JP4194679B2 - Ground improvement method to prevent liquefaction - Google Patents

Description

ここで、ｆｓ：安全率
ｃ ：地滑り粘土の粘着力（ｔ／ｍ2 )
ψ ：地滑り粘土の内部摩擦角
Ｎ ：各細片における滑り面での垂直応力（ｔ）
Ｔ ：各細片における滑り面でのせん断応力（ｔ）
ｌ ：各細片の滑り面の長さ（ｍ）
Ｕ ：各細片における間隙水圧（ｔ）
排土の位置は、地滑り斜面の頭部の切り取りが効果的である。適当な排土を行うことにより、地滑りの安全率が向上し、斜面が安定的になる。
【００１９】
次に、もう一つの従来の地滑り防止のための地表水処理の方法について説明する。
【００２０】
地滑り防止のための地表水処理の方法は、地滑りを誘発または助長する地表水を速やかに地滑り区域外に排出する方法である。図１８に上記地表水排出のため地表排水路工の一例を示す。
【００２１】
【発明が解決しようとする課題】
しかしながら、上記従来の液状化防止のための地盤改良工法、築堤工事における漏水・流失防止工法、盛土の土留工法、地滑り防止のための地盤改良工法は、それぞれ工事が大掛かりであり、したがって工事費も高騰せざるを得なかった。
【００２２】
また、従来の地盤改良等では、元の地盤の土を良質な土やセメント等と入れ替えたりするため、元の地盤の土の廃棄、再利用等を考慮しなければならなかった。
【００２３】
そこで、本発明の解決しようとする課題は、安価で簡単な方法により液状化防止のための地盤改良や築堤工事の漏水・流失防止を実現でき、元の地盤の土等をそのまま利用することができる工法を提供することにある。
【００２４】
【課題を解決するための手段】
本願請求項１に係る液状化防止のための地盤改良工法は、
改良しようとする地盤の地下水位以下であって液状化が生じる深さ以上の土を、埋戻し土を含む粒状物を不透水性シートによって密封した粒状物密封体に置き換える工程を有することを特徴とする。
【００２５】
本願請求項２に係る液状化防止のための地盤改良工法は、
地下構造物の周囲または下部の地下水位以下であって液状化が生じる深さ以上の土を、埋戻し土を含む粒状物を不透水性シートによって密封した粒状物密封体に置き換える工程を有することを特徴とする。
【００２６】
本願請求項３に係る液状化防止のための地盤改良工法は、請求項１または２の地盤改良工法において、
前記粒状物密封体は、掘削した孔の内面に不透水性シートを敷き、前記孔に土を埋戻した後に、前記不透水性シートを密閉してなることを特徴とするものである。
【００２７】
本願請求項４に係る液状化防止のための地盤改良工法は、請求項１または２の地盤改良工法において、
前記粒状物密封体は、粒状物を内部に密封した複数の小密封体からなることを特徴とするものである。
【００２８】
本願請求項５に係る液状化防止のための地盤改良工法は、請求項１ないし４のいずれかの地盤改良工法において、
前記不透水性シートは、伸展性不透水性シート、あるいは非伸展性不透水性シートのいずれかからなることを特徴とする。
【００２９】
本願請求項６に係る液状化防止のための地盤改良工法は、請求項１ないし５のいずれか地盤改良工法において、
前記粒状物密封体は、粒状物密封体の内外部を連通させ、内部にフィルター材を有するドレン管を有し、前記ドレン管は前記粒状物密封体の内部の間隙水圧が所定の値より大きくなったときに、前記粒状物密封体内部の水を排出するように配設されていることを特徴とするものである。
【００３０】
上記請求項１ないし６の液状化防止のための地盤改良工法によれば、改良しようとする地盤を掘削し、掘削した孔に不透水性シートを敷き、その孔に土を埋戻した後に、不透水性シートを密閉することにより地盤の改良工事が完了することができる。したがって、工事が極めて簡単であり、粒状物密封体の中身として埋戻し土を利用することができるので、工事費が安価であり、埋戻し土の処理に困ることもない。
【００３１】
このように、不透水性シートによって密封された粒状物密封体は、地下水の進入を防止することができるので、その内部は地下水によって飽和されることがない。これにより、地震等の強い衝撃を受けても、土の粒子が水分の中に拡散することによって生じる液状化現象を完全に防止することができるのである。
【００５１】
【発明の実施の形態】
次に、本発明による液状化防止のための地盤改良工法、築堤工事における漏水・流失防止工法、盛土の土留工法、および地滑防止のための地盤改良工法の実施の形態について添付の図面を用いて以下に説明する。
【００５２】
最初に液状化防止のための地盤改良工法について説明する。
図１に、地上構造物に対する液状化防止のための地盤改良工法を概念的に示す。
【００５３】
図１の（ａ）部は、改良前の地盤を示している。図１において、符号１は地表、２は地下水位、３は液状化が生じる深さを示している。液状化が生じる深さ３は、液状化が生じる最深の深さをいい、地盤の土質によって変化するが、液状化を生じ易い土質の場合では約１５ｍである。液状化現象は、地下水位２以下であって、液状化が生じる深さ３以上の地盤で生じることが知られている。
【００５４】
ここで、上記「地下水位２以下」の“以下”とは地下水位２と等しいあるいはより深いの意味であり、上記「深さ３以上」の“以上”とは深さ３と等しいあるいはより浅いの意味である。この明細書で“以上”と“以下”は上記の使い方をする。
【００５５】
本実施形態の液状化防止のための地盤改良工法では、好ましくは液状化現象が生じる地盤を全部掘削して、その掘削した孔４の内面に不透水性シート５を敷き、孔４に土を埋戻した後に、不透水性シート５を密閉して粒状物密封体６を形成する。上記工程は図１の（ｂ），（ｃ）部に示されている。粒状物密封体６は、埋戻し後に地下水などが進入しないように不透水性シート５で密閉する。
【００５６】
掘削は、上記実施形態のように液状化が生じる範囲の土をすべて掘削するのが好ましいが、構造物の緩い設計条件により、液状化が生じる深さ３に達しない深さの孔を掘削し、粒状物密封体６を形成してもよい。
【００５７】
上記不透水性シート５は、ゴムシート、ポリエチレンシートの他、耐腐食性を有する柔軟な任意の不透水性材料からなるシートである。さらに、粒状物密封体６を変形させて孔４に密着させたい場合は、伸展性を有する伸展性不透水性シートを用いる。反対に、地中において粒状物密封体６の形状を保持させたい場合は、伸展性を有しない非伸展性不透水性シートを用いる。
【００５８】
不透水性シート５の密閉方法としては、接着剤による接着と、熱による熱溶着、圧力による圧着等がある。
【００５９】
粒状物密封体６の内部を埋戻し土によって充足するのは、埋戻し土を利用できて工事上最も合理的であるためであるが、本願発明は埋戻し土によって粒状物密封体６を形成することに限られず、粒状物であって適度な内部摩擦あるいは粘着力があるものであればよい。
【００６０】
上述したように粒状物密封体６を形成した後は、粒状物密封体６の上方に通常の土を埋め戻し（図１（ｄ）部）、その上に地上構造物を建設することができる（図１（ｅ）部）。
【００６１】
なお、粒状物密封体６は、その大きさ、形状は図１の実施形態のものに限られない。図２に粒状物密封体６の変形例を示す。図２（ａ）の粒状物密封体６は、層状に形成した場合を示している。図２（ｂ）の粒状物密封体６は、多数の土嚢状の小密封体を形成し、全体を一つに拘束したものである。これらの粒状物密封体６の変形例は、粒状物密封体６を予め所定の規格で製造して使用する場合に便利である。
【００６２】
図１（ｅ）部のように、地盤の液状化する部分の土を粒状物密封体６に置き換えることにより、液状化を防止することができる。
【００６３】
液状化は、土の粒子の間に地下水などが入り込み、通常の状態では土の粒子同士の摩擦力によって堆積を維持しているが、地震などの強い衝撃によって間隙水圧が上昇して土の粒子同士の接触が失われ、水の内部に土の粒子が均等に分散し、それらの土の粒子再配列した場合に水が分離して地盤の体積が減少することによって生じる。このような発生のメカニズムにより、液状化は地下水位以下であって液状化が生じる深さ以上の地盤で生じる。
【００６４】
本実施形態によれば、粒状物密封体６内部では埋戻し土が適当な含水量で含まれ、埋戻し後もそれ以上の地下水の進入はない。つまり、粒状物密封体６により地盤中に乾燥した（適度な含水量を有するという意である）土の塊を有し、上述した地下水位以下で液状化が発生するという条件を排除することができる。これにより、液状化が防止される。
【００６５】
図３に本発明の第２の実施形態を示す。図３において図１と同一部分には同一の符号を付して説明を省略する。
【００６６】
本発明の第２実施形態による液状化防止のための地盤改良工法は、図１の第１実施形態の地盤改良工法で使用する粒状物密封体６に対して、漏れ対策を講じたものである。
【００６７】
この第２実施形態による液状化防止のための地盤改良工法では、粒状物密封体６の内外部を連通させ、内部に砕石７を有するドレン管８を有している。このドレン管８は、下端が粒状物密封体６の底部に連通し、上端は地表１より所定の高さ突出し、逆流防止用の逆止弁９を有している。
【００６８】
ドレン管８の内部は、砕石７に限られず、樹脂等からなる繊維状のフィルターの他、公知の任意のフィルター材を使用することができる。
【００６９】
