JP3952138B2

JP3952138B2 - Evaluation method of static earth pressure coefficient of pile or sand compaction pile placement ground and evaluation method of static earth pressure coefficient of sand compaction pile itself of sand compaction pile placement ground

Info

Publication number: JP3952138B2
Application number: JP2001327946A
Authority: JP
Inventors: 秀郎半沢
Original assignee: Toa Corp
Current assignee: Toa Corp
Priority date: 2001-10-25
Filing date: 2001-10-25
Publication date: 2007-08-01
Anticipated expiration: 2021-10-25
Also published as: SG103848A1; JP2003129462A

Description

【０００１】
【発明の属する技術分野】
本発明は、杭またはサンドコンパクションパイルを地盤に打設することにより得られる地盤の強度の上昇を設計時に反映させ、コストダウンに寄与させるために行なう杭またはサンドコンパクションパイル打設地盤の静止土圧係数の評価方法に関する。
【０００２】
【従来の技術】
従来、地盤中に杭またはサンドコンパクションパイル（ＳＣＰ）を打設すれば、その地盤の静止土圧係数（Ｋ_o）が増加し、地盤の強度が上昇することが一般に広く知られているが、このような利点が設計時に取り入れられていないのが現状である。
【０００３】
即ち、地盤の静止土圧係数（Ｋ_o）が増加すると、地盤のせん断強度は増加することになり、このＫ_oが増加することによる砂、粘土のせん断強度増加比を、ＳＣＰが打設された複合地盤の置換え率（ａ_S）、即ち複合地盤のうちＳＣＰの占める面積ａ_Sを例にとり図７の２つの線図に示している。
【０００４】
図７において、砂からなるサンドコンパクションパイルＳＣＰにおいて、静止土圧係数Ｋ_o＝１．０およびａ_S＝０．４のせん断強度は、Ｋ_o＝０．４およびａ_S＝０．７のせん断強度にほぼ等しく、また正規圧密粘土において、静止土圧係数Ｋ_o＝１．０のせん断強度は、Ｋ_o＝０．５のせん断強度の約１．５倍に達する。
【０００５】
即ち、静止土圧係数Ｋ_oの増加を適切に評価することにより、置換え率ａ_Sは０．７から０．４まで低減できる可能性があるにも拘らず、現在のところ、Ｋ_o増加の適切な評価方法と、設計への簡便な適用方法は現在のところ未だ確立されていない。
【０００６】
このような静止土圧係数の増加を適切に評価して設計に適切に適用すれば、当然関連工事のコストダウンに寄与できることに着目して本発明の静止土圧係数の評価方法に到達した。
【０００７】
【発明が解決しようとする課題】
本発明は、杭やサンドコンパクションパイルを打設することによる地盤の静止土圧係数の増加を適切に評価し、その静止土圧係数を適切に、かつ簡便に設計に適用させるため、電気式静的コーン貫入試験（ＣＰＴ）と一面せん断試験（ＤＳＴ）とを組合わせた静止土圧係数増加の評価を行ないうる杭またはサンドコンパクションパイル打設地盤の静止土圧係数の評価方法を提供する。
【０００８】
【課題を解決するための手段】
本発明は、施工区域内の代表地点を選定し、電気式静的コーン貫入試験ＣＰＴを実施して、杭またはサンドコンパクションパイル打設前のコーン先端抵抗（ｑ_T−σ_VO）₍₀₎を得、ＣＰＴ実施後、代表的地点を囲むように試験杭または試験用サンドコンパクションパイルを複数本打設し、次いで杭またはサンドコンパクションパイル間中央部や杭またはサンドコンパクションパイル近傍などの複数点でＣＰＴを実施し、杭またはサンドコンパクションパイル打設後のコーン先端抵抗（ｑ_T−σ_VO）₍₁₎を得た後、杭またはサンドコンパクションパイル打設前後のコーン先端抵抗（ｑ_T−σ_VO）₍₀₎および（ｑ_T−σ_VO）₍₁₎と杭またはサンドコンパクションパイル打設前および打設後それぞれの静止土圧係数Ｋ_o(1)との関係式：
【０００９】
【数３】

