JP2007032044A - Supporting structure of foundation pile and steel pipe pile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a supporting structure of a foundation pile capable of ensuring the effective load transfer to a foot protection section from a pile body and to the bearing ground to exhibit high bearing power and having the excellence in workability at a low cost and a steel pipe pile. <P>SOLUTION: The supporting structure of the foundation pile is constituted of the steel pipe pile having a circular or a spiral projection 2 on the outer circumference of the front end section and the foot protection section 11 formed in a bearing layer in the ground or an area including the bearing layer, and it fulfills the following conditions. [p/h=8 to 15], [H≤S1+S2], [Dp×2≥Dg≥Dp+2×h]. Here, p is the pitch of the projection 2, H is the overall height of the foot protection section 11, Dp is the external diameter of the steel pipe pile 1, and Dg is the external diameter of the foot protection section 11. S1 is the anchorage length of the circumferential projection, S2 is the distance from the front end of the steel pipe pile to the bottom of the foot protection section, and it fulfills the following conditions. [1.75×Dg-2.45×Dp≤S1≤1.75×Dg-1.75×Dp], and [Dp×2≥S2≥(Dg-Dp)/(2×tanβ)]. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a tip support structure for a foundation pile used as a foundation of a structure and a steel pipe pile used therefor.

  The movement of increasing the bearing capacity and increasing the diameter of the embedded pile method (inner dig method, pre-boring method) using pre-made piles (pre-made concrete piles and steel pipe piles) is prosperous. Increasing the bearing capacity of foundation piles not only enables reduction of construction costs by reducing the required pile diameter and number of piles, but also leads to reduction of construction waste. In addition, the supporting force per pile has been increased due to the increase in diameter, and it has become possible to apply to structures that require a large supporting force that cannot be applied to conventional off-the-shelf piles.

  As the above-mentioned ready-made piles have higher bearing capacity and larger diameter, there is a problem in securing integration between the pile body and the root-solidified part built in the supporting ground and effective load transmission to the supporting ground. It has become.

  In other words, the tip of the pile prevents the root consolidation part from being destroyed during the load operation in order to ensure smooth load transmission from the pile body to the root consolidation part and from the root consolidation part to the supporting ground. Therefore, it is necessary to provide a support structure that can transmit a load to a wider range of grounds and exert a large support force.

  On the other hand, attention has been paid in the past to reliably close the tip of the pile body constructed at the open end. In other words, the pile body tip is created by providing multiple steps on the inner peripheral surface of the pile body part embedded in the root consolidation part and welding the reinforcing bars and flat steel, and integrating this with the hardened root consolidation part. The part is closed, and the load is transmitted to the root consolidation part with the pile body closed cross-sectional area.

  However, this method focuses on the load transmission from the cross-section of the tip of the pile body to the root consolidation part, and there is a limit to the yield strength, which may not be sufficient for recent high bearing capacity piles. Yes.

  In order to deal with such problems, the following inventions have been made.

  The one described in Patent Document 1 is a pile body that is embedded in the solidified part of the support layer of the ground in advance when post-embedding a prefabricated concrete pile or steel pipe pile (sinking the pile body in a previously excavated vertical hole) A protrusion is formed on the outer periphery of the tip portion region of the steel plate, and the protrusion is formed by locally expanding a predetermined portion of the tip portion of the steel pipe pile from the inside.

  In this invention, since the protrusion part for transmitting the load from a pile body is formed in a steel pipe outer periphery, by increasing the force transmitted to a ground from a pile body peripheral surface, a big supporting force is demonstrated. It is said that it can be made. However, there are the following problems.

  If the steel pipe is plastically deformed to locally expand the diameter, the steel pipe wall thickness of the expanded diameter portion becomes thin, and as if the steel pipe is locally buckled, the compression strength of the pile body is reduced. In addition, processing costs are required.

  5% to 35% of the pile diameter is recommended as the height of the protrusion, but it is necessary to increase the diameter of the hole by the amount of the protrusion in order to drop it into the hole that has been excavated in advance. Yes, the excavation volume and the amount of soil removal will increase.

  In addition, although the supporting force is increased by increasing the peripheral frictional force in the supporting ground by the projecting portion, the load transmission to the supporting ground is not performed directly with the pile body but via the rooting portion. Therefore, even if the integration of the pile body and the root-solidified part is strong, if the diameter of the root-solidified part is small, the root-solidified part will leave a margin in the proof stress of the integrated part of the protrusion part and the root-solidified part of the pile body The frictional force will be determined between the peripheral surface and the ground, and it is not sufficient to strengthen the integration of the pile body and the root-solidified portion in order to improve the tip support force.

  Furthermore, according to the study by the inventors, the tip support force of the root-solidifying pile is dominated by the reaction force from the ground at the bottom of the root-solidified part, and the contribution of the frictional force from the periphery of the root-solidified part is It turns out to be small. It is not efficient to increase the support force at the tip of the pile by the peripheral frictional force at the root hardening portion, and it is difficult to expect an effective improvement of the support force simply by providing a protrusion.

  Patent Document 2 also discloses a similar invention in which the integration of the root-solidified portion and the pile body is strengthened by welding the supporting protrusions to the inner and outer peripheral surfaces of the pile body tip. Costs are required due to the need for processing and welding work on steel.

  Furthermore, for the same reason as in the above-mentioned Patent Document 1, it is not sufficient to strengthen the integration of the pile body and the root consolidation part in order to improve the bearing capacity of the pile, depending on the shape and dimensions of the root consolidation. Unless a support projection is set, a rational structure cannot be constructed, for example, the proof strength of the pile body and the root-solidified part remains in the state of remaining power.

  Patent Documents 3 to 5 include a spiral wing in which a pile body provided with a spiral wing on the outer periphery of the tip portion is buried in the ground by simultaneous burying (front two) or rear burying (back one). The pile body tip is fixed to the rooting part.

  This also strengthens the integration of the pile body and root consolidation part, but since the load transmitted from the top of the pile body via the spiral wing is transmitted to the root consolidation part, a large load acts on the spiral wing. Will do. At this time, since a large stress is generated at the joint portion between the spiral blade and the pile body, a member having a large plate thickness is required, and there is a disadvantage that material costs, processing costs, and welding costs are increased.

  In order to obtain a large bearing capacity, it is necessary to increase the outer diameter of the spiral blade, and consequently the diameter of the rooting, but not only the trend of increasing material costs, processing costs and welding costs becomes more pronounced, but also the drilling diameter And the amount of soil removal increases, or the rotational torque required for construction increases.

