Enlarged drilling device

Abstract

To provide an expansion drilling device capable of efficiently and reliably expanding an expansion wing.SOLUTION: An expansion drilling device 100 comprises a plurality of support shafts 13 arranged at equal intervals along the circumferential direction of a drilling shaft 10, and expansion blades 11 rotatably attached to each of the plurality of support shafts 13, and, during pile hole drilling work in which the drilling rod rotates forward, the expansion blade 11 receives earth pressure to maintain a reduced diameter state, and during expansion drilling work in which the drilling rod rotates reversely, the expansion blade 11 receives earth pressure to rotate around the support shaft 13 and expand until a part of the expansion blade 11 abuts the outer periphery of the drilling shaft 10, maintaining an expanded diameter state. The expansion blade 11 has a shape in which a midsection thereof is curved or bent outward so that a plurality of drill bits 15a to 15c, arranged in a line on its outer surface from the support shaft 13 side toward a tip 11a side, come into contact with an inner surface of a hole wall in order from the support shaft 13 side toward the tip 11a side as the expansion blade 11 performs its diameter expansion operation.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an enlargement excavation device for enlarging the tip of a pile hole formed in the ground to construct a root ball reinforcement part.

Background Art

[0002] As an enlargement excavation device for enlarging the tip of a pile hole formed in the ground to form a root ball reinforcement part, for example, there is an enlargement excavation device described in Patent Document 1. This enlargement excavation device includes an excavation shaft that can be integrally connected to the tip of an excavation rod, a plurality of support shafts that are parallel to the axis of the excavation shaft on the outer periphery of the excavation shaft and are arranged at equal intervals along the circumferential direction of the excavation shaft, and enlargement wings that are rotatably attached to each support shaft. During the pile hole excavation operation in which the excavation rod rotates forward, the enlargement wings receiving earth pressure maintain a reduced diameter state. During the enlargement excavation operation in which the excavation rod rotates reversely, the enlargement wings receiving earth pressure rotate around the support shafts to become an enlarged diameter state, and in that state, together with the excavation shaft, the plurality of enlargement wings rotate to enlarge and drill the surrounding ground.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] And in this enlargement excavation, the longer the enlargement wings become in order to form a root ball reinforcement part with a larger diameter, the shallower the angle at which the tip of the enlargement wing contacts the inner surface of the hole wall during the enlarged diameter operation becomes, and there is a possibility that the tip of the enlargement wing does not properly engage with the inner surface of the hole wall and the enlarged diameter operation fails.

[0005] Therefore, the objective of the present invention is to provide an expanding excavation device that can efficiently and reliably expand the expanding blades. [Means for solving the problem]

[0006] The present invention provides an enlarged drilling device comprising a drilling shaft that can be connected to a drilling rod so as to rotate integrally with it, a plurality of support shafts arranged on the outer circumference of the drilling shaft parallel to the axis of the drilling shaft and at equal intervals along the circumferential direction of the drilling shaft, and an enlarged wing rotatably attached to each of the plurality of support shafts, wherein during pile hole drilling work in which the drilling rod rotates in the forward direction, the enlarged wing, subjected to earth pressure, maintains a reduced diameter state, and during enlarged drilling work in which the drilling rod rotates in the reverse direction, the enlarged wing, subjected to earth pressure, rotates around the support shafts and expands until a part of the enlarged wing contacts the outer circumference of the drilling shaft, thereby maintaining an expanded diameter state, wherein the enlarged wing has a shape in which its middle section is curved or bent outward so that a plurality of drilling bits arranged in a line from the support shaft side toward the tip side on its outer surface come into contact with the inner surface of the hole wall in order from the support shaft side toward the tip side as the enlarged wing expands in diameter.

[0007] According to the expanding drilling device of the present invention, the drilling bit closest to the support shaft side of the expanding wing contacts the inner surface of the borehole wall at an early stage of the expanding wing's diameter expansion movement, before the drilling bit at the tip of the expanding wing, and engages with the inner surface of the borehole wall, thereby allowing the expanding wing to expand. As the expanding wing expands, the drilling bits from the support shaft side to the tip side contact the inner surface of the borehole wall in sequence, causing the expanding wing to expand while gradually drilling the inner surface of the borehole wall. [Effects of the Invention]

[0008] According to the present invention, the expanding wing can be expanded efficiently and reliably, making it possible to form a large-diameter root-reinforcement bulb with the limited power required to rotate the drilling rod. [Brief explanation of the drawing]