第２実施形態による液状化防止のための地盤改良工法によれば、粒状物密封体６の密封状態が不測の原因によって将来的に浸水した場合でも、液状化を防止することができる。
【００７０】
粒状物密封体６は、不透水性シート５の破損、密閉接合部の剥離によって内部に水が浸入し飽和状態になることが考えられる。しかし、この第２実施形態の液状化防止のための地盤改良工法によれば、ドレン管８が挿通されているので、地震などの強い衝撃のみによって間隙水圧が上昇した時に、過剰な間隙水圧を速やかに外部に排出することができる。このように、間隙水圧の上昇が速やかに抑制されるので、土の粒子の摩擦が失われず、液状化を防止することができるのである。なお、ドレン管８のフィルター材により、泥水のうち水のみが排出される。
【００７１】
なお、図３において、水を排出するようになる間隙水圧は、ドレン管８上端までの揚程にほぼ相当するが、この揚程の調整により、水を排出するようになる間隙水圧を調整することができる。
【００７２】
次に、地下構造物を建設する場合の液状化防止のための地盤改良工法について説明する。図４に本発明の第３実施形態による地下構造物を建設する場合の液状化防止のための地盤改良工法を概念的に示す。図４において図１と同一部分には同一符号を付して説明を省略する。
【００７３】
図４（ａ）部は、改良前の地盤を示している。地下構造物を建設する場合は、図４（ｂ）部に示すように、液状化が生じる深さ３以下の深さまで掘削する。この孔の周面にはシートパイル等の山留材１０を設置する。
【００７４】
この孔の底部の地下構造物の下部に相当する部分には、図１で説明したように、不透水性シート５を敷き、地下構造物の底面以下の深さまで埋戻し、不透水性シート５を密閉して粒状物密封体６を形成する（図４（ｂ）部参照）。
【００７５】
次に、図４（ｃ）部に示すように、上記粒状物密封体６上に地下構造物１１を建設する。
【００７６】
地下構造物１１が建設された後に、図４（ｄ）部に示すように、地下構造物１１の周囲であって、山留材１０との間の空間に不透水性シート５を敷き詰め、埋戻しをする。埋戻しが完了した後は、不透水性シート５を上部で密閉して粒状物密封体６を形成する。
【００７７】
最後に、山留材１０を撤去すれば、図４（ｅ）部に示すように、地下構造物１１の周囲と下部に粒状物密封体６が設置された状態になる。
【００７８】
図４（ｅ）部に示すような構造を有する地下構造物は、第１実施形態で説明したように、周囲の地盤が粒状物密封体６によって水の進入を防止するので、地下水位が上昇した場合でも適度な含水量を有し、水の飽和状態になることがない。これにより、地震等の衝撃を受けても、土の接触が失われず、液状化することがない。この結果、地下構造物１１を安定的に保持することができる。
【００７９】
なお、上述した本発明の第３実施形態では、地下構造物１１の底面が液状化が生じる深さ３より浅い場合について説明したが、地下構造物１１の底面が液状化が生じる深さ３より深い場合には、地下構造物１１下部の粒状物密封体６を省略することができる。地下構造物１１の底面が液状化しない深層地盤によって支持されるからである。
【００８０】
なお、この実施形態においても、粒状物密封体６を複数の小密封体とすること、粒状物密封体６内部に土に代わる粒状物を充填すること、不透水性シート５に伸展性不透水性シートあるいは非伸展性不透水性シートを使用すること、ドレン管を設けること、等は第１、第２実施形態と全く同様にすることができる。
【００８１】
次に、本発明による築堤工事における漏水・流失防止工法について説明する。
【００８２】
本発明の第４実施形態である築堤工事における漏水防止工法を図５に概念的に示す。図５において、図１と同一の部分には同一の符号を付して説明を省略する。
【００８３】
本実施形態の漏水防止工法は、堤体の浸透線に当たる部分に粒状物密封体を設けることものである。このため、本実施形態の漏水防止工法では、図５（ａ）部に示すように、築堤の盛土工程中に粒状物密封体６の形状に凹部１２を形成し、その凹部１２の内面に不透水性シート５を敷き、凹部６に土を入れた後に、不透水性シート５を密閉し、粒状物密封体６を形成する。
【００８４】
粒状物密封体６を形成した後は、堤体１３を予定の高さまで築き、水の進入を防止するために設けられていたシートパイル１４を撤去する。これにより、図５（ｂ）部に示すように、堤防の中心部の水の浸透線に当たる部分に粒状物密封体６が設けられることになる。
【００８５】
上記堤体１３中の粒状物密封体６は、水を通すことがないので、河川等から浸透した水は、粒状物密封体６によって遮られる。図５（ｂ）部に水の浸透線の浸透圧を図示する。水の浸透圧は堤体１３を通過することによって自然に低下するが、粒状物密封体６の後方では、粒状物密封体６の下端の水圧になる。その粒状物密封体６を過ぎた後は、再び低下して堤防外側の地下水と同一の水圧になってそれ以上の流出がなくなる。この水圧の低下と平衡により、堤防の漏水を防止することができる。
【００８６】
なお、上記第４実施形態では、盛土工程中に粒状物密封体６の形状に凹部１２を形成し、それに不透水性シート５を敷いて埋め戻すようにしていたが、この工程には変形例がある。この変形例では、最初に図５（ｂ）の点線Ｘに示した高さまで盛土を行い、粒状物密封体６を形成した後に、残る土を盛るようにする。この場合、粒状物密封体６は堤防の上で形成してもよいし、工場や現場近くのプレハブ場で所定の形状に形成して堤防上に配設するようにしてもよい。この盛土工程における変形例は、本発明の他の実施形態についても共通して採用することができる。
【００８７】
次に、本発明の第５実施形態である築堤工事における土砂等の流失防止工法について説明する。
【００８８】
本発明の第５実施形態による築堤工事における土砂等の流失防止工法を図６に概念的に示す。図６において、図５と同一の部分には同一の符号を付して説明を省略する。
【００８９】
この第５実施形態による築堤工事における土砂等の流失防止工法は、上述した第４実施形態による漏水防止工法と、粒状物密封体６の設置位置のみ異なる。
【００９０】
すなわち、第４実施形態による漏水防止工法が粒状物密封体６を浸透線上、すなわち堤体１３の中心部に設けるのに対し、第５実施形態による築堤工事の土砂等の流失防止工法では、堤体１３の上部に設置する。
【００９１】
本工法では、図６（ａ）部に示すように、築堤工事の盛土工程で堤体の上部に凹部１２を設け、その凹部１２の内面に不透水性シート５を敷き、土を埋め戻す。土を埋め戻した後は、不透水性シート５を密閉する。これにより、図６（ｂ）部に示すように堤体１３の上部に粒状物密封体６が形成される。この粒状物密封体６は、土を内部に封入し、水の進入を防止するので、万一水が堤防の上端を超えた場合でも、その水の流れによって、土砂が流失し、堤防の決壊につながることを防止することができるのである。
【００９２】
なお、上記第４，５実施形態においても、粒状物密封体６を複数の小密封体とすること、粒状物密封体６内部に土に代わる粒状物を充填すること、不透水性シート５に伸展性不透水性シートあるいは非伸展性不透水性シートを使用すること、等は第１ないし第３実施形態と全く同様にすることができる。
【００９３】
また、上記第４，５実施形態において、粒状物密封体６は、堤防の構造に適した形状にすることができ、さらに、漏水防止用の粒状物密封体と土砂流失防止用の粒状物密封体とを組み合わせることもできる。図７に上記漏水防止用の粒状物密封体と土砂流失防止用の粒状物密封体とを組み合わせた例を示す。
【００９４】
次に、本発明による盛土の土留工法について説明する。本発明による盛土の土留工法は、盛土地盤の段差部近傍に粒状物密封体を配設するものである。図８に本発明の第６実施形態である盛土の土留工法を概念的に示す。なお、図５においては、図１と同一の部分には同一の符号を付して説明を省略する。
【００９５】
図５に示すように、この実施形態の盛土は、原地盤１５上に盛土１６を盛り上げたものである。この実施形態では、盛土１６の最も大きな段差部に粒状物密封体６を設けている。
【００９６】
このように、盛土１６の段差部に粒状物密封体６を設けることにより、地下水位１７が上昇した場合でも、粒状物密封体６の内部は水の進入を防止することができる。これにより、盛土段差部の土砂の流失による、崩壊、侵食等を防止することができる。
【００９７】
なお、図８の例では、粒状物密封体６は断面台形としているので、最初に粒状物密封体６を形成した後に、その内側に盛土を盛るようにして工事を行う。
【００９８】
また、この実施形態においても、粒状物密封体６を複数の小密封体とすること、粒状物密封体６内部に土に代わる粒状物を充填すること、不透水性シート５に伸展性不透水性シートあるいは非伸展性不透水性シートを使用すること、ドレン管を設けること、等は第１ないし第３実施形態と全く同様にすることができる。
【００９９】
次に本発明による地滑防止のための地盤改良工法について説明する。
本発明の第７実施形態である地滑防止のための地盤改良工法を図９に概念的に示す。
【０１００】
この第７実施形態による地滑防止のための地盤改良工法は、地滑り斜面の安定計算上間隙水圧を排除して安定性を維持する深さ範囲内の土を粒状物密封体に置き換えるものである。
【０１０１】
図９において、斜面１８に沿って地下水位１９があるとする。この斜面の地滑り面は、円弧地滑り面２０であるとする。
【０１０２】
