JP2005256519A - Axial force measurement method of ground improvement pile - Google Patents

Axial force measurement method of ground improvement pile Download PDF

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JP2005256519A
JP2005256519A JP2004071900A JP2004071900A JP2005256519A JP 2005256519 A JP2005256519 A JP 2005256519A JP 2004071900 A JP2004071900 A JP 2004071900A JP 2004071900 A JP2004071900 A JP 2004071900A JP 2005256519 A JP2005256519 A JP 2005256519A
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ground improvement
axial force
pile
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improvement pile
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JP3823255B2 (en
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Akihiko Uchida
明彦 内田
Takeshi Yamada
毅 山田
Ken Okamoto
謙 岡本
Hiroshi Yamamoto
博 山本
Naomiki Suzuki
直幹 鈴木
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Takenaka Komuten Co Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide an axial force measurement method of a ground improvement pile which measures transmission state of axial force of the ground improvement pile after construction of a structure and evaluates intermittently vertical supporting force by calculating proportional division between tip bearing force and peripheral surface friction force from axial force distribution. <P>SOLUTION: A core hole is provided in the depth direction of the center portion of the ground improvement pile after the ground improvement pile is formed and specified strength is exhibited. A plurality of strain gauges are inserted into the core hole in the depth direction with specified intervals maintained. Soil cement with the same formulation as that of the ground improvement pile is injected into the core hole and the strain gauge is integrated with the ground improvement pile. Thereafter, the structure is constructed on the ground improvement pile, and the transmission state of the axial force of the ground improvement pile which is loaded with weight of the structure is measured by the plurality of the strain gauges. The vertical supporting force is evaluated by calculating the proportional division between the tip supporting force and the peripheral surface friction force based on the measurement of the axial force distribution in the depth direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

この発明は、混合処理工法（深層混合処理工法を含む。以下同じ。）により造成した地盤改良杭の軸力を測定する方法の技術分野に属し、更に云うと、地盤改良杭の上に構造物を築造した後の地盤改良杭の軸力伝達状況を深度方向に測定し、その軸力分布から先端支持力と周面摩擦力との案分を算出して鉛直支持力の実体を評価するための測定方法であり、構造物の供用期間中の長期にわたり継続的に行う地盤改良杭の軸力測定方法に関する。   The present invention belongs to the technical field of a method for measuring the axial force of a ground improvement pile created by a mixed treatment method (including a deep layer mixed treatment method; the same shall apply hereinafter), and more specifically, a structure on a ground improvement pile. In order to evaluate the vertical bearing force by measuring the axial force transmission situation of the ground improvement pile after building the building in the depth direction and calculating the proportion of tip bearing force and peripheral friction force from the axial force distribution The present invention relates to a method for measuring the axial force of a ground improvement pile that is continuously performed over a long period of time during the service period of a structure.

従来、軟弱地盤の支持力増強や液状化地盤の液状化防止対策を目的として混合処理工法により造成された地盤改良杭の鉛直支持力や沈下特性を調査するために、また、設計鉛直支持力の妥当性を評価するために軸力測定が行われている。そして、鉛直支持力の評価は、一般的な基礎工事等で造成される基礎杭の場合と同様の手法により実施されている。つまり、基礎杭先端部の地盤のＮ値と面積から求められる先端支持力と、周辺地盤による周面摩擦力との合成力を算出して鉛直支持力を評価する手法である。前記手法による基礎杭の軸力測定方法の従来技術は次のように開示されている。   Conventionally, in order to investigate the vertical bearing capacity and settlement characteristics of ground improved piles created by the mixed treatment method for the purpose of enhancing bearing capacity of soft ground and preventing liquefaction of liquefied ground, Axial force measurement is performed to evaluate validity. And the evaluation of the vertical bearing capacity is carried out by the same method as in the case of foundation piles constructed by general foundation work. In other words, this is a method for evaluating the vertical support force by calculating the combined force of the tip support force obtained from the N value and area of the ground at the tip of the foundation pile and the peripheral friction force of the surrounding ground. The prior art of the axial pile measuring method of the foundation pile by the said method is disclosed as follows.

