JP7036301B1 - Rotary press-fit steel pipe pile - Google Patents

Abstract

Provided is a rotary press-fit steel pipe pile capable of suppressing damage due to resistance during penetration without hindering smooth penetration into the ground and development of bearing capacity. The rotary press-fit steel pipe pile 10 is a steel pipe pile with blades that is provided with a spiral blade 12 at the tip and is rotationally press-fitted into the ground by excavating the spiral blade 12 while rotating, and the outer diameter of the steel pipe pile is defined as the diameter. The spiral blade 12 having an opening of 0.1 times or more and 0.9 times or less with respect to the area of the circle is welded concentrically to the tip portion 13 of the steel pipe pile having an asymmetric tip shape when viewed from the side surface. It is fixed, and the spiral blade 12 is projected inside and outside the steel pipe pile 10.

Description

The present invention relates to a rotary press-fit steel pipe pile.

Conventionally, there has been known a method of applying a rotational force to a rotary press-fit steel pipe pile in which a spiral blade is attached to the tip of a steel pipe to penetrate the ground (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2001-193063

The rotary press-fit steel pipe pile is penetrated into the ground by the rotational force applied by the construction machine. Specifically, by rotating the rotary press-fit steel pipe pile from the ground, earth and sand are excavated at the tip of the spiral blade, and the earth and sand excavated on the upper surface of the blade is pushed upward as the blade rotates, and the reaction force of the ground. It penetrates into the ground by the propulsive force generated by.

When a rotary press-fit steel pipe pile is penetrated into the ground, a rotational moment in the direction opposite to the rotational direction acts on the steel pipe constituting the steel pipe pile due to the penetration resistance. When this rotational moment increases, the steel pipe may break. In particular, when a rotary press-fit steel pipe pile penetrates into hard ground such as a bedrock layer in the ground, the penetration resistance increases and a large rotational moment acts on the steel pipe. In this case, the probability that the steel pipe will break is high.

As a result of repeated experiments and demonstrations by the present inventors, cracks are formed from the starting end of the steel pipe in the rotational direction along the joint with the blade at the tip of the steel pipe, and the crack propagates as the crack progresses in the rotational direction. It was confirmed that the steel pipe finally broke along the crack and the steel pipe and the blade were separated.

On the other hand, in the rotary press-fit steel pipe pile described in Patent Document 1, the tip of the pile is a support layer (ground such as debris, sand, cohesive soil, etc., and refers to, for example, a layer having an N value of 50 or more. Is the N value of the standard penetration test.) The issues are workability and securing of bearing capacity when reaching the standard penetration test. No measures were taken against the breakage.

Therefore, an object of the present invention is to provide a rotary press-fit steel pipe pile capable of suppressing damage due to resistance during penetration without hindering smooth penetration into the ground and development of bearing capacity.

The gist of this disclosure is as follows.

(1) A steel pipe pile with blades, which is provided with blades at the tip and is rotationally press-fitted into the ground by excavating while rotating the blades.
The blade provided with an opening of 0.1 times or more and 0.9 times or less the area of the circle whose diameter is the outer diameter of the steel pipe pile is concentric with the tip of the steel pipe pile having an asymmetric tip shape when viewed from the side surface. A rotary press-fit steel pipe pile that is welded and fixed in a shape and the blades overhang inside and outside the steel pipe pile.

(2) The wall thickness of the steel pipe pile is thicker than the outside of the predetermined range in a predetermined range of at least a distance corresponding to the outer diameter of the steel pipe pile from the tip of the steel pipe pile in the axial direction of the steel pipe pile. , The rotary press-fit steel pipe pile according to (1) above.

(3) The ratio of the wall thickness outside the predetermined range to the wall thickness within the predetermined range is 0.5 or more, and the ratio of the wall thickness within the predetermined range to the outer diameter of the steel pipe pile is 0.02 or more. The rotary press-fit steel pipe pile according to (2).

(4) The rotary press-fit steel pipe pile according to any one of (1) to (3) above, wherein the blade is a spiral blade and is welded and fixed to the tip of the steel pipe pile cut in a spiral shape. ..

(5) The tip of the steel pipe pile is cut in a spiral shape, and the stepped portion between the start end and the end of the tip portion of the steel pipe pile cut in a spiral shape is an arc, an arbitrary curve, or an arc or a straight line with an arbitrary curve. When the tip of the spiral steel pipe pile is developed in a plane, the circumference of the outer circumference of the steel pipe pile is the base, the pitch of the spiral is the height, and the spiral shape is formed. The area of the triangle whose base is the height of the right triangle and whose apex is the end is 0.25 times or less the area of the right triangle whose diagonal is the tip of the steel pipe pile. )-(4). The rotary press-fit steel pipe pile according to any one of (4).