この斜面の安定計算は、すでに説明したように、地滑り面上の土塊を図９に示すように細片に分割して、下式によってそれぞれの細片のせん断応力に対する垂直応力および内部摩擦角の比を計算し、その分子と分母の総計の比率で安定性の安全率を計算する。
【０１０３】
【数２】

ここで、ｆｓ：安全率
ｃ ：地滑り粘土の粘着力（ｔ／ｍ2 ）
ψ ：地滑り粘土の内部摩擦角
Ｎ ：各細片における滑り面での垂直応力（ｔ）
Ｔ ：各細片における滑り面でのせん断応力（ｔ）
ｌ ：各細片の滑り面の長さ（ｍ）
Ｕ ：各細片における間隙水圧（ｔ）
上式から分かるように、分子の垂直荷重は地下水等の間隙水圧によって減少するので、地下水が浸透する部分では、安定性が低下する。また、安定性の計算のほかにも、地表水は地滑りの誘因となることも知られている。
【０１０４】
これに対して、本実施形態の地滑防止のための地盤改良工法は、地下水が浸透する地盤を粒状物密封体６によって置換する。
【０１０５】
この粒状物密封体６は、上述した通り、地下水等の進入を防止することができる。したがって、粒状物密封体６の設置により、その粒状物密封体６に該当する細片の安定性の計算では、間隙水圧Ｕが０となる。これにより、斜面の安定性が向上し、地滑りの防止を計算設計することができる。また、地滑りの要因、誘因となる地表水が粒状物密封体６によって排除されるので、地滑りし難い地盤を得ることができる。
【０１０６】
次に、本発明の他の方法による地滑防止のための地盤改良工法について説明する。
【０１０７】
本発明の第８実施形態である地滑防止のための地盤改良工法を図１０に概念的に示す。なお、図１０において、図９と同一の部分については同一の符号を付して説明を省略する。
【０１０８】
この第８実施形態では、上述した斜面の安定計算で地下水による間隙水圧の影響の排除に代えて、滑り面のせん断応力を減少させることにより地滑りの防止を図る。
【０１０９】
すなわち、図１０に示すように、地滑り面２０を階段状に掘削してその上に粒状物密封体６を形成する。このように、下面が階段状の粒状物密封体６が形成されることにより、地滑り斜面２０上の土塊であって粒状物密封体６に相当する部分は、上記した安定計算の式の計算において、各細片における滑り面でのせん断応力Ｔは小さくなる。
【０１１０】
これにより、斜面の安定性が向上し、地滑りの防止を計算設計することができる。また、地滑りの要因、誘因となる地表水が粒状物密封体６によって排除され、地滑りの発生を防止することができる点は第７実施形態と同様である。
【０１１１】
なお、上記第７、第８実施形態においても、粒状物密封体６を複数の小密封体とすること、粒状物密封体６内部に土に代わる粒状物を充填すること、不透水性シート５に伸展性不透水性シートあるいは非伸展性不透水性シートを使用すること、ドレン管を設けること、等は第１ないし第３実施形態と全く同様にすることができる。
【０１１２】
最後に、傾斜した斜面上に盛土工事を行った場合の土留と地滑りの双方を防止するために、上述した盛土の土留工法と地滑防止のための地盤改良工法とを組み合わせた例を説明する。
【０１１３】
図１１に上記盛土工事をした場合の地盤の断面を示す。この図において、図８と同一の部分には同一の符号を付して説明を省略する。
【０１１４】
図１１に示すように、このように土留と地滑り防止をする場合は、最初に盛土１６の段差部に土留用の粒状物密封体６ａを形成する。次に、好ましくは原地盤１５の斜面を少し掘削して階段状に形成し、その上に地滑り防止用の粒状物密封体６ｂを形成する。粒状物密封体６ｂを形成した後は、その上に盛土を盛り、表面をひな壇上に造成する。これにより、上述した将来的に地下水位１７が上昇しても、この地下水による法面の崩壊、地滑りを防止することができる。
【０１１５】
【発明の効果】
以上の説明から明らかなように、本願発明の液状化防止のための地盤改良工法によれば、従来のセメント等を地盤に混ぜたり、サンドコンパクション等に比べて、埋戻し土を不透水性シートによって密封する等、工事簡単かつ安価であり、埋戻し土の処理に困ることもない。また、このようにして形成された粒状物密封体は、地下水の進入を防止することができるので、その内部は地下水によって飽和されることがない。これにより、地震等の強い衝撃を受けても、土の粒子が水分の中に拡散することによって生じる液状化現象を防止することができる。
【０１１６】
本願発明の築堤工事における漏水・流失防止工法によれば、堤防の盛土の一部を不透水性シートによって密封することにより、堤防の上部または浸透線に当たる中心部分に粒状物密封体が形成される。この粒状物密封体は、不透水性シートによって密封されているので、水を通すこと、および内部の土砂が流出するのを防止することができる。本発明の工法によれば、従来の前小段、裏小段を設ける方法や土砂流失防止のために土嚢を積み上げる方法より、はるかに簡単に堤防の漏水や土砂の流失を防止することができる。
【０１１７】
本願発明の盛土の土留工法によれば、盛土の一部に段差部に粒状物密封体が形成される。この土留用の粒状物密封体により、盛土の段差部の崩壊を防止でき、また、段差部の法面を保護することができる。
【０１１８】
本願発明の地滑防止のための地盤改良工法によれば、地滑り面付近の地層を粒状物密封体によって置換し、この粒状物密封体によって水の浸透を防止し、斜面の安定性を向上させる。また、粒状物密封体の形状により、地滑り面のせん断応力を減少させ、より安定的な地盤を得ることができる。この工法は、特に斜面に盛土をする場合には、盛土の工程の中で簡単に粒状物密封体を形成することができるので、従来の地表水排出のための地表排路工に比べて簡単、廉価に地滑り防止の施工を行うことができる。
【図面の簡単な説明】
【図１】本発明の第１実施形態による液状化防止のための地盤改良工法が概念的に示した図。
【図２】本発明の第１実施形態による液状化防止のための地盤改良工法の変形例を示した図。
【図３】本発明の第２実施形態による液状化防止のための地盤改良工法が概念的に示した図。
【図４】本発明の第３実施形態による地下構造物を建設する場合の液状化防止のための地盤改良工法を概念的に示した図。
【図５】本発明の第４実施形態による築堤工事における漏水防止工法を概念的に示した図。
【図６】本発明の第５実施形態による築堤工事における土砂等の流失防止工法を概念的に示した図。
【図７】本発明による築堤工事における漏水防止工法と土砂等の流失防止工法とを組み合わせた例を示した図。
【図８】本発明の第６実施形態による盛土の土留工法を概念的に示した図。
【図９】本発明の第７実施形態による地滑防止のための地盤改良工法を概念的に示した図。
【図１０】本発明の第８実施形態による地滑防止のための地盤改良工法を概念的に示した図。
【図１１】本発明の盛土の土留工法と地滑防止のための地盤改良工法とを組み合わせた例を示した図。
【図１２】従来の液状化防止のための地盤の強度増加を図る工法を概念的に示した図。
【図１３】従来の液状化防止のための過剰な間隙水圧を消散させる方法を概念的に示した図。
【図１４】従来の液状化防止のための地下水の水位を低下させる方法を概念的に示した図。
【図１５】従来の堤防の漏水防止または土砂の流失防止の方法を概念的に示した図。
【図１６】従来の盛土の土留工法を概念的に示した図。
【図１７】地滑り斜面の安定性計算を説明した説明図。
【図１８】従来の地滑り防止のための地表水処理の方法を概念的に示した図。
【符号の説明】
１ 地表
２ 地下水位
３ 液状化が生じる深さ
４ 孔
５ 不透水性シート
６ 粒状物密封体
７ 砕石
８ ドレン管
９ 逆止弁
１０ 山留材
１１ 地下構造物
１２ 凹部
１３ 堤体
１４ シートパイル
１５ 原地盤
１６ 盛土
１７ 地下水位
１８ 斜面
１９ 地下水位
２０ 円弧地滑り面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ground improvement method for preventing liquefaction, a water leakage and runoff prevention method for embankment construction, an earth retaining method for embankment, and a ground improvement method for preventing landslides.
[0002]
[Prior art]
As described above, the present invention relates to a construction method having four different purposes, namely, a ground improvement method for preventing liquefaction, a water leakage / runoff prevention method for embankment construction, an earth retaining method for embankment, and a ground improvement method for preventing landslides. Here, the conventional techniques of the above methods will be described.
[0003]
