JP7107723B2 - Construction method of cast-in-place concrete pile and cast-in-place concrete pile - Google Patents

Construction method of cast-in-place concrete pile and cast-in-place concrete pile Download PDF

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JP7107723B2
JP7107723B2 JP2018075067A JP2018075067A JP7107723B2 JP 7107723 B2 JP7107723 B2 JP 7107723B2 JP 2018075067 A JP2018075067 A JP 2018075067A JP 2018075067 A JP2018075067 A JP 2018075067A JP 7107723 B2 JP7107723 B2 JP 7107723B2
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英之 眞野
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Shimizu Corp
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Description

本発明は、場所打ちコンクリート杭の構築方法及び場所打ちコンクリート杭に関する。 The present invention relates to a method for constructing a cast-in-place concrete pile and a cast-in-place concrete pile.

従来、超高層ビルなど重量の大きい建物では、杭基礎として場所打ちコンクリート拡底杭が多用されている。 Conventionally, cast-in-place concrete expanded-bottom piles are often used as pile foundations for heavy buildings such as skyscrapers.

場所打ちコンクリート拡底杭（場所打ちコンクリート杭）は、略一定の径の軸部と、軸部の先端部側を必要な支持力に合わせて拡底してなる略円錐台状の拡底部とを備えて構築され、杭先端部に拡底部を設けることで支持耐力を大幅に向上させることができる（例えば、特許文献１参照）。 A cast-in-place concrete expanded bottom pile (cast-in-place concrete pile) has a substantially constant diameter shaft and a substantially truncated cone-shaped expanded bottom formed by expanding the tip of the shaft according to the required bearing capacity. By providing an enlarged bottom portion at the tip of the pile, it is possible to greatly improve the bearing strength (see, for example, Patent Document 1).

場所打ちコンクリート拡底杭を構築する際には、例えば、掘削機を用いて地表面から略一定の径の掘削孔を所定の深度まで安定液を充填しつつ掘削形成する。次に、ロッドの先端に接続した拡底用掘削機（拡底バケットなどの拡底機）を挿入して掘削孔の先端部に配置した段階で、拡底用掘削機を拡張させつつロッドを中心軸周りに回転させて孔壁部分の地盤を掘削し、掘削孔の先端部を拡底する。そして、拡底した掘削孔に鉄筋籠を建て込むとともにトレミー管を用いて安定液と置換するようにコンクリートを打設し、必要に応じて杭頭部側を埋め戻したり、杭頭基礎を構築するなどし、場所打ちコンクリート拡底杭の施工が完了する。 When constructing a cast-in-place concrete expanded bottom pile, for example, an excavator is used to excavate and form an excavation hole having a substantially constant diameter from the ground surface to a predetermined depth while being filled with a stabilizing liquid. Next, at the stage where a bottom-enlarging excavator (bottom-enlarging machine such as a bottom-enlarging bucket) connected to the tip of the rod is inserted and placed at the tip of the excavation hole, the rod is rotated around the central axis while expanding the excavator for bottom-enlarging. Rotate to excavate the ground of the hole wall portion and widen the tip of the excavated hole. Then, a reinforcing bar cage is built into the expanded excavation hole, and concrete is poured using a tremie pipe to replace the stabilizing liquid, and if necessary, the pile head side is backfilled or the pile head foundation is constructed. And so on, the construction of the cast-in-place concrete expanded bottom pile is completed.

特許第２６０７９６６号公報Japanese Patent No. 2607966

ここで、上記のように構築される場所打ちコンクリート拡底杭１は、図６（ａ）に示すように、各種工法ごとにその大きさが異なるが、現状では軸径（軸部２の径）が最大約３ｍ、拡底径（拡底部３の径）が最大４．８ｍ～５．５ｍである。 Here, as shown in FIG. 6A, the cast-in-place concrete expanded bottom pile 1 constructed as described above has a different size for each construction method, but at present, the shaft diameter (the diameter of the shaft portion 2) is about 3 m at the maximum, and the diameter of the expanded bottom (the diameter of the expanded bottom portion 3) is 4.8 m to 5.5 m at the maximum.

