JP5145995B2 - Synthetic friction pile - Google Patents

Description

  The present invention relates to a synthetic friction pile used for a foundation pile of soft ground.

  In soft ground, etc., a pile of steel pipes or concrete piles, etc. as the core material before the columnar body has hardened in the center of the columnar body such as soil cement or concrete made by mixing cement milk and excavated earth and sand. Synthetic friction piles are often used. FIG. 6 is a conceptual diagram showing this synthetic friction pile, wherein G is the ground, C is a soil cement (columnar body), and P is a core material (ready-made pile). In this structure, the head of the core P is connected to a footing of a structure (not shown) to receive a load, and the outer periphery of the columnar body C comes into contact with the surrounding ground G to be frictionally supported.

In the synthetic friction pile, adhesion between the core material and the columnar body, that is, integration is important. Patent Document 1 describes that a protrusion is formed by rolling on the surface of a steel pipe as a core material, or a protrusion is provided by welding a weld bead or a reinforcing bar.
In Patent Document 2, a ready-made pile used for a synthetic friction pile is a pre-made pile with blades having spiral or disk-like blades on the outer peripheral surface of the pile body, such as sandy soil, viscous soil, etc. It is described that a large frictional force is exerted between the blade and the ground by changing the distance between the blades in accordance with the ground soil quality. This will be briefly described with reference to FIG. In this example, the stratum changes in two layers, the shallow part G ₁ is a sandy soil layer, and the deep part G ₂ is a viscous soil layer. The core P is provided with blades 2 over its entire length, but the interval is changed between the mounting pitch L _S in the G ₁ layer and the mounting pitch L _C in the G ₂ layer, and the mounting pitch is dense in the G ₁ layer. by roughening the mounting pitch is G ₂ layers, and so as to exert a large frictional force with no waste between the corresponding formations.
Japanese Patent Laid-Open No. 62-268422 JP 2003-96771 A

  Protrusions by rolling or welding described in Patent Document 1 are considered to be uniformly formed at the same pitch over the entire length, and the technical idea of partially changing the shape and pitch cannot be read. Further, if high protrusions are formed by rolling or welding, it becomes extremely expensive, and it is considered that the limit is substantially at most about 4 mm. The blade described in Patent Document 2 is much larger than the protrusions in Patent Document 1 and has a large support pressure, and can effectively use the strength of the soil cement columnar body, but the overhang of the blade is large. A large bending moment is generated at the base of the blade, and the strength of both the pile body and the blade must be improved, resulting in extremely high manufacturing costs. In addition, in the case of a hard soil cement in which the mixing amount of cement milk is reduced, if hardening starts during construction, there is a problem that the penetration resistance increases and the capacity of the construction machine must be increased.

  The present invention is to attach a protrusion to the pile body instead of a high-cost blade, and effectively use the strength of the soil cement without increasing the cost by appropriately changing the size and pitch of the protrusion according to the formation, The purpose is to realize an economical synthetic friction pile.

The present invention excavates the ground into a columnar shape, and inserts a core material into the central portion of the soil cement columnar body formed by mixing and stirring the excavated earth and cement milk before the columnar body is cured, and these are integrated. In the synthetic friction pile that is designed to exert a peripheral frictional force, the core material is a core material with a mounting pitch S and a protrusion having a height h formed on the surface,
According to the peripheral frictional force between the soil cement and the ground, the protrusions are expressed by the following formula (1)
τs ≥ fs (1)
(Where τs: adhesion force between the core material and the soil cement, fs: peripheral friction force between the soil cement and the ground)
The adhesion force τ between the core material and the soil cement required to balance the peripheral frictional force fs between the soil cement and the ground and the adhesion force τs between the core material and the soil cement is calculated based on From the calculated required adhesion strength τ and the design strength qu of the soil cement, the following equation (2)
τ = β · qu (2)
(Where τ is the degree of adhesion between the core material and the soil cement, qu is the design strength of the soil cement)
Is used to calculate the necessary adhesion coefficient β, while the ratio S / h between the mounting pitch S and the height h is in the range of 40 to 140 and the adhesion coefficient β is in the range of 0.1 to 0.3. Using the relationship between the previously obtained S / h and the adhesion coefficient β, the S / h for the calculated required adhesion coefficient β is determined, and the determined S / h is determined. In order to satisfy, a synthetic friction pile characterized in that it is a projection formed by determining the mounting pitch S and the height h, and preferably a peripheral friction force is provided between the soil cement and the ground. The stratum where the peripheral friction force cannot be expected in the stratum where the peripheral friction force cannot be expected, the pitch of the protrusion attached to the core material is reduced or the protrusion is increased, and in the stratum where the peripheral friction force cannot be expected, the peripheral friction force can be expected. Increase the pitch of the protrusions attached to the core material compared to Said synthetic friction pile characterized by making low.

  According to the present invention, the state of the ground is previously investigated by boring or the like, and as a result, according to the performance of the peripheral friction obtained between the soil cement and the ground, the size and pitch of the protrusions attached to the pile body It is possible to effectively use the ground strength of the ground and to obtain a large supporting force at a low cost by changing the structure.

