Expansion 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 and excavating the tip of a pile hole formed in the ground to construct a root-protection bulb portion. [Background technology]

[0002] An example of an enlargement drilling device that enlarges and excavates the tip of a pile hole formed in the ground to form a root-hardening bulb is the enlargement drilling device described in Patent Document 1. This enlargement drilling device includes a drilling shaft that can be connected integrally to the tip of the drilling rod, multiple support shafts that are parallel to the axis of the drilling shaft on the outer periphery of the drilling shaft and are equally spaced along the circumferential direction of the drilling shaft, and enlargement blades that are rotatably attached to each support shaft, and during pile hole excavation work when the drilling rod rotates forward, the enlargement blades are held in a reduced-diameter state by receiving earth pressure, and during enlargement drilling work when the drilling rod rotates backward, the enlargement blades are rotated around the support shaft by receiving earth pressure and become expanded in diameter, and the multiple enlargement blades rotate together with the drilling shaft in this state to enlarge the surrounding ground. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-116136 Summary of the Invention [Problem to be solved by the invention]

[0004] In this expansion drilling, the longer the expansion wing is required to form a larger diameter root reinforcement bulb portion, but the longer the expansion wing, the shallower the angle at which the tip of the expansion wing contacts the inner surface of the hole wall during the expansion operation, and the tip of the expansion wing may not properly engage with the inner surface of the hole wall, causing the expansion operation to fail.

[0005] Therefore, an object of the present invention is to provide an expansion drilling device that can efficiently and reliably expand the expansion wings. [Means for solving the problem]

[0006] The expansion drilling device of the present invention comprises a drilling shaft that can be connected to the drilling rod so as to rotate integrally with it, a plurality of support shafts that are parallel to the axis of the drilling shaft on the outer periphery of the drilling shaft and are arranged at equal intervals along the circumferential direction of the drilling shaft, and expansion blades that are rotatably attached to each of the plurality of support shafts, and when the drilling rod is rotating forward to perform pile hole drilling work, the expansion blades that receive earth pressure maintain a reduced diameter state, and when the drilling rod is rotating backward to perform expansion drilling work, the expansion blades that receive earth pressure rotate around the support shafts and expand until a part of the expansion blade abuts the outer periphery of the drilling shaft, maintaining an expanded diameter state.The expansion blades are characterized in that their midsections are curved or bent outward so that a plurality of drill bits that are arranged side by side on their outer surfaces from the support shaft side to the tip side come into contact with the inner surface of the hole wall in order from the support shaft side to the tip side as the expansion blades perform their diameter expansion operation.

[0007] According to the expansion drilling device of the present invention, the drilling bit closest to the support shaft of the expansion blade contacts the inner surface of the hole wall at an early stage of the expansion blade's diameter-expanding movement before the drilling bit at the tip of the expansion blade and engages the inner surface of the hole wall, thereby progressing the expansion movement of the expansion blade. As the expansion blade expands, the drilling bits from the support shaft side to the tip side contact the inner surface of the hole wall in order, gradually excavating the inner surface of the hole wall, and the expansion blade expands. [Effects of the Invention]

[0008] According to the expansion drilling device of the present invention, the expansion wings can be expanded efficiently and reliably, making it possible to form a large-diameter root compaction bulb portion with limited power to rotate the drilling rod. [Brief explanation of the drawings]

[0009] [Figure 1]FIG. 2 is a vertical cross-sectional view showing the expansion drilling device in the embodiment of the present invention in use (with the expansion wings contracted). [Figure 2] FIG. 2 is a perspective view of the expansion drilling device of FIG. 1. [Figure 3] 3 is a view taken along the X arrow in FIG. 2, with the expansion wing omitted. [Figure 4] 1. FIG. 4 is a plan view showing the initial state of the diameter-expanding operation of the excavation device shown in FIG. [Figure 5] 1. FIG. 4 is a plan view showing a state during the diameter-expanding operation of the excavation device of FIG. [Figure 6] FIG. 2 is a plan view showing the maximum diameter expansion state of the expansion drilling device of FIG. [Figure 7] FIG. 10 is an explanatory diagram showing the orientation of the drilling bit at the tip of the expansion wing cutting the hole wall when the angle of the expansion wing support shaft is 0°. [Figure 8] FIG. 10 is an explanatory diagram showing the direction of the drilling bit at the tip of the expansion wing cutting the hole wall when the angle of the expansion wing support shaft is θ. [Figure 9] FIG. 10 is a perspective view of another embodiment of the expansion drilling rig. [Figure 10] 10 is a plan view showing the initial state of the diameter-expanding operation of the expansion drilling device of FIG. 9. [Figure 11] 10 is a plan view showing a state in the middle of the diameter-expanding operation of the expansion drilling device of FIG. 9. [Figure 12] 10 is a plan view showing the maximum diameter expansion state of the expansion drilling device of FIG. 9. DETAILED DESCRIPTION OF THE INVENTION

