Excavation tool, method for reinforcing foundation pile using the same, and pile structure

Abstract

To provide an excavation tool capable of stably excavating the ground around a head of a pile driven into the ground.SOLUTION: An excavation jig 10 excavates the ground around a pile head 31 of a foundation pile 3 buried in the ground. The excavation jig 10 includes: a cylindrical casing 12 that rotates about an axis of the foundation pile 3 as a rotation axis CL; and an excavation blade 15 that is attached to a tip end of the casing 12 and is fixed in a spiral shape so as to make multiple revolutions around the rotation axis CL of the casing 12. A cutting edge 15a formed in a circumferential direction of the excavation blade 15 is formed so that a distance between the rotation axis CL and the cutting edge 15a increases as it moves from a tip 12a of the casing toward a base end.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an excavation tool for excavating the ground around the head of a foundation pile buried in the ground, a method for reinforcing the foundation pile using the same, and a pile structure. [Background technology]

[0002] As an example of this type of technology, Patent Document 1 discloses an excavation tool for excavating the ground around the head of a foundation pile buried in the ground. This excavation tool has a cylindrical casing that rotates around the axis of the foundation pile as its rotation axis, and a propulsion blade (digging blade) that is attached to the tip of the casing and excavates the ground. The propulsion blade has a spiral blade shape that goes around the rotation axis of the casing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-66010 A Summary of the Invention [Problem to be solved by the invention]

[0004] For example, assume that the helical drilling blade shown in Patent Document 1 is provided to rotate around the rotation axis of the casing multiple times while maintaining the same radius in order to improve excavation performance. When such an excavation jig is used, the tip of the drilling blade is in close contact with the ground nearby, so when attempting to pull out (pull up) the excavation jig, negative pressure is generated between them, and air is unlikely to enter from above due to the helical shape that rotates multiple times. As a result, when the excavation jig is pulled out, the ground around the pile head formed by the drilling of the drilling blade collapses, making the ground prone to loosening.

[0005] The present invention has been made in consideration of these points, and its object is to provide an excavation jig that can stably excavate the ground around the head of a pile driven into the ground. [Means for solving the problem]

[0006] In consideration of the above problems, the excavation jig of the present invention is an excavation jig for excavating the ground around the head of a foundation pile buried in the ground, and comprises a cylindrical casing that rotates around the axis of the foundation pile as its rotation axis, and a excavation blade that is attached to the tip side of the casing and fixed in a spiral shape so as to make multiple revolutions around the rotation axis of the casing, and the cutting edge formed in the circumferential direction of the excavation blade is formed so that the distance between the rotation axis and the cutting edge increases as it progresses from the tip of the casing toward the base end.

[0007] According to the present invention, the excavation blade is helical (helical blade-shaped) and fixed so as to rotate multiple times, so that the excavation tool can efficiently excavate the ground around the head of the foundation pile while rotating around the rotation axis of the casing. In particular, the cutting edge formed in the circumferential direction of the excavation blade is formed so that the distance between the rotation axis and the cutting edge increases as it moves from the tip of the casing to the base end side, so that the excavation tool can be pushed into the ground more efficiently while excavating the ground around the head of the pile. Furthermore, when the excavation tool is removed after excavation, air tends to flow from the wall surface of the excavated ground toward the tip of the excavation blade, so that the excavation tool can be easily removed from the ground. As a result, when the excavation tool is removed, the ground around the head of the pile formed by the excavation of the excavation blade is prevented from collapsing, and the ground is prevented from becoming loose.

[0008] In a more preferred embodiment, on a cutting surface of the excavation blade along the rotation axis, among the cutting edges located on both sides of the rotation axis, the multiple cutting edges located on each side are arranged on a straight line.

[0009] According to this aspect, the wall surface of the recess formed in the excavated ground has a tapered circumferential surface close to the circumferential surface of a truncated cone, so that when the excavation jig is pulled out, air tends to flow from the wall surface of the excavated ground toward the tip of the excavation blade, making it easier to pull out the excavation jig from the ground.

[0010] In a more preferred embodiment, at least one notch is formed in the cutting edge of the digging blade when viewed from the direction along the rotation axis.

[0011] According to this aspect, by providing a notch at the cutting edge of the digging blade, air can easily flow from above to below through the notch when the digging jig is pulled out. As a result, the digging jig can be easily pulled out of the ground.

