JP7529051B2 - Construction method of steel pipe soil cement composite pile, steel pipe pile, and steel pipe soil cement composite pile - Google Patents

Description

The present invention relates to a construction method for a steel pipe soil cement composite pile, a steel pipe pile, a steel pipe, and a steel pipe soil cement composite pile formed by placing a steel pipe pile in a soil cement column.

Patent document 1 describes a method of forming a depression on the outer surface of a steel pipe pile as a way to improve the integrity between the soil cement column and the steel pipe pile and increase the bearing capacity of the steel pipe soil cement composite pile.

JP 2008-175055 A

Steel Pipe Soil Cement Composite Pile Method: Steel Pipe Pile and Steel Sheet Pile Technology Association

According to the method described in Patent Document 1, when horizontal displacement occurs in the steel pipe pile due to factors such as an earthquake, the soil cement column cannot elastically follow the behavior of the steel pipe pile due to the difference in elastic modulus. This can cause separation between the steel pipe pile and the soil cement column, reducing the vertical bearing capacity of the steel pipe soil cement composite pile.

The present invention has been made to solve the above problems, and aims to provide a construction method for steel pipe soil cement composite piles, steel pipe piles, steel pipes, and steel pipe soil cement composite piles that can suppress a decrease in the vertical bearing capacity of the steel pipe soil cement composite pile even if horizontal displacement occurs in the steel pipe pile.

The steel pipe soil cement composite pile of the present invention is a steel pipe soil cement composite pile comprising a soil cement column extending from the ground surface into the ground and a steel pipe pile within the soil cement column, and is provided with a plurality of first protrusions having a height of 15 mm or more formed on the outer peripheral surface of the steel pipe pile in the pile head region of the steel pipe soil cement composite pile, and a plurality of second protrusions formed on the outer peripheral surface of the steel pipe pile at intervals of 75 mm or less within a range of at least a distance 3D (D is the outer diameter of the steel pipe pile) from the vertical lower end of the steel pipe soil cement composite pile.

The first protrusion portion may be formed by welding a reinforcing bar to the outer peripheral surface of the steel pipe pile.

The steel pipe pile of the present invention is a steel pipe pile forming a steel pipe soil cement composite pile, and is provided with a plurality of first protrusions having a height of 15 mm or more formed on the outer peripheral surface of the steel pipe pile in the pile head region of the steel pipe soil cement composite pile, and a plurality of second protrusions formed on the outer peripheral surface at intervals of 75 mm or less within a range of at least a distance 3D (D is the outer diameter of the steel pipe pile) from the vertical lower end of the steel pipe soil cement composite pile.

The steel pipe of the present invention is a steel pipe for use in the pile head region of a steel pipe soil cement composite pile, and has a plurality of protrusions having a height of 15 mm or more formed on the outer surface of the steel pipe.

The construction method of the steel pipe soil cement composite pile according to the present invention is a construction method of the steel pipe soil cement composite pile including the steps of: creating a soil cement pillar in the ground that extends from the ground surface into the ground by injecting cement milk into the soil and mixing it with the in-situ soil; and placing a steel pipe pile in the soil cement pillar, wherein the step of placing the steel pipe pile includes the step of placing the steel pipe pile so that the height of the first protrusion formed on the outer peripheral surface of the steel pipe pile in the pile head region of the steel pipe soil cement composite pile is 15 mm or more, and the spacing of the second protrusions formed on the outer peripheral surface of the steel pipe pile is 75 mm or less within a range of at least a distance 3D (D is the outer diameter of the steel pipe pile) from the vertical lower end of the steel pipe soil cement composite pile.

According to the construction method of the steel pipe soil cement composite pile, steel pipe pile, steel pipe, and steel pipe soil cement composite pile of the present invention, a decrease in the vertical bearing capacity of the steel pipe soil cement composite pile can be suppressed even if horizontal displacement occurs in the steel pipe pile.

FIG. 1 is an axial cross-sectional view showing the configuration of a steel-pipe soil-cement composite pile according to one embodiment of the present invention. FIG. 2 is an axial cross-sectional view showing the configuration of a steel-pipe soil-cement composite pile according to one embodiment of the present invention. FIG. 3 is an axial cross-sectional view showing the configuration of a modified example of a steel-pipe soil-cement composite pile according to one embodiment of the present invention. FIG. 4 is an axial cross-sectional view showing the configuration of a modified example of a steel-pipe soil-cement composite pile according to one embodiment of the present invention. FIG. 5 is an axial cross-sectional view showing the configuration of a modified example of a steel-pipe soil-cement composite pile according to one embodiment of the present invention.

Below, with reference to the drawings, we will explain one embodiment of the present invention, a steel pipe soil cement composite pile.

