Rotary penetration pile

Abstract

To provide a rotary penetration pile having excellent penetration efficiency by preventing excessively thick blades to reduce penetration resistance.SOLUTION: A rotary penetration pile 1 comprises: a pile body 3 made of a steel pipe; an expanded diameter portion 5 connected to a lower end of the pile body 3 and having a lower end diameter larger than that of the pile body 3; and a steel blade 7 attached horizontally to a lower end of the expanded diameter portion 5. The expanded diameter portion 5 is made of a short, truncated conical steel pipe whose upper end is connected to the pile body 3 and whose diameter gradually increases toward a lower end. The steel blade 7 is a single, circular steel plate attached to cover a lower end opening of the expanded diameter portion 5, and includes: an upper blade 15 consisting of a sloping surface bent diagonally upward and a lower blade 17 consisting of a sloping surface bent diagonally downward at a part of a peripheral edge. The upper blade 15 is provided in a range from an outer edge of the steel blade 7 to an outer edge of the lower end of the expanded diameter portion 5. The lower blade 17 extends from the outer edge of the steel blade 7 inward beyond the expanded diameter portion 5. By extending the lower blade 17 inward beyond the expanded diameter portion 5, an opening 19 is formed for taking soil and sand into the pile body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a rotary penetration pile having a steel pipe pile body, an expanded diameter portion connected to the lower end of the pile body and having a lower end diameter larger than the diameter of the pile body, and a steel wing attached horizontally to the lower end of the expanded diameter portion. [Background technology]

[0002] Rotary penetration piles have the advantage of being able to provide large vertical bearing capacity by providing wings at the tip of the pile that are larger in area than the pile body. In addition, the wings have a screwing action, so when the pile body is rotated, the screw action causes it to penetrate into the ground. In this process, no soil is discharged onto the ground surface, and unlike concrete piles, no cement is used during construction, so it has been evaluated as an environmentally friendly construction method and has become widely used.

[0003] A recent trend in rotary piles is to increase the diameter of the wings to obtain greater vertical bearing capacity. In this regard, the conventional wing multiplier (ratio of wing diameter to pile body diameter) was mainly 1.5 to 2.0, but recently there has been an increase in the use of wing multipliers of 2.5 to 4.

[0004] Increasing the wing magnification ratio causes the following two problems. The first problem is that the required thickness of the blade increases, reducing its economic viability. The thickness of the blade is determined by the bending moment at the joint between the steel pipe and the blade (hereinafter referred to as the "root"). The greater the difference between the outer diameter of the wing and the outer diameter of the pile body, the greater the bending moment and the greater the required thickness of the wing.

[0005] The second problem is that as the blade outer diameter increases, the resistance force (hereinafter referred to as "penetration resistance") received from the ground during rotational penetration also increases. This is because as the blade area increases, the friction force between the ground and the blade surface also increases. Rotary driving piles generally require the movement of soil above the wings, equal to the volume of the wing area multiplied by the penetration length into the ground, while also compressing and moving soil to the sides of the pile body in an amount equivalent to the volume of the pile body. The greater the amount of lateral movement of soil, the greater the rotation torque of the pile body and the construction time. As a result, the pile driver required for rotary driving becomes larger, making it less economical. To reduce the amount of lateral movement, a method has been applied in which openings are created around the wings to allow some of the soil to enter the pile body.

[0006] The shapes of the wings of rotary penetration piles can be broadly divided into three types: A. those formed in a spiral shape, B. those made by crossing roughly semicircular steel plates, and C. those made by processing part of the periphery of a flat disk to create an inclined blade. The present invention belongs to Type C, and its feature is that the wings are flat plates, making them easy to join to the pile body. Examples of prior art for Type C include Patent Documents 1 and 2 shown below.

[0007] The rotary penetration steel pipe pile disclosed in Patent Document 1 is a rotary penetration steel pipe pile in which "steel wings formed by bending a flat plate are fixed to the tip surface of a steel pipe at right angles to the axial direction of the steel pipe, The steel wing is characterized in that a notch is provided in a predetermined range along the outer periphery of the tip of the pile body, a predetermined range including the notch is cut out in a fan shape to form a cut-out portion, one of the portions where the notch is provided is bent upward using extensions of lines connecting each end of the notch to the center of the pile as bending lines to form an upwardly inclined surface portion, and the other portion where the notch is provided is bent downward to form a downwardly inclined surface portion, and the intersections of the inclined and non-inclined portions of the incisions in the upwardly inclined surface portion and the downwardly inclined surface portion are joined by welding (see claim 1 of Patent Document 1).

