JP4202548B2 - Pile foundation - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pile foundation, a pile foundation construction method, and a support pile.
[0002]
[Prior art]
In a wide land subsidence zone where the soft layer is thickly deposited, a negative downward frictional force acts on the pile due to the land subsidence of the soft ground, which may cause uneven settlement after construction. Therefore, as countermeasures, it has been necessary to deepen the penetration of the pile into the supporting ground existing under the soft ground to increase the supporting force and the positive frictional force at the tip of the pile, and the action of negative frictional force. Coal tar was applied to the upper part of the pile to be provided with a slip layer to reduce the negative frictional force acting on the pile.
[0003]
[Problems to be solved by the invention]
However, deepening the piles into the supporting ground has a problem that the construction is difficult. That is, during pile driving, a positive frictional force acts on the pile over its entire length, so it is difficult to deepen the pile into the support ground unless the pile driving is performed with a considerable force. Therefore, for example, construction is difficult with a small pile driver for a house.
[0004]
In addition, the provision of the slip layer raises the cost and has the problem of requiring labor for construction. For example, it is difficult to adopt this slip layer for a pile used for housing.
[0005]
In view of the conventional problems as described above, the present invention can deepen the support pile into the support ground with a small pile driving force, and slips the occurrence of the uneven settlement due to the ground subsidence of the soft ground. It is an object to provide a pile foundation having a structure that can be effectively and effectively prevented without providing a layer, a method for constructing the pile foundation, and a support pile.
[0006]
[Means for Solving the Problems]
The above problem is that, in a pile foundation that is driven so that the support pile reaches the support ground below it through the soft ground, this support pile is subjected to negative frictional force when subsidence occurs in the soft ground A pile foundation characterized in that the outer peripheral length dimension of the cross section of the length region portion is set smaller than the outer peripheral length dimension of the cross section of the length region portion under which the positive frictional force acts, and It is solved by the support pile.
[0007]
In this structure, even if a ground subsidence occurs in the soft ground and a negative friction force acts on the support pile, the outer peripheral length dimension of the cross section of the portion where the negative friction force acts is set small. Therefore, the contact area with the soft ground is small, so that the negative frictional force can be kept small. Therefore, even if the support pile is not deeply embedded in the support ground and the slip layer is not provided, the occurrence of the uneven settlement can be effectively and effectively prevented.
[0008]
Moreover, since the length region portion where the negative friction force acts is located above the length region portion where the positive friction force acts, the positive friction force acts in the process of driving the support pile. Although the driving friction force between the length region and the surrounding ground is large, the friction force between the length region where the negative friction force acts and the surrounding ground is very small. It can be deeply embedded in the support ground and can be constructed with a small pile driver. Accordingly, the fact that the depth of penetration can be increased in this way can also effectively and effectively prevent the occurrence of uneven settlement due to ground settlement of soft ground.
[0009]
Moreover, since the support pile has set the cross-sectional outer periphery length dimension of the part to which a negative frictional force acts small, it is possible to reduce the material cost of a pile.
[0010]
In the above pile foundation, the support pile is made of steel pipe pile, and when the ground subsidence occurs in the soft ground, the outer diameter of the length region where the negative frictional force acts is the positive frictional force below it When the structure is such that the steel pipe of the length region portion having a small outer diameter is set to be smaller than the outer diameter of the length region portion and the structural filler such as concrete is filled, The yield strength of the small length region can be increased. Accordingly, since the proof stress of the length region portion having a small outer diameter is increased by filling the filler as described above, the outer diameter of the length region portion having a small outer diameter can be further reduced, and the soft ground The negative frictional force due to the ground subsidence can be further reduced.
[0011]
By carrying out the above pile foundation construction by providing a drilling blade at the tip of the support pile and press-fitting while rotating the support pile, the support pile can be penetrated into the support layer with a small force. It becomes possible to deepen.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 shows a state at the time of placing a support pile, where 1 is a soft ground and 2 is a support ground therebelow. FIG. 1 (a) shows a case where the support pile 3 according to the embodiment is used, and FIG. 1 (b) shows a case where a conventional support pile 53 is used.
[0014]
FIG. 2 shows a state when ground subsidence occurs in the soft ground 1. FIG. 2 (a) is for a pile foundation 4 using the support pile 3 of the embodiment, and FIG. 2 (b) is for a pile foundation 54 using a conventional support pile 53.
[0015]
The support pile 3 of embodiment consists of a steel pipe pile, and is driven in via the soft ground 1 so that the support ground 2 under it may be reached. As shown in FIG. 2 (a), the support pile 3 has an outer diameter of a length region portion 5 on which a negative frictional force Rnf acts when a ground subsidence occurs in the soft ground 1, and a positive The upper and lower piles having different outer diameters are set to be smaller than the outer peripheral diameter of the length region portion 6 on which the frictional force Rf acts, with the large diameter steel pipe 6 as the lower pile and the small diameter steel pipe 5 as the upper pile. The materials 5 and 6 are connected to each other. A drilling blade 7 is attached to the tip of the large-diameter steel pipe 6 that is the lower pile. Although not shown, the small diameter steel pipe 5 is filled with a structural filler made of concrete, mortar, or the like, thereby ensuring the strength of the small diameter steel pipe 5.