例えば特許文献１には、コンクリート杭の中央部にコアリングを行い、採取した試料で一軸圧縮試験等を行う方法が開示されている。特許文献２は、杭頭にジャッキを設けて軸力を測定する方法を開示している。特許文献３は、地層毎及び単位深さ毎に軸力試験を繰り返すことによって軸力を測定する方法を開示している。特許文献４は、磁歪素子が杭へひずみを伝達させる動的試験により軸力を測定する方法を開示している。   For example, Patent Document 1 discloses a method in which coring is performed on the center portion of a concrete pile and a uniaxial compression test or the like is performed on the collected sample. Patent Document 2 discloses a method of measuring axial force by providing a jack on a pile head. Patent document 3 is disclosing the method of measuring axial force by repeating an axial force test for every formation and every unit depth. Patent Document 4 discloses a method of measuring axial force by a dynamic test in which a magnetostrictive element transmits strain to a pile.

また、特許文献５には、ソイルセメント合成杭の周面に作用する摩擦応力τの計算を地盤の種別によらずＮ値を用いた一式で算定する技術が開示されている。   Further, Patent Document 5 discloses a technique for calculating the frictional stress τ acting on the peripheral surface of the soil cement composite pile with a set using the N value regardless of the type of the ground.

更に、特許文献６には、鉄筋かごを用いて施工された場所打ちコンクリート杭の鉄筋に埋め込まれた光ファイバー、ひずみ計測装置とにより、杭全長にわたる深度方向の軸力伝達状況を（ひずみ）測定する技術が開示されている。
特許第２８５１５３７号公報 特公平６−２９８４４号公報 特開平９−２７９５６１号公報 特開２００３−１９４６３６号公報 特開２００３−８２６４８号公報 特開平１１−２２２８１０号公報 Furthermore, in Patent Document 6, the axial force transmission state in the depth direction over the entire length of the pile (strain) is measured by an optical fiber embedded in the reinforcing bar of a cast-in-place concrete pile constructed using a reinforcing steel cage. Technology is disclosed.
Japanese Patent No. 2851537 Japanese Patent Publication No. 6-29844 JP-A-9-279561 JP 2003-194636 A JP 2003-82648 A JP-A-11-222810

上述の特許文献１〜６に開示されたように、基礎杭の先端支持力と周面摩擦力との合成力の算出により鉛直支持力を評価する手法と、そのための軸力測定方法は、既に公知である。しかし、これらの従来技術はいずれも、構造物を築造する以前に、基礎杭の鉛直支持力が如何ほどのものかを試験する方法であり、基礎杭の上へ構造物を築造した後に生じる、実際の軸力を測定して先端支持力と周面摩擦力の案分を算出し正確な鉛直支持力を評価したり、或いは構造物の供用期間中の長期にわたって継続的に鉛直支持力の測定、評価を行う内容ではない。   As disclosed in the above-mentioned Patent Documents 1 to 6, the method for evaluating the vertical support force by calculating the combined force of the tip support force and the peripheral friction force of the foundation pile, and the axial force measurement method therefor are already It is known. However, each of these conventional techniques is a method of testing how the vertical bearing capacity of the foundation pile is before building the structure, and occurs after building the structure on the foundation pile. Measure the actual axial force and calculate the appropriate amount of tip support force and peripheral friction force to evaluate the correct vertical support force, or measure the vertical support force continuously over the long term during the service period of the structure It is not the content to be evaluated.

ところで、地盤を掘削し、その掘削土中へ安定材を混合し攪拌する混合処理工法により造成された地盤改良杭の軸力を測定する場合には、以下のような問題点がある。   By the way, when measuring the axial force of the ground improvement pile created by the mixing processing method in which the ground is excavated, and the stabilizer is mixed and stirred in the excavated soil, there are the following problems.

地盤改良杭の軸力を測定する場合、特に周面摩擦力の評価が非常に重要とされている。しかし、地盤改良杭は、場所打ちコンクリート杭などとは異なって、掘削した原位置の掘削土とセメントとを混合したソイルセメントによる低強度改良杭であるため、周面摩擦力の算出において、打設コンクリートと地盤の摩擦から求められた関係式がそのまま地盤改良杭の周面摩擦力の算出に当てはまるかどうか不明であり、その測定値の信頼性は低いと考えられる。   When measuring the axial force of ground improvement piles, it is especially important to evaluate the peripheral frictional force. However, unlike the cast-in-place concrete piles, the ground improvement piles are low-strength improved piles made of soil cement that is a mixture of excavated soil and cement from the original site. It is unclear whether the relational expression obtained from the friction between the concrete and the ground is directly applicable to the calculation of the peripheral friction force of the ground improvement pile, and the reliability of the measured value is considered to be low.

