Design method for steel pipe piles, and steel pipe piles
The design of steel pipe piles with a slip layer to reduce frictional force addresses the high torque and extraction challenges, enabling easier and cost-effective removal.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- NIPPON STEEL METAL PROD CO LTD
- Filing Date
- 2024-11-26
- Publication Date
- 2026-06-05
AI Technical Summary
Existing methods for extracting and removing steel pipe piles are costly and face challenges such as high torque requirements and difficulty in extraction due to high circumferential friction, especially in ground compositions with varying N-values.
A design method for steel pipe piles that includes providing a slip layer on the outer surface, particularly at locations with high expected circumferential friction, using materials like bituminous material to reduce frictional force during extraction.
Facilitates easier and lower-cost extraction by reducing torque requirements and circumferential friction, ensuring efficient removal without significant impact on pile head bearing capacity.
Smart Images
Figure 2026092527000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a design method for steel pipe piles that are pulled out and removed after use, and to steel pipe piles.
Background Art
[0002] In recent years, due to the increasing awareness of global environmental issues, in structures with a limited service period such as the Olympics, international expositions, and wind power generation facilities, the extraction and removal of steel pipe piles have been increasingly considered actively from the initial planning stage. Regarding the extraction and removal of steel pipe piles, there are known construction methods such as drilling holes around the steel pipe pile with a casing to cut off the ground and the steel pipe pile and then pulling out the steel pipe pile (see, for example, Patent Document 1).
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] However, in the construction method using the above-mentioned casing, there is a concern that the cost required for removal increases. As a construction method for extraction and removal, there is also known a method in which a rotary pile having blades at the tip of a steel pipe pile is used, and the pile is rotated in the reverse direction to perform extraction and removal. In this method, particularly, the torque required at the start of extraction is large, and depending on the ground composition, there are problems such as difficulty in extraction or it taking a long time.
[0005] Therefore, an object of the present invention is to provide a design method for steel pipe piles and a steel pipe pile that can perform extraction and removal more easily and at a lower cost by reducing the circumferential frictional force during extraction in the extraction and removal performed while rotating the steel pipe pile.
Means for Solving the Problems
[0006] [1] A method for designing a steel pipe pile that is removed by rotation, comprising a steel pipe pile design step of designing the steel pipe pile such that a slip layer layer is provided on the outer surface of the steel pipe pile. [2] A method for designing a steel pipe pile according to [1], comprising a ground structure acquisition step for acquiring the structure of the ground into which the steel pipe pile penetrates, wherein in the steel pipe pile design step, the steel pipe pile is designed such that the slip layer layer is provided on a part of the outer surface of the steel pipe pile where the circumferential friction is expected to be high based on the ground structure acquired in the ground structure acquisition step. [3] The steel pipe pile design method according to [2], wherein the part of the steel pipe pile design process includes a position corresponding to a geological layer in which the N value obtained in the steel pipe pile design process is 1.5 times or more the average N value of the ground. [4] The slip layer contains bituminous material, a design method for steel pipe piles according to any one of [1] to [3]. [5] The steel pipe pile is a rotating pile having a cylindrical portion formed by a steel pipe and a blade joined to the end face on the tip side of the cylindrical portion, the design method for a steel pipe pile according to any one of [1] to [3]. [6] The steel pipe pile is a rotating pile having a cylindrical portion formed by a steel pipe and a helical vane joined to the outer surface of the cylindrical portion, the design method for a steel pipe pile according to any one of [1] to [3]. A steel pipe pile designed according to the steel pipe pile design method described in any of [7], [1], or [3]. [Effects of the Invention]
[0007] According to the present invention, in the extraction and removal of steel pipe piles while rotating them, the frictional force on the circumferential surface during extraction can be reduced, thereby enabling extraction and removal at a lower cost and with less torque. [Brief explanation of the drawing]
[0008] [Figure 1]This graph shows an example of the N-value measured by a ground survey and the torque during penetration and extraction of steel pipe piles. [Figure 2] This diagram shows the composition of the ground where the steel pipe piles are to be installed, and the state of the steel pipe piles after they have been driven into the ground. [Figure 3] This diagram shows other forms of steel pipe piles. [Modes for carrying out the invention]
[0009] The present invention relates to a design method for steel pipe piles that are to be removed by extraction after use, and more particularly to a design method that facilitates extraction and removal while rotating the steel pipe pile. The inventors measured the torque generated when steel pipe piles are driven into and out of the ground (the torque required to drive and withdraw steel pipe piles into the ground), recognized a correlation between the properties of the ground and the torque, and concluded that by performing a treatment on the steel pipe piles to reduce the frictional force on the surface based on the properties of the ground, they could facilitate the extraction and removal of the piles, leading to the present invention. The measurements and considerations conducted leading up to the present invention will be described below.
