JPH0583684B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a soil-cement composite pile using a soil-cement method using steel pipe piles.

[Prior art] In the soil cement method, an auger or stirring rod mounted on a running vehicle is generally driven into the ground using electric power, etc., and while drilling, a cement-based hardener is poured from the center of the tip of the auger or stirring rod. An injection material such as cement milk is poured out, and a soil cement column is formed while being forcibly stirred with a stirring blade or the like. In addition, the support pile using the soil cement construction method is one in which the steel pipe pile is erected before the cement of the soil cement column hardens.

[Problems to be Solved by the Invention] The above-mentioned support piles have the following problems in terms of pile tip blockage, horizontal resistance, and frictional resistance.

(1) Problems related to pile tip blockage Since the adhesive force between the inner peripheral surface of the steel pipe pile tip and soil cement is mainly adhesive force, the relationship between the adhesive force and displacement is brittle as shown in Figure 5. If the stiffness of the soil cement is very small compared to the stiffness of the steel pipe, progressive fracture may occur. For this reason, steel pipe piles with large diameters (for example, diameters of 1000
mm or more) and the required adhesion force increases, the reliability of the occlusion effect decreases.

Furthermore, even if the adhesion between the inner circumferential surface of the steel pipe pile and the soil cement is strong, in order to obtain a complete blockage effect at the tip of the support pile, the ultimate resistance force F in the pipe must be equal to the ultimate bearing capacity of the ground at the tip. It is necessary to exceed Rp.

That is, F≧Rp Rp=A×q _d …[1] F=f×U×L …[2] However, A: Pile tip area A=π/4D ² q _d : Unit area supported by the pile tip Ultimate bearing capacity per unit area f: Adhesion force per unit area between the inner peripheral surface of the steel pipe and soil cement U: Pile circumference U = πD L: Required penetration length D: Pile diameter Here, the tip ground is gravel, and the N value A trial calculation in the case where is 50 or more shows that even if q _d ≧ 600 ton/m ² and soil cement strength q _u is guaranteed to be 100 Kg/cm ² or more, f is at most about 2 Kg/cm ² , and the conventional Accordingly, the required penetration length L to maintain the blocking effect is long, L≧7.5D, from formulas [1] and [2] above.

(2) Problems related to horizontal resistance Due to concerns about the integrity of the steel pipe pile and soil cement, only the shear resistance and bending strength of the steel pipe pile itself could be expected.

(3) Problems related to frictional resistance In designing the frictional resistance of steel pipe piles, the outer periphery of the steel pipe pile 3 with a diameter of Dp is used instead of the outer periphery of the soil cement column 1 with a diameter of Ds, as shown in Figure 7. ,
In addition, the circumferential surface friction force was determined using the value between the steel pipe pile 3 and the soft layer 5. That is, in the conventional cement construction method, the bearing capacity of the steel pipe pile 3 and the strength of the soil cement are not fully utilized in normal ground.

As mentioned above, the support piles made using the conventional soil cement method are positioned as simply one of the pile installation methods, and there is little interest in effectively utilizing the advantages of soil cement, such as its strength. I wasn't there.

The present invention aims to solve the above problems by improving the integrity of soil cement and steel pipe piles when constructing support piles using the soil cement construction method.

[Means for Solving the Problems] The soil cement composite pile of the present invention has a soil cement column formed in the ground and a steel pipe pile built into the soil cement column.
A plurality of protrusions with a height of mm are provided in a direction intersecting the pipe axis over almost the entire length of the outer peripheral surface of the steel pipe pile, and when the diameter of the steel pipe pile is Dp, from the tip of the steel pipe pile at least The inner peripheral surface of the steel pipe pile within a range of 0.5Dp, or at least from the tip of the steel pipe pile
A plurality of pipes are provided on the inner circumferential surface of the steel pipe pile in the range of 0.5Dp and on the inner circumferential surface of the head of the steel pipe pile in a direction intersecting the pipe axis.

[Function] According to the first invention, the peripheral surface friction force of the steel pipe pile increases, and the adhesion between the steel pipe pile and the soil cement on the inner circumferential surface of the pile tip is increased, thereby improving the blocking effect of the pile tip.

Moreover, in the second invention, in addition to the effect of the first invention, the adhesion force between the steel pipe pile and the soil cement on the inner circumferential surface of the pile head is sufficiently increased to strengthen the resistance against horizontal force.

