JP3679197B2 - Screw for medium digging method - Google Patents

Description

ケース（１）〜（３）については、杭地上突出高さ２ｍとして施工した。いずれもトラブルを全く生ずることなく、正常に施工することができた。ケース（１）の施工タイムチャートを表１及び図１０に例示した。
【００２０】
ケース（４）については、施工の翌日油圧ショベルにて球根全部を掘り出し、地上において球根の外観、形状、寸法を観察記録した。所定形状寸法の球根が形成されていた。
【００２１】
【表１】

【００２２】
【発明の効果】
本発明によれば、スクリューのピッチと外径との比Ｐ／Ｄを適正に定め、複数条の羽根を備えたオーガースクリューを備えることによって、従来不可能であった杭外径３００〜４５０ｍｍの小径のコンクリート杭に中掘工法を適用することが可能となった。この場合にボイリング現象を生ずることは全くない。
【図面の簡単な説明】
【図１】実施例の正面図である。
【図２】図１のＡ−Ａ矢視断面図である。
【図３】実施例の正面図である。
【図４】図３のＢ−Ｂ矢視図である。
【図５】実施例の側面図である。
【図６】図５のＣ−Ｃ矢視図である。
【図７】従来例の正面図である。
【図８】図７のＥ−Ｅ矢視図である。
【図９】実施例を施工した地層柱状図である。
【図１０】実施例の施工タイムチャートである。
【符号の説明】
１ スクリュー
２ 羽根
３ 中心軸
４ 突起
５ 突起
６ ヘッド爪
７ ヘッド部
１０ フィッシュテール
１１ 先端
１２ 超硬チップ
１３ 空間部
１４ スクリュー羽根
１５ 捩れ部
２０ 空気弁
２１ ジェット噴射孔[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a medium excavation method in which a screw auger is inserted into a hollow portion of a precast concrete pile or a steel pipe pile, and the pile is built into the ground while excavating the ground, and is particularly used in an intermediate excavation method of a small diameter pile. It relates to a screw for excavation method.
[0002]
[Prior art]
Conventionally, the screw for the medium digging method used in the medium digging method is designed so that the screw diameter D and the pitch P are substantially equal in order to effectively discharge the soil by the principle of transporting the soil upward as a screw conveyor. ing. For this reason, in the case of the viscous soil adhering to the screw blades, spattering due to the adhesive force occurs, and even if compressed air is used as an auxiliary, the soil removal efficiency cannot be significantly reduced. In the case of small-diameter piles, it is necessary to reduce the rod diameter in order to obtain the height of the screw blades. However, in order to transmit excavation torque, there is a limit to the rod diameter. The construction method is limited to the application to a minimum pile outer diameter of 450 mm, and there has never been a medium digging method used for concrete piles with a pile outer diameter of 450 mm or less.
[0003]
In Japanese Examined Patent Publication No. 63-43533, an auger having an auger screw only at the tip portion is dug, and compressed air is blown above the auger, and the excavated earth and sand is made into a compacted plug shape and discharged in the pile. Technology is shown. There is a description of the purpose of preventing the auger torque from increasing in the technology. In plug-like transport that lifts excavated earth and sand into a compact plug without using a screw and lifts the inside of the pile, there is no blade, so the lower limit of the outer diameter of the pile that can be dug can be relaxed somewhat. It is believed that there is. However, the above publication has no suggestion about excavation of a small-diameter pile. On the other hand, the technique has a problem in that the so-called boiling development that brings in the surrounding ground more than necessary and causes ground subsidence cannot be prevented.
[0004]
[Problems to be solved by the invention]
The present invention was developed in order to solve the above-mentioned problems.
(A) To realize a small-diameter medium digging method such as a concrete pile having an outer diameter of 300 to 450 mm and a steel pipe pile having an outer diameter of 200 to 300 mm.
[0005]
(B) Do not cause a boiling phenomenon.
It is.
[0006]
[Means for Solving the Problems]
The present invention provides a screw for a medium digging method characterized in that a ratio P / D between a screw pitch P and a screw outer diameter D is 2 to 8, and a plurality of continuous screw blades that bear a twisting force are provided. It is to provide. Even if the screw has a small diameter, there are a plurality of screw blades, that is, two or more screws, and the screw blades are mounted symmetrically with respect to the shaft, and thus bear a twisting force. Therefore, the screw of the present invention has a large torsional resistance and enables construction of a small-diameter pile. In the concrete pile, when the outer diameter of the pile is 450 mm, the outer diameter of the screw needs to be 250 mm or less. The present invention makes it possible for the first time to apply the medium digging method to a concrete pile having an outer diameter of 450 mm or less by using such a small-diameter medium digging screw.
[0007]
Moreover, if the center axis of the screw is a double pipe, the above-described medium excavation method can be used, and a bulb can be formed at the tip of the pile by one step excavation, which is preferable.
Further, by combining a fishtail having a cemented carbide tip edge composed of a single sword or a plurality of swords and a screw coupling portion of the same pitch connected to the lower end of the screw with the above-mentioned screw for the digging method, It is possible to construct piles in the stratum.
[0008]
In addition, the screw of the present invention is suitable when the length of the head portion is 1.5 m or more. When a bulb is formed at the tip of the pile, the screw protrudes about 1 m below the lower end of the pile and is excavated. Since the screw of the present invention has a large P / D and a small diameter, the head portion is bent when the excavated ground is hard, gravel or cobblestone is present, or the formation is inclined. If stress is received, the joint portion of the head portion may be forced. Therefore, the length of the head portion is set to 1.5 m or more, preferably 2 m or more, and the joint portion is positioned in the pile under the severe conditions as described above, so that a large stress is not applied to the joint portion. It is preferable.
[0009]
When the ratio P / D between the screw pitch P and the screw outer diameter D is less than 2, it is difficult for the screw of the present invention to effectively raise the soil with a multi-thread screw and is not suitable as a small-diameter screw. When P / D exceeds 8, the pitch is too large, and soil removal becomes difficult. The number of screw blades is at least two so that the blades are strength members that bear the torsional strength. The number of screw blades can be three or four depending on the outer diameter of the screw and other conditions, which is more suitable in terms of improving the torsional strength of the shaft.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a screw for a pile digging method, and is particularly characterized in that the ratio P / D between the screw pitch P and the screw diameter D is set to 2 to 8, and the screw blades are wound in plural numbers.
