Construction method for steel pipe piles and steel pipe pile foundations

Abstract

To provide a construction method of a steel pipe pile which can improve workability.SOLUTION: A construction method of a steel pipe pile is a construction method of a steel pipe pile for rotationally pressing-in a steel pipe pile 2 having spiral projections therein into the ground, and includes a first rotational press-in step of rotationally pressing-in the steel pipe pile 2 in a reverse turning direction R1 that a downward inclination angle θ1 formed by the spiral projections 4 and a steel pipe axis Z, and a construction angle θ2 composed of a displacement amount D2 in a rotation direction in rotational press-in and a displacement amount D1 in a vertical direction become as quadrants on opposite sides across a steel pipe axis Z. The first rotational press-in step penetrates the tip of the steel pipe pile 2 into a support layer, after the first rotational press-in step, the construction method includes a second rotational press-in step of rotationally pressing-in the steel pipe pile 2 in a normal turning direction R2 that the inclination angle θ1 and the construction angle θ2 become the same quadrant.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a construction method of a steel pipe pile having spiral protrusions on its inner surface and a steel pipe pile foundation.

Background Art

[0002] When a plain steel pipe pile is rotationally pressed into the ground, there is a risk that sediment taken into the steel pipe pile from the opening at the tip of the steel pipe pile may be mixed in. In this case, tip clogging occurs where the sediment at the pile tip is compacted, increasing the pressing resistance of the steel pipe pile and taking time for the construction of each steel pipe pile.

[0003] Conventionally, Patent Documents 1 and 2 disclose techniques for rotationally pressing a steel pipe pile having spiral protrusions on its inner surface into the ground.

[0004] The construction method of the steel pipe pile in Patent Document 1 rotationally presses the steel pipe pile in the positive rotation direction in which the downward inclination angle formed by the spiral protrusion and the steel pipe axis and the construction angle composed of the rotational displacement amount and the vertical displacement amount during rotational pressing are in the same quadrant. As a result, it becomes easier to take in the sediment invading the steel pipe pile along the spiral protrusions toward the upper part inside the steel pipe pile. Therefore, even when sediment or the like is mixed in the pile tip opening, the tip clogging of the sediment at the pile tip is adjusted, and the construction torque and the pressing pressure of the rotational pressing device for rotationally pressing the steel pipe pile are reduced to improve the workability.

[0005] Also, the construction method of the steel pipe pile in Patent Document 1, when stopping the steel pipe pile, performs a reverse rotation process of simply reversely rotating the steel pipe pile to compact the soil inside the steel pipe pile. Thereby, it is said that the tip clogging of the sediment at the pile tip is promoted and the tip bearing capacity is improved by compacting the soil inside the pipe by pushing down the soil inside the pipe by the protrusion.

[0006] The steel pipe in Patent Document 2 has a ground loosening member provided at the tip of the steel pipe and extending spirally in the circumferential direction of the steel pipe to loosen the ground. In the steel pipe of Patent Document 2, the ground loosening member provided at the tip of the steel pipe main body excavates the ground when the steel pipe rotates. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2011-157780 [Patent Document 2] Japanese Patent Publication No. 2022-40470 [Overview of the project] [Problems that the invention aims to solve]

[0008] Thus, conventional technology involves rotating and pressing steel pipe piles, which have spiral protrusions on their inner surface, into the ground in a forward rotational direction. Therefore, there is a need for technology that can further improve constructability.

[0009] Therefore, the present invention was devised in view of the above-mentioned problems, and its objective is to provide a method for constructing steel pipe piles and a steel pipe pile foundation that can improve constructability. [Means for solving the problem]

[0010] The inventors diligently studied how to utilize the characteristics of steel pipe piles having spiral projections on their inner surface. As a result, they found that when the steel pipe pile is rotated and pressed in in a counter-rotating direction, where the downward inclination angle between the spiral projections and the steel pipe axis, and the construction angle formed by the rotational displacement and vertical displacement during rotational press-in, are in the quadrant opposite the steel pipe axis, the occurrence of tip blockage is more easily inhibited than when rotating and pressing in in a forward rotation direction. Therefore, the press-in resistance of the steel pipe pile can be reduced, and construction efficiency can be improved.

[0011] The method for constructing a steel pipe pile according to the first invention is a method for constructing a steel pipe pile having a spiral projection on its inner surface, which is rotated and pressed into the ground, and is characterized by comprising a first rotational pressing step in which the steel pipe pile is rotated and pressed in in a counter-rotational direction such that the downward inclination angle formed by the spiral projection and the steel pipe axis, and the construction angle formed by the amount of displacement in the rotational direction and the amount of displacement in the vertical direction during rotational pressing, are in the quadrants opposite each other across the steel pipe axis.