(6) The tip of the steel pipe pile is cut in a spiral shape, and the stepped portion between the start end and the end of the tip of the steel pipe pile cut in a spiral shape is formed in an arc shape, and the radius R of the arc is as follows (1). ), The rotary press-fit steel pipe pile according to any one of (1) to (5) above.
R = k × P ・ ・ ・ (1)
However, in the equation (1), P is a spiral pitch and k is a predetermined coefficient (0.8 ≦ k ≦ 1.5).

(7) At the beginning of the rotational press-fitting in the rotational direction,
The rotary press-fit steel pipe pile according to any one of (1) to (6) above, wherein the bead for welding the blade and the tip of the steel pipe pile is formed so as to be continuous from the outer circumference to the inner circumference of the steel pipe pile.

(8) At the beginning of the rotational press-fitting in the rotational direction,
Any of the above (1) to (7), wherein the cross-sectional shape of the bead for welding the blade and the tip of the steel pipe pile forms an acute-angled slope with respect to the surface of the blade. Described rotary press-fit steel pipe pile.

(9) The blade is arranged so that the outer edge is lower than the inner edge or the inner edge and the outer edge are located at the same height in an upright state with the tip of the steel pipe pile facing down. The rotary press-fit steel pipe pile according to any one of (8).

According to the present invention, it is possible to suppress damage due to resistance during penetration without hindering smooth penetration into the ground and development of bearing capacity.

It is a figure which shows the steel pipe pile which concerns on one Embodiment. It is a figure which shows the steel pipe pile which concerns on one Embodiment. It is a figure which shows the steel pipe pile which concerns on one Embodiment. It is a figure which shows the steel pipe pile which concerns on one Embodiment. It is a figure which shows the steel pipe pile which concerns on one Embodiment. It is a characteristic diagram which shows the analysis result of the distribution of the stress applied to the steel pipe pile at the time of penetration. It is a characteristic diagram which shows the analysis result of the distribution of the stress applied to the steel pipe pile at the time of penetration. It is a characteristic diagram which shows the analysis result of the distribution of the stress applied to the steel pipe pile at the time of penetration. It is a characteristic diagram which shows the analysis result of the distribution of the stress applied to the steel pipe pile at the time of penetration. It is a figure which shows the steel pipe pile which concerns on the comparative example of this embodiment. It is a development view which developed the steel pipe pile in the vicinity of a step portion. In the plan view shown in FIG. 5, it is an enlarged view which shows the region A1. FIG. 3 is an enlarged view showing the vicinity of the starting end shown in FIG. 9 is a diagram showing a state in which the vicinity of the start end is viewed from the direction of arrow A3 in FIG. FIG. 3 is an enlarged vertical cross-sectional view showing the vicinity of the spiral blade of FIG. 2. It is a schematic diagram for demonstrating the shape of a step portion. It is a schematic diagram for demonstrating the shape of a step portion. It is a side view which shows the example of the steel pipe pile tip part having an asymmetric tip shape. It is sectional drawing which shows in detail the vicinity of the boundary where the wall thickness of a steel pipe pile changes from thick wall to thin wall. It is sectional drawing which shows in detail the vicinity of the boundary where the wall thickness of a steel pipe pile changes from thick wall to thin wall.

First, the configuration of the rotary press-fit steel pipe pile 10 according to the embodiment of the present invention will be described with reference to FIGS. 1 to 5. 1 to 5 are views showing a steel pipe pile 10 according to an embodiment. Specifically, FIG. 1 is a front view of the steel pipe pile 10, FIG. 2 is a vertical sectional view of the steel pipe pile 10, FIG. 3 is an upward perspective view of the steel pipe pile 10, FIG. 4 is a downward perspective view of the steel pipe pile 10, and FIG. It is a top view of the steel pipe pile 10. In FIGS. 1 to 5, the bead 30 described later is not shown.

The tip of the steel pipe pile 10 is an open end, and the tip thereof is provided with a spiral blade 12 whose inner edge 20 and outer edge 21 project to the inside and outside of the steel pipe pile 10 by predetermined dimensions. Further, the tip portion 13 of the steel pipe pile is cut in a spiral shape, and the stepped portion 16 between the start end 15 and the end 14 is formed in an arc shape.

The outer diameter (D ₂ ) of the spiral blade 12 is approximately 1.2 to 3 times the outer diameter of the steel pipe pile outer diameter (D), and the inner diameter (D ₃ ) of the spiral blade 12 is the inner diameter of the steel pipe pile (D). The spiral blade 12 is configured by using an annular steel plate (doughnut-shaped steel plate) having an inner diameter approximately 0.2 to 0.3 times that of ₁ ). That is, this annular steel plate is cut at one point in the radial direction, one is set as the circumferential start end 18 and the other is the circumferential end 17, and is welded and fixed concentrically to the spirally cut steel pipe pile tip portion 13. The inner edge 20 and the outer edge 21 of the spiral blade 12 are formed so as to project inside and outside the steel pipe pile tip portion 13. An excavation tooth 24 is provided at the start end 18 in the circumferential direction.