In the present invention, first, the ratio P / D between the screw pitch P and the screw diameter D is set to 2 to 8, and the screw blades that enhance the conveying effect by compressed air while retaining the earth and sand conveying force upward as a screw conveyor. It is characterized by its use. As a result, even in the case of viscous soil, since the conveying force by the compressed air effectively acts on the adhesion force, the soil removal efficiency does not decrease even with a small-diameter pile. The second feature of the present invention is that a plurality of screw blades are wound. Even if the rod diameter is small, since the screw blades are wound around a plurality of strips, the blades can be used as strength members, and a torsional force can be borne. Therefore, it can be applied to small-diameter piles, and construction with the compressed air stopped is also possible. It is also possible to construct the medium excavation method while preventing boiling development. And this invention can implement | achieve the digging method of a small-diameter pile reliably which was impossible conventionally by the synergistic effect of the said characteristic technical means.
[0011]
Embodiments of the present invention will be described below with reference to the drawings.
First, a conventional large-diameter screw will be described with reference to FIGS. FIG. 7 is a front view of the auger screw 1, in which a blade 2 is attached in a swiveling manner around a central axis 3. The ratio P / D between the screw pitch P and the screw outer diameter D is approximately 1. That is, P and D are almost equal values. An auger head 7 having a head claw 6 is attached to the distal end side of the screw. As shown in FIG. 8, a cross section taken along the line E-E of the screw has only one screw blade 2 protruding outside the central shaft 3. In this structure, only the shaft bears the torsional force of the shaft 3, and the cross section of the blade 2 is unbalanced due to the shaft center being out of alignment with the torsion of the shaft 3, thereby reducing the torsional strength of the shaft.
[0012]
1-6 shows the screw 1 of the Example of this invention. 1 is a front view of the embodiment, FIG. 2 is a cross-sectional view taken along the line AA, FIG. 3 is a front view of the head, FIG. 4 is a view taken along the line BB, and FIG. FIG. 6 is a CC arrow view. The screw 1 of an Example has the 2 blade | wing 2 and the ratio P / D of the screw pitch P and the screw outer diameter D is 2-8. In FIG. 1, a P / D of about 4.8 is shown. As shown in FIG. 2, the cross section of the screw 1 has a shape in which the blades 2, 2 protrude from the central axis 3 at a position of 180 degrees in axial symmetry. Accordingly, the blades 2 and 2 increase the torsional rigidity of the shaft 3. That is, the blades 2 and 2 cooperate with the shaft 3 to transmit an effective torsional moment. Therefore, the screw 1 of the embodiment can transmit a large torque even when the shaft and the overall outer diameter are small, and enables a small-diameter pile digging method.
[0013]
3 and 5 show the head portion 7 of the embodiment. A single-sword fishtail 10 is attached to the tip of the head portion 7. FIG. 4 is a front view of the fishtail 10 as viewed in the direction of arrows BB in FIG. A carbide tip 12 is attached to the tip 11 of the fishtail 10. The fish tail 10 is attached to the main body of the head portion 7 with the same screw blade 14 to form a twisted portion 15, and a space portion 13 is provided at the center thereof. Such a fishtail 10 has a simple and strong cutting edge and is suitable for excavating hard rocks, and can construct a small-diameter pile on a hard formation. FIG. 6 is a view taken along the line CC of FIG. 5 and shows the connection structure of the head unit 7. The protrusion 4 is fitted in the hole of the screw, and the protrusion 5 transmits torque. The total length of the head part 7 is 1.5 m or more. In the example, it was 2 m. By increasing the length of the head part in this way, when building a bulb at the bottom of the pile, the head part is drilled about 1 meter downward from the tip of the pile. Even if it receives, the joint of a head part exists in a pile, and it can avoid that a local stress acts on a joint part.
[0014]
Furthermore, the head unit 7 includes an air valve 20 that blows out low-pressure air and a jet injection hole 21 that jets out high-pressure fluid. In order to send these low-pressure air and high-pressure fluid, the central shaft 3 of the screw 1 is a double pipe. The low-pressure air is used as a transport aid for the discharge of excavated soil. Used for injection.
[0015]
【Example】
Examples of the present invention will be described below.
A prestressed concrete pile having a small diameter of 350 mm and an outside diameter of 350 mm was set in the ground by a medium digging method using a special spiral auger for a small diameter having a diameter of 170 mm shown in FIG. After the completion of the installation, bulbs were continuously created on the bottom of the pile. The stratum of the construction site is as follows, as shown in FIG.
[0016]
From ground to 6m Silty clay N value = 0
From 6m to 18m Fine sand N value = Average about 25
From 18m to 26m Fine sand N value = average 48
The test was conducted on the following four cases.
(1) Pile outer diameter 350 mm x length 30 m, blade thickness 9 mm x length 100 mm
Draining with compressed air.
[0017]
Water injection to prevent boiling is not performed.
After completion of the installation, the bulbs were built and construction was completed.
(2) Pile outer diameter 350 mm x length 30 m, blade thickness 9 mm x length 100 mm
Ogre forward rotation. Draining with compressed air.
Water injection for preventing boiling is performed from 2 m before the support layer.
[0018]
(3) Pile outer diameter 350 mm x length 30 m, blade thickness 12 mm x length 100 mm
While reversing the auger, muddy water is jetted from the jet jet hole at the tip of the bit and mixed with the ground, making the ground mud and forcibly sinking the pile by pressure input with the pile's own weight and dredging as reaction force, Install.
(4) Pile outer diameter 350 mm x length 4 m, blade thickness 9 mm x length 100 mm
Construction of expanded bulbs and excavation confirmation of natural ground.
[0019]
Investigate whether the planned amount of root hardening used and the speed of fine movement lifting are appropriate.
For each case, bulbs were built under the following conditions.