[0010] First, we will explain the composition of the ground where the steel pipe piles are installed, and the results of torque measurements during penetration and withdrawal of the steel pipe piles. The steel pipe pile is a rotating pile having a cylindrical section formed by a steel pipe and a blade joined to the end face of the tip of the cylindrical section. The pile diameter of the steel pipe pile is 500 mm (nominal diameter), and the tip blade diameter is 750 mm (1.5 times diameter).
[0011] Figure 1 is a graph showing an example of N-values measured by a ground investigation and the torque during penetration / extraction of steel pipe piles. In Figure 1, the vertical axis represents depth, and the horizontal axis represents N-value / torque. In the example shown in Figure 1, the ground consists of a sand layer L1 with an N-value of approximately 10 at a depth of 0m to 6m, a gravel layer L2 with an N-value exceeding 60 at a depth of 6m to 9m, a sand layer L3 with an N-value of approximately 30 at a depth of 9m to 12m, a cohesive soil layer L4 with an N-value of 20 to 50 at a depth of 12m to 15m, and a sand layer L5 with an N-value of approximately 40 to 60 at a depth of 15m and above. In other words, in this ground, the N-value increases in the gravel layer L2, and also increases in the deepest sand layer L5.
[0012] Figure 1 shows that, regarding the torque during penetration and extraction, the torque of the steel pipe pile increases or decreases in accordance with the N value during penetration, indicating a correlation between the N value and torque. On the other hand, during extraction, the torque is highest at the beginning of the extraction and decreases as the depth decreases. During penetration, the torque is greater at depths with high N-values because the torque generated by the blades is dominant during penetration, and is more pronounced at locations with high N-values. On the other hand, during extraction, the circumferential friction force (the force at the contact surface between the steel pipe pile and the ground that attempts to prevent the rotational movement of the steel pipe pile) is dominant, and it is thought that the torque required to begin extraction can be reduced by performing a process to reduce this circumferential friction force at locations where it is large.
[0013] The inventors reasoned that since the N-value and the circumferential friction force can be considered proportional, reducing the circumferential friction force at positions corresponding to depths with large N-values would reduce the torque at the start of extraction, leading them to conceive of the steel pipe pile design method of the present invention.
[0014] Next, we will explain the design method for steel pipe piles based on the above findings. The design method for steel pipe piles comprises a ground structure acquisition step for acquiring the ground structure on which the steel pipe piles will be constructed, and a steel pipe pile design step for designing the steel pipe piles based on the acquired ground structure.
[0015] The ground structure acquisition process involves conducting known ground investigations, such as boring surveys, to obtain the ground structure, including N-values. Through this process, boring data like that shown in Figure 2 can be obtained. Alternatively, the ground structure may be acquired using known boring data without conducting a ground investigation.
[0016] In the steel pipe pile design process, the steel pipe piles are designed based on boring data obtained from ground investigations. Specifically, the specifications of the steel pipe piles (length, pile diameter, diameter of the tip vanes, etc.) are determined using known methods. In addition, in the design process of steel pipe piles, the steel pipe piles are designed such that a slip layer is provided on the outer peripheral surface of the steel pipe piles. Specifically, in the design process of steel pipe piles, the position where the slip layer is to be provided is determined in the longitudinal direction of the steel pipe piles.