【００１０】
から、杭またはサンドコンパクションパイル打設後の砂質地盤の静止土圧係数を算定する杭またはサンドコンパクションパイル打設地盤の静止土圧係数の評価方法からなる。
【００１１】
また本発明は、施工区域内の代表的地点を選定し、電気式静的コーン貫入試験ＣＰＴを実施して、サンドコンパクションパイル打設前のコーン先端抵抗（ｑ_T−σ_VO）₍₀₎を得ると同時に、同一地点で不攪乱試料を採取し、全不攪乱試料に対して再圧縮法による一面せん断試験ＤＳＴを実施し、サンドコンパクションパイル打設前の非排水せん断強度Ｓ_u(B)を求め、Ｓ_u(B)と（ｑ_T−σ_VO）₍₀₎の相関関係を求めた後、代表的不攪乱試料により正規圧密状態でのＤＳＴを実施し、正規圧密状態のせん断強度増加率（Ｓ_un(DST)／σ^' _V）を求め、次に代表的地点を囲むように試験サンドコンパクションパイルを複数本打設し、圧密終了後、ＣＰＴを複数点で実施し、サンドコンパクションパイル打設後のコーン先端抵抗（ｑ_T−σ_VO）₍₁₎を得、Ｓ_u(B)と（ｑ_T−σ_VO）₍₀₎の相関関係を、サンドコンパクションパイル打設後の非排水せん断強度Ｓ_u(D)と（ｑ_T−σ_VO）₍₁₎の関係に適用してＳ_u(D)を求めた後、サンドコンパクションパイル打設前および打設後それぞれの静止土圧係数Ｋ_o(0)およびＫ_o(1)とＳ_u(D)およびＳ_un(DST)／σ^' _Vとの関係式：
【００１２】
【数４】

【００１３】
から、サンドコンパクションパイル打設後の粘土地盤の静止土圧係数を算定するサンドコンパクションパイル打設地盤の静止土圧係数の評価方法からなり、さらに本発明は、上記したサンドコンパクションパイル打設後に算定した静止土圧係数を、サンドコンパクションパイル自体の静止土圧係数として評価するサンドコンパクションパイル打設地盤のサンドコンパクションパイル自体の静止土圧係数の評価方法からなり、また本発明は、複数のサンドコンパクションパイルと粘土の境界付近で電気式静的コーン貫入試験ＣＰＴを実施して、得られた複数のコーン先端抵抗（ｑ_T−σ_VO）₍₁₎の平均値を求め、前記本発明の方法に従って得られる静止土圧係数を、サンドコンパクションパイル自体の静止土圧係数として評価するサンドコンパクションパイル打設地盤のサンドコンパクションパイル自体の静止土圧係数の評価方法からなる。
【００１４】
【発明の実施の形態】
以下図面を参照しながら本発明の杭またはサンドコンパクションパイル打設地盤の静止土圧係数の評価方法を適用した実施の形態につき説明するが、以下の説明において使用する用語とその記号および簡単な説明を下記の表に纏めている。
【００１５】
【表１】

【００１６】
そこで、本発明の一実施形態における杭またはＳＣＰ打設による砂地盤の静止土圧係数Ｋ_o増加の評価方法につき杭またはＳＣＰが打設された砂地盤を対象に、Ｋ_o増加を求めるための調査と評価方法の手順を以下の１項から５項のフローに沿って説明する。
【００１７】
１．施工区域全域でＣＰＴを実施し、（ｑ_T−σ_VO）₍₀₎、地盤構成を把握する。ただし、事前に充分な土質調査が行われて、施工区域全域の代表的地点が選定できる場合は不要である。
【００１８】
２．上記の調査から代表的地点を選定し（必要に応じて複数点）、ＣＰＴを実施する。この際、ＣＰＴは１地点につき２回以上行なうことが好ましく、このＣＰＴの実施の状態は図１に示す通りである。この試験より、杭１またはＳＣＰ打設前の（ｑ_T −σ_VO）₍₀₎ が得られる。
【００１９】
３．ＣＰＴ実施後、代表的地点を囲むように試験杭あるいは試験ＳＣＰを複数本打設する。なお、図１に示すこの実施形態では杭１を４本打設した正方形配置の場合であるが、三角形配置で３本打設する場合や、多角形配置で５本以上打設する場合もあり得る。
【００２０】
４．次いで、杭１まはＳＣＰ間中央部や杭１またはＳＣＰ近傍などの複数点でＣＰＴを実施する。本試験より（ｑ_T−σ_VO）₍₁₎が得られる。なお、（ｑ_T−σ_VO）₍₀₎と（ｑ_T−σ_VO）₍₁₎の測定例を図２に示している。
【００２１】
５．（ｑ_T−σ_VO）₍₀₎と（ｑ_T−σ_VO）₍₁₎から式（１）により、Ｋ_o(1)を算定する。ただし一般的にはＫ_o(0)＝０．４とすることが多い。
【００２２】
【数５】