[0009] [Figure 1]This is a vertical cross-sectional view showing the state of use of the enlarged drilling device according to an embodiment of the present invention (with the enlarged blades in a reduced diameter state). [Figure 2] Figure 1 is a perspective view of the enlarged drilling machine. [Figure 3] This is a view from the X-arrow, with the enlarged wing in Figure 2 omitted. [Figure 4] Figure 1 is a plan view showing the initial state of the diameter expansion operation of the enlargement drilling device. [Figure 5] This is a plan view showing the intermediate state of the diameter expansion operation of the enlargement drilling machine shown in Figure 1. [Figure 6] Figure 1 is a plan view showing the maximum diameter expansion state of the enlargement drilling device. [Figure 7] This is an explanatory diagram showing the orientation of the drilling bit at the tip of the expanding wing that cuts the hole wall when the angle of the expanding wing's support axis is 0°. [Figure 8] This is an explanatory diagram showing the orientation of the drilling bit at the tip of the expanding wing that cuts the hole wall when the angle of the expanding wing's support axis is θ. [Figure 9] This is a perspective view showing another embodiment of the expansion drilling device. [Figure 10] Figure 9 is a plan view showing the initial state of the diameter expansion operation of the enlargement drilling device. [Figure 11] Figure 9 is a plan view showing the intermediate state of the diameter expansion operation of the enlargement drilling device. [Figure 12] Figure 9 is a plan view showing the maximum diameter expansion state of the enlargement drilling device. [Modes for carrying out the invention]

[0010] As shown in Figure 1, the enlargement excavation device 100 in the embodiment of the present invention is for enlarging and excavating the tip of a pile hole H formed in the ground to construct a root-reinforcement bulb (not shown). The enlargement excavation device 100 is provided at the tip of the excavation rod 1. The excavation rod 1 comprises a drive shaft 2 that is rotated in forward and reverse directions by a driving means (not shown) such as an auger machine, and a helical excavation blade 3 provided on the outer circumference of the drive shaft 2.

[0011] As shown in Figure 2, the enlargement drilling device 100 comprises a drilling shaft 10 that can be connected to the drilling rod 1 (see Figure 1) so as to rotate integrally with it, two support shafts 13 provided on the outer circumference of the drilling shaft 10, and two enlargement blades 11 that are rotatably attached to each support shaft 13. A drilling head 20 is connected to the lower end of the drilling shaft 10, as shown in Figure 1.

[0012] The drilling shaft 10 has a shaft portion 12 that is shaped like a cylinder with a central axis 10c, with a portion of the side surface cut off by two planes 12a, 12a. The two planes 12a, 12a are formed parallel to the axis 10c, facing the two expanding wings 11 on either side of the axis 10c, at positions that avoid the areas where each support shaft 13 is located. The drilling shaft 10 is connected to the tip of the drive shaft 2 of the drilling rod 1 so as to rotate integrally with the drilling rod 1. A hexagonal prism-shaped connector 14a is provided protruding from the upper end of the shaft portion 12 of the drilling shaft 10 for connection to the lower end of the drive shaft 2 of the drilling rod 1. A connector hole 14b is drilled in the direction of the axis 10c at the lower end of the shaft portion 12 of the drilling shaft 10, into which a connector 22 (see Figure 1) protruding from the upper end of the drive shaft 21 of the drilling head 20 can be fitted.

[0013] The two support shafts 13 are positioned at equal intervals (180° intervals) along the circumferential direction of the drilling shaft 10, on the arcuate surfaces 12b, 12b of the outer circumference of the shaft portion 12 of the drilling shaft 10, at an angle θ (see Figure 3) with respect to the axis 10c of the drilling shaft 10. Each support shaft 13 is fixed away from the arcuate surfaces 12b, 12b of the outer circumference of the shaft portion 12 of the drilling shaft 10 via a pair of brackets 16, 16 that are spaced apart in a direction parallel to the axis 10c and inclined at an angle θ with respect to the horizontal direction, as shown in Figure 3.