[0012] In a further preferred embodiment, the cutting edge has a plurality of notches formed at positions adjacent to each other in the vertical direction. According to this embodiment, since the plurality of notches are formed at positions adjacent to each other in the vertical direction, when the excavation jig is pulled out, a flow path for air to flow between the notches is easily formed. In particular, it is preferable that, in a pair of notches adjacent to each other in the vertical direction, when viewed from below along the rotation axis, the notch located at the upper side is inserted into the notch located at the lower side. This makes it even easier to form a flow path for air to flow between the notches when the excavation jig is pulled out.

[0013] In a more preferred embodiment, a through hole penetrating into the inside of the casing is formed on the base end side of the casing. According to this embodiment, when the drilling jig is pulled out of the ground, negative pressure is likely to be generated inside the casing, but by providing the through hole, air can be taken into the inside of the casing through the through hole.

[0014] In this specification, a method for reinforcing the foundation pile driven into the ground using the above-mentioned excavation tool is proposed. This reinforcement method includes at least the steps of: rotating the excavation tool around the rotation axis and pushing the excavation tool into the ground so that the pile head fits inside the casing from the tip of the casing, while excavating the ground around the pile head of the foundation pile with the excavation blade; and forming a reinforcing body having a truncated cone shape whose diameter increases as it advances to the ground surface and is placed in the excavated ground so as to be inserted into the pile head.

[0015] In the reinforcement method according to the present invention, first, by using the above-mentioned excavation tool, the excavation tool is rotated and pushed in, while the excavation tool is used to efficiently excavate the ground around the head of the foundation pile with the excavation blade. Furthermore, after excavation, a truncated cone-shaped excavation hole is formed around the head of the pile, so that a truncated cone-shaped reinforcement body can be easily formed in this excavation hole.

[0016] Furthermore, the present invention proposes the following pile structure, which includes a foundation pile driven into the ground, and a reinforcing body having a truncated cone shape whose diameter increases toward the ground surface and is disposed so as to pass through the pile head of the foundation pile.

[0017] According to this pile structure, a reinforcing body having a truncated cone shape is inserted into the head of the foundation pile and placed on the ground, thereby increasing the bearing capacity of the foundation pile in both the vertical and horizontal directions. Effect of the Invention

[0018] According to the present invention, it is possible to stably excavate the ground around the head of a pile driven into the ground. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1(a) is a side view of a drilling jig according to a first embodiment of the present invention, and (b) is a schematic perspective view of the drilling jig shown in (a). [Diagram 2]FIG. 2(a) is a bottom view of the excavation jig shown in FIG. 1 as viewed from below along the rotation axis, and FIG. 2(b) is a cross-sectional view taken along line AA in FIG. [Diagram 3] FIG. 2(a) is a side view of an excavator connected to the excavation jig shown in FIG. 1, and FIG. 2(b) is a front view of FIG. [Figure 4] 2(a) to 2(f) are diagrams illustrating a method for reinforcing a foundation pile using the excavation jig shown in FIG. [Diagram 5] FIG. 11 is a schematic perspective view showing a drilling jig according to a second embodiment. [Figure 6] 6(a) is a bottom view of the excavation jig shown in FIG. 5, viewed from below along the rotation axis, and FIG. 6(b) is a partially enlarged cross-sectional view showing the excavation jig being pulled out of the ground. [Figure 7] 6(a) to 6(d) are schematic diagrams illustrating modified examples of the excavation jig shown in FIG. [Figure 8] 1A is an analysis result showing the horizontal displacement of the pile head when a horizontal load is applied to the pile structures of the embodiment and the comparative example, FIG. 1B is an example of an analysis result of the ground near the pile head of the pile structure of the comparative example when a horizontal load is applied, and FIG. 1C is an example of an analysis result of the ground near the pile head of the pile structure of the embodiment when a horizontal load is applied. [Figure 9] 13(a) is an analysis result showing the vertical displacement of the pile head when a vertical load is applied to the pile structures of the embodiment and the comparative example, (b) is an example of an analysis result of the ground near the pile head of the pile structure of the comparative example when a vertical load is applied, and (c) is an example of an analysis result of the ground near the pile head of the pile structure of the embodiment when a vertical load is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an excavation tool according to a first and second embodiment of the present invention, a method for reinforcing a foundation pile using the same, and a pile structure will be described with reference to Figs. 1 to 9.