一方、超高層ビルなど非常に大きな柱軸力を受ける杭では、最大拡底径でも支持力が不足する場合があり、支持力の不足を補うために、例えば図６（ｂ）に示すように、拡底部３を複数形成するなどの対策工法が提案、実用化されている。 On the other hand, in piles that receive a very large axial force of a column such as a skyscraper, the bearing capacity may be insufficient even with the maximum bottom expansion diameter. Countermeasures such as forming a plurality of enlarged bottom portions 3 have been proposed and put into practical use.

しかしながら、拡底部３を２つ以上形成する場合には、その分硬質な支持層Ｇ１を掘削して杭長を長くする必要があり、工費、工程に与える影響が非常に大きい。このため、より効率的且つ効果的に支持耐力を向上させることを可能にする手法が強く望まれている。 However, when two or more expanded bottom portions 3 are formed, it is necessary to excavate the hard support layer G1 to increase the pile length, which greatly affects the construction cost and the process. For this reason, there is a strong demand for a technique that enables more efficient and effective improvement of supporting strength.

上記事情に鑑み、本発明は、従来と比較し、より効率的且つ効果的に支持耐力を向上させることが可能な場所打ちコンクリート杭の構築方法及び場所打ちコンクリート杭を提供することを目的とする。 In view of the above circumstances, it is an object of the present invention to provide a method for constructing a cast-in-place concrete pile and a cast-in-place concrete pile that can improve the bearing capacity more efficiently and effectively than conventional methods. .

上記の目的を達するために、この発明は以下の手段を提供している。 In order to achieve the above objects, the present invention provides the following means.

本発明の場所打ちコンクリート杭の構築方法は、円柱状の軸部と、該軸部の先端部を拡張してなる拡底部を備えた場所打ちコンクリート杭を構築する方法であって、杭用の掘削機を用いて地盤の所定の深度まで前記軸部の掘削孔を先行掘削して形成し、前記軸部の掘削孔よりも小径の軸部用の拡底用掘削機を前記軸部の掘削孔の先端部に挿入するとともに、前記拡底用掘削機の中心軸を前記軸部の中心軸に対して所定量偏心させて配置し、先行掘削して形成した前記軸部の掘削孔の先端部の孔壁を前記拡底用掘削機で拡張するように複数箇所で後行掘削して前記拡底部の掘削孔を形成し、前記軸部と前記拡底部の掘削孔にコンクリートを打設することを特徴とする。 A method for constructing a cast-in-place concrete pile of the present invention is a method for constructing a cast-in-place concrete pile having a cylindrical shaft and an enlarged bottom formed by expanding the tip of the shaft. An excavator is used to preliminarily excavate an excavation hole for the shaft portion to a predetermined depth in the ground, and an excavator for bottom expansion of the shaft portion having a diameter smaller than that of the excavation hole for the shaft portion is used to form the excavation hole for the shaft portion. and the central axis of the bottom-enlarging excavator is placed eccentrically by a predetermined amount with respect to the central axis of the shaft, and the tip of the excavation hole formed in the shaft is pre-excavated. The drilling hole of the expanded bottom portion is formed by following excavation at a plurality of locations so as to expand the hole wall by the excavator for expanding the bottom, and concrete is placed in the excavated hole of the shaft portion and the expanded bottom portion. and

本発明の場所打ちコンクリート杭の構築方法においては、前記拡底用掘削機の先端部に、前記拡底用掘削機の中心軸と同軸で掘削刃よりも下方に突出する位置決め凸部であるスタビライザーを設け、前記スタビライザーを掘削孔の底面の地盤に突き刺すようにして後行掘削することが望ましい。 In the cast-in-place concrete pile constructing method of the present invention, a stabilizer, which is a positioning projection projecting downward from the excavation blade, is provided at the tip of the bottom enlarging excavator coaxially with the central axis of the bottom enlarging excavator. It is preferable that the trailing excavation is performed by sticking the stabilizer into the ground of the bottom surface of the excavation hole.

本発明の場所打ちコンクリート杭の構築方法においては、予め、杭底部となる前記掘削孔の底面の直下の地盤を杭支持力の３倍以上の一軸圧縮強度となるように地盤改良しておくことがより望ましい。 In the construction method of the cast-in-place concrete pile of the present invention, the ground immediately below the bottom surface of the excavation hole, which will be the pile bottom, is improved in advance so that the uniaxial compressive strength is at least three times the pile bearing capacity. is more desirable.

