JP2004019110A

JP2004019110A - Strength measuring method of ground at the present position

Info

Publication number: JP2004019110A
Application number: JP2002171189A
Authority: JP
Inventors: Takao Kishida; 岸田　隆夫; Yoshio Mitarai; 御手洗　義夫; Nobuyuki Yamane; 山根　信幸; Akinori Nakamura; 中村　明教
Original assignee: Toa Corp
Current assignee: Toa Corp
Priority date: 2002-06-12
Filing date: 2002-06-12
Publication date: 2004-01-22
Anticipated expiration: 2022-06-12
Also published as: JP3966769B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a strength measuring method of the ground at the present position, in which the ground strength at the present position can be efficiently measured by SST by grasping the correlation between CPT (cone penetration test) and the SST (Swedish sound test) to improve the work efficiency. <P>SOLUTION: CPT and SST are performed at points near a ground G to be measured, respectively. Data of depth in which a measured value of tip resistance q<SB>t</SB>when a cone 2 passes through in the CPT is abruptly changed are not adopted. In rotary passing through section of SST, a value of tip resistance q<SB>t</SB>when the cone 2 passes through which is obtained by CPT is made to correspond to the number of half rotation N<SB>SW</SB>obtained in SST by obtaining a mean value of upper 25 cm parts from depth of a tip of the cone 2 to obtain its correlation. Converted tip resistance is obtained from data of the performed SST and the correlation with the CPT which is obtained already. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、スウェーデン式サウンディング試験を使用した原位置における地盤の強度測定方法に関する。
【０００２】
【従来の技術】
従来、原位置における地盤の深度方向に連続した強度の測定には、電気式静的コーン貫入試験（ＪＧＳ１４３５−１９９５、以下本説明ではＣＰＴと略称する）が用いられていた。
【０００３】
このＣＰＴは、地盤にコーンを静的に貫入させ、電気的に先端抵抗と間隙水圧を求める試験方法であり、このＣＰＴ試験は、地盤にコーンを設置して貫入させるので反力が必要であるので、コーン、ロッド、貫入装置、深さ測定器、測定装置及び固定装置から構成される機具類が大掛かりとなり、その移動や設置に時間がかかる等の問題があった。
【０００４】
そこで、上記ＣＰＴ試験方法に比較し、より簡易な装置を使用してＣＰＴと同様に原位置における連続した地盤強度に関するデータが効率よく、かつ機動性良く得られるスウェーデン式サウンディング試験（ＪＩＳＡ１２２１、以下本説明ではＳＳＴと略称する）があり、この試験方法は、その装置及びその操作が容易で、かつ迅速に測定可能であり、また簡易なサウンディングのなかでは比較的貫入能力に優れているなどの利点を有していることで知られている。
【０００５】
上記ＳＳＴの試験装置は、主にハンドル、おもり、載荷用クランプ、ロッド及びスクリューポイント等から構成されており、スクリューポイントにロッドを介しておもりで荷重を載荷し、荷重で地盤に貫入停止後に、ロッドをハンドルで回転させた時の、回転数と貫入量との関係を求めるようにしている。
【０００６】