[0021] [First embodiment] 1. About the drilling jig 10 The excavation jig 10 according to this embodiment is a jig for excavating the ground around the pile head 31 of the foundation pile 3 buried in the ground, using an excavator 50 described later. In this embodiment, the foundation pile 3 is an existing pile driven into the ground G, and is not particularly limited to a wooden pile, a steel pipe pile, a concrete pile, or the like.

[0022] The drilling jig 10 comprises a connection part 11 connected to the drilling machine 50, a casing 12 whose base end is fixed to the connection part 11 and whose tip end is open, and a drilling blade 15 attached to the tip side of the casing 12. The connection part 11 is a part that is attached to the lifting head 52 of the drilling machine 50, and has a locking protrusion 11a that is locked to the lifting head 52 around the rotation axis CL. The connection part 11 and the casing 12 are cylindrical, and the casing 12 has a larger outer diameter than the connection part 11. The connection part 11 is connected to the casing 12 along the axial direction.

[0023] The casing 12 is connected to the lifting head 52 via the connection part 11, and is a part that rotates around the axis of the foundation pile 3 as the rotation axis CL during excavation. The casing 12 has a cylindrical main body 12e, and an opening 12b into which the pile head part 31 of the foundation pile 3 is inserted is formed at a tip 12a corresponding to the lower end of the cylindrical main body 12e. A top plate part 12c that covers the opening of the cylindrical main body 12e is formed at the base end side of the casing 12. Through holes 12h, 12j, and 12k that penetrate the casing 12 are formed at (the base end side of) the cylindrical main body 12e of the casing 12 so as to communicate the internal space of the cylindrical main body 12e of the casing 12 with the outside air.

[0024] More specifically, as shown in Figs. 1(a) and (b), a through hole 12k is formed in the side wall of the cylindrical body 12e so as to communicate the internal space of the cylindrical body 12e of the casing 12 with the outside air. The through hole 12k is a long hole formed in the upper part of the side wall of the cylindrical body 12e and above the drilling blade 15 along the axial direction of the cylindrical body 12e. The through hole 12k is of a size that allows the inside of the cylindrical body 12e to be visually confirmed from the outside through the through hole 12k. As a result, when the drilling jig 10 is pulled out of the ground, negative pressure is likely to be generated inside the casing, but by providing the through hole 12k, air can be smoothly taken into the inside of the cylindrical body 12e of the casing 12 through the through hole 12k. Furthermore, during drilling, the position of the pile head 31 relative to the casing 12 can be confirmed through the through hole 12k. Furthermore, after drilling, the soil and sand stuck in the cylindrical body 12e can also be removed through the through hole 12k. It is preferable that the through-holes 12k are formed within a circumferential angle range of 20° to 45° of the cylindrical main body 12e, for example.

[0025] 2, a through hole 12j is formed in the center of the top plate portion 12c, which communicates the internal space of the cylindrical main body 12e with the internal space of the cylindrical connecting portion 11. The through hole 12j is a circular hole having a size substantially equal to the inner diameter of the connecting portion 11. Air can be smoothly taken in from the open opening of the connecting portion 11 through the internal space of the connecting portion 11 and the through hole 12j into the internal space of the cylindrical main body 12e of the casing 12. In addition, a through hole 12h communicating with the internal space of the cylindrical main body 12e may be formed on the periphery of the top plate portion 12c.

[0026] The excavation blade 15 is attached to the tip 12a side of the casing 12, and is fixed in a spiral shape so as to make a plurality of revolutions around the rotation axis CL of the casing 12. In this embodiment, the excavation blade 15 has four consecutive stages of excavation blades 15A to 15D formed so as to make four revolutions around the rotation axis CL of the casing 12. These excavation blades 15A to 15D are fixed at positions forming a spiral on the outer circumferential surface of the casing 12, and in this embodiment, as an example, the pitch of the spiral is the same pitch.

[0027] In this embodiment, the cutting edge 15a formed in the circumferential direction of the excavation blade 15 is formed so that the distance between the rotation axis CL and the cutting edge 15a increases as the cutting edge 15a moves from the tip 12a of the casing 12 toward the base end. Specifically, as shown in FIG. 2(a), when the excavation jig 10 is viewed from below along the rotation axis CL, the cutting edge 15a is formed in a spiral shape. Therefore, the distances increase in the order of the distance R1 between the cutting edge 15a of the excavation blade 15A and the rotation axis CL, the distance R2 between the cutting edge 15a of the excavation blade 15B and the rotation axis CL, the distance R3 between the cutting edge 15a of the excavation blade 15C and the rotation axis CL, and the distance R4 between the cutting edge 15a of the excavation blade 15D and the rotation axis CL.