本発明の場所打ちコンクリート杭の構築方法においては、前記スタビライザーを突き刺すように配設する偏心位置の前記掘削孔の底面の直下の地盤を局部的に地盤改良するようにしてもよい。 In the method for constructing cast-in-place concrete piles of the present invention, the ground immediately below the bottom surface of the excavation hole at the eccentric position where the stabilizer is pierced may be locally improved.

本発明の場所打ちコンクリート杭は、円柱状の軸部と、該軸部の先端部を拡張してなる拡底部を備えた場所打ちコンクリート杭であって、前記拡底部が平断面視で前記軸部の中心軸を中心とした円形外面から径方向外側に突出する複数の凸円弧部を備えた形で構築されていることを特徴とする。 The cast-in-place concrete pile of the present invention is a cast-in-place concrete pile having a cylindrical shaft and an expanded bottom formed by expanding the tip of the shaft, wherein the expanded bottom is the shaft in plan cross-sectional view. It is characterized in that it is constructed with a plurality of convex circular arc portions projecting radially outward from a circular outer surface centered on the central axis of the portion.

本発明の場所打ちコンクリート杭の構築方法及び場所打ちコンクリート杭においては、超高層ビルなど非常に大きな柱軸力を好適に支持できる高支持耐力の場所打ちコンクリート拡底杭を、効率的且つ効果的に構築することが可能になる。 In the cast-in-place concrete pile construction method and the cast-in-place concrete pile of the present invention, a cast-in-place concrete expanded bottom pile with a high supporting strength that can suitably support a very large axial force of a column such as a skyscraper can be efficiently and effectively constructed. becomes possible to build.

本発明の一実施形態に係る場所打ちコンクリート杭の構築方法を示す図である。It is a figure which shows the construction method of the cast-in-place concrete pile which concerns on one Embodiment of this invention. 従来の拡底掘削機を用いて拡底部を形成した場合を示す図である。It is a figure which shows the case where the conventional bottom-enlarging excavator is used and an enlarged-bottom part is formed. 本発明の一実施形態に係る場所打ちコンクリート杭を示す図であり、３箇所の偏心位置で拡底掘削を行った場合の場所打ちコンクリート杭を示す図である。It is a figure which shows the cast-in-place concrete pile which concerns on one Embodiment of this invention, and is a figure which shows the cast-in-place concrete pile when bottom expansion excavation is performed at three eccentric positions. 本発明の一実施形態に係る場所打ちコンクリート杭を示す図であり、４箇所の偏心位置で拡底掘削を行った場合の場所打ちコンクリート杭を示す図である。It is a figure which shows the cast-in-place concrete pile which concerns on one Embodiment of this invention, and is a figure which shows the cast-in-place concrete pile when bottom expansion excavation is performed at four eccentric positions. 本発明の一実施形態に係る場所打ちコンクリート杭の構築方法の変更例を示す図である。It is a figure which shows the modification of the construction method of the cast-in-place concrete pile which concerns on one Embodiment of this invention. 従来の場所打ちコンクリート杭（拡底杭）を示す図である。It is a figure which shows the conventional cast-in-place concrete pile (enlarged bottom pile).

以下、図１から図５を参照し、本発明の一実施形態に係る場所打ちコンクリート杭の構築方法及び場所打ちコンクリート杭について説明する。 Hereinafter, a method for constructing a cast-in-place concrete pile and a cast-in-place concrete pile according to an embodiment of the present invention will be described with reference to FIGS. 1 to 5 .