[Example] Fig. 1a is a schematic diagram of an embodiment of the present invention, b is an enlarged view of part B, partially shown in cross section, and c is an enlarged view of part C. In the figure, 1 is a soil cement column formed in the ground, 3 is a steel pipe pile built inside this soil cement column 1, and the outer peripheral surface has b
As shown in part in the figure, a protrusion 4 is provided over almost the entire length, and also on the inner peripheral surface at the tip (in the example, within a range of 1.0 Dp from the tip) as shown in figure c. A protrusion 4a is provided. Note that 6 is a support layer.

FIG. 6 is a diagram schematically showing the adhesion properties of soil cement to a flat steel plate without ridges on the surface and a steel plate with ridges. As is clear from the figure, the adhesion of soil cement to the steel plate with ridges is not only strong, but also has extremely good toughness against displacement. On the other hand, the adhesion force between the flat steel plate and soil cement is small and, moreover, it is brittle.

Due to these characteristics, in steel pipe piles with flat inner and outer circumferential surfaces, fracture progresses progressively, so only the adhesion near the pile tip contributes to the blockage effect.
Therefore, reliability regarding the occlusion effect is low. On the other hand, in the support pile according to the present invention, as shown in FIG. 1, a protrusion 4 is provided over almost the entire length of the outer circumference of the steel pipe pile, and a protrusion 4a is also provided on the inner circumference at the tip. , the adhesion and toughness of soil cement are greatly improved, resulting in progressive fracture, so a complete occluding effect can be obtained.

Now, if soil cement strength q _u =100Kg/cm ² can be guaranteed, the adhesive force between the steel pipe pile 3 and the filling soil cement 2 according to the present invention will be increased by the adhesive strength f due to the provision of the ridges 4a. = 30Kg/cm ² is expected, and from equations [1] and [2] above, L≧0.5Dp, and the penetration length of only about 0.5Dp is required to maintain complete blockage of the tip of the steel pipe pile 3. In other words, it can be seen that it is sufficient to provide a protrusion on the inner circumferential surface of the tip of the steel pipe pile in a range of 0.5Dp or more.

FIG. 2a is a schematic diagram of an example in which protrusions are provided on almost the entire length of the outer circumferential surface of a steel pipe pile and on the inner circumferential surface of the head, FIG. 2b is an enlarged view of section A, and FIG. 2c is an enlarged view of section B. In this example, a protrusion 4 is provided over almost the entire length of the outer peripheral surface of the steel pipe pile 3, and a protrusion 4a is provided on the inner peripheral surface of the pile head (in the example, within a range of 4.0 Dp from the top). It is.

In this embodiment as described above, the adhesion force between the inner circumferential surface of the pile head of the steel pipe pile 3 and the filling soil cement 2 is sufficiently large, so that the soil cement 2 and the steel pipe pile 3 are subjected to horizontal force. When, we can resist as one. Therefore, the bending rigidity, bending strength, shear rigidity, and shear strength of the filled soil cement can be improved, so it is possible to obtain greater horizontal resistance than support piles made using the conventional soil cement construction method. FIG. 3a is a schematic diagram showing still another embodiment of the present invention;
d is an enlarged view of each section A, B, and C. In this embodiment, a protrusion 4 is provided over almost the entire length of the outer circumferential surface of the steel pipe pile 3, and protrusions 4a are provided on the inner circumferential surfaces of the head and tip of the pile, respectively.

In this example, the adhesion strength S ₂ between the soil cement 1 and the steel pipe pile 3 is set to be larger than S ₁ ×D _s /Dp with respect to the peripheral surface friction strength S ₁ between the soft layer and the soil cement 1. By selecting the composition and strength of soil cement ₁ in
There will be no slippage between the soil cement 1 and the steel pipe pile 3. That is, when determining the circumferential friction resistance of the steel pipe pile 3, the strength of the support pile was conventionally used as the outer circumference πDp of the steel pipe pile 3 as described above, but in the present invention, the outer circumference πDp of the steel pipe pile 3 was used as the strength of the support pile. Since the outer circumference πDs can be used, the friction resistance can be made larger than before (see Fig. 7).

The steel pipe pile according to the present invention is made by spirally winding a steel plate with ridges 4, 4a on both sides by hot rolling, welding the seams to form a cylinder with ridges on both sides, and forming a cylinder with ridges on one side. The steel plate provided with the protrusion 4 is the protrusion 4.
A cylinder is formed by welding a spirally wound seam on the outside, and a cylinder with protrusions on both sides is welded to the upper or lower part or upper and lower parts of this cylinder.
In the example, the height h of the protrusion 4 is set as shown in FIG.
2.5 mm or more, and the interval l was 40 mm or less (the fourth
(The figure shows a steel plate with ridges on one side.)