As described above, the steel pipe pile 10 may break due to the penetration resistance generated at the time of penetration into the ground. In order to investigate the cause of the breakage of the steel pipe pile 10, the present inventors analyzed the distribution of stress applied to the steel pipe pile 10 at the time of penetration by the finite element method (FEM). 6A to 6D are characteristic diagrams showing the analysis results of the stress distribution applied to the steel pipe pile 10 at the time of penetration. 6A to 6D show analysis results when the thick portion described later is not provided and the wall thickness of the steel pipe pile 10 is constant over the entire area. 6A and 6B show the stress in the circumferential direction at the torsion angle of 6.15 °, FIG. 6A shows the stress on the outer surface of the steel pipe pile 10, and FIG. 6B shows the stress on the inner surface of the steel pipe pile 10. ing. 6C and 6D show the axial stress of the steel pipe pile 10 at the torsion angle of 6.15 °, FIG. 6C shows the stress on the outer surface of the steel pipe pile 10, and FIG. 6D shows the stress of the outer surface of the steel pipe pile 10. Shows the stress on the inner surface of. 6A to 6D show that the higher the density of dots, the higher the stress. The torsion angle is an angle formed by the radius at the initial position of the circle on the upper surface when the lower surface is fixed in the cylinder and the radius rotated by the action of torque.

As can be seen from FIGS. 6A to 6D, the stress generated in the steel pipe pile 10 at the time of penetration is high within a predetermined distance L upward from the tip of the steel pipe pile 10. Above the range of the predetermined distance L, the stress generated in the steel pipe pile 10 is within the allowable range. Here, the predetermined distance L is about the diameter of the steel pipe.

Further, in particular, in the steel pipe pile tip portion 13 joined to the spiral blade 12, the stress becomes high near the positions of the start end 15 that first enters the ground, the end 14 that finally enters the ground, and the step portion 16. ing.

FIG. 7 is a diagram showing a steel pipe pile 10'without improvement of (1) to (6) described later according to a comparative example of the present embodiment, in which a crack 32 is generated when penetrating into the ground. It shows how to do it. In the steel pipe pile 10'according to the comparative example, if the penetration resistance at the time of penetrating into the ground is large, the crack 32 advances in the rotational direction and the steel pipe pile 10'breaks. According to the results demonstrated by the present inventors through repeated experiments, the crack 32 starts from the most stressful starting end 15 and propagates along the rotation direction. The crack 32 finally propagates around the steel pipe pile 10 so that the steel pipe pile 10 breaks. As a result, the steel pipe pile 10 and the spiral blade 12 are separated from each other. The position where the crack 32 first enters corresponds to the position of the starting end 15 where the stress is particularly high in the analysis result of the stress distribution shown in FIG.

Therefore, based on the analysis results of the stress distribution shown in FIGS. 6A to 6D, measures are taken to reduce the stress in the high stress area, and the shape and structure of the steel pipe pile 10 are determined at the time of penetration. It is possible to construct a steel pipe pile 10 in which breakage is suppressed.

In the present embodiment, four measures are taken for the steel pipe pile 10'according to the comparative example in order to prevent breakage during penetration. By these measures, the generation of the crack 32 as shown in FIG. 7 is suppressed. Further, measures are taken to enhance the support function after the steel pipe pile 10 is penetrated. Each of the improvements will be described below.

(1) Steel pipe thick portion According to the stress analysis results shown in FIGS. 6A to 6D, the stress generated in the steel pipe pile 10 at the time of penetration becomes particularly high within a predetermined distance L from the tip of the steel pipe pile 10 upward. ing. Therefore, as shown in the vertical sectional view of FIG. 2, the wall thickness of the steel pipe pile 10 is a distance (predetermined distance L) corresponding to at least the outer diameter D of the steel pipe pile from the tip portion 13 of the steel pipe pile 10 in the axial direction of the steel pipe pile 10. ) In the above predetermined range, the wall thickness is thicker than that outside the predetermined range. As an example, when the pile diameter of the steel pipe pile 10 is 1000 [mm], the wall thickness of the steel pipe pile 10 is t ₁ = 22 [mm] in the range of the predetermined distance L, and t ₂ outside the range of the predetermined distance L. = 13 [mm]. As described above, since the predetermined distance L with high stress is about the diameter of the steel pipe pile 10, the steel pipe pile 10 is thickened at a distance corresponding to about the diameter of the steel pipe pile 10 from the tip of the steel pipe pile 10. .. However, since this predetermined distance L is a condition of preventing damage when penetrating into hard ground having an N value of 50 or more, which is generally regarded as a support layer, for example, the superstructure of the steel pipe pile 10 is compared. It is lightweight, and the distance L may be shortened when, for example, the N value 15 is used as the support layer. From the viewpoint of reducing stress, it is conceivable to increase the thickness of the entire steel pipe pile 10, but since the weight of the steel pipe pile 10 increases and the manufacturing cost also increases, it is outside the range of the predetermined distance L. It is preferable that the steel pipe pile 10 is thin.