  In Patent Document 6, in order to solve the above-described problem, a lower outer peripheral surface of a pile main body in a pre-auger hole substantially equal to the outer diameter of the pile main body and a lower pre-auger hole having a diameter larger than the spiral blade diameter and filled with soil cement. A composite structure of a ready-made pile and soil cement is disclosed, in which a ready-made pile having a plurality of spiral blades of approximately one rotation is installed, and the spiral blade is embedded in a lower pre-auger hole.

  According to the present invention, since the excavation is performed with the pile main body diameter until the root consolidation part is reached, the excavation volume of the ground, and thus the soil discharge volume, can be suppressed.

  However, a pile body having a plurality of spiral blades having an outer diameter larger than the hole diameter is embedded in a hole excavated in advance, so that depending on the ground, the hole wall may collapse and earth and sand may fall into the hole. Concerns that the pile body will remain high, or that the unstirred upper soft ground will be mixed in the soil cement of the root consolidation part, and the quality of the root consolidation part will deteriorate and the required yield strength will not be obtained Is done.

  In addition, the outer diameter of the spiral wing is recommended to be 1.5 to 3.0 times the pile diameter. However, since the wing width of the wing increases, the same as described in Patent Documents 3 to 5 above. It is necessary to use a material with a large plate thickness, which increases material costs, processing costs, and welding costs.

  In addition, the present invention also refers to the shape of the root solidified portion for obtaining the necessary supporting force, and the length of the root solidified portion may be about 3.0 times the blade diameter, and more than 5.0 times. It is enough. The diameter of the root hardening part is sufficient if it is about 1.5 times the blade diameter from the blade diameter depending on the hardness of the ground.

  However, if the outer diameter of the spiral blade is 1.5 to 3.0 times the pile diameter, the length and diameter of the root consolidation part will be very large compared to the diameter of the pile body. Many problems remain from the viewpoint of workability, such as the time required, the load when expanding the excavating blades, and the construction equipment becoming larger.

  There exists invention of patent document 7 as a policy which eliminates the fault at the time of using a spiral wing for the above-mentioned pile body tip. Prior to this invention, Patent Document 8 discloses a rotary penetrating steel pipe pile in which a spiral rib having a height of 20 mm or less made of a round bar or a square bar material is attached to the outer surface and inner surface of the pile tip portion over a predetermined length. However, because it is expected to transmit the load to the support ground at the cross-sectional area of the steel pipe, the supporting force is insufficient, or the steel pipe pile with a diameter of 600 mm or more also has a reduced tip clogging effect due to the soil in the pipe and the pile tip supporting force is insufficient. Therefore, the invention of Patent Document 7 has been made to solve this problem.

  This is because the stratum at the pile installation position is excavated in advance to a predetermined penetration depth, and the hardened material powder is injected in the vicinity of the planned insertion tip position, and then the rotary penetration steel pipe pile described in Patent Document 8 is inserted into the pile. It penetrates to the depth. As a result, when the pile tip reaches the vicinity of the hardened powder, the soil in the pipe and the surrounding soil and the hardened powder are mixed, and by mixing with the groundwater, a solid body of soil cement (hereinafter referred to as rooting part) is added to the tip of the pile. To form.

  The reason why the hardened powder is used is to avoid the fact that the use of cement milk that has been liquefied in advance causes the work site to become dirty and the working environment to deteriorate, and industrial waste to be generated during construction.

  However, the mixing of the hardened powder and the ground is limited only by the stirring and mixing action obtained at the time of the rotation penetration of the pile body, the size and strength of the root consolidation formed are uncertain, and the resulting pile tip Supporting power is also uncertain.

  Patent Document 9 and Patent Document 10 disclose an invention that is structurally similar to Patent Document 7 but aims to obtain a large support force in consideration of the shape and dimensions of the root-fixed portion. That is, a steel pipe pile provided with a projection having a height of 6 mm or more on the outer periphery of the tip and a support layer in the ground or a section including the support layer, and the tip of the steel pipe pile is inserted and integrated. It is characterized by having a solidified pillar. In the present invention, similarly to Patent Document 5 and Patent Document 6, since the agglomeration portion is mechanically enlarged and excavated using an auger head having an expansion / contraction mechanism, the size and strength of the root consolidation portion are more reliable. It becomes.

In this invention, the load transmitted from the upper part of the steel pipe by the protrusions on the outer periphery of the pile tip is dispersed and transmitted in the root consolidation, so that the root consolidation part is less likely to crack and a large support force is obtained. In order to ensure the dispersion effect, it is desirable to satisfy the following conditions.
Dt ＋2 ・ h ・ tanβ ≦ Dg
In addition,
Dt is the diameter of the tip of the pile including the protrusion,
h is the length from the uppermost protrusion embedded in the root consolidation pillar to the bottom of the root consolidation pillar ("h" in the above equation is different from "h" in the present application).

  Furthermore, in order to give a sufficient fixing force between the root hardening column and the steel pipe pile tip, and to effectively increase the tip support force, the insertion length S of the steel pipe tip to the root hardening column is increased. The thickness H is preferably 0.6 to 0.9 times.

  However, when the load is transmitted from the steel pipe to the supporting ground through the root consolidation part, if the load distribution range (Dt + 2 · h · tan β) is smaller than the root consolidation diameter Dg, the entire root consolidation bottom is used. In addition to not being able to effectively transmit the load to the supporting ground, the solidified portion outside the load transmission range becomes structurally unstable and may cause cracks and shear failure.

  Furthermore, if the distance (HS) from the steel pipe tip to the bottom of the root is smaller than the difference between the root diameter Dg and the steel pipe diameter Dp (Dg-Dp), the root is solidified against the compressive force from the cross section of the steel pipe. There is a risk that the part will cause punching shear failure and the supporting force will be reduced.

  Although it depends on the conditions of the pile diameter Dp and root consolidation diameter Dg, considering that the ground below the root consolidation bottom is not a rigid body and is a material that generates elastic and plastic deformation, the distance from the steel pipe tip to the root consolidation bottom ( H−S) must be secured to some extent, and strictly speaking, the sizes of S, Dg, and Dp are not defined independently, but should be determined comprehensively in relation to each other. .

  In addition, the height of the protrusion is preferably 10% or less of the pile diameter, but when the steel pipe with the protrusion close to 10% of the pile diameter attached to the outer periphery of the steel pipe rotates into the ground and penetrates The resistance is obviously larger than that of steel pipes without protrusions, which not only increases the load on construction equipment, but also disturbs the surrounding ground during penetration, reducing the peripheral frictional force, As in Patent Documents 3 to 5, a large load acts in the integration with the device, and thus the manufacturing cost may be increased. The protrusion height is preferably about 20 mm or less as described in Patent Document 8. .

