Steel pipe foundation, foundation structure, construction method of foundation structure, and removal method of steel pipe foundation

Abstract

To provide a steel pipe foundation, a foundation structure, a construction method of foundation structure, and a removal method of steel pipe foundation capable of easily constructing and removing without using special equipment with respect to hard ground.SOLUTION: A steel pipe foundation 1 includes: an excavation ring part 4 formed at a tip part; a steel pipe part 3 with rib which is positioned above the excavation ring part 4, and in which a spiral inner surface side rib 7 is formed on an inner surface 5 and a spiral outer surface side rib 8 is formed on an outer surface 6; and a steel pipe part 2 without rib formed above the steel pipe part 3 with rib. When constructing a foundation structure 19, the steel pipe foundation 1 is rotated normally and is press-fitted until the steel pipe part 3 with rib is buried in ground 15. In the foundation structure 19, the steel pipe part 3 with rib is buried in the ground 15, and the steel pipe part 2 without rib is exposed above the ground 15. When removing the steel pipe foundation 1 from the foundation structure 19, the steel pipe foundation 1 is rotated reversely and is pulled out from the ground 15.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a steel pipe foundation, a foundation structure, a construction method of the foundation structure, and a removal method of the steel pipe foundation.

Background Art

[0002] In recent years, as one of the renewable energies, the construction of wind power generation facilities has been booming around the world. The foundation structure of wind power generation facilities is most commonly constructed by driving a monopile foundation with a simple structure and high economic efficiency using a hydraulic hammer.

[0003] Further, as a construction method of a monopile foundation on hard ground or rock, while rotating a casing with a double pipe structure and excavating the bottom ground with a cutter bit to form a circumferential groove, the fluid injected near the lower end of the casing from between the excavation shear and the double pipe is raised along a spiral rib provided on the inner peripheral surface of the inner pipe, and after pulling out the casing from the circumferential groove, a method of building a monopile in the circumferential groove has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when constructing a large-diameter monopile on hard ground, if it is driven with a hydraulic hammer, vibration and noise are large, and the environmental load on the ecosystem increases. In addition, considering the fatigue generated in the monopile due to an increase in the number of blows, a design is required. Although the method described in Patent Document 1 solves these problems, it is necessary to use a special casing. Further, since the casing is pulled out and reused after excavation of the circumferential groove, the number of processes and types of work increases, and the construction period becomes longer.

[0006] The present invention has been made in view of the above-described problems, and an object thereof is to provide a steel pipe foundation, a foundation structure, a method for constructing a foundation structure, and a method for removing a steel pipe foundation that can be easily constructed and removed without using special equipment for hard ground.

Means for Solving the Problems

[0007] In order to achieve the above-described object, a first invention is a steel pipe foundation, which includes an excavation ring portion formed at a tip portion, and is located above the excavation ring portion, at least a ribbed steel pipe portion having spiral inner surface side ribs formed on an inner surface, and a ribless steel pipe portion formed above the ribbed steel pipe portion. and, in the axial cross-section of the steel pipe foundation, the inner surface side end of the inner surface side rib is located on a substantially extended line of the inner surface of the excavation ring portion The steel pipe foundation is characterized by this. It is desirable that the ribbed steel pipe portion has spiral outer surface side ribs formed on the outer surface, and the inner surface side ribs have a higher protruding height than the outer surface side ribs.

[0008] The steel pipe foundation of the first invention can excavate the ground with the excavation ring portion formed at the tip portion, and can raise the excavation chips to the ground using the spiral ribs, so that it can be easily driven into hard ground or rock without using special equipment.

[0009] Preferably, the excavation ring portion has a cutting portion for cutting the ground and a taking-in portion for taking in the excavation chips formed alternately in the circumferential direction. The cutting portion is formed at a position corresponding to the position where the ribs are formed at the lower end portion of the ribbed steel pipe portion, and the taking-in portion is formed at a position corresponding to the space between the ribs at the lower end portion of the ribbed steel pipe portion. Thereby, when the steel pipe foundation is rotated to cut the ground with the cutting portion, the excavation chips generated by the cutting can be guided to the taking-in portion and efficiently taken in from the taking-in portion between the ribs.

