JP3945901B2

JP3945901B2 - Groundwater imperviousness evaluation method

Info

Publication number: JP3945901B2
Application number: JP10176798A
Authority: JP
Inventors: 晋士郎大本; 洋伊藤; 潤二安井; 良典北野
Original assignee: Kumagai Gumi Co Ltd
Current assignee: Kumagai Gumi Co Ltd
Priority date: 1998-03-31
Filing date: 1998-03-31
Publication date: 2007-07-18
Anticipated expiration: 2018-03-31
Also published as: JPH11280100A

Description

【０００１】
【発明の属する技術分野】
本発明は、地中連続壁の人工底盤その他各種地盤の遮水性評価方法に関する。
【０００２】
【従来の技術】
例えば、地中連続壁工法では、通常、地中連続壁を地中に存在するシルト層のような難透水層に達するまで十分根入れし、この難透水層を地中連続壁の底盤とし、その強度，遮水性により、地中連続壁内の掘削時に生じる底部からの土圧，水圧を受け持たせ、底盤からの出水，盤ぶくれ，パイピングなどを防止している。前記の従来工法では、難透水層を地中連続壁の底盤とするものであるから、この難透水層の深度が、地中連続壁内で掘削する所期の掘削深度と離れていても、地中連続壁を難透水層に達するまで施工し、その難透水層に十分な根入れを行う。そのため従来工法では、所期の掘削深度と難透水層深度が離れるほど、地中連続壁の施工は不経済なものとなる。
【０００３】
そこで最近の新しい工法として、所期の地盤掘削深度に合わせて難透水層を人工的に構築する方法が開発された。これは、コラムジェット工法などと称される方法で、地盤掘削深度にあわせて柱状の地盤改良体を複数列施工し、地中連続壁の根入れに必要な難透水層を人工的に構築する方法である。このように、前記の工法は地中連続壁内の掘削深度に合わせ、かつ必要な厚さに、地盤改良体による人工底盤を作ることで、地中連続壁の施工深度を必要最小限に抑えることができ、地中連続壁の施工コスト低減につながる工法である。
【０００４】
【発明が解決しようとする課題】
前述の地盤改良工法では、人工底盤が十分な遮水性能を有する必要があるが、その遮水性能を適正に評価する技術はまだ実用化されていない。従来の地盤改良体の品質評価技術としては、(A) 超音波，弾性波測定法、(B) 電気比抵抗測定法があるが、これらはいずれも２極の検出端子を間隔を離して人工底盤に接触させて測定するものであり、次の欠点がある。
▲１▼ 人工底盤を構成する複数の各柱状体単体のみの健全性（強度，欠損部）を評価する方法であり、複数列の柱状体相互間の遮水性を評価できない。
▲２▼ 検出端子取付けのため地盤改良体（人工底盤）に直接削孔を施すため、改良体自体に遮水性を損なうような欠損を加える可能性がある。
▲３▼ 改良体の状態を通して遮水性能を評価する間接評価であるため、直接透水性を評価できない。
【０００５】
前記▲１▼，▲２▼，▲３▼から現状では、(A),(B) の測定法は地盤改良体（人工底盤）全体の遮水性評価技術として適用されていない。このように、地盤改良工法の問題点は、その遮水性能評価法が確立されていないことである。
【０００６】
本発明は前記従来技術の課題を解決したもので、人工地盤その他の地盤改良体に適用できるのは勿論、その他各柱地盤の遮水性能評価に適用できる、地盤の遮水性評価方法を提供することを目的とする。なお、以下の説明において、地盤とは、地中における締め切り壁の人工底盤またはその締め切り壁（つまり側壁）を意味し、さらに改良地盤、非改良体地盤、その他の遮水体等の意味で使用する。
【０００７】
【課題を解決するための手段】
本発明に係る地盤の遮水性評価方法は、観測パイプの通水孔を測定対象である地盤の表面に近づけて配置し、前記観測パイプ内の水位変化により地盤の遮水性を測定する地盤の遮水性評価方法において、前記観測パイプを前記地盤の複数の地点に設置し、それぞれの観測パイプの水位変化曲線の差によって地盤の遮水性を評価することを特徴とする。
また、本発明は、前記地盤の遮水性評価地点に設置された複数配置の前記観測パイプのそれぞれの水位変化曲線から算出される透水係数の平面分布から、前記地盤の全体的および／または局所的遮水性を評価することを特徴とする。
また、本発明は、前記複数の観測パイプのそれぞれの水位変化の差またはそれぞれの透水係数の差から漏水箇所を特定することを特徴とする。
