Small-diameter steel pipe pile and support structure for building foundation

Abstract

To provide a small-diameter steel pipe pile and a building foundation support structure that can be efficiently constructed even on ground with underground obstacles and can exhibit high supporting force. 【Solution means】The small-diameter steel pipe pile includes a steel pipe body 10 formed by connecting a plurality of cylindrical single steel pipes 10a in the longitudinal direction, and a tip portion provided at the tip of the steel pipe body 10. The tip portion includes a tapered conical body 21 and a pile-shaped body 22 disposed inside the conical body 21 and protruding from the tip of the conical body 21. The pile-shaped body 22 has a columnar pile body and a penetration end that protrudes tapering from the tip of the pile body. The building foundation support structure includes a small-diameter steel pipe pile extending from a construction space provided under the foundation of the building to the support layer, a support base inserted between the head of the small-diameter steel pipe pile and the bottom surface of the foundation, and a backfill material filled in the construction space, and supports the load of the building through the small-diameter steel pipe pile and the support base.

Description

Technical Field

[0001] The present invention relates to a small-diameter steel pipe pile and a support structure for building foundations, and particularly to a small-diameter steel pipe pile and a support structure for building foundations that can be efficiently constructed even in a ground with underground obstacles and can exhibit high supporting force.

Background Art

[0002] When the building site is a soft ground or a reclaimed land with insufficient compaction, differential settlement may occur where the ground subsides unevenly and the building tilts. To repair the tilt of a differentially settled building, the sunken foundation is jacked up to level the building tilted due to differential settlement. There are various construction methods for these settlement repair methods, such as underpinning method, bearing plate method, point jack method, etc. Among these, the underpinning method is a method in which the ground under the foundation is excavated to provide a construction space, a reaction force is taken on the foundation, a small-diameter steel pipe pile is pressed into the ground with a hydraulic jack, the tip is made to reach the support layer, and this is used as a support pile to jack up the foundation to correct the settlement. After jacking up, a spacer is inserted between the head of the small-diameter steel pipe pile and the foundation, and the load of the building is supported by the tip supporting force and the circumferential friction force of the small-diameter steel pipe pile.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a reclaimed land or a constructed land such as a demolition site, there may be obstacles such as concrete slabs, stones, and large waste buried in the ground up to the support layer. When the tip of a small-diameter steel pipe pile hits these obstacles, the pressing-in is hindered and it becomes difficult to reach the support layer. In particular, since the underpinning method involves construction under the foundation of a building, it is not possible to conduct prior boring, and there are quite a few cases where the presence of obstacles is only grasped after the press-in of small-diameter steel pipe piles. In this case, during the construction process, since a reexamination of the press-in position and the construction method is required, there is a large setback, which may lead to construction delays and increased construction costs.

[0005] An object of the present invention is to provide a small-diameter steel pipe pile and a support structure for a building foundation for solving the above problems.

Means for Solving the Problems

[0006] The small-diameter steel pipe pile of the present invention includes a steel pipe body formed by connecting a plurality of cylindrical single steel pipes in the longitudinal direction, and a tip portion provided at the tip of the pile body, and the tip portion includes a tapered conical body and a pile-shaped body disposed inside the conical body and protruding from the tip of the conical body, and the pile-shaped body has a cylindrical pile body and a penetration end protruding taperingly from the tip of the pile body, which is characterized in that.

[0007] In the small-diameter steel pipe pile of the present invention, the taper angle of the conical body may be smaller than the tip angle of the penetration end.

[0008] In the small-diameter steel pipe pile of the present invention, the taper angle of the conical body may be larger than the tip angle of the penetration end.

[0009] In the small-diameter steel pipe pile of the present invention, the tip portion may be provided with a receiving plate that shields the inside of the conical body in the transverse direction, and the bottom surface of the receiving plate may be in contact with the head of the pile body.

[0010] In the small-diameter steel pipe pile of the present invention, the tip portion may be provided with a plurality of reinforcing ribs connecting the inner surface of the conical body and the outer surface of the pile body.

[0011] In the small-diameter steel pipe pile of the present invention, the pile-shaped body may be a chisel for an air hammer.

[0012] The support structure for the building foundation of the present invention comprises a small-diameter steel pipe pile extending from a construction space provided under the building foundation to a support layer, a support base inserted between the head of the small-diameter steel pipe pile and the bottom surface of the foundation, and a backfill material filled in the construction space, and is characterized in that the load of the building is supported through the small-diameter steel pipe pile and the support base.