[0028] 2(b), in the cutting surface of the excavation blade 15 along the rotation axis CL, among the cutting edges 15a located on both sides of the rotation axis CL, the multiple cutting edges 15a located on each side are arranged on a straight line L. By linearly increasing the distance between the rotation axis CL and the cutting edges 15a as one moves from the tip 12a of the casing 12 toward the base end, the multiple cutting edges 15a can be arranged on the straight line L.

[0029] Furthermore, the straight line L and the rotation axis CL are inclined at a predetermined inclination angle θ, which is preferably in the range of 1° to 45°, and more preferably in the range of 10° to 45°. The inclination angle θ can be set by setting the rate of increase in the distance between the rotation axis CL and the cutting edge 15a as it progresses from the tip 12a of the casing 12 toward the base end.

[0030] As shown in Figs. 3(a) and (b), the excavator 50 is provided with a control room and an engine room on a chassis 50A. An arm 51 is held vertically on the chassis 50A, and the arm 51 is configured so that the angle can be changed to an inclined state or a horizontal state by a hydraulic cylinder. A lifting head 52 is attached to the arm 51 so as to be movable up and down. The lifting head 52 is provided with a chuck mechanism (not shown) for gripping the connection part 11 of the excavation jig 10, and the excavation jig 10 is connected and fixed below the lifting head. Furthermore, a drive part (not shown), such as a hydraulic motor for rotating the excavation jig 10, is incorporated in the lifting head 52. The excavation jig 10 is attached to such an excavator 50 to reinforce the foundation pile 3 driven into the ground G shown in Fig. 4.

[0031] 2. Reinforcement method for foundation pile 3 A method for reinforcing a foundation pile 3 driven into the ground G using the excavation jig 10 will be described below. In this embodiment, as shown in FIG. 4(a), the foundation pile 3 is driven into the ground G such that the pile head 31 is located below the ground surface GL, as an example. In this embodiment, a recess HA is provided in the ground surface GL, so that the pile head 31 is exposed from the ground surface GL. The excavation jig 10 is placed above the foundation pile 3 such that the rotation axis of the excavation jig 10 coincides with the axis of the pile head 31 of the foundation pile 3.

[0032] Next, as shown in FIG. 4(b), the drilling jig 10 is rotated around the rotation axis CL so that the pile head 31 of the foundation pile 3 fits inside the casing 12 from the tip of the casing 12, and while the drilling jig 10 is pushed into the ground G, the ground G around the pile head 31 of the foundation pile 3 is excavated with the drilling blade 15. In this way, by using the driven foundation pile (existing pile) 3 as a guide, it is possible to excavate concentrically with the foundation pile 3, and excavation can be performed with high accuracy without having to excavate the ground around the pile greatly and loosening it. In addition, damage to the foundation pile 3 during excavation can be avoided.

[0033] According to this embodiment, the excavation blade 15 is helical (helical blade-shaped) and fixed so as to rotate around the rotation axis of the casing multiple times, so that the ground G around the pile head 31 of the foundation pile 3 can be efficiently excavated while rotating the excavation jig 10 around the rotation axis CL of the casing 12. In particular, the cutting edge 15a formed in the circumferential direction of the excavation blade 15 is formed so that the distance between the rotation axis CL and the cutting edge 15a increases as it proceeds from the tip 12a of the casing 12 to the base end side. This allows the excavation jig 10 to be smoothly pushed into the ground G while excavating the ground G around the pile head 31. As a result, the wall surface Ha of the excavation hole HB can be compacted while part of the soil C of the excavated ground G is scraped out to the ground surface GL by the helical excavation blade 15.

[0034] Next, as shown in FIG. 4(c) and (d), after the completion of excavation, the drilling jig 10 is pulled out from the ground G. At this time, the drilling jig 10 may be rotated around the rotation axis CL in the opposite direction to that during excavation. In this embodiment, when the drilling jig 10 is pulled out from the ground G, air is likely to flow from the wall surface Ha of the drilling hole HB of the excavated ground G toward the tip of the drilling blade 15 due to the cutting edge 15a of the drilling blade 15, so that the drilling jig 10 is easily pulled out from the ground G. As a result, when the drilling jig 10 is pulled out (pulled up), the ground G around the pile head 31 formed by the drilling of the drilling blade 15 is prevented from collapsing, and the ground G is prevented from becoming loose. In particular, drilling the drilling hole HB in a tapered shape is more effective in protecting (holding) the hole wall than vertical drilling.