また、本発明は、前記地盤は地中における締め切られた壁の底盤であることを特徴とする。
また、本発明は、前記観測パイプに前記地中における締め切られた壁外の地下水位より高い初期水位を与えることを特徴とする
また、本発明は、前記地盤が改良体よりなることを特徴とする。
【０００８】
第１発明によると、地盤を貫通する水の流出に比例して観測パイプ内の水位が変化するので、この水位変化を測定するだけで、複雑な装置や施工を必要とせず簡単に地盤の遮水性を評価できる。
【０００９】
また、第１〜第６発明によると、第１発明における前半部分の前提とする原理の応用により、地盤の複数地点での遮水性を複雑な装置や施工を必要としないで簡単に特定でき、地盤の遮水性能の品質管理を容易に行うことが可能となる。
【００１０】
【発明の実施の形態】
以下本発明の実施形態を図を参照して説明する。
図１は本発明の基本原理図を示し、地表１から所定の深さ根入れした地中連続壁２が構築され、この地中連続壁２の下部に所定の厚みの人工底盤３が構築されている。この人工底盤３には欠損などにより上下に貫通する水みち４が発生し、水みち４からの漏水が生じることがある。この水みち４の発生個所の検知手段として地中連続壁２の内側に複数本の観測パイプ５が所定の間隔を離して複数本挿入されている。
【００１１】
地中連続壁２の内側の地層には、シルト・粘土層６、砂・シルト層７などの層が堆積されており、観測パイプ５はこの各地層を通って挿入され、パイプ上端８は地表１に達しており、パイプ先端１０は人工底盤３の上表面１１近くに達している。図１から理解されるように、複数の観測パイプ５を地中連続壁２内に挿入したとき、地中連続壁２の周辺地盤１２の地下水位１３よりも、地中連続壁２内の地下水位が高い状態にあっては、人工底盤３の水みち４からの水の流出によりパイプ内初期水位１４は時間の経過により水位低下位置１５まで低下する。しかも、パイプ先端１０が水みち４の直上ないし至近距離の位置にある観測パイプ５ａ内の水位低下の速度が最も早く、パイプ先端１０が水みち４からより遠く離れている観測パイプ５内の水位低下速度が、前記水みち直上の観測パイプ５の水位低下速度よりも遅いことが分かる。
【００１２】
したがって、複数本の各観測パイプ５内の地下水位の低下速度を測定し、それにより人工底盤３の各部位の透水係数を算定することにより、その地下水透水個所、つまり水みち４のある個所を指定できる。
【００１３】
図２は図１で説明した測定方法の原理が単純化して図示されている。すなわち人工底盤（地盤改良体）３があたかも容器の底であり、観測パイプ５が容器の周壁と考え、容器内、つまり観測パイプ５内の初期水位１４が容器外、つまり地中連続壁２外の地下水位１３よりも高く、しかも人工底盤１３に水みち４があってこの水みち４によって容器内外が連通しているとき、容器内の初期水位１４は図２のグラフ曲線に示すように時間の経過に伴って低下し、地中連続壁外の地下水位１３に近づく。したがって、このときの容器内の初期水位の低下速度から各観測パイプ５の透水係数を算定し、それに基づいて水みち４の個所を特定できるのである。
【００１４】
図１に示した方法で人工底盤３の水みち４の特定を行なう場合の測定順序を説明する。
▲１▼ 遮水性の評価したい人工底盤３上に観測パイプ５を設置する。観測パイプ５の先端部１０にはストレーナ部（孔開け）を加工しておく。初期水位１４として観測パイプ５内に地中連続壁外地下水位１３より高い水位を与える。
▲２▼ 地中連続壁内外の水位差により、人工底盤３に水が浸透し、図２に示した原理から観測パイプ５内水位は、時間経過に伴って徐々に低下する。この水位低下曲線から透水係数（cm／sec)が算出できる。
▲３▼ つまり、観測パイプ５を平面的に複数配置すれば、それぞれのパイプの水位低下速度からパイプ周辺の透水係数が求められる。特に水みち４の近辺個所に配置の観測パイプ５では、他のパイプよりも水位低下速度が早くなるので透水係数が大きく算出される。
▲４▼ 各観測パイプ５で計測した透水係数の平面分布から、人工底盤３の全体的および局所的遮水性が直接評価できる。
【００１５】
なお、観測パイプ５の初期水位１４として２通りの観測方法がある。
(1A) 地中連続壁２が人工底盤施工により、周辺地盤の地下水位よりも高くなっている場合は、そのまま観測する。
(1B) 地中連続壁２内の水位と連続壁外の水位との差が小さい場合には、観測パイプ５内に注水して連続壁内外の水位差を生じさせたうえ、パイプ内の水位低下を観測する。
【００１６】
［実施例］
本発明の具体的実施例を説明する。
本発明では、人工底盤３上の複数の計測ポイントをランダムに決め、各計測ポイントに設けた観測パイプ内の水位変化から透水係数を求める方法で、現場透水試験の一種と考えることができる。
【００１７】
観測パイプ５の施工手順を具体的に示すと以下のようになる。