  The synthetic friction pile of the present invention is a synthetic friction pile characterized in that a projection is attached to the surface of the core material by changing the attachment pitch and height according to the friction performance between the soil cement and the ground. In the formation where the peripheral friction force can be expected between the soil cement and the ground, such as sandy soil layer or support layer, the pitch of the protrusions attached to the core material is reduced or the protrusions are increased, and the peripheral friction force cannot be expected. In the ground layer, for example, a cohesive soil layer, the pitch of the protrusions attached to the core material may be increased or the protrusions may be lowered. In extreme cases, the protrusions may not be provided.

FIG. 1 is a schematic view of a synthetic friction pile which is an embodiment of the present invention. P core material such as a steel tube, 1 a to 1 c are projections formed on its surface, C is soil cement, G ₁ ~G ₃ is ground, G ₁ is a layer that can be expected to skin friction, G ₂ is the circumferential surface layer frictional force can not be expected, G ₃ the support layer, or skin friction is a layer that can be expected.
The projections 1a to 1c are steel materials having a smaller size or a smaller cross section than the blades described in the prior art, such as round bars (bars), deformed reinforcing bars, flat bars, and angle bars. In order to increase the adhesive force, it is preferable that the surface has irregularities such as deformed reinforcing bars. The shape may be a ring shape or a spiral shape. Although the welding method is practical, it may be continuous welding or discontinuous welding. In addition, since the attachment of the protrusion is a simple operation, it is not always performed at the factory, and may be performed locally. In particular, even if it becomes clear at the time of construction that the stratum structure is different from the preliminary survey, it can be easily handled on site.

A layer that can be expected to have a peripheral frictional force, such as the ground G ₁ and G ₃ , is a layer having a large N value (for example, an N value of 5 or more), such as a sandy soil-based layer. On the contrary, the layer such as the ground G ₂ in which the peripheral frictional force cannot be expected is a layer having a relatively small N value (for example, less than N value 5), and generally means a clay soil layer. The pitch of the projections 1a and 1c attached to the core material P is smaller than that of the formation in which the peripheral friction force can be expected between the soil cement and the ground, that is, in the ground G ₁ and G _{3 where} the peripheral friction force cannot be expected. and increasing the protrusion, strata circumferential surface frictional force can not be expected, increasing the pitch of the projections 1b for mounting the core material P as compared to the formations in the ground G ₂ skin friction can be expected, also has lower protrusions.

As shown in the schematic diagram of FIG. 2, since the composite friction pile is one in which the core material P and the soil cement C are integrated to support the load, the core material P and the soil cement C are provided for each layer. Adhesive force τ _s ≧
Frictional force f _s between soil cement C and ground G (1)
It is necessary to satisfy this relationship.

  Fig. 3 shows a synthetic friction pile using a core material with a uniform projection over the entire length in the conventional technique, and the pitch and height of the projection (which are referred to as the "mode" of the projection) according to the formation. The states of the adhesion force τ and the frictional force f for each formation with the synthetic friction pile of the present invention that has been made are schematically shown. If the adhesion force τ and the frictional force f are the same, it can be said that the structure is a rational structure that takes advantage of the overall capacity of the synthetic friction pile, but in the conventional one, the protrusions are excessively attached and the adhesion force is wasted. I understand that. In the present invention, protrusions are provided in accordance with the maximum frictional force of the ground so that an adhesive force without waste is expressed. Thereby, the operation | work which attaches protrusion is also reduced.

In the conventional technique of providing a uniform protrusion over the entire length of the core material, when the diameter of the pile cement is made constant and the diameter of the soil cement is increased, the frictional force f _s between the soil cement C and the ground G is increased, and the above inequality However, in the present invention, it is possible to change both the height and pitch of the protrusions. Therefore, the above inequality is always satisfied by taking measures such as increasing the protrusions instead of reducing the pitch, and the desired support. You can gain power.

4A and 4B illustrate the adhesive force between the core material and the soil cement. FIG. 4A is a perspective view of the core material, FIG. 4B is a partial cross-sectional view (schematic diagram), P is the core material, and 1 is a protrusion. . S is the mounting pitch of the protrusion 1, h is the height of the protrusion 1, and the adhesion force can be organized by the relationship between the ratio of S and h, S / h, and the strength of the soil cement.
The adhesive force τ between the steel pipe as the core material and the soil cement is expressed as a linear equation: τ = β · q _u (2)
It can be expressed as. β is called an adhesion coefficient and is generally obtained by experiment. For example, in the steel pipe soil cement pile which is an existing pile construction method, a value of 0.4 is used as β. Further, q _u is the design strength (uniaxial compressive strength) of the soil cement, and is assumed to be, for example, 1.0 N / mm ² .