[0010] The steel pipe portion with ribs is formed with the ribs at least on the inner surface side, the thickness of the intake portion is thinner than that of the cutting portion, and it is desirable that the intake portion forms a concave portion in the thickness direction on the inner surface side. Further, it is desirable that the cutting portion has a tapered shape in which the length on the outer surface side is long and the length toward the inner surface side is short. If the intake portion forms a concave portion in the thickness direction on the inner surface side of the excavation ring portion, it becomes easier to take in the excavation drag cut by the cutting portion to the inner surface side of the intake portion. Further, if the cutting portion has a tapered shape in which the length from the outer surface side toward the inner surface side becomes shorter, the excavation drag can be guided to the inner surface side of the cutting portion. If the excavation drag is guided to the inner surface side of the cutting portion and taken into the inner surface side of the intake portion in the excavation ring portion, and the excavation drag is lifted along the ribs on the inner surface side in the steel pipe portion with ribs, the ground on the outer surface side is not disturbed by the excavation drag, so that reduction of the horizontal ground resistance can be prevented, and water pollution during removal of the excavation drag can also be reduced.

[0011] It is desirable that the cutting portion has a saw-shaped shape in the circumferential direction. This makes it easier to guide the excavation drag cut by the cutting portion to the intake portion. Further, when rotating reversely at the time of removal, since an upward reaction force is received from the ground due to the saw-shaped gradient at the tip of the cutting portion, it contributes to the pulling-out.

[0012] A second invention is a foundation structure using the steel pipe foundation of the first invention, characterized in that the steel pipe portion with ribs is embedded in the ground and the steel pipe portion without ribs is exposed on the ground.

[0013] In the foundation structure of the second invention, ribs are provided in the portion that is rooted in the ground, and no ribs are provided in the portion that is exposed on the ground, so that the formation range of the ribs on the steel pipe foundation can be minimized.

[0014] The ground is an underwater ground and may be used as a monopile foundation for an offshore windmill. Thereby, a large monopile-type offshore windmill can be installed on hard ground.

[0015] The third invention is a construction method of a foundation structure using the steel pipe foundation of the first invention, characterized in that while rotating the steel pipe foundation forward, it is press-fitted until the steel pipe part with ribs is buried in the ground.

[0016] According to the third invention, the steel pipe foundation can be accurately driven to a predetermined depth against hard ground without using special equipment. Also, since no impact is applied to the steel pipe foundation, the environmental load on the ecosystem can be significantly reduced, and the steel pipe foundation can be designed without considering fatigue due to impact.

[0017] The fourth invention is a method for removing the steel pipe foundation from the foundation structure of the second invention, characterized in that it is pulled out from the ground while rotating the steel pipe foundation backward.

[0018] According to the fourth invention, the entire length of the steel pipe foundation can be easily recovered without using special equipment.

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a steel pipe foundation, a foundation structure, a construction method of the foundation structure, and a method for removing the steel pipe foundation that can be easily constructed and removed against hard ground without using special equipment.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0022] FIG. 1 is an elevation view of the steel pipe foundation 1, FIG. 2 is a cross-sectional view of the steel pipe foundation 1 taken along line A1 - A1 shown in FIG. 1, and FIG. 3 is a view showing the excavation ring portion 4 as seen from the direction of arrow A2 shown in FIG. 1. FIGS. 4 and 5 are views showing details in the vicinity of the excavation ring portion 4, FIG. 4 is an enlarged view of the range B shown in FIG. 2, FIG. 5(a) is a cross-sectional view taken along line D1 - D1 shown in FIG. 4, and FIG. 5(b) is a cross-sectional view taken along line D2 - D2 shown in FIG. 4.

[0023] As shown in FIGS. 1 and 2, the steel pipe foundation 1 is composed of a ribless steel pipe portion 2, a ribbed steel pipe portion 3, an excavation ring portion 4, etc. The lower side of the steel pipe foundation 1 shown in FIGS. 1 and 2 is the tip side, and it is rotated clockwise when being constructed and counterclockwise when being removed.

[0024] The ribless steel pipe portion 2 is formed above the ribbed steel pipe portion 3. The ribless steel pipe portion 2 is a steel pipe similar to a normal monopile and has the bearing capacity and durability required during construction and in service.