[0008] The steel pipe pile disclosed in Patent Document 2 is "a steel pipe pile having an end plate with a diameter larger than that of the steel pipe pile body that closes the lower end of the steel pipe pile body, and is installed in the ground by a rotary press-in method, The end plate has a discharge port formed in the center and a pair of cutouts on the periphery that are symmetrically arranged with the steel pipe pile body in between, and a drilling bit is supported on the circumferential edges of both cutouts facing diagonally downward in the same circumferential direction" (see claim 1 of Patent Document 2). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-281205 [Patent Document 2] Japanese Patent Application Publication No. 2022-167394 Summary of the Invention [Problem to be solved by the invention]

[0010] In the case of the blade disclosed in Patent Document 1, as the blade magnification ratio increases, the bending moment at the root portion increases, as mentioned above as the first problem, and the blade thickness inevitably increases. Furthermore, since soil cannot be taken into the pile body, the penetration resistance increases and the penetration efficiency decreases. Furthermore, when penetrating hard ground, the lower inclined part (lower blade) may be subjected to large horizontal forces from the soil and sand, causing it to deform.

[0011] In the case of the blade disclosed in Patent Document 2, similar to Patent Document 1, the bending moment at the root portion becomes large, and the blade thickness inevitably becomes large. In addition, an outlet is provided in the center of the end plate (wing) to encourage the intake of soil into the pile body, but the inventors' experience has shown that the amount of soil intake is very small. Since the soil near the discharge port is undisturbed, on hard ground the port quickly becomes clogged with soil, making it impossible to take the soil into the pile body. As a result, it is difficult to expect the effects of reducing rotational torque or shortening rotation time. To avoid this, the amount of soil taken in can be increased by increasing the hole diameter (the diameter of the discharge port), but the wing area decreases, which inevitably reduces vertical bearing capacity.

[0012] The present invention has been made to solve such problems, and aims to provide a rotary penetration pile that does not have excessively thick wings, can reduce penetration resistance, and has excellent penetration efficiency. [Means for solving the problem]

[0013] (1) The rotary penetration pile according to the present invention has a steel pipe pile body, an expanded diameter portion connected to the lower end of the pile body and having a lower end diameter larger than the diameter of the pile body, and a steel wing attached horizontally to the lower end of the expanded diameter portion, The expanded diameter portion is connected to the pile body with an upper end diameter approximately the same as the lower end of the pile body, and is made of a truncated conical short steel pipe whose diameter gradually expands toward the lower end, The steel blade is a disk-shaped steel plate attached to cover the lower end opening of the enlarged diameter portion, and has an upper blade consisting of an inclined surface bent obliquely upward on a part of the peripheral edge, and a lower blade consisting of an inclined surface bent obliquely downward, the upper blade being provided in a range from the outer edge of the blade to the outer edge of the lower end of the enlarged diameter portion, and the lower blade being provided extending from the outer edge of the blade further inward than the enlarged diameter portion, The lower blade extends inward beyond the enlarged diameter portion to form an opening for taking soil and sand into the pile body.

[0014] (2) Furthermore, in the above (1), there is a protrusion that passes near the center of the underside of the wing and extends radially, and the radial length of the protrusion is at least 2 / 3 of the diameter of the pile body, and it is characterized in that it can perform the two functions of disturbing soil and sand and stiffening the wing.

[0015] (3) In addition, in the above (1) or (2), a lower blade support member is provided that connects the enlarged diameter portion and the lower blade and supports the lower blade.

[0016] (4) Furthermore, in any of the above (1) to (3), an upper blade support member is provided that connects the lower side of the enlarged diameter portion to the upper blade and supports the upper blade.