First, the ground improvement method for preventing liquefaction will be described. Conventionally, in order to prevent liquefaction, (1) a method to increase the strength of the ground, (2) a method to dissipate excess pore water pressure, (3) a method to lower the groundwater level, (4) design of the structure There was a method to restrain the deformation of the structure at the time of earthquake.
[0004]
The method (1) for increasing the strength of the ground is a method for increasing the strength of the soil itself. This method includes a compaction method such as sand compaction, and a cement-based mixed stirring method. Sand compaction is a method of compacting the soil of the ground. According to the sand compaction, as shown in FIG. 12 (a), the soil containing a lot of gaps before the improvement, the soil particles are densely arranged after the compaction, and as a result, the frictional resistance between the particles increases, Can be prevented.
[0005]
The cement-based mixed stirring method is a method of mixing and solidifying a binder such as cement with the soil of the ground to be improved. According to this cement-based mixing and stirring method, as shown in FIG. 12 (b), cement can enter between the soil particles after the improvement, and the particles can be bonded together, thereby preventing liquefaction.
[0006]
The method of dissipating the excess pore water pressure in (2) is a method of suppressing the pore water pressure by discharging the excessive increase in the pore water pressure causing ground liquefaction to the outside of the ground through a drain pipe such as a crushed drain pipe. Say. In order to realize this method, as shown in FIG. 13, a drain pipe is inserted so as to reach a depth below the groundwater level of the ground, and a filter such as crushed stone is discharged so that only water can be discharged into the drain pipe. Fill the material. By providing such a structure, when there is a strong impact such as an earthquake, excess water can be quickly discharged to the outside. As a result, since the pore water pressure is kept low, the contact of soil particles is not lost, and liquefaction can be prevented.
[0007]
The method for lowering the groundwater level in (3) focuses on the fact that liquefaction occurs in shallow ground within 15 m from the ground surface and occurs in ground where groundwater penetrates.
[0008]
Specifically, as shown in FIG. 14, a pipe is inserted deep underground of the structure, the groundwater is pumped up by a pump, and the groundwater level is kept low. By this method, the ground supporting the structure is prevented from being infiltrated by the groundwater, and the supporting ground of the structure can be prevented from being liquefied even by a strong impact such as an earthquake.
[0009]
The method of restraining deformation of a structure at the time of earthquake by designing the structure in (4) is a method in which piles are driven into a deep ground that is not liquefied and the structures are supported by these piles. According to this construction method, even if liquefaction occurs in the shallow ground, the structure can be inclined and prevented.
[0010]
Next, a conventional method for preventing leakage from a dike or preventing sediment from flowing out will be described with reference to FIG. Generally, river embankments are formed by raising soil. Since the water of this levee can pass water, the water pressure (water pressure of the seepage line) gradually decreases. However, when the cross-sectional area of the levee body is insufficient, water leakage occurs over a long period of time.
[0011]
On the other hand, conventionally, the cross-sectional area of the levee body has been increased so that the water pressure of the seepage line is equal to the pressure of groundwater outside the river inside the dam body. As shown in FIG. 15, the cross-sectional area of the levee body has been increased by providing additional layers (portions indicated as front and back steps in FIG. 15) on the dam body. Due to this increased cross-sectional area of the dam body, river water will not leak out of the levee.