このＳＳＴの試験方法における測定値の地盤強度の換算は通常Ｎ値との相関関係からＮ値に換算することが行なわれているが、原位置における地盤の強度は、特に粘性土地盤の場合などでは、Ｎ値よりもコーン貫入抵抗の方が正確に評価できることに着目し、本発明者等はＳＳＴの結果からコーン貫入抵抗を換算できる方法の検討を行ない本発明に到達した。
【０００７】
【発明が解決しようとする課題】
本発明は、ＣＰＴとＳＳＴとの相関関係を把握して、ＳＳＴによって原位置における地盤強度を効率良く測定でき、作業効率の向上をはかりうる原位置における地盤の強度測定方法を提供する。
【０００８】
【課題を解決するための手段】
本発明は、電気式静的コーン貫入試験ＣＰＴと、スウェーデン式サウンディング試験ＳＳＴとを、測定地盤の１から２ｍ程度離れた地点でそれぞれ実施し、得られたデータからＣＰＴのコーン貫入時の先端抵抗ｑ_ｔの計測値が急激に変化している深度のデータは採用せず、ＳＳＴの回転貫入区間では、ＣＰＴで得られるコーン貫入時の先端抵抗ｑ_ｔの値を、コーン先端の深度から上方２５ｃｍ分の平均値を求め、ＳＳＴで得られる半回転数Ｎ_ＳＷとを対応させて、その相関関係を求め、ＳＳＴの自沈区間は、自沈がスクリューポイントの長さ以上連続している部分のデータのみを使用し、各載荷重と自沈した深度区間のコーン貫入時の先端抵抗ｑ_ｔとを対応させて、その相関関係を求めた後、実施したＳＳＴのデータと、既に求めてあるＣＰＴとの相関関係とから換算先端抵抗を求める原位置における地盤の強度測定方法からなり、また本発明は、土被り圧σ_Ｖ０が大きい場合は、ＳＳＴで得られる半回転数Ｎ_ＳＷとＣＰＴにより得られた先端抵抗ｑ_ｔに土被り圧σ_Ｖ０を考慮した先端抵抗ｑ_ｔ−σ_Ｖ０との相関関係を求め、各載荷重とＣＰＴにより得られた先端抵抗ｑ_ｔに土被り圧σ_Ｖ０を考慮した先端抵抗ｑ_ｔ−σ_Ｖ０との相関関係を求める原位置における地盤の強度測定方法からなる。
【０００９】
【発明の実施の形態】
以下図１を参照して本発明の地盤の強度測定方法における一実施形態につき説明する。
【００１０】
まず、前記のＳＳＴと、その試験を行なった地盤Ｇの１から２ｍ程度離れた近傍の地点でＣＰＴを同時に実施し、それぞれの試験結果から得られたデータを整理検討した。
【００１１】
ここで実施したＳＳＴの装置は、地盤Ｇの強度に合わせて、荷重による貫入、即ち自沈時の荷重段階を自動的に０．０５，０．１５，０．２５，０．５０，０．７５，１．００ｋＮの６段階に調整できるものとし、１．００ｋＮ以下の荷重では自沈し、自沈停止後、自動的に回転貫入に切り替わる仕組になっており、その荷重段階の切り替えは、その貫入速度から自動的に変化させることができ、深度、半回転数、荷重段階が自動的に計測され、その装置は分解可能で、その本体には車輪がついており、人力での移動及び設置が可能になっている。
【００１２】
図１はＳＳＴ及びＣＰＴのそれぞれの試験方法による地盤Ｇの強度の測定深度の相関関係を示す図であり、ＳＳＴにおいては、長さＬ＝２０ｃｍのスクリューポイント１の先端が２５ｃｍ進む間の半回転数Ｎ_ＳＷ（層厚１．０ｍに換算した値）を計測し、地盤Ｇの強度を推定するものであり、従って計測された半回転数Ｎ_ＳＷは、スクリューボイント１の先端の深度から上部２５ｃｍ分の平均地盤強度を示す。
【００１３】
これに対し、ＣＰＴにおいては、約３ｃｍのコーン２先端部分のコーン貫入時の先端抵抗ｑ_ｔを１．０ｃｍピッチで計測するもので、ほぼその深度における地盤強度を計測するものである。
【００１４】
従って、半回転数Ｎ_ＳＷと先端抵抗ｑ_ｔとの相関関係をとるには、コーン２先端の深度から上２５ｃｍの分の先端抵抗ｑ_ｔの平均値と半回転数Ｎ_ＳＷとを対応させている。
【００１５】
次に、ＳＳＴの自沈区間では、自沈がスクリューポイント１の長さ以上連続している部分のデータのみを使用し、各載荷重と自沈した深度区間のコーン２の貫入時の先端抵抗ｑ_ｔを対応させて、その相関関係を求める。
【００１６】
また、ＣＰＴのコーン２貫入時の先端抵抗ｑ_ｔの計測値が急激に変化している深度のデータは採用しないこととした。何故ならば、地盤Ｇの深度が急激に変化する地点では、長さＬ＝２０ｃｍのスクリューポイント１がその両方の地盤Ｇの境界部で回転しており、スクリューポイント１の貫入時の抵抗は硬い層のみによる影響が大きいと考えられるからである。
【００１７】
ＳＳＴの回転貫入区間では、ＣＰＴで得られるコーン２貫入時の先端抵抗ｑ_ｔの値を、コーン２先端の深度から上方２５ｃｍの平均値を求め、ＳＳＴで得られる半回転数Ｎ_ＳＷとを対応させて、このｑ_ｔとＮ_ＳＷとの相関関係を求めるが、その際に、土被り圧σ_Ｖ０が大きい場合は、ＳＳＴで得られる半回転数Ｎ_ＳＷとＣＰＴにより得られた先端抵抗ｑ_ｔに土被り圧σ_Ｖ０を考慮したｑ_ｔ−σ_Ｖ０との相関関係を求める。図２は上記Ｎ_ＳＷとｑ_ｔ−σ_Ｖ０とで得られた相関関係を示す図表である。
【００１８】
この結果により、Ｎ_ＳＷ＝３０及び３００で変曲点があり、Ｎ_ＳＷが小さいほど１半回転当たりのｑ_ｔ−σ_Ｖ０が増加する割合が大きく、Ｎ_ＳＷ≧３００ではＮ_ＳＷが増加してもｑ_ｔ−σ_Ｖ０がほとんど増加しないことが分かる。
【００１９】
