JP3920158B2 - Ground improvement method - Google Patents

Description

なお、上記のＮＰとは非塑性土の意味であるが、原土の液性限界Ｗ_Lおよび塑性限界Ｗ_Pの値が規定された方法による試験によって求められないことを示している。
【００１５】
事前配合試験として、水／改良材比率である水セメント比Ｗ／Ｃが１００％、１３０％、１６０％であって且つそれぞれのセメント添加量（改良材添加量）を５０ｋｇ／ｍ³、１００ｋｇ／ｍ³、１５０ｋｇ／ｍ³としたミルク状改良材として複数種類のセメントミルクを用意し、上記原土試料に対して各セメントミルクを混合した直後（混練後１０分以内のもの）のスランプ試験によるスランプ値を測定する。さらに、同じ原土試料とセメントミルクとを用いて強度試験用の供試体を作製するとともに、所定の養生日数を経た後に一軸圧縮強さをそれぞれに測定する。その時の試験結果を表１に示す。なお、スランプ試験は先に述べたようにコンクリートのスランプ試験（ＪＩＳ Ａ １１０１−１９７５）に準拠して行う。
【００１６】
そして、表１のデータをもとに、図１に示すように水セメント比別のセメント添加量と一軸圧縮強さとの相関特性図を作成する。
【００１７】
【表１】

【００１８】
図１の相関特性図より目標強度ｑｕをｑｕ＝５００ｋＮ／ｍ²としたときの各水セメント比別のセメント添加量を読み取ると次のようになる。
【００１９】
・水セメント比Ｗ／Ｃが１００％のときのセメント添加量＝５５ｋｇ／ｍ³
・水セメント比Ｗ／Ｃが１３０％のときのセメント添加量＝７５ｋｇ／ｍ³
・水セメント比Ｗ／Ｃが１６０％のときのセメント添加量＝１１２ｋｇ／ｍ³
同様にして、表１のデータをもとに、図２に示すように水セメント比別のセメント添加量とスランプ値との相関特性図を作成する。さらに、先に求めた各水セメント比別のセメント添加量の点を図２のようにＡ，Ｂ，Ｃと定め、それらの点Ａ，Ｂ，Ｃを結ぶ相関曲線（Ａ−Ｂ−Ｃ曲線）を図２の相関特性図の上に描く。
【００２０】
この実施の形態では、処理土の品質を流動性の指標であるスランプ値をもって評価，管理するものであるが、地盤改良の対象となる土質性状と構造目的とを考慮して管理値である設定スランプ値を経験的に例えば５ｃｍ以上と定めて施工を行うものとする。
【００２１】
そこで、処理土の流動性の指標であるスランプ値が５ｃｍ以上となるのに必要な水セメント比とセメント添加量を図３の相関特性図から求める。すなわち、図３は基本的には図２と同じものであるが、同図に示すように設定スランプ値５ｃｍの線とＡ−Ｂ−Ｃ曲線との交点Ｄにおける水セメント比とセメント添加量を求めると、水セメント比≒１３８％、セメント添加量≒８３ｋｇ／ｍ³の結果を得ることができる。
【００２２】
ただし、上記水セメント比およびセメント添加量の決定に際しては、土質性状のばらつきや試験誤差等を考慮するべく先に求めた値に補正を加えるものとする。具体的には、図３に示すようにＡ−Ｂ−Ｃ曲線の基礎となっているＷ／Ｃ＝１３０％時の特性線図とＷ／Ｃ＝１６０％時の特性線図との間を１０％単位で細区分することにより、Ｗ／Ｃ＝１４０％時とＷ／Ｃ＝１５０％時の特性線図をそれぞれ加えた上で、交点Ｄより上方側（スランプ値が５ｃｍ以上の領域）であって且ついずれかの特性線図とＡ−Ｂ−Ｃ曲線との交点のうち先の交点Ｄに最も近い交点Ｅを目標値として決定する。図３から明らかなように、この交点Ｅにおける水セメント比はＷ／Ｃ＝１４０％、セメント添加量はα＝８８ｋｇ／ｍ³であって、これらの値を実際の施工の際の条件とする。
【００２３】
そして、実際の施工の際には、水セメント比が１４０％、セメント添加量が８８ｋｇ／ｍ³となるように予め調整したセメントミルクを常法により地中に噴射しながら撹拌混合処理を行う。その際に、処理土の流動性を評価するべく定期的に撹拌混合直後の処理土の試料を採取してスランプ試験を行い、そのスランプ値が常に５ｃｍ以上となるように施工管理を行う。ただし、撹拌混合後の処理土は時間の経過とともに改良材であるセメントの固化反応が進行するため、撹拌混合直後のもの（撹拌混合後１０分以内のもの）をもって試験を行う。こうすることにより、処理土の流動性を定量的に評価，管理することができるようになる。
【００２４】
ここで、上記の設定スランプ値＝５ｃｍ以上とした施工条件の妥当性について検証してみる。
【００２５】
先ず、先に例示した保有含水量Ｗ₁＝０．４４８ｔ／ｍ³の原土について、その原土に含まれる水重量に対し水セメント比Ｗ／Ｃが１００％、１３０％、１６０％であって且つそれぞれのセメント添加量を５０ｋｇ／ｍ³、１００ｋｇ／ｍ³、１５０ｋｇ／ｍ³としたセメントミルクに含まれる水重量を加えて、撹拌混合処理直後の処理土に含まれる総合的な水重量（含水量もしくは水分量）を表２にように求める。なお、表２に併記したスランプ値は表１の値をそのまま転記したものである。そして、表２のデータをもとに、処理土に含まれる水重量とスランプ値との相関として図４の相関特性図を作成する。そして、同図に示すように、水セメント比Ｗ／Ｃが１００％、１３０％、１６０％の時のそれぞれの相関特性を合成して合成相関曲線Ｐを描く。
【００２６】
【表２】

