Hydraulic and earth engineering – Foundation – Columnar structure
Reexamination Certificate
1999-11-10
2002-05-28
Bagnell, David (Department: 3673)
Hydraulic and earth engineering
Foundation
Columnar structure
C405S253000, C405S249000, C405S231000
Reexamination Certificate
active
06394704
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to steel piles used for foundation of buildings and others. More particularly, the present invention relates to screwed steel piles-having blades for digging and also relates to a method of construction management therefor.
DESCRIPTION OF THE PRIOR ART
In the pile driving method or the pile displacing method, which is a conventional construction method for foundation piles used for construction of buildings and others, problems may be caused by noise and vibration generated in the process of construction. In order to solve the above problems, screwed steel piles have already been proposed. For example, Japanese Examined Patent Publication No. 2-62648 discloses a screwed steel pile characterized in that: an opening of a forward end portion of a steel pile body is closed by a bottom plate; a excavation blade is provided on the bottom plate so as to reduce a penetrative resistance of the pile; and a spiral wing is provided on an outer face of a lower end portion of the pile body. This screwed pile is buried in the soil in such a manner that soil and sand located at the forward end of the pile body is weakened by the excavation blade provided at the forward end of the pile body, and the pile is screwed into soil and sand, which has not been drilled yet, so that the wing can drill into the soil and sand.
However, the following problems may be encountered in the above screwed steel pile. The wing is arranged at an upper position of the bottom plate on the side of the pile body, and further the excavation blade and the wing are uncontinuously arranged with each other. Therefore, it is difficult for soil and sand, which is located at a position lower than the bottom plate, to be moved upward in the process of construction. Accordingly, it becomes difficult to generate a sufficiently high intensity of thrust. Especially when the soil at the bottom plate portion is hard and the soil close to the wing is soft, it very difficult for soil and sand to be moved to an upper portion of the wing.
In order to enhance the excavation effect, it is effective to provide a large size of blade on the bottom plate. However, the following problems may be encountered according to this structure. Although the efficiency of excavation can be enhanced, even if drilling of the pile is finished, the ground at the forward end of the pile is softened. Therefore, it is impossible to obtain an effectively high intensity of bearing capacity.
In order to solve the above problems, the following method is proposed. For example, according to Japanese Unexamined Patent Publication No. 8-226124, in the case of a steel pipe pile having a screw wing at the forward end, there are provided opening ribs for blocking soil and sand during penetrating the steel pipe pile, which are arranged inside the steel pipe pile at an upper position of the forward end of the steel pipe. That is, no conventional bottom plate is arranged at the lower end of the steel pipe pile. Accordingly, a penetrative resistance is low, and it is possible to penetrate the steel pipe pile by torque of low intensity. However, even if the above steel pipe pile is used, it is impossible to enhance the construction accuracy of the steel pipe pile. The reason why it is impossible to enhance the construction accuracy the steel pipe pile is that configurations of the spiral wing and the forward end portion of the steel pipe are not appropriate. Further, Japanese Unexamined Patent Publication No. 8-291518 discloses a steel pipe pile in which a plurality of rows of spiral wings are provided at a forward end of the outer circumferential portion of the steel pipe pile, and the interval, length and height of the spiral wing are specified, and further an incomplete wing is arranged at the lower end of the steel pipe pile. In this steel pipe pile, since this incomplete wing is attached to the side of the steel pipe, a projected area of the wing exceeds 360°, and the construction efficiency is deteriorated.
Japanese Unexamined Patent Publication No. 8-326053 discloses a steel pipe pile in which a forward end portion of the pipe pile body is spirally cut out along the outer circumference, and a spiral bottom plate, which is used as an excavation cutter, the diameter of which is approximately twice as large as that of the pile body, is fixed to a forward end face which has been cut out.
When this steel pipe pile is used, it is possible for the spiral bottom plate, which is also used as an excavation blade, to facilitate drilling and softening soil and sand at the forward end portion of the pile body, and even in the case of a pile body, the diameter of which is large, it can be easily rotated and advanced into the ground. However, essentially, the above steel pipe pile is a pile, the forward end portion of which is closed by the bottom plate. Therefore, in the process of construction, this steel pipe pile is given a high intensity of reaction force by the ground located in a portion close to the bottom plate.
For the purpose of reducing the penetrative resistance given to the forward end of the pipe so that the drilling torque can be reduced in the process of construction, the present inventors have already proposed a pile, the forward end of which is open, in Japanese Patent Application No. 9-314461. The present invention is accomplished as a variation of the above patent application. According to the present invention, the excavation efficiency can be remarkably enhanced, that is, the drilling torque can be remarkably reduced and the penetration efficiency of can be remarkably enhanced.
As shown in
FIG. 23
, according to the method of construction of this screwed steel pile, the screwed pile
1
includes a spiral wing
2
, which will be referred to as a wing hereinafter in this specification, arranged at a lower end portion of the pile
1
, wherein soil and sand is pushed in the direction of the side of the pile by the wing so that the pile can be given thrust.
In this connection, usually, a large number of piles are excavated into the ground. Therefore, in order to shorten the work period of pilling, it is important to enhance the efficiency of excavation of one pile.
According to the prior art described before, in the case where the strength of the ground
100
changes suddenly, the resistance given to the bottom plate
4
arranged at the lower end of the pile
1
exceeds a force of thrust generated by the wing. In this case, an amount of penetration of the pile is approximately not more than 5 mm. Therefore, a gap is formed under the lower face of the wing. When the above state continues, the wing is idly rotated, that is, it becomes impossible for the pile to generate a force of thrust. The aforementioned prior art has the above disadvantages.
In order to solve the above problem of the prior art in which it becomes impossible for the pile to generate a force of thrust, force F is given to the pile top as shown in
FIG. 23
so that the ground close to the bottom plate can be scraped off a little. In this way, the pile is rotated until a predetermined intensity of thrust can be obtained. When a capacity of a pile driver used for burying the pile is insufficient, it becomes necessary to replace the pile driver with another pile driver having a large capacity.
As described above, when the prior art is used for constructing the piles, it takes a long time, which causes a large loss.
A configuration of the excavation blade attached to the bottom plate portion has been improved, and also a configuration of the forward end portion of the wing has been improved. However, these configurations are determined according to the nature of the ground to be excavated so that the ground can be excavated effectively. Therefore, when the nature of the ground is changed, the excavated efficiency is greatly deteriorated. That is, it is difficult to replace the wing and the pile with the most appropriate ones according to the nature of the ground
100
.
In this connection, in order to build buildings and others stably on the ground, it
Ooki Hitoshi
Saeki Eiichiro
Takeda Tomoki
Bagnell David
Kenyon & Kenyon
Lagman Frederick L.
Nippon Steel Corporation
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