▲１▼ 改良体（つまり人工底盤）施工のために掘削した掘削孔、あるいはボーリングによって新たに掘削した孔に観測パイプを建て込む。観測パイプの材質は比較的硬質であれば、特に限定しない。
▲２▼ 観測パイプの先端部周壁に孔を開け、掘削孔壁からの土砂の流れにより観測パイプ先端に目詰まりを起こさない様メッシュを巻き、ストレーナー部分を構成する（図３を参照して後述する）。
▲３▼ 観測パイプの設置深さは、パイプストレーナー部分が遮水性を評価したい人工底盤直上となる深さとする。
▲４▼ パイプ設置後、ケーシングを引き抜くときに、セメントミルクをパイプ周辺に充填し、パイプ周辺に水みちができないようにする。この時ストレーナー部分にセメントミルクが回らないように、シール材を巻き付けておく（図３を参照して後述する）。
▲５▼ 人工底盤上に図１に示すようにシルト，粘土層（難透水層）があると、観測パイプ周辺の水みちがより確実に防止されるので、より厳密に人工底盤の遮水性を評価できる。
【００１８】
図３（Ａ），（Ｂ），（Ｃ）によって観測パイプ５の先端１０におけるストレーナー部１６の作成工程を説明する。図３（Ａ）に示すように外径７６mm、内径６５mmの塩ビ製の観測パイプ５の下端から約１０００mmの長さにわたりパイプ周壁に約２０mmφの小孔１７を多数開削すると共に、パイプ先端開口に塩ビ製キャップ１８を嵌着する。図３（Ｂ）に示すように、６０メッシュのメッシュ材１９を前記小孔１７を開削の範囲に亘ってパイプに二重に巻き付ける。図３（Ｃ）に示すように、メッシュ材１９の上に麻布２０を巻き付け番線で締める。このようにストレーナー部１６においてパイプにメッシュ材１９や麻布２０を巻き付けるのは、小孔１７に土砂が目詰まりするのをより完全に防止して、地下水の流入を円滑ならしめ計測精度をより高めるためである。
【００１９】
小孔１７への土砂の目詰まり防止をさらに完璧ならしめるため、麻布２０の巻付け部の上側において、観測パイプ５の外周に所定幅で、所定厚みの水膨潤性シール材２１を所定の間隔をあけて３段に巻き付ける。さらに、水膨潤性シール材２１の上側に例えば、市販のシャンプーハットのような逆円錐状の受け部材２２を取付ける。この受け部材２２は逆円錐状部２３が、水平３６０°方向に亘って内外方向にジグザグに折り曲げてあり、下部筒体２４が観測パイプ５に嵌合されその外周を番線２５で締結して観測パイプ５外周に固定する。
【００２０】
したがって、前記構成の観測パイプ５のストレーナー部１６を、掘削孔に予め挿入したケーシング内に挿入し、ケーシングを引き抜きながら孔壁と観測パイプ５との隙間にセメントミルクを充填するとき、そのセメントミルクは、まずシャンプーハット状の受け部材２２の逆円錐状部２３で受けられて、これが掘削孔内周壁に接触するように拡がることで下方へのセメントミルクの落下が阻止される。また、万一、受け部材２２の外側を落下するセメントミルクは３段の水膨潤性シール材２１で受けられて下側への落下が止められ、ストレーナー部１６に回り込むのが確実に防止される。
【００２１】
前述のように、ストレーナー部１６の小孔１７には複数の目詰まり防止手段が施されているので、小孔１７には目詰まりが生じず、地下水は自然に小孔１７に流れ込み、より厳密に人工底盤３の遮水性を評価できる。図４には、観測パイプ５の先端部とその設置深の概要が示されている。同図から分かるとおり、パイプ先端のストレーナー部１６は出来るだけ改良体施工部分（つまり人工底盤３）の表面に近づけて配置することで、水みち４と観測パイプ５とが緊密に連通し、外乱となる遠方の地下水がストレーナー部１６に流入することが少なく、それ故に、水みち４からの地下水の流出を観測パイプ５内の水位低下として正確に反応させることができ、より高精度の測定ができる。これに関連して、ストレーナー部１６より上方の位置においては、ケーシングを引き抜いたあとの観測パイプ５と掘削孔壁との間隙にセメントミルク２６を充填していることにより、パイプ周辺に前記ストレーナー部１６に通じる水みちができるのを確実に防止している。それにより、人工底盤３の水みち４からの流水量を正確にパイプ内水位１４の低下として反応させることが可能となって高精度の測定ができる。
【００２２】
次に具体的観測例として、地中連続壁の人工底盤部分に改良体施工が適用されている実際の現場において、本発明の方法により改良体の遮水性の評価を行った結果について、図５〜図９によって説明する。
【００２３】
図５には、図示寸法の地中連続壁２内部の改良体施工部上における観測パイプの設置位置が示され、図６（Ａ），（Ｂ）には、その設置深度および地中連続壁外（自然地盤）の水位が示されている。図５において、部分的に重なり合った○図示部分２７が改良体１本の施工範囲を示す。また、●点で示し、No１〜No１０で示すのが１０本の観測パイプの設置位置である。そして、No１の観測パイプ設置位置において、斜線で示す範囲２８が未改良部分（つまり水みちのある部分）である。