[0012]
Also, the river head may rise beyond expectations due to abnormal weather such as a typhoon and flow out beyond the top of the dike. In such a case, the soil above the levee may be washed away by flooded water, and some breaching holes may grow rapidly, leading to large levee breaching.
[0013]
On the other hand, conventionally, sandbags have been piled up in order to prevent the soil on the top of the bank from being washed away. As a result, it was possible to prevent the soil from flowing over the top of the dike, and to prevent the breakage of a large dike.
[0014]
Next, a conventional earth retaining method for embankment will be described. As shown in FIG. 16, the embankment is formed by raising the soil on the slope. At the step portion of this embankment, a slope is formed for stability. The slope of the conventional embankment is a slope with a gentle slope less than a certain slope, except when special earth retaining work such as concrete protective walls or piles for retaining soil is applied. Vegetation was applied on top to prevent runoff of earth and sand. The earth retaining of the embankment is realized by the gentle slope of the slope and the vegetation that prevents the sediment from being washed away.
[0015]
Next, a conventional ground improvement method for preventing landslide will be described. Conventional methods for preventing landslides were largely based on soil removal and surface water treatment.
[0016]
Excavation is a method of reducing the load on the landslide slope and reducing the sliding force, either cutting off a part of the soil mass on the slope or removing all the sliding soil mass on the landslide slope to stabilize the slope.
[0017]
As shown in FIG. 17, in the case of arc slip, the amount of earth removal is divided into blocks on the landslide surface of the slope, and the stability calculation shown in the following equation is performed for each divided block to exceed a certain safety factor. To be determined.
[0018]
[Expression 1]

Where fs: safety factor
c: Adhesive strength of landslide clay (t / m2)
ψ: Internal friction angle of landslide clay
N: Normal stress (t) on the sliding surface in each strip
T: Shear stress (t) at the sliding surface in each strip
l: Length of sliding surface of each strip (m)
U: pore water pressure in each strip (t)
Cutting the head of the landslide slope is effective for the position of earth removal. Appropriate soil removal improves the landslide safety factor and stabilizes the slope.
[0019]
Next, another conventional surface water treatment method for preventing landslide will be described.
[0020]
The surface water treatment method for preventing landslide is a method for quickly discharging surface water that induces or promotes landslide to the outside of the landslide area. FIG. 18 shows an example of surface drainage works for the surface water discharge.
[0021]
[Problems to be solved by the invention]
However, the conventional ground improvement method for preventing liquefaction, water leakage and runoff prevention method for embankment construction, earth retaining method for embankment, and ground improvement method for prevention of landslide are respectively large work, and therefore the construction cost is also high. I had to soar.
[0022]
Moreover, in the conventional ground improvement etc., in order to replace the soil of the original ground with high quality soil, cement, etc., it was necessary to consider the disposal and reuse of the soil of the original ground.
[0023]
Therefore, the problem to be solved by the present invention is that it is possible to realize ground improvement for preventing liquefaction and prevention of water leakage and runoff of embankment construction by an inexpensive and simple method, and to use the soil of the original ground as it is. It is to provide a method that can be used.
[0024]
[Means for Solving the Problems]
The ground improvement construction method for preventing liquefaction according to claim 1 of the present application is:
It has a step of replacing the soil below the groundwater level of the ground to be improved and above the depth where liquefaction occurs with a sealed granular material in which the granular material containing backfilled soil is sealed with an impermeable sheet. And
[0025]
The ground improvement method for preventing liquefaction according to claim 2 of the present application is:
Substituting soil that is below the groundwater level around or below the underground structure and deeper than liquefaction with a sealed granular material in which the granular material including backfilled soil is sealed with an impermeable sheet. It is characterized by.
[0026]
The ground improvement construction method for preventing liquefaction according to claim 3 of the present application is the ground improvement construction method of claim 1 or 2,
The granular material sealing body is characterized in that an impervious sheet is laid on the inner surface of an excavated hole, and the impervious sheet is hermetically sealed after soil is backfilled in the hole.
[0027]
The ground improvement construction method for preventing liquefaction according to claim 4 of the present application is the ground improvement construction method of claim 1 or 2,
The granular material sealing body is composed of a plurality of small sealed bodies in which the granular material is sealed.
[0028]
The ground improvement construction method for preventing liquefaction according to claim 5 of the present application is the ground improvement construction method according to any one of claims 1 to 4,
The water-impermeable sheet is composed of either an extensible impermeable sheet or a non-extensible impermeable sheet.
[0029]
The ground improvement construction method for preventing liquefaction according to claim 6 of the present application is the ground improvement construction method according to any one of claims 1 to 5,
The granular material sealing body has a drain pipe having a filter material in the inside and communicating with the inside and outside of the granular material sealing body, and the drain pipe has a pore water pressure inside the granular material sealing body larger than a predetermined value. When it becomes, it is arrange | positioned so that the water inside the said granular material sealing body may be discharged | emitted.
[0030]
According to the ground improvement construction method for preventing liquefaction according to claims 1 to 6, after excavating the ground to be improved, laying an impermeable sheet in the excavated hole, and backfilling the soil in the hole, The ground improvement work can be completed by sealing the water-impermeable sheet. Therefore, the construction is extremely simple, and the backfilling soil can be used as the contents of the granular material sealing body. Therefore, the construction cost is low, and there is no difficulty in processing the backfilling soil.
[0031]
Thus, since the granular material sealing body sealed with the water-impermeable sheet can prevent the ingress of groundwater, the inside thereof is not saturated with the groundwater. As a result, even when subjected to a strong impact such as an earthquake, the liquefaction phenomenon caused by the diffusion of soil particles into moisture can be completely prevented.
[0051]
DETAILED DESCRIPTION OF THE INVENTION
Next, referring to the attached drawings, embodiments of the ground improvement method for preventing liquefaction according to the present invention, the method for preventing leakage and runoff in embankment construction, the earth retaining method for embankment, and the ground improvement method for preventing landslide are used. Will be described below.
[0052]
First, the ground improvement method for preventing liquefaction will be described.
FIG. 1 conceptually shows a ground improvement method for preventing liquefaction with respect to a ground structure.
[0053]
Part (a) of FIG. 1 shows the ground before improvement. In FIG. 1, reference numeral 1 is the ground surface, 2 is the groundwater level, and 3 is the depth at which liquefaction occurs. Depth 3 at which liquefaction occurs is the deepest depth at which liquefaction occurs and varies depending on the soil quality, but is about 15 m in the case of soils that are liable to liquefy. It is known that the liquefaction phenomenon occurs in the ground having a groundwater level of 2 or less and a depth of 3 or more where liquefaction occurs.
[0054]
Here, “below” of “groundwater level 2 or lower” means that it is equal to or deeper than groundwater level 2, and “more than” of “depth 3 or higher” is equal to or shallower than depth 3. Is the meaning. In this specification, “above” and “below” are used as described above.
[0055]
In the ground improvement method for preventing liquefaction according to the present embodiment, preferably, all ground where liquefaction occurs is excavated, and an impervious sheet 5 is laid on the inner surface of the excavated hole 4, and soil is put into the hole 4. After the backfilling, the water-impermeable sheet 5 is sealed to form the granular material sealing body 6. The above process is shown in FIGS. 1B and 1C. The granular material sealing body 6 is sealed with an impermeable sheet 5 so that groundwater or the like does not enter after the backfilling.
[0056]
As for the excavation, it is preferable to excavate all the soil in the range where liquefaction occurs as in the above embodiment. The granular material sealing body 6 may be formed.