[0035] In particular, the wall surface Ha of the drilling hole HB formed in the excavated ground G has a tapered circumferential surface close to the circumferential surface of a truncated cone, so that when the drilling jig 10 is pulled out, air tends to flow from the wall surface Ha of the drilling hole HB in the excavated ground G toward the tip of the drilling blade 15, making it easy to pull out the drilling jig 10 from the ground G. In this way, a reinforcing drilling hole HB as shown in Fig. 4(d) can be formed. In addition, since there is no need to provide equipment for supplying air to the tip of the drilling jig 10, this is economical and easy to maintain.

[0036] Furthermore, the base end side of the casing 12 is formed with through holes 12h, 12j, and 12k penetrating into the inside of the casing 12, so that when the drilling jig 10 is pulled out of the ground G, negative pressure is likely to be generated inside the casing, but by providing the through holes 12h, 12j, and 12k, air can be taken into the inside of the casing through the through holes 12h, 12j, and 12k. Note that, although three through holes 12h, 12j, and 12k are provided in this embodiment, it is not necessary to provide all of these, and it is sufficient to provide at least one through hole as long as air can be smoothly taken into the inside of the cylindrical main body 12e of the casing 12.

[0037] Next, as shown in FIG. 4(e), concrete is poured into the excavated hole HB to form the reinforcing body 41. This allows the reinforcing body 41 to be placed in the excavated ground so that it is inserted into the pile head 31 of the foundation pile 3. The reinforcing body 41 has a truncated cone shape with a larger diameter as it advances to the ground surface GL. The reinforcing body 41 may be formed as a truncated cone-shaped ground improvement body made by mixing the excavated soil and cement, or a concrete block to be the reinforcing body 41 may be formed and inserted into the pile head 31 to be placed in the excavated hole HB. After that, as shown in FIG. 4(f), the foundation 42 of the building is placed so as to cover the pile head 31 from above.

[0038] In this manner, by using the drilling jig 10, the ground G around the pile head 31 of the foundation pile 3 can be efficiently excavated by the drilling blade 15 while rotating and pushing the drilling jig 10. Furthermore, after excavation, a drilled hole HB having a truncated cone shape is formed around the pile head 31, and a reinforcing body 41 having a truncated cone shape can be easily formed in this drilled hole HB.

[0039] Furthermore, the pile structure 1 thus obtained is a structure including the foundation pile 3 driven into the ground G, and the reinforcing body 41, which is arranged to be inserted into the pile head 31 of the foundation pile 3 and has a truncated cone shape whose diameter increases toward the ground surface GL. As a result, the reinforcing body 41 having a truncated cone shape is arranged in the ground G in a state where it is inserted into the pile head 31 of the foundation pile 3, so that the bearing capacity of the foundation pile 3 in the vertical and horizontal directions can be increased.

[0040] Furthermore, by using the excavation jig 10 according to this embodiment, it is possible to attach it to a small crane-type construction machine such as a pole erection vehicle for excavation, so that the excavated soil can be easily removed, and construction can be carried out even in narrow areas. Also, since excavation can be carried out with a small crane type, it does not affect the construction of the pile driver, and it is highly workable and economical.

[0041] Second Embodiment The drilling jig 10 according to the second embodiment, the method for reinforcing a foundation pile using the same, and the pile structure 1 will be described below with reference to Figures 5 to 7. The drilling jig 10 of the second embodiment differs from that of the first embodiment in that a notch 16 is provided in the drilling jig 10. Therefore, the following mainly describes the differences, and other detailed descriptions are omitted.

[0042] 5 and 6(a), in this embodiment, at least one notch 16 is formed in the cutting edge 15a of the excavation blade 15 when viewed from a direction along the rotation axis CL of the excavation jig 10. Specifically, in this embodiment, a plurality of notches 16 are formed in the cutting edge 15a at equal intervals in the circumferential direction (specifically, at equal angles: 180° positions).