また、特許文献６のように、場所打ちコンクリート杭の鉄筋かごの主筋の一部に光ファイバーを設置し、同杭に発生する深度方向の軸力伝達状況（ひずみ）を光ファイバーを介して計測する技術は注目に値する。しかし、地盤改良杭には鉄筋が入っていないため、光ファイバーやひずみ計等を取り付けるべき対象物が存在しないという問題もある。   In addition, as in Patent Document 6, an optical fiber is installed on a part of the main bar of a cast-in-place concrete pile and the axial force transmission state (strain) in the depth direction generated in the pile is measured via the optical fiber. Is noteworthy. However, since the ground improvement pile does not contain reinforcing bars, there is also a problem that there is no object to which an optical fiber, a strain gauge, or the like is to be attached.

本発明の目的は、混合処理工法により造成された地盤改良杭に作用する軸力を、ひずみ計により深度方向に測定可能とすること、とりわけ地盤改良杭の上に構造物が築造された後に当該地盤改良杭に生じる実際の軸力伝達状況をひずみ計を用いて測定し、その軸力分布に基づいて先端支持力と周面摩擦力との案分を正確に算出し鉛直支持力を評価することが可能であり、更に構造物の完成後もその供用期間中の長期にわたり継続的に軸力の測定とこれに基づく鉛直支持力の評価が可能な地盤改良杭の軸力測定方法を提供することにある。   The object of the present invention is to make it possible to measure the axial force acting on the ground improvement pile created by the mixed processing method in the depth direction with a strain gauge, especially after the structure is built on the ground improvement pile. Measure the actual axial force transmission situation that occurs in the ground improvement pile using a strain gauge, and calculate the proration between the tip support force and the peripheral friction force based on the axial force distribution and evaluate the vertical support force Further, it is possible to provide a method for measuring the axial force of ground improved piles capable of continuously measuring the axial force and evaluating the vertical bearing force based on the axial force continuously for a long period after the structure is completed. There is.

上述した従来技術の課題を解決するための手段として、請求項１に記載した発明に係る地盤改良杭の軸力測定方法は、
地盤を掘削し、その掘削土中へ安定材を混合し攪拌する混合処理工法により造成された地盤改良杭の軸力を測定する方法において、
地盤改良杭を造成し一定の強度を発現した後に、同杭の中心部の深度方向へコア孔を設け、前記コア孔の中へ深度方向に一定の間隔を保持して複数個のひずみ計を挿入し、地盤改良杭と同じ配合のソイルセメントを前記コア孔へ注入して前記ひずみ計を地盤改良杭と一体化し、しかる後に前記地盤改良杭の上に構造物を築造し、同構造物の重量を負担した地盤改良杭の軸力伝達状況を前記複数個のひずみ計により測定し、深度方向における軸力分布の測定に基づいて先端支持力と周面摩擦力との案分を算出し鉛直支持力を評価することを特徴とする。 As a means for solving the above-described problems of the prior art, the axial force measuring method of the ground improvement pile according to the invention described in claim 1 is:
In the method of measuring the axial force of ground improvement piles created by the mixed processing method of excavating the ground, mixing stabilizers into the excavated soil and stirring them,
After constructing a ground improvement pile and expressing a certain strength, a core hole is provided in the depth direction of the center part of the pile, and a plurality of strain gauges are installed in the core hole by keeping a constant interval in the depth direction. Insert the soil cement of the same composition as the ground improvement pile into the core hole to integrate the strain gauge with the ground improvement pile, and then build a structure on the ground improvement pile. The axial force transmission situation of the ground improved pile that bears the weight is measured by the plurality of strain gauges, and the proportion of tip support force and peripheral friction force is calculated based on the measurement of axial force distribution in the depth direction and vertical It is characterized by evaluating the supporting force.

