Enlarged-base piles and enlarged-base buckets

Abstract

The present invention provides an enlarged-base pile with a shape that prevents damage to the overhang of the enlarged base without increasing the height of the rising section, and an enlarged-base bucket that can easily form such an enlarged base. [Solution] The enlarged-base pile 100 has an enlarged base portion 102 formed at the bottom of the pile, with a diameter larger than that of the shaft portion 101. Furthermore, an upward-sloping surface 103b is formed on the bottom surface 103 of the enlarged base portion, sloping upward toward the outer edge. On the other hand, the widened-base bucket is a bucket for forming a widened base at the bottom of the pile, with a diameter larger than that of the shaft, and the bottom of the widened wing section is formed to slope upward toward the outer edge, and a movable plate that can move in the vertical direction is attached to it.

Description

Technical Field

[0001] The present invention relates to an under-reamed pile in which a bottom portion having a diameter larger than that of a shaft portion is formed at the bottom of the pile, and an under-reaming bucket for constructing the under-reamed pile.

Background Art

[0002] As disclosed in Patent Documents 1-3, an under-reamed pile as a cast-in-place concrete pile provided with an under-reamed portion having a diameter larger than that of a shaft portion at the bottom of the pile is known. This under-reamed pile is constructed by excavating the ground with an excavator to form a portion that becomes the shaft portion, and forming a portion that becomes the under-reamed portion by gradually expanding and cutting the diameter of the shaft portion downward with an under-reaming bucket.

[0003] A general under-reamed portion is composed of a frustum-shaped inclined widening portion whose side line linearly widens downward, and a columnar rising portion provided below it. In the conventional building foundation structure design standard (Japan Society of Civil Engineers), since the inclination angle of the inclined widening portion was regulated to be within 12°, when it was desired to increase the diameter of the under-reamed portion with respect to the shaft portion, the under-reaming rate (diameter of the under-reamed portion / diameter of the shaft portion) was increased by increasing the height of the inclined widening portion.

[0004] On the other hand, Non-Patent Document 1 discloses the results of FEM analysis that a large tensile stress concentration occurs near the bottom surface of the pile when the inclination angle of the inclined widening portion is made larger than 12° and 21°. Although a reinforcing cage is arranged at a location projected on the shaft portion of the under-reamed pile, the overhanging portion outside the reinforcing cage of the under-reamed portion is in a non-reinforced state.

[0005] When the inclination angle of the inclined widening portion is increased, this non-reinforced overhanging portion also becomes larger, so it is necessary to reduce the tensile stress concentration that occurs near the bottom surface of the pile so as not to damage this portion. In Non-Patent Document 1, as a solution to this problem, it is proposed to reduce the tensile stress concentration that occurs on the bottom surface of the pile by setting the height of the rising portion of the under-reamed portion to 1500 mm, which is three times the normal height.

Prior Art Documents

[0006] [Patent Document 1] Patent No. 4699304 [Patent Document 2] Japanese Patent Publication No. 2008-240270 [Patent Document 3] Japanese Patent Publication No. 2014-141844 [Non-patent literature]

[0007] [Non-Patent Document 1] Muramatsu et al., Development of a Cast-in-Place Concrete Enlarged-Base Pile Construction Method with a Maximum Diameter of 6.1m, Part 4: How to Determine the Height of the Enlarged-Base and Rising Sections, Proceedings of the Architectural Institute of Japan Annual Meeting, pp. 423-424, August 10, 2023. [Overview of the project] [Problems that the invention aims to solve]

[0008] However, as the rise of the excavation section increases, the amount of excavated soil required also increases, and the enlarged bucket used becomes larger. This makes it impossible to attach it to a small excavator, requiring the use of a sub-crane or switching to a larger excavator.

[0009] Therefore, the present invention aims to provide an enlarged-base pile with a shape that prevents damage to the overhang of the enlarged base without increasing the height of the rising portion, and an enlarged-base bucket that can easily form such an enlarged base. [Means for solving the problem]

[0010] To achieve the above objective, the enlarged-base pile of the present invention is an enlarged-base pile in which an enlarged-base portion is formed at the bottom of the pile, the diameter of which is larger than that of the shaft portion, and the bottom surface of the enlarged-base portion is characterized in that an upward-sloping surface is formed which slopes upward toward the outer edge.