JP 2000-045274 A Japanese Patent Publication No. 01-025848 JP 2000-291002 A Japanese Patent Laid-Open No. 05-230830 JP-A-60-238515 JP 2002-054135 A Japanese Patent Laid-Open No. 05-295731 Japanese Patent Laid-Open No. 01-094112 JP 2002-356847 A JP 2005-139900 A

  The present invention has been made in order to solve the above-described problems and incomplete portions of the prior art, and prevents the destruction of the root-solidified portion during the application of a load. A foundation pile support structure that is capable of exerting a large bearing capacity by ensuring effective load transmission from the compacted part to the support ground and transmitting the load to a wide range of ground, and that is inexpensive and has excellent workability. The steel pipe pile used for construction is provided.

  The support structure for a foundation pile according to the present invention is formed in a steel pipe pile provided with an annular or spiral projection on the outer periphery of the tip, and a support layer in the ground or a region including the support layer, and the tip of the steel pipe pile Is composed of a root-solidified portion that is inserted and integrated, and the root-solidified portion is defined by the following shape.

p / h = 8-15
H ≧ S1 + S2
Dp × 2 ≧ Dg ≧ Dp + 2 × h
here,
p is the protrusion pitch of the outer peripheral surface of the tip,
h is the height of the protrusion on the outer peripheral surface of the tip,
H is the total height of the root hardening part,
Dp is the outer diameter of the steel pipe pile,
Dg represents the outer diameter of the root hardening part,
S1 is the fixing length of the outer peripheral projection,
S2 represents the distance from the steel pipe pile tip to the bottom of the root portion and satisfies the following conditions.

1.75 · Dg−2.45 · Dp ≦ S1 ≦ 1.75 · Dg−1.75 · Dp
Dp × 2 ≧ S2 ≧ (Dg−Dp) / (2 · tan β)
here,
β represents the spread angle of the support load in the root-solidified portion.

  The reasons for limitation and the reasons for limitation of claim 2 and below will be described in the best mode for carrying out the invention to be described later together with specific analysis examples.

  According to a second aspect of the present invention, in the foundation pile support structure of the first aspect, an annular or helical projection is also provided on the inner periphery of the tip of the steel pipe pile.

According to a third aspect of the present invention, in the foundation pile support structure of the second aspect, the fixing length S3 of the protrusion provided on the inner periphery of the tip of the steel pipe pile is defined as follows.
0.3 ・ Dp ≦ S3 ≦ 1.5 ・ Dp

  Claim 4 is the support structure of the foundation piles according to claims 1 to 3, wherein the solidified liquid injected to constitute the solidified portion of the root-solidified portion is cement milk mixed with a fibrous tensile resistance material. It is characterized by.

  Steel fiber, carbon fiber, glass fiber, aramid fiber, etc. can be used as the tensile resistance material to be mixed.

  Claim 5 is the support structure of the foundation pile according to claims 1 to 4, wherein the solidification liquid injected to constitute the solidified body of the root-solidified portion is cement milk having a concentration of W / C <60%, and is viscous It is characterized in that admixtures (fluidizing material, water reducing material, AE water reducing agent, etc.) for reducing water content are mixed.

Claim 6 is a steel pipe pile for use in the support structure of the foundation pile according to claim 1, and is a steel pipe pile provided with an annular or spiral protrusion on the outer periphery of the tip part. The height h, the projection pitch p, and the range S1 in which the projections are installed are formed so as to satisfy the following relationship.
p / h = 8-15
1.75 · Dg−2.45 · Dp ≦ S1 ≦ 1.75 · Dg−1.75 · Dp

In the steel pipe pile according to claim 6, in the steel pipe pile according to claim 6, an annular or spiral protrusion is also provided on the inner periphery of the tip, and the protrusion on the inner periphery of the tip has a protrusion height h, a protrusion pitch p, and a range S3 in which the protrusion is installed. It is formed so as to satisfy the following relationship.
p / h = 8-15
0.3 · Dp ≤ S3 ≤ 1.5 · Dp

  An eighth aspect of the present invention is the steel pipe pile according to the sixth or seventh aspect, wherein the protrusion on the outer periphery of the tip and / or the protrusion on the inner periphery is formed by depositing a weld bead on the surface of the steel pipe.

  Claim 9 is the steel pipe pile according to claim 7 or 8, wherein the protrusions on the outer periphery and the inner periphery of the tip are formed in the same material, the same height, the same pitch, and in a spiral shape continuous in the same direction. It is characterized by this.

  According to the present invention, it is possible to prevent destruction of the root-solidified part during the load operation, and to ensure effective load transmission from the pile body to the root-solidified part, and further from the root-solidified part to the supporting ground, to a wide range of ground. A large supporting force can be exhibited by transmitting the load.

  The present invention is based on the idea that the shortage is compensated by the portion provided with the protrusion on the outer peripheral surface of the steel pipe in consideration of load transmission from the cross section of the steel pipe to the root hardening portion. Compared to the conventional structure described, the construction length is more economical because the embedding length of the steel pipe in the root-sealed portion and the processing range of the protrusions are reduced.

  Hereinafter, the best mode of the present invention will be specifically described based on analysis results and the like.

(1) Schematic structure and strength mechanism of root consolidation part Fig. 1 is a conceptual diagram of the schematic structure and strength mechanism of root consolidation part 11, filled with solidification liquid, the entire length, or at least deeper than the tip of steel pipe pile 1 Is a steel tube pile 1 in which a plurality of spiral or annular protrusions 2 and 3 are installed on the outer peripheral surface and the inner peripheral surface of the tip end portion in a root consolidation bulb constructed so as to be located in the support layer. Inserted so as to include the circumferential protrusions 2 and 3 and the adhesion force between the steel pipe outer peripheral protrusion 2 and the solidified body outside the steel pipe expressed after the solidification liquid is solidified, and the steel pipe inner peripheral protrusion 3 and the steel pipe The tip of the steel pipe pile is rooted and fixed in the bulb by utilizing both the adhesive strength between the solidified body and the solidified body.

  As shown in FIG. 2, the analysis was carried out by modeling only the solidified portion in the vicinity of the support layer and applying a downward equally distributed load corresponding to the soil covering pressure on the upper surface of the model. The steel pipe and root consolidation, and the root consolidation and ground were shared contacts (completely coupled). The strength of the tip ground assumes an N value of 60.

  The characteristics of the structure obtained from the results of the analysis conducted by the inventors are as follows.