[0017] (5) Furthermore, in the above-mentioned (1) to (4), the upper blade and the lower blade are arranged opposite each other, and when the opposing upper blade and lower blade are taken as one set, the steel blade has two or three sets of upper blades and lower blades. [Effects of the Invention]

[0018] According to the present invention, a truncated cone-shaped expanded section is provided at the lower end of the pile body, and a steel wing having an upper blade and a lower blade is provided at the lower end of the expanded section.The lower blade is extended inward beyond the expanded section to form an opening for taking soil and sand into the pile body.This prevents the thickness of the steel wing from becoming excessively thick, reduces penetration resistance, and makes it possible to obtain a rotary penetration pile with excellent penetration efficiency. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is an explanatory diagram of a rotary penetration pile according to an embodiment. [Figure 2] FIG. 2 is a bottom view of the rotary penetration pile of FIG. 1. [Figure 3] FIG. 1 is an explanatory diagram of a bending moment acting on a steel blade. [Figure 4] FIG. 10 is a diagram showing a comparative example of an expanded diameter portion. [Figure 5] This is a diagram explaining the relationship between the gap B when viewing the steel blades from the vertical direction and the opening width C from the perspective of sediment intake. [Figure 6] FIG. 10 is an explanatory diagram of the mounting range of the lower blade. [Figure 7] 10A and 10B are diagrams illustrating the effect of the opposed arrangement of the upper blade and the lower blade. [Figure 8] FIG. 10 is an explanatory diagram (part 1) of another aspect of the present embodiment. [Figure 9] FIG. 10 is an explanatory diagram (part 2) of another aspect of the present embodiment. [Figure 10] FIG. 10 is an explanatory diagram of the provision of a notch between the upper blade and the lower blade. [Figure 11] 10 is an explanatory diagram of the relationship between the inclination angle of the lower blade and the force received from soil and sand. FIG. [Figure 12] FIG. [Figure 13] FIG. 10 is a diagram showing a rotary penetration pile provided with a lower blade support member. [Figure 14] FIG. 10 is an explanatory view of another embodiment of the protrusion (part 1). [Figure 15] FIG. 10 is an explanatory diagram of another embodiment of the protrusion (part 2). [Figure 16] 10A to 10C are explanatory diagrams of a method for manufacturing the expanded diameter portion. DETAILED DESCRIPTION OF THE INVENTION

[0020] As shown in Figures 1 and 2, the rotary penetration pile 1 according to this embodiment comprises a steel pipe pile body 3, an expanded diameter section 5 connected to the lower end of the pile body 3 and having a lower end diameter larger than that of the pile body 3, steel wings 7 attached horizontally to the lower ends of the expanded diameter section 5, and protrusions 9 that pass near the centers of the undersides of the steel wings and extend radially. Each component will be described in detail below.

[0021] <Expanded diameter part> The expanded diameter section 5 is connected to the pile body 3 with an upper end diameter approximately the same as the lower end of the pile body, and is made of a truncated conical short steel pipe whose diameter gradually expands towards the lower end. Here, the function of the expanded diameter portion 5 will be described. When the outer diameter of the steel blade 7 increases, the distance between the outer edge of the blade and the base (the joint with the pile body 3) increases, and the bending moment at the base increases (see FIG. 3(a)). As a result, the thickness of the tip blade increases, and the required joint strength (welding strength, etc.) at the base also increases, resulting in higher manufacturing costs. In this regard, it is possible to reduce the bending moment generated at the base of the wing by increasing the diameter of the pile body 3, but this would increase the material cost of the pile body 3 and is not realistic. Therefore, in this embodiment, an expanded diameter portion 5 is provided at the lower end of the pile body 3, thereby shortening the distance between the outer edge of the wing and the base, thereby reducing the bending moment (see FIG. 3(b)). As a result, even if the blade diameter of the steel blade 7 is increased, the thickness can be suppressed, enabling cost reduction. It is preferable that the length of the expanded diameter portion 5 is 0.5 to 1.5 times the diameter of the pile body 3, taking into consideration the stress transmission mechanism and economic efficiency.