このことにより、各変曲点間で直線近似を行ない、次の相関関係の式が得られた。
【００２０】
ｑ_ｔ−σ_Ｖ０＝５０．３Ｎ_ＳＷ＋６２０　　　　・・・・・　（１）
（０≦Ｎ_ＳＷ＜３０）
ｑ_ｔ−σ_Ｖ０＝８．９Ｎ_ＳＷ＋１８６０　　　　・・・・・　（２）
（３０＜Ｎ_ＳＷ＜３００）
ｑ_ｔ−σ_Ｖ０＝０．３３Ｎ_ＳＷ＋４４３０　　　・・・・・　（３）
（３００≦Ｎ_ＳＷ）
また、ＳＳＴの自沈区間では、載荷重Ｗ_ＳＷ＝１．０ｋＮで回転から自沈に変わる時のｑ_ｔ−σ_Ｖ０は、平均で６２０ｋＮ／ｍ^２（３８０〜８６０ｋＮ／ｍ^２）となり、以下、各自沈荷重Ｗ_ＳＷと換算ｑ_ｔ−σ_Ｖ０の関係は以下の表に示すとおりとなった。
【００２１】
【表１】

【００２２】
上記の相関関係の式から換算した土被り圧σ_Ｖ０を考慮した先端抵抗ｑ_ｔ−σ_Ｖ０の実測値を図３に示しており、細い線で示すのがＣＰＴ方法による線図で、また太い線で示すのがＳＳＴからの換算の線図であり、多少のバラツキは認められるがほぼ一致した値が得られることを確認した。
【００２３】
【発明の効果】
以上に説明した本発明の原位置における地盤の強度測定方法により地盤の強度測定を実施すれば、ＣＰＴを使用した場合に比べ、作業効率が３から５倍程度向上する。
【００２４】
すなわち、ＳＳＴは操作が簡易で、装置が軽量であることから、装置の移動に要する時間が大幅に短縮でき、ＣＰＴの３倍以上のデータが取得可能であり、調査にかゝる時間や費用が削減できる。
【図面の簡単な説明】
【図１】本発明の地盤の強度測定方法の一実施形態におけるＳＳＴ及びＣＰＴを地盤上の近傍の地点で行なった測定深度の関係を示す図である。
【図２】図１の実施形態における半回転数Ｎ_ＳＷと土被り圧を考慮した先端抵抗ｑ_ｔ−　σ_Ｖ０との相関関係を示す図表である。
【図３】図１の換算ｑ_ｔ−σ_Ｖ０の深度分布を示す図表である。
【符号の説明】
１　　スクリューポイント
２　　コーン
Ｇ　　地盤[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for measuring the strength of ground in situ using a Swedish sounding test.
[0002]
[Prior art]
Conventionally, an electric static cone penetration test (JGS1435-1995, hereinafter abbreviated as CPT in the present description) has been used to measure the strength continuous in the depth direction of the ground at the original position.
[0003]
This CPT is a test method in which a cone is statically penetrated into the ground, and the tip resistance and pore water pressure are electrically determined. This CPT test requires a reaction force because the cone is set in the ground and penetrated. Therefore, the equipment including the cone, the rod, the penetrating device, the depth measuring device, the measuring device, and the fixing device becomes large-scale, and there is a problem that it takes time to move and install the device.
[0004]
Therefore, in comparison with the above CPT test method, a Swedish sounding test (JISA1221; hereinafter referred to as “JISA1221”) in which data on continuous ground strength at the original position can be obtained efficiently and with good mobility using a simpler apparatus as in the case of CPT. This test method has advantages such as easy and quick measurement of the device and its operation, and relatively excellent penetration performance among simple soundings. Is known to have.