[0010] As shown in Figure 1, an enlarged drilling device 100 in an embodiment of the present invention is used to enlarge and excavate the tip of a pile hole H formed in the ground to construct a root protection bulb (not shown). The enlarged drilling device 100 is attached to the tip of a drilling rod 1. The drilling rod 1 comprises a drive shaft 2 that is driven to rotate in forward and reverse directions by a drive means (not shown) such as an auger machine, and a spiral drilling blade 3 attached to the outer periphery of the drive shaft 2.

[0011] As shown in Figure 2, the expansion 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 therewith, two support shafts 13 provided on the outer periphery of the drilling shaft 10, and two expansion wings 11 rotatably attached to each support shaft 13. A drilling head 20 is connected to the lower end side of the drilling shaft 10 as shown in Figure 1.

[0012] The drilling shaft 10 has a shaft portion 12 in the shape of a cylinder with two flat surfaces 12a, 12a cut off from a portion of its side surface centered on the axis 10c. The two flat surfaces 12a, 12a are formed parallel to the axis 10c, facing each of the two expansion wings 11 across the axis 10c, at positions that avoid the areas where the support shafts 13 are arranged. 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 protrudes 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 from the lower end of the shaft portion 12 of the drilling shaft 10, into which a connector 22 (see FIG. 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 arranged on arcuate surfaces 12b, 12b on the outer periphery of the shaft portion 12 of the drilling shaft 10, forming an angle θ (see Figure 3) with the axis 10c of the drilling shaft 10, and are arranged at equal intervals (180° intervals) along the circumferential direction of the drilling shaft 10. The support shafts 13 are fixed at positions spaced apart from the arcuate surfaces 12b, 12b on the outer periphery 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] During pile hole excavation work in which the drilling rod 1 rotates forward in the direction of arrow R, the expansion blade 11 is subjected to earth pressure and rotates around the support shaft 13 as shown in Fig. 4, becoming a reduced-diameter state housed within the rotation trajectory of the drilling blade 3. On the other hand, during enlarged excavation work in which the drilling rod 1 rotates backward in the direction of arrow L, the expansion blade 11 is subjected to earth pressure and rotates around the support shaft 13, becoming an enlarged-diameter state protruding radially outward from the rotation trajectory of the drilling blade 3 as shown in Figs. 5 and 6.

[0015] The expansion wing 11 has a shape in which the midway portion between the tip 11a and the support shaft 13 is curved or bent outward. The outer surface 11b of the expansion wing 11 is provided with first to third drilling bits 15a, 15b, 15c. The first to third drilling bits 15a to 15c are arranged in order from the support shaft 13 side toward the tip 11a side.

[0016] As shown in Figure 4, the first drilling bit 15a is in a position where it first contacts the inner surface T1 of the hole wall when the drilling rod 1 starts to reversely rotate. The second drilling bit 15b is in a position where it contacts the inner surface T2 of the hole wall after the first drilling bit 15a when the expansion blade 11 expands from the position shown in Figure 4 to the position shown in Figure 5. The third drilling bit 15c is provided at the tip 11a of the expansion blade 11. The third drilling bit 15c contacts the inner surface T3 of the hole wall after the second drilling bit 15b when the expansion blade 11 expands from the position shown in Figure 5 to the position shown in Figure 6.

[0017] In addition, the upper and lower surfaces of the expansion wing 11 near the tip 11a are provided with a plurality of drilling bits 15d that cut the upper and lower surfaces of the hole wall into which the expansion wing 11 has entered when the expansion wing 11 is in an expanded diameter state.

[0018] 5 and 6, the expansion wing 11 has a front surface in the direction of arrow L, i.e., a surface that receives earth pressure during expansion excavation work, which has a convex surface 11c that faces rearward in the direction of arrow L as it moves away from the support shaft 13, and a concave surface 11d that is continuous with the convex surface 11c and curves forward on the opposite side, i.e., forward in the direction of arrow L. Furthermore, the base end of the expansion wing 11 is provided with a protrusion 11e that protrudes in a direction away from the tip end 11a, as shown in Fig. 4. In this embodiment, the expansion wing 11 is arranged at two locations 180° apart on the outer periphery of the drilling shaft 10, but the shape, number, and spacing of the expansion wing 11 are not limited to this embodiment.

