JP2004124692A

JP2004124692A - Method of preventing liquefaction of saturated ground in earthquake by compressed gas injection

Info

Publication number: JP2004124692A
Application number: JP2003120929A
Authority: JP
Inventors: Makoto Nishigaki; 西垣　誠; Masatoshi Ouchi; 大内　正敏; Keiji Kawashima; 河島　敬二; Toshikazu Shiraishi; 白石　俊多
Original assignee: Shiraishi Co Ltd
Current assignee: Shiraishi Co Ltd
Priority date: 2002-05-01
Filing date: 2003-04-25
Publication date: 2004-04-22
Anticipated expiration: 2023-04-25
Also published as: JP3757216B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a safe method of preventing liquefaction at a low construction cost without causing ground subsidence by settlement due to consolidation as a method of preventing liquefaction. <P>SOLUTION: An impermeable layer is naturally or artificially formed to exist at the upper part of the ground to be prevented from liquefaction, and an injection well and a drain well reaching the ground to be prevented from liquefaction, are formed from the ground surface. Compressed gas with a pressure equivalent to the underground water pressure is injected into the ground to be prevented from liquefaction, from the injection well, and underground water is eliminated from the drain well without lowering the underground water level of the impermeable layer existing in the lower part of the ground to be prevented from liquefaction. The injection of the compressed air from the injection well is then stopped, and the underground water eliminated from the drain well is returned into the ground to be prevented from liquefaction, through the injection well to lower the saturation degree of the ground. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、地震時に液状化する地盤の液状化防止方法に関する。
【０００２】
【従来の技術】
地盤の液状化とは、含水率の高い地盤が地震により衝撃、振動を受けて変形した場合、土粒子間に飽和状態で存在している間隙水の水圧が急激に上昇して土粒子間の摩擦抵抗が消失してしまい、その結果、地盤があたかも液体のように挙動して支持耐力を失ってしまう現象をいう。
【０００３】
地盤を液状化しないように改良する工法としては、従来、強力な振動等により地盤を締め固め地盤の密度を増大する工法、薬液注入等により地盤を固結する工法、良質の土と地盤土を置き換える工法、地盤の飽和度（地層の粒子間空隙内における水の容積と空隙の全容積との比を百分率で表した値。）を低下する工法が実施されてきた。
【０００４】
【特許文献１】
特開平８−３９７５号公報
【特許文献２】
特開２００１−１２３４３８号公報
【０００５】
【発明が解決しようとする課題】
従来工法としての、前記地盤密度を増大する工法、地盤を固結する工法、地盤置換工法は、局部的な液状化防止工法としては採用可能であるけれども、都市部の広範囲に液状化防止工法として適用した場合、莫大な費用と時間を必要とし、現実的な液状化防止工法とはいえない。
【０００６】
地盤の飽和度を低下する従来工法としては、地下水位を低下させ復水する工法（特開平８−３９７５号公報）と、地盤に圧縮空気または空気溶存水を井戸から注入し、併行して一方の井戸から地下水を汲み上げて気泡を水平方向へ浸透させる工法（特開２００１−１２３４３８号公報）があるが、地下水位を低下させ復水する工法においては、地下水位の低下によって地盤内有効応力が変化するため、液状化防止工法の対象地盤の上部あるいは下部に難透水気層が存在すると、この層の圧密により地盤沈下が生じる可能性がある。また、地下水位低下の影響が工事区域外に生じることを防ぐため、工事区域との境界に止水壁を設ける必要がある。
圧縮空気または空気溶存水を注入する工法においては、注入口の井戸周辺で空気溜りが形成され、気泡を分散・注入することが困難になる。また、地盤中に第二酸化鉄が存在すると注入される空気と反応し地盤中に酸欠空気が発生する。
【０００７】
本発明は、従来の液状化防止工法の問題点を解決するため、圧密沈下による地盤沈下を抑制した施工コストの安い液状化防止工法を提供することを目的とする。
【０００８】
【問題を解決するための手段】
本願発明は、上記課題を解決するために下記のように構成される。