Now, the diameter of the steel pipe is 500 mm, and the diameter of the soil cement columnar body is 1000 mm. The frictional performance between the soil cement and the ground in the present invention, that is, the peripheral frictional force (kN / m ² ) is used as a parameter, and the peripheral frictional force (kN) per unit length (1 m) of the steel pipe is first determined. In the case where the equal sign is established in the equation (1), the necessary adhesion strength between the steel pipe and the soil cement (the above-mentioned τ described above) for the peripheral frictional force of the columnar body to be balanced with the peripheral frictional force of the steel pipe , KN / m ² ), and substituting it into the above equation (2) and dividing by q _u gives the value of β required in the present invention, not the actual measurement value.

  Table 1 shows the results of calculating these numerical values while varying the peripheral frictional force between the soil cement and the ground.

  On the other hand, when the relationship between the ratio of S and h, S / h, and the adhesion coefficient β is obtained by experiment, it becomes as shown in FIG. 5, and the adhesion force decreases as S / h increases. Therefore, it is only necessary to determine the S / h based on the obtained β and design the projection. In the example of Table 1, if β obtained is 0.4 or more, S / h is 1 to 40, 40 to 60 if 0.3 to 0.4, 60 to 100 if 0.2 to 0.3, and 0.1 to 0.2. Design protrusions with a guideline of 100 to 140, no protrusions if 0.1 or less.

Since there are infinite combinations of S / h, it is desirable to determine the size and pitch of the protrusions by comprehensively judging the material that can be secured, the processing cost, and the like.
In addition, although demonstrated by the example of the steel pipe as a core material above, the core material of this invention is not limited to a steel pipe. For example, it may be a ready-made pile of concrete pipe. In this case, it is possible to easily form protrusions on the surface by providing recesses in the mold when manufacturing by the centrifugal method, and it is possible to embed or wrap the steel sheet on which the protrusions are formed on the surface. Good.

The construction of the composite friction pile of the present invention includes a post-sinking method in which a core material is built after a soil cement columnar body is pre-constructed, and a simultaneous sedimentation method in which a core material is built at the same time as the soil cement columnar body is created. . When the pile length is relatively short, a post-sinking method that is easy to set up is suitable. When the pile length is long, a simultaneous sedimentation method that easily holds the core material vertically during construction is suitable.
As the soil cement of the peripheral surface portion, necessary cement milk is injected so that a predetermined strength can be exhibited, but generally a poor blending amount of cement is used. In addition, when rich blended cement milk is used, the specially mentioned pitch can be roughened, so that processing costs can be reduced.

  The tip support force is provided with protrusions on the inner surface and the outer surface of the core member, and exerts a large support force due to the bearing effect. The soil cement corresponding to the tip portion should be increased in strength as a rich blend of cement milk.

It is a schematic diagram of the synthetic | combination friction pile of this invention Example. It is a schematic diagram which shows the adhesive force and frictional force in this invention. It is a typical graph which shows the relationship between the prior art and the adhesive force and frictional force in this invention. It is the (a) perspective view and (b) partial sectional view of the core material concerning this invention. It is a graph which shows the relationship between the adhesion coefficient in this invention, and the aspect of a protrusion. It is a conceptual diagram which shows the synthetic | combination friction pile concerning this invention. It is a conceptual diagram of the synthetic friction pile which shows an example of the prior art.

Explanation of symbols

1 Protrusion 2 Feather C Soil cement G Ground P Core material (pile)

Claims (2)

The core material is penetrated into the central part of the soil cement columnar body formed by excavating the ground into a columnar shape and mixing and agitating the excavated soil and cement milk, and the columnar body does not harden. In synthetic friction piles that are designed to exert surface friction,
The core material is a core material on the surface of which a protrusion having a mounting pitch S and a height h is formed,
The protrusion,
According to the degree of circumferential friction force between the soil cement and the ground,
Based on the following formula (1), the core material and the soil cement, which are necessary for balancing the peripheral friction force fs between the soil cement and the ground and the adhesion force τs between the core material and the soil cement, Calculate the adhesion strength τ of
From the necessary adhesion strength τ obtained and the design strength qu of the soil cement, the necessary adhesion coefficient β is calculated using the relationship of the following formula (2):
On the other hand, the ratio S / h between the mounting pitch S and the height h is in the range of 40 to 140 and the adhesion coefficient β is in the range of 0.1 to 0.3 .
Using the relationship between the previously determined S / h and the adhesion coefficient β, the S / h for the calculated necessary adhesion coefficient β is determined,
A synthetic friction pile characterized in that the mounting pitch S and the height h are determined so as to satisfy the determined S / h.
Record
τs ≥ fs (1)
Where τs: adhesion between the core material and the soil cement,
fs: peripheral friction force between the soil cement and the ground
τ = β · qu (2)
Where τ: degree of adhesion between the core material and the soil cement,
qu: Design strength of soil cement   In the formation where the peripheral friction force can be expected between the soil cement and the ground, compared to the formation where the peripheral friction force cannot be expected, the pitch of the protrusion attached to the core material is reduced or the protrusion is increased, and the peripheral friction force is increased. The synthetic friction pile according to claim 1, wherein in a stratum that cannot be expected, the pitch of the protrusions attached to the core material is increased or the protrusions are lowered as compared with a stratum in which the peripheral friction force can be expected.

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