[0014] When the auger rod 1 rotates forward in the direction of the arrow R during the pile hole excavation operation, the expanding wing 11 receives the earth pressure and rotates around the support shaft 13 as shown in FIG. 4, and enters a reduced diameter state accommodated within the rotation locus of the excavation blade 3. On the other hand, during the expanding excavation operation when the auger rod 1 rotates reversely in the direction of the arrow L, the expanding wing 11 receives the earth pressure and rotates around the support shaft 13, and enters an expanded diameter state protruding radially outward from the rotation locus of the excavation blade 3 as shown in FIGS. 5 and 6.

[0015] The expanding wing 11 has a shape in which the middle part between the tip 11a and the support shaft 13 is curved or bent outward. On the outer surface 11b of the expanding wing 11, a plurality of first to third excavation bits 15a, 15b, 15c are provided. The first to third excavation bits 15a to 15c are arranged in order from the support shaft 13 side toward the tip 11a side.

[0016] The first excavation bit 15a is located at a position where it first contacts the inner surface T1 of the hole wall at the start of the reverse rotation of the auger rod 1 as shown in FIG. 4. The second excavation bit 15b is located at a position where it contacts the inner surface T2 of the hole wall next to the first excavation bit 15a when the expanding wing 11 expands from the position shown in FIG. 4 to the position shown in FIG. 5. The third excavation bit 15c is provided at the tip 11a of the expanding wing 11. The third excavation bit 15c contacts the inner surface T3 of the hole wall next to the second excavation bit 15b when the expanding wing 11 expands from the position shown in FIG. 5 to the position shown in FIG. 6.

[0017] Also, on the upper and lower surfaces near the tip 11a of the expanding wing 11, a plurality of excavation bits 15d are provided for cutting the upper and lower surfaces of the hole wall into which the expanding wing 11 enters in the expanded diameter state of the expanding wing 11.

[0018] Furthermore, as shown in Figures 5 and 6, the expanding wing 11 has a convex surface 11c that curves towards the rear in the direction of arrow L as it moves away from the support shaft 13, and a concave surface 11d that is continuous with this convex surface 11c and curves toward the front in the direction of arrow L.

[0019] As shown in Figure 1, the drilling head 20 comprises a cylindrical drive shaft 21, a hexagonal prism-shaped connector 22 protruding from the upper end of the drive shaft 21, and spiral drilling blades 23 provided on the outer circumference of the drive shaft 21. A drilling bit 24 is provided at the tip of each drilling blade 23. The drilling head 20 and the drilling device 100 are integrally connected by inserting the connector 22 on the upper end of the drilling head 20 into the connector hole 14b on the lower end of the drilling shaft 10 of the drilling device 100 and fixing it with a predetermined fixing means.

[0020] Next, the operation of the enlargement drilling device 100 with the above configuration will be described. As shown in Figures 1 and 4, during pile hole excavation, the excavation rod 1 is rotated forward in the direction of arrow R. At this time, the tip 11a of the expanding wing 11, which is subjected to earth pressure, remains close to the excavation shaft 10, so the expanding wing 11 is kept in a reduced diameter state. Therefore, by rotating the excavation rod 1 forward in the direction of arrow R, pile hole excavation can be performed smoothly.

[0021] On the other hand, during the enlargement excavation operation, the excavation rod 1 is pulled up while rotating in the opposite direction in the direction of arrow L. At this time, as shown in Figures 5 and 6, the multiple enlargement wings 11 that are subjected to earth pressure each rotate around the support shaft 13, and the enlargement wings 11 gradually expand. At this time, the first excavation bit 15a of the enlargement wing 11 makes contact with the inner surface T1 of the borehole wall first. That is, the first excavation bit 15a closest to the support shaft 13 makes contact with the inner surface T1 of the borehole wall at an early stage of the enlargement movement of the enlargement wing 11, and the enlargement movement of the enlargement wing 11 progresses as it engages with the inner surface T1 of the borehole wall.

[0022] As the expanding wing 11 expands in diameter, the second drilling bit 15b and the third drilling bit 15c, located from the support shaft 13 side to the tip 11a side, sequentially contact the inner surfaces T2 and T3 of the borehole wall, as shown in Figures 5 and 6. In other words, as the expanding wing 11 expands in diameter, the drilling bits 15a, 15b, and 15c, located from the support shaft 13 side to the tip 11a side, sequentially contact the inner surfaces T1, T2, and T3 of the borehole wall, thereby gradually drilling the inner surfaces T2 and T3 of the borehole wall while the expanding wing 11 expands. Therefore, the expanding wing 11 can be expanded efficiently and reliably, and a large-diameter root-reinforcement bulb can be formed with the limited power of the driving means that rotates the drilling rod 1.

