JP7539763B2 - Spiral pile - Google Patents

Description

This invention belongs to the technical field of spiral piles, which are made by forming flat steel into a spiral shape.

Various spiral piles (twisted flat bars) made by forming flat bars into a spiral shape (helical shape) have been developed and put into practice (see, for example, Patent Documents 1 and 2).

The invention of Patent Document 1 discloses a foundation for a structure characterized in that multiple twisted flat bars (1) made by twisting flat bars are screwed into the ground, the upper part of each twisted flat bar is solidified with a steel-reinforced concrete block (3), and an anchor bolt (4) is attached to the upper part (see claim 1 and Figure 1).
According to this invention, the twisted flat bar formed into a spiral shape is screwed into the ground like a corkscrew, so the pile will not come out unless the twisted flat bar turns or the ground cracks, providing strong resistance to pulling forces.

The invention in Patent Document 2 discloses a pile (twisted flat bar) in which flat bar is twisted multiple times at the same pitch while keeping it straight (see claim 1). Specifically, as shown in Figure 1 (a), by forming the tip of the twisted flat bar (1) to be slightly pointed, it becomes easier to screw the twisted flat bar into the ground by hitting the head of the twisted flat bar. Therefore, compared to twisted flat bar with a flat tip, it has the effect of reducing the effort and time required to drive the pile into the ground.

JP 2001-323479 A JP 2001-323460 A

The spiral piles (twisted flat steel) disclosed in the above-mentioned Patent Documents 1 and 2 have in common that the effect of peripheral friction of the pile body is large, and as the driving depth increases, depending on the strength of the ground and the size (cross section) of the pile, the frictional resistance increases, causing the pile body to buckle and making driving difficult, and there were issues that needed to be improved.

Therefore, the present invention was devised in consideration of the problems in the background art described above, and its purpose is to provide a spiral pile that, compared to the spiral piles (twisted flat steel) described in Patent Documents 1 and 2, maintains the effect of providing strong resistance to pull-out forces while facilitating construction by driving.

As a means for solving the above problems, the spiral pile of the invention described in claim 1 is characterized in that it comprises a spiral pile body formed by twisting flat steel at the same pitch into a spiral shape, and a peripheral friction reducing member attached to the spiral pile body so as to protrude in the thickness direction on at least one side beyond the spiral pile body by a width dimension equal to or greater than the width dimension of the spiral pile body, and which reduces peripheral friction of the spiral pile body located above the attachment position .
The invention described in claim 2 is characterized in that, in the spiral pile described in claim 1, the protruding portion of the peripheral friction reduction member includes a shape in which, when viewed in a plane, a half piece having a width dimension equal to or more than half that of the spiral pile main body is arranged at a corner of the spiral pile main body and is point-symmetrical with respect to the center of the spiral pile main body.

The invention described in claim 3 is characterized in that, in the spiral pile described in claim 1 or 2 , the peripheral friction reducing member is protruded beyond the tip of the spiral pile body.

The invention described in claim 4 is characterized in that, in the spiral pile described in claim 3 , the peripheral friction reducing member has an inclined portion that slopes in a mountain shape toward the tip.

The invention described in claim 5 is characterized in that, in the spiral pile described in claim 1 or 2 , the peripheral friction reduction member is provided in the twisted portion further forward than the axial center of the spiral pile body.

The invention described in claim 6 is characterized in that, in the spiral pile described in claim 1 , the peripheral friction reducing member is provided around the entire circumference of the twisted portion at the tip of the spiral pile body.

The invention described in claim 7 is characterized in that, in the spiral pile described in any one of claims 4 to 6 , the peripheral friction reduction member is arranged at an incline in a direction along the rotational direction of the spiral pile body.

The invention described in claim 8 is a spiral pile described in any one of claims 1 to 7 , characterized in that protrusions for assisting the rotational force of the spiral pile body are provided on the front and back surfaces of the twisted portion located above the peripheral friction reduction member, and are inclined in a direction along the rotational direction of the spiral pile body.