[0012] The construction method for steel pipe piles according to the second invention is characterized in that, in the first invention, after the first rotational press-in step, the steel pipe pile is rotated and pressed in in a positive rotational direction such that the inclination angle and the construction angle are in the same quadrant.

[0013] The construction method for steel pipe piles according to the third invention is characterized in that, in the second invention, the tip of the steel pipe pile is driven into the supporting layer of the ground in the first rotary press-in step, and the second rotary press-in step is provided after the first rotary press-in step.

[0014] The steel pipe pile foundation according to the fourth invention is characterized by being constructed by penetrating a steel pipe pile having spiral projections on its inner surface into the ground using the steel pipe pile construction method described in any one of the first to third inventions. [Effects of the Invention]

[0015] According to the first invention, the method includes a first rotational press-in step in which the steel pipe pile is rotated and pressed in in the reverse rotational direction. This increases the effect of disturbing the soil inside the pipe, making it easier to prevent tip blockage. As a result, the resistance to pressing in the steel pipe pile can be reduced, and workability can be improved.

[0016] According to the second invention, a second rotational press-in step is provided after the first rotational press-in step, in which the steel pipe pile is rotated and pressed in in the forward rotational direction. This makes tip blockage more likely to occur compared to when rotational press-in is continued in the reverse rotational direction. Therefore, it is possible to improve the tip bearing capacity of the steel pipe pile.

[0017] According to the third invention, in the first rotary press-in step, the tip of the steel pipe pile is penetrated into the supporting layer of the ground, and after the first rotary press-in step, a second rotary press-in step of rotary press-in of the steel pipe pile in the normal rotation direction is provided. Thereby, in the steel pipe pile penetrated into the supporting layer, tip blockage is likely to occur. Therefore, with the tip of the steel pipe pile penetrated into the supporting layer of the ground, by making tip blockage likely to occur, it becomes possible to further improve the tip supporting force of the steel pipe pile.

[0018] According to the fourth invention, it is possible to construct a steel pipe pile foundation that can improve construction performance. Further, according to the fourth invention, it is possible to construct a steel pipe pile foundation that can improve the tip supporting force of the steel pipe pile.

Brief Description of the Drawings

[0019] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a steel pipe pile foundation in an embodiment. [Figure 2] FIG. 2(a) is a diagram for explaining the rotary press-in of the steel pipe pile in the reverse rotation direction in the embodiment, and FIG. 2(b) is a diagram for explaining the rotary press-in of the steel pipe pile in the normal rotation direction in the embodiment. [Figure 3] FIG. 3(a) is a diagram for explaining the behavior of the soil inside the pipe when rotary press-in is performed in the reverse rotation direction, and FIG. 3(b) is a diagram for explaining the behavior of the soil inside the pipe when rotary press-in is performed in the normal rotation direction. [Figure 4] FIG. 4 is a diagram for explaining a method of measuring the rising value of the soil height inside the pipe when the steel pipe is penetrated. [Figure 5] FIG. 5 is a diagram showing the relationship between the penetration amount and the rising value of the soil height inside the pipe.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, a method for constructing a steel pipe pile to which the present invention is applied and an embodiment for implementing a steel pipe pile foundation will be described in detail with reference to the drawings.

[0021] As shown in Fig. 1, the steel pipe pile foundation 1 includes steel pipe piles 2 penetrated into the ground G. The steel pipe piles 2 are penetrated into the ground G by a rotary pressing method in which the steel pipe piles 2 are rotated by a rotary pressing device and pressed downward. The steel pipe pile 2 is a steel pipe with an inner surface projection in which a spiral projection 4 is formed on the inner peripheral surface 3. The projection 4 is formed in a clockwise spiral shape in the depth direction (downward in Fig. 1), and the inclination thereof is defined as an inclination angle θ1 formed with the steel pipe axis Z.

[0022] The steel pipe pile 2 may be formed, for example, by making a steel plate with the projection 4 formed in advance into a cylindrical shape like a spiral steel pipe. The steel pipe pile 2 may be formed by welding a steel bar or flat steel to the inner peripheral surface 3 of a steel pipe formed into a cylindrical shape in advance, or by raising the welding metal to attach the projection 4 later. Thus, the order of installation of the projection 4 is arbitrary.