Advantages of the Invention

[0013] The small-diameter steel pipe pile and the support structure for the building foundation of the present invention have at least one of the following effects compared with the above structure. <1>Since the tip portion has a configuration including a conical body and a pile body, even when there are obstacles such as concrete debris in the ground, the pile body penetrates into the obstacle first, and the conical body expands the penetration portion, so that the obstacle can be destroyed or penetrated (Fig. 5), and the risk of penetration inhibition by the obstacle can be reduced. As a result, in the underpinning method where prior boring is difficult, it is possible to prevent construction interruption and setback due to the presence of obstacles, and suppress the risk of construction period delay and cost increase. <2>The conical body with an inclined gradient advances while expanding the ground, so that it can be pressed into the ground with less force compared to a straight steel pipe. Therefore, the construction is easy and the construction efficiency is high. <3>A high vertical support force can be exerted in the support layer by the circumferential frictional force acting on the outer peripheral surface of the conical body. <4>In the case of cohesive soil, the taper angle of the conical body is designed to be large to mainly exert the compaction effect and circumferential frictional force on the surrounding soil of the conical body. In the case of a ground with a thick debris layer or sandy soil, the taper angle of the conical body is designed to be small to mainly exert the penetration force and tip support force of the pile body. Thus, by selecting the taper angle of the conical body and the length of the penetration end, an optimal support structure according to the ground conditions can be set.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

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Figure 7

Mode for Carrying Out the Invention

[0015] Hereinafter, with reference to the drawings, the small-diameter steel pipe pile and the support structure of the building foundation of the present invention will be described in detail. In the present invention, directional terms such as "upper", "lower", "head", "tip", "bottom", etc. mean the respective directions in a state where the head of the small-diameter steel pipe pile is upward and the tip is downward and penetrated into the ground.

Example

[0016] <1> Support structure of building foundation (Fig. 1) The support structure A of the building foundation (hereinafter simply referred to as "support structure A") is a support structure constructed by the underpinning method. The support structure A extends from the construction space D provided under the foundation B of the building to the support layer C, and includes at least a small-diameter steel pipe pile 1, a support base A1, and a backfill material A2. The head of the small-diameter steel pipe pile 1 is located within the construction space D of the building, and the tip is located within the support layer C. The support base A1 is interposed between the head of the small-diameter steel pipe pile 1 and the bottom surface of the foundation B. The backfill material A2 is filled within the construction space D. One feature of the support structure A of the present invention is that it has a structure capable of ensuring high support force performance by the circumferential frictional force of the conical body 21 provided at the tip of the small-diameter steel pipe pile 1.

[0017] <2> Small-diameter steel pipe pile (Fig. 2) The small-diameter steel pipe pile 1 is a member that supports the load of the building by the tip support force and the circumferential frictional force. The small-diameter steel pipe pile 1 includes at least a steel pipe body 10 and a tip portion 20 provided at the tip of the steel pipe body 10. The steel pipe body 10 is formed by connecting a plurality of cylindrical single steel pipes 10a in the longitudinal direction. Specifically, an annular joint member 10b is welded to the head of the single steel pipe 10a pressed into the ground, and the single steel pipe 10a is added to the upper part through the joint member 10b and welded to extend the length of the steel pipe body 10. In this example, a carbon steel pipe for general structure (JIS G 3444) is adopted as the single steel pipe 10a. The length of the single steel pipe 10a is arbitrary, but in relation to the height of the construction space D and the pressing operation by the jack F, it is preferably about 60 to 70 cm.

[0018] <3>Tip part (Figs. 3, 4) The tip part 20 is a structure provided at the tip of the steel pipe body 10. The tip part 20 is provided at the tip of the single steel pipe 10a that constitutes the foremost end of the steel pipe body 10, and includes at least a tapered conical body 21 and a pile-shaped body 22 protruding from the tip of the conical body 21. In this example, a receiving plate 23, a holding plate 24, and a plurality of reinforcing ribs 25 are further provided. In this example, about 1 / 3 of the tip of the pile-shaped body 22 protrudes toward the tip side of the conical body 21.