A. The proof strength of the root consolidation part can be evaluated as (tip support pressure + outer periphery adhesion force), and the relationship between the tip support pressure and the outer periphery adhesion force is the same as the relationship between the tip support force of the pile and the peripheral friction force (Fig. 3). (See (a) and (b)).
Here, the tip support pressure is a load transmitted from the closed cross section of the steel pipe tip to the solidified solidified body, and the outer peripheral adhesion force is transmitted to the solidified solidified body by the adhesive force at the outer peripheral surface protrusion of the steel pipe tip. It is a load.

I. The load bearing capacity that can be shared by the tip support pressure is that the restraint pressure that acts on the root consolidation from the surrounding ground is constant, and the distance S2 from the steel pipe tip to the bottom of the root consolidation is secured to a certain value or more (details will be described later). It is almost constant regardless of the shape (diameter expansion rate Dg / Dp, height H) (see FIG. 4B). However, the assumption is that the inside of the steel pipe is completely closed by the protrusions on the inner peripheral surface of the steel pipe.

C. On the other hand, the size of the outer periphery adhesion changes depending on the fixing length (which is distinguished from the embedding length in the range where the protrusion is attached) to the root (see FIG. 4C). Accordingly, the proof stress can be adjusted by changing the fixing length (see FIG. 4A).

D. Furthermore, if the adhesion performance of the steel pipe outer peripheral projection is known in advance, it is possible to construct a support structure for the rooting portion having a required proof strength by adjusting the fixing length.

(2) Shape of root consolidation structure (shape of support structure at the tip of pile consisting of solidified solidified body and steel pipe)
By preventing the destruction of root consolidation during loading, ensuring effective load transmission from the pile body to the root consolidation, and further from the root consolidation to the supporting ground, and transmitting the load to a wide range of ground Identify a shape that can provide great support.

A. Prevention of punching shear fracture of root consolidation (necessary distance from steel pipe tip to root consolidation bottom)
In order to prevent cracking and punching shear fracture of the solidified root solidified body and to obtain a large supporting force by effectively transmitting the load to the supporting ground immediately below the bottom surface over the entire diameter Dg of the solidified base, The distance S2 from the steel tube tip to the bottom surface of the root is set so as to satisfy the following conditions.
Dp +2 ・ S2 ・ tanβ ≧ Dg
Also,
S2 ≦ 1.5 ・ Dp
Than,
Dp × 1.5 ≧ S2 ≧ (Dg−Dp) / (2 · tan β) (1)

  Formula (1) pays attention to the transmission of the compressive force from the steel pipe tip closed cross-section that is most critical for punching shear among the load transmission from the steel pipe to the root consolidation part (lower broken line in FIG. 6). S2 is set so that the broken line representing the spread of the load from the steel pipe tip crosses the root surface.

  In a type in which the height H of the conventional root hardening portion as shown in FIG. 5 is small and S2 is also small in relation to the embedding length, there is a high possibility of punching shear failure.

  In this regard, the present invention is based on the idea that the shortage is compensated by the adhesive force of the portion provided with the protrusion on the outer peripheral surface of the steel pipe after considering the load transmission from the steel pipe tip cross section to the root consolidation part. On the other hand, in the inventions described in Patent Document 9 and Patent Document 10, the idea of applying load transmission from the outer peripheral surface of the steel pipe rather than load transmission from the steel pipe front end section is taken, and as a result, the reverse limitation is performed. However, in the case of the present invention, since the processing range of the embedding part and the projection in the root-clamping part of the steel pipe is small, a more economical structure is obtained.

  In addition, (beta) represents the angle of the spread of a load, and is about 30 to 45 degrees normally according to analytical examination.

  According to the analytical study conducted by the inventors, the proof stress of the tip bearing increases as S2 increases, but eventually the proof stress converges to a certain value, and S2 increases. However, the proof stress is almost constant, and if it is limited to a solidified diameter expansion ratio Dg / Dp ≦ 2.0 (described later), the proof stress will reach its peak even if S2 = 1.5 · Dp or more. It is obtained (see FIG. 8 (a)).

  As proof data, the result of the analysis performed under the condition that there is no protrusion (no adhesion) on the outer peripheral surface of the steel pipe in the same model as FIG. 2 is shown below. FIG. 7 shows an analysis example in which S2 is changed under the condition of Dg / Dp = 2.0 and the tip ground N value of 60. FIG. 8 is a table summarizing the results of similar analysis performed by changing Dg / Dp.

  From FIG. 7A, it can be seen that the supporting force varies depending on the magnitude of S2. From FIG. 7 (b), in the case of S2 ≦ 1.0Dp where the reduction in support force is large, the displacement of the bottom surface of the root is uneven, and the amount of displacement differs greatly between the portion directly below the steel pipe and the outside thereof. As a result, punch shear fracture occurs. When punching shear failure occurs, the load cannot be transmitted to the supporting ground over the entire root consolidation diameter Dg, resulting in a decrease in supporting force.

  FIG. 8 is different in that the lowering of the supporting force is clarified by Dg / Dp. The required S2 depends on Dg and Dp. The larger the Dg / Dp, the larger the S2 / Dp that makes the reduction in bearing capacity clearer. This is because the larger the Dg / Dp, the greater the distance required to disperse the load throughout the root consolidation, which is consistent with the trend expressed by equation (1).

  Table 1 shows the minimum S2 determined by the equation (1) with β = 30 °.

  According to FIG. 8, it can be seen that the support force of 80% or more when S2 is sufficiently large can be obtained with S2 in Table 1.

  Furthermore, considering that the ground directly below the root is not a rigid body but an elastic / plastically deformed ground, the extra length should be taken into account in S2 according to equation (1) for reliable prevention of punching shear. Is more desirable. That is, it is desirable to set S2 ′ that satisfies Expression (1) ′.

S2 '= S2 + (Dg-Dp) / 2
Dp × 1.5 ≧ S2 ≧ (tan β + 1) · (Dg−Dp) / (2 · tan β) (1) ′
Table 2 shows the result of obtaining S2 ′ satisfying the expression (1) ′ with β = 30 °.

  If S2 'in Table 2, it can be seen from the comparison with FIG. 8 that a support force substantially equivalent to that when S2 is sufficiently large can be obtained.

I. Necessary fixing length within the root of the steel pipe tip (securing the required outer periphery adhesion)
As described above, the load bearing capacity that can be shared by the tip bearing pressure is constant if the restraining pressure that acts on the root consolidation from the surrounding ground is constant, and the distance S2 from the steel pipe tip to the bottom surface of the root consolidation is secured to a certain value or more (Details) As will be described later, it is almost constant regardless of the shape of root consolidation (diameter expansion rate Dg / Dp, height H) (see Fig. 4 (b)). The magnitude of the proof stress (the proof strength of the solidified solid body against the compressive proof force transmitted from the closed cross section at the tip of the steel pipe) is governed by the diameter of the steel pipe (λ × Ap × qu, λ : Coefficient, Ap: closed cross-sectional area of steel pipe, qu: uniaxial compressive strength of solidified body) results.