[0017] FIG. 2 is a diagram showing the configuration of the ground where the steel pipe pile is constructed and the steel pipe pile in a state of being penetrated into the ground. The steel pipe pile 10 shown in FIG. 2 is a steel pipe pile 10 designed by the steel pipe pile design method of the present invention, and is a steel pipe pile 10 provided with a slip layer SL on the outer peripheral surface. Further, FIG. 2 also shows the N value of the ground obtained in the ground configuration acquisition process. As shown in FIG. 2, the ground of the present embodiment is composed of a sand layer L1 with an N value of about 10 at a depth of 0 m to 6 m, a gravel layer L2 with an N value exceeding 60 at a depth of 6 m to 9 m, a sand layer L3 with an N value of about 30 at a depth of 9 m to 12 m, a clay layer L4 with an N value of 20 to 50 at a depth of 12 m to 15 m, and a sand layer L5 with an N value of about 40 to 60 at a depth of 15 m or more, but is not limited thereto.
[0018] The steel pipe pile 10 of the present embodiment has a cylindrical portion 11 formed of a steel pipe and blades 12 joined to the end face on the tip side of the cylindrical portion 11, and is a rotary pile that is penetrated into the ground by rotary pressing using a construction machine (not shown). The steel pipe pile 10 is an open-ended rotary pile, and an opening is formed at the tip portion. By adjusting the penetration amount per rotation during rotary penetration to the spiral pitch of the blades 12, the steel pipe pile 10 can be penetrated into the ground while taking soil into the inside of the steel pipe pile 10 from the opening at the tip portion of the steel pipe pile 10 without disturbing the ground. In addition, the steel pipe pile 10 can be pulled out and removed by reverse rotation. That is, the steel pipe pile 10 of the present embodiment can be pulled out and removed without using a casing for cutting the edge between the ground and the pile.
[0019] In the steel pipe pile design process, the steel pipe pile 10 is designed such that a slip layer SL (SL layer) for reducing the circumferential frictional force is provided on the outer peripheral surface of the cylindrical portion 11. The slip layer SL is a layer formed by a slip layer, which is a circumferential friction reducing material. The slip layer is formed from a material containing a low-friction material such as bituminous material (asphalt). The slip layer SL may be provided by applying the slip layer, or by attaching a sheet formed from the slip layer. Furthermore, in order to protect the surface of the slip layer SL, a surface protective material such as a nonwoven fabric may be provided on top of the slip layer SL.
[0020] Specifically, in the steel pipe pile design process, a slip layer SL is provided on a portion of the outer surface of the steel pipe pile 10 where the circumferential friction force is expected to be high based on the ground structure obtained in the ground structure acquisition process. As mentioned above, since the circumferential friction force is proportional to the N value, the location where the slip layer SL is installed can be a location corresponding to a depth with a large N value. For example, a portion of the area where the slip layer SL is installed can be determined to include a location corresponding to a geological layer where the N value obtained in the steel pipe pile design process is 1.5 times or more the average N value of the ground. In this embodiment, since the N value is large in the gravel layer L2 at a depth of 7m to 9m and the sand layer L5 at a depth of 14m to 16m, the slip layer SL can be installed at least in these locations. The area where the slip layer SL is installed is preferably as wide as possible, but it can be made smaller as appropriate depending on the cost. Also, as shown in Figure 2, two or more slip layer SLs may be installed at intervals, and different coatings may be applied to the spaced-out areas, or no coating may be applied at all.
[0021] Furthermore, the area to which the slip layer layer SL is installed can also be determined based on the evaluation formula for pile surface friction force established by a designated evaluation organization. For example, in the case of rotary piles with a pile diameter of 100 mm to 1,600 mm and a blade diameter of 2,400 mm or less, there are construction methods in which the pile surface friction force is evaluated as follows: 2NsLs (Ns: average N value of sandy soil, Ls: thickness of sandy soil) in the case of sandy soil, and qu / 2×Lc (qu: average value of uniaxial compressive strength of cohesive soil, Lc: thickness of clayey soil) in the case of cohesive soil. In this case, the slip layer layer SL can be designed to be installed in the layers where these pile surface friction forces are large.