[0023] Furthermore, as shown in Figures 4 to 6, the first to third drilling bits 15a to 15c are positioned such that their respective front cutting edge angles φ1, φ2, and φ3 are 5° to 15° when they sequentially contact the inner surfaces T1, T2, and T3 of the borehole wall. In other words, as the expanding wing 11 expands, the angles (front cutting edge angles φ1, φ2, φ3) of the first to third drilling bits 15a to 15c when they sequentially contact the inner surface of the borehole wall are always maintained within the range of 5° to 15°. As a result, during the expansion operation of the expanding wing 11, the first to third drilling bits 15a to 15c always contact the inner surface of the borehole wall at the optimal angle for drilling, enabling the efficient formation of a large-diameter root-reinforcement bulb.

[0024] Furthermore, the shaft portion 12 of the drilling shaft 10 has a shape in which a part of the side surface of a cylinder centered on the axis 10c is cut off toward the two expanding wings 11 by two planes 12a, 12a parallel to the axis 10c, with the axis 10c in between. As a result, excavated soil exists in this cut-off space, and when the drilling rod 1 rotates in the reverse direction, the excavated soil in this space flows toward the expanding wings 11, increasing the earth pressure experienced by the expanding wings 11.

[0025] Furthermore, the expanding wing 11 has a space formed by its convex surface 11c and concave surface 11d that is conducive to receiving excavated soil, so that the excavated soil flows smoothly along the convex surface 11c and concave surface 11d toward the rear outer perimeter, allowing the expanding wing to open quickly.

[0026] In this way, the expanding wing 11 expands until the projection 11e contacts the outer circumference of the drilling shaft 10, and is maintained in the expanded diameter state shown in Figure 6. Then, the third drilling bits 15c and drilling bits 15d of the multiple expanding wings 11, which are pulled up while rotating in the opposite direction in the arrow line L with a larger turning radius than the drilling blade 23 (see Figure 1), excavate the ground around the expanding wing 11 of the pile hole H formed in the ground as shown in Figure 1, and a root-reinforcement bulb (not shown) with an inner diameter larger than that of the pile hole H is formed.

[0027] The expanding blades 11 of the expanding drilling device 100 rotate in the direction of arrow L with a large radius of rotation to enlarge and excavate the ground around the pile hole H (see Figure 1), thus increasing the enlargement rate compared to conventional expanding drilling devices. Furthermore, in the state of maximum diameter expansion of the expanding blades 11, the third drilling bit 15c contacts the inner surface T3 of the borehole wall, and as the expanding blades 11 enter the borehole wall and are pulled up, the drilling bit 15d contacts the upper surface of the borehole wall, allowing for precise cutting of the borehole wall and enlargement drilling.

[0028] Furthermore, when the expanding wing 11 rotates in the direction of arrow L to excavate the ground, the reaction force of the earth pressure generated on the projection 11e is supported by the outer circumference of the excavation shaft 10 (the part in contact with the projection 11e), making it less susceptible to damage and providing high strength despite its simple structure. In addition, since the support shaft 13 is positioned away from the outer circumference of the excavation shaft 10, soil and sand accumulated between the support shaft 13 and the reaction point (projection 11e) do not get caught when the expanding wing 11 expands, ensuring smooth expansion.

[0029] After the enlarged excavation work is completed, when the excavation rod 1 (see Figure 1) is rotated in the direction of arrow R, the multiple enlarged wings 11 that have been subjected to earth pressure return to the reduced diameter state shown in Figure 4, and the enlarged excavation device 100 and the excavation head 20 can be easily lifted to the ground together with the excavation rod 1.

[0030] The expanding blades 11 of the expanding drilling device 100 expand or contract in diameter simply by rotating the drilling shaft 10 in the forward or reverse direction via the drilling rod 1, thus eliminating the need for hydraulic or electrical operating systems. For this reason, the expanding drilling device 100 can be constructed using only mechanical elements, resulting in a simple structure.

[0031] Next, the rotation angle of the enlarged wing 11 will be explained with reference to Figures 7 and 8. First, as a basic condition, the rotational speed of the drilling rod 1 is often set in the range of 5 rpm to 25 rpm. Therefore, for example, if the enlarged drilling diameter is φ1000 mm, the sliding distance of the tip 11a of the enlargement wing 11 (φ1000 mm × 3.14 × rotational speed ÷ 60) will be approximately 261.8 mm / s to 1309 mm / s. In addition, the lifting speed of the drilling rod 1 during enlarged drilling is often set in the range of 0.5 m / min (8.3 mm / s) to 2.0 m / min (33.3 mm / s).