The portion of the predetermined distance L having a thick wall thickness may be configured as a short pipe, or the long pipe above the predetermined distance L and the short pipe may be joined by welding. On the other hand, the portion of the predetermined distance L having a thick wall thickness and the portion above the predetermined distance L may be configured by an integral pipe.

By increasing the wall thickness of the steel pipe pile 10 within a predetermined distance L, stress concentration is relaxed when the steel pipe pile 10 is rotated and penetrates into the ground. Therefore, the generation of the crack 32 as shown in FIG. 7 is surely suppressed.

On the other hand, even when the wall thickness of the steel pipe pile 10 is increased within the range of the predetermined distance L, stress concentration occurs in the vicinity of the boundary 19 where the wall thickness of the steel pipe pile 10 changes from thick to thin. , Breakage may occur. Therefore, the ratio of the wall thickness of the steel pipe pile 10 having a predetermined distance L to the wall thickness of the steel pipe pile 10 other than the predetermined distance L, or the ratio of the wall thickness of the steel pipe pile 10 having a predetermined distance L to the outer diameter D of the steel pipe pile is set. It is preferable to set an appropriate value that does not cause breakage. Table 1 shows the wall thickness t ₁ (thickness of the short pipe) of the steel pipe pile 10 in the range of the predetermined distance L shown in FIG. 2 and the wall thickness t ₂ (wall thickness of the long pipe) of the steel pipe pile 10 outside the range of the predetermined distance L. The results of examining the appropriate values of the wall thickness ratio (t ₂ / t ₁ ) to the wall thickness) and the ratio of the wall thickness t ₁ to the outer diameter D of the steel pipe pile (t ₁ / D) are shown. ing. As shown in Table 1, if the wall thickness ratio (t ₂ / t ₁ ) is 0.5 or more and the ratio of wall thickness to pile diameter (t ₁ / D) is 2% or more, the steel pipe is near the boundary 19. It was found that the pile can be penetrated into the general support layer (N value ≧ 50) without causing breakage at the wall thickness change portion where the wall thickness of the pile 10 changes from thick to thin (○ mark in Table 1). (good)). Further, the wall thickness ratio (t ₂ / t ₁ ) is 0.7 or more, or the wall thickness ratio (t ₂ / t ₁ ) is 0.5 or more, and the ratio of the wall thickness to the pile diameter (t ₁ / D). ) Is 4% or more, rubble ground (N value ≧ 50) in which an uneven load is likely to be applied without causing breakage at the wall thickness change portion where the wall thickness of the steel pipe pile 10 changes from thick wall to thin wall. It was found that the pile can be penetrated into the support layer of) (marked with ◎ (very good) in Table 1).

16 and 17 are cross-sectional views showing in detail the vicinity of the boundary 19 where the wall thickness of the steel pipe pile 10 changes from thick to thin. In FIGS. 16 and 17, the steel pipe pile 10 is configured as a short pipe 10b within a predetermined distance L in which the wall thickness is thick, and the long pipe 10a and the short pipe 10b outside the range of the predetermined distance L are welded. When the steel pipe pile 10 is joined and formed, the vicinity of the region A4 shown in FIG. 2 is enlarged and shown. In the example shown in FIG. 16, the axial end faces of the long pipe 10a and the short pipe 10b are joined by the weld bead 40, and the weld bead 40 is formed along the circumferential direction between the opposite end faces. ing. According to the configuration example shown in FIG. 16, since the weld bead 40 is melted between the opposite end faces of the long pipe 10a and the short pipe 10b, it is possible to prevent the wall thickness change portion from breaking during penetration. In the example shown in FIG. 17, in addition to the configuration of FIG. 16, a backing metal 42 is provided along the inner circumference of the portion where the long pipe 10a and the short pipe 10b are joined, and the backing metal 42 is provided. It is welded to the inner peripheral surface of either the long pipe 10a or the short pipe 10b.

(2) Radius of curvature of the stepped portion As described above, the stepped portion 16 of the start end 15 and the end 14 of the spirally cut steel pipe pile tip portion 13 is formed in an arc shape. FIG. 8 is a developed view of the steel pipe pile 10 developed in the vicinity of the step portion 16. Further, FIG. 9 is an enlarged view of the region A1 in the plan view shown in FIG.