[0022] Further, the expanded diameter portion 5 of this embodiment has a truncated cone shape that gradually expands in diameter toward the lower end, and the reason for this will be explained below. As shown in Figure 4, the expanded diameter section 5 can also be constructed from a cylinder 11 and a perforated disk 13 attached to the top surface of the cylinder 11, but this would increase the amount of steel used and would generate a large bending moment near the joints of each member, which would increase the cost of dealing with this. On the other hand, if the expanded diameter section 5 is made into a truncated cone shape, a truncated cone steel pipe is used and its upper end diameter is made approximately the same as the diameter of the pile body, thereby reducing the amount of steel used, preventing the generation of bending moments like those at the joints of the cylindrical body 11, and ensuring smooth force transmission.

[0023] <Steel wing> The steel blade 7 is a single disk-shaped steel plate attached to cover the lower end opening of the enlarged diameter portion 5. As shown in Figures 1 and 2, part of the periphery has an upper blade 15 consisting of an inclined surface bent obliquely upward, and a lower blade 17 consisting of an inclined surface bent obliquely downward. The upper blade 15 is provided in a range from the outer edge of the blade to the outer edge of the lower end of the enlarged diameter portion 5, and the lower blade 17 is provided extending from the outer edge of the blade further inward than the enlarged diameter portion 5 (see FIG. 2). The lower blade 17 extends inward beyond the enlarged diameter portion 5 to form an opening 19 for taking soil and sand into the pile body.

[0024] <About the function of the lower and upper blades> The lower blade 17 has the function of excavating and disturbing the unexcavated soil below the steel blade 7 during rotational penetration. Furthermore, when the pile body is rotated in the forward direction (in the direction in which the pile body penetrates downward), the soil and sand strike the inclined portion of the lower blade 17 facing diagonally downward, generating a component force that pushes the lower blade 17 downward, and thus generating a force that propels the pile body downward.

[0025] However, according to the inventors' experience, the downward propulsive force acting on the lower blade 17 alone is insufficient, and the pile body spins freely and does not penetrate downward. To compensate for this lack of propulsive force, the upper blade 15 is provided. The soil excavated by the lower blade 17 moves to the upper surface of the steel wing 7, and as the pile body rotates, it hits the upper blade 15. At this time, a force that propels the pile body downward is generated, just like the lower blade 17.

[0026] <Regarding the intake of sediment into the pipe> If the tip of the pile is completely blocked, all of the soil equivalent to the volume of the pile penetrating the ground must be pushed out to the outside of the pile, resulting in a large penetration resistance. In this regard, in the present invention, the lower blade 17 extends to the inside of the enlarged diameter portion 5, forming an opening 19. As a result, some of the soil excavated by the lower blade 17 moves radially inward along the slope of the lower blade 17 and is taken into the pile body through the opening 19. As a result, the penetration resistance during construction is reduced.

[0027] It is also possible to drill a hole near the center of the steel blade 7 to capture the water, but if the soil is compacted, the hole is likely to become clogged as mentioned above, and no significant effect can be expected. In this regard, in the present invention, by providing an expanded diameter section 5 whose lower end diameter is larger than the diameter of the pile body, the width of the lower blade 17 can be increased and a wide opening 19 can be provided, making it less likely that the problem of blockage will occur.

[0028] <About the orientation of the opening> The penetration resistance can be reduced by providing the openings 19 in the steel blades 7. On the other hand, the presence of the openings 19 may reduce the tip support force. When looking at the underside of the steel wing from below, the larger the area of ​​the missing part, the stronger the tendency for the tip bearing capacity to decrease. For example, if a circular hole (opening) is made near the center of the steel wing 7, the larger the hole diameter, the greater the amount of soil and sand that can be taken into the pipe, but the tip bearing capacity will definitely decrease. Conversely, if the hole diameter is small, the hole will be blocked by soil and sand during construction, defeating the purpose of having an opening.

[0029] In this embodiment, the steel blade 7 is cut out in the radial direction and bent obliquely downward to form the lower blade 17, so the opening 19 does not face vertically, but faces in the direction of the inclination angle of the lower blade 17. This makes it possible to keep the gap when viewed vertically small. This point will be explained with reference to FIG. If the length of the lower blade 17 is L, the inclination angle of the lower blade 17 is θ, and the gap when the steel blade 7 is viewed vertically is B, then B = L(1 - cosθ). In other words, the opening width C from the perspective of sediment intake is relatively large as shown in Figure 5, but the gap B from the perspective of tip bearing capacity is small.