The spiral pile according to the present invention has the following advantages.
(1) By having the peripheral friction reducing member protrude from the pile body in the thickness direction, etc. , the peripheral friction force acting on the part of the pile body above the attachment position of the peripheral friction reducing member is reduced, making it easier to drive into the pile. In particular, if the peripheral friction reducing member is configured to protrude around the entire circumference of the pile body, the friction reduction effect becomes more pronounced, making it easier to drive into the pile.
(2) As with conventional technology, the spiral pile is made of flat steel formed into a spiral shape, so the original effects of the spiral pile can be maintained as before. In other words, the pile can exert pull-out resistance immediately after driving, and since no excavation is required, waste soil disposal is not required, and the construction period can be shortened, contributing to cost reduction.
(3) In summary, compared to conventional technologies, it is possible to realize a spiral pile that is excellent in workability, economy, and environment friendliness, while maintaining the effect of strong resistance to pull-out forces and making construction by casting easier.

FIG. 1A is a front view showing the spiral pile according to Example 1, FIG. 1B is a side view of the same, and FIG. FIG. 1A is an enlarged front view of the peripheral friction reduction member provided at the tip of the spiral pile of Example 1, FIG. 1B is a side view of the same, FIG. 1C is an oblique view of the same, and FIG. 2B is a cross-sectional view taken along line XX in FIG. 2A. 6A to 6M (excluding D, I, K, and M) are explanatory diagrams showing variations of the cross-sectional shape of the peripheral friction reducing member according to the first embodiment. FIG. 1A is a front view showing the spiral pile according to Example 2, FIG. 1B is a side view of the same, and FIG. 6 is a plan view showing a cross-sectional shape of the peripheral friction reducing member shown in FIG. 5 . 6A to 6M (excluding D, I, K, and M) are explanatory diagrams showing variations of the cross-sectional shape of the peripheral friction reducing member according to the second embodiment. 13A and 13B are front views showing a spiral pile according to Example 3.

Next, an embodiment of the spiral pile according to the present invention will be described with reference to the drawings.

As shown in Figures 1 and 2, the spiral pile 10 of Example 1 is composed of a spiral pile main body 1 formed by twisting flat steel at the same pitch into a spiral shape, and a peripheral friction reducing member 2 that is attached to the spiral pile main body 1 so as to protrude in the thickness direction on at least one side beyond the spiral pile main body 1 by a width greater than or equal to the width of the spiral pile 1 main body, and that reduces peripheral friction of the spiral pile main body 1 located above the attachment position .
The peripheral friction reducing member 2 is provided so as to protrude beyond the tip of the spiral pile main body 1 (hereinafter sometimes abbreviated to pile main body 1).
In this specification, the "spiral pile body 1 formed by twisting flat steel at the same pitch into a spiral shape" refers to any one of the following spiral piles: a spiral pile body 1 formed by applying an external force to flat steel to twist it into a spiral shape, a spiral pile body 1 produced by a 3D printer using flat steel as the material, or a spiral pile body 1 that is a casting (integrally molded product) using flat steel as the material.

The spiral pile body 1, for example, has a uniform cross-sectional shape with a plate thickness of about 6 to 12 mm, a width (=pile diameter) of about 100 to 150 mm, and a length of about 500 to 1,500 mm, and is formed into a spiral shape at a predetermined pitch.
Incidentally, although not shown in the drawings, a disk member, a cylindrical member, etc. are integrated into the head (upper end) of the spiral pile main body 1 by a joining means such as welding so that it can be efficiently driven into the ground by hand using a hammer or the like. The design of the disk member, cylindrical member, etc. is appropriately changed depending on the installation form of the ground structure such as a stand or tent supported by the pile main body 1.