[0043] The notch 16 is a V-shaped notch, and is formed so that the tip of the notch 16 forms an acute angle. By providing such a V-shaped notch, the ground G comes into contact with the oblique side forming the notch 16 during excavation, making it easier to crush the ground G and also making it easier to push the soil C of the crushed ground G outward beyond the cutting edge 15a of the excavation blade 15.

[0044] In this embodiment, the multiple notches 16 are formed at positions adjacent to each other in the vertical direction. Specifically, as shown in Fig. 6(a), two notches 16 are formed in the cutting edge 15a of each of the excavation wings 15A to 15D that rotate around the rotation axis CL. The two notches 16 formed in each of the excavation wings 15A to 15D are formed at positions facing each other across the rotation axis CL. Among the notches 16A to 16D of each of the excavation wings 15A to 15D, the notches 16A to 16D located in the vertical direction are formed at the same position in the circumferential direction.

[0045] Here, "the notches 16A to 16D are at the same circumferential position" means that in polar coordinates centered on the rotation axis CL, a part of the internal space of the notches 16 located in the vertical direction is present at the same angle around the rotation axis CL. Therefore, when viewed from below along the rotation axis CL, the notches 16A to 16D are arranged in the radial direction. Note that, in the present embodiment, as an example, the tips of the V-shaped notches 16 coincide around the rotation axis CL.

[0046] Further, as shown in FIG. 6(a), when viewed from below along the rotation axis CL, a pair of adjacent cutouts 16 in the vertical direction have the cutout 16 located on the upper side inserted into the cutout 16 located on the lower side. Specifically, the cutout 16B of the excavation wing 15B located above the cutout 16A of the excavation wing 15A is inserted into the cutout 16A of the excavation wing 15A. Similarly, the cutout 16C of the excavation wing 15C located above the cutout 16B of the excavation wing 15B is inserted into the cutout 16B of the excavation wing 15B, and the cutout 16D of the excavation wing 15D located above the cutout 16C of the excavation wing 15C is inserted into the cutout 16C of the excavation wing 15C.

[0047] In this embodiment, as shown in Fig. 6(b), by providing a notch 16 on the cutting edge 15a of the digging blade 15, when the digging jig 10 is pulled out, air A can easily flow from above to below through the notch 16. As a result, the digging jig 10 can be easily pulled out from the ground G. In particular, since the multiple notches 16A-16D are formed at positions adjacent to each other in the vertical direction, when the digging jig 10 is pulled out, a flow path through which air A flows is easily formed between the vertically adjacent notches 16A-16D.

[0048] In particular, in a pair of vertically adjacent notches 16, when viewed from below along the rotation axis CL, the upper notch 16 is inserted inside the lower notch 16, so that when the drilling jig 10 is pulled out, a flow path through which air A flows is more easily formed between the vertically adjacent notches 16.

[0049] In this embodiment, two notches 16 are provided in each of the excavation wings 15A to 15D, but for example, one notch 16 may be provided in the circumferential direction as shown in Fig. 7(a), three notches 16 may be provided at equal intervals in the circumferential direction as shown in Fig. 7(b), or four notches 16 may be provided at equal intervals in the circumferential direction as shown in Fig. 7(c). Furthermore, in this embodiment, the shape of the notch 16 is V-shaped, but for example, the shape of the notch 16 may be an arc shape as shown in Fig. 7(d), or may be a U-shape or a trapezoid shape.

[0050] The pile structure was analyzed as follows. As an example, an analytical model of the pile structure (with a truncated cone-shaped reinforcement) as shown in FIG. 4(e) was created, and the displacement of the pile head when a horizontal load and a horizontal load were applied to the pile head was analyzed. As a comparative example, an analytical model with a cylindrical reinforcement of the same volume and length as the example was created, and the displacement of the pile head when a horizontal load and a horizontal load were applied to the pile head was analyzed. The results of these analyses are shown in FIG. 8 and FIG. 9.

[0051] FIG. 8(a) is an analysis result showing the horizontal displacement of the pile head when horizontal or vertical load is applied to the pile structure according to the embodiment and the comparative example, FIG. 8(b) is an example of an analysis result of the ground near the pile head of the pile structure according to the comparative example when horizontal load is applied, and FIG. 8(c) is an example of an analysis result of the ground near the pile head of the pile structure according to the embodiment when horizontal load is applied. FIG. 9(a) is an analysis result showing the vertical displacement of the pile head when vertical load is applied to the pile structure according to the embodiment and the comparative example, FIG. 9(b) is an example of an analysis result of the ground near the pile head of the pile structure according to the comparative example when vertical load is applied, and FIG. 9(c) is an example of an analysis result of the ground near the pile head of the pile structure according to the embodiment when vertical load is applied. Note that the tapered ones shown in FIG. 8(a) and FIG. 9(b) are the results corresponding to the embodiment, and the ones without the tapered ones are the results corresponding to the comparative example.