【００２７】
一方、先に決定した水セメント比Ｗ／Ｃ＝１４０％、セメント添加量α＝８８ｋｇ／ｍ³の条件で撹拌混合処理を行った場合の処理土に含まれる総合的な水重量を下記により求める。
【００２８】

そして、図４に示すように、同図上の合成相関曲線Ｐにつき先に求めた混合直後の水分量Ｗ₃＝０．５７１ｔ／ｍ³の時のスランプ値を読み取ると、その値はおよそ５．８ｃｍとして読み取ることができる。この５．８ｃｍというスランプ値は、先に決定した施工時の設定スランプ値として５ｃｍ以上という条件を満たしており、したがって地盤改良処理品質をスランプ値をもって評価，管理することに十分に妥当性があると推測できることになる。
【００２９】
次に第２の実施の形態について説明する。
【００３０】
第１の実施の形態の土質と類似土質で原土の含水比や湿潤密度等が異なる場合には、目標強度を満足させるのに必要なセメント添加量が異なってくることがある。しかしながら、その都度先に説明したような事前配合試験を実施していたのでは多大な時間と費用を要することとなって好ましくない。そこで、類似土質であることを前提に第１の実施の形態の事前配合試験で得られたデータを一部使用すれば、適正な水セメント比やセメント添加量を比較的容易に求めることが可能であり、以下その場合の例を説明する。
【００３１】
図１の相関特性図をもとにして、目標強度をｑｕ＝５００ｋＮ／ｍ²とした時のセメントミルクに含まれる水重量（含水量）とセメント添加量αとの相関特性図を作成する。より詳しくは、図１に示すように水セメント比Ｗ／Ｃ＝１００％の時のセメント添加量αが５５ｋｇ／ｍ³、水セメント比Ｗ／Ｃ＝１３０％の時のセメント添加量αが７５ｋｇ／ｍ³、水セメント比Ｗ／Ｃ＝１６０％の時のセメント添加量αが１１２ｋｇ／ｍ³であるから、それぞれのセメント添加量αのセメントミルクに含まれる水分量（含水量）を次式によって算出する。
【００３２】
・水セメント比Ｗ／Ｃ＝１００％でセメント添加量が５５ｋｇ／ｍ³の時のセメントミルクの水分量
＝（α／１０００）×（Ｗ／Ｃ）
＝（５５／１０００）×１．０
＝０．０５５
・水セメント比Ｗ／Ｃ＝１３０％でセメント添加量が７５ｋｇ／ｍ³の時のセメントミルクの水分量
＝（α／１０００）×（Ｗ／Ｃ）
＝（７５／１０００）×１．３
＝０．０９７５
・水セメント比Ｗ／Ｃ＝１６０％でセメント添加量が１１２ｋｇ／ｍ³の時のセメントミルクの水分量
＝（α／１０００）×（Ｗ／Ｃ）
＝（１１２／１０００）×１．６
＝０．１７９２
そして、上記の各セメント添加量を横軸とし、算出したセメントミルクに含まれる各含水量を縦軸とした図５の相関特性図を作成する。さらに、同図の相関特性図に縦軸として水セメント比Ｗ／Ｃを書き加える。
【００３３】
次いで、処理対象となる原土すなわち第１の実施の形態の土質と類似土質の原土についてその自然含水比Ｗ_nと湿潤密度ρ_tを測定し、例えば原土の自然含水比Ｗ_nがＷ_n＝３７．４％、湿潤密度ρ_tがρ_t＝１．７９０ｔ／ｍ³を示す時、原土の乾燥密度ρ_Dと原土の保有含水量Ｗ₁を次式によって算出する。
【００３４】

一方、第１の実施の形態における土質の原土では、図３に基づいて先に求めたように、スランプ値が５ｃｍ以上で目標強度を満足する水セメント比Ｗ／Ｃとセメント添加量αは、それぞれＷ／Ｃ＝１３８％、α≒８３ｋｇ／ｍ³であるから、この条件下での混合直後の処理土に含まれる総水分量を次式により求める。
【００３５】

以上のことから、第１の実施の形態の原土では、混合直後の処理土の含水量として０．５６３ｔ／ｍ³以上を確保すれば、スランプ値として５ｃｍ以上を確保できることがわかる。
【００３６】
その一方、第１の実施の形態の土質と類似土質の原土では先に述べたようにその原土の保有含水量Ｗ₁＝０．４８７ｔ／ｍ³であるから、第１の実施の形態の原土での混合直後の総含水量Ｗ₃（＝０．５６３ｔ／ｍ³）から類似土質の原土自体の保有含水量Ｗ₁（＝０．４８７ｔ／ｍ³）を差し引いて、０．５６３−０．４８７＝０．０７６ｔ／ｍ³分の水分を含むセメントミルクを原土に添加して混合すれば、スランプ値として５ｃｍ以上という条件を満たすことができるようになる。
【００３７】
一方、図５の相関特性図において、目標強度ｑｕ（＝５００ｋＮ／ｍ²）を満足し且つセメントミルクの含水量０．０７６ｔ／ｍ³を越える位置での水セメント比Ｗ／Ｃは１００％と１２０％の間であって、おおよそ１２０％に近い位置となる。同時に水セメント比Ｗ／Ｃ＝１２０％の時のセメント添加量αはα≒６９ｋｇ／ｍ³となる。
【００３８】
そこで、水セメント比Ｗ／Ｃ＝１２０％でセメント添加量α＝６９ｋｇ／ｍ³の時のスランプ値を確認してみる。
【００３９】
先に示したように、類似土質の原土の保有含水量Ｗ₁はＷ₁＝０．４８７（ｔ／ｍ³）であるから、セメントミルクに含まれる水分量Ｗ₂を次式によって求める。
【００４０】