[0019] 1, the drilling head 20 comprises a cylindrical drive shaft 21, a hexagonal column-shaped connector 22 protruding from the upper end side of the drive shaft 21, and spiral drilling blades 23 provided on the outer periphery of the drive shaft 21. A drilling bit 24 is provided at the tip of each drilling blade 23. The connector 22 on the upper end side of the drilling head 20 is fitted into the connector hole 14b on the lower end side of the drilling shaft 10 of the enlarged drilling device 100, and fixed by a predetermined fixing means, whereby the enlarged drilling device 100 and the drilling head 20 are integrally connected.

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

[0021] On the other hand, during the expansion drilling operation, the drill rod 1 is pulled up while being rotated in the reverse direction of the arrow L. At this time, as shown in Figures 5 and 6, the multiple expansion wings 11, under soil pressure, rotate around the support shaft 13, gradually expanding. At this time, the first drilling bit 15a of the expansion wings 11 first comes into contact with the inner surface T1 of the hole wall. That is, at an early stage of the expansion operation of the expansion wings 11, the first drilling bit 15a closest to the support shaft 13 comes into contact with the inner surface T1 of the hole wall and engages with the inner surface T1 of the hole wall, thereby progressing the expansion operation of the expansion wings 11.

[0022] As the expansion blade 11 expands, the second drilling bit 15b and the third drilling bit 15c from the support shaft 13 to the tip 11a contact the hole wall inner surfaces T2, T3 in sequence, as shown in Figures 5 and 6. That is, as the expansion blade 11 expands, the drilling bits 15a, 15b, and 15c from the support shaft 13 to the tip 11a contact the hole wall inner surfaces T1, T2, and T3 in sequence, thereby gradually excavating the hole wall inner surfaces T2 and T3, and the expansion blade 11 expands. This makes it possible to efficiently and reliably expand the expansion blade 11, and a large-diameter foot protection bulb can be formed with the limited power of the drive means that rotates the drill rod 1.

[0023] As shown in Figures 4 to 6, the first to third drilling bits 15a to 15c are configured so that their respective leading cutting edge angles φ1, φ2, and φ3 are 5° to 15° when they sequentially contact the hole wall inner surfaces T1, T2, and T3. That is, as the expansion blade 11 performs its diameter expansion operation, the angles (leading cutting edge angles φ1, φ2, and φ3) at which the first to third drilling bits 15a to 15c sequentially contact the hole wall inner surface are always maintained within the range of 5° to 15°. As a result, during the diameter expansion operation of the expansion blade 11, the first to third drilling bits 15a to 15c always contact the hole wall inner surface at an angle optimal for drilling, allowing for efficient formation of large-diameter root compaction bulbs.

[0024] In addition, the shaft portion 12 of the drilling shaft 10 has a shape in which part of the side of a cylinder centered on the axis 10c is cut off by two flat surfaces 12a, 12a parallel to the axis 10c, sandwiching the axis 10c, toward the two expansion wings 11. Therefore, excavated soil is present 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 expansion wings 11, increasing the earth pressure that the expansion wings 11 receive.

[0025] Furthermore, the convex surface 11c and the concave surface 11d of the expansion wing 11 form a space that is easy to receive the excavated soil, so that the excavated soil flows smoothly along the convex surface 11c and the concave surface 11d toward the rear of the outer periphery, allowing the expansion wing to open quickly.

[0026] In this way, the expansion blades 11 expand until the protrusions 11e come into contact with the outer periphery of the drilling shaft 10, and are maintained in the expanded diameter state shown in Fig. 6. Then, the third drilling bits 15c and 15d of the multiple expansion blades 11 are pulled up while rotating in the reverse direction of arrow L with a larger rotation radius than the drilling blade 23 (see Fig. 1), and the ground around the expansion blades 11 in the pile hole H formed in the ground shown in Fig. 1 is excavated and expanded, forming a foot compaction bulb (not shown) with an inner diameter larger than that of the pile hole H.

[0027] The expansion wing 11 of the expansion drilling device 100 rotates in the direction of the arrow L with a large radius of rotation to expand and excavate the ground around the pile hole H (see Figure 1), thereby increasing the expansion excavation rate compared to conventional expansion drilling devices. Furthermore, when the expansion wing 11 is in the maximum expansion state, the third drilling bit 15c comes into contact with the inner surface T3 of the hole wall, and the expansion wing 11 enters the hole wall and is pulled up, so that the drilling bit 15d comes into contact with the upper surface of the hole wall, thereby enabling the hole wall to be precisely cut and enlarged.