[0019] <3.1>Conical body (Figs. 3, 4) The conical body 21 is a structure having both a function of assisting the pressing into the ground and a supporting function within the support layer C. The conical body 21 has a conical hollow structure. In this example, the conical body 21 is composed of a combination of vertically divided semi-conical bodies. The two semi-conical bodies are combined and the joints are welded to form the conical body 21. The conical body 21 has its tip notched, and the pile-shaped body 22 is arranged inside, with the tip of the pile-shaped body 22 protruding from the tip of the conical body 21. The taper angle of the conical body 21 in this example is about 15°.

[0020] <3.2>Pile-shaped body (Figs. 3, 4) The pile-shaped body 22 is a protruding structure at the tip part 20. The pile body 22 includes at least a cylindrical pile main body 22a and a penetration end 22b that protrudes tapering from the tip of the pile main body 22a. In this example, further, a flange portion 22c that protrudes annularly is provided at a position about 1 / 5 of the total length from the head of the pile main body 22a. In this example, as the pile body 22, a steel chisel for an air hammer is adopted. The steel chisel has high penetration performance at the penetration end 22b, is an off-the-shelf product and thus is easy to obtain, and is easy to replace when damaged. The tip angle of the penetration end 22b in this example is about 20°.

[0021] <3.3>Receiving plate, holding plate, reinforcing rib (Figs. 3, 4) The receiving plate 23, the holding plate 24, and the plurality of reinforcing ribs 25 are internal reinforcing structures of the tip portion 20. The receiving plate 23 is made of a circular steel plate that shields the internal space of the conical body 21 in the transverse direction. The receiving plate 23 is fixed by full-circumference welding to the inner surface of the conical body 21. The receiving plate 23 supports the head of the pile main body 22a at the bottom surface within the conical body 21. A receiving hole 23a for fitting the head of the pile body 22 may be provided at the center of the receiving plate 23. The holding plate 24 is made of a circular steel plate that shields the internal space of the conical body 21 in the transverse direction. The holding plate 24 is fixed by full-circumference welding to the inner surface of the conical body 21. The holding plate 24 is provided with a holding hole 24a through which the pile main body 22a is inserted at the center, and supports the flange portion 22c of the pile main body 22a at the bottom surface near the holding hole 24a. The reinforcing rib 25 is disposed between the receiving plate 23 and the holding plate 24 in the internal space of the conical body 21, and is fixed by partial welding to the outer surface of the pile main body 22a and the inner surface of the conical body 21.

[0022] <3.4>Function of the tip portion (Fig. 5) In the small-diameter steel pipe pile 1 of the present invention, since the conical body 21 of the tip portion 20 has an inclination gradient, the press-in resistance into the ground is smaller than that of a straight steel pipe. Particularly in this example, since the taper angle (about 15°) of the conical body 21 is smaller than the tip angle (about 20°) of the penetration end 22b, the resistance by the conical surface of the conical body 21 is small and press-in is easy. Also, when the tip 20 contacts an obstacle E in the ground during press-fitting, the sharp penetration end 22b penetrates into the obstacle E, and the cone 21 further pushes open the penetration part, so that the obstacle E can be destroyed or penetrated to reach the support layer C. Therefore, it is particularly effective for ground with a thick gravel layer. Furthermore, after reaching the support layer C, the outer peripheral surface of the cone 21 exerts circumferential frictional force within the support layer C, so that a high vertical support force can be ensured.

[0023] <4>Support base (Figure 6) The support base A1 is a member that holds the height of the jacked-up foundation B. In this example, the support base A1 includes a top plate A11, a bottom plate A12, and four columns A13 connecting the top plate A11 and the bottom plate A12. By adopting a structure in which nuts are screwed onto the bolt bars of the columns A13, the distance between the top plate A11 and the bottom plate A12 after jacking up (the height of the support base A1) can be maintained. However, the support base A1 is not limited to the above. For example, a spacer may be inserted between the head of the small-diameter steel pipe pile 1 and the bottom surface of the foundation B after jacking up.

[0024] <5>Backfill material The backfill material A2 is a member filled in the construction space D. In this example, cement milk is adopted as the backfill material A2. However, it is not limited to cement milk, and it may be excavated soil, improved soil, fluidized treatment soil, gravel-crushed stone, mortar, concrete, or a combination thereof.