【００２３】
実務上、φ増加をＫ_o増加に含め、式（２）のように単純化してもよい。
【００２４】
【数６】

【００２５】
なお、シルト質砂や粘土質砂のように、排水速度の遅い地盤では、ＪＧＳ１４３５−１９９５「電気式静的コーン貫入試験方法」に示されている標準的貫入速度（１〜２cm/s）にとらわれず、貫入中の過剰間隙水圧が０となるような速度でＣＰＴを実施する。
【００２６】
上記の実施形態における評価方法のフローチャートを図３に示しており、またこの評価で得られた杭打設後のＫ_o(1)の具体的使用例として、次式による杭の周面摩擦力の算定が挙げられる。
【００２７】
τ＝σ' _VO tanφ₍₁₎Ｋ_{o (1)}
次に、本発明の他の実施形態におけるＳＣＰ打設による粘土地盤の静止土圧係数Ｋ_o増加の評価方法につき、ＳＣＰが打設された粘土を対象に、Ｋ_o増加を求めるための調査と評価方法の手順を以下の１項から６項のフローに沿って説明する。
【００２８】
１．施工区域全域でＣＰＴを実施し、（ｑ_T−σ_VO）₍₀₎、地盤構成を把握する。ただし、事前に充分な土質調査が行われて、施工区域全域の代表的地点が設定できる場合は不要である。
【００２９】
２．上記の調査から代表的地点を選定し（必要に応じて複数点）、ＣＰＴを実施する。この試験よりＳＣＰ２打設前の（ｑ_T−σ_VO）₍₀₎が得られる。
【００３０】
３．上記２項と同時に同一地点で不攪乱試料を採取し、全不攪乱試料に対して再圧縮法によるＤＳＴを実施し、Ｓ_u(B)を求める。次いで、式（３）に示す（ｑ_T−σ_VO）₍₀₎とＳ_u(B)の相関関係を求める。
【００３１】
【数７】

【００３２】
なお、再圧縮法とは、試料を原位置の有効土被り圧で圧密した後に試験を行う方法である。２ヶ所の粘土から得られた（ｑ_T−σ_VO）₍₀₎とＳ_u(B)の関係を図４に示す。両者のあいだには図に示したような良い相関関係が通常認められる。
【００３３】
４．代表的な不攪乱試料により正規圧密状態でのＤＳＴを実施し、（Ｓ_un _(DST)／σ’_V）を求める。
【００３４】
５．代表的地点を囲むように試験ＳＣＰ２を打設する。なお、図５に示すごとく、この実施形態では４本打設した場合を示しているが、三角形配置で３本打設する場合や、多角形配置で５本以上打設する場合もあり得る。打設による圧密が終了した後、複数点でＣＰＴを図５のように実施する。本試験より、（ｑ_T−σ_VO）₍₁₎が得られる。平均（ｑ_T−σ_VO）₍₁₎と式（３）で得られたｋを用いて式（４）によりＳ_u(D)を求める。
【００３５】
【数８】

【００３６】
６．Ｓ_u(D)を用い、式（５）よりＫ_o(1)を算定する。ただし、Ｋ_o(0)＝０．５とすることが多い。
【００３７】
【数９】

【００３８】
上記の実施形態における評価方法のフローチャートを図６に示しており、この評価方法で得られたＫ_o(1)の具体的使用例として、次式によるＳＣＰ打設後の地盤に盛土を行う際の粘土地盤のせん断力の算定が挙げられる。
【００３９】
【数１０】