[0028] Furthermore, the reaction force of the earth pressure generated at the protrusion 11e when the expansion blade 11 rotates in the direction of arrow L to excavate the ground is supported by the outer periphery of the drilling shaft 10 (the portion where the protrusion 11e abuts), making it less susceptible to damage and providing high strength despite its simple structure. In addition, because the support shaft 13 is positioned away from the outer periphery of the drilling shaft 10, the soil accumulated between the support shaft 13 and the reaction point (protrusion 11e) does not get caught when the expansion blade 11 expands, ensuring smooth expansion operation.

[0029] After the enlargement excavation work is completed, when the drilling rod 1 (see Figure 1) is rotated forward in the direction of arrow R, the multiple expansion wings 11 that have received earth pressure each return to the reduced diameter state shown in Figure 4, so that the enlargement excavation device 100 and the drilling head 20 can be easily pulled up to the ground together with the drilling rod 1.

[0030] The expansion wing 11 constituting the expansion drilling device 100 expands or contracts in diameter simply by rotating the drilling shaft 10 in the forward or reverse direction via the drilling rod 1, so no hydraulic or electrical operating system is required. Therefore, the expansion drilling device 100 can be constructed only with mechanical elements, and the structure is simple.

[0031] Next, the rotation angle of the expansion wing 11 will be described with reference to FIGS. First, as a basic condition, the rotation speed of the drilling rod 1 is often in the range of 5 rpm to 25 rpm. Therefore, for example, when the expansion drilling diameter is φ1000 mm, the sliding distance of the tip 11a of the expansion wing 11 (φ1000 mm × 3.14 × rotation speed ÷ 60) is approximately 261.8 mm / s to 1309 mm / s. Furthermore, the lifting speed of the drilling rod 1 during expansion drilling work is often in the range of 0.5 m / min (8.3 mm / s) to 2.0 m / min (33.3 mm / s).

[0032] Within the above application range, when enlargement drilling is performed by mechanical means using reverse rotation, it is effective to position the third drilling bit 15c attached to the tip 11a of the expansion wing 11 in a direction that allows it to efficiently receive the mechanical stress applied from the hole wall and cut the hole wall. As the drilling rod 1 rotates, the third drilling bit 15c moves along side ab of the isosceles triangle shown in Figure 7. Furthermore, 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 resultant vector of these.

[0033] Here, in the model case of an enlarged drilling diameter of 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 typical enlarged drilling diameters are φ600mm to φ2000mm, θ is generally between 0.2° and 12°. However, considering play due to mechanical tolerances, it is best to set θ between 0° and 25°.

[0034] In this embodiment, an example has been described in which the drilling rod 1 is pulled up while being rotated in the reverse direction to enlarge the hole wall, but it is also possible to configure the drilling rod 1 to be pushed down while being rotated in the reverse direction to enlarge the hole wall. In this case, the angle θ is reversed (-).

[0035] In the expansion drilling device 100 of this embodiment, the two support shafts 13 that rotatably support the expansion blades 11 are arranged so as to form an angle θ with the axis 10c of the drilling shaft 10, so that the expansion blades 11 can be rotated in the direction of the angle θ. This allows the expansion blades 11 to efficiently receive the mechanical stress applied from the hole wall and open quickly when the drilling rod 1 is pulled up or down while rotating in the reverse direction to perform expansion drilling of the hole wall.

[0036] In particular, when the drilling rod 1 is rotated in the reverse direction and pulled up to enlarge and drill the hole wall, the expansion blades 11 are tilted at an angle θ, and gravity also acts, making it easier for the expansion blades 11 to open.In addition, the downward stress applied when cutting the hole wall is dispersed, improving the load-bearing capacity of the expansion blades 11.

[0037] 8, by tilting the orientation of the third drilling bit 15c by an angle θ relative to the reverse rotation direction of the drilling rod 1, the third drilling bit 15c can move while pressing perpendicularly against the hole wall surface. As a result, when the drilling rod 1 is pulled up or down while rotating in the reverse direction to drill an enlarged hole wall, the third drilling bit 15c efficiently receives the mechanical stress applied from the hole wall and cuts the hole wall, improving the hole wall drilling efficiency. Furthermore, the mechanical strength of the third drilling bit 15c is improved.

[0038] Next, another embodiment of the expansion excavation device of the present invention will be described with reference to Figures 9 to 12. In Figures 9 to 12, components common to the expansion excavation device 100 described above are given the same reference numerals, and detailed description thereof will be omitted.