本第１発明は、圧縮気体注入による飽和地盤の地震時液状化防止方法において、液状化防止対象地盤の上部に天然あるいは人工的に難透水気層を存在させ、地表より液状化防止対象地盤に達する注入井戸と水抜き井戸を形成し、注入井戸から液状化防止対象地盤に液状化防止対象地盤の地下水圧に相当する圧力の圧縮気体を注入し、周囲の地下水位を低下することなく水抜き井戸から地下水を排除し、その後、注入井戸からの圧縮気体の注入を止め、水抜き井戸から排除された地下水を注入井戸を通して液状化防止対象地盤内に復帰させることにより地盤の飽和度を低下するようにしたことを特徴とする。
【０００９】
本第２発明は、本第１発明の圧縮気体注入による飽和地盤の地震時液状化防止方法において、前記水抜き井戸から排除された地下水を注入井戸を通して液状化防止対象地盤内に復帰させる際に、前記排除された地下水に適量の界面活性剤を混入することを特徴とする。
【００１０】
本第３発明は、本第１又は第２発明の圧縮気体注入による飽和地盤の地震時液状化防止方法において、前記注入井戸からの圧縮気体の注入は、工事区域外への圧縮気体の拡散を防止するために指向性を持たせた注入井戸より行うことを特徴とする。
【００１１】
本第４発明は、本第１〜第３発明のいずれか１つの発明の圧縮気体注入による飽和地盤の地震時液状化防止方法において、前記水抜き井戸は下端部のみが開口していることを特徴とする。
【００１２】
本第５発明は、本第１〜第４発明のいずれか１つの発明の圧縮気体注入による飽和地盤の地震時液状化防止方法において、前記注入井戸および水抜き井戸を地表部から液状化防止対象地盤下方に曲線状に延びる曲線状井戸としたことを特徴とする。
【００１３】
本第６発明は、本第１〜第５発明にいずれか１つの発明の圧縮気体注入による飽和地盤の液状化防止方法において、前記液状化防止工事区域の周囲に、液状化防止対象地盤の下部層に達する止水壁を構築することを特徴とする。
【００１４】
本第７発明は、圧縮気体注入による飽和地盤の地震時液状化防止方法において、液状化防止対象地盤の上部に天然あるいは人工的に難透水気層を存在させ、地表より液状化防止対象地盤に達する曲線状の注入井戸を形成し、注入井戸から液状化防止対象地盤に液状化防止対象地盤の地下水圧に相当する圧力の圧縮気体を注入し、周囲の地下水位を低下することなく地盤の飽和度を低下するようにしたことを特徴とする。
【００１５】
本第８発明は、圧縮気体注入による飽和地盤の地震時液状化防止方法において、液状化防止対象地盤の上部に天然あるいは人工的に難透水気層を存在させ、地表より液状化防止対象地盤に達する立坑を掘削し、立坑下部から液状化防止対象地盤に向けて放射状に水平方向に延びる注入井戸を形成し、注入井戸から液状化防止対象地盤に液状化防止対象地盤の地下水圧に相当する圧力の圧縮気体を注入し、周囲の地下水位を低下することなく地盤の飽和度を低下するようにしたことを特徴とする。
【００１６】
本第９発明は、本第１〜第８発明のいずれか１つの発明の圧縮気体注入による飽和地盤の液状化防止方法において、前記液状化対象地盤に水圧計、飽和度計を設置し、各計器のデータに基づいて注入井戸からの圧縮気体の注入圧力及び注入量が制御されることを特徴とする。
【００１７】
【作用】
上述したように、本発明においては、液状化防止工法として、液状化防止対象地盤の飽和度を低下する工法を採用し、液状化防止対象地盤の上部に天然または人工的に難透水気層を存在させた状態で、注入井戸から液状化防止対象地盤の地下水圧に相当する圧力の圧縮気体を液状化防止対象地盤に注入し、地下水位を低下することなく液状化防止対象地盤に位置する水抜き井戸の下部開口から地下水を排除し、液状化防止対象地盤下部まで飽和度を低下させた後、圧縮気体の注入を止め、水抜き井戸から排除された地下水を注入井戸を通して液状化防止対象地盤に復帰させることにより液状化防止対象地盤の飽和度を低下させる工法を採用しているので、注入された圧縮気体が液状化防止対象地盤の上部から脱気することがなく、液状化防止対象地盤内の地下水圧に相当する圧力の圧縮気体を注入することで、周囲の地下水位を低下させることがなく地盤内の有効応力を変化させないため、液状化防止対象地盤の上下部の粘性土層の圧密沈下が抑制され、安全で施工コストの安い液状化防止工法を可能とする。
水抜き井戸から排除された地下水を注入井戸を通して液状化防止対象地盤内に復帰させる際に、前記排除された地下水に適量の界面活性剤を混入する構成により、界面活性剤を構成する親油基が空気と、親水基が水と結びついて、独立して壊れにくい安定な微小気泡を形成し、不飽和土を効率よく地盤に生成する。
また、注入井戸からの圧縮気体の注入が工事区域外に拡散するのを防止するために指向性を持たせて実施されるので、工事区域外への地盤沈下等の影響を抑制することができる。
注入井戸および水抜き井戸を曲線状井戸とすることにより、注入井戸と水抜き井戸の地表部分での間隔が長い場合でも効率よく液状化防止方法を施工することができ、液状化防止工事区域の地表部に大きな構造物等が存在するような場合には有効である。
液状化防止工事区域の周囲に、液状化防止対象地盤の下部層に達する止水壁を構築することにより、工事区域周辺への圧縮空気の漏出や地下水位の影響をより確実に抑制することができる。
また、液状化防止工事区域の周囲に、工事により影響を受ける構造物等が存在しない場合には、水抜き井戸を設けることなく、地表より液状化防止対象地盤に達する曲線状の注入井戸を形成するか、地表より液状化防止対象地盤に達する立坑を掘削し、立坑下部から液状化対象地盤に向けて放射状に水平方向に延びる注入井戸を形成し、注入井戸から液状化防止対象地盤に液状化防止対象地盤の地下水圧に相当する圧力の圧縮気体を注入し、周囲の地下水位を低下することなく地盤の飽和度を低下することができるので、より施工コストの低減化を図ることができる。
さらに、圧縮気体の注入等の作業が液状化防止対象地盤に設置した水圧計、飽和度計等の計器からのデータにより制御されるので、信頼性の高い液状化防止工法とすることができる。
【００１８】
【発明の実施の形態】