本実施形態の場所打ちコンクリート杭の構築方法では、従来と同様、アースドリルなどの掘削機を用いて地表面から所定の深度まで安定液を充填しつつ掘削し、場所打ちコンクリート杭１’の略一定の径の円柱状の軸部２の掘削孔１０を形成する（図１参照）。次に、ロッド４の下端に接続した拡底用掘削機（拡底バケットなどの拡底機）５を軸部２の掘削孔１０に挿入して先端部に配置し、拡底用掘削機５を拡張しつつ中心軸Ｏ１周りに回転させて先端部の掘削孔１０の孔壁部分を拡底掘削し、先端部に略円錐台状の拡底部３の掘削孔１１を形成する。そして、掘削孔１０、１１にトレミー管を用いて安定液と置換するようにコンクリートを打設し場所打ちコンクリート杭１’を構築する。なお、掘削孔１０、１１内に鉄筋篭を挿入したり、必要に応じて杭頭部側を埋め戻したり、杭頭基礎を構築するなどし、場所打ちコンクリート拡底杭の施工が完了する。 In the construction method of the cast-in-place concrete pile of the present embodiment, as in the conventional method, an excavator such as an earth drill is used to excavate from the ground surface to a predetermined depth while filling the stable liquid, and the cast-in-place concrete pile 1 ' stands for A bore 10 is formed in the cylindrical shaft portion 2 with a constant diameter (see FIG. 1). Next, a bottom-enlarging excavator (bottom-enlarging machine such as a bottom-enlarging bucket) 5 connected to the lower end of the rod 4 is inserted into the excavation hole 10 of the shaft portion 2 and placed at the tip, and the bottom-enlarging excavator 5 is expanded. Rotating around the central axis O1, the hole wall portion of the excavation hole 10 at the tip is enlarged to form an excavation hole 11 with an enlarged bottom portion 3 having a substantially truncated cone shape at the tip. Then, concrete is cast into the excavated holes 10 and 11 using tremie pipes so as to replace the stabilizing liquid, thereby constructing the cast-in-place concrete pile 1'. Reinforcing cages are inserted into the excavation holes 10 and 11, the pile head side is backfilled as necessary, the pile head foundation is constructed, and the construction of the cast-in-place concrete expanded bottom pile is completed.

ここで、従来周知の通り、拡底用掘削機５は、図２に示すように、例えばφ２．１～３．０ｍなど、ある範囲の径の軸部２に対応して拡底部３（軸部２の掘削孔１０に対応して拡底部３の掘削孔１１）を形成できるようになっている。 Here, as is well known in the art, the bottom-enlarging excavator 5, as shown in FIG. The excavated hole 11) of the expanded bottom portion 3 can be formed corresponding to the excavated hole 10 of 2.

本実施形態の場所打ちコンクリート杭の構築方法では、この拡底用掘削機５がある範囲の径の軸部２に対応して拡底部３を形成できることを利用する。 In the construction method of the cast-in-place concrete pile of this embodiment, the fact that the excavator 5 for bottom enlargement can form the enlarged bottom portion 3 corresponding to the shaft portion 2 having a certain range of diameters is utilized.

具体的に、本実施形態の場所打ちコンクリート杭の構築方法では、図１に示すように、掘削機（軸部大径用拡底機）５によって例えば３．０ｍなどの大きな軸径で軸部２の掘削孔１０を先行掘削し、次に、例えば、最大拡底径が２．１ｍなどの拡底用掘削機（軸部小径用拡底機）５を用い、軸部２の中心軸Ｏ１に対して拡底用掘削機５（ロッド４）の中心軸Ｏ２を偏心させて、先行掘削して形成した軸部２の掘削孔１０の先端部の孔壁を拡底掘削する。また、複数箇所の偏心位置に拡底用掘削機５を配置して拡底掘削を行い、拡底部３の掘削孔１１を形成する。 Specifically, in the construction method of the cast-in-place concrete pile of this embodiment, as shown in FIG. The excavation hole 10 is pre-drilled, and then, for example, using a bottom expansion excavator (bottom expansion machine for small shaft diameter) 5 with a maximum bottom expansion diameter of 2.1 m or the like, the bottom is expanded with respect to the central axis O1 of the shaft portion 2. The central axis O2 of the excavator 5 (rod 4) is made eccentric, and the hole wall at the tip of the excavation hole 10 of the shaft portion 2 formed by pre-excavation is expanded. In addition, bottom enlarging excavators 5 are arranged at a plurality of eccentric positions to perform bottom enlarging excavation to form excavation holes 11 of the enlarging bottom portion 3 .

これにより、本実施形態の場所打ちコンクリート杭の構築方法によれば、図３や図４に示すように、拡底用掘削機５の最大拡底径を超えた場所打ちコンクリート杭（拡底杭）１’、すなわち、高支持耐力の場所打ちコンクリート杭１’を構築することが可能になる。例えば、軸部大径用拡底機５を用いて従来通りに拡底部３を形成した場合の杭底面積に対し、本実施形態の場所打ちコンクリート杭の構築方法においては１．３倍以上の杭底面積の拡底部３を形成、構築することが可能である。 As a result, according to the construction method of the cast-in-place concrete pile of the present embodiment, as shown in FIGS. That is, it becomes possible to construct a cast-in-place concrete pile 1' with a high bearing capacity. For example, in the cast-in-place concrete pile construction method of the present embodiment, the pile bottom area when the enlarged bottom portion 3 is formed in the conventional manner using the shaft portion large-diameter bottom expander 5 is 1.3 times or more. It is possible to form and construct an enlarged bottom portion 3 with a bottom area.