[0005]
The SST test apparatus is mainly composed of a handle, a weight, a loading clamp, a rod, a screw point, and the like. The screw point is loaded with a weight via a rod, and after stopping to penetrate the ground with the load, The relationship between the number of revolutions and the amount of penetration when the rod is rotated by the handle is determined.
[0006]
In the SST test method, the ground strength of the measured value is usually converted into an N value based on the correlation with the N value. Then, paying attention to the fact that the cone penetration resistance can be more accurately evaluated than the N value, the present inventors have studied the method of converting the cone penetration resistance from the result of SST and arrived at the present invention.
[0007]
[Problems to be solved by the invention]
The present invention provides a method of measuring the strength of the ground at the original position where the correlation between the CPT and the SST can be grasped and the ground strength at the original position can be efficiently measured by the SST, and the work efficiency can be improved.
[0008]
[Means for Solving the Problems]
In the present invention, an electric static cone penetration test CPT and a Swedish sounding test SST are respectively performed at a point about 1 to 2 m away from the measurement ground, and the tip resistance at the time of cone penetration of the CPT is obtained from the obtained data. data of depth measurement values of q _t is changing abruptly without adopting, in rotation penetration section SST, the value of resistor tip q _t during cone penetration obtained with CPT, upwardly 25cm from the depth of the cone tip The average value of the minute is obtained, and the half-rotation speed N _SW obtained in the SST is associated with the correlation, and the correlation is obtained. using, in correspondence with the tip resistance q _t during cone penetration depth interval was scuttled each mounting load, after determining the correlation, the SST data were performed, it has already been determined C The method comprises a method of measuring the strength of the ground at the original position to obtain the converted tip resistance from the correlation with PT, and the present invention uses the half rotation number N _SW obtained by SST and CPT when the overburden pressure σ _V0 is large. the resulting calculated the correlation between the distal tip considering resistance q _t soil overburden pressure sigma _V0 resistance q _t -σ _V0, a pressure sigma _V0 overburden the resulting tip resistance q _t by the mounting load and CPT It consists strength measuring method of the ground in situ using the relationship between the tip resistance q _t - [sigma] _V0 in consideration.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the method for measuring the strength of the ground according to the present invention will be described below with reference to FIG.
[0010]
First, the above-mentioned SST and CPT were simultaneously performed at a point about 2 m away from the ground G where the test was performed, and data obtained from the respective test results were arranged and examined.
[0011]
The SST apparatus implemented here automatically adjusts the load stage at the time of self-sinking by 0.05, 0.15, 0.25, 0.50, 0.75 in accordance with the strength of the ground G, that is, the load stage at the time of self-subsidence. , 1.00 kN can be adjusted in six stages, and it is self-sinking under a load of 1.00 kN or less, and after the self-sinking stops, it automatically switches to rotary intrusion. Can be changed automatically, the depth, half-turn, load stage are automatically measured, the device can be disassembled, its body is equipped with wheels, it can be moved and installed manually Has become.
[0012]
FIG. 1 is a diagram showing the correlation between the measured depths of the strength of the ground G by the respective test methods of SST and CPT. In the SST, a half rotation while the tip of the screw point 1 having a length L = 20 cm advances 25 cm. The number N _SW (value converted to a layer thickness of 1.0 m) is measured to estimate the strength of the ground G. Therefore, the measured half rotation number N _SW is 25 cm above the depth of the tip of the screw point 1. Indicates the average ground strength per minute.
[0013]
In contrast, in CPT it is intended to measure the tip resistance q _t during cone penetration of the cone 2 tip of about 3cm in 1.0cm pitch, and measures the ground intensity at approximately its depth.
[0014]
Therefore, the take a correlation between the half rotational speed N _SW and tip resistance q _t, in correspondence with an average value and half the rotational speed N _SW of minute tip resistance q _t top 25cm from the depth of the cone 2 tip I have.
[0015]
Next, in the scuttled section SST, scuttled can use only the data portion is continuous over the length of the screw point 1, the tip resistance q _t during penetration of the cone 2 of depth interval was scuttled each mounting load Correspondingly, the correlation is obtained.
[0016]
Also, data of the depth measurements of the tip resistance q _t during CPT cone 2 penetration is changing rapidly was not adopted. This is because at the point where the depth of the ground G changes rapidly, the screw point 1 having a length of L = 20 cm is rotating at the boundary between both the grounds G, and the resistance when the screw point 1 penetrates is hard. This is because the effect of only the layer is considered to be large.