[0023] As shown in Fig. 1, the projection 4 is continuously formed, for example, on the inner peripheral surface 3 of the steel pipe pile 2. Note that the projection 4 may be intermittently formed, for example, on the inner peripheral surface 3 of the steel pipe pile 2. Also, the projection 4 is installed, for example, over the entire length of the steel pipe pile 2. The projection 4 may be installed in a range of about 1 to 5 times the outer diameter of the steel pipe pile 2 from the tip of the steel pipe pile 2.

[0024] Next, the construction method of the steel pipe pile will be described. The construction method of the steel pipe pile is to rotationally press a steel pipe pile 2 having a spiral projection 4 on the inner surface into the ground. As shown in Fig. 2, in the steel pipe pile 2 being rotationally pressed, a vertical displacement amount D1 due to the load in the vertical pressing direction Q and a rotational displacement amount D2 due to the load in the rotational direction R occur. The construction method of the steel pipe pile includes a first rotational pressing step of rotationally pressing the steel pipe pile 2 in the reverse rotational direction R1, and a second rotational pressing step of rotationally pressing the steel pipe pile 2 in the forward rotational direction R2 after the first rotational pressing step.

[0025] As shown in Figure 2(a), first, in the first rotational press-in process, the steel pipe pile 2 is rotated and pressed in in the counter-rotation direction R1, where the downward inclination angle θ1 formed by the spiral projection 4 and the steel pipe axis Z, and the construction angle θ2 formed by the rotational displacement D2 and D1 when the displacement of the steel pipe during rotational press-in is divided into a rotational displacement D2 and a vertical displacement D1, are in the quadrant opposite to the steel pipe axis Z.

[0026] As a result, as shown in Figure 3(a), the soil inside the pipe moves in a way that it continuously rides up onto the spiral projections 4. Because the soil inside the pipe is disturbed by riding up onto the projections 4, the occurrence of tip blockage is more easily inhibited. Therefore, the resistance to driving the steel pipe pile can be reduced, and the workability can be improved.

[0027] In the first rotary driving step, the tip of the steel pipe pile 2 is driven into the supporting layer of the ground. Preferably, the first rotary driving step is carried out until, for example, the embedment depth of the steel pipe pile 2 into the supporting layer of the ground is equal to or greater than the outer diameter of the steel pipe pile 2. However, depending on the required tip bearing capacity, the second rotary driving step may be started before the tip of the steel pipe pile reaches the supporting layer, or even if the embedment depth into the supporting layer is less than or equal to the outer diameter of the steel pipe pile 2. Furthermore, even after reaching the supporting layer, if sufficient tip closure occurs and the predetermined tip bearing capacity can be secured, the first rotary driving step may be continued.

[0028] Here, the bearing layer refers to a layer with sufficient strength and rigidity to support a structure, and can generally be selected based on boring data obtained in advance from the site where the structure will be built. Furthermore, even if the bearing layer is determined in advance at the design stage, differences in ground strength may occur due to the undulation of the bearing layer or the presence of unconfirmed geological layers in areas where boring has not been performed, so the bearing layer may need to be re-selected during construction. The conditions for the ground strength required for the bearing layer differ depending on the various design guidelines, but for example, according to the "Specifications for Road Bridges and Commentary (2017)", as a general guideline for a bearing layer, if it is a cohesive soil layer, an N value of about 20 or higher is acceptable, and if it is a sand or gravel layer, an N value of about 30 or higher is acceptable.

[0029] Next, as shown in Figure 2(b), in the second rotational press-in process, after the first rotational press-in process, the steel pipe pile 2 is rotated and pressed in in the positive rotation direction R2, where the inclination angle θ1 and the construction angle θ2 are in the same quadrant.

[0030] As a result, as shown in Figure 3(b), although the soil inside the pipe moves along the spiral projection 4, the effect of disturbing the soil inside the pipe is smaller than in the counter-rotation direction R1. Therefore, tip blockage, in which the soil at the tip of the steel pipe pile 2 is compacted, is more likely to occur. Consequently, it becomes possible to improve the tip bearing capacity of the steel pipe pile 2.

[0031] In particular, the second rotational press-in process is preferably carried out by rotating and press-in the steel pipe pile 2 in the forward rotational direction R2, for example, when the tip of the steel pipe pile 2 has penetrated the supporting layer of the ground. This makes it easier for tip occlusion to occur in the steel pipe pile that has penetrated the supporting layer. Therefore, by making it easier for tip occlusion to occur when the tip of the steel pipe pile 2 has penetrated the supporting layer of the ground, it is possible to further improve the tip bearing capacity of the steel pipe pile 2.

[0032] This completes one example of a steel pipe pile construction method. This constructs a steel pipe pile foundation 1 in which a steel pipe pile 2 having spiral projections 4 on its inner surface is driven into the ground. At this time, a bit may be formed in advance at the tip of the steel pipe pile 2. This reduces the resistance to driving the steel pipe pile, as the steel pipe pile is rotated and pressed in while the ground is excavated, thereby improving workability.