Here, the height h of the protrusion is set to 2.5 mm or more because
When the strength of the soil cement is guaranteed to be a certain value (for example, q _u = 100 Kg/cm ² ) at this ridge height, there is sufficient adhesion strength between the steel pipe pile 3 and the filling soil cement 2 (f = 30 Kg/cm 2 ). cm ² ) can be expected. However, since it is difficult to form a protrusion with a height exceeding 4 mm during rolling, it is actually desirable to have a height of about 4 mm at most.

In addition, the reason for setting the spacing between the protrusions to be 40 mm or less is that when the protrusions are provided by hot rolling, if the protrusions have a height of 2.5 mm to 4 mm and the spacing between the protrusions is 40 mm or less, it is sufficient in experiments. This is because a good adhesion strength was obtained.

It should be noted that the above-mentioned method for manufacturing the steel pipe, method for forming the protrusions, and shape, height, and spacing of the protrusions 4 are merely examples, and other manufacturing methods and forming methods may be used. The shape, height, interval, etc. of 4 are not limited to these.

[Effect of the invention] According to the first invention, the adhesion between the steel pipe pile and the soil cement column is increased, and the load acting on the steel pipe pile is
It is transmitted to the soil cement column via the external ridges of the steel pipe pile, and then to the surrounding ground. At the same time, the inner protrusion at the tip of the steel pipe pile improves the blocking effect.
Load bearing capacity can be set by soil cement column diameter. Therefore, it is possible to obtain a composite pile that makes full use of the bearing capacity of the steel pipe pile and the strength of the soil cement column, and also allows the steel pipe pile to be embedded in approximately half the diameter of the steel pipe pile.

According to the second invention, in addition to the effects of the first invention, the internal protrusions of the pile head improve the bending rigidity, bending strength, shear rigidity, and shear strength against horizontal forces, and the resistance force against horizontal forces is improved. Large synthetic piles can be obtained.

[Brief explanation of the drawing]

FIG. 1a is a schematic diagram showing the configuration of an embodiment of the present invention,
b and c are enlarged sectional views of parts B and C in Figure a, respectively; Figure 2 a is a schematic diagram of an example in which protrusions are provided on almost the entire length of the outer circumferential surface of a steel pipe pile and on the inner circumferential surface of the head; b, c is an enlarged sectional view of part A and part B of Fig. 3a, Fig. 3a is a schematic diagram of still another embodiment of the present invention, b, c, d
Figure 4 is an enlarged cross-sectional view of parts A, B, and C in Figure a, Figure 4 a is a developed view of a steel pipe pile with a ridge on one side, and b
is a bottom view, Figure 5 is a diagram showing the relationship between the adhesion force and displacement between the inner peripheral surface of the tip of the steel pipe pile and soil cement, and Figure 6 is the adhesion force between the flat steel plate, the steel plate with ridges, and soil cement. Fig. 7 is a schematic diagram showing the outline of a support pile using the soil cement construction method. 1...Soil cement column, 3...Steel pipe pile, 4,
4a... Projection.

Claims (1)

[Scope of Claims] 1. In a pile formed by forming a soil cement column on the ground and installing a steel pipe into the soil cement column, a protrusion with a height of at least 2.5 mm is provided along approximately the entire length of the outer peripheral surface of the steel pipe pile. A plurality of steel pipe piles are provided in the direction intersecting the pipe axis, and when the diameter of the steel pipe pile is Dp, at least 0.5Dp from the tip of the steel pipe pile.
A soil cement composite pile characterized in that a plurality of steel pipe piles are provided on the inner circumferential surface of the steel pipe pile in a direction intersecting the pipe axis. 2. In a pile formed by forming a soil cement column in the ground and erecting a steel pipe into the soil cement column, a protrusion with a height of at least 2.5 mm is connected to the pipe axis over almost the entire length of the outer circumferential surface of the steel pipe pile. A plurality of them are provided in the intersecting direction, and when the diameter of the steel pipe pile is Dp, at least 0.5Dp from the tip of the steel pipe pile.
A soil cement composite pile characterized in that a plurality of steel pipe piles are provided on the inner peripheral surface of the steel pipe pile in the range and on the inner peripheral surface of the head of the steel pipe pile in a direction intersecting the pipe axis.