〔composition〕
First, the configuration of a steel-pipe soil-cement composite pile according to one embodiment of the present invention will be described with reference to Figs. 1 and 2 .

As shown in FIG. 1(a), a steel pipe soil cement composite pile 1 according to one embodiment of the present invention comprises a soil cement column 2 and a steel pipe pile 3. In this embodiment, the steel pipe soil cement composite pile 1 extends from the ground surface to the supporting ground underground. In the following description, the pile diameter of the steel pipe soil cement composite pile 1 refers to the outer diameter of the soil cement column 2, and the pile length of the steel pipe soil cement composite pile 1 refers to the length from the upper end to the lower end of the steel pipe pile 3.

The soil cement column 2 is a structure constructed by injecting cement milk into the soil while stirring and mixing it with the in-situ soil, and extends from the ground surface into the ground. In this embodiment, the soil cement column 2 extends vertically.

The steel pipe pile 3 is placed in the center of the soil cement column 2 by pressing and/or sinking. In this embodiment, the steel pipe pile 3 is in the soil cement column 2 along the vertical direction. As shown in Figures 1(a) and (b), a plurality of protrusions 4 with a height H1 of 15 mm or more are formed on the outer circumferential surface of at least the pile head region R1 of the steel pipe pile 3. In this embodiment, the pile head region R1 means a region that is a distance of 1D or more (D: outer diameter of the steel pipe pile, hereinafter referred to as the steel pipe pile diameter) in the vertical direction from the vertical upper end of the steel pipe pile 3 (the ground surface in Figure 1(a)). The protrusions 4 function as the first protrusions according to the present invention. The protrusions 4 can also be formed in the case of a "slanted pile" that extends diagonally from the ground surface into the ground. In this case, however, the starting point of the pile head region R1 is on the pile axis of the steel pipe soil cement composite pile 1.

In general, horizontal displacement caused by factors such as earthquakes becomes larger the closer to the ground. For this reason, when horizontal displacement occurs, the risk of the vertical bearing capacity of the steel pipe soil cement composite pile decreasing due to separation of the soil cement column from the steel pipe pile increases the closer to the pile head. In addition, steel pipe soil cement composite piles are generally designed so that the horizontal displacement acting on the steel pipe soil cement composite pile is 1% or less of the diameter (pile diameter) of the steel pipe soil cement composite pile (however, 15 mm if the pile diameter is 1500 mm or less). Furthermore, the maximum displacement that occurs instantaneously in the steel pipe pile due to the inertial force when the displacement occurs returns to its original state somewhat due to the elastic behavior of the steel pipe pile, so the residual displacement after the displacement occurs is smaller than the maximum displacement.

Therefore, by forming a protrusion 4 with a height H1 of 15 mm or more on the outer circumferential surface of at least the pile head region R1 of the steel pipe pile 3, even if a 15 mm separation occurs between the soil cement column 2 and the steel pipe pile 3 at the ground surface, contact between the soil cement column 2 and the protrusion 4 is maintained below the ground surface. This makes it possible to prevent a decrease in the vertical bearing capacity of the steel pipe soil cement composite pile 1 even if horizontal displacement occurs.

This embodiment assumes a steel pipe pile diameter of 1500 mm or less, which is the normal application range of steel pipe soil cement composite piles, but can also be applied to steel pipe soil cement composite piles of larger diameter sizes. If the displacement amount of the steel pipe pile when displacement occurs and the residual displacement of the steel pipe pile after displacement can be accurately evaluated, the size of the pile head region R1 may be changed based on the evaluation results. There is no benefit to making the height of the protrusion 4 too high, and conversely, there is a risk that resistance will increase when placing the steel pipe pile 3 in the soil cement column 2, making construction difficult, etc., so it is recommended to make the height 5% or less of the steel pipe pile diameter D.

The fracture strength of the anchorage structure between the soil cement column 2 and the steel pipe pile 3 is determined by the lower of (a) the bearing fracture strength and (b) the shear strength shown below, so the balance between the height of the protrusions 4 and their arrangement spacing P1 (see Figure 1 (b)) is important. Although there are variations depending on the conditions, the bearing fracture strength of the soil cement column 2 is thought to be about five times its shear strength. For this reason, it is recommended that the height H1 of the protrusions 4 be no more than 1/5 of the arrangement spacing P1 of the protrusions 4.

(a) Bearing failure of the soil cement column 2 at the contact surface with the protrusion 4. The bearing failure strength can be evaluated by multiplying the height H1 of the protrusion 4 by the bearing failure strength of the soil cement column 2.
(b) Shear failure of the soil cement pillar 2. The shear failure strength can be evaluated by multiplying the arrangement spacing P1 of the protrusions 4 by the shear strength of the soil cement pillar 2.