混合直後の処理土の総含水（水分）量Ｗ₃はＷ₃＝Ｗ₁＋Ｗ₂であるから、Ｗ₃＝０．４８７＋０．０８３＝０．５７ｔ／ｍ³となる。そして、先に示した図４において、この総含水（水分）量Ｗ₃＝０．５７ｔ／ｍ³に対応するスランプ値を読み取ると、その値は先の場合と同様に５．８ｃｍ程度となる。
【００４１】
これらの関係から明らかなように、特定の土質と類似した土質であるならば原土の自然含水比Ｗ_nと湿潤密度ρ_tのみを測定することによって、スランプ値で５ｃｍ以上という条件を満たしつつ、目標強度ｑｕ（＝５００ｋＮ／ｍ²）を満足するのに必要な水セメント比Ｗ／Ｃ（＝１２０％）とセメント添加量α（＝６９ｋｇ／ｍ³）を容易に決定することが可能となる。
【００４２】
次に第３の実施の形態として、下記に示す土質の原土について目標強度ｑｕ＝６００ｋＮ／ｍ²としたときの適正な水セメント比Ｗ／Ｃとセメント添加量αを求めた上で、処理土の品質を流動性の指標であるスランプ値をもって評価，管理する場合の例を示す。
【００４３】

事前に行う配合試験として、上記の自然含水比のままの原土の試料（試料１）のほか、含水比が４０％、５０％、６０％となるように予め水分調整した含水比調整土（試料２〜４）を用意し、水セメント比Ｗ／Ｃを標準的なＷ／Ｃ＝１００％とした上で、セメント添加量αを５０ｋｇ／ｍ³、１００ｋｇ／ｍ³、１５０ｋｇ／ｍ³、２００ｋｇ／ｍ³としたセメントミルクと混合した供試体をそれぞれ作製し、所定の養生日数を経た後の各供試体（試料１〜４）の強度を一軸圧縮強さ（ｋＮ／ｍ²）として測定する。なお、各試料１〜４の含水比Ｗ_nと湿潤密度ρ_tとの関係を表３に示し、各試料１〜４の一軸圧縮強さの値を表４に示す。
【００４４】
【表３】

【００４５】
【表４】

【００４６】
そして、表４の値をもとに図６に示すようにセメント添加量αと一軸圧縮強さの相関特性図を作成し、目標強度ｑｕ＝６００ｋＮ／ｍ²を満足するセメント添加量αを求める。すなわち、図６の相関特性図において一軸圧縮強さ６００ｋＮ／ｍ²を示す横の線と各相関特性曲線との交点の値を読み取る。各含水比別の試料１〜４のセメント添加量αは図６のほか表５に示すように、それぞれ９１ｋｇ／ｍ³、９５ｋｇ／ｍ³、１２２ｋｇ／ｍ³、２３２ｋｇ／ｍ³となる。
【００４７】
【表５】

【００４８】
次に、水セメント比Ｗ／Ｃが例えば標準的な１００％であることを前提として、各含水比別の試料１〜４に上記セメント添加量αのセメントミルクを混合したと想定したときの混合直後の含水比Ｗ_Nを求める。
【００４９】
（ａ）試料１

（ｂ）試料２

（ｃ）試料３

（ｄ）試料４

次に、上記（ａ）〜（ｄ）で求めた混合直後の含水比Ｗ_Nとセメント添加量αをもとに両者の相関特性図を作成し、その相関特性図を図７に示す。
【００５０】
ここで、原土の塑性指数Ｉ_Pの値とコンシステンシー指数Ｉ_Cの値、およびセメントミルクにおける水セメント比Ｗ／Ｃとの相関を図８の相関特性図をもって予め定めておき、これらの相関関係から原土の塑性指数Ｉ_Pの値とコンシステンシー指数Ｉ_Cの値を指定したときのセメントミルクにおける適正な水セメント比Ｗ／Ｃの値を上記相関特性図から直接読み取る。先に述べたように、地盤改良の対象となる原土の塑性指数Ｉ_Pの値は２２．５、コンシステンシー指数Ｉ_Cの値は０．５４であるから、これら原土の塑性指数Ｉ_Pの値とコンシステンシー指数Ｉ_Cの値の交点を図８上で求めると、セメントミルクの適正な水セメント比Ｗ／Ｃの値は１４０％となる。
【００５１】
そして、適正な水セメント比Ｗ／Ｃ＝１４０％としたときの混合直後の含水比Ｗ_Nを求める。ただし、ここでの改良材であるセメントの暫定添加量を９５ｋｇ／ｍ³とする。
【００５２】