本発明の実施形態を図により説明する。図１〜１０は、本発明の飽和度低下による液状化防止方法の一実施例を示すものである。粘着力が微弱な砂質地盤等からなる液状化防止対象地盤１の上部に、天然あるいは人工的な難透水気性（水と気体の透過性が小さい）の地盤２を存在させる。人工的に難透水気性の地盤を存在させるとは、液状化防止対象地盤の上部に天然の難透水気性の地盤が存在しない場合、上部地盤を薬液注入による地盤固結或いは機械による締め固めによる地盤密度の増大等の地盤改良をして人工的に難透水気性の地盤を形成するということである。液状化防止対象地盤１の下部には、難透水気性の地盤３が存在する。液状化防止対象地盤１の上部に難透水気性の地盤を存在させる技術的意義は、液状化防止対象地盤１に注入される圧縮気体が、上部地盤を通して漏気するのを防止するためである。
【００１９】
本発明の液状化防止方法を一定幅の帯状区域に沿って実施する形態において、帯状区域の両側の工事区域の境界近傍に一定間隔で地表より液状化防止対象地盤１の下部に達する注入井戸４を掘削する。注入井戸４は、液状化防止対象地盤１に対応する部分に複数の注入孔５を形成した注入管６を直接井戸掘削機により設置して形成しても、井戸を井戸掘削機により掘削した後、液状化防止対象地盤１に対応する部分に複数の注入孔５を形成した注入管６を設置し、井戸と注入管６との間隙に砕石７等を充填して注入井戸４を形成しても良い。注入管６は、地表に設置したコンプレッサ等の圧縮気体供給手段８と送気管９を介して連結される。圧縮気体としては通常圧縮空気が使用される。注入井戸４の液状化防止対象地盤１に対応する部分に形成される注入孔５は、工事区域である帯状区域外への圧縮気体の漏気を防止するため、例えば、注入井戸４の帯状区域外側をカバー板１０等で塞ぎ、圧縮気体の注入方向に指向性を持たせている。また、帯状区域のほぼ中央部に一定間隔で地表より液状化防止対象地盤１の下部に達する水抜き井戸１１を掘削する。水抜き井戸１１の下端には開口部１２が形成される。水抜き井戸１１の上部には、排水管１３が連結され、排水管１３には必要に応じてポンプのような排水手段を設置する。
図４に示されるように地震時液状化防止工事区域の周囲に、鋼矢板等を液状化対象地盤１の下部の下部難透水気地盤３に達するように打設して止水壁１８を構築し、地震時液状化防止工事区域外への圧縮気体の漏出や、地下水位の変動等の影響をより確実に抑制してもよい。
図５に示されるように、注入井戸４からの地下水圧に相当する圧力の圧縮気体の注入により、液状化対象地盤中の地下水の一部が圧縮気体により置き換えされ、液状化対象地盤上部から下部方向に向かって飽和地盤が不飽和地盤に移行する。
【００２０】
図６、図７は、本発明の他の実施形態を示す。
この実施形態においては、液状化防止工事区域の地表部に大きな構造物等が存在する場合、注入井戸４と水抜き井戸１１の地表部での設置位置の間隔が長くなり、液状化防止工事の施工性が低下する。そのような場合、注入井戸４と水抜き井戸１１を曲線ボーリング機で形成される曲線状注入井戸１９、曲線状水抜き井戸２０とすることにより施工性のよい圧縮気体注入による飽和地盤の地震時液状化防止方法とすることが可能となる。
【００２１】
図８は、本発明の他の実施形態を示すものである。
この実施形態においては、液状化防止工事区域の周辺に、工事により影響を受ける構造物等が存在しない場合には、水抜き井戸を設けることなく、地表より液状化防止対象地盤１の下部に達する曲線状注入井戸１９のみを形成し、曲線状注入井戸１９から液状化防止対象地盤１内の地下水圧に相当する圧縮気体を注入し、液状化防止対象地盤１の飽和度を低下させるものである。
図９、図１０は、本発明の他の実施形態を示すものである。
この実施形態においては、液状化防止工事区域の周辺に、工事により影響を受ける構造物等が存在しない場合に、地表から液状化防止対象地盤１の下部に達する立坑２１を掘削し、立坑２１の下部から液状化防止対象地盤１に複数の水平注入井戸２２を放射状に形成し、水平注入井戸２２から液状化防止対象地盤１内の地下水圧に相当する圧縮気体を注入し、液状化防止対象地盤１の飽和度を低下させるものである。
【００２２】
注入井戸４近傍の液状化防止対象地盤１内には、液状化防止対象地盤１の地下水圧および液状化防止対象地盤１の飽和度を測定する圧力センサ１４および飽和度計１５が深さ方向に沿って複数設置され、各センサ１４、１５はライン１６により地表の圧縮気体注入手段７の制御装置１７と連結される。
【００２３】
本発明の圧縮気体注入による液状化防止方法の手順を説明する。
（１）注入井戸４に設置した液状化防止対象地盤１の地下水圧を測定する圧力センサ１４のデータが制御装置１７に送られ、地表に設置した圧縮気体供給手段８から供給される圧縮気体の圧力を地下水圧と同じ圧力に圧力調節して注入井戸４に供給する。
（２）注入井戸４から液状化防止対象地盤１に注入された圧縮気体は、液状化防止対象地盤１の上部に難透水気性地盤２が存在するため、上部に排気されることなく、液状化防止対象地盤１内の地下水を排除する圧力として作用する。圧縮空気の注入により排除される地下水は、水抜き井戸１１の下端開口１２から水抜き井戸内に入り、水抜き井戸１１、排水管１３を通して排水される。
（３）水抜井戸１１からの地下水の排除により飽和状態から不飽和状態に移行する。不飽和状態への移行は、液状化防止対象地盤１の上部から下部に徐徐に進行する。
（４）液状化防止対象地盤１の地下水位と飽和度の変化は、注入井戸４の近傍の液状化防止対象地盤１内に深さ方向に複数配置された水圧計１４と飽和度計１５からなる各センサにより計測され、各センサ１４、１５からのデータが制御装置１７に送られ、制御装置１７が圧縮気体供給手段７を制御し、圧縮気体の注入圧力及び注入量を調節する。
（５）各センサ１４，１５からのデータが、不飽和状態が液状化防止対象地盤１の最下部まで達したことを検知すると、圧縮気体供給手段８からの圧縮気体の供給を止める。
（６）圧縮気体の供給を止め、水抜き井戸１１から排水された地下水を、注入井戸４を通して液状化防止対象地盤１内に復帰させる。液状化防止対象地盤１内に注入された圧縮空気の一部は水抜き井戸１１を通して排気される。
水抜き井戸１１から排水された地下水を、注入井戸４を通して液状化防止対象地盤１内に復帰させる際、地下水に適量の界面活性剤を混入する。界面活性剤分子は、油となじみ易い親油基（疎水基）と水になじみ易い親水基の２つの相反する性質の部分から成っており、親油基は空気と、親水基は水とそれぞれ結びついて、独立した壊れにくい安定な微小気泡を形成する。
（７）液状化防止対象地盤１内の地下水は元の状態に復帰するが、液状化対象地盤の土壌内には安定した微小気泡が無数に存在することにより、地下水が元の状態に復帰しても液状化対象地盤全体の不飽和状態が継続する。