【００２４】
図６には、観測パイプ５の設置深度、その初期設定水位，地中連続壁２の外（自然地盤中）の水位が示されている。また、人工底盤（地盤改良体）３は第１砂層２９に設けられ、その上に第１シルト層３０、第２砂層３１、第２シルト層３２の順に地層が堆積され、その上は砂およびシルト層の互層３３となっている。また、初期設置水位が約Ｇ・Ｌ−７．５ｍ、第１砂層２９の水位約Ｇ・Ｌ−１2.０ｍ、第２砂層３１の水位約−6.５ｍである。地表１から人工地盤３の下面までの深さ５7.５ｍ、人工地盤３の大きさ１7.４×１2.４ｍで、その他の寸法も図示した通りである。また、観測パイプ５は複数本のパイプ単体をジョイント３４で相互に連結して、ストレーナー部１６が１ｍ、その上部が約５０ｍの観測パイプ５が構成されている。観測パイプ５内には圧力式水位センサー３５が挿入され、これから導出されたリード線３６が歪アンプへ導かれている。
【００２５】
地中連続壁の人工底盤施工に際して、図４，図５に示す観測手段により、前図No１の観測パイプ設置位置の周辺部分に水みち（未改良部分）がある状態でのNo１〜No１０の観測パイプ設置位置における計測と、その未改良部分を塞いだ改良体完了後の状態での同じくNo１〜No１０の観測パイプ設置位置における計測を行って得られた結果を図７と図８に示す。図７には、人工底盤３に水みち４がある状態での各No１〜No１０に配置のパイプ内の水位変化を示す。同図から分かるとおり、No１に近い、No２，No９のパイプではほぼ同じ水位低下曲線を描くが、No１から離れたNo３，No４，No７，No６のパイプでは水位低下曲線は緩やかになる。
【００２６】
図８には人工底盤３に水みち４がない状態での各No１〜No１０に配置のパイプ内の水位変化を示す。同図から分かるとおり、改良後、つまり水みち４がない状態では、No１〜No１０のいずれのパイプもほぼ同じ水位低下曲線となった。
【００２７】
図９には、No１〜No１０の各位置の観測パイプの水位低下曲線から得られた透水係数が示されている。すなわち同図において、No１〜No１０において、人工底盤３に模擬的な水みちがある状態と、改良体施工完了後の状態について、パイプ内水位から透水係数を求めた結果を示す。横軸は未改良部分上にあるNo１からの各パイプまでの距離、縦軸は透水係数である。図から分かるとおり、改良体完了後の各点の透水係数はほぼ一定の値を示しており、改良体の透水係数ｋ＝4.５×１０^-7cm／sec と評価できる。また、No１周辺に模擬的な水みちのある状態での結果を見ると、No１近辺の透水係数が大きくなっており、水みちの場所を捉えていることが分かる。
【００２８】
以上の水みちありと、改良体完了後（水みちなし）の２ケースの計測結果から、水みちがなければ、全体的な改良体の透水係数が求められ、遮水性の評価を行うことができる。水みちがある場合は、その周辺の透水係数が大きな値を示すため水みちの位置の特定が可能であることが分かる。なお、透水係数の算定は、未改良部分のある状態と、改良体完了後における前述のパイプ内の水位変化から算定するが、その理論式は一般の透水試験における式に準じる。
【００２９】
なお、前記の実施形態では、地中連続壁の人工底盤について説明したが、本発明は改良された地盤に限らず、非改良の通常の地盤や地層の遮水性の評価にも適用できる。例えば、前記人工底盤の上部を締め切る壁は、地中連続壁の代わりにシートパイル，ＳＭＷ柱列壁等で締め切られた山留め壁であってもよい。さらに本発明は、側壁の遮水性の評価にも適用できる。その場合は、側壁に沿って観測パイプを（当該パイプが複数の場合は深さ方向または、水平方向に数ケ所）配設すれば、その側壁の遮水性を評価できる。またさらに、人工底盤と側壁とで締め切られた仕切りの内側が地層である場合に限らず、水や泥水で満たされている場合でもよく、その場合も前記人工底盤や側壁の遮水性を評価できる。
【００３０】
【発明の効果】
以上説明したように、本発明によると次の効果がある。
▲１▼ 観測パイプ内の水位観測のみから、各種地盤の遮水性を容易に評価できる。
▲２▼ 地盤の全体的および局所的な遮水性能を同時に測定することができる。
▲３▼ 観測パイプを地盤表面に近接して設置すればよい、いわゆる非接触方式なので地盤に損傷を与えない。
▲４▼ 観測パイプ設置位置の各点周辺の透水係数が直接、個々に測定できるため観測結果の信頼性が高い。
▲５▼ 観測パイプ内の水位変化を測るのみなので、複雑な計測システムを必要としない。
▲６▼ 平面的な透水係数の分布から、水みちの特定が可能である。
▲７▼ 計測結果に対して複雑な解析を必要としない。
▲８▼ 地盤改良体施工途中で、この評価技術により十分な遮水性が認められた場合、それ以降の改良体の追加施工は不要となり、地盤改良体（人工底盤）の施工費を低減する事が可能となる。