[0033] According to this embodiment, the method includes a first rotational press-in step in which the steel pipe pile 2 is rotated and pressed in in the reverse rotational direction R1. This increases the effect of disturbing the soil inside the pipe, making it easier to prevent tip blockage. As a result, the resistance to pressing in the steel pipe pile 2 can be reduced, and workability can be improved.

[0034] According to this embodiment, after the first rotational press-in step, a second rotational press-in step is provided in which the steel pipe pile 2 is rotated and pressed in in the forward rotation direction R2. This makes tip blockage more likely to occur compared to when rotational press-in is continued in the reverse rotation direction. Therefore, it is possible to improve the tip bearing capacity of the steel pipe pile 2.

[0035] According to this embodiment, the first rotary press-in step involves penetrating the tip of the steel pipe pile 2 into the supporting layer of the ground, and the second rotary press-in step involves rotating and pressing the steel pipe pile 2 in the forward rotation direction R2 after the first rotary press-in step. This makes it easier for tip occlusion to occur in the steel pipe pile 2 that has been penetrated into the supporting layer. Therefore, by making it easier for tip occlusion to occur when the tip of the steel pipe pile 2 has been penetrated into the supporting layer of the ground, it is possible to further improve the tip bearing capacity of the steel pipe pile 2.

[0036] According to this embodiment, the first rotational press-in step involves rotating and press-in the steel pipe pile 2 in the counter-rotating direction R1 until the embedment depth of the steel pipe pile 2 into the supporting layer of the ground is equal to or greater than the outer diameter of the steel pipe pile 2. After the first rotational press-in step, a second rotational press-in step is provided in which the steel pipe pile 2 is rotated and press-in in the forward rotation direction R2. This makes it easier for tip blockage to occur in the steel pipe pile 2 once a sufficient embedment depth into the supporting layer of the ground has been secured. Therefore, it is possible to more reliably improve the tip bearing capacity of the steel pipe pile 2.

[0037] According to this embodiment, the steel pipe pile 2 is rotated and pressed into place in the reverse rotation direction R1 to construct the steel pipe pile foundation 1. This makes it possible to construct a steel pipe pile foundation 1 that improves constructability.

[0038] Furthermore, according to this embodiment, in the first rotational press-in step, the tip of the steel pipe pile 2 is driven into the supporting layer of the ground, and after the first rotational press-in step, the steel pipe pile 2 is rotated and pressed in in the forward rotation direction R2 to construct the steel pipe pile foundation 1. This makes it possible to construct a steel pipe pile foundation 1 that can improve the tip bearing capacity.

[0039] Next, the effects of the present invention will be explained using experimental results. In this experiment, steel pipes were used as model test samples. Standard steel pipes (plain pipes) with and without internal spiral protrusions were prepared, and these were rotated and pressed into sandy ground composed of dry sand. For the steel pipes with internal spiral protrusions, rotational pressing was performed in both the reverse and forward directions. The outer diameter of the steel pipe was 101.6 mm, the height of the internal spiral protrusions was 3 mm (approximately 3% of the outer diameter), and the internal spiral was installed only in a range equal to the length of the outer diameter from near the tip of the pile.

[0040] In this experiment, the penetration depth and the rise in the height of the soil inside the pipe were measured when various steel pipes were rotated and pressed into the ground. As shown in Figure 4, a wire displacement gauge 9 installed inside the steel pipe can measure the position of the top of the soil S inside the pipe as it penetrates the sandy ground over time. The rise in the height of the soil inside the pipe H was calculated from the difference between the position of the top of the soil S inside the pipe at a reference point A and the position of the top of the soil S inside the pipe at a certain point B after a certain time has elapsed from point A.

[0041] Figure 5 is a graph showing the relationship between the penetration amount and the increase in the height of the soil inside the pipe in this experiment. In Figure 5, the result of rotational press-fitting in the reverse rotation direction is labeled "reverse rotation," the result of rotational press-fitting in the forward rotation direction is labeled "forward rotation," and the result for the raw pipe is labeled "raw pipe."

[0042] As shown in Figure 5, for example, when the penetration depth is 300 mm, the increase in the soil height inside the pipe when rotated and pressed in the reverse direction, and the increase in the soil height inside the pipe when rotated and pressed in the forward direction, were both greater than the increase in the soil height inside the pipe in the case of a plain pipe. This is thought to be because, in the case of rotational pressing in the reverse direction and in the forward direction, the soil inside the pipe moved upward more easily due to the internal spiral protrusions. As a result, it is thought that the occurrence of tip blockage is more easily inhibited in the case of rotational pressing in the reverse direction and in the forward direction than in the case of a plain pipe.