【００４０】
さらに、サンドコンパクションパイルＳＣＰ自体の静止土圧係数Ｋ_oの評価方法につき説明すると、サンドコンパクションパイルＳＣＰと粘土から構成される複合地盤では、ＳＣＰ自体のＫ_o評価も重要となる。ＳＣＰ打設により発揮される水平応力は、図５に示すようにＳＣＰ中心で高く、粘土地盤に向けて低下する。ここでは、下記の２通りの方法を、ＳＣＰ自体のＫ_o評価法として示す。どちらを採用するかは設計者の判断となる。
【００４１】
Ａ）式（５）から得られる粘土のＫ_o(1)をＳＣＰ自体のＫ_oと見なす。
【００４２】
Ｂ）ＳＣＰと粘土の境界付近（図５のNo.1' 〜No.4' ）でＣＰＴを実施する。平均（ｑ_T−σ_VO）₍₁₎を求め、式（４）および式（５）から得られるＫ_o(1)をＳＣＰ自体のＫ_oとする。
【００４３】
以上の通り、本発明の杭まはたサンドコンパクションパイル打設地盤の静止土圧係数の評価方法においては、実際の現場の地盤に試験的に杭１またはサンドコンパクションパイルＳＣＰ２を打設する前の状態をある決められた試験方法で試験した後、杭１またはサンドコンパクションパイルＳＣＰ２を打設後の状態も同じような試験方法で試験し、これら打設前と打設後との結果から、静止土圧係数Ｋ_o(0)とＫ_o(1)とを評価しようとするものであり、図３に示す実施形態のように砂地盤のＫ_o増加の評価を行なう場合には、電気式静的コーン貫入試験ＣＰＴだけの試験を行って評価をする一方、図６に示す実施形態のように粘土地盤のＫ_o増加の評価を行なう場合には、電気式静的コーン貫入試験ＣＰＴと一面せん断試験ＤＳＴの２つの試験を行なって評価をすることを特徴としたものである。
【００４４】
【発明の効果】
以上に説明した本発明の杭またはサンドコンパクションパイル打設地盤の静止土圧係数の評価方法によれば、杭やサンドコンパクションパイルを打設することによる地盤の静止土圧係数を適切に評価して、設計に適切、かつ簡便に適用することができ、関連する工事のコストダウンをはかることができ、工事の経済性を高めることができる。
【図面の簡単な説明】
【図１】本発明の方法により杭またはＳＣＰ打設による砂地盤のＫ_o増加の評価を行なう一実施形態における４本の杭の打設前及び打設後のＣＰＴ試験実施位置説明図である。
【図２】図１の実施形態における杭打込み前と後のＣＰＴによる先端抵抗力を示す線図である。
【図３】図１の実施形態における評価方法のフローチャートである。
【図４】本発明の方法によりＳＣＰ打設による粘土地盤のＫ_o増加の評価を行なう他の実施形態における２ヶ所の粘土から得られたＣＰＴによる先端抵抗力（ｑ_T−σ_VO）₍₀₎と非排水せん断強度Ｓ_un(DST)の関係線図である。
【図５】本発明の方法によりＳＣＰ打設による粘土地盤のＫ_o増加の評価を行う一実施形態における４本のＳＣＰの打設前及び打設後のＣＰＴ試験実施位置の説明図である。
【図６】図５の実施形態における評価方法のフローチャートである。
【図７】地盤のＫ_oが増加することによる砂、粘土のせん断強度増加比を、ＳＣＰが打設された複合地盤の置換え率で示す線図である。
【符号の説明】
１杭
２ＳＣＰ[0001]
BACKGROUND OF THE INVENTION
The present invention reflects the increase in strength of the ground obtained by placing piles or sand compaction piles on the ground at the time of design, and performs static earth pressure on piles or sand compaction pile placing grounds to contribute to cost reduction. The present invention relates to a coefficient evaluation method.
[0002]
[Prior art]
Conventionally, it is generally well known that if a pile or sand compaction pile (SCP) is placed in the ground, the static earth pressure coefficient (K _o ) of the ground increases and the strength of the ground increases. At present, such advantages are not taken into account at the time of design.
[0003]
That is, if the static earth pressure coefficient (K _o ) of the ground increases, the shear strength of the ground will increase, and the SCP will be set to increase the shear strength ratio of sand and clay as this K _o increases. FIG. 7 shows two examples of the composite ground replacement rate (a _S ), that is, the area a _S occupied by the SCP in the composite ground.
[0004]
7, the sand compaction pile SCP consisting sand, the shear strength of the stationary earth pressure coefficient K _o = 1.0 and a _S = 0.4, the shearing of K _o = 0.4 and a _S = 0.7 The shear strength with a static earth pressure coefficient K _o = 1.0 reaches approximately 1.5 times the shear strength with K _o = 0.5 in a normally consolidated clay.
[0005]
That is, although the replacement rate a _S may be reduced from 0.7 to 0.4 by appropriately evaluating the increase in the static earth pressure coefficient K _o , at present, the increase in K _o An appropriate evaluation method and a simple application method to design have not been established yet.
[0006]
The evaluation of the static earth pressure coefficient according to the present invention has been achieved by paying attention to the fact that if such an increase in the static earth pressure coefficient is appropriately evaluated and appropriately applied to the design, it can naturally contribute to the cost reduction of the related work.
[0007]
[Problems to be solved by the invention]
The present invention appropriately evaluates the increase in the static earth pressure coefficient of the ground by placing piles and sand compaction piles, and applies the static earth pressure coefficient to the design appropriately and simply. A method for evaluating a static earth pressure coefficient of a pile or a sand compaction pile placement ground capable of evaluating an increase in a static earth pressure coefficient by combining a static cone penetration test (CPT) and a one-plane shear test (DST).
[0008]
[Means for Solving the Problems]
In the present invention, a representative point in the construction area is selected, an electric static cone penetration test CPT is performed, and the cone tip resistance (q _T −σ _VO ) ₍₀₎ before placing a pile or a sand compaction pile is calculated. After the CPT, a plurality of test piles or sand compaction piles for testing are placed so as to surround a representative point, and then CPT is performed at a plurality of points such as a central portion between the piles or the sand compaction piles and the vicinity of the piles or the sand compaction piles. After obtaining the cone tip resistance (q _T −σ _VO ) ₍₁₎ after placing the pile or sand compaction pile, the cone tip resistance (q _T −σ _VO ) before and after placing the pile or sand compaction pile is obtained. Relational expression between ₍₀₎ and (q _T −σ _VO ) ₍₁₎ and static earth pressure coefficient K _{o (1)} before and after placing pile or sand compaction pile:
[0009]
[Equation 3]