[0011] Here, it is preferable that the angle of inclination of the widened base portion with respect to the vertical line extending downward from the shaft portion is 3° or more and 45° or less, and the angle of the upward inclined surface with respect to the horizontal is 1° or more and 30° or less.

[0012] Furthermore, the invention of the widened-base bucket is a widened-base bucket for forming a widened-base portion at the bottom of a pile, with a diameter larger than that of the shaft portion, comprising a cylindrical body portion and a widened-wing portion formed to be openable in order to enlarge the diameter of the body portion, wherein the bottom of the widened-wing portion is formed to be inclined upward toward the outer edge, and a movable plate that can move in the vertical direction is attached to it.

[0013] Here, the amount of vertical movement of the movable plate can be configured to increase as it approaches the outer edge of the widened wing portion. [Effects of the Invention]

[0014] In the enlarged-base pile of the present invention configured in this way, an upward-sloping surface is formed on the bottom surface of the enlarged base, sloping upward toward the outer edge. As will be described later, the horizontal component of the reaction force from the contacting ground acts on the upward-sloping surface as a compressive horizontal force inside the overhang.

[0015] Therefore, the tensile stress generated inside the enlarged base can be reduced, and the overhang of the enlarged base can be prevented from being damaged without increasing the height of the rising section.

[0016] Furthermore, in the invention of the widened-bottom bucket, the bottom of the widened wing section is formed to slope upward toward the outer edge, and a movable plate that can move in the vertical direction is attached.

[0017] Therefore, when the widened wings are closed to recover the excavated soil, the soil and sediment accumulated on the upward-sloping excavation bottom can be cleanly removed by the moving plate. As a result, it is possible to construct widened-base piles with high support performance and quality. [Brief explanation of the drawing]

[0018] [Figure 1] This is an explanatory diagram for explaining the schematic configuration of the under-reamed pile of this embodiment. [Figure 2] This is an explanatory diagram for explaining the influence of the reaction force acting on the upward inclined surface of the enlarged bottom part. [Figure 3] This is an explanatory diagram summarizing the results of analyzing the relationship between the taper angle of the upward inclined surface of the enlarged bottom part and the tensile stress degree by analysis. [Figure 4] This is an explanatory diagram for explaining the schematic configuration of the enlarged bottom bucket of Example 1. [Figure 5] This is an enlarged view for explaining the configuration and operation of the moving plate. [Figure 6] This is a cross-sectional view taken along the arrow A-A direction of FIG. 5. [Figure 7] This is an explanatory diagram showing the fully open state for explaining the soil discharging method of the enlarged bottom bucket. [Figure 8] This is an explanatory diagram showing the semi-closed state for explaining the soil discharging method of the enlarged bottom bucket. [Figure 9] This is an explanatory diagram showing the fully closed state for explaining the soil discharging method of the enlarged bottom bucket.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing the configuration of the under-reamed pile 100 of this embodiment.

[0020] The under-reamed pile 100 of this embodiment is mainly composed of a shaft part 101 provided in a columnar shape with a predetermined diameter from the ground, and an enlarged bottom part 102 formed by enlarging the diameter below the shaft part 101.

[0021] The enlarged-base pile 100 is a cast-in-place concrete pile formed by installing steel materials such as a reinforcing cage into a hole excavated in the ground and pouring concrete. Generally, the area projected by the shaft portion 101, including the enlarged-base portion 102, is reinforced concrete with reinforcing bars, while the overhanging portion of the enlarged-base portion 102 is made of unreinforced concrete.

[0022] The widened base portion 102 is composed of an upward sloping portion 102a that widens in a truncated cone shape from the lower end of the shaft portion 101, a vertical portion 102b that is formed in a cylindrical shape at the cross-section of the bottom surface of the upward sloping portion 102a, and a downward sloping portion 102c that is formed in an inverted truncated cone shape that tapers towards the bottom surface 103 from the lower end of the vertical portion 102b.

[0023] The upper inclined portion 102a has an inclination angle θ1 with respect to the side line of the vertical shaft portion 101 that is between 3° and 45°. For example, the inclination angle θ1 can be set to 12°, 18°, 21°, 30°, etc. For example, setting the inclination angle θ1 to 20° or 30° makes it possible to create an enlarged-base pile 100 with a large enlargement ratio (diameter of enlarged base / diameter of shaft portion), where the diameter of the enlarged base portion is larger than the diameter of the shaft portion.