  On the other hand, even if the steel pipe diameter is the same, the bearing strength (necessary proof stress of the support structure of the root consolidation part) varies depending on the root consolidation diameter. Secure by fixing peripheral protrusions and roots. Since the required proof stress changes depending on the root diameter Dg, the required fixing length S1 also changes.

  Therefore, the adhesion length (fixing distance) S1 between the outer peripheral protrusion installation portion and the root consolidation portion has a required yield strength in consideration of the steel pipe diameter Dp and the ratio (Dg / Dp) of the root consolidation diameters Dg and Dp. Set as follows. That is, the fixing length S1 can be defined in the form of S1 / Dp = f (Dg / Dp), and FIG. 9 illustrates this relationship.

Strictly speaking, the relationship varies depending on the conditions of the protrusion (protrusion pitch p, protrusion height h, cross-sectional shape), solidified body strength of the root consolidation part, and the supporting force of the ground, but the inventor's previous experimental and analytical examination According to (3) below, the condition of the steel pipe outer peripheral projection, and the general solidified body strength (about 20 N / mm ² ) and the general supporting ground strength (N = 50-60) It has been confirmed that a support structure having a required proof stress can be constructed if it is approximately within the range shown in the figure.

The range of S1 shown in FIG. 9 is expressed by equation (2).
1.75 · Dg−2.45 · Dp ≦ S1 ≦ 1.75 · Dg−1.75 · Dp (2)

  As shown in FIG. 9, the required S1 differs depending on Dg / Dp, but if Dg / Dp ≦ 2, the range where the outer peripheral projection is provided is about 1.5 Dp from the steel pipe tip, and at most 2Dp. .

C. Necessary root consolidation height From the examination of a and b, the minimum necessary root consolidation height is H = S1 + S2.

  In consideration of the accuracy of construction, the embedding length S is set to S ≧ S1 and the rooting height H is set to satisfy H ≧ S1 + S2 so that the outer peripheral protrusion is securely embedded in the root consolidation. It is desirable.

  In consideration of the above a and b, in the range of 1.25 ≦ Dg / Dp ≦ 2.0, the necessary root-height height H is generally about 0.3 ≦ H ≦ 3.0 Dp. .

D. Upper limit value of diameter expansion ratio Dg / Dp From the formula (1) or (1) ′, the required S2 increases as Dg / Dp increases, and the required S1 also increases as Dg / Dp increases from FIG. Therefore, the necessary root-height height H tends to increase rapidly as Dg / Dp increases.

  On the other hand, in order to construct a rooted part by expanding excavation in solid support ground, the load on construction equipment increases. Therefore, if Dg / Dp is too large, the excavation speed will be extremely low for general construction equipment. If the Dg / Dp is large, the H is also large, so there is a concern that the construction efficiency is extremely lowered.

  Also, as Dg and H increase, the amount of excavated soil (volume) in the root consolidation part increases and the amount of solidification material (cement, etc.) required increases. A lot of time is required.

  Furthermore, when Dg / Dp is large and the necessary H is large, the layer thickness of the necessary supporting ground is also large, so that it may be impossible to apply depending on the ground conditions.

  Considering the time required for the construction and the load on construction equipment, the practical solidification height H is preferably about 2.0 to 3.0 Dp. Also, considering that the support layer thickness is required to be about 5 to 10 times as large as Dg (consolidation diameter = loading diameter), when Dg / Dp> 2.0, the thickness of the support layer> 10 Dp to 20 Dp, Applicable ground is limited.

  In view of the above, it is desirable that the root diameter expansion rate be Dg / Dp ≦ 2.0.

(3) About the projection conditions and adhesion performance of the steel pipe outer peripheral surface a. Adhesion performance due to protrusions on the outer periphery of the steel pipe Adhesion performance due to protrusions varies depending on the relationship between the protrusion height h and the protrusion pitch p, and it has been conventionally known that the fracture pattern changes at about p / h = 8-15. Yes.

  That is, if p / h is smaller than that, shear fracture that connects the tops of the protrusions occurs (see FIG. 10 (a)). If the adhesion area is constant, the yield strength is constant, and conversely, if p / h is larger than that, If the adhesion area is constant, the yield strength decreases as p / h increases.

Therefore, if the fixing length is the same, it is optimal to perform p / h = about 8-15. Moreover, if p / h is the range below it, adhesion performance will be represented by the following formula.
τout = βout · qu
here,
τout is the adhesion stress,
qu is the uniaxial strength of the solidified solidified body,
βout is a coefficient, and βout = 0.15 to 0.5 in the case where the protrusion and the mortar material adhere to the outer peripheral surface of the steel pipe.

I. Projection height, pitch, cross-sectional shape From the standpoint of constructing an optimum projection without waste, p / h = 8-15.

  Considering that the practical range of S1 is S1 ≦ 1.5 to 2.0Dp as described above, for example, when the projection height is 10% of the pile diameter Dp, the optimum projection interval is 0.8. It becomes ˜1.5 Dp, and the number of protrusions in S <b> 1 becomes 1 to 2 and stable adhesion performance cannot be obtained. If the number of steps is increased, a protrusion height of 0.1 Dp is unnecessary, that is, an efficient protrusion cannot be configured.

  Therefore, it is more rational to keep the protrusion height h at most several percent of the pile diameter and to secure at least three protrusion stages.

  In addition, if the height h of the protrusion is increased, the excavation diameter increases when the pile is buried, and the discharged soil increases, or the penetration resistance increases when the excavation diameter is about the steel pipe diameter. Arise. Furthermore, depending on the construction method, the ground near the pile may be disturbed, and the peripheral frictional force may be reduced.

Considering that the height of the conventional reinforcing plate and friction cutter attached to the tip of the steel pipe is about 9 to 15 mm, and that the projection height of the conventional steel pipe with external projection is about 2.5 to 5.0 mm. The conditions for obtaining reliable adhesion performance without causing deterioration in performance and peripheral surface friction performance are as follows.
Projection height h: 5.0 to 15.0 mm,
Protrusion pitch p: 40-200 mm,
Number of protrusions n: 3 steps or more

  Furthermore, considering the ease of manufacturing, the relationship between the rotational speed and the penetration speed when rotating and penetrating into the ground of the steel pipe, the projection height is about 10 mm, the projection pitch is about 100 mm, and the number of projection steps is within the required S1 range. It is most preferable to secure three or more stages.