[0016]
On the other hand, the conventional support pile 53 also consists of a steel pipe pile, and the outer diameter is the same over the entire length, and the outer diameter is the same as the outer diameter of the large-diameter steel pipe 6 in the support pile 3 of the embodiment. .
[0017]
As shown in FIG. 1 (a), in the support pile 3 of the embodiment, the outer peripheral surface of the large-diameter steel pipe portion 6 is in contact with the surrounding grounds 1 and 2 in the process of driving by rotary press-fitting, and the contact area thereof However, since the small-diameter steel pipe portion 5 enters the soft ground 1 away from the inner peripheral surface of the hole 8 dug by the large-diameter steel pipe portion 6, there is no contact with the surrounding ground 1 or , If any. Therefore, the positive frictional force Rf acting on the support pile 3 of the embodiment at the time of placing only acts mainly on the large-diameter steel pipe portion 6, so that the support pile 3 can be supported with a small pile driving force with the support ground. 2 can be deeply embedded. The excavating blade 7 makes the effect even greater.
[0018]
On the other hand, in the conventional support pile 53, as shown in FIG. 1 (b), in the process of placing, the outer peripheral surface is in contact with the surrounding grounds 1 and 2 over the entire length, and the contact area is It is so large that it cannot be compared with the support pile 3 in the form. For this reason, the positive frictional force Rf at the time of driving acts over the entire length of the support pile 53. Therefore, the support pile 53 must be driven with a large pile driving force. It is difficult to get deep into the supporting ground 2.
[0019]
Thus, according to the support pile 3 of embodiment, the penetration of the support pile 3 to the support ground 2 can be deepened with a small pile driving force.
[0020]
When ground subsidence occurs in the soft ground 1, as shown in FIG. 2 (a), the negative frictional force Rnf mainly acts on the outer peripheral surface of the small-diameter steel pipe 5, and the small-diameter steel pipe 5 has an outer diameter. Since the contact area with the surrounding ground 1 is small, the negative frictional force Rnf acting on the support pile 3 is small. Therefore, the occurrence of uneven settlement due to ground settlement in the soft ground 1 is prevented. Moreover, since the penetration depth to the support ground 2 can be increased as described above, it is possible to more effectively prevent the occurrence of uneven settlement. Furthermore, since the small diameter steel pipe portion 5 is filled with the structural filler, the portion is not buckled by the axial compressive force caused by the ground subsidence of the soft ground 1. In addition, P is a pile head load and Rp is the support force of a pile front-end | tip.
[0021]
On the other hand, in the conventional support pile 53, when the ground subsidence occurs in the soft ground 1, the contact area between the support pile 53 and the ground 1 in the soft ground 1 is very small as shown in FIG. Therefore, the negative frictional force Rnf acting on the support pile 53 is very large. For this reason, it is possible that the subsidence of the soft ground 1 due to subsidence occurs due to the action of the negative frictional force Rnf.
[0022]
Thus, according to the support pile 3 of the embodiment, even if the ground subsidence occurs in the soft ground 1, it is possible to effectively and effectively prevent the occurrence of the subsidence.
[0023]
As mentioned above, although embodiment of this invention was shown in the comparison with a prior art example, this invention is not limited to this, A various change is possible in the range which does not deviate from an invention thought. For example, the present invention is not limited to the case where the present invention is applied to a pile foundation 4 that is based directly on the support pile 3, and in addition, for the horizontal restoration of a non-settled building, a support pile is placed near the foundation, The present invention may be applied to a pile foundation structure for repair in which an eccentric load is applied to the support pile. By using the structure of the present invention for this horizontal restoration method, it is possible to drive the restoration support pile deeply with a small pile driver. Needless to say, the construction of the support pile of the present invention may be performed by a driving method other than the rotary press-fitting method.
[0024]
【The invention's effect】
As described above, since the present invention has the above-described configuration, it is possible to deepen the support pile into the support ground with a small pile driving force, and due to the ground subsidence of the soft ground. The occurrence of uneven settlement can be effectively and effectively prevented without providing a slip layer.
[Brief description of the drawings]
FIG. 1 shows a state at the time of placing a support pile, in which FIG. (A) is an embodiment and FIG. (B) is a sectional side view showing a conventional one.
FIG. 2 shows a state in which ground subsidence has occurred in soft ground. FIG. (A) is an embodiment and FIG. (B) is a sectional side view showing a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Soft ground 2 ... Support ground 3 ... Support pile 4 ... Pile foundation 5 ... Small diameter steel pipe (length area part where a negative frictional force acts)
6 ... Large diameter steel pipe (length area where positive frictional force acts)
7 ... Drilling blade

Claims (1)

When the ground subsidence occurs in the soft ground, the outer diameter of the length area where the negative friction force acts is set smaller than the outer diameter of the length area where the positive friction force acts A pile foundation formed by driving a support pile made of steel pipe piles into the support ground under the soft ground without slip layer and by pressing it in while rotating.
A pile foundation characterized in that a structural filler such as concrete is filled in a steel pipe in a length region portion having a small outer diameter.

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