[0024] On the other hand, the downward sloping portion 102c is a configuration that does not exist in conventional conical enlarged-base piles. The downward sloping portion 102c has a flat surface 103a that forms the pile bottom of the enlarged-base pile 100 and has a diameter approximately the same as the diameter of the shaft portion 101, and an upward sloping surface 103b that slopes upward from the periphery of the circular flat surface 103a toward the lower end of the vertical portion 102b which forms the outer edge of the enlarged-base portion 102.

[0025] The angle θ2 of this upward-sloping surface 103b with respect to the horizontal can be between 1° and 30°. For example, the angle θ2 can be set to 5°, 10°, 30°, etc.

[0026] Figure 2 is a diagram illustrating the shape effect of the upward-sloping surface 103b of the enlarged-base pile 100 in this embodiment. When a vertical load is applied to the pile head of the enlarged-base pile 100, an upward reaction force is received on the bottom surface 103, which forms the base of the pile, from the ground, such as the supporting ground to which it is anchored.

[0027] Here, a vertically upward reaction force acts on the nearly horizontal flat surface 103a of the widened base 102, as shown in the upper diagram of Figure 2. On the other hand, an obliquely upward reaction force acts on the upward inclined surface 103b of the downward inclined portion 102c, perpendicular to the direction from the contacting ground.

[0028] This upward-sloping reaction force can be decomposed into horizontal and vertical components (see the upper diagram in Figure 2). In the mechanical model shown in the lower diagram of Figure 2, the horizontal component of this reaction force is applied as a horizontal force to the widened base 102. That is, a horizontal force can be applied that pushes the upward-sloping surface 103b in the direction of the pile center.

[0029] This horizontal force is a compressive force for the concrete of the enlarged base 102, and it is a force that can cancel out the tensile stress generated in the enlarged base 102. This compressive horizontal force is obtained because an upward-sloping surface 103b is formed on the bottom surface 103 of the enlarged base 102.

[0030] Therefore, the effect of providing such an upward-sloping surface 103b to the enlarged-base pile 100 was confirmed by analysis. In short, a load was applied to the upper end of the mesh-divided analysis model of the enlarged-base pile 100, and an analysis was performed using the finite element method (FEM).

[0031] Figure 3 summarizes the results of this FEM analysis. The analysis was performed using four base analysis models. The inclination angles θ1 of the analysis models were set to 12°, 18°, 21°, and 30°, respectively. The shaft diameter of the shaft section 101 was set to 2.8m, and the enlarged base diameter of the enlarged base section 102 was set to 6.6m. The bottom surface of each analysis model was set to 9N / mm², assuming an N-value of 60 for the supporting ground. 2 The reaction force was applied with a uniform distribution.

[0032] Next, the tensile stress generated when the angle θ2 (taper angle) of the upward-sloping surface 103b was changed was confirmed in the mesh of interest. Specifically, Figure 3 is a graph summarizing the relationship between the taper angle of the upward-sloping surface 103b and the tensile stress obtained from the analysis.

[0033] In Figure 3, the taper angle is shown in radians (rad). As can be seen from this figure, in the analysis results from all analysis models, the tensile stress is larger (negative value) when the taper angle is close to 0.00 rad (angle θ2 = 0°).

[0034] Furthermore, it can be seen that the tensile stress decreases as the taper angle (angle θ2) increases. On the other hand, the tensile stress of the concrete in the widened base 102 differs depending on the concrete strength used (Fc24, Fc60), as shown in Figure 3.

[0035] If no tensile stress is expected in the concrete (tensile stress = 0), then under conditions where the inclination angle θ1 is between 12° and 30°, the angle θ2 (taper angle) of the upward inclined surface 103b can be set to 8.6° (approximately 0.15 rad) to 18.3° (approximately 0.32 rad) or greater, thereby preventing tensile stress from occurring in the widened base 102.

[0036] On the other hand, the tensile stress of concrete is 1.8 N / mm². 2 If (Fc24) can be expected, then under conditions where the inclination angle θ1 is between 12° and 30°, the angle θ2 (taper angle) of the upward inclined surface 103b can be set from 2.86° (approximately 0.05 rad) to 14.3° (approximately 0.25 rad) or more, thereby preventing tensile stress from occurring in the widened base portion 102.