[0052] As shown in Fig. 8(a), when comparing a pile structure provided with a reinforcement body of the comparative example (without taper) with a pile structure provided with a reinforcement body of the embodiment (with taper), it was found that the horizontal bearing capacity was increased and the horizontal displacement (subsidence) was reduced by providing a reinforcement body as in the embodiment. This is also clear from the fact that the range of plastic deformation of the ground around the pile head in the pile structure of the embodiment in Fig. 8(c) is smaller than the range of plastic deformation of the ground around the pile head in the pile structure of the comparative example in Fig. 8(b).

[0053] As shown in Fig. 9(a), when comparing a pile structure provided with a reinforcement body of the comparative example (without taper) with a pile structure provided with a reinforcement body of the embodiment (with taper), it was found that by providing a reinforcement body as in the embodiment, a wedge effect is also added, increasing the vertical bearing capacity, and the vertical displacement (subsidence) of the tip of the pile head is reduced. This is also clear from the fact that the range of plastic deformation of the ground around the pile head in the pile structure of the embodiment in Fig. 9(c) is smaller than the range of plastic deformation of the ground around the pile head in the pile structure of the comparative example shown in Fig. 9(b).

[0054] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as described in the claims.

[0055] In this embodiment, one continuous helical excavation blade is formed as the excavation blade, but for example, multiple (for example, two) helical excavation blades may be provided. For example, when two excavation blades are provided, the excavation blades may be provided so that the multiple excavation blades are continuously arranged between the multiple excavation blades shown in FIG. [Explanation of symbols]

[0056] 1: pile structure, 3: foundation pile, 10: drilling tool, 12: casing, 12h: through hole, 15: drilling blade, 15a: cutting edge, 16: notch, 31: pile head, 41: reinforcing body, CL: rotating shaft, G: ground, GL: ground surface

Claims

1. An excavation tool for excavating the ground around the pile head of a foundation pile buried in the ground, A cylindrical casing that rotates about the axis of the foundation pile as a rotation axis; A digging blade is attached to the tip side of the casing and is fixed in a spiral shape so as to rotate around the rotation axis of the casing multiple times, A drilling tool characterized in that the cutting edge formed in the circumferential direction of the drilling blade is formed so that the distance between the rotation shaft and the cutting edge increases as the blade moves from the tip of the casing toward the base end.

2. The excavation tool according to claim 1, characterized in that, on the cutting surface of the excavation blade along the rotation axis, the cutting edges located on both sides of the rotation axis, and the multiple cutting edges located on each side are arranged in a straight line.

3. The excavation tool according to claim 1, wherein at least one notch is formed in the cutting edge of the excavation blade when viewed from a direction along the rotation axis.

4. The excavation jig according to claim 3 , wherein a plurality of notches are formed in the cutting edge, and the plurality of notches are formed at positions adjacent to each other in the vertical direction.

5. The drilling jig described in claim 4, characterized in that in a pair of adjacent notches in the vertical direction, when viewed from below along the rotation axis, the upper notch is inserted inside the lower notch.

6. The drilling jig according to claim 1 , wherein a through hole penetrating into the inside of the casing is formed on a base end side of the casing.

7. A method for reinforcing the foundation piles driven into the ground using the excavation jig according to claim 1, A step of rotating the excavation tool around the rotation axis so that the pile head fits inside the casing from the tip of the casing, and excavating the ground around the pile head of the foundation pile with the excavation blade while pushing the excavation tool into the ground; A step of forming a reinforcing body having a truncated cone shape that is placed in the excavated ground so as to be inserted into the pile head and has a diameter that increases toward the ground surface; A method for reinforcing a foundation pile, comprising at least the steps of:

8. Foundation piles driven into the ground, A pile structure comprising: a reinforcing body that is arranged to be inserted into the pile head of the foundation pile and has a truncated cone shape whose diameter increases as it extends toward the ground surface.

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