[0025] The ribbed steel pipe portion 3 is located above the excavation ring portion 4, an inner surface rib 7 is formed on the inner surface 5, and an outer surface rib 8 is formed on the outer surface 6. The inner surface rib 7 and the outer surface rib 8 are in a spiral shape inclined so that the front in the clockwise rotation direction is the tip side. The ribbed steel pipe portion 3 is formed by spiral processing of a ribbed rolled steel strip. The plate thickness of the ribbed steel pipe portion 3 is set so as to obtain the bearing capacity and durability required for the root insertion portion.

[0026] The excavation ring portion 4 is formed at the tip of the steel pipe foundation 1. As shown in FIG. 3, in the excavation ring portion 4, a cutting portion 9 for cutting the ground and a taking-in portion 10 for taking in the excavation slip are alternately formed in the circumferential direction. In the excavation ring portion 4, the thickness of the taking-in portion 10 is thinner than that of the cutting portion 9, and on the inner surface side, the taking-in portion 10 forms a concave portion in the thickness direction. In the excavation ring portion 4, the inner surface 12a of the taking-in portion 10 is recessed from the inner surface 12 of the cutting portion 9 on the inner surface side.

[0027] As shown in FIG. 4, in the excavation ring portion 4, the cutting portion 9 is formed at a position corresponding to the formation position 24 of the inner surface side rib 7 at the lower end portion 11 of the ribbed steel pipe portion 3. Further, the taking-in portion 10 is formed at a position corresponding to the positions between the formation positions 24 of the inner surface side ribs 7 at the lower end portion 11 of the ribbed steel pipe portion 3.

[0028] At least the cutting portion 9 of the excavation ring portion 4 has a saw-like shape in the circumferential direction as shown in FIG. 4, and has a tapered shape in which the length from the lower end portion 11 is long in the front in the normal rotation direction and gradually shortens toward the rear. Further, as shown in FIG. 5(a), the cutting portion 9 is cut so that the tip on the outer surface 13 side has an acute angle in the radial cross section of the excavation ring portion 4, and has a tapered shape in which the length from the lower end portion 11 is long on the outer surface 13 side and shortens toward the inner surface 12 side. That is, the cutting portion 9 has a gradient formed in the circumferential direction and the radial direction of the excavation ring portion 4, and has a tapered surface 14 that inclines from the outer surface 13 side near the formation position 24 of the inner surface side rib 7 toward the inner surface 12 side of the boundary position 25 with the taking-in portion 10.

[0029] As shown in Fig. 5, the inner surface side rib 7 formed on the steel pipe part 3 with ribs has a larger vertical cross-section than the outer surface side rib 8, and it is desirable that the protruding height 26 from the inner surface 5 of the inner surface side rib 7 is larger than the protruding height 27 from the outer surface 6 of the outer surface side rib 8. At this time, the end 21 of the outer surface side rib 8 is located on a substantially extended line of the outer surface 13 of the excavation ring part 4. The end 22 of the inner surface side rib 7 is located on a substantially extended line of the inner surface 12 in the cutting part 9, and is located inside the extended line of the inner surface 12a in the capturing part 10. The inner surface 12a of the capturing part 10 is continuous with the inner surface 5 (the inner surface of the part other than the inner surface side rib 7) of the steel pipe part 3 with ribs. That is, the capturing part 10 is thinner than the cutting part 9 by the amount of the protruding height 26 of the inner surface side rib 7. Also, the cross-sectional shape, pitch, number, etc. of the ribs are not limited to the illustrated example.

[0030] Next, the foundation structure 19 using the steel pipe foundation 1 and its construction method will be described. Fig. 6 is a diagram showing the construction procedure of the foundation structure 19. Fig. 6(a) is a diagram showing the state where the steel pipe foundation 1 is built in, and Fig. 6(b) is a diagram showing the state where the steel pipe foundation 1 is pressed into the ground 15 underwater.

[0031] To construct the foundation structure 19 using the steel pipe foundation 1, first, the large-diameter full-rotation excavator 16 mounted on the large-sized SEP23 and the steel pipe foundation 1 are transported to the vicinity of the planned construction position of the foundation structure 19. Then, as shown in Fig. 6(a), the full-rotation excavator 16 is installed on the overhanging girder of the large-sized SEP23, and the steel pipe foundation 1 is built into the full-rotation excavator 16. The steel pipe foundation 1 is built in such that the tip part where the excavation ring part 4 is formed faces the ground 15 side.