【００２４】
【発明の効果】
本発明においては、液状化防止工法として、液状化防止対象地盤の飽和度を低下する工法を採用し、液状化防止対象地盤の上部に天然または人工的に難透水気層を存在させた状態で、注入井戸から液状化防止対象地盤の地下水圧に相当する圧力の圧縮気体を液状化防止対象地盤に注入し、周囲の地下水位を低下することなく液状化防止対象地盤に位置する水抜き井戸の下部開口から地下水を排除し、液状化防止対象地盤下部まで飽和度を低下させた後、圧縮気体の注入を止めて、水抜き井戸から排除された地下水を注入井戸を通して液状化防止対象地盤に復帰させることにより液状化防止対象地盤の飽和度を低下させる工法を採用しているので、注入された圧縮気体が液状化防止対象地盤の上部から脱気することがなく、液状化防止対象地盤内の地下水圧に相当する圧力の圧縮気体を注入することで、地下水位を低下させることがなく地盤内の有効応力を変化させないため、液状化防止対象地盤の上下部の粘性土層の圧密沈下が抑制され、安全で施工コストの安い液状化防止工法を可能とする。
水抜き井戸から排除された地下水を注入井戸を通して液状化防止対象地盤内に復帰させる際に、前記排除された地下水に適量の界面活性剤を混入する構成により、界面活性剤を構成する親油基が空気と、親水基が水と結びついて、独立して壊れにくい安定な微小気泡を形成し、不飽和土を効率よく地盤に生成する。
また、注入井戸からの圧縮気体の注入が工事区域外に拡散するのを防止するために指向性を持たせて実施されるので、工事区域外への地盤沈下等の影響を抑制することができる。
注入井戸および水抜き井戸を曲線状井戸とすることにより、注入井戸と水抜き井戸の地表部分での間隔が長い場合でも効率よく液状化防止方法を施工することができ、液状化防止工事区域の地表部に大きな構造物等が存在するような場合には有効である。
液状化防止工事区域の周囲に、液状化防止対象地盤の下部層に達する止水壁を構築することにより、工事区域周辺への圧縮空気の漏出や地下水位の影響をより確実に抑制することができる。
また、液状化防止工事区域の周囲に、工事により影響を受ける構造物等が存在しない場合には、水抜き井戸を設けることなく、地表より液状化防止対象地盤に達する曲線状の注入井戸を形成するか、地表より液状化防止対象地盤に達する立坑を掘削し、立坑下部から液状化対象地盤に向けて放射状に水平方向に延びる注入井戸を形成し、注入井戸から液状化防止対象地盤に液状化防止対象地盤の地下水圧に相当する圧力の圧縮気体を注入し、周囲の地下水位を低下することなく地盤の飽和度を低下することができるので、より施工コストの低減化を図ることができる。
さらに、圧縮気体の注入等の作業が液状化防止対象地盤に設置した水圧計、飽和度計等の計器からのデータにより制御されるので、信頼性の高い液状化防止工法とすることができる。
【図面の簡単な説明】
【図１】本発明の液状化防止方法の一実施例を示す断面図
【図２】本発明の液状化防止方法の一実施例を示す平面図
【図３】本発明の液状化防止方法の一実施例の注入井戸の拡大断面図
【図４】本発明の液状化防止方法の一実施例を示す断面図
【図５】本発明の液状化防止方法の一実施例の概略図
【図６】本発明の液状化防止方法の一実施例を示す断面図
【図７】本発明の液状化防止方法の一実施例を示す平面図
【図８】本発明の液状化防止方法の一実施例を示す断面図
【図９】本発明の液状化防止方法の一実施例を示す断面図
【図１０】本発明の液状化防止方法の一実施例を示す平面図
【符号の説明】
１：液状化防止対象地盤
２：上部難透水気地盤
３：下部難透水気地盤
４：注入井戸
５：注入孔
６：注入管
７：砕石
８：圧縮気体供給手段
９：送気管
１０：カバー板
１１：水抜き井戸
１２：下端開口
１３：排水管
１４：圧力センサ
１５：飽和度計
１６：ライン
１７：制御装置
１８：止水壁
１９：曲線状注入井戸
２０：曲線状水抜き井戸
２１：立坑
２２：水平注入井戸[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for preventing liquefaction of a ground that liquefies during an earthquake.
[0002]
[Prior art]
Soil liquefaction means that when the ground with a high water content is deformed by shock or vibration due to an earthquake, the water pressure of the pore water existing in a saturated state between the soil particles suddenly rises and the soil A phenomenon in which the frictional resistance disappears, and as a result, the ground behaves like a liquid and loses its bearing strength.
[0003]
Conventionally, the method of improving the ground so as not to liquefy is a method of compacting the ground by strong vibration, etc., increasing the density of the ground, a method of consolidating the ground by injection of chemicals, etc., a method of good soil and ground soil. A replacement method and a method of lowering the degree of saturation of the ground (a value representing the ratio of the volume of water in the interparticle voids of the stratum to the total volume of the voids in percentage) have been implemented.