[0032] Within the scope of application described above, when enlargement drilling is performed by mechanical means using reverse rotation, it is effective to position the third drilling bit 15c, which is provided at the tip 11a of the enlargement wing 11, in a direction that efficiently receives the mechanical stress applied from the borehole wall, thereby cutting the borehole wall. As the drilling rod 1 rotates, the third drilling bit 15c moves along side ab of the isosceles triangle shown in Figure 7. Also, as the drilling rod 1 is pulled up, the third drilling bit 15c moves along side bc. As a result, the third drilling bit 15c follows the trajectory of side ac, which is the combined vector of these two sides.

[0033] In the model case where the enlarged drilling diameter is φ1000mm, if the rotation speed is slow (261.8mm / s) and the lifting speed is fast (33.3mm / s), then θ1 = tan-1(b / a) ≈ 7.3°. On the other hand, if the rotation speed is fast (1309mm / s) and the lifting speed is slow (33.3mm / s), then θ2 ≈ 0.4°. Since the typical enlarged drilling diameter is φ600mm to φ2000mm, θ is generally between 0.2° and 12°. However, considering the play due to mechanical tolerances, it is best to set θ to between 0° and 25°.

[0034] In this embodiment, an example was described in which the borehole wall is enlarged by pulling up the drilling rod 1 while rotating it in the reverse direction. However, it is also possible to configure the borehole wall to be enlarged by pushing down the drilling rod 1 while rotating it in the reverse direction. In this case, the angle θ will be reversed (-).

[0035] In the enlargement drilling device 100 of this embodiment, the two support shafts 13 that rotatably support the enlargement blades 11 are arranged to form an angle θ with the axis 10c of the drilling shaft 10, thereby allowing the enlargement blades 11 to rotate in the direction of angle θ. This makes it possible to efficiently receive the mechanical stress applied from the borehole wall on the enlargement blades 11 when enlarging the borehole wall by pulling up or pushing down while rotating the drilling rod 1 in the reverse direction, and to quickly open the enlargement blades 11.

[0036] In particular, when the drilling rod 1 is pulled up while rotating in the reverse direction to enlarge the borehole wall, the expansion wings 11 are tilted at an angle θ, and gravity also acts on them, making it easier for the expansion wings 11 to open further. Additionally, the downward stress applied when cutting the borehole wall is distributed, improving the load-bearing capacity of the expansion wings 11.

[0037] Furthermore, as shown in Figure 8, by tilting the orientation of the third drilling bit 15c by an angle θ with respect to the reverse rotation direction of the drilling rod 1, the third drilling bit 15c can move while pressing against the borehole wall surface at a right angle. As a result, when expanding the borehole wall by pulling up or pushing down while rotating the drilling rod 1 in reverse, the mechanical stress applied from the borehole wall is efficiently received by the third drilling bit 15c, thereby cutting the borehole wall and improving the efficiency of borehole wall drilling. In addition, the mechanical strength preservation of the third drilling bit 15c is improved.

[0038] Next, another embodiment of the enlargement drilling apparatus of the present invention will be described with reference to Figures 9 to 12. In Figures 9 to 12, components common to the aforementioned enlargement drilling apparatus 100 are denoted by the same reference numerals, and their detailed descriptions are omitted.

[0039] The expanding blade 31 in the expanding drilling device 200 shown in Figures 9 to 12 has a curved protrusion 32 that curves outward in the middle section between the tip 31a and the support shaft 13. The outer surface of the expanding blade 31 is also equipped with a plurality of first and second drilling bits 33a and 33b. The first and second drilling bits 33a and 33b are arranged in order from the support shaft 13 side toward the tip 31a. The first drilling bit 33a is located in a position that first contacts the inner surface T4 of the borehole wall when the drilling rod 1 starts to rotate in the reverse direction, as shown in Figure 10. The second drilling bit 33b is located at the tip of the expanding blade 31.

[0040] The protrusion 32 is located between the first drilling bit 33a and the second drilling bit 33b. As shown in Figure 11, when the expanding wing 31 expands and the first drilling bit 33a and the second drilling bit 33b lie on the same circumference T5, the apex of the protrusion 32 also lies on this circumference T5.