[0030] <<Bedknife installation range>> The attachment range of the lower blade 17, that is, the radially inward extension length of the lower blade 17, is determined taking into consideration the ease of installation, the structural stability of the steel blade 7, and the effect on the tip support force. Figure 6(a) shows a case where the mounting range is short, resulting in a short opening range, while Figure 6(b) shows a case where the mounting range is long, resulting in a long opening range. If the length of the lower blade 17 (the distance from the outer edge to the inner edge of the lower blade 17) is S, the distance S is preferably defined by the following formula (1). Do / 4 <S<(Dw+Do) / 4 ··· (1) Do: Outer diameter of pile body Dw: Outer diameter of steel blade

[0031] <Arrangement of upper and lower blades> In this embodiment, the upper blade 15 and the lower blade 17 are arranged opposite each other, and when the opposing upper blade 15 and lower blade 17 are combined into one set, the steel blade 7 has two sets of upper blade 15 and lower blade 17. The reason for this arrangement will be explained below.

[0032] The soil excavated by the lower blade 17 rises along the slope of the lower blade 17 and moves to the upper surface side of the steel blade 7. In this case, for example, as shown in Figure 7(a), if the upper blade 15 is not positioned opposite the lower blade 17 (the upper blade 15 is positioned differently from the lower blade 17), the gap between the end face of the steel blade 7 and the lower blade 17 becomes narrower, making it difficult for the soil to move, and the penetration resistance increases. In contrast to this, when the upper blade 15 is disposed opposite the lower blade 17, the gap becomes larger as shown in FIG. 7(b), which increases excavation efficiency and reduces penetration resistance.

[0033] The number of pairs of upper blades 15 and lower blades 17 is not limited to two, and may be three or more, but two or three pairs are preferred.

[0034] In addition, in this embodiment, the upper blade 15 and the lower blade 17 are arranged opposite each other for the reasons stated above, but the arrangement of the upper blade 15 and the lower blade 17 of the rotary penetration pile of the present invention is not limited to this, and also includes an embodiment in which the upper blade 15 and the lower blade 17 are arranged in different positions. The overall shape of the rotary penetration pile 1, in which the upper blade 15 and the lower blade 17 are provided in different positions, is shown in Fig. 8. Also, Fig. 9 shows the steel wing 7 of the rotary penetration pile 1 shown in Fig. 8, viewed from the back side.

[0035] In addition, since there is a risk that large-grained soil and sand, such as in ground mixed with boulders, may clog the opening 19, in such cases, as shown in Figure 10, it is sufficient to first make a cutout in the steel blade 7 and then position the lower blade 17 and upper blade 15.

[0036] <Reinforcement of the lower blade> In order to improve the excavation efficiency of the lower blade 17, it is effective not only to increase the area of ​​the lower blade 17 but also to increase the inclination angle. FIG. 11 shows a schematic diagram of the force that the lower blade 17 receives from the earth and sand depending on the inclination angle of the lower blade 17. In tests conducted by the inventors, the penetration efficiency increased when the inclination angle (angle from horizontal) was set to 30° to 45°. On the other hand, if the inclination angle was set to this large, a large bending moment would be generated at the base of the lower blade 17 when penetrating hard ground, causing it to bend at the base and preventing it from functioning as a lower blade 17. To prevent this, it is conceivable to increase the bending strength (thickness and material) of the lower blade 17 or to attach a rib to the underside of the lower blade 17 to prevent deformation, but this would increase costs. Therefore, in this embodiment, as shown in FIGS. 12 and 13, a lower blade support member 21 that connects the enlarged diameter portion 5 and the lower blade 17 and supports the lower blade 17 is provided.

[0037] The shape of the lower blade support member 21 is not particularly limited, but the one shown in Figures 12 and 13 is made by fastening a triangular steel plate to the lower end of the enlarged diameter portion 5 and the upper surface of the lower blade by welding or the like. This makes it possible to prevent deformation of the lower blade 17 at low cost.