[0032] Next, while rotating the steel pipe foundation 1 forward as shown by the arrow E1 and pressing it into the ground 15 as shown by the arrow E2, the steel pipe part 3 with ribs is embedded in the ground 15, and the foundation structure 19 shown in Fig. 6(b) is completed. In the foundation structure 19, the entire length of the steel pipe part 3 with ribs is embedded in the ground 15, and the steel pipe part 2 without ribs is exposed on the ground 15.

[0033] After the foundation structure 19 is completed, a platform and a windmill (not shown) are installed on the steel pipe foundation 1, and an offshore windmill using the foundation structure 19 as a monopile foundation is assembled.

[0034] Figures 7 to 9 are diagrams showing the steel pipe foundation 1 being jacked into the ground 15. Figure 7(a) shows a vertical cross-section near the surface of the ground 15. Figure 7(b) is a diagram showing the portion corresponding to the range C shown in FIG. 3 of the steel pipe foundation 1 being jacked in. Figures 8(a) and 8(b) are diagrams showing the portions corresponding to FIGS. 5(a) and 5(b) of the steel pipe foundation 1 being jacked in respectively, and Figure 9 is a diagram showing the portion corresponding to FIG. 4 of the steel pipe foundation 1 being jacked in.

[0035] When the steel pipe foundation 1 is rotated forward by the full-circumference rotary excavator 16, as shown in Figure 7(a), the ground 15 is cut by the excavation ring portion 4 to form an excavation groove 20. Also, due to the effect of the spiral inner surface side ribs 7 and outer surface side ribs 8, a pushing force is generated that screws in like a screw due to friction with the surrounding ground 15. The ribbed steel pipe portion 3 is pressed into the excavation groove 20 by this pushing force, the pressing force by the full-circumference rotary excavator 16, and the self-weight of the steel pipe foundation 1.

[0036] Here, as described above, in the excavation ring portion 4, the cutting portion 9 and the intake portion 10 are alternately arranged in the circumferential direction. The tapered surface 14 is provided on the cutting portion 9, and the inner surface 12a of the intake portion 10 is recessed from the inner surface 12 of the cutting portion 9. Therefore, when the excavation ring portion 4 is rotated forward, most of the excavation chips 17 cut by the cutting portion 9 are guided along the tapered surface 14 to the rear side in the forward rotation direction and the inner surface 12 side, as shown by the arrows in Figure 7(b) and Figure 8(a), and are taken into the recess on the inner surface 12a side of the intake portion 10. The excavation chips 17 taken into the inner surface 12a side of the intake portion 10 enter between the inner surface side ribs 7 formed on the ribbed steel pipe portion 3, as shown by the arrows in Figure 8(b) and Figure 9, and are carried upward by the spiral effect and discharged onto the ground 15 inside the steel pipe foundation 1, as shown in Figure 7(a). Since the protruding height 26 of the inner surface side ribs 7 is larger than the protruding height 27 of the outer surface side ribs 8, by taking in between the inner surface side ribs 7, excavation chips 17 approximately equal in volume to the excavation groove 20 can be lifted and discharged.

[0037] On one hand, a small amount of excavation shear 18 that has entered the outer surface 13 side of the cutting part 9 enters between the outer surface side ribs 8 of the ribbed steel pipe part 3 and is carried upward by the spiral effect, and is discharged onto the ground 15 outside the steel pipe foundation 1 as shown in Fig. 7(a). Since the protruding height 27 of the outer surface side rib 8 is small, there is little over-excavation on the outer surface 6 side of the steel pipe foundation 1, and the ground 15 is not disturbed much by the excavation shear 18. Therefore, the reduction of the horizontal resistance is suppressed at the root part of the ground 15.

[0038] Next, a method for removing the steel pipe foundation 1 from the foundation structure 19 will be described. Fig. 10 is a diagram showing the removal procedure of the steel pipe foundation 1. Fig. 10(a) is a diagram showing the state where the removal preparation of the steel pipe foundation 1 is completed, and Fig. 10(b) is a diagram showing the state where the steel pipe foundation 1 is being pulled out from the ground 15.