In the developed view shown in FIG. 8, the radius R of the arc of the stepped portion 16 connecting the start end 15 and the end end 14 of the spirally cut steel pipe pile tip portion 13 uses the spiral pitch P of the spiral blade 12. It is expressed by the following equation (1). The spiral pitch P corresponds to an axial displacement when rotated by 360 ° about the central axis of the steel pipe pile 10 along the spiral steel pipe pile tip portion 13. Further, k is a predetermined coefficient. As the value of k changes, the angle θ ₁ between the start end 15 and the end end 14 shown in FIG. 9 changes, and there is a relationship of θ ₁ = 360-360 × k [deg].
R = k × P ・ ・ ・ (1)

The present inventors analyzed the stress distribution in the same manner as in FIGS. 6A to 6D by changing the value of k, verified the stress level in the vicinity of the step portion 16, and obtained the results shown in Table 2 below. rice field. In Table 2, the circles indicate that the stress of the step portion 16 was 315 N / mm ² or less. On the other hand, in Table 2, the x mark indicates that the stress of the step portion 16 exceeded 315 N / mm ² (yield point), and a plasticized portion was formed in the steel pipe. From this result, it is preferable that the value of k is 0.8 ≦ k ≦ 1.5.

As described above, by setting the radius of curvature of the arc of the step portion 16 to about the pitch P of the spiral blade 12, the stress concentration at the start end 15, the step portion 16 and the end 14, which are likely to be the starting points of fracture, is relaxed and penetrates. Breaking of the steel pipe pile 10 due to resistance is suppressed.

Although the developed view of FIG. 8 shows an example in which the step portion 16 is connected by a circle, the step portion 16 may be connected by an arbitrary curve, an arc, or a combination of an arbitrary curve and a straight line.

13 and 14 are schematic views for further explaining the shape of the step portion 16. FIG. 13 shows a side view of the steel pipe pile 10 including the steel pipe pile tip portion 13 in the upper stage, and shows a developed view of the steel pipe pile tip portion 13 including the step portion 16 in the lower stage. In FIG. 13, the blade 12 is not shown. Further, FIG. 14 is a developed view of the steel pipe pile 10 developed all around the circumference including the step portion 16.

As shown in FIG. 13, assuming that the outer diameter of the steel pipe pile 10 is Dp, the peripheral length of the outer diameter of the steel pipe pile 10 is π · Dp. As shown in FIG. 14, the tip portion 13 of the steel pipe pile cut in a spiral shape becomes a diagonal straight line on the developed view, and this straight line is the hypotenuse, the pitch P is the height, and the peripheral lengths π and Dp are the bases. A right triangle is constructed. Note that FIG. 14 shows a case where the pitch P is 0.3 times the outer diameter Dp. The area of the triangle composed of both ends of the pitch P (= 0.3Dp) and the three points of the terminal 14 is 0.25 times or less with respect to the area of the right triangle. That is, the angle between the start end 15 and the end end 14 with respect to the central axis of the steel pipe pile 10 is (π / 4) · Dp or less. When the steel pipe pile 10 is rotationally press-fitted, earth and sand are taken into the inside of the steel pipe pile 10 from the side opening formed by the step portion 16 of the steel pipe pile tip portion 13, but both ends of the pitch P with respect to the area of the right triangle. If the area of the triangle composed of the three points of the end 14 and the end 14 is 0.25 times or less, the distance from the bottom of the right triangle to the end 14 (the axial height of the steel pipe pile 10 of the step portion 16) is sufficient. Because it can be secured, the side opening becomes large and it becomes easy for earth and sand to enter the pipe. This reduces the penetration resistance. On the other hand, if the area of the triangle composed of both ends of the pitch P and the end 14 exceeds 0.25 times the area of the right triangle, the distance from the base of the right triangle to the end 14 becomes short, so that the side The opening becomes smaller and it becomes difficult for earth and sand to enter the pipe. Since the earth and sand that do not enter the pipe must be extruded around the steel pipe pile 10, the penetration resistance becomes large, and as a result, rotational press-fitting becomes difficult.

The shape of the step portion 16 (arc, arbitrary curve, or combination of arc or arbitrary curve and straight line) is defined to connect the start end 15 and the end point 14 defined as described above. Here, when the end point 14 defined as described above and the start end point 15 are connected by a straight line, the penetration resistance can be reduced because a large side opening is secured, but the start end point 15, the end point 14, And because stress is concentrated in the vicinity of the step portion 16, the shape of the step portion 16 is defined by connecting the start end 15 and the end 14 by an arc, an arbitrary curve, or a combination of an arc or an arbitrary curve and a straight line. Is preferable. As a result, a large side opening is secured to reduce the penetration resistance, and stress concentration in the vicinity of the start end 15, the end 14, and the step portion 16 is suppressed.