In this embodiment, the peripheral friction reducing member 2 is integrally provided by welding to the tip (lower end) of the spiral pile main body 1. The peripheral friction reducing member 2 is formed to be larger than the cross-sectional area of the spiral pile main body 1 (flat steel) so that Fig. 3 can be easily understood. Specifically, the peripheral friction reducing member 2 has a rectangular cross-sectional shape larger in the width direction and thickness direction than the cross section of the spiral pile main body 1 (flat steel), and is provided with a plurality of inclined surfaces 2a that are inclined in a mountain shape from the middle part to the tip and also inclined with respect to the rotation direction.
The peripheral friction reduction member 2 in the illustrated example has a large cross-section that evenly protrudes about 2 mm in the width direction and about 2 mm in the thickness direction from the spiral pile main body 1 (flat steel), and the lower part of the rectangular metal member with a height of about 26 mm is formed with the inclined surface (chamfer) 2a in a direction that provides less resistance to the rotation direction of the spiral track of the spiral pile 10 (spiral pile main body 1).
Regarding the joint between the lower end of the pile main body 1 and the peripheral friction reduction member 2, a recess capable of accepting the lower end of the spiral pile main body 1 to a depth of several millimeters is formed in the upper surface of the peripheral friction reduction member 2, and appropriate measures are taken to join the pile so as to enhance its fixation (integrity).

In the spiral pile 10 configured as described above, when the head of the vertically oriented spiral pile main body (flat steel) 1 is driven with a hammer or the like, the peripheral friction reducing member 2 provided at the tip of the spiral pile main body 1 leads the way, so that the frictional resistance of the ground that hinders the penetration of the spiral pile 10 acts only on the peripheral friction reducing member 2. The trailing spiral pile main body 10 has a smaller cross-sectional area than the peripheral friction reducing member 2, so the frictional resistance of the ground hardly acts on it.
Therefore, compared with a conventional spiral pile body formed only from flat steel, the frictional resistance acting when driving the spiral pile 10 is significantly reduced, and the spiral pile can be driven efficiently to a specified depth without buckling even when driven deep.
On the other hand, when it comes to pulling out the pile, the diameter of the cylindrical pile has only increased by a few mm, but the only frictional force acting between the circumferential surface of the pile body and the ground (circumferential frictional force) is the same as with conventional spiral pile bodies formed only from flat steel, so the pile can be pulled out with the same amount of force as before.

Therefore, the spiral pile 10 according to the present invention has the following effects.
(1) Since the peripheral friction reduction member 2 protrudes from the pile main body 1 in the thickness direction, etc. , the peripheral friction force acting on the portion of the pile main body 1 above the mounting position of the peripheral friction reduction member 2 is reduced, making it easier to drive into the pile.
In particular, as in the present embodiment 1, when the peripheral friction reducing member 2 is configured to protrude beyond the tip of the pile body 1 and to be larger overall than the cross-sectional area of the pile body 1, the friction reducing effect becomes significant and the pile can be driven in more easily. The peripheral friction reducing member 2 further includes the inclined surface 2a, which makes it even easier to drive the pile in.
(2) As in the conventional technology, the spiral pile 10 has the same structure of flat steel formed into a spiral shape, so the original effects of the spiral pile 10 can be maintained as before. In other words, it can exert pull-out resistance immediately after driving the pile into the ground, and since no excavation is required, waste soil disposal is not required. It can contribute to cost reduction by shortening the construction period, etc.
(3) In summary, compared to conventional technologies, it is possible to realize a spiral pile that is excellent in workability, economy, and environment friendliness, while maintaining the effect of strong resistance to pull-out forces and making construction by casting easier.

The embodiment of the spiral pile 10 that achieves the effect of (3) above is not limited to the peripheral friction reducing member 2 shown in Figures 1 to 3. The peripheral friction reducing member 2 according to the present invention can be implemented in a wide variety of different ways. Examples are shown in Figures 4A to 4M. However, among A to M in Figure 4, D, I, K, and M are not examples but reference examples.