[0010]
Therefore, it consists of the evaluation method of the static earth pressure coefficient of the pile or sand compaction pile placement ground which calculates the static earth pressure coefficient of the sandy ground after pile or sand compaction pile placement.
[0011]
In the present invention, representative points in the construction area are selected, an electric static cone penetration test CPT is performed, and the cone tip resistance (q _T −σ _VO ) ₍₀₎ before the sand compaction pile is set. At the same time, undisturbed samples are collected at the same point, and the single-sided shear test DST by the recompression method is performed on all undisturbed samples, and the undrained shear strength Su _(B) before sand compaction pile placement is obtained. After obtaining the correlation between Su _(B) and (q _T −σ _VO ) ₍₀₎ , DST is performed in the normal consolidated state using a typical undisturbed sample, and the shear strength increase rate in the normal consolidated state is obtained. (S _{un (DST)} / σ ^' _V ) is obtained, and then a plurality of test sand compaction piles are placed so as to surround a representative point, and after completion of consolidation, CPT is performed at a plurality of points. Cone tip resistance after installation (q _T −σ _VO ) ₍₁₎ is obtained, and _{Su (B)} And (q _T −σ _VO ) ₍₀₎ is applied to the relationship between undrained shear strength Su _(D) and (q _T −σ _VO ) ₍₁₎ after sand compaction pile placement. After obtaining _{u (D)} , before and after sand compaction pile placement, static earth pressure coefficients K _{o (0)} and K _{o (1)} and S _{u (D)} and S _{un (DST)} / σ ^' Relation to _V :
[0012]
[Expression 4]