(3) Shape of welded portion between blade tip and steel pipe FIG. 10 is an enlarged view showing the vicinity of the start end 15 of the steel pipe pile tip 13, and is a perspective view showing the region A2 shown in FIG. 3 in an enlarged manner. Is. FIG. 11 is a diagram showing a state in which the vicinity of the start end 15 is viewed from the direction of arrow A3 in FIG. In the steel pipe pile 10, the tip portion 13 of the steel pipe pile cut in a spiral shape is abutted against the spiral upper surface of the spiral blade 12, and is joined to the spiral blade 12 by welding.

As shown in FIGS. 9 to 11, a weld bead 30 is formed along the outer periphery of the steel pipe pile 10, and the steel pipe pile 10 and the spiral blade 12 are joined to each other. Further, in the vicinity of the start end 15, a bead 30 is formed so as to surround the start end 15 in a U shape by turning welding. That is, the bead 30 is formed so as to be continuous from the outer circumference to the inner circumference of the steel pipe pile 10 in the vicinity of the starting end 15.

In the inner circumference of the steel pipe pile 10, a spiral backing metal 25 is provided along the inner circumference of the steel pipe pile at the portion where the tip portion 13 of the steel pipe pile and the spiral blade 12 are joined, as shown in FIG. It may be arranged. The backing metal 25 has, for example, a steel pipe pile 10 having an axial length of about 30 mm and a radial thickness of about 10 mm. At the inner circumference of the steel pipe pile 10, welding is not performed except for the portion where the rotation welding is performed, but the weld bead 30 formed along the outer circumference of the steel pipe pile 10 reaches the backing metal of the inner circumference and melts into it. I'm out. Since the backing metal 25 is for welding from one side (outer peripheral side of the steel pipe pile 10) to fasten the weld metal of the bead 30 to the groove portion, both sides (outer peripheral side and inner circumference of the steel pipe pile 10) are used. The backing metal 25 may not be provided in the rotating welded portion where welding is performed from the side). That is, in the inner circumference of the steel pipe pile 10, the backing metal 25 may not be provided at the portion where the rotation welding is performed. On the other hand, even if the backing metal 25 is extended to the position of the starting end 15 on the inner circumference of the steel pipe pile 10, the backing metal 25 is also provided in the portion where the turning welding is performed, and the backing metal 25 is melted together by the turning welding. good.

By turning welding, the bead 30 is formed so as to be continuous from the outer circumference to the inner circumference of the steel pipe pile 10 in the vicinity of the start end 15, so that the tip of the spiral blade 12 in the rotational direction (near the excavation tooth 24) in particular during rotational press fitting. In the above, since the spiral blade 12 is firmly fixed to the tip portion 13 of the steel pipe pile from the outer periphery of the steel pipe pile 10 through the start end 15 to the inner circumference, the vicinity of the excavation tooth 24 of the spiral blade 12 at the time of rotational press fitting is performed. Since the movement is suppressed and the amount of deformation of the tip of the spiral blade 12 is reduced, the stress is reduced. Therefore, the breakage of the spiral blade 12 or the steel pipe pile 10 is suppressed.

As shown in FIG. 9, the position P1 of the end of the bead 30 on the inner circumference of the steel pipe pile 10 is the point P2 (or the excavated tooth 24 and the spiral blade 12 where the inner edge 20 of the drilled tooth 24 and the spiral blade 12 intersects. It is preferably located on the opposite side of the starting end 15 from the one-dot chain line L1 connecting the point P3) where the outer edges 21 intersect and the center O of the steel pipe pile 10. The excavated tooth 24 receives a large force during rotational press-fitting, but since the end position P1 of the bead 30 on the inner circumference of the steel pipe pile 10 is located on the opposite side of the one-dot chain line L1 to the start end 15, during rotational press-fitting. The movement of the spiral blade 12 in the vicinity of the excavated tooth 24 is suppressed, and the amount of deformation of the tip of the spiral blade 12 is reduced, so that the stress is reduced. Therefore, the breakage of the spiral blade 12 or the steel pipe pile 10 is suppressed.

As shown in FIGS. 9 to 11, at the start end 15, the weld bead 30 is formed in a slope shape. The bead 30 is configured as a slope that intersects the surface of the spiral blade 12 at an angle of 45 ° or less at the starting end 15. More preferably, at the start end 15, the weld bead 30 is formed as a concave slope. In other words, at the start end 15, the bead 30 has the shape of the bow of a ship. Such a shape is formed, for example, by forming the bead 30 and then cutting the bead 30 with a grinding machine or the like to finish it smoothly. By making the bead 30 a concave slope in the vicinity of the starting end 15 and finishing it smoothly, when the steel pipe pile 10 is penetrated, the earth and sand are excavated by the slope of the bead 30, so that the penetration resistance is suppressed and the rotational torque is smaller. The steel pipe pile 10 is pierced at. Further, since the earth and sand are excavated by the slope of the bead 30, the stress concentration at the time of penetrating the steel pipe pile 10 is relaxed, so that the steel pipe pile 10 is suppressed from cracking or breaking.