4A to 4H show peripheral friction reducing members 2 whose cross sections protrude in the width and thickness directions beyond the spiral pile main body 1 (flat steel). In the embodiment shown in Fig. 4G, the protruding portions of the peripheral friction reducing members 2 are arranged such that half pieces each having a width dimension equal to or greater than half the width of the spiral pile main body 1 in plan view are located at the corners of the spiral pile main body 1 and are point symmetrical with respect to the center of the spiral pile main body 1.
FIG. 4I shows a peripheral friction reducing member 2 whose cross section protrudes only in the width direction beyond the spiral pile main body 1 (flat steel).
4J and 4K show a peripheral friction reducing member 2 whose cross section protrudes beyond the spiral pile main body 1 (flat steel) only in the thickness direction.
4L and 4M show a peripheral friction reducing member 2 whose cross section protrudes beyond the spiral pile main body 1 (flat steel) on only one side in the thickness direction.

The lower limit of the projection dimension of the peripheral friction reducing member 2 from the pile body 1 can achieve the above effect even if it is about 1 mm. On the other hand, the upper limit is set on the condition that the pile body 1 can be driven without disturbing the ground, and although this varies depending on the ground properties in the construction, it is set to about 3 to 5 mm in the applicant's experience. If the projection dimension is large, the soil around the pile will be disturbed, and there is a concern that the pull-out resistance will decrease.
The peripheral friction reducing member 2 may be attached to a portion beyond the tip of the spiral pile main body 1 as shown in the first embodiment, or may be attached to one of the twisted portions 1a constituting the pile main body 1. This will be described in the second embodiment.

As shown in FIG. 5, the spiral pile 11 according to the second embodiment is composed of a spiral pile main body 1 formed by twisting flat steel at the same pitch into a spiral shape, and a peripheral friction reducing member 3 attached to the spiral pile main body 1 so as to protrude in the thickness direction on at least one side beyond the spiral pile main body 1 by a width greater than or equal to the width of the spiral pile 1 main body, and located above the attachment position to reduce peripheral friction of the spiral pile main body 1 .
The peripheral friction reducing member 3 is provided on the twisted portion 1a at the tip of the spiral pile main body 1 rather than the axial center of the spiral pile main body 1. More specifically, the peripheral friction reducing member 3 in the illustrated example is provided around the entire circumference of the twisted portion 1a at the tip of the spiral pile main body 1, although it is illustrated only diagrammatically (see also FIG. 6).

The spiral pile body 1 is the same as that in Example 1 above, so its description is omitted (see paragraph [0019] above).

In this embodiment, the peripheral friction reducing member 3 is integrally provided by welding means around the entire circumference of the twisted portion 1a at the tip of the spiral pile main body 1. That is, the peripheral friction reducing member 3 is formed to be larger than the cross-sectional area of the spiral pile main body 1 (flat steel) so that Fig. 6 can be easily understood. Specifically, the peripheral friction reducing member 3 is formed into a protrusion having a joining width to the pile main body 1 of about 4 mm and a height (protruding dimensions in the width direction and thickness direction) of about 2 mm, and is joined to the pile main body 1 by welding means.
Thus, the peripheral friction reduction member 3 in the illustrated example has a large cross-section that evenly protrudes about 2 mm in the width direction and about 2 mm in the thickness direction from the spiral pile main body 1 (flat steel), and is attached to the pile main body 1 at a slight inclination in a direction that provides less resistance to the rotation direction of the spiral track of the spiral pile 11 (spiral pile main body 1).