[0013]
From the evaluation method of the static earth pressure coefficient of the sand compaction pile placement ground, which calculates the static earth pressure coefficient of the clay ground after the sand compaction pile placement, further, the present invention is calculated after the sand compaction pile placement described above The present invention comprises a method for evaluating the static earth pressure coefficient of the sand compaction pile itself of the sand compaction pile placement ground, wherein the static earth pressure coefficient is evaluated as the static earth pressure coefficient of the sand compaction pile itself. An electric static cone penetration test CPT was performed near the boundary between the pile and the clay, and the average value of the obtained plurality of cone tip resistances (q _T -σ _VO ) ₍₁₎ was determined. According to the method of the present invention, Sand compaction that evaluates the obtained static earth pressure coefficient as the static earth pressure coefficient of the sand compaction pile itself It consists of a method for evaluating the static earth pressure coefficient of the sand compaction pile itself.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments to which a method for evaluating a static earth pressure coefficient of a pile or sand compaction pile placement ground of the present invention is applied will be described below with reference to the drawings, but the terms used in the following description, their symbols, and a brief description Are summarized in the table below.
[0015]
[Table 1]

[0016]
Therefore, in the embodiment of the present invention, the evaluation method for increasing the static earth pressure coefficient K _{o of} sand ground by pile or SCP placement is to obtain an increase in K _o for sand ground in which pile or SCP is placed. The procedure of the investigation and the evaluation method will be described along the flow of items 1 to 5 below.
[0017]
1. CPT will be conducted throughout the construction area, and (q _T −σ _VO ) ₍₀₎ to understand the ground structure. However, it is not necessary if sufficient soil survey is conducted in advance and representative points in the entire construction area can be selected.
[0018]
2. Select representative points from the above survey (multiple points if necessary) and implement CPT. At this time, the CPT is preferably performed twice or more per point , and the state of implementation of the CPT is as shown in FIG. From this test, (q _T −σ _VO ) ₍₀₎ before pile 1 or SCP placement is obtained.
[0019]
3. After the CPT, a plurality of test piles or test SCPs are placed around a representative point. In addition, in this embodiment shown in FIG. 1, it is the case of the square arrangement | positioning which 4 piles 1 were laid, but when placing 3 pieces by a triangular arrangement | positioning, it may place 5 or more pieces by polygon arrangement | positioning. obtain.
[0020]
4). Next, the CPT is performed at a plurality of points such as the pile 1 or the central portion between SCPs, the pile 1 or the vicinity of the SCP. From this test, (q _T −σ _VO ) ₍₁₎ is obtained. Note that measurement examples of (q _T −σ _VO ) ₍₀₎ and (q _T −σ _VO ) ₍₁₎ are shown in FIG.
[0021]
5). K _{o (1)} is calculated from (q _T −σ _VO ) ₍₀₎ and (q _T −σ _VO ) _{(1) according} to equation (1). In general, however, K _{o (0)} = 0.4 is often used.
[0022]
[Equation 5]

[0023]
In practice, the increase in φ may be included in the increase in K _o and simplified as shown in Equation (2).
[0024]
[Formula 6]

[0025]
In the case of ground with a slow drainage speed, such as silty sand and clay sand, the standard penetration speed (1-2 cm / s) shown in JGS1435-1995 “Electrical Static Cone Penetration Test Method” is used. Regardless of the CPT, the excess pore water pressure during the penetration is zero.
[0026]
The flowchart of the evaluation method in the above embodiment is shown in FIG. 3, and as a concrete example of use of Ko ₍₁₎ after pile driving obtained by this evaluation, the peripheral frictional force of the pile according to the following formula: Calculation.
[0027]
τ = σ ' _VO tanφ ₍₁₎ K _{o (1)}
Next, a method of evaluating the static earth pressure coefficient K _o increase in Clay by SCP hitting set according to another embodiment of the present invention, the target SCP is pouring clay, and investigation for determining the K _o increase The procedure of the evaluation method will be described along the flow of the following items 1 to 6.
[0028]
1. CPT will be conducted throughout the construction area, and (q _T −σ _VO ) ₍₀₎ to understand the ground structure. However, it is not necessary if sufficient soil survey is conducted in advance and representative points in the entire construction area can be set.
[0029]
2. Select representative points from the above survey (multiple points if necessary) and implement CPT. From this test, (q _T −σ _VO ) ₍₀₎ before SCP2 placement is obtained.
[0030]
3. Simultaneously with the above two items, undisturbed samples are collected at the same point, DST is performed on all undisturbed samples by the recompression method, and Su _(B) is obtained. Next, the correlation between (q _T −σ _VO ) ₍₀₎ and Su _(B) shown in Equation (3) is obtained.
[0031]
[Expression 7]