ここで、図３は３箇所の偏心位置で拡底掘削を行った場合の場所打ちコンクリート杭１’、図４は４箇所の偏心位置で拡底掘削を行った場合の場所打ちコンクリート杭１’の形状をそれぞれ示している。
Here, FIG. 3 shows the cast-in-place concrete pile 1 ' when bottom expansion excavation is performed at three eccentric positions, and FIG. 4 shows the cast-in-place concrete pile 1 ' when bottom expansion excavation is performed at four eccentric positions. Each shape is shown.

図３、図４に示すように、上記のように構築した本実施形態の場所打ちコンクリート杭１’は、その拡底部（杭底面１ａ）が平断面視で軸部２の中心軸Ｏ１を中心とした円形外面から径方向外側に突出する凸円弧部（凸円弧面）６を備えた形で構築される。これにより、拡底部３が円弧凹凸状の外面によって従来の円錐台形状の拡底部３よりも鉛直部分の面の摩擦耐力を向上させることができ、この点からも、高支持耐力の拡底杭を実現することが可能になる。 As shown in FIGS. 3 and 4, the cast-in-place concrete pile 1′ of the present embodiment constructed as described above has an enlarged bottom portion (pile bottom surface 1a) centered on the central axis O1 of the shaft portion 2 in plan cross-sectional view. It is constructed with a convex arc portion (convex arc surface) 6 projecting radially outward from the circular outer surface. As a result, the outer surface of the expanded bottom portion 3 having a circular arc uneven shape can improve the friction resistance of the surface of the vertical portion compared to the conventional expanded bottom portion 3 having a truncated cone shape. realization becomes possible.

一方、従来、アースドリルなどの掘削機によって形成した杭の底面は、中心軸Ｏ１から径方向外側に向かうに従い漸次上方に傾斜するすり鉢状になる。このため、例えば、支持層Ｇ１が砂礫などの場合には、拡底用掘削機（軸部小径用拡底機）５の中心軸Ｏ２を偏心させた状態で後行掘削する際に杭の底面に当接する掘削機５の底部が安定せず、底面地盤が崩壊したり、拡底用掘削機５が軸部２の中心軸Ｏ１側に滑って芯ずれが生じ、小口径の拡底用掘削機５で拡底部３の掘削孔１１を拡張形成できなくなることも考えられる。 On the other hand, conventionally, the bottom surface of a pile formed by an excavator such as an earth drill has a mortar shape that gradually slopes upward as it goes radially outward from the central axis O1. For this reason, for example, when the support layer G1 is gravel or the like, when following excavation is performed with the center axis O2 of the excavator for bottom enlargement (bottom enlarger for small shaft diameter) 5 being eccentric, it will hit the bottom surface of the pile. The bottom of the excavator 5 in contact is not stable, and the bottom ground collapses, or the excavator 5 for bottom expansion slips to the central axis O1 side of the shaft portion 2 and misalignment occurs, and the excavator 5 for bottom expansion with a small diameter causes bottom expansion. It is also conceivable that the excavation hole 11 of the part 3 cannot be expanded.

これに対し、本実施形態では、図１に示すように、拡底用掘削機５の底部に、中心軸Ｏ１と同軸で底面から下方に突出し、掘削孔１０の底面に突き当たって突き刺さるなどし拡底用掘削機５を安定させるための位置決め凸部であるスタビライザー７を設ける。また、スタビライザー７は、拡底用掘削機５の底部の掘削刃よりも下方に突出するように形成されている。なお、本実施形態のスタビライザー７はその突出方向先端部がテーパー状、尖った形で形成されている。また、ドリルやオーガー状にして下方地盤に突き刺さりやすくしても良い。 On the other hand, in this embodiment, as shown in FIG. A stabilizer 7, which is a positioning protrusion for stabilizing the excavator 5, is provided. Moreover, the stabilizer 7 is formed so as to protrude downward from the excavating blade at the bottom of the bottom enlarging excavator 5 . In addition, the stabilizer 7 of this embodiment is formed in a tapered and pointed shape at the leading end in the projecting direction. It may also be shaped like a drill or an auger so that it can easily penetrate into the ground below.