The protrusions 4 are preferably formed in the circumferential direction of the steel pipe pile 3 so that the anchoring function between the soil cement column 2 and the steel pipe pile 3 works effectively, but they may also be formed in a spiral shape at an angle to the circumferential direction. The protrusions 4 may be formed by rolling the steel pipe in a factory, or by welding reinforcing bars or flat bars to the steel pipe. The protrusions 4 may also be formed by a weld bead.

As shown in Figures 2(a) and (b), a plurality of protrusions 5 are formed on the outer peripheral surface of the steel pipe pile 3 in a region (pile tip region R2) that is a distance 3D or more in the axial direction from the vertical lower end of the steel pipe soil cement composite pile 1, with an axial spacing P2 of 75 mm or less. The protrusions 5 function as second protrusions according to the present invention. Protrusions 5 can also be formed in the same manner in the case of "inclined piles," which are piles that extend obliquely from the ground surface into the ground. However, in this case, the starting point of the vertical lower end is on the pile axis of the steel pipe soil cement composite pile 1.

At the vertical lower end of a steel pipe soil cement composite pile located deep underground, horizontal displacement is slight, so there is no need to ensure a protrusion height to prevent separation between the soil cement column and the steel pipe pile. Meanwhile, the vertical lower end is embedded in a relatively solid ground called the support layer, but the ground that can become the support layer is often gravel ground mixed with sand and stones. For this reason, when stones, particularly large in diameter, get mixed in or get stuck between the protrusions arranged in multiple layers in the vertical direction, voids that are not sufficiently filled with soil cement can occur, and the vertical bearing capacity of the steel pipe soil cement composite pile 1 can be reduced.

In contrast, when the protrusions 5 on the outer circumferential surface of the steel pipe pile 3 have an axial spacing P2 of 75 mm or less, stones classified as 75 mm or more in particle size are mixed in or sandwiched between the protrusions 5 arranged in multiple vertical rows when the steel pipe pile 3 is embedded in the hard supporting ground. This makes it possible to prevent a decrease in the vertical bearing capacity of the steel pipe soil cement composite pile 1. Non-Patent Document 1 states that the standard embedment length of the steel pipe pile into the pile tip solidification part where the supporting layer is located is 1.5 D or more, but the actual supporting layer has a transition section at the boundary with the ground layer located above it. For this reason, in this embodiment, the spacing of the protrusions 5 within a range of at least a distance of 3 D from the vertical lower end of the steel pipe soil cement composite pile 1 is set to 75 mm or less.

The protrusion 5 is preferably formed in the circumferential direction of the steel pipe pile 3 so that the above-mentioned function can be effectively performed, but it may also be formed in a spiral shape at an angle to the circumferential direction. The protrusion 5 may be formed by rolling the steel pipe in a factory, or by welding reinforcing bars or flat bars to the steel pipe. The protrusion 5 may also be formed by a weld bead. In this embodiment, the case where there are no protrusions on the inner surface of the steel pipe pile 3 has been described, but the present invention is not limited to this. Depending on the specifications and performance of the steel pipe soil cement composite pile 1, appropriate protrusions may be provided on the inner surface of the steel pipe pile 3.

In this embodiment, the case of a "vertical pile" that extends vertically from the ground surface into the ground has been described, but the present invention is not limited to this. For example, a similar effect can be obtained in the case of an "inclined pile", which is a pile that extends diagonally from the ground surface into the ground. In the case of an inclined pile, resistance to external forces such as horizontal and/or vertical forces can be considered to be provided by two component forces, one perpendicular to the pile axis of the steel pipe soil cement composite pile 1 and the other in the pile axial direction. For this reason, the resistance conditions can be considered to be the same as those of a "vertical pile".

[Modifications]
Next, the configuration of a modified example of the steel-pipe soil-cement composite pile according to one embodiment of the present invention will be described with reference to Figs.

In general, the rate of increase in the horizontal displacement of the steel pipe pile 3 increases in the region from the pile head to a depth of about 1/β. β is a characteristic value of the steel pipe pile 3 calculated by the following formula (1). In formula (1), _kC is the lateral subgrade reaction coefficient, D is the outer diameter of the steel pipe pile, and El is the bending rigidity of the steel pipe pile. Therefore, as shown in Figure 3, the region from the pile head to a depth of about 1/β is set as the pile head region R1, and a protrusion 4 with a height H1 of 15 mm or more may be formed on the outer peripheral surface of this pile head region R1.