[0032]
The recompression method is a method in which a test is performed after a sample is consolidated with an effective soil covering pressure in situ. FIG. 4 shows the relationship between (q _T −σ _VO ) ₍₀₎ and Su _(B) obtained from two clays. A good correlation as shown in the figure is usually observed between the two.
[0033]
4). Performed DST in normally consolidated state by typical undisturbed samples, obtaining the _{_{(S u n (DST) /}} σ 'V).
[0034]
5). Test SCP2 is placed so as to surround a representative point. As shown in FIG. 5, this embodiment shows a case where four are placed, but there are cases where three are placed in a triangular arrangement or five or more are placed in a polygonal arrangement. After the consolidation by placing is completed, CPT is performed at a plurality of points as shown in FIG. From this test, (q _T −σ _VO ) ₍₁₎ is obtained. Using the average (q _T −σ _VO ) ₍₁₎ and k obtained from Equation (3), _{Su (D)} is obtained by Equation (4).
[0035]
[Equation 8]

[0036]
6). Using S _{u (D)} , K _{o (1)} is calculated from equation (5) . However, K _{o (0)} = 0.5 is often set.
[0037]
[Equation 9]

[0038]
The flowchart of the evaluation method in the above embodiment is shown in FIG. 6. As a concrete example of use of _{Ko (1)} obtained by this evaluation method, when embankment is performed on the ground after the SCP placement according to the following equation: Calculation of the shear force of clay ground.
[0039]
[Expression 10]

[0040]
Furthermore, when explained method for evaluating stationary earth pressure coefficient K _o of sand compaction pile SCP itself, in the composite soil composed of sand compaction pile SCP and clay, K _o Evaluation of SCP itself is also important. As shown in FIG. 5, the horizontal stress exerted by the SCP placement is high at the center of the SCP and decreases toward the clay ground. Here, the following two methods are shown as the _Ko evaluation method of the SCP itself. It is up to the designer to decide which one to use.
[0041]
A) K _{o (1)} of the clay obtained from the formula (5) is regarded as K _o of the SCP itself.
[0042]
B) CPT is performed near the boundary between SCP and clay (No. 1 'to No. 4' in FIG. 5). The average (q _T −σ _VO ) ₍₁₎ is obtained, and K _{o (1)} obtained from the equations (4) and (5 ₎ is defined as the K _o of the SCP itself.
[0043]
As described above, in the method for evaluating the static earth pressure coefficient of the pile or sand compaction pile placement ground of the present invention, before the pile 1 or sand compaction pile SCP2 is experimentally placed on the actual ground, After testing the state by a predetermined test method, the state after placing the pile 1 or the sand compaction pile SCP2 is also tested by the same test method. From the results before and after placing, is intended to be evaluated for the soil pressure coefficient _{_{K o (0) K o (}} 1) and, in the case of the evaluation of K _o increase in sand as in the embodiment shown in FIG. 3, an electrical static manner cone penetration test while only test carried out in the evaluation CPT, when the evaluation of K _o increase in clay as in the embodiment shown in FIG. 6, the electric static cone penetrometer CPT and shear Two tests of test DST In which was characterized by a ringing evaluation.
[0044]
【The invention's effect】
According to the method for evaluating the static earth pressure coefficient of the pile or sand compaction pile placement ground of the present invention described above, the static earth pressure coefficient of the ground by placing the pile or sand compaction pile is appropriately evaluated. Therefore, it can be applied to the design appropriately and easily, the cost of the related construction can be reduced, and the economic efficiency of the construction can be improved.
[Brief description of the drawings]
FIG. 1 is an explanatory view of a CPT test execution position before and after placing four piles in one embodiment in which an evaluation of _Ko increase of sand ground by pile or SCP placement according to the method of the present invention is performed. .
FIG. 2 is a diagram showing tip resistance force by CPT before and after pile driving in the embodiment of FIG. 1;
FIG. 3 is a flowchart of an evaluation method in the embodiment of FIG.
[4] tip resistance by resulting CPT from two places of the clay in the other embodiments to evaluate the K _o increase in Clay by SCP hitting set by the method of the present invention (q _T -σ _VO) _{(0 )} And undrained shear strength S _{un (DST)} .
FIG. 5 is an explanatory diagram of a CPT test execution position before and after placing four SCPs in an embodiment in which an evaluation of _Ko increase of clay ground by SCP placement is performed according to the method of the present invention.
6 is a flowchart of an evaluation method in the embodiment of FIG.
FIG. 7 is a diagram showing the ratio of increase in shear strength of sand and clay due to an increase in _{Ko of the} ground in terms of the replacement rate of the composite ground where SCP is placed.
[Explanation of symbols]
1 Pile 2 SCP