[0004]
[Patent Document 1]
JP-A-8-3975 [Patent Document 2]
JP 2001-123438 A
[Problems to be solved by the invention]
As a conventional method, the method of increasing the ground density, the method of consolidating the ground, and the ground replacement method can be used as a local liquefaction prevention method, but as a liquefaction prevention method in a wide area of an urban area. When applied, it requires enormous cost and time, and is not a realistic liquefaction prevention method.
[0006]
Conventional methods for lowering the degree of ground saturation include a method for lowering the groundwater level and condensing water (JP-A-8-3975) and a method in which compressed air or air-dissolved water is injected into the ground from a well and simultaneously. There is a method (Japanese Patent Laid-Open Publication No. 2001-123438) in which groundwater is pumped up from a well to penetrate air bubbles in the horizontal direction. Due to the change, if there is a poorly permeable layer above or below the ground to be subjected to the liquefaction prevention method, there is a possibility that land subsidence may occur due to the consolidation of this layer. In order to prevent the effect of lowering the groundwater level from occurring outside the construction area, it is necessary to provide a water stop wall at the boundary with the construction area.
In the method of injecting compressed air or air-dissolved water, an air pocket is formed around the well of the inlet, making it difficult to disperse and inject bubbles. In addition, if ferric oxide is present in the ground, it reacts with the injected air to generate oxygen-deficient air in the ground.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to provide a low-cost liquefaction-preventing construction method that suppresses ground subsidence due to consolidation settlement in order to solve the problems of the conventional liquefaction-preventing method.
[0008]
[Means to solve the problem]
The present invention is configured as follows to solve the above problems.
The first invention relates to a method for preventing liquefaction of saturated ground due to earthquake by injection of compressed gas, in which a hardly permeable gas layer is present naturally or artificially on the top of the liquefaction prevention target ground, and from the surface to the liquefaction prevention target ground. Form a filling well and a draining well to reach, and inject compressed gas at a pressure corresponding to the groundwater pressure of the liquefaction prevention target ground from the injection well to drain water without lowering the surrounding groundwater level The ground saturation is reduced by removing the groundwater from the well, then stopping the injection of compressed gas from the injection well, and returning the groundwater removed from the drainage well to the liquefaction prevention target ground through the injection well. It is characterized by doing so.
[0009]
The second invention provides the method for preventing liquefaction of saturated ground caused by compressed gas injection during an earthquake according to the first invention, wherein the groundwater removed from the drain well is returned to the liquefaction prevention target ground through the injection well. And mixing an appropriate amount of a surfactant into the removed groundwater.
[0010]
According to a third aspect of the present invention, in the method for preventing liquefaction of saturated ground due to earthquake by injecting compressed gas according to the first or second aspect of the invention, the injection of compressed gas from the injection well reduces diffusion of the compressed gas outside the construction area. In order to prevent this, injection is performed from an injection well having directivity.
[0011]
According to a fourth aspect of the present invention, in the method for preventing liquefaction of a saturated ground during an earthquake by compressed gas injection according to any one of the first to third aspects of the present invention, only the lower end of the drain well is open. Features.
[0012]
The fifth invention is directed to the method for preventing liquefaction of saturated ground due to earthquake by compressed gas injection according to any one of the first to fourth inventions, wherein the injection well and the drainage well are subjected to liquefaction prevention from a surface portion. It is characterized by a curved well extending below the ground in a curved manner.
[0013]
The sixth invention is the method for preventing liquefaction of a saturated ground by compressed gas injection according to any one of the first to fifth inventions, wherein the liquefaction prevention construction area is provided with a lower part of the liquefaction prevention target ground. It is characterized by the construction of a waterproof wall reaching the layer.
[0014]
The seventh invention is a method for preventing liquefaction of a saturated ground during an earthquake by injection of compressed gas, wherein a hardly permeable gas layer is naturally or artificially present above the ground to be liquefied, A curved injection well is formed, and compressed gas is injected from the injection well into the liquefaction prevention target ground at a pressure equivalent to the groundwater pressure of the liquefaction prevention target ground, thereby saturating the ground without lowering the surrounding groundwater level. It is characterized in that the degree is reduced.
[0015]
The eighth invention relates to a method for preventing liquefaction of saturated ground due to earthquake by injection of compressed gas, wherein a hardly permeable gas layer is present naturally or artificially on the top of the liquefaction prevention target ground, and from the surface to the liquefaction prevention target ground. Excavation of the shaft to be reached, forming an injection well extending horizontally from the bottom of the shaft to the liquefaction prevention target ground, and the pressure corresponding to the groundwater pressure of the liquefaction prevention target ground from the injection well to the liquefaction prevention target ground Compressed gas is injected to reduce the degree of saturation of the ground without lowering the surrounding groundwater level.
[0016]
The ninth invention is directed to the method for preventing liquefaction of a saturated ground by compressed gas injection according to any one of the first to eighth inventions, wherein a water pressure gauge and a saturation meter are installed on the liquefaction target ground. The injection pressure and the injection amount of the compressed gas from the injection well are controlled based on the data of the instrument.
[0017]
[Action]
As described above, in the present invention, as the liquefaction prevention method, a method of reducing the saturation of the liquefaction prevention target ground is adopted, and a natural or artificially impervious gas layer is formed on the upper part of the liquefaction prevention target ground. In the state where it is present, compressed gas is injected from the injection well into the liquefaction prevention target ground at a pressure equivalent to the groundwater pressure of the liquefaction prevention target ground, and water located on the liquefaction prevention target ground without lowering the groundwater level After removing the groundwater from the lower opening of the drainage well and lowering the saturation to the lower part of the liquefaction prevention target ground, the injection of compressed gas is stopped, and the groundwater removed from the drainage well is injected into the liquefaction prevention ground through the injection well. To reduce the degree of saturation of the liquefaction-prevented ground by returning to the ground, so that the injected compressed gas does not escape from the top of the liquefaction-prevented ground, preventing liquefaction. By injecting compressed gas at a pressure equivalent to the underground water pressure in the elephant ground, the surrounding groundwater level does not decrease and the effective stress in the ground does not change. The consolidation settlement of the layer is suppressed, and a liquefaction prevention method that is safe and inexpensive in construction costs is enabled.