請求項２に記載した発明は、請求項１に記載した地盤改良杭の軸力測定方法において、
コア孔へ挿入されるひずみ計は、その両側に突き出された鉄筋同士を、又は鉄筋間に間隔保持用の鉄筋を介在させて複数個一連に接続したものを挿入することを特徴とする。 The invention described in claim 2 is the axial force measuring method of the ground improvement pile described in claim 1,
The strain gauge inserted into the core hole is characterized by inserting rebars protruding on both sides thereof or a plurality of rebars connected in series with interposing reinforcing bars between the reinforcing bars.

請求項３に記載した発明は、請求項１又は２に記載した地盤改良杭の軸力測定方法において、
鉄筋には、その深度方向の複数箇所に、コア孔の内周面に当たる振れ止め治具を取り付けていることを特徴とする。 The invention described in claim 3 is the axial force measuring method of the ground improvement pile described in claim 1 or 2,
The reinforcing bar is provided with a steady rest jig that hits the inner peripheral surface of the core hole at a plurality of locations in the depth direction.

請求項１〜３に記載した発明に係る地盤改良杭の軸力測定方法によれば、造成した地盤改良杭の深度方向に複数個のひずみ計を一定の間隔を保持して挿入し、地盤改良杭と同じ配合のセメントで一体化し、当該地盤改良杭の上に築造した構造物の重量を負担した地盤改良杭に生じる実際の軸力伝達状況を前記ひずみ計により測定するから、その測定結果に基づいて行う先端支持力と周面摩擦力との案分、及び鉛直支持力の評価を具体的且つ正確に行うことが可能である。したがって、深度方向の軸力伝達状況に基づいて周面摩擦力を正確に算出（案分）でき、信頼性の高い鉛直支持力の評価ができる。   According to the axial force measuring method of the ground improvement pile according to the invention described in claims 1 to 3, a plurality of strain gauges are inserted in the depth direction of the created ground improvement pile while maintaining a constant interval. The actual axial force transmission situation that occurs in the ground improved pile that bears the weight of the structure built on the ground improved pile integrated with the cement of the same composition as the pile is measured by the strain gauge. It is possible to specifically and accurately evaluate the appropriation of the tip support force and the peripheral surface friction force performed based on the vertical support force. Accordingly, the peripheral friction force can be accurately calculated (proposed) based on the axial force transmission state in the depth direction, and a highly reliable vertical support force can be evaluated.

しかも、構造物の供用期間中の長期にわたり継続的に地盤改良杭の軸力測定とこれに基づく鉛直支持力の評価が可能であるため、自然環境の変化、構造物の年数により地盤改良杭の軸力がどのように変化するかを具体的、実際的に把握してその特性や傾向を予測することが可能である。
よって、本発明の方法により測定したデータを他の構造物を建設する際の地盤改良杭の設計に生きた有力データとして役立てることができる。 In addition, since it is possible to continuously measure the axial force of the ground improvement pile and evaluate the vertical bearing capacity based on this measurement over a long period of time during the service period of the structure, It is possible to specifically and practically grasp how the axial force changes, and to predict its characteristics and trends.
Therefore, the data measured by the method of the present invention can be used as useful data for the design of ground improvement piles when constructing other structures.

図１は、公知、周知の地盤改良機により地盤Ｇを掘削し、その掘削土中へセメント系安定材を混合し攪拌する混合処理工法によってラップ状配置に造成した複数の地盤改良杭１…のうち、測定対象の杭体に深度方向へ所定の深さまでコア孔２を掘削し、同コア孔２の中へ、深度方向に一定の間隔を保持してひずみ計３を挿入した段階を示している。   FIG. 1 shows a plurality of ground improvement piles 1 formed in a lap-like arrangement by excavating the ground G with a known and well-known ground improvement machine, mixing the cement stabilizer into the excavated soil, and stirring it. Among them, the core hole 2 is excavated to a predetermined depth in the depth direction in the pile body to be measured, and the strain gauge 3 is inserted into the core hole 2 while maintaining a constant interval in the depth direction. Yes.