【図面の簡単な説明】
【図１】本発明の地盤改良体としての人工底盤の遮水性を評価する方法の原理を示す図である。
【図２】図１の原理をより単純化して示す図である。
【図３】（Ａ），（Ｂ），（Ｃ）は観測パイプ先端のストレ−ナ部の製作工程を示す説明図である。
【図４】観測パイプ先端のストレ−ナ部とパイプ設置深との関係の概要図である。
【図５】観測パイプの設置位置を示す平面的説明図である。
【図６】（Ａ）は観測パイプの設置深度および地下連続壁外の地下水位を示す説明図、（Ｂ）は観測パイプの側面詳細図である。
【図７】人工底盤の各観測パイプ位置での模擬的な水みちがある状態での水位変化をグラフで示す図である。
【図８】人工底盤の各観測パイプ位置での水みちがない状態での水位変化をグラフで示す図である。
【図９】人工底盤の各位置での透水係数をグラフで示す図である。
【符号の説明】
１地表
２地中連続壁
３地盤改良体（人工底盤）
４水みち
５観測パイプ
６シルト、粘土層
７砂シルト層
８パイプ上端
１０パイプ先端
１１上表面
１２周辺地盤
１３地下水位
１４パイプ内初期水位
１５水位低下位置
１６ストレ−ナ部
１７小孔
１８塩ビ製キャップ
１９メッシュ材
２０麻布
２１水膨潤性シ−ル材
２２受け部材
２３逆円錐状部
２４下部筒体
２５番線
２６セメントミルク
２７ ○図示部分
２８斜線範囲
２９第１砂層
３０第１シルト層
３１第２砂層
３２第２シルト層
３３互層
３４ジョイント
３５圧力式水位センサー
３６リード線[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for evaluating water-imperviousness of an artificial bottom of a continuous underground wall and other various grounds.
[0002]
[Prior art]
For example, in the underground continuous wall construction method, the underground continuous wall is usually deeply rooted until it reaches a hardly permeable layer such as a silt layer existing in the ground, and this difficult permeable layer is used as the bottom of the underground continuous wall. Due to its strength and water-imperviousness, soil pressure and water pressure from the bottom that occurs during excavation in the underground continuous wall are taken into account, preventing flooding from the bottom, flooding, and piping. In the conventional method described above, since the hardly permeable layer is the bottom of the underground continuous wall, even if the depth of the difficult permeable layer is far from the intended excavation depth to be excavated in the underground continuous wall, The underground continuous wall is constructed until it reaches the poorly permeable layer, and the deeply permeable layer is fully embedded. Therefore, in the conventional construction method, the construction of the underground continuous wall becomes uneconomical as the intended excavation depth and the difficult-permeability depth are separated.
[0003]