Claims

Select a representative point in the construction area, conduct an electrical static cone penetration test CPT, obtain the cone tip resistance (q _T -σ _VO ) ₍₀₎ before placing the pile or sand compaction pile, and conduct the CPT After that, a plurality of test piles or sand compaction piles for testing are placed so as to surround a representative point, and then CPT is performed at a plurality of points such as a central portion between the piles or the sand compaction piles and the vicinity of the piles or the sand compaction piles. After obtaining the cone tip resistance (q _T −σ _VO ) ₍₁₎ after placing the pile or sand compaction pile, the cone tip resistance (q _T −σ _VO ) ₍₀₎ before and after placing the pile or sand compaction pile _{_{_{(q T -σ VO) (1}}} ) and the pile or sand compaction pile hitting設前and after casting the respective stationary earth pressure coefficient K _{o (0)} and K _{o (1)} and the relationship:

The method of evaluating the static earth pressure coefficient of piles or sand compaction pile placement ground, which calculates the static earth pressure coefficient of sandy ground after pile or sand compaction pile placement.

Select a representative point in the construction area and conduct an electrical static cone penetration test CPT to obtain the cone tip resistance (q _T -σ _VO ) ₍₀₎ before placing the sand compaction pile. the undisturbed samples were taken at the point, conduct direct shear test DST by recompression method for all undisturbed sample, determine the undrained shear strength of the sand compaction pile hitting設前_{S u (B), S u} ( _After obtaining the correlation between ₍ _B) and (q _T −σ _VO ) ₍₀₎ , DST was performed in a normal consolidated state using a typical undisturbed sample, and the shear strength increase rate (S _{un (DST )} / Σ ^' _V ), and then several test sand compaction piles are placed so as to surround a representative point. After completion of consolidation, CPT is performed at multiple points, and the tip of the cone after sand compaction pile placement Resistance (q _T −σ _VO ) ₍₁₎ is obtained, and Su _(B) and (q _T −σ _VO ) The correlation of ₍₀₎ was applied to the relationship between undrained shear strength Su _(D) and (q _T −σ _VO ) ₍₁₎ after sand compaction pile placement, and Su _(D) was obtained. Then, before and after sand compaction pile casting, the relationship between static earth pressure coefficients K _{o (0)} and K _{o (1)} and S _{u (D)} and S _{un (DST)} / σ ^' _V :

From the above, the static earth pressure coefficient evaluation method of the sand compaction pile placement ground is calculated to calculate the static earth pressure coefficient of the clay ground after the sand compaction pile placement.

The method for evaluating the static earth pressure coefficient of the sand compaction pile of the sand compaction pile in which the static earth pressure coefficient according to claim 2 calculated after the sand compaction pile is cast is evaluated as the static earth pressure coefficient of the sand compaction pile itself. .

An electric static cone penetration test CPT is performed near the boundary between a plurality of sand compaction piles and clay, and an average value of a plurality of cone tip resistances (q _T −σ _VO ) ₍₁₎ obtained is obtained, The evaluation method of the static earth pressure coefficient of the sand compaction pile itself of the sand compaction pile placement ground which evaluates the static earth pressure coefficient obtained according to the method of 2 or 3 as the static earth pressure coefficient of the sand compaction pile itself.