When the groundwater removed from the drainage well is returned to the liquefaction prevention target ground through the injection well, a suitable amount of the surfactant is mixed into the removed groundwater, whereby the lipophilic base constituting the surfactant is formed. The air and the hydrophilic group are combined with water to form independently stable microbubbles that are not easily broken, thereby efficiently generating unsaturated soil on the ground.
Further, since the injection of the compressed gas from the injection well is performed with directivity in order to prevent the injection from diffusing outside the construction area, it is possible to suppress the influence of land subsidence outside the construction area. .
By making the injection well and drainage well curved, the liquefaction prevention method can be implemented efficiently even when the distance between the injection well and the drainage well at the ground surface is long, and the liquefaction prevention work area This is effective when a large structure or the like exists on the ground surface.
By constructing a water stop wall around the liquefaction prevention construction area that reaches the lower layer of the liquefaction prevention target ground, it is possible to more reliably suppress the leakage of compressed air around the construction area and the effect of the groundwater level. it can.
If there is no structure affected by the construction around the liquefaction prevention construction area, a curved injection well reaching the liquefaction prevention target ground from the ground surface without forming a drainage well Or excavate a shaft that reaches the ground to be liquefied from the surface of the ground, form an injection well that extends horizontally from the bottom of the shaft to the ground to be liquefied, and liquefy from the injection well to the ground to be liquefied. A compressed gas having a pressure corresponding to the groundwater pressure of the ground to be prevented is injected, and the degree of saturation of the ground can be reduced without lowering the surrounding groundwater level, so that the construction cost can be further reduced.
Further, since operations such as injection of compressed gas are controlled by data from instruments such as a water pressure gauge and a saturation meter installed on the liquefaction prevention target ground, a highly reliable liquefaction prevention method can be achieved.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. 1 to 10 show one embodiment of the method for preventing liquefaction due to a decrease in the degree of saturation of the present invention. Above the liquefaction-preventing ground 1 made of a sandy ground or the like having a weak adhesive strength, a natural or artificial hard-to-permeate (low water and gas permeability) ground 2 is present. The existence of artificially impervious ground means that if there is no natural impervious ground above the liquefaction-prevented ground, the upper ground is consolidated by chemical injection or ground by mechanical compaction. It means that the ground is improved by increasing the density and the like to artificially form a ground with poor water permeability. At the lower part of the liquefaction prevention target ground 1, there is a ground 3 having poor water permeability. The technical significance of the presence of the hardly permeable air base above the liquefaction prevention target ground 1 is to prevent the compressed gas injected into the liquefaction prevention target ground 1 from leaking through the upper ground.
[0019]
In the embodiment in which the liquefaction prevention method of the present invention is carried out along a belt-shaped zone having a certain width, an injection well 4 reaching the lower part of the ground 1 to be liquefaction-prevented from the ground surface at regular intervals near the boundary of the construction zone on both sides of the belt-shaped zone. Drilling. Even if the injection well 4 is formed by directly installing an injection pipe 6 having a plurality of injection holes 5 in a portion corresponding to the liquefaction prevention target ground 1 by using a well excavator, the well is excavated by the well excavator. An injection pipe 6 having a plurality of injection holes 5 is provided in a portion corresponding to the liquefaction prevention target ground 1, and a crushed stone 7 is filled in a gap between the well and the injection pipe 6 to form an injection well 4. Is also good. The injection pipe 6 is connected to a compressed gas supply means 8 such as a compressor installed on the ground via an air supply pipe 9. Normally, compressed air is used as the compressed gas. The injection hole 5 formed in a portion of the injection well 4 corresponding to the liquefaction prevention target ground 1 is provided with, for example, a strip-shaped section of the injection well 4 in order to prevent leakage of the compressed gas outside the strip-shaped section which is a construction area. The outside is closed by a cover plate 10 or the like so as to have directivity in the direction of compressed gas injection. In addition, a drain well 11 that reaches the lower part of the liquefaction prevention target ground 1 from the surface of the ground is excavated at a constant interval substantially in the center of the belt-shaped area. An opening 12 is formed at the lower end of the drain well 11. A drain pipe 13 is connected to the upper part of the drain well 11, and drain means such as a pump is installed in the drain pipe 13 as necessary.
As shown in FIG. 4, around the liquefaction prevention construction area during an earthquake, a steel sheet pile or the like is cast so as to reach the lower impervious ground 3 below the ground 1 to be liquefied, and the water blocking wall 18 is constructed. However, the leakage of the compressed gas to the outside of the liquefaction prevention construction area during an earthquake and the fluctuation of the groundwater level may be more reliably suppressed.
As shown in FIG. 5, part of the groundwater in the ground to be liquefied is replaced by the compressed gas by injecting the compressed gas having a pressure corresponding to the pressure of the groundwater from the injection well 4, and from the upper part to the lower part of the ground to be liquefied. The saturated ground shifts to the unsaturated ground toward the direction.
[0020]
6 and 7 show another embodiment of the present invention.
In this embodiment, when a large structure or the like is present at the surface of the liquefaction prevention construction area, the interval between the installation positions of the injection well 4 and the drainage well 11 at the surface is long, and the liquefaction prevention work is not performed. Workability decreases. In such a case, the injection well 4 and the drainage well 11 are made into a curved injection well 19 and a curved drainage well 20 formed by a curved boring machine, so that the compressed ground gas injection with good workability can be performed at the time of the earthquake of the saturated ground. A liquefaction prevention method can be provided.