前記地盤改良杭１は、隣接する地盤改良杭１、１同士を一部ラップさせて基礎等として必要な本数造成するが、ひずみ計３を挿入する地盤改良杭１は全ての杭体である必要はなく、軸力測定に適切と判断し選択した位置の杭体にのみ実施する。   The ground improvement piles 1 are formed by wrapping the adjacent ground improvement piles 1 and 1 partly and forming the necessary number of foundations, etc., but the ground improvement piles 1 into which the strain gauges 3 are inserted need to be all pile bodies. Rather, it is only applied to piles at selected positions that are deemed appropriate for axial force measurement.

前記コア孔２は、前記地盤改良杭１…を造成し、それが一定の強度を発現した後に、同地盤改良杭１の中心部に公知のコアボーリング機により深度方向に向かってコア抜きして設ける。前記コア孔２の直径は、地盤改良杭１の外径が１０００ｍｍ〜１５００ｍｍである場合に、例えば１００ｍｍ程度とされる。前記コア孔２としては、現場で地盤改良杭１について行われる強度確認試験のためのコア抜きサンプリング後の孔を利用できることを付言する。   The core hole 2 is formed with the ground improvement piles 1... After the core hole 2 exhibits a certain strength, the core hole 2 is cored in the depth direction by a known core boring machine at the center of the ground improvement piles 1. Provide. The diameter of the core hole 2 is, for example, about 100 mm when the outer diameter of the ground improvement pile 1 is 1000 mm to 1500 mm. As the core hole 2, it is added that a hole after core extraction sampling for a strength confirmation test performed on the ground improvement pile 1 at the site can be used.

ひずみ計３は、図２に示すように、剛性のある真直ぐな鉄筋４を利用し、深度方向に一定の間隔を保持して複数個当該鉄筋４へ取り付ける（請求項２記載の発明）。ひずみ計３は、例えば深度方向に３００ｍｍ程度の間隔をあけて、杭の全長にわたりひずみ計測が可能な個数取り付ける。前記ひずみ計３に必要な計測ケーブル３ａは鉄筋４に沿うように配置する。   As shown in FIG. 2, the strain gauge 3 uses a rigid straight reinforcing bar 4 and is attached to a plurality of reinforcing bars 4 while maintaining a constant interval in the depth direction (the invention according to claim 2). For example, the strain gauge 3 is attached in a number that allows strain measurement over the entire length of the pile with an interval of about 300 mm in the depth direction. The measurement cable 3 a necessary for the strain gauge 3 is arranged along the reinforcing bar 4.

前記ひずみ計３の具体的構成を図３に示した。これは、一般的にひずみ式変換器又は鉄筋計と称されているもので鉄筋に加わる応力を測定する構成とされている。つまり、ひずみ計３の両側に異形鉄筋３ｂ、３ｂを突き出させた構成とされ、このひずみ計３の設置は、その両側に突き出させた異形鉄筋３ｂ、３ｂ同士を直接、又は異形鉄筋３ｂ、３ｂ間に間隔保持用鉄筋４を介在させて一連に接続して行われる。   A specific configuration of the strain gauge 3 is shown in FIG. This is generally referred to as a strain transducer or a rebar meter and is configured to measure the stress applied to the rebar. In other words, the deformed reinforcing bars 3b and 3b are projected on both sides of the strain gauge 3, and the strain gauge 3 is installed directly on the deformed reinforcing bars 3b and 3b projected on both sides or the deformed reinforcing bars 3b and 3b. It is carried out by connecting them in series with interposition of reinforcing bars 4 between them.