[0038] <Reinforcement of the upper blade> As the pile body rotates, the soil excavated by the lower blade 17 and moved above the steel wing 7 strikes the upper blade 15, generating a force that pushes the pile body downward. This force generates a bending moment at the base of the upper blade 15 and the steel wing 7. When penetrating hard ground or when the inclination angle of the lower blade 17 is large, the upper blade 15 may be deformed. Therefore, it is preferable to provide an upper blade support member (not shown) that connects the enlarged diameter portion 5 and the upper blade 15 and supports the upper blade 15 at the lower part of the outer surface of the enlarged diameter portion 5. By providing the upper blade support member, deformation of the upper blade 15 can be prevented.

[0039] <Protrusion> The protrusion 9 is provided so as to pass through the vicinity of the center of the lower surface of the wing and extend in the radial direction. Since the lower blade 17 cannot excavate or disturb the soil near the center of the steel blade, the protrusion 9 is provided near the center of the underside of the steel blade so that the soil near the center of the steel blade can be excavated and disturbed. Furthermore, by providing the lower blade 17 and upper blade 15 on a portion of the steel wing 7, the rigidity and strength of the steel wing 7 are reduced compared to a simple disk 13. For this reason, it is desirable that the projections 9 be sized and positioned so as to also reinforce the steel wing 7. For example, by making the radial length of the projections 9 at least two-thirds of the diameter of the pile body 3, the projections 9 can fulfill the dual functions of disturbing soil and reinforcing the wing.

[0040] The shape of the protrusion 9 may be rectangular, trapezoidal, triangular, or other steel plate. The number of protrusions 9 may be one or more. The size of the protrusions 9 should be determined taking into consideration the reinforcing effect of the steel blade 7.

[0041] A specific example of the protrusion 9 will be described. 14 shows a structure in which large cross-shaped protrusions 9 are arranged. These protrusions 9 not only disturb the soil and sand, but also serve to increase the rigidity and strength of the steel blades 7.

[0042] The example shown in Figure 15 has three projections 9. All three projections have the function of disturbing soil and sand, but the central projection 9 has a length of more than two-thirds the diameter of the pile body 3, and also serves to reinforce the steel wings 7. The two side projections 9 are provided near the opening 19 and have the function of guiding earth and sand to the opening 19 in order to take as much earth and sand as possible into the pile body. The arrows in Figures 14 and 15 indicate the rotation direction of the pile as viewed from the bottom side. It should be noted that the projections 9 are not essential for the rotary penetration pile 1 according to the present invention, and the rotary penetration pile 1 may also have no projections 9.

[0043] In the rotary penetration pile 1 of this embodiment, a truncated conical expansion section 5 is provided at the lower end of the pile body 3, and a steel wing 7 having an upper blade 15 and a lower blade 17 is provided at the lower end of the expansion section 5, and the lower blade 17 is extended inward beyond the expansion section 5 to form an opening 19 for taking soil and sand into the pile body.This prevents the thickness of the steel wing 7 from becoming excessively thick, reduces penetration resistance, and makes it possible to obtain a rotary penetration pile 1 with excellent penetration efficiency.

[0044] In addition, the protrusion 9 passes near the center of the underside of the wing and extends radially, and the radial length of the protrusion 9 is more than 2 / 3 of the diameter of the pile body 3, so that the protrusion 9 can perform the dual functions of disturbing soil and stiffening the wing.

[0045] Furthermore, by providing a lower blade support member 21 that connects the enlarged diameter portion 5 and the lower blade 17 and supports the lower blade 17, deformation of the lower blade 17 can be suppressed even if the inclination angle of the lower blade 17 is increased to an appropriate angle. As a result, the penetration efficiency can be improved. Similarly, by providing an upper blade support member that connects the lower side surface of the enlarged diameter portion 5 and the upper blade 15 and supports the upper blade 15, deformation of the upper blade 15 can be suppressed.