[0041] Furthermore, as shown in Figure 12, the upper and lower surfaces of the expanding wing 31 near the tip 31a are provided with multiple drilling bits 33c that cut the upper and lower surfaces of the hole wall into which the expanding wing 11 enters when the expanding wing 31 is in its expanded diameter state. In addition, a projection 34 is provided on the base end side of the expanding wing 31, projecting away from the tip 31a as shown in Figure 10. The expanding wing 31 expands until the projection 34 contacts the outer circumference of the drilling shaft 10, and is maintained in the state of maximum expanded diameter T6 shown in Figure 12.

[0042] In the above-described expansion drilling device 200, as shown in Figure 10, when the drilling shaft 10 is rotated in the direction of arrow L via the drilling rod 1 to enter the expansion drilling state, the first drilling bit 33a penetrates the inner surface T4 of the borehole wall and attempts to start drilling. However, the curved protrusion 32 that precedes the rotational direction of the drilling shaft 10 circles the inner surface of the borehole wall that has not yet been expanded by the first drilling bit 33a, so the expansion drilling is generally suppressed to about the diameter of the borehole wall.

[0043] In other words, the first drilling bit 33a exerts a force that attempts to open the expanding wing 31 by drilling into the borehole wall, while the curved protrusion 32 exerts a resistive force that prevents it from opening along the borehole wall. As these forces balance each other, the borehole wall is gradually enlarged through drilling, and the excessive drilling torque that occurs when reverse rotation begins is suppressed.

[0044] Then, when the borehole wall is enlarged by the first drilling bit 33a to the position of the circumference T5 shown in Figure 11, the operation of drilling the borehole wall with the first drilling bit 33a is transitioned to the operation of drilling the borehole wall with the second drilling bit 33b. Subsequently, the second drilling bit 33b at the tip of the expanding wing 31 enlarges the borehole wall to the maximum enlarged diameter T6 shown in Figure 12.

[0045] In this way, the enlarged drilling device 200 can achieve enlarged drilling while suppressing the excessive drilling rotation torque in the initial stage when enlarged drilling is started by reverse rotation. [Industrial applicability]

[0046] The enlargement excavation device according to the present invention can be widely used in fields such as civil engineering and construction as a device for carrying out construction work to enlarge the tip of a pile hole formed in the ground and form a root-reinforcement bulb. [Explanation of Symbols]

[0047] 1. Excavation Rod 2 drive shafts 3. Excavation blades 4 connector holes 10 Drilling shafts 10c axis center 11. Extended Wing 11a Tip 11b External surface 11c Convex 11d concave 11e Protrusion 12 Shaft section 12a plane 12b Circular arc surface 13 Spindle 14a connector 14b Connector hole 15a, 15b, 15c, 15d drilling bits 16 brackets 20 drilling heads 21 Drive shaft 22 connectors 23 Excavation blades 24 drilling bits 31. Enlarged Wing 31a Tip 32 Convex part 33a, 33b, 33c drilling bits 34 Protrusion 100,200 Enlarged drilling machine

Claims

1. An expanding drilling device comprising: a drilling shaft that can be connected to a drilling rod so as to rotate integrally with it; a plurality of support shafts arranged on the outer circumference of the drilling shaft parallel to the axis of the drilling shaft and at equal intervals along the circumferential direction of the drilling shaft; and expanding wings rotatably attached to each of the plurality of support shafts, wherein during pile hole drilling work when the drilling rod rotates in the forward direction, the expanding wings, under the influence of earth pressure, maintain a reduced diameter state, and during expanding drilling work when the drilling rod rotates in the reverse direction, the expanding wings, under the influence of earth pressure, rotate around the support shafts and expand until a part of the expanding wings contacts the outer circumference of the drilling shaft, thereby maintaining an expanded diameter state, The aforementioned expanding wing is an expanding drilling device in which a plurality of drilling bits arranged in a line on its outer surface from the support shaft side toward the tip side come into contact with the inner surface of the hole wall sequentially from the support shaft side toward the tip side as the expanding wing expands in diameter, with the middle portion of the wing being curved or bent toward the outward direction.

2. The enlargement drilling device according to claim 1, wherein the front cutting edge angle of each of the plurality of drilling bits in sequential contact with the inner surface of the hole wall is 5° to 15°.

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