これにより、先行掘削した掘削孔１０の底面がすり鉢状に形成されていたり、砂礫などの崩れやすい地盤Ｇであっても、後行掘削によって拡底部３の掘削を行う際に、軸部２の掘削孔１０の中心軸Ｏ１から偏心した位置の底面にスタビライザー７が突き刺さるなどして拡底用掘削機５が安定し、この状態で拡底用掘削機５が中心軸Ｏ２周りに回転して掘削孔１０の孔壁を拡底掘削することができる。すなわち、偏心位置に配置した拡底用掘削機５が芯ずれすることなく拡底掘削を行うことができ、確実で好適に拡底用掘削機５の最大拡底径を超えた場所打ちコンクリート杭（拡底杭）１’を構築することが可能になる。 As a result, even if the bottom surface of the pre-excavated excavation hole 10 is formed in a mortar shape, or even if the ground G is easy to collapse such as sand and gravel, when excavating the expanded bottom portion 3 by subsequent excavation, the shaft portion 2 can be easily removed. The excavator 5 for bottom expansion is stabilized by, for example, stabbing the stabilizer 7 into the bottom surface of the excavation hole 10 at a position eccentric from the central axis O1, and in this state, the excavator 5 for bottom expansion rotates around the central axis O2 and the excavation hole 10 is opened. It is possible to excavate the bottom of the hole wall. That is, the excavator 5 for bottom expansion arranged at an eccentric position can perform bottom expansion excavation without misalignment, and the cast-in-place concrete pile (bottom expansion pile) that exceeds the maximum bottom expansion diameter of the excavator 5 for bottom expansion reliably and suitably. 1' can be constructed.

以上、本発明に係る場所打ちコンクリート杭の構築方法の一実施形態について説明したが、本発明は上記の一実施形態に限定されるものではなく、その趣旨を逸脱しない範囲で適宜変更可能である。 An embodiment of the method for constructing a cast-in-place concrete pile according to the present invention has been described above, but the present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the gist thereof. .

例えば、図５に示すように、予め、杭底部直下の地盤Ｇ全体やスタビライザー７が突き刺さる部分の地盤Ｇ（偏心位置の杭底部直下の地盤Ｇ）を、深層地盤改良工法などを用いて地盤改良（地盤改良部８）しておいてもよい。この場合には、後行掘削によって拡底部３の掘削を行う際に、さらに拡底用掘削機５を安定した状態にして掘削孔１０の孔壁を拡底掘削することができ、より確実で好適に拡底用掘削機５の最大拡底径を超えた拡底杭１’を構築することが可能になる。なお、この地盤改良部８は、例えば、杭支持力の３倍以上の一軸圧縮強度となるように形成する。 For example, as shown in FIG. 5, in advance, the entire ground G directly under the pile bottom and the ground G in the part where the stabilizer 7 pierces (the ground G directly under the pile bottom at the eccentric position) are improved using a deep ground improvement method or the like. (Soil improvement unit 8) may be used. In this case, when the expanded bottom portion 3 is excavated by the subsequent excavation, the bottom expanding excavator 5 can be further stabilized to excavate the wall of the excavating hole 10 in a more stable manner. It is possible to construct a bottom-enlarging pile 1' exceeding the maximum bottom-enlarging diameter of the excavator 5 for bottom-enlarging. In addition, this soil improvement section 8 is formed so as to have a uniaxial compressive strength of, for example, three times or more of the pile bearing capacity.

１ 従来の場所打ちコンクリート杭（拡底杭）
１’ 場所打ちコンクリート杭（拡底杭）
２ 軸部
３ 拡底部
４ ロッド
５ 拡底用掘削機
６ 凸円弧部
７ スタビライザー（位置決め凸部）
８ 地盤改良部
１０ 軸部の掘削孔
１１ 拡底部の掘削孔
Ｇ 地盤
Ｇ１ 支持層 1 Conventional cast-in-place concrete pile (enlarged bottom pile)
1' cast-in-place concrete pile (enlarged bottom pile)
2 Axle 3 Enlarged bottom 4 Rod 5 Excavator for enlarging bottom 6 Convex arc 7 Stabilizer (positioning convex)
8 Soil improvement part 10 Drilling hole 11 of shaft part Drilling hole G of expanded bottom part Ground G1 Support layer