[0021]
FIG. 8 shows another embodiment of the present invention.
In this embodiment, when there is no structure or the like affected by the construction around the liquefaction prevention construction area, the water reaches the lower part of the liquefaction prevention target ground 1 from the surface without providing a drainage well. Only the curved injection well 19 is formed, and compressed gas corresponding to the groundwater pressure in the liquefaction prevention target ground 1 is injected from the curved injection well 19 to reduce the saturation of the liquefaction prevention target ground 1. .
9 and 10 show another embodiment of the present invention.
In this embodiment, when there is no structure or the like affected by the construction around the liquefaction prevention construction area, the shaft 21 reaching the lower part of the liquefaction prevention target ground 1 is excavated from the ground surface, A plurality of horizontal injection wells 22 are formed radially from the lower part on the liquefaction prevention target ground 1, and a compressed gas corresponding to the groundwater pressure in the liquefaction prevention target ground 1 is injected from the horizontal injection well 22, and the liquefaction prevention target ground is formed. 1 lowers the degree of saturation.
[0022]
In the liquefaction prevention target ground 1 near the injection well 4, a pressure sensor 14 and a saturation meter 15 for measuring the underground water pressure of the liquefaction prevention target ground 1 and the saturation of the liquefaction prevention target ground 1 are arranged in the depth direction. A plurality of sensors 14 and 15 are connected along a line 16 to a controller 17 of the compressed gas injection means 7 on the ground.
[0023]
The procedure of the method for preventing liquefaction by injection of compressed gas of the present invention will be described.
(1) The data of the pressure sensor 14 for measuring the underground water pressure of the liquefaction prevention target ground 1 installed in the injection well 4 is sent to the control device 17, and the compressed gas supplied from the compressed gas supply means 8 installed on the surface of the ground is The pressure is adjusted to the same level as the groundwater pressure and supplied to the injection well 4.
(2) The compressed gas injected from the injection well 4 into the liquefaction prevention target ground 1 is not evacuated to the upper part because the poorly permeable airy ground 2 is present above the liquefaction prevention target ground 1. It acts as a pressure for removing groundwater in the ground 1 to be prevented. The groundwater removed by the injection of the compressed air enters the drainage well through the lower end opening 12 of the drainage well 11, and is drained through the drainage well 11 and the drain pipe 13.
(3) The state changes from a saturated state to an unsaturated state due to the removal of groundwater from the drain well 11. The transition to the unsaturated state gradually progresses from the upper portion to the lower portion of the liquefaction prevention target ground 1.
(4) The change in the groundwater level and the degree of saturation of the liquefaction prevention target ground 1 is obtained from the water pressure gauge 14 and the saturation meter 15 arranged in the depth direction in the liquefaction prevention target ground 1 near the injection well 4. , And data from the sensors 14 and 15 are sent to the control device 17, which controls the compressed gas supply means 7 to adjust the injection pressure and the injection amount of the compressed gas.
(5) When the data from the sensors 14 and 15 detects that the unsaturated state has reached the bottom of the liquefaction prevention target ground 1, the supply of the compressed gas from the compressed gas supply means 8 is stopped.
(6) The supply of the compressed gas is stopped, and the groundwater drained from the drain well 11 is returned to the liquefaction prevention target ground 1 through the injection well 4. A part of the compressed air injected into the liquefaction prevention target ground 1 is exhausted through the drain well 11.
When the groundwater drained from the drainage well 11 is returned to the liquefaction prevention target ground 1 through the injection well 4, an appropriate amount of surfactant is mixed into the groundwater. Surfactant molecules are composed of two contradictory parts: a lipophilic group (hydrophobic group) that is compatible with oil and a hydrophilic group that is compatible with water. The lipophilic group is air and the hydrophilic group is water. Together, they form independent, non-breakable, stable microbubbles.
(7) The groundwater in the liquefaction prevention ground 1 returns to the original state, but the groundwater returns to the original state due to the myriad of stable microbubbles in the soil of the liquefaction ground. However, the unsaturated state of the entire ground to be liquefied continues.
[0024]
【The invention's effect】
In the present invention, as a method of preventing liquefaction, a method of reducing the degree of saturation of the liquefaction prevention target ground is employed, and a natural or artificially hardly permeable air layer is present above the liquefaction prevention target ground. Injecting compressed gas at a pressure equivalent to the groundwater pressure of the liquefaction prevention ground from the injection well into the liquefaction prevention ground without lowering the surrounding groundwater level. After removing the groundwater from the lower opening and lowering the saturation to the lower part of the liquefaction prevention target ground, stop the injection of compressed gas, return the groundwater removed from the drainage well to the liquefaction prevention target ground through the injection well Since the method adopts a construction method that lowers the degree of saturation of the liquefaction prevention target ground, the injected compressed gas does not deaerate from the upper part of the liquefaction prevention target ground, and the liquefaction prevention target ground By injecting compressed gas at a pressure equivalent to the groundwater pressure of the ground, the groundwater level does not decrease and the effective stress in the ground does not change, so the consolidation settlement of the viscous soil layer at the top and bottom of the liquefaction prevention target ground It enables a liquefaction-prevention method that is controlled, safe, and inexpensive in construction costs.
When the groundwater removed from the drainage well is returned to the liquefaction prevention target ground through the injection well, a suitable amount of the surfactant is mixed into the removed groundwater, whereby the lipophilic base constituting the surfactant is formed. The air and the hydrophilic group are combined with water to form independently stable microbubbles that are not easily broken, thereby efficiently generating unsaturated soil on the ground.
Further, since the injection of the compressed gas from the injection well is performed with directivity in order to prevent the injection from diffusing outside the construction area, it is possible to suppress the influence of land subsidence outside the construction area. .