[0017]
The SST rotation penetration section, the value of resistor tip _{q t} when the cone 2 penetration obtained with CPT, the average value of the upper 25cm from the depth of the cone 2 tip, corresponding to the half rotational speed _{N SW} obtained by SST Then, the correlation between q _t and N _SW is obtained. At this time, if the overburden pressure σ _V0 is large, the half-speed N _SW obtained by SST and the tip resistance q _t obtained by CPT are obtained. using the relationship between the _q t - [sigma] _V0 in consideration of the pressure sigma _V0 overburden on. FIG. 2 is a chart showing a correlation obtained by the above N _SW and q _t −σ _{V 0} .
[0018]
This _result, there is an inflection point in _N SW = 30 and _300, a large proportion _{of q} t - [sigma] _V0 per one half rotation as _{N SW} is small _increases, and increases _{N SW} ≧ 300 In _{N SW} It can also be seen that q _t -σ _V0 hardly increases.
[0019]
As a result, linear approximation was performed between each inflection point, and the following correlation equation was obtained.
[0020]
_{_{_{q t -σ V0 = 50.3N SW +620}}} ····· (1)
(0 ≦ N _SW <30)
_{_{_{q t -σ V0 = 8.9N SW +1860}}} ····· (2)
(30 <N _SW <300)
_{_{_{q t -σ V0 = 0.33N SW +4430}}} ····· (3)
(300 ≦ N _SW )
Further, in the scuttled section SST, _q t - [sigma] _V0 when changing to scuttled from rotating in mounting load _W SW = 1.0 kN is on average at ^{^{620kN / m 2 (380~860kN / m}} 2) , and the following, each The relationship between the sinking load W _SW and the converted q _t −σ _{V 0} is as shown in the following table.
[0021]
[Table 1]

[0022]
Shows the measured values of resistor tip q _t - [sigma] _V0 in consideration of the pressure sigma _V0 overburden converted from the above equation correlation in Figure 3, a line diagram by CPT method show a thin line, also thick The line is a conversion diagram from the SST, and it was confirmed that although there was some variation, a substantially consistent value was obtained.
[0023]
【The invention's effect】
If the strength of the ground is measured by the above-described method of measuring the strength of the ground at the original position of the present invention, the working efficiency is improved about 3 to 5 times as compared with the case where CPT is used.
[0024]
That is, since the SST is easy to operate and the device is lightweight, the time required to move the device can be significantly reduced, data more than three times as large as the CPT can be obtained, and the time and cost required for the survey can be improved. Can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a relationship between measured depths obtained by performing SST and CPT at a nearby point on the ground in one embodiment of the ground strength measuring method of the present invention.
FIG. 2 is a table showing a correlation between a half rotation speed N _SW and a tip resistance q _t −σ _V0 in consideration of an overburden pressure in the embodiment of FIG. 1;
FIG. 3 is a chart showing a depth distribution of a converted q _t −σ _V0 of FIG. 1;
[Explanation of symbols]
1 screw point 2 cone G ground

Claims

And electrical static cone penetrometer CPT, a Swedish sounding test SST, performed respectively at a distance of about 2m from the first measurement ground, from the obtained data, when CPT cone penetration tip resistance q _t data of depth measurement values change abruptly without adopting, in rotation penetration section SST, the value of resistor tip q _t during cone penetration obtained with CPT, the average from the depth of the cone tip of the upper 25cm min A value is obtained, and a correlation is obtained by associating the half-rotation speed N _SW obtained in SST, and a self-sinking section of SST uses only data of a part where auto-sinking is continuous for more than the length of the screw point, a tip resistance q _t during cone penetration depth interval was scuttled each mounting load in correspondence, phase after determining the correlation, the SST data was conducted, and CPT that is already determined A method of measuring the strength of the ground at the original position where the converted tip resistance is determined from the relationship.

If Overburden pressure sigma _V0 is large, the correlation between the tip resistance _q t - [sigma] _V0 in consideration of the pressure sigma _V0 overburden the tip resistance _{q t} obtained by half rotation speed _{N SW} and CPT obtained by SST determined, the strength measuring method of the ground in situ according to claim 1, wherein using the relationship between the tip resistance q _t - [sigma] _V0 in consideration of the pressure sigma _V0 overburden the resulting tip resistance q _t by the mounting load and CPT .