[0039] To remove the steel pipe foundation 1 from the foundation structure 19, first, a windmill and a platform (not shown) are removed, and a full-circle rotary excavator 16 is installed on the steel pipe foundation 1 using the overhanging girder of the large SEP23 as shown in Fig. 10(a). Next, while rotating the steel pipe foundation 1 in the reverse direction as shown by the arrow F1 during construction, it is pulled up as shown by the arrow F2, and the ribbed steel pipe part 3 is pulled out from the ground 15 as shown in Fig. 10(b). When the entire length of the ribbed steel pipe part 3 is pulled out from the ground 15, the steel pipe foundation 1 is placed on the large SEP23 and transported to the disposal site.

[0040] When the steel pipe foundation 1 is rotated in the reverse direction by the full-circle rotary excavator 16, due to the effects of the excavation ring part 4, the spiral inner surface side rib 7, and the outer surface side rib 8, a pulling force is generated that loosens the screw by the reaction force at the tip with the saw-shaped circumferential taper shape and the friction with the surrounding ground 15. The ribbed steel pipe part 3 is pulled out from the excavation groove 20 by this pulling force and the pulling force of the full-circle rotary excavator 16.

[0041] Thus, according to the steel pipe foundation 1 of this embodiment, the ground 15 can be excavated by the excavation ring part 4 formed at the tip of the steel pipe foundation 1, and the excavation shears 17 and 18 can be lifted up to the ground 15 by the spiral inner surface side rib 7 and the outer surface side rib 8. Therefore, the steel pipe foundation 1 can be easily constructed without using special equipment for hard ground or rock.

[0042] In the steel pipe foundation 1, the excavation ring portion 4 has a cutting portion 9 and a taking-in portion 10 alternately formed in the circumferential direction. The cutting portion 9 has a saw-tooth shape facing the circumferential direction and has a tapered surface 14, and the taking-in portion 10 is recessed in the thickness direction with respect to the cutting portion 9 on the inner surface side. Therefore, most of the excavation chips 17 cut by the cutting portion 9 can be guided along the tapered surface 14 in the direction of the taking-in portion 10 and taken into the inner surface 12a side of the taking-in portion 10.

[0043] Further, since the cutting portion 9 is formed at a position corresponding to the formation position 24 of the inner surface side rib 7 and the taking-in portion 10 is formed at a position corresponding to the space between the inner surface side ribs 7, the excavation chips 17 taken into the inner surface 12a side of the taking-in portion 10 can be efficiently carried between the inner surface side ribs 7 and lifted along the inner surface 5 side of the ribbed steel pipe portion 3 and discharged onto the ground 15. That is, the excavation chips generated during excavation can be preferentially discharged to the inner surface 5 side of the ribbed steel pipe portion 3. The remaining excavation chips 18 are lifted along the outer surface 6 side of the ribbed steel pipe portion 3, but since the amount is small, the ground 15 on the outer surface 6 side is not disturbed by the excavation chips 18, and since the overexcavation is small, the horizontal ground reaction force that resists the horizontal load can be obtained as expected. Also, water pollution during the removal of the excavation chips 18 is suppressed.

[0044] In the foundation structure 19 of this embodiment, the ribbed steel pipe portion 3 is embedded in the ground 15, and the ribless steel pipe portion 2 is exposed on the ground 15. Therefore, the formation range of the inner surface side rib 7 and the outer surface side rib 8 on the steel pipe foundation 1 can be minimized. Also, in the exposed portion from the ground 15, since there are no irregularities such as ribs, it is not easily affected by resistance such as water flow.

[0045] According to the construction method of the basic structure 19 of this embodiment, due to the pressing force of the full-circle rotary excavator 16 and the pushing force generated by the spiral inner surface side rib 7 and the outer surface side rib 8, the steel pipe foundation 1 can be accurately driven to a predetermined depth against the hard ground 15 without using special equipment. Also, since no impact is applied to the steel pipe foundation 1, the wall thickness of the steel pipe foundation 1 can be set without considering fatigue due to impact, and the environmental load on the ecosystem during construction can be significantly reduced.