[0043] Furthermore, for example, when the penetration depth was 300 mm, the increase in the height of the soil inside the pipe when rotating and pressing in the reverse direction was greater than the increase in the height of the soil inside the pipe when rotating and pressing in the forward direction. This is because, when rotating and pressing in the reverse direction, as shown in Figure 3(a), the soil inside the pipe moves by continuously riding up onto the spiral protrusions, whereas when rotating and pressing in the forward direction, as shown in Figure 3(b), the soil inside the pipe moves along the spiral protrusions. As a result, it is thought that the soil inside the pipe is disturbed more when rotating and pressing in the reverse direction compared to when rotating and pressing in the forward direction, and the voids in the soil inside the pipe increase. Therefore, it is thought that rotating and pressing in the reverse direction has a greater effect of disturbing the soil inside the pipe by the protrusions on the inner surface compared to rotating and pressing in the forward direction, and that the occurrence of tip blockage is more easily inhibited. For this reason, rotating and pressing in the reverse direction can reduce the pressing resistance compared to rotating and pressing in the forward direction.

[0044] Therefore, by rotating and pressing in the reverse direction, the pressing resistance can be reduced. This makes it possible to improve workability.

[0045] On the other hand, rotational press-fitting in the forward rotation direction is more likely to result in tip blockage than rotational press-fitting in the reverse rotation direction. Therefore, compared to continuing rotational press-fitting in the reverse rotation direction, switching the rotation direction from the reverse rotation direction to the forward rotation direction makes it possible to improve the tip bearing capacity of the steel pipe pile. In particular, when the tip of the steel pipe pile has penetrated the bearing layer of the ground, switching the rotation direction from the reverse rotation direction to the forward rotation direction makes it possible to further improve the tip bearing capacity of the steel pipe pile.

[0046] Furthermore, it has been found that the internal spiral does not need to be installed along the entire length of the pile; it can be effective even if it is limited to the vicinity of the pile tip. From the standpoint of reducing processing costs, it is desirable for the spiral installation range to be within 1 to 5 times the outer diameter from the pile tip.

[0047] It should be noted that the present invention is not limited to the embodiments described above, and includes other configurations that can achieve the objectives of the present invention, and modifications such as those shown below are also included in the present invention. For example, in the embodiments described above, a steel pipe pile foundation 1 that can be used as a foundation for civil engineering structures and building structures was exemplified, but the steel pipe pile of the present invention is not limited to those used as foundations, but may also be used for retaining walls, underground continuous walls, etc.

[0048] While embodiments of this invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. Furthermore, this invention can be implemented in various novel forms in addition to the embodiments described above. Therefore, the above embodiments can be omitted, replaced, or modified in various ways without departing from the spirit of this invention. Such novel forms and modifications are included in the scope and spirit of this invention, as well as in the invention described in the claims and its equivalents. [Explanation of Symbols]

[0049] 1: Steel pipe pile foundation 2: Steel pipe pile 3: Inner surface 4: Protrusion 9: Wire displacement sensor D1: Vertical displacement D2: Rotational displacement G: Ground R: Direction of rotation R1: Counter-rotation direction R2: Forward rotation direction Q: Press-fit direction Z: Steel pipe shaft θ1: Inclination angle θ2: Construction angle

Claims

1. A method for constructing steel pipe piles, which involves rotating and pressing a steel pipe pile having spiral projections on its inner surface into the ground, A first rotational press-in step in which the steel pipe pile is rotated and pressed in in a counter-rotating direction such that the downward inclination angle formed by the helical projection and the steel pipe shaft, and the construction angle formed by the amount of displacement in the rotational direction and the amount of displacement in the vertical direction during rotational press-in, are in the quadrant opposite to the steel pipe shaft, After the first rotary press-fitting step, the inclination angle and the installation angle are in the same quadrant. The system includes a second rotational press-fitting step in which the steel pipe pile is rotated and pressed into place in the rotational direction. A construction method for steel pipe piles characterized by the following.

2. In the first rotary press-in step, the tip of the steel pipe pile is driven into the support layer, The second rotary press-fitting step is provided after the first rotary press-fitting step. A method for constructing steel pipe piles according to claim 1, characterized by the above.

3. A steel pipe pile foundation characterized by being constructed by penetrating a steel pipe pile having spiral projections on its inner surface into the ground using the steel pipe pile construction method described in claim 1 or 2.

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