When the head of the vertically-positioned spiral pile main body (flat steel) 1 of the spiral pile 11 configured as described above is driven into the pile main body 1 with a hammer or the like, the frictional resistance of the ground which prevents the spiral pile 11 from penetrating acts on the pile main body 1 for the first few centimeters to a depth, but thereafter the frictional resistance of the ground is borne by the circumferential friction reducing member 3 which is integrated with the twisted portion 1a at the tip, and since the subsequent spiral pile main body 11 has a smaller cross-sectional area than the circumferential friction reducing member 3, the frictional resistance of the ground has almost no effect.
Therefore, compared with a conventional spiral pile body formed only from flat steel, the frictional resistance acting when driving the spiral pile 11 is significantly reduced, and the spiral pile can be driven efficiently to a specified depth without buckling even when driven deep.
On the other hand, when it comes to pulling out the pile, the diameter of the cylindrical pile has only increased by a few mm, but the only frictional force acting between the circumferential surface of the pile body and the ground (circumferential frictional force) is the same as with conventional spiral pile bodies formed only from flat steel, so the pile can be pulled out with the same amount of force as before.

Therefore, the spiral pile 11 according to the present invention has the following effects.
(1) Since the peripheral friction reduction member 3 protrudes from the pile main body 1 in the thickness direction, etc. , the peripheral friction force acting on the portion of the pile main body 1 above the mounting position of the peripheral friction reduction member 3 is reduced, making it easier to drive into the pile.
(2) As in the conventional technology, the spiral pile 11 has the same structure of a flat steel formed into a spiral shape, so the original effect of the spiral pile 11 can be maintained as before. In other words, it can exert pull-out resistance immediately after driving the pile into the ground, and since no excavation is required, waste soil disposal is not required. It can contribute to cost reduction by shortening the construction period, etc.
(3) In summary, compared to conventional technologies, it is possible to realize a spiral pile that is excellent in workability, economy, and environment friendliness, while maintaining the effect of strong resistance to pull-out forces and making construction by casting easier.

The embodiment of the spiral pile 11 that achieves the effect of (3) above is not limited to the peripheral friction reducing member 3 shown in Figures 5 and 6. The peripheral friction reducing member 3 according to the present invention can be implemented in a wide variety of different ways. Examples are shown in Figures 7A to 7M. However, among A to M in Figure 7, D, I, K, and M are not examples but reference examples.

7A to 7H show peripheral friction reducing members 3 whose cross sections protrude in the width and thickness directions beyond the twisted portion 1a of the pile main body 1. In the embodiment shown in Fig. 7G, the protruding portions of the peripheral friction reducing members 2 are arranged such that half pieces each having a width dimension equal to or greater than half the width of the spiral pile main body 1 are at the corners of the spiral pile main body 1 and are point symmetrical with respect to the center of the spiral pile main body 1 when viewed in plan.
FIG. 7I shows a peripheral friction reducing member 3 whose cross section protrudes beyond the twisted portion 1 a of the pile main body 1 only in the width direction.
7J and 7K show a peripheral friction reducing member 3 whose cross section protrudes beyond the twisted portion 1a of the pile main body 1 only in the thickness direction.
7L and 7M show a peripheral friction reducing member 3 whose cross section protrudes beyond the twisted portion 1a of the pile main body 1 on only one side in the thickness direction.

The lower limit of the projection dimension of the peripheral friction reducing member 3 from the pile body 1 can achieve the above effect even if it is about 1 mm. On the other hand, the upper limit is set on the condition that the pile body 1 can be driven without disturbing the ground, and although this varies depending on the ground properties in the construction, it is set to about 3 to 5 mm in the applicant's experience. If the projection dimension is large, the soil around the pile will be disturbed, and there is a concern that the pull-out resistance will decrease.
In this embodiment 2, the peripheral friction reducing member 3 is provided on the twisted portion 1a at the tip of the spiral pile main body 1, but this is not limited to this, and a corresponding effect will be obtained even if it is provided on the twisted portion 1a other than the tip.