(4) Aperture ratio of blades In the illustrated example, when the outer diameter (D) of the steel pipe pile 10 is 100 mm to 1600 mm, the outer diameter (D ₂ ) of the spiral blade 12 is in the range of 250 mm to 2400 mm.

By projecting the inner edge 20 and the outer edge 21 of the spiral blade 12 to the inside and the outside of the steel pipe pile tip portion 13, an opening 22 is formed in the central portion thereof, and the rotary press-fit steel pipe pile 10 becomes an open end pile. .. The outer diameter (D ₂ ) of the spiral blade 12 is approximately 1.2 to 3 times the outer diameter of the steel pipe pile (D), and the circular opening 22 of the inner edge 20 when the steel pipe pile 10 is viewed from the axial direction. The area was set to 0.1 times or more and 0.9 times or less with respect to the area of the circle whose diameter is the outer diameter D of the steel pipe pile 10. The ratio of the area of the opening 22 (opening ratio (%)) to the area of the circle whose diameter is the outer diameter D of the steel pipe pile 10 is a numerical value obtained as a result of experiments and simulations as shown in Table 3 below. When the opening ratio is 0.1 times or more and 0.9 times or less, it is possible to satisfy both the conditions of smooth penetration of the large-diameter pile into the ground and securing of the support function of the steel pipe pile 10. be. On the other hand, if it deviates from this value, it was difficult to satisfy both conditions smoothly. As shown in Table 3, if the opening ratio is 0.1 times (10%) or more and 0.9 times (90%) or less, the pile can be penetrated without damage to the normal ground (N value ≧ 15). , Support function can be secured (○ mark (good) in Table 3). Furthermore, if the aperture ratio is 20 to 50%, smooth penetration and support function can be ensured even for the support layer of hard ground (N value ≧ 50) (◎ mark (very good) in Table 3). ).

If the steel pipe pile 10 is clogged with earth and sand when the steel pipe pile 10 penetrates into the ground, the rotational torque required for the penetration increases and the possibility that the steel pipe pile 10 breaks increases. As shown in Table 3, there is a trade-off relationship between the penetration resistance and the support function, and the larger the opening ratio, the easier it is for earth and sand to enter the inside of the steel pipe pile 10 from the opening, so that the penetration resistance decreases. On the other hand, the larger the aperture ratio, the smaller the area of the spiral blade 12 on the plan view, and the smaller the installation surface of the steel pipe pile 10 with respect to the ground, resulting in lower stability and the rigidity of the spiral blade 12. Therefore, the support function for supporting the steel pipe pile 10 after penetration is reduced.

As a result of experiments and simulations, by setting the aperture ratio in the range of 20% to 50%, it is possible to satisfy both of the above conditions even for a support layer with hard ground (N value ≥ 50). If it exceeds%, the wall thickness for ensuring the rigidity required for the blade becomes large, so that an aperture ratio of 20% to 30% is more suitable. More specifically, if the opening ratio is 10% or more, the pile can be penetrated into the normal ground (N value ≧ 15) without damage, and if the opening ratio is 20% or more, the hard ground (N value ≧ 50). It was possible to penetrate smoothly into the support layer of. Further, when the aperture ratio was 90% or less, both pile stability and blade rigidity after penetration could be secured as a support function (marked with ◯ (good) in Table 3), but the aperture ratio was 80. If it is% or less, the pile stability after penetration can be ensured well as a support function (◎ mark (very good) in Table 3), and if the opening ratio is 50% or less, the pile stability can be secured. Both the blade rigidity and the blade rigidity were successfully secured (◎ mark (very good) in Table 3).

(5) Blade Shape FIG. 12 is a vertical cross-sectional view showing the vicinity of the spiral blade 12 of FIG. 2 in an enlarged manner. As shown in FIG. 12, the spiral blade 12 is inclined so that the inner edge 20 and the outer edge 21 are located horizontally, or are located above the inner edge 20 and below the outer edge 21.

After being penetrated into the ground, the steel pipe pile 10 receives a large load in the vertical direction downward. When the outer edge 21 is located above the inner edge 20 of the spiral blade 12 in the vertical direction, the outer side of the spiral blade 12 tends to bend upward when a load downward in the vertical direction is applied. Then, if the outside of the spiral blade 12 bends upward, the support function of the steel pipe pile 10 deteriorates. Therefore, it is preferable to incline the inner edge 20 and the outer edge 21 so that they are located horizontally or are located above the inner edge 20 and below the outer edge 21.