[0039] The expansion wing 31 in the expansion drilling device 200 shown in Figures 9 to 12 has a curved convex portion 32 that curves outward midway between the tip 31a and the support shaft 13. The outer surface of the expansion wing 31 is provided with first and second drill bits 33a, 33b. The first and second drill bits 33a, 33b are arranged in order from the support shaft 13 side toward the tip 31a. As shown in Figure 10, the first drill bit 33a is located in a position that first contacts the inner surface T4 of the hole wall when the drilling rod 1 starts to rotate in the reverse direction. The second drill bit 33b is located at the tip of the expansion wing 31.

[0040] The convex portion 32 is located between the first drilling bit 33a and the second drilling bit 33b. When the expansion wing 31 expands and the first drilling bit 33a and the second drilling bit 33b are on the same circumference T5 as shown in Figure 11, the apex of the convex portion 32 is also located on this circumference T5.

[0041] The top and bottom surfaces of the expansion wing 31 near the tip 31a are provided with a plurality of drilling bits 33c that cut the upper and lower surfaces of the hole wall into which the expansion wing 11 has entered when the expansion wing 31 is in an expanded diameter state, as shown in Fig. 12. The base end of the expansion wing 31 is provided with a protrusion 34 that protrudes in a direction away from the tip 31a, as shown in Fig. 10. The expansion wing 31 expands until the protrusion 34 abuts against the outer periphery of the drilling shaft 10, and is maintained in a state of maximum expansion diameter T6 as shown in Fig. 12.

[0042] In the enlargement drilling device 200 configured as described above, when the drilling shaft 10 is rotated in the reverse direction of the arrow L via the drilling rod 1 to enter the enlargement drilling state as shown in Figure 10, the first drilling bit 33a penetrates the inner surface T4 of the hole wall and begins drilling. However, the curved convex portion 32, which is ahead in the rotation direction of the drilling shaft 10, circles around the inner surface of the hole wall that has not yet been enlarged by the first drilling bit 33a, so enlargement drilling is limited to approximately the diameter of the hole wall.

[0043] That is, the force of the first drilling bit 33a drilling the hole wall and opening the expansion wing 31 is countered by a resistance force that prevents the curved convex portion 32 from opening along the hole wall. The balance of these forces results in the hole wall being gradually expanded and the excessive drilling rotation torque generated when the reverse rotation starts is suppressed.

[0044] Then, when the hole wall is expanded by the first drilling bit 33a to the position of circumference T5 shown in Fig. 11, the operation of drilling the hole wall by the first drilling bit 33a shifts to the operation of drilling the hole wall by the second drilling bit 33b. After that, the second drilling bit 33b at the tip of the expansion wing 31 expands the hole to the maximum expanded diameter T6 shown in Fig. 12.

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

[0046] The enlargement drilling device of 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 and excavate the tip of a pile hole formed in the ground and form a root-hardening bulb portion. [Explanation of symbols]

[0047] 1 drilling rod 2 drive shafts 3. Excavation blade 4 connector holes 10 Drilling shaft 10c axis center 11 Expanding Wings 11a Tip 11b External surface 11c Convex 11d concave 11e Protrusion 12 Shaft 12a plane 12b Arc surface 13 Spindle 14a connector 14b Connector hole 15a, 15b, 15c, 15d Drilling bits 16 Bracket 20 Drilling Head 21 Drive shaft 22 Connectors 23 Excavation blade 24 drilling bits 31 Expanding Wings 31a Tip 32 Convex part 33a, 33b, 33c Drilling bits 34 Protrusion 100,200 Expansion Drilling Rig

Claims

1. An enlargement drilling device comprising: a drilling shaft connectable to a drilling rod so as to rotate integrally with the drilling shaft; a plurality of support shafts on the outer periphery of the drilling shaft, the support shafts being parallel to the axis of the drilling shaft and being equally spaced along the circumferential direction of the drilling shaft; and expansion wings rotatably attached to the plurality of support shafts, wherein, during pile hole excavation work in which the drilling rod rotates forward, the expansion wings receive earth pressure and maintain a reduced diameter state, and during enlargement drilling work in which the drilling rod rotates backward, the expansion wings receive earth pressure and rotate around the support shafts, so that a part of the expansion wings expands until it abuts against the outer periphery of the drilling shaft and maintains an expanded diameter state, The expansion wing has a shape in which the middle part is curved or bent outward so that the multiple drilling bits arranged in a line on its outer surface from the support shaft side to the tip side come into contact with the inner surface of the hole wall in sequence from the support shaft side to the tip side as the expansion wing moves in diameter.

2. 2. The expansion drilling device according to claim 1, wherein the front cutting edge angle of each of the plurality of drill bits when they are in contact with the inner surface of the hole wall in sequence is 5° to 15°.

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