  Further, the width B of the protrusion is desirably 0.5 times or more the height h. This is because the projection has sufficient shear strength against the force acting on the projection from the solidified solidified body, and a stress state close to a cantilever occurs in the projection, and the bending stress becomes dominant and the strength is increased. This is to avoid being disadvantaged.

  Considering the formation of protrusions by the weld bead later, the height h is high considering the heat input (heat effect on the steel pipe material that is the base material), penetration depth, and stability of the protrusion shape, as well as the above protrusion height. About 1.0 times or less is desirable.

  Finally, the cross-sectional shape of the protrusion may be any shape such as a rectangle, a trapezoid, a mountain, or a substantially triangle, but in order to ensure stable adhesion performance without causing slippage at the contact portion between the protrusion and the solidified solidified body, the protrusion It is necessary to set the angle of the side straight portion to 45 ° or more with respect to the steel pipe surface.

C. Protrusion manufacturing method As a method of forming the protrusion, bending a reinforcing bar or round steel, winding it around a steel pipe and fixing it by welding, or using a steel plate with a protrusion provided in advance by rolling into a steel pipe However, by forming the projections directly with the weld bead, material costs and bending costs for reinforcing bars and round steel can be omitted, and projections can be provided only for the required fixing length of the projections. Therefore, it can be processed inexpensively and in a short time, and becomes economical.

  When forming projections with weld beads, considering the heat input (heat effect on the steel pipe material that is the base material), penetration depth, and stability of the projection shape, etc., relative to the thickness of a general steel pipe pile The height of the protrusion that can be formed in one pass (one build-up) is about 5 to 10 mm, and the protrusion having the height of about 5 to 15 mm can be formed in one or two passes. Considering that the range S1 in which the protrusion is provided is a limited range of 1.5 to 2.0 Dp, it is preferable to form the protrusion with the weld bead under the current protrusion condition.

FIG. 11 shows an example of a projection by a weld bead. As an example of dimensions, in FIG. 11A, the projection height h = 8 to 12 mm, the projection effective height (up to the intersection with the 45 ° gradient tangent line) height) h _e = 6 mm or more, projections width b = 6 to 10 mm, in FIG. 11 (b), the can be given protrusion pitch p = 100 ± 10mm. Moreover, t = 9-28 mm can be mentioned as plate | board thickness of an applicable steel pipe.

D. The shape of the protrusion in the extending direction The protrusion is continuous with the spiral protrusion 2a (see FIG. 12 (a)), and the winding spiral protrusion 2b is intermittently spaced at multiple stages (see FIG. 12 (b)). Alternatively, a plurality of stages (see Fig. 12 (c)) can be considered with annular projections (ring-like projections 2c with one winding closed) spaced apart, but if the steel pipe is rotated and penetrated during construction, it is propelled by rotation. It is desirable to provide a continuous projection in a spiral because it has the function of obtaining a force and assisting in the excavation of the steel pipe.

(4) Protrusion on the inner peripheral surface of the steel pipe In order to secure the strength as a support structure for the root-clamping part, not only the outer peripheral protrusion but also the inner peripheral surface of the steel pipe is provided with a closed cross section to ensure the tip support pressure. Must be obtained. As described above, the tip bearing strength is almost constant depending on the steel pipe diameter, that is, the tip closing cross-sectional area Ap if the restraint pressure is constant. Accordingly, the conditions such as the height of the protrusions on the inner peripheral surface of the steel pipe and the required number of steps are determined by the diameter of the steel pipe, and it is necessary to set the tip bearing strength = λ × Ap × qu. Although the bearing coefficient λ depends on the restraint pressure, according to the experimental and analytical studies conducted by the inventors, the practical range as a pile is about 0.9 to 1.5.

A. Adhesion performance and protrusion installation range (fixing length S3)
Regarding the steel pipe inner periphery, the adhesion performance due to the projection is optimally set to p / h = 8 to 15 like the outer peripheral surface, and in the range below this,
τin = βin · qu
The adhesion performance can be expressed in the form of
here,
τin is the adhesion stress,
qu is the uniaxial compressive strength of the solidified solidified body,
βint is a coefficient, and βin = about 0.2 to 0.6 in the case of adhesion between the protrusions on the inner periphery of the steel pipe and the mortar material.

Therefore, if As is the adhesion area, As = Dp × S3 (S3 is the fixing length of the inner peripheral surface of the steel pipe),
λ × Ap × qu ≦ τin · As
Therefore, the fixing length S3 of the inner peripheral surface of the steel pipe is in the following range.
0.3 · Dp ≦ S3 ≦ 1.5 · Dp (3)

I. Protrusion height, pitch, and cross-sectional shape As for the inner peripheral surface of the steel pipe, in order to ensure the most efficient adhesion with the same fixing length, the protrusion height is preferably about 5 to 15 mm as in the outer periphery. .

  If the protrusions are too large, soil will adhere to the protrusions during construction, and the hollow part at the tip of the steel pipe will become smaller, hindering the embedding of the steel pipe, and there is a concern that sufficient adhesion will not be obtained due to the attached soil mass Is done. Further, considering the case of medium digging (simultaneous embedment with the excavation rod and excavation head inserted into the steel pipe), it is not preferable that the protrusion height is large in terms of workability.

  Protrusion conditions (height, width, pitch) can be the same as in the case of the outer peripheral surface of a steel pipe. By applying weld bead protrusions, protrusions can be formed reasonably and economically, with a predetermined adhesion. Yield strength (adhesive force for securing the end clogging in the steel pipe) is obtained, and a support structure for the solidified portion that is excellent in workability and peripheral surface friction performance can be configured.

C. The shape of the projection in the direction of extension The projection is continuous in a spiral shape, with multiple turns intermittently spaced by a single spiral, or multiple steps with annular projections (ring-like projections with one turn closed) spaced apart Although it is conceivable, when the steel pipe is rotated and penetrated, the soil taken into the steel pipe is smoothly raised upward, and the continuous spiral protrusion is passed so that the effect of preventing the clogging of the steel pipe tip by the excavated soil can be obtained. The effect of improving workability can be expected.

  At this time, if the inner and outer protrusions are continuous spiral protrusions in the same direction, the outer protrusions exert a driving force to penetrate the steel pipe into the ground by the rotation of the steel pipe, and the inner peripheral protrusions are taken into the steel pipe. Since it exhibits the function of smoothly raising the soil upward, it can be constructed with excellent workability. At this time, if the projection conditions of p / h = 8 to 15 and the projection height of 5 to 15 mm are selected for both the inner and outer peripheral surfaces, the projections of the same condition are formed in the same extension direction shape on the inner and outer peripheral surfaces. .