[0057]
The water-impermeable sheet 5 is a sheet made of a flexible water-impermeable material having corrosion resistance in addition to a rubber sheet and a polyethylene sheet. Furthermore, when the granular material sealing body 6 is to be deformed to be brought into close contact with the hole 4, an extensible impermeable sheet having extensibility is used. On the other hand, when it is desired to maintain the shape of the granular material sealing body 6 in the ground, a non-extensible impermeable sheet having no extensibility is used.
[0058]
As a sealing method of the water-impermeable sheet 5, there are adhesion by an adhesive, thermal welding by heat, pressure bonding by pressure, and the like.
[0059]
The reason why the inside of the granular material sealing body 6 is filled with the backfilling soil is that the backfilling soil can be used and is the most rational in construction. In the present invention, the granular material sealing body 6 is formed by the backfilling soil. It is not limited to the above, and any particulate material having appropriate internal friction or adhesive strength may be used.
[0060]
After forming the granular material sealing body 6 as described above, normal soil can be backfilled above the granular material sealing body 6 (FIG. 1 (d)), and a ground structure can be constructed thereon. (FIG. 1 (e) part).
[0061]
In addition, the magnitude | size and shape of the granular material sealing body 6 are not restricted to the thing of embodiment of FIG. FIG. 2 shows a modified example of the granular material sealing body 6. The granular material sealing body 6 of FIG. 2A shows a case where it is formed in a layer shape. The granular material sealing body 6 in FIG. 2B is formed by forming a large number of sandbag-like small sealing bodies and constraining the whole. These modified examples of the granular material sealing body 6 are convenient when the granular material sealing body 6 is manufactured according to a predetermined standard and used.
[0062]
As shown in FIG. 1 (e), liquefaction can be prevented by replacing the soil of the liquefied portion of the ground with the granular material sealing body 6.
[0063]
In liquefaction, groundwater enters between the soil particles, and in normal conditions, sedimentation is maintained by the frictional force between the soil particles. The contact between each other is lost, the soil particles are evenly dispersed in the water, and when the soil particles are rearranged, the water is separated and the volume of the ground is reduced. Due to such a generation mechanism, liquefaction occurs in the ground below the groundwater level and above the depth at which liquefaction occurs.
[0064]
According to this embodiment, the backfill soil is contained in the granular material sealing body 6 with an appropriate water content, and no further groundwater enters after the backfill. That is, it is possible to eliminate the condition that the granular material sealing body 6 has a lump of soil dried (meaning having an appropriate water content) in the ground and liquefaction occurs below the groundwater level. it can. Thereby, liquefaction is prevented.
[0065]
FIG. 3 shows a second embodiment of the present invention. In FIG. 3, the same parts as those of FIG.
[0066]
In the ground improvement method for preventing liquefaction according to the second embodiment of the present invention, measures against leakage are taken for the granular material sealing body 6 used in the ground improvement method of the first embodiment of FIG. .
[0067]
In the ground improvement method for preventing liquefaction according to the second embodiment, the inside and outside of the granular material sealing body 6 are communicated, and the drain pipe 8 having the crushed stone 7 is provided inside. The drain pipe 8 has a lower end communicating with the bottom of the granular material sealing body 6, an upper end protruding a predetermined height from the ground surface 1, and has a check valve 9 for preventing a backflow.
[0068]
The inside of the drain pipe 8 is not limited to the crushed stone 7, and any known filter material can be used in addition to a fibrous filter made of resin or the like.
[0069]
According to the ground improvement method for preventing liquefaction according to the second embodiment, liquefaction can be prevented even if the sealed state of the granular material sealing body 6 is flooded in the future due to an unexpected cause.
[0070]
It is conceivable that the granular material sealing body 6 is saturated due to water entering the inside due to breakage of the water-impermeable sheet 5 and peeling of the sealed joint portion. However, according to the ground improvement method for preventing liquefaction of the second embodiment, since the drain pipe 8 is inserted, when the pore water pressure rises only by a strong impact such as an earthquake, an excessive pore water pressure is generated. It can be discharged quickly to the outside. Thus, since the increase in pore water pressure is quickly suppressed, the friction of soil particles is not lost, and liquefaction can be prevented. Note that only the water in the muddy water is discharged by the filter material of the drain pipe 8.
[0071]
In FIG. 3, the pore water pressure at which water is discharged substantially corresponds to the head up to the upper end of the drain pipe 8, but the pore water pressure at which water is discharged can be adjusted by adjusting the head. it can.
[0072]
Next, the ground improvement construction method for preventing liquefaction when an underground structure is constructed will be described. FIG. 4 conceptually shows a ground improvement method for preventing liquefaction when an underground structure according to the third embodiment of the present invention is constructed. In FIG. 4, the same parts as those in FIG.
[0073]
Part (a) of FIG. 4 shows the ground before improvement. When constructing an underground structure, as shown in FIG. 4B, excavation is performed to a depth of 3 or less where liquefaction occurs. A mountain retaining material 10 such as a sheet pile is installed on the peripheral surface of the hole.
[0074]
As described with reference to FIG. 1, the portion corresponding to the lower portion of the underground structure at the bottom of the hole is laid with a water-impermeable sheet 5 and backfilled to a depth below the bottom surface of the underground structure. Is sealed to form the granular material sealing body 6 (see FIG. 4B).
[0075]
Next, as shown in FIG. 4C, the underground structure 11 is constructed on the granular material sealing body 6.
[0076]
After the underground structure 11 is constructed, as shown in FIG. 4D, the impermeable sheet 5 is spread around the underground structure 11 and in the space between the mountain retaining materials 10 and buried. Return. After the backfilling is completed, the impervious sheet 5 is sealed at the top to form the granular material sealing body 6.
[0077]
Finally, when the mountain retaining material 10 is removed, as shown in FIG. 4 (e), the granular material sealing body 6 is installed around and below the underground structure 11.
[0078]
In the underground structure having the structure shown in FIG. 4 (e), as described in the first embodiment, since the surrounding ground prevents water from entering by the granular material sealing body 6, the underground water level rises. Even if it does, it has moderate water content and does not become a saturated state of water. Thereby, even if it receives impacts, such as an earthquake, the contact of soil is not lost and it does not liquefy. As a result, the underground structure 11 can be stably held.
[0079]
In the above-described third embodiment of the present invention, the case where the bottom surface of the underground structure 11 is shallower than the depth 3 at which liquefaction occurs is described. However, the depth of the bottom surface of the underground structure 11 from depth 3 at which liquefaction occurs. When deep, the granular material sealing body 6 below the underground structure 11 can be omitted. This is because the bottom surface of the underground structure 11 is supported by the deep ground that is not liquefied.
[0080]
In this embodiment as well, the granular material sealing body 6 is made into a plurality of small sealed bodies, the granular material sealing body 6 is filled with granular materials in place of soil, and the impermeable sheet 5 is made to be extensible impermeable water. The use of an expandable sheet or a non-extensible impermeable sheet, the provision of a drain pipe, etc. can be made exactly the same as in the first and second embodiments.
[0081]
Next, the leakage and runoff prevention method in the embankment construction according to the present invention will be described.
[0082]
FIG. 5 conceptually shows a water leakage prevention method in embankment construction that is the fourth embodiment of the present invention. In FIG. 5, the same parts as those in FIG.
[0083]
The water leakage prevention method of this embodiment is to provide a granular material sealing body at a portion corresponding to the seepage line of the bank body. For this reason, in the water leakage prevention method of this embodiment, as shown in FIG. 5 (a), the recess 12 is formed in the shape of the granular material sealing body 6 during the embankment embedding process, and the inner surface of the recess 12 is not formed. After the water-permeable sheet 5 is laid and soil is put in the recess 6, the water-impermeable sheet 5 is sealed to form the granular material sealing body 6.