[0046] In addition, the upper blade 15 and the lower blade 17 are arranged opposite each other, and when the opposing upper blades 15 and lower blades 17 are taken as a set, the steel wing 7 has two or three sets of upper blades 15 and lower blades 17, which increases the gap between the upper blades 15 and lower blades 17, improving excavation efficiency and reducing penetration resistance. [Example]

[0047] <Example of dimensions> 1 shows an example of dimensions of the components of a rotary penetration pile. Pile body diameter: 300 mm Steel blade diameter: 900mm Diameter of the expanded section (conical steel pipe): 600 mm Length of expanded diameter section (conical steel pipe): 300 mm Distance from the outer edge of the steel wing to the base of the pile body: (900-600) / 2 = 150 mm

[0048] If the enlarged diameter portion 5 were not present, the distance from the outer edge of the steel wing to the base of the pile body 3 would be (900-300) / 2 = 300 mm. In contrast, in this embodiment, by providing the enlarged diameter portion 5, this distance becomes 150 mm as described above, and the bending moment at the base of the steel wing 7 can be reduced to less than half.

[0049] <Manufacturing method> The steel blade 7 can be produced by cutting a steel plate into a disk shape, making notches in parts of the plate, and bending the notches obliquely upward and downward using a press or the like. The protrusions 9 can be formed by welding a steel plate processed into a predetermined shape to the bottom surface of the steel blade 7 .

[0050] The enlarged diameter portion 5 is preferably made of cast steel. The reason for this is that, as shown in Figure 16, the groove portion 25 and backing metal 27 required for welding the pile body 3 and steel wings 7 to the enlarged diameter portion 5 can be manufactured integrally with the enlarged diameter portion body. Furthermore, when a lower blade support member 21 and an upper blade support member are provided, they can also be manufactured integrally with the enlarged diameter portion 5.

[0051] It is advisable to provide a parallel section 29 at the top of the enlarged section 5, as shown in Figure 16. When an axial force acts on the pile body, a bending moment is generated in the enlarged section 5. If the pile body 3 were directly joined to a truncated cone without the parallel section 29, this bending moment would be transmitted to the pile body 3, increasing the required thickness of the pile body 3. In this regard, providing the parallel section 29 can prevent this moment from being transmitted to the pile body 3. [Explanation of symbols]

[0052] 1 Rotary penetration pile 3 Pile body 5 Expanded diameter part 7 steel wings 9 protrusions 11 Cylinder 13 Disc 15 Upper blade 17 Lower blade 19 Opening 21 Lower blade support member 25 Bevel 27 Backing Fund 29 Parallel section

Claims

1. A rotary penetration pile having a steel pipe pile body, an expanded diameter portion connected to the lower end of the pile body and having a lower end diameter larger than the diameter of the pile body, and a steel wing attached horizontally to the lower end of the expanded diameter portion, The expanded diameter portion is connected to the pile body with an upper end diameter approximately the same as the lower end of the pile body, and is made of a truncated conical short steel pipe whose diameter gradually expands toward the lower end, The steel blade is a disk-shaped steel plate attached to cover the lower end opening of the enlarged diameter portion, and has an upper blade consisting of an inclined surface bent obliquely upward on a part of the peripheral edge, and a lower blade consisting of an inclined surface bent obliquely downward, the upper blade being provided in a range from the outer edge of the steel blade to the outer edge of the lower end of the enlarged diameter portion, and the lower blade being provided extending from the outer edge of the steel blade further inward than the enlarged diameter portion, A rotary penetration pile characterized in that the lower blade extends inward beyond the enlarged diameter portion to form an opening for taking soil and sand into the pile body.

2. 2. The rotary penetration pile according to claim 1, characterized in that it has a protrusion that passes near the center of the underside of the steel wing and extends radially, the radial length of which is at least two-thirds of the diameter of the pile body, and it can perform the dual functions of disturbing soil and stiffening the steel wing.

3. 3. The rotary penetration pile according to claim 1, wherein a lower blade support member is provided at the lower end of the enlarged diameter portion to connect the enlarged diameter portion and the lower blade and support the lower blade.

4. 3. The rotary penetration pile according to claim 1, wherein an upper blade support member is provided on a lower portion of the outer surface of the enlarged diameter portion, connecting the enlarged diameter portion and the upper blade and supporting the upper blade.

5. The rotary penetration pile according to claim 1 or 2, characterized in that the upper blade and the lower blade are arranged opposite each other, and when the opposing upper blade and lower blade are taken as one set, the steel wing has two or three sets of upper blades and lower blades.

Images