  By using the support structure of the foundation pile with the above configuration, it is possible to prevent destruction of the root-solidified part during load action, and to transmit effective load from the pile body to the root-solidified part and further from the root-solidified part to the supporting ground. By securing and transmitting the load to a wide range of ground, a large supporting force can be exhibited.

  Furthermore, as described above, the tip bearing strength from the tip section of the steel pipe and the outer adhesion force due to the protrusions attached to the outer peripheral surface of the steel pipe both increase in proportion to the strength qu of the solidified body constituting the root consolidation part. In consideration of the above, it is possible to further reduce the necessary fixing length S1 and the length S2 from the tip of the steel pipe to the bottom of the root consolidation by increasing the strength q u of the solidified root solidified body. Further, if S1 and S2 are the same, it is possible to increase the yield strength and to construct a support structure that is more stable and has a large margin.

  When the solidified liquid to be injected is cement milk, the strength qu of the root solidified part depends on its W / C (W and C are the weight of water to be mixed and the weight of cement, respectively). Later, it develops a large strength, but because the viscosity increases, the resistance that occurs when pumping cement milk deep into the ground increases, and the amount that can be injected decreases, or it is necessary to prepare a large pump There is a problem, and it is general that the W / C of cement milk is about 60% or more.

  In order to solve such a problem, the cement milk may be mixed with a cement milk by mixing a fluidizing agent, a water reducing agent, an AE water reducing agent or other admixture having a surface active action used in concrete. It is possible to reduce the increase in viscosity while improving the solidified body strength after curing by setting / C to a value smaller than 60% of the conventional value.

  As another method having the same effect, a solidified portion is also obtained by mixing and dispersing fibrous tensile reinforcing materials such as steel fibers (steel fibers), carbon fibers, glass fibers, and aramid fibers in cement milk. The strength of the solidified body can be improved.

  In particular, the adhesion due to the protrusion on the outer peripheral surface of the steel pipe tip portion causes a radial split crack spt as shown in FIG. 13, and this may determine the adhesion strength. Increasing the tensile strength and preventing splitting cracks are effective in reducing the required fixing length S1 or forming a support structure with higher yield strength.

(5) Example 1 of construction method of support structure
The steel pipe pile 1 provided with the protrusions 2 and 3 on the inner and outer peripheral surfaces is penetrated until the tip position reaches the vicinity of the upper surface of the support layer 21 in the ground or a predetermined depth in the support layer 21, It is a construction method of a rooted steel pipe pile in which the solidified portion 11 is constructed and the tip of the steel pipe pile 1 is inserted therein.

  The rod 25 with the auger head 26 attached to the tip is inserted into the steel pipe pile 1 and rotated while the diameter of the auger head 26 is less than the diameter of the steel pipe. The steel pipe pile 1 is rotated (using the propulsive force of the spiral protrusion 2 on the outer periphery of the steel pipe) and penetrates into the ground (see FIG. 14 (a)).

  In a state where at least the tip of the auger head 26 has reached a position included in the support layer 21, the auger head 26 is expanded to a root diameter for constructing the excavating diameter (see FIG. 14B).

  While excavating the ground for a predetermined length (H ≧ S1 + S2) so that at least the root of the root is located in the support layer 21, the solidified liquid 28 is discharged from the tip of the auger head 26 and stirred by the enlarged excavating blade. After mixing (see FIG. 14 (c)), the enlarged excavator blade is reduced again.

  The steel pipe pile 1 is left in a state where the tip end portion is inserted at least the fixing length S1 into the constructed root hardening portion 11, and the rod 25 in the steel pipe and the auger head 26 connected to the tip end portion are collected. (See FIG. 14 (d)).

  After a certain time has elapsed, if the solidified liquid 28 is cured, a predetermined support structure is constructed.

  When excavating the general part above the support layer 21, a steel pipe having a small outer peripheral projection 2 with a height of about 10 mm at the tip is rotated and penetrated in a state where the excavation diameter is less than the diameter of the steel pipe. By avoiding the disturbance of the ground to prevent the peripheral frictional force from decreasing and expanding only the necessary area of the root consolidation part 11 to construct a predetermined support structure, the amount of excavated soil can be reduced and the amount of soil removed can be reduced. Reduce.

  Moreover, by adopting a construction in which the rod 25 with the auger head 26 attached at the tip is inserted in the steel pipe, the hole wall can be prevented from collapsing, and the collapsed earth and sand can be prevented from being mixed in the root consolidation. Therefore, a more reliable support structure can be constructed.

  In the construction of the above support structure, when excavating the general portion above the support layer 21, a rod with an auger head attached to the tip is inserted into the steel pipe, and the excavation diameter by the auger head is greater than the diameter of the steel pipe. This is rotated in an enlarged state, and a solidified liquid such as cement milk is discharged from the tip of the auger head to excavate and agitate the ground, and the steel pipe pile is rotated (the propulsive force of the spiral protrusion on the outer periphery of the steel pipe is increased). It is possible to penetrate into the ground) and improve the peripheral friction force by improving the ground around the pile not only in the solidified part near the support layer but also in the general part above it. You can also.

  In the above construction method, when the tip of the steel pipe pile reaches the upper surface of the support layer in the ground or in the vicinity thereof, the depth of the steel pipe is fixed and only the auger head is excavated to increase the excavated diameter and After the construction is completed, if the steel pipe is inserted into the prescribed built-up root bulb for a predetermined length, the penetration resistance and rotation resistance of the steel pipe when penetrating into the support layer can be reduced. The load and construction time can be reduced.

(6) Example 2 of construction method of support structure
The steel pipe pile 1 provided with the protrusions 2 and 3 on the inner and outer peripheral surfaces is penetrated until the tip position reaches the vicinity of the upper surface of the support layer 21 in the ground or a predetermined depth in the support layer 21, It is a construction method of a rooted steel pipe pile in which the solidified portion 11 is constructed and the tip of the steel pipe pile 1 is inserted therein.

  A rod 25 having an auger head 26 having a digging diameter larger than the outer diameter of the steel pipe pile 1 (steel pipe diameter +100 to 400 mm) is rotated, and drilling fluid such as fresh water or bentonite mud from the tip of the auger head 26 as necessary. Alternatively, the ground is excavated while discharging the solidified liquid 27 such as cement milk (see FIG. 15A).