次いで、図８から求めた適正な水セメント比Ｗ／Ｃ＝１４０％の場合であって且つ上記の混合直後の含水比Ｗ_N＝４６％のときのセメント添加量を図９から直接読み取る。すなわち、図９は図７と基本的に同じであるが、図９に示すように含水比Ｗ_N＝４６％の仮想線と特性曲線との交点を求めると９４ｋｇ／ｍ³となる。これにより、実際の施工時の条件として水セメント比はＷ／Ｃ＝１４０％、セメント添加量αは９４ｋｇ／ｍ³と決定する。
【００５３】
そして、実際の施工の際には、過去の実績データ等を考慮しながら設定スランプ値を例えば４．０ｃｍ以上と定めた上で、水セメント比Ｗ／Ｃが１４０％、セメント添加量αが９４ｋｇ／ｍ³となるように予め調整したセメントミルクを常法により地中に噴射しながら撹拌混合処理を行う。その際に、先の実施の形態と同様に処理土の流動性を評価するべく定期的に撹拌混合直後の処理土の試料を採取してスランプ試験を行い、そのスランプ値が常に４．０ｃｍ以上となるように施工管理を行う。こうすることにより、処理土の流動性を定量的に評価，管理することができるようになる。
【００５４】
本発明者による実験では、スランプ値の設定値（管理目標値）としては過去の実績データ等により４ｃｍ以上と定めていたが、上記のような施工管理を行うことにより定常的に４．５ｃｍ以上の結果が得られた。因みに、従来であれば多くの場合に標準的な水セメント比と言われているＷ／Ｃ＝１００％で施工を実施していたが、その場合には予備試験時等において測定されるスランプ値は２ｃｍ程度にすぎなかった。
【００５５】
また、従来の水セメント比で施工したとするならば、地盤の撹拌混合のための必要羽根切り回数を満足するには３０ｍ³／Ｈ程度の作業量が限界であったが、本実施の形態のように適正な水セメント比（Ｗ／Ｃ＝１４０％）とすることによって、４５ｍ³／Ｈ程度の作業量まで可能となり、経済的効果は大である。
【００５６】
その上、品質的な面から見た場合、目標強度ｑｕ＝６００ｋＮ／ｍ²、水セメント比Ｗ／Ｃ＝１４０％としたときの強度ばらつきは５５０〜６６０ｋＮ／ｍ²の範囲内に納まっており、従来の施工時のばらつき幅４００〜７００ｋＮ／ｍ²に比べて非常に小さくなることが判明した。このように、地盤改良の処理品質をスランプ値をもって評価，管理することで、経済的で且つ処理土品質に優れた地盤改良工法を提供できるようになる。
【図面の簡単な説明】
【図１】セメント添加量と一軸圧縮強さとの相関を示す特性図。
【図２】セメント添加量とスランプ値との相関を示す特性図。
【図３】同じくセメント添加量とスランプ値との相関を示す特性図。
【図４】処理土に含まれる水分量とスランプ値との相関を示す特性図。
【図５】セメント添加量とセメントミルクの含水量との相関を示す特性図。
【図６】セメント添加量と一軸圧縮強さとの相関を示す特性図。
【図７】セメント添加量と混合直後の処理土の含水比との相関を示す特性図。
【図８】原土の塑性指数とコンシステンシー指数との相関を示す特性図。
【図９】セメント添加量と混合直後の処理土の含水比との相関を示す特性図。[0001]
BACKGROUND OF THE INVENTION
The present invention is a mixture of ground improvement material such as cement itself and water-like improvement material (slurry-like improvement material), that is, so-called cement milk, which is mixed with water and subjected to stirring and mixing treatment. The present invention relates to a ground improvement method for improving the strength of treated soil.
[0002]
[Prior art and problems to be solved by the invention]
In the ground improvement method in which cement milk is stirred and mixed with the raw soil while injecting the cement milk into the ground, the treated soil becomes fluidized immediately after stirring and mixing, so it is basically compacted as a subsequent secondary treatment. It is a construction method that does not require treatment (rolling treatment from the top surface). However, depending on the soil properties of the raw soil, moisture may be insufficient and voids may be generated in the treated soil, resulting in insufficient strength. In addition, if the above phenomenon is predicted during the pre-mixing test, construction will be performed using cement milk with a high amount of moisture in advance to promote fluidization. There are variations due to individual differences, and adding cement more than necessary to satisfy the target strength can be uneconomical, and processing quality tends to vary.
[0003]
The present invention has been made paying attention to the problems as described above. In particular, the fluidity of the treated soil immediately after stirring and mixing can be quantitatively grasped or evaluated, thereby stabilizing and improving the treatment quality. However, it provides a ground improvement method with excellent economic efficiency.
[0004]
[Means for Solving the Problems]
There is a concrete slump test (JISA 1101-1975) as an index representing the fluidity of concrete. This slump test is: “After smoothing the top surface of the concrete packed in the slump cone with the top end of the slump cone, immediately raise the slump cone gently and measure the fall at the center of the concrete, and use this as the slump.” Is defined. For example, in the case of a structure with unreinforced concrete and a large cross section, it is recommended to set the slump value as 3 to 8 cm as a standard value and select the smallest possible value within a range suitable for work such as transportation and driving. ing.
[0005]
Therefore, the slump value is used as an indicator of the fluidity of the treated soil in the ground improvement method, and the fluidity of the target soil that covers a wide range of soil such as gravel and organic matter as well as sandy and cohesive soil is quantitatively grasped or evaluated. It is the present invention that is intended.
[0006]
