JP5407266B2 - Friction pile - Google Patents

Description

  The present invention relates to a friction pile that penetrates as a core material into a columnar body such as soil cement or concrete used for a foundation portion that supports a structure such as a building.

  In soft ground, etc., friction piles such as steel pipe piles and concrete piles are used as the core material in the central part of soil cement and concrete pillars made by mixing cement milk and excavated sediment. A pile foundation with a composite pile structure that penetrates the pile may be used. FIG. 4 is a conceptual diagram showing this composite pile structure, where G is the ground, S is a columnar body, and P is a friction pile (core material). The head of the friction pile P is connected to the footing of the structure to receive a load, and the outer periphery of the columnar body S comes into contact with the surrounding ground G to support friction.

In this structure, it is important to integrate the core material and the columnar body. However, in Patent Document 1, an annular or spiral node is formed on the surface of the steel pipe as the core material, and the height of the node is 1.5. It is described that the ratio of the height of the nodes to the interval of ˜10 mm is 0.06 or less. Patent Document 2 describes that a steel pipe pile with blades provided with spiral blades in the lowermost end portion and near the pile head portion of the steel pipe and in the intermediate portion is inserted into the columnar body.
JP 2001-323459 A JP 2001-317050 A

In the case of a friction pile that penetrates into the columnar body of such improved ground, the bearing capacity of the entire composite pile including the columnar body is the frictional force between the ground and the columnar body, and the columnar body and core material (friction pile). It is the sum of the adhesion force between. No matter how firmly one is connected, if the other slips, total support cannot be obtained.
The bearing capacity of the pile is evaluated as a load value acting on the pile when a displacement occurs in the pile. In general, the allowable displacement of the pile is δa, and the vertical load W acting at that time is considered as the supporting force of the pile. The allowable displacement δa of the pile is generally set to a displacement corresponding to 10% of the pile diameter. For example, if the pile diameter is 1000 mm, the vertical load acting when the displacement is 100 mm (settlement) is the support force, and if the pile diameter is 100 mm, the vertical load when the pile displacement is 10 mm (settlement) is the support force. Therefore, as the pile diameter is smaller, it is necessary to develop a predetermined supporting force with a smaller amount of displacement, and the load to displacement performance necessary for the pile is defined by the pile diameter.

FIG. 5 is a schematic diagram showing a state in which a vertical load (hereinafter simply referred to as a load) W is applied to the friction pile (core material) P of FIG. If the relative displacement between the pile and the soil cement with respect to the load W shown in this figure is δ _PS , and the relative displacement between the soil cement and the ground with respect to the load W is also δ _SG ,
δ _PS + δ _SG ≦ δa (1)
Is satisfied, the load becomes W or more when the displacement (settlement amount) of the pile reaches δa.

FIG. 6 is a graph showing the previous equation (1), and the total displacement is the sum of the displacement between the pile and the soil cement and the displacement between the soil cement and the ground. What is necessary is just to determine the specifications of the protrusions so that the overall displacement is within the allowable displacement δa at the load W.
Displacement due to friction between the ground and the soil cement is mainly determined by the characteristics of the ground and is not related to the pile diameter, but the displacement characteristics between the soil cement and the pile vary depending on the strength of the soil cement and the specifications of the protrusions. It changes, and conversely, intentional control is possible.

If the pile diameter is large, the allowable value of the relative displacement between the soil cement and the pile is large, so the protrusion specification that gradually develops adhesive force may be used, but if the pile diameter is small, the relative displacement is acceptable. Since the value is small, it is necessary to have a projection specification that immediately increases the adhesion force.
An object of the present invention is to realize a small-diameter friction pile having a specification of a protrusion that immediately exhibits a large adhesion force from a small displacement stage.

The present invention relates to a small-diameter friction pile that penetrates into the center of a soil cement columnar body formed by excavating the ground into a columnar shape and stirring the excavated earth and cement milk before the columnar body is cured. The friction pile is characterized in that 2-4 linear protrusions are provided at equal intervals in the longitudinal direction on the surface of a pre-made pile made of a steel pipe having an outer diameter of 300 mm or less .

  According to the present invention, there is an excellent effect that it is possible to realize a small-diameter friction pile that develops adhesive force at an early stage.

  When providing projections on the surface of a ready-made pile, various methods can be considered depending on the mounting angle, that is, the angle between the projection and the horizontal plane. For example, in FIG. 1, (a) is when the attachment angle θ is 0, (c) is when θ is close to 90 degrees, and (b) is between these. Since the present invention attaches the protrusions in the vertical direction (axial direction), (c) corresponds to an example, and (a) and (b) are comparative examples.

FIG. 2 shows the results of a load test performed on two types (a) and (c) in FIG.
In the case of (c), the adhesive force can be expressed with the smallest displacement. On the other hand, in the case of (a), the adhesive force gradually appears with displacement. In the case of (a), if the distance between the protrusions is close, the amount of displacement that can develop the adhesive force can be reduced. In this pile diameter, it can be seen that (c) is satisfied with respect to the allowable displacement value corresponding to 10%, but (a) cannot be handled.

In particular, when the diameter of the ready-made pile is small, it is necessary to bend the material to a small diameter and weld it in order to attach the protrusion in a spiral shape. It is.
FIG. 3 shows a horizontal cross section of the friction pile of the embodiment. In this example, a steel pipe is used as a ready-made pile.
In the small diameter pipe with a diameter of 120 mm or less of the ready-made pile (steel pipe) shown in FIG. 4 items are arranged at equal intervals. The protrusion 2 is called a deformed steel bar having irregularities formed on the surface, and attachment is performed by tap welding alternately on the left and right sides at a predetermined length on both sides of the protrusion 2.

  The example of (a) when using steel pipes as ready-made piles is as follows. Steel pipe diameter is 76.3mm, protrusions are two deformed rebars called D16, tap welding is 60mm length, 920mm interval per steel pipe There are 6 places. In the example of (b), the steel pipe has a diameter of 139.8 mm, the protrusion has three deformed rebars called D16, the tap weld has a length of 60 mm, and there are six locations per steel pipe at intervals of 920 mm. In the example of (c), the steel pipe has a diameter. 267.4mm, the protrusions are four deformed bars called D25, tap welding is 80mm long, leg length is 15mm, there are 6 places per steel pipe at intervals of 920mm.

  In addition, as the ready-made piles of the core material, steel pipe piles, high-strength prestressed concrete piles (PHC piles), concrete piles with outer shell steel pipes (SC piles), ready-made concrete piles such as joint piles, etc. can be used. It is most desirable to use steel pipe piles from the viewpoint of achieving both high horizontal strength and economy.

It is a perspective view which shows the friction pile of the Example of this invention in contrast with a comparative example. It is a graph which shows the result of the load test of the friction pile shown in FIG. It is a horizontal sectional view of the friction pile of the Example of this invention. It is a conceptual diagram which shows the synthetic pile structure which concerns on this invention. It is a schematic diagram which shows the state which the load W acted on the friction pile P of FIG. It is a graph which shows the relationship between the load and displacement which were shown in FIG.

Explanation of symbols

1 Ready-made pile (steel pipe)
2 Protrusion G Ground P Friction pile (core material)
S soil cement (columnar body)

Claims (1)

It is a friction pile that penetrates the ground into a columnar shape and penetrates as a core material before the columnar body hardens at the center of the soil cement columnar body formed by stirring the excavated soil and cement milk. A friction pile, wherein the pile is provided with two to four linear protrusions in the longitudinal direction at equal intervals on the surface of a ready-made pile made of a steel pipe having an outer diameter of 300 mm or less .

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