Figure 8A shows a structure in which protrusion portions 4 for assisting the rotational force of the spiral pile main body 1 are provided on the front and back surfaces of the twisted portion 1a located above the peripheral friction reduction member 2 of the spiral pile 10 of Example 1 (see Figures 1 to 3) and are inclined in the direction of rotation of the spiral pile main body 1.
Figure 8B shows a structure in which protrusions 4 for assisting the rotational force of the spiral pile main body 1 are provided on the front and back surfaces of the twisted portion 1a located above the peripheral friction reduction member 3 of the spiral pile 11 of Example 2 (see Figures 5 and 6) and are inclined in the direction of rotation of the spiral pile main body 1.
The protruding portion 4 is shown diagrammatically in FIGS. 8A and 8B, but the protruding dimension thereof is approximately the same as the protruding dimension of the peripheral friction reducing members 2 and 3.

Thus, as described above, the spiral piles 10, 11 of Example 3 are configured such that the protrusion portions 4 are inclined above the peripheral friction reduction members 2, 3 so that a couple of forces act thereon, thereby making it possible to realize spiral piles 10, 11 that are even easier to drive into the ground than the above-mentioned Examples 1 and 2 in which the protrusion portions 4 are not provided.
On the other hand, when it comes to pulling out the pile, the diameter of the cylindrical pile has only increased by a few mm, but the only frictional force acting between the circumferential surface of the pile body and the ground (circumferential frictional force) is the same as with conventional spiral pile bodies formed only from flat steel, so the pile can be pulled out with the same amount of force as before.

Although the embodiments have been described above based on the drawings, it should be noted that the present invention is not limited to the illustrated examples, and includes the range of design modifications and application variations that would normally be made by a person skilled in the art, provided that the scope does not deviate from the technical concept of the present invention .
In this specification, the definition of the "spiral pile main body 1 formed by forming flat steel into a spiral shape" is as described in paragraph [0018] above. However, when producing it using a 3D printer or casting, it is also possible to produce a shape in which the spiral pile main body 1 and the peripheral friction reduction members 2, 3 are combined into one piece, in which case it is possible to realize a spiral pile that is both economical and strong.

Reference Signs List 1 Spiral pile body 1a Twisted portion 2 Circumferential friction reducing member 2a Inclined surface 3 Circumferential friction reducing member 10 Spiral pile 11 Spiral pile

Claims (8)

A spiral pile characterized in that it is composed of a spiral pile body formed by twisting flat steel at the same pitch into a spiral shape, and a peripheral friction reducing member attached to the spiral pile body so as to protrude in the thickness direction on at least one side beyond the spiral pile body by a width dimension equal to or greater than the width dimension of the spiral pile body, and located above the attachment position to reduce peripheral friction of the spiral pile body . The spiral pile according to claim 1, characterized in that the protruding portion of the peripheral friction reducing member includes a shape in which, when viewed in a plane, a half piece having a width dimension equal to or more than half that of the spiral pile main body is arranged at a corner portion of the spiral pile main body and is point-symmetrical with respect to the center of the spiral pile main body. 3. The spiral pile according to claim 1 or 2 , wherein the peripheral friction reducing member is provided so as to protrude beyond the tip of the spiral pile body. 4. The spiral pile according to claim 3 , wherein the peripheral friction reducing member has an inclined portion that slopes in a mountain shape toward a tip. 3. The spiral pile according to claim 1 or 2 , characterized in that the peripheral friction reducing member is provided at a twisted portion further forward than the axial center of the spiral pile body. 2. The spiral pile according to claim 1 , wherein the peripheral friction reducing member is provided around the entire circumference of the twisted portion at the tip of the spiral pile body. The spiral pile according to any one of claims 4 to 6 , characterized in that the peripheral friction reducing member is provided inclined in a direction along the rotation direction of the spiral pile body. The spiral pile according to any one of claims 1 to 7, characterized in that protrusions for assisting the rotational force of the spiral pile body are provided on the front and back surfaces of the twisted portion located above the peripheral friction reducing member, the protrusions being inclined in a direction along the rotational direction of the spiral pile body.

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