That is, the invention according to claim 1 is a ground improvement method in which treated soil is a ground improvement method in which a milk-like improvement material mixed with an improvement material (C) and water (W) is stirred and mixed with the raw soil. Determines the water / improvement ratio (W / C) and the amount of improvement material added to the milk-like improvement material that satisfies the target strength and exhibits fluidization immediately after the stirring and mixing treatment, and does not require a compaction treatment as a secondary treatment. In doing so, a correlation between the water / improvement material ratio (W / C) of the milk-like improving material and the slump value, which is an index of the improving material addition amount and the fluidity of the treated soil, is determined in advance. When the slump value is specified, the water / improvement material ratio (W / C) of the milk-like improvement material and the addition amount of the improvement material are obtained, respectively. Mixing with the original soil while injecting the original milky improvement material into the ground And performing focus processing.
[0007]
In this case, as described in claim 2, the treated soil after the stirring and mixing treatment is sampled to obtain a slump value based on a concrete slump test, and the measured slump value is within a preset slump value range. It is more desirable to manage the ground improvement processing quality so that it becomes a thing.
[0008]
The set slump value shall be determined with a certain range based on the data collected during past compounding tests and the past construction performance data.
[0009]
In addition, the basic method of ground improvement is the same as the conventional method. For example, a stirring / mixing head comprising a plurality of stirring blades mounted on an endless chain driven in the vertical direction is supported by a base machine such as a backhoe, and this stirring is performed. Cement milk shall be discharged or jetted from an improved material discharge mechanism provided at a part of the stirring and mixing head while penetrating the mixing head into the ground.
[0010]
The invention according to claim 3 is a ground improvement method in which a milky improvement material obtained by mixing the improvement material (C) and water (W) is stirred and mixed with the raw soil while being injected into the ground. When the ratio of the improved material (C) and water (W) in the milk-like improved material to be sprayed is the water / improved material ratio (W / C), the treated soil satisfies the target strength and immediately after the stirring and mixing process. in determining the water / modifying material ratio of milky modifying material which exhibits a fluidization does not require compaction process as a secondary processing (W / C), plasticity index of the original soil (I _P) and consistency index In addition to (I _C ), a correlation with the water / improvement ratio (W / C) of the milky improved material is determined in advance, and the plasticity index (I _P ) and consistency index ( I _C) and for water / modifying material ratio of milky improvement agent when specifying (W / C), and Slurry test of concrete by collecting the mixed soil with the raw soil while injecting the milk-like improved material with the water / improved material ratio (W / C) obtained by And the ground improvement processing quality is managed so that the actually measured slump value falls within a preset slump value range.
[0011]
【The invention's effect】
According to the first to third aspects of the invention, since the treatment quality of ground improvement can be quantitatively grasped or evaluated with the slump value, voids in the treatment layer are generated or an improvement material is added more than necessary. As a result, the processing quality can be stabilized and improved, as well as cost reduction, that is, economic improvement can be achieved.
[0012]
In particular, according to the inventions described in claims 2 and 3, the slump value is taken into consideration in the calculation of the water / improvement material ratio (W / C) and the amount of improvement material added necessary to achieve the target strength. On the other hand, since the processing quality after construction is also managed with the slump value, there is an advantage that the economic improvement effect becomes more remarkable in addition to the stabilization of the processing quality and the quality improvement effect.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
As a first embodiment, an example of evaluating and managing the quality of treated soil with a slump value, which is an index of fluidity, will be shown in performing ground improvement on a soil soil having the following soil properties.
[0014]