[0022] According to the above embodiment, in the design of the steel pipe pile 10, by providing a slip layer SL to reduce the circumferential friction force and thereby reducing the torque during extraction, extraction and removal can be made easier. Specifically, by providing a slip layer SL at a position corresponding to a depth with a high N value where the circumferential friction force is large, the circumferential friction force at the start of extraction is reduced, making it easier to separate the ground from the steel pipe pile 10 and thus facilitating extraction and removal.
[0023] Furthermore, by providing the slip layer SL only in a portion of the steel pipe pile 10, rather than along its entire length, the manufacturing cost of the steel pipe pile 10 having the slip layer SL can be reduced. Furthermore, by using the correlation between N-value and torque to determine the area where the slip layer SL is to be installed, it is possible to confirm whether the area where the slip layer SL is to be installed is located in a layer with high surface friction for all steel pipe piles being constructed. In other words, it becomes possible to construct steel pipe pile foundations that are easy to pull out and remove with high precision.
[0024] Furthermore, regarding the effect of the slip layer on the compression bearing capacity of steel pipe piles, since the tip bearing capacity accounts for a large proportion (often more than 80%) of the pile head bearing capacity (= tip bearing capacity + pile circumferential bearing capacity) of steel pipe piles, even if the slip layer is placed in a position where the circumferential friction force is large, the effect on the pile head bearing capacity is small. Therefore, it is possible to reduce the torque during pile extraction and removal while ensuring the compression bearing capacity of the steel pipe piles.
[0025] Furthermore, in the above embodiment, the steel pipe pile 10 is a rotating pile having a blade 12 joined to the end face at the tip, but it is not limited to this. For example, it may be a rotating pile having a cylindrical portion 11A formed by a steel pipe and a helical blade 12A joined to the outer circumferential surface of the cylindrical portion 11A, as shown in Figure 3. It is also applicable to steel pipe piles consisting only of a cylindrical portion without blades. [Explanation of symbols]
[0026] 10...Steel pipe pile, 11...Cylindrical section, 12...Blade, L1...Sand layer, L2...Sand and gravel layer, L3...Sand layer, L4...Cohesive soil layer, L5...Sand layer, SL...Slip layer layer.
Claims
1. A design method for steel pipe piles that are removed by rotation, A method for designing a steel pipe pile, comprising a steel pipe pile design step of designing the steel pipe pile such that a slip layer layer is provided on the outer surface of the steel pipe pile.
2. The process includes a ground structure acquisition step to acquire the structure of the ground into which the steel pipe pile penetrates, The steel pipe pile design method according to claim 1, wherein in the steel pipe pile design step, the slip layer is provided on a portion of the outer surface of the steel pipe pile where the circumferential friction is expected to be high based on the ground structure obtained in the ground structure acquisition step.
3. The steel pipe pile design method according to claim 2, wherein the part of the steel pipe pile design process includes a position corresponding to a geological layer where the N value obtained in the steel pipe pile design process is 1.5 times or more the average N value of the ground.
4. The design method for steel pipe piles according to any one of claims 1 to 3, wherein the slip layer contains bituminous material.
5. The steel pipe pile design method according to any one of claims 1 to 3, wherein the steel pipe pile is a rotating pile having a cylindrical portion formed by a steel pipe and a blade joined to the end face on the tip side of the cylindrical portion.
6. The steel pipe pile design method according to any one of claims 1 to 3, wherein the steel pipe pile is a rotating pile having a cylindrical portion formed by a steel pipe and a helical vane joined to the outer surface of the cylindrical portion.
7. A steel pipe pile designed by the steel pipe pile design method described in any one of claims 1 to 3.