Cases (1) to (3) were constructed with a pile ground protrusion height of 2 m. In both cases, the construction was successful without any trouble. The construction time chart of case (1) is illustrated in Table 1 and FIG.
[0020]
In case (4), the bulbs were all excavated with a hydraulic excavator the day after construction, and the appearance, shape and dimensions of the bulbs were observed and recorded on the ground. A bulb having a predetermined shape and dimension was formed.
[0021]
[Table 1]

[0022]
【The invention's effect】
According to the present invention, the ratio P / D of the pitch and the outer diameter of the screw is appropriately determined, and by providing the auger screw having a plurality of blades, the pile outer diameter of 300 to 450 mm, which has not been conventionally possible, is achieved. It has become possible to apply the medium excavation method to small diameter concrete piles. In this case, no boiling phenomenon occurs.
[Brief description of the drawings]
FIG. 1 is a front view of an embodiment.
FIG. 2 is a cross-sectional view taken along the line AA in FIG.
FIG. 3 is a front view of the embodiment.
4 is a view taken along arrow BB in FIG. 3;
FIG. 5 is a side view of the embodiment.
6 is a view taken along the line CC of FIG. 5;
FIG. 7 is a front view of a conventional example.
FIG. 8 is a view taken in the direction of arrows EE in FIG.
FIG. 9 is a geological column diagram in which an example was constructed.
FIG. 10 is a construction time chart of the example.
[Explanation of symbols]
1 screw 2 blade 3 central axis 4 protrusion 5 protrusion 6 head claw 7 head portion 10 fish tail 11 tip 12 carbide tip 13 space portion 14 blade blade 15 twist portion 20 air valve 21 jet injection hole

Claims (5)

A screw for a medium digging method having a ratio P / D between a screw pitch P and a screw outer diameter D of 2 to 8, and comprising a plurality of continuous screw blades that bear a twisting force . The screw for an underground digging method according to claim 1, wherein the outer diameter of the screw is 250 mm or less. 3. The screw for a medium digging method according to claim 1 or 2, wherein a central axis of the screw is a double pipe. The head portion is provided with a fish tail having a cemented carbide tip edge composed of a single sword or a plurality of swords, and a screw coupling portion of the same pitch connected to the lower end of the screw. 4. The screw for a medium digging method according to any one of 3 The length of a head part is 1.5 m or more, The screw for medium digging methods in any one of Claims 1-4 characterized by the above-mentioned.

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