[0084]
After the granular material sealing body 6 is formed, the bank body 13 is built up to a predetermined height, and the sheet pile 14 provided to prevent water from entering is removed. Thereby, as shown in FIG.5 (b) part, the granular material sealing body 6 will be provided in the part which hits the permeation line of the water of the center part of a bank.
[0085]
Since the particulate matter sealing body 6 in the dam body 13 does not allow water to pass through, the water that has permeated from the river or the like is blocked by the particulate matter sealing body 6. FIG. 5B illustrates the osmotic pressure of the water osmosis line. Although the osmotic pressure of water naturally decreases by passing through the dam body 13, the water pressure at the lower end of the granular material sealing body 6 is behind the granular material sealing body 6. After passing through the granular material sealing body 6, it drops again and becomes the same water pressure as the groundwater outside the dike, and no further outflow occurs. Leakage of the levee can be prevented by this decrease and balance of water pressure.
[0086]
In the fourth embodiment, the concave portion 12 is formed in the shape of the granular material sealing body 6 during the embankment process, and the water-impermeable sheet 5 is laid on the backfill. There is. In this modified example, the embankment is first performed up to the height indicated by the dotted line X in FIG. 5B, and the remaining soil is accumulated after the granular material sealing body 6 is formed. In this case, the granular material sealing body 6 may be formed on a dike, or may be formed in a predetermined shape at a prefab site near a factory or a site and disposed on the dike. The modification in this embankment process can be adopted in common with other embodiments of the present invention.
[0087]
Next, an explanation will be given of a method for preventing runoff of earth and sand in embankment construction that is a fifth embodiment of the present invention.
[0088]
FIG. 6 conceptually shows a method for preventing runoff of earth and sand in embankment construction according to the fifth embodiment of the present invention. In FIG. 6, the same parts as those in FIG.
[0089]
The method for preventing the loss of earth and sand in the embankment work according to the fifth embodiment differs from the water leakage preventing method according to the fourth embodiment described above only in the installation position of the granular material sealing body 6.
[0090]
That is, the water leakage prevention method according to the fourth embodiment provides the granular material sealing body 6 on the permeation line, that is, at the center of the levee body 13, whereas the erosion prevention method such as earth and sand of embankment construction according to the fifth embodiment Installed on top of body 13.
[0091]
In this construction method, as shown in FIG. 6 (a), in the embankment process of embankment construction, a recess 12 is provided in the upper part of the bank body, and an impervious sheet 5 is laid on the inner surface of the recess 12 to refill the soil. After refilling the soil, the impermeable sheet 5 is sealed. Thereby, the granular material sealing body 6 is formed in the upper part of the bank 13 as shown in FIG.6 (b) part. Since this granular material sealing body 6 encloses the soil and prevents the ingress of water, even if the water exceeds the upper end of the embankment, the sediment will be washed away by the water flow and the embankment will break. Can be prevented.
[0092]
In the fourth and fifth embodiments, the granular material sealing body 6 is a plurality of small sealed bodies, the granular material sealing body 6 is filled with a granular material instead of soil, and the water-impermeable sheet 5 is filled. The use of a stretchable water-impermeable sheet or a non-stretchable water-impermeable sheet can be performed in exactly the same manner as in the first to third embodiments.
[0093]
In the fourth and fifth embodiments, the granular material sealing body 6 can be formed into a shape suitable for the structure of a dike, and further, a granular material sealing body for preventing water leakage and a granular material sealing for preventing sediment loss. It can also be combined with the body. FIG. 7 shows an example in which the granular material sealing body for preventing water leakage is combined with the granular material sealing body for preventing sediment loss.
[0094]
Next, the earth retaining method for embankment according to the present invention will be described. The earth retaining method for embankment according to the present invention is to dispose a granular material sealing body in the vicinity of a stepped portion of the embankment. FIG. 8 conceptually shows the embankment earth retaining method according to the sixth embodiment of the present invention. In FIG. 5, the same parts as those in FIG.
[0095]
As shown in FIG. 5, the embankment according to this embodiment is obtained by embedding an embankment 16 on an original ground 15. In this embodiment, the granular material sealing body 6 is provided at the largest step portion of the embankment 16.
[0096]
Thus, by providing the granular material sealing body 6 at the step portion of the embankment 16, even when the groundwater level 17 rises, the inside of the granular material sealing body 6 can prevent water from entering. Thereby, collapse, erosion, etc. due to runoff of earth and sand at the stepped portion of the embankment can be prevented.
[0097]
In addition, in the example of FIG. 8, since the granular material sealing body 6 is made into the trapezoidal cross section, after forming the granular material sealing body 6 initially, it constructs so that embankment may be piled up inside.
[0098]
Moreover, also in this embodiment, the granular material sealing body 6 is made into a plurality of small sealing bodies, the granular material sealing body 6 is filled with a granular material in place of soil, and the impermeable sheet 5 is extensible and impermeable. The use of an expandable sheet or a non-extensible impermeable sheet, the provision of a drain pipe, etc. can be made exactly the same as in the first to third embodiments.
[0099]
Next, the ground improvement method for preventing landslide according to the present invention will be described.
A ground improvement method for preventing landslide according to a seventh embodiment of the present invention is conceptually shown in FIG.
[0100]
The ground improvement method for preventing landslide according to the seventh embodiment is to replace soil in a depth range in which stability is maintained by eliminating pore water pressure in stability calculation of a landslide slope with a sealed granular material. .
[0101]
In FIG. 9, it is assumed that there is a groundwater level 19 along the slope 18. It is assumed that the landslide surface of this slope is an arc landslide surface 20.
[0102]
As described above, the slope stability calculation is performed by dividing the mass on the landslide surface into pieces as shown in FIG. 9 and calculating the normal stress and the internal friction angle with respect to the shear stress of each piece according to the following equation. Calculate the ratio and calculate the safety factor of stability by the ratio of the sum of its numerator and denominator.
[0103]
[Expression 2]

Where fs: safety factor
c: Adhesive strength of landslide clay (t / m2)
ψ: Internal friction angle of landslide clay
N: Normal stress (t) on the sliding surface in each strip
T: Shear stress (t) at the sliding surface in each strip
l: Length of sliding surface of each strip (m)
U: pore water pressure in each strip (t)
As can be seen from the above equation, the vertical load of the molecule is reduced by the pore water pressure such as groundwater, so the stability is lowered in the portion where the groundwater penetrates. In addition to stability calculations, surface water is also known to trigger landslides.
[0104]
On the other hand, the ground improvement method for preventing landslide according to the present embodiment replaces the ground into which groundwater penetrates with the granular material sealing body 6.
[0105]
As described above, the granular material sealing body 6 can prevent entry of groundwater or the like. Therefore, the pore water pressure U is 0 in the calculation of the stability of the strip corresponding to the granular material sealing body 6 by installing the granular material sealing body 6. Thereby, stability of a slope improves and the prevention of landslide can be designed. Moreover, since the surface water which becomes the cause of a landslide and an incentive is excluded by the granular material sealing body 6, the ground which is hard to landslide can be obtained.
[0106]
Next, a ground improvement method for preventing landslide according to another method of the present invention will be described.
[0107]
FIG. 10 conceptually shows a ground improvement method for preventing landslide that is an eighth embodiment of the present invention. In FIG. 10, the same parts as those of FIG.
[0108]
In the eighth embodiment, instead of eliminating the influence of pore water pressure due to groundwater in the slope stability calculation described above, landslide is prevented by reducing the shear stress of the sliding surface.