前記鉄筋４（又は３ｂ）には、その深度方向の複数箇所に、コア孔２の内周面に当たる振れ止め治具５が取り付けられている（請求項３記載の発明）。この振れ止め治具５は、具体的には図４に平面図を示したように、車輪のスポークの如き４本の腕部５ａと、コア孔２の内周面に接する外径の円形リング部５ｂとから構成され、各腕部５ａの一端は鉄筋４と十字形の配置で接続され、他端は円形リング部５ｂの内周面と接合して構成されている。要するに、鉄筋４（又は３ｂ）を介してひずみ計３をコア孔２内へ挿入する作業及びその後にコア孔２へソイルセメントを注入し充填する際に、鉄筋４、異形鉄筋３ｂとひずみ計３に位置ずれやひずみ計の傾斜が生じることを振れ止め治具５によって確実に防止できる。
上記構成により必要数のひずみ計３…を前記コア孔２の中空部へ所定の配置及び間隔で挿入する。 The reinforcing bars 4 (or 3b) are provided with a steady rest jig 5 that hits the inner peripheral surface of the core hole 2 at a plurality of locations in the depth direction (invention according to claim 3). Specifically, as shown in the plan view of FIG. 4, the steady rest jig 5 includes a circular ring having an outer diameter in contact with four arm portions 5 a such as wheel spokes and an inner peripheral surface of the core hole 2. The arm 5a has one end connected to the reinforcing bar 4 in a cruciform arrangement, and the other end joined to the inner peripheral surface of the circular ring portion 5b. In short, when the strain gauge 3 is inserted into the core hole 2 through the reinforcing bar 4 (or 3b), and then the soil cement is injected and filled into the core hole 2, the reinforcing bar 4, the deformed reinforcing bar 3b and the strain gauge 3 are inserted. It is possible to reliably prevent the position shift and the strain gauge from being tilted by the steadying jig 5.
The required number of strain gauges 3... Are inserted into the hollow portion of the core hole 2 at a predetermined arrangement and interval.

その後に、地盤改良杭１と同じ配合となるように地上で、掘削土とセメント系安定材を混合攪拌したソイルセメントを前記コア孔２へ注入し密実に充填して前記ひずみ計３を当該地盤改良杭１と一体化させる。後打ちしたソイルセメントが固まるまでは鉄筋４を地盤改良杭１の上端より上方へ突き出させておき、固まった後に改良地盤杭１の上面位置で切断する。このとき構造物の重量が鉄筋４へ集中しないように、鉄筋４（又は３ｂ）の上端は、杭体の上面位置より少し低い位置で切断することが好ましい。   After that, soil cement mixed with agitated soil and cement-based stabilizer is mixed and stirred into the core hole 2 so as to have the same composition as the ground improvement pile 1, and the strain gauge 3 is filled with the ground. Integrate with the improved pile 1 The rebar 4 is protruded upward from the upper end of the ground improvement pile 1 until the post-soiled soil cement is solidified, and then cut at the upper surface position of the improved ground pile 1 after hardening. At this time, it is preferable to cut the upper end of the reinforcing bar 4 (or 3b) at a position slightly lower than the upper surface position of the pile body so that the weight of the structure does not concentrate on the reinforcing bar 4.

ひずみ計３の計測ケーブル３ａは地盤改良杭１より上方及び側方へ引き出して、図示省略の測定・記録装置（パーソナルコンピュータ等）と接続し、測定結果をリアルタイムで得ると共に、記録格納できるようにしておく。つまり構造物の供用期間中の長期にわたり軸力を測定できる構成とする。   The measurement cable 3a of the strain gauge 3 is drawn upward and laterally from the ground improvement pile 1 and connected to a measurement / recording device (such as a personal computer) not shown so that the measurement result can be obtained in real time and recorded and stored. Keep it. That is, it is set as the structure which can measure axial force over the long term in the service period of a structure.

その後に、図５に示すように前記地盤改良杭１の上に実際の構造物Ｙを築造する。すると、ひずみ計３は、構造物Ｙの重量を負担した地盤改良杭１に生じている実際の軸力の大きさを個別に測定する。そうした測定結果の統計により、深度方向の軸力伝達状況（ひずみ）を軸力分布（ひずみ分布）として具体的且つ正確にリアルタイムに測定することができる。   After that, as shown in FIG. 5, an actual structure Y is built on the ground improvement pile 1. Then, the strain gauge 3 individually measures the magnitude of the actual axial force generated in the ground improvement pile 1 bearing the weight of the structure Y. Based on the statistics of such measurement results, the axial force transmission state (strain) in the depth direction can be specifically and accurately measured in real time as an axial force distribution (strain distribution).