[0037] Furthermore, the tensile stress of the concrete is 3.46 N / mm². 2 If (Fc60) can be expected, then when the inclination angle θ1 is 12°, it becomes unnecessary to provide an upward inclined surface 103b. On the other hand, under conditions where the inclination angle θ1 is between 18° and 30°, the angle θ2 (taper angle) of the upward inclined surface 103b can be set to 3.4° (approximately 0.06 rad) or 10.6° (approximately 0.185 rad) or more, thereby preventing tensile stress from occurring in the widened base portion 102.

[0038] In short, if you want to construct an enlarged-base pile 100 with a larger enlargement ratio than the typical enlarged-base pile's inclination angle θ1 (=12°) by increasing the inclination angle θ1, depending on the strength (tensile stress) of the concrete, you can significantly reduce or eliminate the tensile stress generated in the enlarged-base section 102 by making the angle θ2 of the upward-sloping surface 103b with respect to the horizontal 1° or more. On the other hand, if the angle θ2 becomes too large, the height of the downward-sloping section 102c will increase, so it is preferable to keep it to around 30°.

[0039] Next, the operation of the enlarged-base pile 100 of this embodiment will be described. In this embodiment, the enlarged-base pile 100 has an upward-sloping surface 103b formed on the bottom surface 103 of the enlarged-base portion 102, which slopes upward toward the outer edge.

[0040] As described above with reference to Figure 2, the horizontal component of the reaction force from the contacting ground acts on this upward-sloping surface 103b as a compressive horizontal force inside the overhang of the widened base 102.

[0041] Therefore, the tensile stress generated inside the enlarged base 102 can be reduced, and the protruding portion of the enlarged base 102 can be prevented from being damaged without increasing the height of the vertical portion 102b. [Examples]

[0042] The following describes the enlarged-base bucket 1 for constructing the enlarged-base pile 100 of the above-described embodiment. Parts that are the same as or equivalent to those described in the above embodiment will be denoted by the same reference numerals.

[0043] Figure 4 is an explanatory diagram showing the configuration of the widened-base bucket 1 of Embodiment 1 used when constructing the widened-base pile 100. First, to explain the configuration, the widened-base bucket 1 of Embodiment 1 comprises a cylindrical main body portion 11 and two widening wing portions 12, 12 that are formed to be openable in order to enlarge the diameter of the main body portion 11.

[0044] This widened-base bucket 1 is a device that is attached to an earth drill (not shown), and more specifically, is detachably attached via a connecting flange 141 to the lower end of the Kelly bar of an earth drill which is equipped with a slewing body, boom, Kelly rope, Kelly bar, etc.

[0045] The main body 11 of the widened-base bucket 1 is formed to a diameter that allows it to be inserted into a borehole excavated by a drilling bucket (not shown), and an annular stabilizer 3 is positioned on top of it.

[0046] The widening wing section 12 closes when the widening bucket 1 is lifted, forming a part of the side surface of the cylindrical main body section 11 (see Figure 9), and opens when inserted into the borehole, cutting and widening the wall surface of the borehole (see Figures 8 and 7).

[0047] As shown in Figure 4, the widened wing section 12 has a section with a nearly constant width near its lower end, and above that, a tapering triangular section is formed, resulting in an arc shape in plan view, as shown in the upper part of Figure 7.

[0048] Inside the main body 11 is a transmission shaft 14, which is connected to the lower end of the earth drill's Kelly bar via a connecting flange 141. The upper end of a connecting member (not shown) for applying force to open and close the widening wing section 12 is flexibly connected to the lower end of this transmission shaft 14 by a universal joint structure.

[0049] Multiple bits 122 for cutting the ground are provided at the side ends of the widened wing section 12, spaced apart in the direction of extension of the side ends. The portion cut by the bits 122 at the side ends that form the hypotenuse of the triangular section becomes the upward sloping portion 102a of the widened base section 102 (see Figure 1).

[0050] On the other hand, the equal-width section of the widened wing section 12 is formed to a height of, for example, about 500 mm, and the portion cut by this equal-width section becomes the vertical section 102b of the widened base section 102, which is about 500 mm thick (see Figure 1).

[0051] In this embodiment, the widened-bottom bucket 1 has a widened wing section 12 whose bottom is formed as an upwardly inclined surface 121 that slopes upward toward the outer edge, and a movable plate 2 that can move in the vertical direction is attached to it.

[0052] In detail, a projection 13 is formed at the lower end of the main body 11, projecting downward from the widening wing portion 12, and the upward inclined surface 121 of the widening wing portion 12 is formed so as to slope upward from the upper end position of the projection 13 toward the outer edge.