Although the above NP is meant a non-plastic soil, shows that not required by the test according to how the value of the liquid limit W _L and plastic limit W _P of the original soil is defined.
[0015]
As a pre-mixing test, the water cement ratio W / C, which is the ratio of water / improving material, is 100%, 130%, 160%, and each cement addition amount (improvement material addition amount) is 50 kg / m ³ , 100 kg / m ^3, to prepare a plurality kinds of cement milk as milky improved material was 150 kg / m ^3, by the slump test immediately after mixing the cement milk to said original soil sample (within 10 minutes after kneading) Measure the slump value. Further, a specimen for strength test is prepared using the same raw soil sample and cement milk, and uniaxial compressive strength is measured for each after a predetermined curing period. The test results at that time are shown in Table 1. The slump test is performed according to the concrete slump test (JIS A 1101-1975) as described above.
[0016]
And based on the data of Table 1, as shown in FIG. 1, the correlation characteristic figure of the cement addition amount according to water cement ratio and uniaxial compressive strength is created.
[0017]
[Table 1]

[0018]
The amount of cement added for each water cement ratio when the target strength qu is set to qu = 500 kN / m ² from the correlation characteristic diagram of FIG. 1 is as follows.
[0019]
-Addition amount of cement when water / cement ratio W / C is 100% = 55 kg / m ³
-Addition amount of cement when water-to-cement ratio W / C is 130% = 75 kg / m ³
Cement addition amount when water / cement ratio W / C is 160% = 112 kg / m ³
Similarly, based on the data of Table 1, as shown in FIG. 2, a correlation characteristic diagram between the cement addition amount and the slump value for each water cement ratio is created. Further, the points of the amount of cement added for each water cement ratio obtained previously are defined as A, B, C as shown in FIG. 2, and a correlation curve (A-B-C curve) connecting these points A, B, C. ) Is drawn on the correlation characteristic diagram of FIG.
[0020]
In this embodiment, the quality of the treated soil is evaluated and managed by the slump value, which is an index of fluidity, but the setting is a management value in consideration of the soil properties and the structural purpose to be ground improvement. The slump value is empirically determined to be, for example, 5 cm or more.
[0021]
Accordingly, the water cement ratio and the amount of cement added necessary for the slump value, which is an index of the fluidity of the treated soil, to be 5 cm or more are obtained from the correlation characteristic diagram of FIG. That is, FIG. 3 is basically the same as FIG. 2, but the water cement ratio and the amount of cement added at the intersection D between the line with the set slump value of 5 cm and the ABC curve as shown in FIG. As a result, it is possible to obtain a result of a water cement ratio≈138% and a cement addition amount≈83 kg / m ³ .
[0022]
However, in determining the water cement ratio and the amount of cement added, the previously obtained values are corrected to take into account variations in soil properties and test errors. Specifically, as shown in FIG. 3, the gap between the characteristic diagram at W / C = 130% and the characteristic diagram at W / C = 160%, which are the basis of the ABC curve, is shown. By subdividing in units of 10%, after adding the characteristic diagrams at W / C = 140% and W / C = 150%, respectively, above the intersection D (area with a slump value of 5 cm or more) The intersection E closest to the previous intersection D among the intersections of any of the characteristic diagrams and the ABC curve is determined as a target value. As is clear from FIG. 3, the water cement ratio at the intersection E is W / C = 140%, and the cement addition amount is α = 88 kg / m ³ , and these values are used as the actual construction conditions. .
[0023]
In actual construction, stirring and mixing are performed while spraying cement milk that has been adjusted in advance so that the water-cement ratio is 140% and the cement addition amount is 88 kg / m ³ . At that time, in order to evaluate the fluidity of the treated soil, a sample of the treated soil immediately after stirring and mixing is periodically taken and a slump test is performed, and the construction management is performed so that the slump value is always 5 cm or more. However, since the solidification reaction of cement, which is an improving material, progresses over time with the treated soil after stirring and mixing, the test is performed with the immediately after stirring and mixing (within 10 minutes after stirring and mixing). By doing so, the fluidity of the treated soil can be quantitatively evaluated and managed.
[0024]
Here, the validity of the construction conditions with the above set slump value = 5 cm or more will be verified.
[0025]
First, regarding the raw soil having the retained water content W ₁ = 0.448 t / m ³ exemplified above, the water cement ratio W / C is 100%, 130%, and 160% with respect to the water weight contained in the raw soil. And the total water weight contained in the treated soil immediately after the stirring and mixing treatment by adding the water weight contained in the cement milk with the respective cement addition amounts being 50 kg / m ³ , 100 kg / m ³ and 150 kg / m ^3. (Water content or water content) is determined as shown in Table 2. In addition, the slump value written together in Table 2 is the value of Table 1 transferred as it is. Then, based on the data in Table 2, the correlation characteristic diagram of FIG. 4 is created as the correlation between the weight of water contained in the treated soil and the slump value. Then, as shown in the figure, the correlation characteristics when the water cement ratio W / C is 100%, 130%, and 160% are combined to draw a combined correlation curve P.
[0026]
[Table 2]

[0027]
On the other hand, the total water weight contained in the treated soil in the case of performing the stirring and mixing process under the conditions of the water cement ratio W / C = 140% and the cement addition amount α = 88 kg / m ³ determined previously is obtained as follows. .
[0028]

Then, as shown in FIG. 4, when the slump value at the time of the water content W ₃ immediately after the mixing W ₃ = 0.571 t / m ³ obtained for the composite correlation curve P in the same figure is read, the value is about 5 .8 cm can be read. This slump value of 5.8 cm satisfies the condition of 5 cm or more as the set slump value at the time of construction determined earlier, and therefore it is sufficiently valid to evaluate and manage the ground improvement treatment quality with the slump value. It can be guessed.
[0029]
Next, a second embodiment will be described.
[0030]
When the water content ratio and wet density of the raw soil are different between the soil according to the first embodiment and the similar soil, the amount of cement added to satisfy the target strength may be different. However, if a pre-blending test as described above is performed each time, it takes a lot of time and money, which is not preferable. Therefore, it is possible to determine an appropriate water cement ratio and cement addition amount relatively easily by using a part of the data obtained in the pre-mixing test of the first embodiment on the assumption that the soil is similar. An example in that case will be described below.
[0031]
Based on the correlation characteristic diagram of FIG. 1, a correlation characteristic diagram between the weight of water (water content) contained in the cement milk and the cement addition amount α when the target strength is qu = 500 kN / m ² is created. More specifically, as shown in FIG. 1, when the water cement ratio W / C = 100%, the cement addition amount α is 55 kg / m ³ , and when the water cement ratio W / C = 130%, the cement addition amount α is 75 kg. / m ^3, the following equation because the cement addition amount when the water-cement ratio W / C = 160% α is 112 kg / m ^3, the amount of water contained in the cement milk of each cement amount alpha of (water content) Calculated by
[0032]
Water content of cement milk when water cement ratio W / C = 100% and cement addition amount is 55 kg / m ³ = (α / 1000) × (W / C)
= (55/1000) x 1.0
= 0.055
Water content of cement milk when water cement ratio W / C = 130% and cement addition amount is 75 kg / m ³ = (α / 1000) × (W / C)
= (75/1000) x 1.3
= 0.0975
Water content of cement milk when water cement ratio W / C = 160% and cement addition amount is 112 kg / m ³ = (α / 1000) × (W / C)
= (112/1000) x 1.6
= 0.1792
Then, the correlation characteristic diagram of FIG. 5 is created with each cement addition amount as the horizontal axis and each water content contained in the calculated cement milk as the vertical axis. Further, the water cement ratio W / C is added as a vertical axis to the correlation characteristic diagram of FIG.
[0033]
Next, the natural water content W _n and the wet density ρ _t of the raw soil to be treated, that is, the soil similar to that of the first embodiment, are measured. For example, the natural water content W _{n of the} raw soil is W _{When n} = 37.4% and the wet density ρ _t indicates ρ _t = 1.790 _t / m ³ , the dry density ρ _D of the raw soil and the retained water content W ₁ of the raw soil are calculated by the following equations.
[0034]

On the other hand, in the soil soil of the first embodiment, the water cement ratio W / C and the cement addition amount α satisfying the target strength when the slump value is 5 cm or more, as previously obtained based on FIG. Since W / C = 138% and α≈83 kg / m ³ , respectively, the total amount of water contained in the treated soil immediately after mixing under this condition is obtained by the following equation.
[0035]