(6) Asymmetric tip shape The steel pipe pile tip portion 13 has an asymmetric tip shape when viewed from the side surface. When the tip portion 13 of the steel pipe pile has a symmetrical shape, the force for penetrating the steel pipe pile 10 and the reaction force due to the hard ground are balanced, and the penetration tends to be difficult. On the other hand, when the steel pipe pile tip portion 13 having an asymmetric tip shape when viewed from the side surface is rotated, the force for penetrating the steel pipe pile 10 and the reaction force are difficult to balance, and the penetrability is improved.

FIG. 15 is a side view showing an example of a steel pipe pile tip portion 13 having an asymmetric tip shape when viewed from the side surface. Examples of the steel pipe pile tip portion 13 having an asymmetric tip shape when viewed from the side surface include a shape having a step portion 16 and a steel pipe pile having a slope 34 as shown in FIG.

In the embodiment described above, the spiral blade 12 is exemplified as the blade fixed to the steel pipe pile 10, but the blade fixed to the steel pipe pile 10 is not limited to the spiral shape. For example, the blade may be composed of a flat plate. Further, although the example in which the spiral blade 12 is divided at one position of the step portion 16 in the circumferential direction is exemplified, the spiral blade 12 may be divided at a plurality of points.

10 Rotational press-fit steel pipe pile 12 Spiral blade 13 Steel pipe pile tip 14 Termination 15 Starting end 16 Stepped part 17 Circumferential ending 18 Circumferential starting end 19 Boundary 20 Inner edge 21 Outer edge 22 Opening 25, 42 Backing metal 30 Bead 32 Crack 34 slope

Claims (7)

It is a steel pipe pile with blades that has blades at the tip and is rotationally press-fitted into the ground by excavating the blades while rotating.
The blade provided with an opening of 0.1 times or more and 0.9 times or less the area of a circle whose diameter is the outer diameter of the steel pipe pile is concentric with the tip of the steel pipe pile having an asymmetric tip shape when viewed from the side surface. It is welded and fixed in a shape, and the blades are projected inside and outside the steel pipe pile.
The tip of the steel pipe pile is cut in a spiral shape, and the stepped portion between the start end and the end of the tip portion of the steel pipe pile cut in a spiral shape is an arc, an arbitrary curve, or a combination of an arc or an arbitrary curve and a straight line. When the tip of the spiral steel pipe pile is developed in a plane, the circumference of the outer circumference of the steel pipe pile is the base, the spiral pitch is the height, and the spiral steel pipe is formed. The area of the triangle whose base is the height of the right triangle and whose apex is the end is 0.25 times or less with respect to the area of the right triangle whose diagonal is the tip of the pile.
A rotary press-fit steel pipe pile in which the step portion is formed in an arc shape and the radius R of the arc is defined by the following equation (1) .
R = k × P ・ ・ ・ (1)
However, in the equation (1), P is a spiral pitch and k is a predetermined coefficient (0.8 ≦ k ≦ 1.5). The wall thickness of the steel pipe pile is thicker than the outside of the predetermined range in a predetermined range of at least a distance corresponding to the outer diameter of the steel pipe pile from the tip of the steel pipe pile in the axial direction of the steel pipe pile. The rotary press-fit steel pipe pile according to 1. According to claim 2, the ratio of the wall thickness outside the predetermined range to the wall thickness within the predetermined range is 0.5 or more, and the ratio of the wall thickness within the predetermined range to the outer diameter of the steel pipe pile is 0.02 or more. Described rotary press-fit steel pipe pile. The rotary press-fit steel pipe pile according to any one of claims 1 to 3, wherein the blade is a spiral blade and is welded and fixed to the tip of the steel pipe pile cut in a spiral shape. At the beginning of the rotational press-fitting in the rotational direction,
The rotary press-fit steel pipe pile according to any one of claims 1 to 4, wherein a bead for welding the blade and the tip of the steel pipe pile is formed so as to be continuous from the outer circumference to the inner circumference of the steel pipe pile. At the beginning of the rotational press-fitting in the rotational direction,
The invention according to any one of claims 1 to 5, wherein the cross-sectional shape of the bead for welding the blade and the tip of the steel pipe pile forms an acute-angled slope with respect to the surface of the blade. Rotational press-fit steel pipe pile. Any of claims 1 to 6, wherein the blade is arranged so that the outer edge is lower than the inner edge or the inner edge and the outer edge are located at the same height in an upright state with the tip of the steel pipe pile facing down. The rotary press-fit steel pipe pile according to item 1.

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