[0053] Figure 5 is an enlarged view illustrating the details of the configuration and operation of the movable plate 2. Figure 6 is a cross-sectional view taken in the direction of arrow AA in Figure 5. As shown in Figure 5, the movable plate 2 is a trapezoidal plate when viewed from the front, and as shown in Figure 6, a pair of movable plates 2,2 are arranged so as to sandwich the bottom of the widened wing section 12.

[0054] A sled plate 23 is placed between the lower end surfaces of a pair of movable plates 2,2, allowing them to move smoothly over the excavation bottom. The bolts 22 connecting the pair of movable plates 2,2 are inserted into elongated holes 21 drilled in the bottom of the widening wing section 12, as shown in Figure 5.

[0055] Multiple elongated holes 21 are drilled at intervals from the main body portion 11 side of the widened wing portion 12 toward the outer edge. The vertical length of the elongated holes 21 is shorter on the main body portion 11 side and becomes longer toward the outer edge.

[0056] The movable plate 2 acts as a guide for the bolts 22 inserted into each of the elongated holes 21, allowing it to move vertically within a predetermined range L (see Figure 6). In other words, the amount of vertical movement of the movable plate 2 is determined by the length of the elongated holes 21, so the closer it is to the outer edge of the widened wing section 12, the greater the amount of movement.

[0057] The movement of the movable plate 2 is caused by its own weight. That is, when the warped plate 23 moves away from the excavation bottom, the movable plate 2 will also descend due to its own weight. Conversely, when the excavation bottom rises, the warped plate 23 in contact with it is pushed up, causing the movable plate 2 to rise.

[0058] The upper diagrams in Figures 4 and 5 show the state where the movable plate 2 is in its highest position and the sled plate 23 is in contact with the upward inclined surface 121. On the other hand, the lower diagram in Figure 5 shows the state where the movable plate 2 is in its lowest position.

[0059] Next, we will explain the method for constructing an enlarged-base pile 100 using the enlarged-base bucket 1 of Example 1, and also explain its operation.

[0060] First, a drilling bucket (not shown in the diagram) is attached to the lower end of the earth drill's Kelly bar to construct a cylindrical borehole. Then, the drilling bucket is temporarily lifted out of the borehole and detached from the Kelly bar, and a widened-bottom bucket 1 is attached to the lower end of the Kelly bar in its place.

[0061] In this state, the widened-bottom bucket 1 is lowered into the borehole, and the protruding portion 13, which forms the bottom surface of the widened-bottom bucket 1, is brought into contact with the bottom of the borehole. Next, when the earth drill is driven and the Kelly bar is rotated, the widened-bottom bucket 1 begins to rotate due to the transmitted rotational force.

[0062] When the lower surface of the widened-bottom bucket 1 is in contact with the bottom of the excavation hole, the main body 11 of the widened-bottom bucket 1 cannot be lowered any further. In contrast, the transmission shaft 14, which transmits the weight of the Kelly bar, can be lowered along the guide cylinder (not shown).

[0063] When only the transmission shaft portion 14 descends while the main body portion 11 does not descend, the lower end of the connecting member (not shown), which is flexibly connected to the lower end of the transmission shaft portion 14, spreads outwards, causing the widening wing portions 12, 12 to open slightly (see Figure 8).

[0064] Multiple bits 122 are provided at the side ends of the widening wing section 12, which cut the excavation wall surface. As the excavation wall surface is cut, the widening wing section 12 becomes more likely to spread outward, and as the Kelly bar rotates, the widening bucket 1 rotates, and the opening of the widening wing section 12 gradually increases, ultimately forming a widened excavation hole in which the widened base section 102 is constructed (see Figure 9).

[0065] Meanwhile, the widened excavated soil generated during this widening excavation is gathered into the main body 11 by the rotating widening wings 12, 12. When the Kelly bar is lifted, the transmission shaft 14 rises, the connecting member connected to the transmission shaft 14 rises, and the widening wings 12 close (see Figures 8 and 9).

[0066] If the lifting of the Kelly bar continues in this state, the main body 11 will be lifted. The expanded-bottom bucket 1, which has the excavated soil contained inside, is then moved to the soil disposal site, and when the lid of the protruding part 13 is opened, the excavated soil is discharged from the expanded-bottom bucket 1.