[0025] <6>Construction method The support structure A can be constructed, for example, by the following procedure. Excavate the ground directly below the foundation B of the building to form the construction space D. The size of the construction space D is arbitrary. For example, when a space with a width: depth: depth of about 1m×1m×1.5m is secured under the foundation, the working efficiency is high. Stand the single steel pipe 10a with the tip 20 on the bottom surface of the construction space D, insert a jack F between the head of the single steel pipe 10a and the bottom surface of the foundation B, and take the reaction force on the bottom surface of the foundation B to press it into the ground. Weld the joint member 10b to the head of the single steel pipe 10a that has been previously press-fitted, weld the tip of the subsequent single steel pipe 10a onto the joint member 10b, and then press it into the ground. Repeat the same operation to reach the tip portion 20 to the support layer C. After reaching the support layer C, install the support base A1 on the head of the small-diameter steel pipe pile 1, insert the jack F between the top plate A11 and the bottom plate A12, and push up the foundation B through the top plate A11. When the foundation B is pushed up to a predetermined height, tighten the nut of the support column A13 to fix the distance between the top plate A11 and the bottom plate A12, and remove the jack F from the support base A1. Finally, fill the backfill material A2 into the construction space D and backfill the construction space D together with the support base A1.

Example

[0026] [Example with a large taper angle of the cone] (Fig. 7) In this example, the taper angle of the cone 21 is made larger than that in Example 1. Specifically, the taper angle of the cone 21 is set to about 22°, which is designed to be larger than the tip angle (about 20°) of the penetration end 22b. In this example, since the length of the cone 21 becomes shorter, the pile body 22 is projected more toward the tip side than in Example 1, the head of the pile body 22a is supported by the bottom surface of the receiving plate 23, and the upper surface of the flange portion 22c is supported by the tip of the cone 21. In this example, the protruding length of the pile body 22 is about 4 / 5 on the tip side. In this example, since the taper angle (about 22°) of the cone 21 is larger than the tip angle (about 20°) of the penetration end 22b, the compacting effect by the outer peripheral surface of the cone 21 pushing the surrounding ground during press-fitting is high, and a high vertical supporting force can be ensured by the circumferential frictional force of the cone 21.

Explanation of symbols

[0027] 1 Small-diameter steel pipe pile 10 Steel pipe body 10a Single steel pipe 10b Joint member 20 Tip portion 21 Cone 22 Pile body 22a Pile main body 22b Penetration end 22c flange 23 receiving plate 23a receiving hole 24 retaining plate 24a retaining hole 25 reinforcing rib A support structure for building foundation A1 support base A11 top plate A12 bottom plate A13 support column A2 backfill material B foundation C support layer D construction space E obstacle

Claims

1. A steel pipe body formed by longitudinally connecting a plurality of cylindrical single steel pipes, and a tip portion provided at the tip of the steel pipe body, wherein the tip portion includes a tapered conical body and a pile-shaped body disposed inside the conical body and protruding from the tip of the conical body, and the pile-shaped body has a columnar pile body and a penetrating end that protrudes tapering from the tip of the pile body, Small-diameter steel pipe pile.

2. The small-diameter steel pipe pile according to claim 1, wherein the taper angle of the conical body is smaller than the tip angle of the penetrating end. The small-diameter steel pipe pile according to claim 1.

3. The small-diameter steel pipe pile according to claim 1, wherein the taper angle of the conical body is larger than the tip angle of the penetrating end. The small-diameter steel pipe pile according to claim 1.

4. The tip portion includes a receiving plate that shields the inside of the conical body in the transverse direction, and the bottom surface of the receiving plate abuts against the head of the pile body. The small-diameter steel pipe pile according to claim 2 or 3.

5. The tip portion includes a plurality of reinforcing ribs that connect the inner surface of the conical body and the outer surface of the pile body. The small-diameter steel pipe pile according to claim 4.

6. The small-diameter steel pipe pile according to claim 1, wherein the pile-shaped body is a chisel for an air hammer. The small-diameter steel pipe pile according to claim 1.

7. The small-diameter steel pipe pile according to claim 2 or 3, extending from a construction space provided under the foundation of a building to a support layer, a support base inserted between the head of the small-diameter steel pipe pile and the bottom surface of the foundation, and a backfill material filled in the construction space, characterized in that the load of the building is supported through the small-diameter steel pipe pile and the support base. Support structure for building foundation.

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