[0046] According to the removal method of the steel pipe foundation 1 of this embodiment, due to the pulling force of the full-circle rotary excavator 16 and the pulling force generated by the spiral inner surface side rib 7 and the outer surface side rib 8, the entire length of the steel pipe foundation 1 can be easily recovered and removed without using special construction equipment. Therefore, no part of the steel pipe foundation remains in the ground 15, and the entire length can be reused as scrap.

[0047] According to this embodiment, during the construction of the basic structure 19 and the removal of the steel pipe foundation 1, the amount of modification of the ground 15 is small. Therefore, the load on the environment of the ground 15 can be reduced.

[0048] As described above, the preferred embodiments of the present invention have been described with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that those skilled in the art can conceive of various modification examples or correction examples within the scope of the technical idea disclosed in this application, and it is naturally understood that they also belong to the technical scope of the present invention.

[0049] For example, the basic structure 19 of the present invention can be applied not only to monopile foundations for offshore wind turbines. Also, in the steel pipe foundation 1, spiral ribs are provided on both the inner surface 5 and the outer surface 6. However, in order to more preferentially transport the excavation slip 17 on the inner surface upward, ribs may be formed only on the inner surface 5 without providing ribs on the outer surface 6. Also, if it is easy to remove the excavation slip 18, etc., ribs may be provided only on the outer surface 6 without providing ribs on the inner surface 5.

Explanation of Reference Numerals

[0050] 1.........Steel pipe foundation 2.........Steel pipe part without rib 3………Ribbed steel pipe section 4...Drilling ring section 5, 12, 12a………Inner surface 6, 13……External surface 7………Inner rib 8………Outer rib 9……Cutting part 10: Capture section 11……Lower end 14...Tapered surface 15……ground 16...……Full-circle rotary excavator 17, 18: Excavated waste 19……Fundamental structure 20... Excavation trench 21, 22...End 23……Large SEP 24……Formation position 25……Boundary position 26, 27………Projection height

Claims

1. A steel pipe foundation, comprising: an excavation ring portion formed at the tip; a ribbed steel pipe portion located above the excavation ring portion and having spiral inner surface side ribs formed at least on the inner surface; a ribless steel pipe portion formed above the ribbed steel pipe portion; and in the axial cross-section of the steel pipe foundation, the inner surface side end of the inner surface side rib is located substantially on the extension of the inner surface of the excavation ring portion.

2. The ribbed steel pipe portion has spiral outer surface side ribs formed on the outer surface, and the inner surface side rib has a higher protruding height than the outer surface side rib. The steel pipe foundation according to Claim 1.

3. In the excavation ring portion, a cutting portion for cutting the ground and a taking-in portion for taking in the excavation slip are alternately formed in the circumferential direction, the cutting portion is formed at a position corresponding to the formation position of the rib in the lower end portion of the ribbed steel pipe portion, and the taking-in portion is formed at a position corresponding to the space between the ribs in the lower end portion of the ribbed steel pipe portion. The steel pipe foundation according to Claim 1 or Claim 2.

4. The taking-in portion is thinner than the cutting portion, and on the inner surface side, the taking-in portion forms a concave portion in the thickness direction. The steel pipe foundation according to Claim 3.

5. The cutting portion has a tapered shape with a longer outer surface side length and a shorter length toward the inner surface side. The steel pipe foundation according to Claim 3 or Claim 4.

6. The cutting portion has a saw-tooth shape in the circumferential direction. The steel pipe foundation according to any one of Claims 3 to 5.

7. A foundation structure using the steel pipe foundation according to any one of Claims 1 to 6, wherein the ribbed steel pipe portion is embedded in the ground and the ribless steel pipe portion is exposed on the ground.

8. The ground is an underwater ground, and it is used as a monopile foundation for an offshore wind turbine. The foundation structure according to Claim 7.

9. A construction method of a foundation structure using the steel pipe foundation according to any one of Claims 1 to 6, wherein the steel pipe foundation is press-fitted while being rotated clockwise until the ribbed steel pipe portion is buried in the ground.

10. A method for removing the steel pipe foundation from the foundation structure according to Claim 7 or Claim 8, wherein the steel pipe foundation is pulled out from the ground while being rotated counterclockwise.

Images