図６、図７には、深度が浅い方から順にａ、ｂ、ｃ、ｄ、ｅと付記したひずみ計３ごとの個別の軸力を継続的に測定して得た軸力分布のグラフ例を示した。図６には、軸力を縦軸に、日付を横軸にとり深度方向に設置されたひずみ計３（ａ〜ｅ）それぞれの軸力測定値を示した。図７は、深度を縦軸に、軸力を横軸にとり深度方向に設置されたひずみ計３（ａ〜ｅ）それぞれの軸力測定値を示した。   FIG. 6 and FIG. 7 are graph examples of axial force distributions obtained by continuously measuring individual axial forces for each strain gauge 3 affixed as a, b, c, d, e in order from the shallowest depth. showed that. FIG. 6 shows measured axial force values of the strain gauges 3 (a to e) installed in the depth direction with the axial force on the vertical axis and the date on the horizontal axis. FIG. 7 shows the axial force measurement values of the strain gauges 3 (a to e) installed in the depth direction with the vertical axis representing depth and the horizontal axis representing axial force.

図６のグラフに注目すると、構造物の構築が開始される前の５月９日を起点として、その時の軸力を０．０ｋＮと設定している。その後構造物Ｙを築造するにしたがって地盤改良杭１が支持する軸力が増加していることが分かる。因みに構造物Ｙの完成は１１月１８日ごろである。このグラフにより特に環境（温度又は季節）の変化等々により地盤改良杭１の軸力がどのように変化するかを把握できるので、当該地盤改良杭１がもつ特性や傾向を予測することができる。   If attention is paid to the graph of FIG. 6, the axial force at that time is set to 0.0 kN starting from May 9 before the construction of the structure is started. Thereafter, it can be seen that the axial force supported by the ground improvement pile 1 increases as the structure Y is built. Incidentally, the completion of the structure Y is around November 18th. Since this graph makes it possible to grasp how the axial force of the ground improvement pile 1 changes due to changes in the environment (temperature or season), etc., the characteristics and trends of the ground improvement pile 1 can be predicted.

図７に示したグラフは、鉛直支持力の評価をする際に利用する事が好ましい。鉛直支持力の評価、更に云うと鉛直支持力の妥当性の評価は、前記ひずみ計３…により得られた図７の軸力分布に基づいて、地盤改良杭１の先端支持力と周面摩擦力との案分を算出することによって行われる。   The graph shown in FIG. 7 is preferably used when evaluating the vertical support force. The evaluation of the vertical bearing force, more specifically the validity of the vertical bearing force, is based on the axial force distribution of FIG. 7 obtained by the strain gauge 3... This is done by calculating the proration with the force.

即ち、深度が浅い箇所のひずみ計３（ａ）の軸力測定値が大きく、深くなるにしたがって軸力が次第に小さくなる場合、地盤改良杭１の周面摩擦力は地盤が深くなるにしたがって十分に働いて構造物Ｙの重量を支持し、先端支持力の負担を低減している事が分かり、鉛直支持力が周面摩擦力と先端支持力の合算で構成していると評価することができる。   That is, when the axial force measurement value of the strain gauge 3 (a) at a shallow depth is large and the axial force gradually decreases as the depth increases, the peripheral friction force of the ground improvement pile 1 is sufficiently increased as the ground becomes deeper. It can be seen that the weight of the structure Y is supported and the burden of the tip support force is reduced, and that the vertical support force is composed of the sum of the peripheral friction force and the tip support force. it can.

その逆に、深度が深くなるにしたがって軸力測定値が次第に低下していなかったり大きくなる場合は、周面摩擦力が働いていない、又は負の摩擦力が働き、構造物の重量の大半を地盤改良杭１の先端部によって支持して、先端支持力の負担が大きいと評価することができる。そのような結果から、将来的に沈下する等の危険性があることを予測することができる。したがって、図７の軸力分布は、深度が深くなるにしたがって次第に軸力が低下していることから、地盤改良杭１の鉛直支持力は周面摩擦力と先端支持力で分担していると評価できる。このように、地盤改良杭１の鉛直支持力を継続的に評価することができるのである。   On the other hand, if the axial force measurement value does not gradually decrease or increases as the depth increases, the peripheral friction force is not working or negative friction force is working, and most of the weight of the structure is reduced. It can be evaluated that it is supported by the tip of the ground improvement pile 1 and the load of the tip support force is large. From such a result, it can be predicted that there is a risk of sinking in the future. Therefore, in the axial force distribution of FIG. 7, since the axial force gradually decreases as the depth increases, the vertical support force of the ground improvement pile 1 is shared by the peripheral surface friction force and the tip support force. Can be evaluated. Thus, the vertical support force of the ground improvement pile 1 can be continuously evaluated.