By making the injection well and drainage well curved, the liquefaction prevention method can be implemented efficiently even when the distance between the injection well and the drainage well at the ground surface is long, and the liquefaction prevention work area This is effective when a large structure or the like exists on the ground surface.
By constructing a water stop wall around the liquefaction prevention construction area that reaches the lower layer of the liquefaction prevention target ground, it is possible to more reliably suppress the leakage of compressed air around the construction area and the effect of the groundwater level. it can.
If there is no structure affected by the construction around the liquefaction prevention construction area, a curved injection well reaching the liquefaction prevention target ground from the ground surface without forming a drainage well Or excavate a shaft that reaches the ground to be liquefied from the surface of the ground, form an injection well that extends horizontally from the bottom of the shaft to the ground to be liquefied, and liquefy from the injection well to the ground to be liquefied. A compressed gas having a pressure corresponding to the groundwater pressure of the ground to be prevented is injected, and the degree of saturation of the ground can be reduced without lowering the surrounding groundwater level, so that the construction cost can be further reduced.
Further, since operations such as injection of compressed gas are controlled by data from instruments such as a water pressure gauge and a saturation meter installed on the liquefaction prevention target ground, a highly reliable liquefaction prevention method can be achieved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing one embodiment of the liquefaction prevention method of the present invention. FIG. 2 is a plan view showing one embodiment of the liquefaction prevention method of the present invention. FIG. FIG. 4 is an enlarged cross-sectional view of an injection well according to one embodiment; FIG. 4 is a cross-sectional view illustrating one embodiment of a liquefaction prevention method of the present invention; FIG. 5 is a schematic diagram of one embodiment of a liquefaction prevention method of the present invention; FIG. 7 is a sectional view showing one embodiment of the liquefaction prevention method of the present invention. FIG. 7 is a plan view showing one embodiment of the liquefaction prevention method of the present invention. FIG. 8 is one embodiment of the liquefaction prevention method of the present invention. FIG. 9 is a cross-sectional view showing one embodiment of the liquefaction prevention method of the present invention. FIG. 10 is a plan view showing one embodiment of the liquefaction prevention method of the present invention.
1: Ground to be prevented from liquefaction 2: Upper impervious ground 3: Lower impervious ground 4: Injection well 5: Injection hole 6: Injection pipe 7: Crushed stone 8: Compressed gas supply means 9: Air supply pipe 10: Cover plate 11: Drainage well 12: Lower end opening 13: Drain pipe 14: Pressure sensor 15: Saturation meter 16: Line 17: Control device 18: Water blocking wall 19: Curved injection well 20: Curved drainage well 21: Vertical shaft 22: Horizontal injection well

Claims

An impervious gas layer is present naturally or artificially above the liquefaction prevention target ground, forming injection wells and drainage wells that reach the liquefaction prevention target ground from the surface of the ground. Compressed gas is injected at a pressure equivalent to the pressure of the groundwater at the target ground, and groundwater is removed from the drainage well without lowering the surrounding groundwater level.After that, the injection of compressed gas from the injection well is stopped, A method for preventing liquefaction of saturated ground by compressed gas injection, characterized by lowering the degree of saturation of ground by returning groundwater removed from the drainage well to the liquefaction prevention ground through the injection well. .

The groundwater removed from the drainage well is returned to the liquefaction prevention target ground through the injection well, and an appropriate amount of a surfactant is mixed into the removed groundwater. A method for preventing liquefaction of saturated ground during an earthquake by injecting compressed gas.

The injection of compressed gas from the injection well is performed by an injection well having directivity in order to prevent diffusion of the compressed gas outside the liquefaction prevention construction area. To prevent liquefaction of saturated ground during earthquake by injection of compressed gas.

The method for preventing liquefaction of saturated ground by an injection of compressed gas during an earthquake according to any one of claims 1 to 3, wherein only the lower end of the drain well is open.

The saturation by compressed gas injection according to any one of claims 1 to 4, wherein the injection well and the drainage well are curved wells extending in a curved manner from the surface to below the liquefaction prevention target ground. How to prevent liquefaction during ground earthquake.

The saturated ground by compressed gas injection according to any one of claims 1 to 5, wherein a water stop wall reaching the lower layer of the liquefaction prevention target ground is constructed around the liquefaction prevention construction area. How to prevent liquefaction during an earthquake.

A natural or artificially impervious gas layer is present above or below the liquefaction prevention target ground to form a curved injection well that reaches the liquefaction prevention target ground from the ground surface, and liquefies from the injection well to the liquefaction prevention target ground In the event of a saturated ground due to compressed gas injection, a compressed gas with a pressure equivalent to the groundwater pressure of the ground to be prevented is injected to reduce the saturation of the ground without lowering the surrounding groundwater level. Liquefaction prevention method.

An impervious gas layer is present naturally or artificially at the top of the liquefaction prevention target ground, excavating a shaft that reaches the liquefaction prevention target ground from the surface of the ground, and radiating horizontally from the bottom of the shaft toward the liquefaction prevention target ground The injection well that extends to the liquefaction prevention target ground is injected from the injection well with compressed gas having a pressure equivalent to the groundwater pressure of the liquefaction prevention target ground, and the saturation of the ground is reduced without lowering the surrounding groundwater level. A method for preventing liquefaction of saturated ground during an earthquake by injection of compressed gas, characterized in that the liquefaction is reduced.

A water pressure gauge and a saturation meter are installed on the liquefaction prevention target ground, and an injection pressure and an injection amount of the compressed gas from an injection well are controlled based on data of each instrument. The method for preventing liquefaction of saturated ground during an earthquake by injecting compressed gas according to any one of the above.