[0109]
That is, as shown in FIG. 10, the landslide surface 20 is excavated stepwise to form the granular material sealing body 6 thereon. Thus, by forming the granular material sealing body 6 having a stepped bottom surface, a portion corresponding to the granular material sealing body 6 on the landslide slope 20 is calculated in the above-described stability calculation formula. The shear stress T at the sliding surface in each strip becomes small.
[0110]
Thereby, stability of a slope improves and the prevention of landslide can be designed. Moreover, the surface water used as the cause and cause of a landslide is excluded by the granular material sealing body 6, and it can prevent generation | occurrence | production of a landslide similarly to 7th Embodiment.
[0111]
In addition, also in the said 7th, 8th embodiment, the granular material sealing body 6 is made into a some small sealing body, the granular material instead of soil is filled inside the granular material sealing body 6, and the water-impermeable sheet 5 The use of a stretchable water-impermeable sheet or a non-stretchable water-impermeable sheet, the provision of a drain pipe, etc. can be performed in exactly the same manner as in the first to third embodiments.
[0112]
Finally, in order to prevent both earth retaining and landslide when embankment work is performed on an inclined slope, an example of combining the above earth retaining method and ground improvement method for preventing landslide will be described. .
[0113]
FIG. 11 shows a cross section of the ground when the above-mentioned embankment work is performed. In this figure, the same parts as those in FIG.
[0114]
As shown in FIG. 11, in order to prevent the earth retaining and the landslide in this way, the granular material sealing body 6 a for the earth retaining is first formed on the step portion of the embankment 16. Next, preferably, the slope of the original ground 15 is excavated a little to form a stepped shape, and a granular material sealing body 6b for preventing landslide is formed thereon. After the granular material sealing body 6b is formed, the embankment is piled on it and the surface is formed on a platform. Thereby, even if the groundwater level 17 rises in the future mentioned above, it is possible to prevent the slope collapse and landslide due to the groundwater.
[0115]
【The invention's effect】
As is clear from the above description, according to the ground improvement method for preventing liquefaction of the present invention, conventional cement or the like is mixed with the ground, or the backfill soil is impervious compared to sand compaction or the like. The construction is easy and inexpensive, such as sealing with, and there is no problem with the disposal of backfill soil. Moreover, since the granular material sealing body formed in this way can prevent the ingress of groundwater, the inside thereof is not saturated with the groundwater. Thereby, even if it receives a strong impact such as an earthquake, it is possible to prevent a liquefaction phenomenon caused by diffusion of soil particles into moisture.
[0116]
According to the water leakage / runoff prevention method in the embankment construction of the present invention, by sealing a part of the embankment of the embankment with an impermeable sheet, a granular sealed body is formed at the upper part of the embankment or in the central part that hits the permeation line. . Since this granular material sealing body is sealed by the water-impermeable sheet, it is possible to prevent water from passing therethrough and outflow of earth and sand inside. According to the construction method of the present invention, it is possible to prevent leakage of levee and sediment loss much more easily than the conventional method of providing front and rear steps and the method of stacking sandbags to prevent sediment loss.
[0117]
According to the earth retaining method for embankment of the present invention, a granular material sealing body is formed at a step portion on a part of the embankment. By this granular material sealing body for earth retaining, collapse of the step portion of the embankment can be prevented, and the slope of the step portion can be protected.
[0118]
According to the ground improvement method for preventing landslide of the present invention, the formation in the vicinity of the landslide surface is replaced with a granular material sealing body, water penetration is prevented by this granular material sealing body, and the stability of the slope is improved. . In addition, the shape of the granular material sealing body can reduce the shear stress of the landslide surface and obtain a more stable ground. This method is easier than the conventional surface drainage for surface water discharge because it can easily form a granular sealed body in the embedding process, especially when embankment on slopes. It is possible to carry out construction for preventing landslides at low cost.
[Brief description of the drawings]
FIG. 1 is a diagram conceptually showing a ground improvement method for preventing liquefaction according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a modification of the ground improvement method for preventing liquefaction according to the first embodiment of the present invention.
FIG. 3 is a diagram conceptually showing a ground improvement method for preventing liquefaction according to a second embodiment of the present invention.
FIG. 4 is a diagram conceptually showing a ground improvement method for preventing liquefaction when an underground structure according to a third embodiment of the present invention is constructed.
FIG. 5 is a diagram conceptually showing a water leakage prevention method in embankment work according to a fourth embodiment of the present invention.
FIG. 6 is a diagram conceptually showing a method for preventing the loss of earth and sand in embankment work according to a fifth embodiment of the present invention.
FIG. 7 is a view showing an example in which a water leakage prevention method and a sediment prevention method such as earth and sand are combined in the embankment work according to the present invention.
FIG. 8 is a diagram conceptually showing an embankment earth retaining method according to a sixth embodiment of the present invention.
FIG. 9 is a diagram conceptually showing a ground improvement method for preventing landslide according to a seventh embodiment of the present invention.
FIG. 10 is a diagram conceptually showing a ground improvement method for preventing landslide according to an eighth embodiment of the present invention.
FIG. 11 is a diagram showing an example in which the embankment earth retaining method according to the present invention and the ground improvement method for preventing landslide are combined.
FIG. 12 is a diagram conceptually showing a conventional method for increasing the strength of the ground for preventing liquefaction.
FIG. 13 is a diagram conceptually illustrating a conventional method for dissipating excess pore water pressure for preventing liquefaction.
FIG. 14 is a diagram conceptually showing a conventional method for lowering the level of groundwater for preventing liquefaction.
FIG. 15 is a diagram conceptually showing a conventional method for preventing leakage of a dike or preventing the loss of earth and sand.
FIG. 16 is a diagram conceptually showing a conventional earth retaining method for embankment.
FIG. 17 is an explanatory diagram for explaining stability calculation of a landslide slope.
FIG. 18 is a diagram conceptually showing a conventional surface water treatment method for preventing landslides.
[Explanation of symbols]
1 surface
2 Groundwater level
3 Depth of liquefaction
4 holes
5 Impervious sheet
6 granular sealed body
7 Crushed stone
8 Drain pipe
9 Check valve
10 Yamadome
11 Underground structures
12 recess
13 Embankment
14 Sheet pile
15 Original ground
16 Filling
17 Groundwater level
18 slope
19 Groundwater level
20 Arc landslide surface

Claims (6)

  It has a step of replacing the soil below the groundwater level of the ground to be improved and above the depth where liquefaction occurs with a sealed granular material in which the granular material containing backfilled soil is sealed with an impermeable sheet. Ground improvement method for preventing liquefaction.   Substituting soil that is below the groundwater level around or below the underground structure and deeper than the depth where liquefaction occurs with a sealed granular material in which the granular material containing backfilled soil is sealed with an impermeable sheet. A ground improvement method for preventing liquefaction.   The granular material sealing body is formed by laying an impermeable sheet on the inner surface of an excavated hole, and sealing the impermeable sheet after the soil is backfilled in the hole. The ground improvement construction method for prevention of liquefaction described in 1.   The ground improvement construction method for preventing liquefaction according to claim 1 or 2, wherein the granular material sealing body is composed of a plurality of small sealing bodies in which the granular material is sealed.   The ground for preventing liquefaction according to any one of claims 1 to 4, wherein the water-impermeable sheet is composed of either an extensible impermeable sheet or a non-extensible impermeable sheet. Improvement method.   The granular material sealing body has a drain pipe having a filter material in the inside and communicating with the inside and outside of the granular material sealing body. The drain pipe has a pore water pressure inside the granular material sealing body larger than a predetermined value. The ground improvement construction method for preventing liquefaction according to any one of claims 1 to 5, wherein the ground material sealing body is disposed so as to discharge water when it becomes.

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