[0067] In this embodiment, the widened-bottom bucket 1 has an upwardly sloping surface 121 at the lower end of the widened wing portion 12. As shown in Figure 9, the excavation bottom surface of the overhang portion also becomes a sloping surface that slopes upward towards the outer edge.

[0068] Therefore, if we attempt to recover the excavated soil by simply closing the widened wing section 12 as described above, there will be areas where soil remains on the bottom surface of the excavation, as illustrated on the left side of the lower diagram in Figure 9.

[0069] Therefore, in the widened-bottom bucket 1 of this embodiment, the movable plate 2 is moved up and down in accordance with the opening and closing of the widened wing portion 12, so that soil and sand accumulated on the excavation bottom surface of the overhang portion can also be cleanly removed.

[0070] Specifically, upon completion of the widening excavation, the widening wings 12, 12 are fully open, as shown in Figure 7. When the widening bucket 1 is rotated in this state, the widened excavated soil accumulated over the entire excavation bottom surface is pushed and moved by the widening wings 12, 12.

[0071] As described above, the widening wing sections 12, 12 gradually close while rotating, so they also reach a semi-closed state as shown in Figure 8. When the widening wing sections 12, 12 are fully open, the movable plate 2 is at its highest position, in contact with the upward inclined surface 121, but as the widening wing sections 12, 12 close, the movable plate 2 also gradually descends.

[0072] As the movable plate 2 descends, a constant contact is maintained between the excavation bottom and the movable plate 2, and the widened-base excavated soil accumulated on the excavation bottom is recovered from the excavation bottom by the movable plate 2 without being left behind.

[0073] Figure 9 shows the widening wing sections 12, 12 in the fully closed state. As shown on the excavation bottom on the right side of the lower part of Figure 9, the widened excavated soil is constantly removed from the excavation bottom by the movable plate 2, so that ultimately all of the widened excavated soil is recovered into the main body section 11.

[0074] In this way, after the soil and sediment have been completely removed from the bottom of the excavation hole, a reinforcing cage is inserted and concrete is poured to complete the enlarged-base pile 100 made of cast-in-place concrete.

[0075] In the widened-bottom bucket 1 of Embodiment 1, the bottom of the widened wing portion 12 is formed on an upwardly inclined surface 121 that slopes upward toward the outer edge, and a movable plate 2 that can move in the vertical direction is attached to it.

[0076] Therefore, when the excavated soil is recovered by closing the widened wing section 12, the soil accumulated on the excavation bottom surface, which becomes an upward-sloping surface, can be neatly removed by the movable plate 2. As a result, a widened-base pile 100 with high support performance and quality can be constructed.

[0077] Furthermore, the other configurations and effects are substantially the same as those of the above-described embodiment, so their explanation will be omitted.

[0078] While embodiments and examples of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and examples, and any design modifications that do not depart from the spirit of the present invention are included in the present invention.

[0079] For example, the enlarged-base pile 100 described in the above embodiment is not limited to the one constructed by the enlarged-base bucket 1 described in Example 1, but may also be constructed using an enlarged-base bucket of a different mechanism or a deep foundation method. [Explanation of Symbols]

[0080] 1: Wide-bottom bucket 2: Movable plate 11: Main body 12: Widened wing section 121:Upward slope 100: Enlarged base pile 101: Shaft 102: Widened base 103b: Upward inclined surface θ1: Inclination angle θ2 :Angle

Claims

1. An enlarged-base pile is formed in which an enlarged base portion is formed at the bottom of the pile, with a diameter larger than that of the shaft portion. The enlarged-base pile is characterized in that an upward-sloping surface is formed on the bottom surface of the enlarged-base portion, sloping upward toward the outer edge.

2. The enlarged-base pile according to claim 1, characterized in that the angle of inclination of the enlarged base portion with respect to the vertical line extending downward from the shaft portion is 3° or more and 45° or less, and the angle of the upward inclined surface with respect to the horizontal is 1° or more and 30° or less.

3. An enlarged-base bucket for forming an enlarged base portion at the bottom of a pile, with a diameter larger than that of the shaft portion, A cylindrical main body, The main body comprises an expandable wing portion formed to be openable so as to increase the diameter of the main body, The widened-base bucket is characterized in that the bottom of the widened wing section is formed to slope upward toward the outer edge, and a movable plate that can move in the vertical direction is attached to it.

4. The widened-bottom bucket according to claim 3, characterized in that the amount of vertical movement of the movable plate increases as it approaches the outer edge of the widened wing portion.

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