  In a state where at least the tip of the auger head 26 reaches a position included in the support layer 21, the auger head 26 is expanded to a root consolidation diameter for constructing the excavation diameter (see FIG. 15 (b)), and at least the root consolidation is performed. With the excavating blade expanded by discharging the solidified liquid 28 such as cement milk from the tip of the auger head 26 while expanding and excavating the ground by a predetermined length (H ≧ S1 + S2) so that the bottom surface is located in the support layer 21 After stirring and mixing (see FIG. 15 (c)), the expanded excavation blade is reduced again and collected (see FIG. 15 (d)).

  Next, before the solidified liquid 28 is hardened, the steel pipe pile 1 provided with the projections 2 and 3 on the inner and outer peripheral surfaces is sunk in the excavation hole (see FIG. 15 (e)), and the constructed root consolidation portion 11 is constructed. The steel pipe pile 1 is left in a state where the tip end portion is inserted at least the fixing length S1 (see FIG. 15 (f)).

  When the solidified liquid 28 is cured, a predetermined support structure is constructed.

  In the pre-boring type construction method, it is possible to set the steel pipe without rotating it, so that the outer peripheral projection 2 at the tip of the steel pipe pile 1 or the inner / outer peripheral projections 2 and 3 are not spiraled. An annular ring structure that is easy to manufacture can also be used.

  Moreover, since it is not necessary to penetrate into the ground while simultaneously rotating the rod 25 connected to the auger head 26 and the steel pipe pile 1, it is possible to simplify and downsize the construction equipment.

  It is suitable for ground conditions that can ensure the quality without breaking the hole wall and for relatively small pile length that allows the steel pipe pile 1 to be laid down in the time until the solidified liquid 28 is hardened.

It is a conceptual diagram of the schematic structure of a root-hardening part and a proof stress mechanism. It is an analysis model figure. The analysis result regarding the load-bearing mechanism of the root hardening part is shown, (a) is a load sharing diagram, (b) is an axial force diagram. Examples of analysis results regarding changes in yield strength due to differences in fixing length are shown. (A) is a graph for overall yield strength, (b) is a graph for tip bearing, and (c) is a graph for adhesion to the outer periphery. It is. It is a conceptual diagram of the punching shear fracture | rupture of the conventional root hardening part solidification body. It is a model figure of the shape of the root hardening part in this invention. An example of the analysis results regarding the difference in bearing capacity depending on the distance from the steel pipe tip to the rooting bottom is shown. (A) is a graph of the loading load-loading point displacement relationship, (b) is the displacement distribution of the rooting bottom. It is a graph of. It is a graph which shows the change of the bearing force by the distance from a steel pipe tip to a rooting bottom. It is a graph which shows the relationship between Dg / Dp and required fixing length S1. It is a conceptual diagram which shows the destruction pattern of a protrusion adhesion part. It is explanatory drawing which shows the example of the cross-sectional shape of the processus | protrusion by a welding bead. It is explanatory drawing of the example of how to wind protrusion. It is explanatory drawing of the radial split fracture | rupture of a root solidified part solidification body. It is a schematic diagram which shows the construction procedure in the medium digging type construction method. It is a schematic diagram which shows the construction procedure in the pre-boring type construction method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steel pipe pile, 2 ... Protrusion (outer periphery), 3 ... Protrusion (inner periphery), 11 ... Root hardening part, 21 ... Support layer, 25 ... Rod, 26 ... Auger head, 27 ... Solidification liquid (low concentration) 28 ... Solidified liquid

Claims (9)

A steel pipe pile provided with an annular or spiral projection on the outer periphery of the tip and a support layer in the ground or a region including the support layer, and a root formed by inserting and integrating the tip of the steel pipe pile A support structure for a foundation pile, comprising a solidified portion, wherein the root solidified portion is defined by the following shape.
p / h = 8-15
H ≧ S1 + S2
Dp × 2 ≧ Dg ≧ Dp + 2 × h
here,
p is the protrusion pitch of the outer peripheral surface of the tip,
h is the height of the protrusion on the outer peripheral surface of the tip,
H is the total height of the root hardening part,
Dp is the outer diameter of the steel pipe pile,
Dg represents the outer diameter of the root hardening part,
S1 is the fixing length of the outer peripheral projection,
S2 represents the distance from the steel pipe pile tip to the bottom of the root portion and satisfies the following conditions.
1.75 · Dg−2.45 · Dp ≦ S1 ≦ 1.75 · Dg−1.75 · Dp
Dp × 2 ≧ S2 ≧ (Dg−Dp) / (2 · tan β)
here,
β represents the spread angle of the support load in the root-solidified portion.   The support structure for a foundation pile according to claim 1, wherein an annular or spiral projection is provided on the inner periphery of the tip of the steel pipe pile. The support structure for a foundation pile according to claim 2, wherein the fixing length S3 of the protrusion provided on the inner periphery of the tip end portion of the steel pipe pile is defined as follows.
0.3 ・ Dp ≦ S3 ≦ 1.5 ・ Dp   The support structure for a foundation pile according to claim 1, 2 or 3, wherein the solidification liquid injected to constitute the solidified body of the root consolidation part is cement milk mixed with a fibrous tensile resistance material. .   The solidified liquid injected to constitute the solidified body of the root-solidified portion is cement milk having a concentration of W / C <60%, and is mixed with an admixture for reducing viscosity. Item 5. A support structure for a foundation pile according to claim 1, 2, 3 or 4. It is a steel pipe pile provided with an annular or spiral protrusion on the outer periphery of the tip part, and the protrusion on the outer peripheral surface of the tip part is such that the protrusion height h, the protrusion pitch p, and the range S1 where the protrusion is installed satisfy the following relationship: The steel pipe pile for using for the support structure of the foundation pile of Claim 1 currently formed.
p / h = 8-15
1.75 · Dg−2.45 · Dp ≦ S1 ≦ 1.75 · Dg−1.75 · Dp An annular or spiral protrusion is also provided on the inner periphery of the tip, and the protrusion on the inner periphery of the tip is formed so that the protrusion height h, the protrusion pitch p, and the area S3 where the protrusion is installed satisfy the following relationship: The steel pipe pile according to claim 6 characterized by things.
p / h = 8-15
0.3 · Dp ≤ S3 ≤ 1.5 · Dp   The steel pipe pile according to claim 6 or 7, wherein the protrusion on the outer periphery of the tip and / or the protrusion on the inner periphery is formed by depositing a weld bead on the surface of the steel pipe.   The steel pipe pile according to claim 7 or 8, wherein the protrusions on the outer periphery and the inner periphery of the tip end portion are formed in a spiral shape having the same material, the same height, the same pitch, and continuing in the same direction.

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