本発明に係る地盤改良杭の軸力測定方法の実施例を示した図である。It is the figure which showed the Example of the axial-force measuring method of the ground improvement pile which concerns on this invention. コア孔へ挿入されるひずみ計の実施例を示した図である。It is the figure which showed the Example of the strain meter inserted in a core hole. 図２におけるひずみ計周辺の拡大図である。FIG. 3 is an enlarged view around a strain gauge in FIG. 2. コア孔の平面図である。It is a top view of a core hole. 地盤改良杭の上へ構造物が築造された状態を示す斜視図である。It is a perspective view which shows the state by which the structure was built on the ground improvement pile. ひずみ計により得られた軸力分布の一例を示した図である。It is the figure which showed an example of axial force distribution obtained with the strain gauge. ひずみ計により得られた軸力分布の一例を示した図である。It is the figure which showed an example of axial force distribution obtained with the strain gauge.

符号の説明Explanation of symbols

１ 地盤改良杭
２ コア孔
３ ひずみ計
３ａ 計測ケーブル
３ｂ 異形鉄筋
４ 鉄筋
５ 鉄筋振れ止め治具
５ａ 腕部
５ｂ 円形リング部
Ｙ 構造物 DESCRIPTION OF SYMBOLS 1 Ground improvement pile 2 Core hole 3 Strain gauge 3a Measurement cable 3b Deformed bar 4 Reinforcing bar 5 Rebar stabilization jig 5a Arm part 5b Circular ring part Y Structure

Claims (3)

地盤を掘削し、その掘削土中へ安定材を混合し攪拌する混合処理工法により造成された地盤改良杭の軸力を測定する方法において、
地盤改良杭を造成し一定の強度を発現した後に、同杭の中心部の深度方向へコア孔を設け、前記コア孔の中へ深度方向に一定の間隔を保持して複数個のひずみ計を挿入し、地盤改良杭と同じ配合のソイルセメントを前記コア孔へ注入して前記ひずみ計を地盤改良杭と一体化し、しかる後に前記地盤改良杭の上に構造物を築造し、同構造物の重量を負担した地盤改良杭の軸力伝達状況を前記複数個のひずみ計により測定し、深度方向における軸力分布の測定に基づいて先端支持力と周面摩擦力との案分を算出し鉛直支持力を評価することを特徴とする、地盤改良杭の軸力測定方法。 In the method of measuring the axial force of ground improvement piles created by the mixed processing method of excavating the ground, mixing stabilizers into the excavated soil and stirring them,
After constructing a ground improvement pile and expressing a certain strength, a core hole is provided in the depth direction of the center part of the pile, and a plurality of strain gauges are installed in the core hole by keeping a constant interval in the depth direction. Insert the soil cement of the same composition as the ground improvement pile into the core hole to integrate the strain gauge with the ground improvement pile, and then build a structure on the ground improvement pile. The axial force transmission situation of the ground improved pile that bears the weight is measured by the plurality of strain gauges, and the proportion of tip support force and peripheral friction force is calculated based on the measurement of axial force distribution in the depth direction and vertical A method for measuring an axial force of a ground improved pile, characterized by evaluating a supporting force. コア孔へ挿入されるひずみ計は、その両側に突き出された鉄筋同士を、又は鉄筋間に間隔保持用の鉄筋を介在させて複数個一連に接続したものを挿入することを特徴とする、請求項１に記載した地盤改良杭の軸力測定方法。   The strain gauge to be inserted into the core hole is characterized by inserting rebars protruding on both sides or a plurality of rebars connected in series with interposing reinforcing bars between the reinforcing bars. The axial force measuring method of the ground improvement pile described in claim | item 1. 鉄筋には、その深度方向の複数箇所に、コア孔の内周面に当たる振れ止め治具を取り付けていることを特徴とする、請求項１又は２に記載した地盤改良杭の軸力測定方法。   3. The method of measuring axial force of a ground improved pile according to claim 1 or 2, wherein a steadying jig that hits the inner peripheral surface of the core hole is attached to the reinforcing bar at a plurality of locations in the depth direction.
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