Claims (5)

円柱状の軸部と、該軸部の先端部を拡張してなる拡底部を備えた場所打ちコンクリート杭を構築する方法であって、
杭用の掘削機を用いて地盤の所定の深度まで前記軸部の掘削孔を先行掘削して形成し、
前記軸部の掘削孔よりも小径の軸部用の拡底用掘削機を前記軸部の掘削孔の先端部に挿入するとともに、前記拡底用掘削機の中心軸を前記軸部の中心軸に対して所定量偏心させて配置し、
先行掘削して形成した前記軸部の掘削孔の先端部の孔壁を前記拡底用掘削機で拡張するように複数箇所で後行掘削して前記拡底部の掘削孔を形成し、
前記軸部と前記拡底部の掘削孔にコンクリートを打設することを特徴とする場所打ちコンクリート杭の構築方法。 A method for constructing a cast-in-place concrete pile having a cylindrical shaft and an expanded bottom formed by expanding the tip of the shaft, comprising:
Preliminarily excavating the excavation hole of the shaft portion to a predetermined depth in the ground using an excavator for piles,
A bottom enlarging excavator for the shaft having a diameter smaller than that of the excavation hole of the shaft is inserted into the tip of the excavation hole of the shaft, and the center axis of the excavator for bottom enlarging is set with respect to the center axis of the shaft. are placed eccentrically by a predetermined amount,
forming the bottom-enlarged excavation hole by performing subsequent excavation at a plurality of locations so as to expand the hole wall at the tip of the excavated hole of the shaft portion formed by the preceding excavation with the excavator for expanding the bottom;
A method for constructing a cast-in-place concrete pile, characterized in that concrete is poured into excavated holes of the shaft portion and the expanded bottom portion. 請求項１記載の場所打ちコンクリート杭の構築方法において、
前記拡底用掘削機の先端部に、前記拡底用掘削機の中心軸と同軸で掘削刃よりも下方に突出する位置決め凸部であるスタビライザーを設け、
前記スタビライザーを掘削孔の底面の地盤に突き刺すようにして後行掘削することを特徴とする場所打ちコンクリート杭の構築方法。 In the construction method of the cast-in-place concrete pile according to claim 1,
A stabilizer, which is a positioning projection projecting downward from the excavating blade, is provided at the tip of the bottom-enlarging excavator, coaxially with the center axis of the bottom-enlarging excavator,
A method for constructing a cast-in-place concrete pile, characterized in that trailing excavation is performed so as to pierce the ground at the bottom of an excavation hole with the stabilizer. 請求項２記載の場所打ちコンクリート杭の構築方法において、
予め、杭底部となる前記掘削孔の底面の直下の地盤を杭支持力の３倍以上の一軸圧縮強度となるように地盤改良しておくことを特徴とする場所打ちコンクリート杭の構築方法。 In the construction method of the cast-in-place concrete pile according to claim 2,
A method for constructing a cast-in-place concrete pile, characterized in that the ground immediately below the bottom of the excavated hole, which will be the bottom of the pile, is improved in advance so that the uniaxial compressive strength is three times or more the bearing capacity of the pile. 請求項３記載の場所打ちコンクリート杭の構築方法において、
前記スタビライザーを突き刺すように配設する偏心位置の前記掘削孔の底面の直下の地盤を局部的に地盤改良することを特徴とする場所打ちコンクリート杭の構築方法。 In the construction method of the cast-in-place concrete pile according to claim 3,
A method for constructing a cast-in-place concrete pile, characterized by locally improving the ground immediately below the bottom surface of the excavated hole at the eccentric position where the stabilizer is pierced. 円柱状の軸部と、該軸部の先端部を拡張してなる拡底部を備えた場所打ちコンクリート杭であって、
前記拡底部が平断面視で前記軸部の中心軸を中心とした円形外面から径方向外側に突出する複数の凸円弧部を備えた形で構築されていることを特徴とする場所打ちコンクリート杭。 A cast-in-place concrete pile having a cylindrical shaft and an expanded bottom formed by expanding the tip of the shaft,
A cast-in-place concrete pile characterized in that said expanded bottom part is constructed in a form provided with a plurality of convex arc parts protruding radially outward from a circular outer surface centered on the central axis of said shaft part in plan cross-sectional view. .
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