From the above, it can be seen that, in the raw soil of the first embodiment, if the water content of the treated soil immediately after mixing is secured to 0.563 t / m ³ or more, a slump value of 5 cm or more can be secured.
[0036]
On the other hand, since the retained water content W ₁ = 0.487 t / m ³ of the soil of the soil similar to that of the first embodiment as described above, the first embodiment Subtracting the retained water content W ₁ (= 0.487 t / m ³ ) of the raw soil of similar soil quality from the total water content W ₃ (= 0.563 t / m ³ ) immediately after mixing in the original soil. If cement milk containing water of 563-0.487 = 0.076 t / m ³ minutes is added to the raw soil and mixed, the slump value of 5 cm or more can be satisfied.
[0037]
On the other hand, in the correlation characteristic diagram of FIG. 5, the water cement ratio W / C at a position satisfying the target strength qua (= 500 kN / m ² ) and exceeding the water content of cement milk of 0.076 t / m ³ is 100%. The position is between 120% and approximately 120%. At the same time, the cement addition amount α when the water cement ratio W / C = 120% is α≈69 kg / m ³ .
[0038]
Accordingly, the slump value when the water cement ratio W / C = 120% and the cement addition amount α = 69 kg / m ³ is confirmed.
[0039]
As previously indicated, the retained water content W ₁ of the raw soil of similar soil is W ₁ = 0.487 (t / m ³ ), so the water content W ₂ contained in the cement milk is obtained by the following equation.
[0040]

Since the total water content (moisture) W ₃ of the treated soil immediately after mixing is W ₃ = W ₁ + W ₂ , W ₃ = 0.487 + 0.083 = 0.57 t / m ³ . Then, in FIG. 4 shown above, when the slump value corresponding to the total water content (water content) W ₃ = 0.57 t / m ³ is read, the value is about 5.8 cm as in the previous case. .
[0041]
As is clear from these relationships, if the soil is similar to a specific soil, only the natural water content W _n and wet density ρ _{t of the} raw soil are measured, while satisfying the slump value of 5 cm or more. It is possible to easily determine the water cement ratio W / C (= 120%) and the cement addition amount α (= 69 kg / m ³ ) necessary to satisfy the target strength qua (= 500 kN / m ² ). Become.
[0042]
Next, as a third embodiment, after obtaining an appropriate water cement ratio W / C and a cement addition amount α when the target strength qu = 600 kN / m ² for the soil soil shown below, the treatment is performed. An example of evaluating and managing soil quality with a slump value that is an indicator of fluidity is shown.
[0043]

In addition to the natural soil sample (Sample 1) with the above natural moisture content, the water content adjusted soil (water content adjusted so that the moisture content is 40%, 50%, 60% in advance) Samples 2 to 4) were prepared, and the water cement ratio W / C was set to the standard W / C = 100%, and the cement addition amount α was 50 kg / m ³ , 100 kg / m ³ , 150 kg / m ³ , Specimens mixed with cement milk of 200 kg / m ³ were prepared, and the strength of each specimen (samples 1 to 4) after a predetermined curing period was measured as uniaxial compressive strength (kN / m ² ). To do. Incidentally, the relation between the water content ratio W _n and wet density [rho _t of the samples 1-4 shown in Table 3, shows the values of uniaxial compressive strength of each sample 1-4 in Table 4.
[0044]
[Table 3]

[0045]
[Table 4]

[0046]
Then, based on the values in Table 4, a correlation characteristic diagram between the cement addition amount α and the uniaxial compressive strength is created as shown in FIG. 6, and the cement addition amount α satisfying the target strength qu = 600 kN / m ² is obtained. . That is, in the correlation characteristic diagram of FIG. 6, the value of the intersection of the horizontal line indicating the uniaxial compression strength of 600 kN / m ² and each correlation characteristic curve is read. As cement amount α of the water content of another sample 1-4 shown in addition to Table 5 of FIG. 6, the respective ^{91kg / m 3, 95kg / m} 3, 122kg / m 3, 232kg / m 3.
[0047]
[Table 5]

[0048]
Next, on the assumption that the water cement ratio W / C is, for example, standard 100%, mixing when it is assumed that the cement milk having the above cement addition amount α is mixed with the samples 1 to 4 for each water content ratio. Obtain the water content W _N immediately after.
[0049]
(A) Sample 1

(B) Sample 2

(C) Sample 3

(D) Sample 4

Next, based on the water content ratio W _N immediately after mixing determined in the above (a) to (d) and the cement addition amount α, a correlation characteristic diagram of both is created, and the correlation characteristic diagram is shown in FIG.
[0050]
Here, the correlation between the value of the plastic index I _P of the raw soil, the value of the consistency index I _C , and the water-cement ratio W / C in cement milk is determined in advance using the correlation characteristic diagram of FIG. From the relationship, the value of the appropriate water cement ratio W / C in the cement milk when the value of the plasticity index I _P and the consistency index I _C of the raw soil is designated is directly read from the above correlation characteristic diagram. As described above, since the value of the plasticity index I _P of the raw soil subject to ground improvement is 22.5 and the value of the consistency index I _C is 0.54, the plasticity index I _{P of} these raw soils. When the intersection of the value of the value and the value of the consistency index I _C is obtained in FIG. 8, the appropriate value of the water-cement ratio W / C of the cement milk is 140%.
[0051]
Then, the water content ratio W _N immediately after mixing when the appropriate water cement ratio W / C = 140% is obtained. However, the provisional addition amount of cement as an improvement material here is 95 kg / m ³ .
[0052]