In general, the change in bending strain of the steel pipe pile 3 increases in the region from the pile head to a depth of about 3/β. Therefore, as shown in FIG. 4, the region from the pile head to a depth of about 3/β may be defined as the pile head region R1, and a protrusion 4 with a height H1 of 15 mm or more may be formed on the outer periphery of this pile head region R1. Normally, at a position deeper than the pile head region R1, the horizontal displacement and bending strain of the steel pipe pile 3 are low, so there is no need to make the height of the protrusion 15 mm or more. On the other hand, if a high protrusion is formed at a deep depth, there is a risk that resistance will increase when placing the steel pipe pile 3 in the soil cement column 2, making construction difficult, and so on, so the height of the protrusion should be 5 mm or less.

[Construction method]
Finally, a method for constructing a steel-pipe soil-cement composite pile according to one embodiment of the present invention will be described.

When constructing a steel pipe soil cement composite pile 1, which is one embodiment of the present invention, first, cement milk is injected into the soil while being stirred and mixed with the in-situ soil to create a soil cement column 2. Next, a steel pipe pile 3 having a protrusion 4 on its outer periphery is placed in the soil cement column 2. In actual steel pipe pile construction, since the length of a steel pipe pile that can be transported is limited, it is common to construct a steel pipe pile 3 by connecting multiple steel pipes vertically. Specifically, as shown in FIG. 5, the upper pile 3a, the middle pile 3b, and the lower pile 3c are connected vertically to construct the steel pipe pile 3. Therefore, in this case, a protrusion 4 having a height H1 of 15 mm or more is formed on the outer periphery of the upper pile 3a passing through the pile head region R1, and protrusions having a height of 2 mm to 5 mm are formed on the outer periphery of the middle pile 3b and the lower pile 3c (region R3). The upper pile 3a functions as a steel pipe according to the present invention.

Although the above describes an embodiment of the invention made by the present inventors, the present invention is not limited by the description and drawings that form part of the disclosure of the present invention according to this embodiment. In other words, other embodiments, examples, operational techniques, etc. made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

According to the present invention, it is possible to provide a construction method for steel pipe soil cement composite piles, steel pipe piles, steel pipes, and steel pipe soil cement composite piles that can suppress a decrease in the vertical bearing capacity of the steel pipe soil cement composite pile even if horizontal displacement occurs in the steel pipe pile.

1 Steel pipe soil cement composite pile 2 Soil cement column 3 Steel pipe pile 4, 5 Projection part

Claims (4)

A steel pipe soil cement composite pile comprising a soil cement column extending from the ground surface into the ground and a steel pipe pile within the soil cement column, the diameter of the soil cement column not changing in the extension direction,
A plurality of first protrusions having a height of 15 mm or more formed on the outer peripheral surface of the steel pipe pile in the pile head region of the steel pipe soil cement composite pile;
A plurality of second protrusions having a height of 2 mm to 5 mm formed on the outer peripheral surface of the steel pipe pile at intervals of 75 mm or less within a range of at least a distance 3D (D is the outer diameter of the steel pipe pile) from the vertical lower end of the steel pipe soil cement composite pile;
A steel pipe soil cement composite pile comprising: The steel pipe soil cement composite pile according to claim 1, wherein the first protrusion is formed by welding a reinforcing bar to the outer circumferential surface of the steel pipe pile. A steel pipe pile forming a steel pipe soil cement composite pile comprising a soil cement column extending from the ground surface into the ground and a steel pipe pile located within the soil cement column, the diameter of the soil cement column not changing in the extension direction,
A plurality of first protrusions having a height of 15 mm or more formed on the outer peripheral surface of the steel pipe pile in the pile head region of the steel pipe soil cement composite pile;
A plurality of second protrusions having a height of 2 mm to 5 mm formed on the outer peripheral surface at intervals of 75 mm or less within a range of at least a distance 3D (D is the outer diameter of the steel pipe pile) from the vertical lower end of the steel pipe soil cement composite pile;
A steel pipe pile comprising: A method for constructing a soil cement column extending from the ground surface into the ground by injecting cement milk into the soil and mixing it with the in-situ soil, and a method for constructing a steel pipe pile in the soil cement column, the diameter of the soil cement column not changing in the extension direction,
The step of placing the steel pipe pile includes a step of placing the steel pipe pile so that a height of a first protrusion formed on the outer peripheral surface of the steel pipe pile in the pile head region of the steel pipe soil cement composite pile is 15 mm or more, and a height of a second protrusion formed on the outer peripheral surface of the steel pipe pile is 2 mm or more and 5 mm or less, and the placement interval is 75 mm or less, within a range of at least a distance 3D (D is the outer diameter of the steel pipe pile) from the vertical lower end of the steel pipe soil cement composite pile.

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