of the inner shaft fall prevention bolt, with the outer shaft acting as a reaction force, acts on the inner shaft protection plate, thereby preventing the inner shaft from falling. The process of connecting the upper shaft to the lower shaft, which is left in the ground with both the outer shaft and the inner shaft prevented from falling, is as follows: The steps include lowering the upper shaft and connecting the female inner shaft portion of the upper shaft with the male inner shaft portion of the lower shaft to form the inner shaft connecting portion, A method for connecting the shaft connection structure of a ground improvement device, characterized by comprising at least the step of unscrewing the inner shaft fall prevention bolt, which prevents the inner shaft from falling, from the inner shaft fall prevention bolt helical hole of the lower shaft.

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