Next, the amount of cement added when the appropriate water cement ratio W / C obtained from FIG. 8 is 140% and the water content ratio W _N after mixing is 46% is directly read from FIG. That is, FIG. 9 is basically the same as FIG. 7, but the intersection of the imaginary line with the water content W _N = 46% and the characteristic curve as shown in FIG. 9 is 94 kg / m ³ . Thereby, as conditions at the time of actual construction, the water cement ratio is determined as W / C = 140%, and the cement addition amount α is determined as 94 kg / m ³ .
[0053]
In actual construction, the set slump value is set to, for example, 4.0 cm or more in consideration of past performance data and the like, and the water cement ratio W / C is 140% and the cement addition amount α is 94 kg. The mixture is stirred and mixed while spraying cement milk that has been adjusted beforehand to / m ³ into the ground by a conventional method. At that time, similarly to the previous embodiment, in order to evaluate the fluidity of the treated soil, a sample of the treated soil immediately after stirring and mixing is periodically taken and a slump test is performed, and the slump value is always 4.0 cm or more. The construction is managed so that By doing so, the fluidity of the treated soil can be quantitatively evaluated and managed.
[0054]
In the experiment by the present inventor, the set value (management target value) of the slump value was determined to be 4 cm or more based on past performance data or the like, but it is regularly 4.5 cm or more by performing the construction management as described above. Results were obtained. Incidentally, in the past, construction was carried out at W / C = 100%, which is said to be the standard water cement ratio in many cases, but in this case, the slump value measured at the time of preliminary tests, etc. Was only about 2 cm.
[0055]
Further, if the construction is performed with the conventional water cement ratio, the work amount of about 30 m ³ / H is the limit to satisfy the necessary number of blade cutting operations for stirring and mixing the ground. By setting the water cement ratio as appropriate (W / C = 140%) as described above, a work amount of about 45 m ³ / H is possible, and the economic effect is great.
[0056]
In addition, when viewed from the quality aspect, the strength variation when the target strength qu = 600 kN / m ² and the water cement ratio W / C = 140% is within the range of 550 to 660 kN / m ^2. It has been found that the variation width during the conventional construction is very small as compared with 400 to 700 kN / m ² . Thus, by evaluating and managing the processing quality of the ground improvement with the slump value, it is possible to provide a ground improvement method that is economical and excellent in the quality of the treated soil.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing the correlation between the amount of cement added and uniaxial compressive strength.
FIG. 2 is a characteristic diagram showing the correlation between the amount of cement added and the slump value.
FIG. 3 is a characteristic diagram showing the correlation between the cement addition amount and the slump value.
FIG. 4 is a characteristic diagram showing the correlation between the amount of water contained in the treated soil and the slump value.
FIG. 5 is a characteristic diagram showing the correlation between the amount of cement added and the water content of cement milk.
FIG. 6 is a characteristic diagram showing the correlation between the amount of cement added and uniaxial compressive strength.
FIG. 7 is a characteristic diagram showing the correlation between the amount of cement added and the water content of the treated soil immediately after mixing.
FIG. 8 is a characteristic diagram showing the correlation between the plasticity index and the consistency index of the raw soil.
FIG. 9 is a characteristic diagram showing the correlation between the amount of cement added and the water content of the treated soil immediately after mixing.

Claims (3)

A ground improvement method in which a milk-like improvement material mixed with an improvement material (C) and water (W) is stirred and mixed with the raw soil while being injected into the ground,
Water / improvement ratio (W / C) of milk-like improvement material and improvement material addition that the treated soil satisfies the target strength and exhibits fluidization immediately after the stirring and mixing treatment and does not require a compaction treatment as a secondary treatment In determining the quantity,
Predetermining the correlation between the water / improvement material ratio (W / C) of the milky improver and the slump value, which is an indicator of the addition amount of the improver and the fluidity of the treated soil,
From these correlations, the water / improvement ratio (W / C) of the milk-like improving material when the slump value is specified and the amount of the improving material added are respectively determined.
A ground improvement characterized by performing agitation and mixing with the raw soil while injecting a milk-like improvement material into the ground under the water / improvement material ratio (W / C) thus obtained and the addition amount of the improvement material. Construction method. Collect the treated soil after stirring and mixing treatment to obtain the slump value based on the concrete slump test,
The ground improvement method according to claim 1, wherein the ground improvement processing quality is managed so that the actually measured slump value falls within a preset slump value range. A ground improvement method in which a milk-like improvement material mixed with an improvement material (C) and water (W) is stirred and mixed with the raw soil while being injected into the ground,
When the ratio of the improved material (C) and water (W) in the milk-like improved material to be injected into the ground is the water / improved material ratio (W / C),
In determining the water / improvement ratio (W / C) of the milk-like improver that the treated soil satisfies the target strength and exhibits fluidization immediately after the stirring and mixing process and does not require a compaction process as a secondary process. ,
The correlation between the plasticity index (I _P ) of the raw soil and the consistency index (I _C ) as well as the water / improving material ratio (W / C) of the milk-like improving material is determined in advance.
From these correlations, the water / improvement ratio (W / C) of the milk-like improving material when the plasticity index (I _P ) and the consistency index (I _C ) of the raw soil are specified,
While stirring the milk-like improving material of this obtained water / improving material ratio (W / C) into the ground, stirring and mixing treatment with the raw soil,
Collect the treated soil after stirring and mixing treatment to obtain the slump value based on the concrete slump test,
A ground improvement construction method characterized by managing the ground improvement processing quality so that the actually measured slump value falls within a preset slump value range.

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