Therefore, as a recent new construction method, a method of artificially constructing a poorly permeable layer according to the desired ground excavation depth has been developed. This is a method called the column jet method, etc., where multiple rows of columnar ground improvement bodies are constructed in accordance with the depth of ground excavation to artificially construct the poorly permeable layer necessary for laying underground continuous walls. Is the method. In this way, the construction method described above is adapted to the depth of excavation in the underground continuous wall, and by making an artificial bottom with a ground improvement body to the required thickness, the construction depth of the underground continuous wall is minimized. This is a construction method that can reduce the construction cost of underground continuous walls.
[0004]
[Problems to be solved by the invention]
In the ground improvement method described above, the artificial bottom board needs to have sufficient water shielding performance, but a technique for appropriately evaluating the water shielding performance has not yet been put into practical use. There are (A) ultrasonic and elastic wave measurement methods and (B) electrical resistivity measurement methods as conventional quality evaluation techniques for ground improvement bodies, both of which are artificially spaced apart from two pole detection terminals. It is measured by contacting the bottom plate, and has the following disadvantages.
(1) This is a method for evaluating the soundness (strength, defect portion) of only a plurality of individual columnar bodies constituting the artificial bottom board, and the water-imperviousness between the plurality of columns of columnar bodies cannot be evaluated.
(2) Since the ground improvement body (artificial bottom) is directly drilled for mounting the detection terminal, there is a possibility that the improvement body itself may have a defect that impairs the water shielding property.
(3) Since it is an indirect evaluation for evaluating the water shielding performance through the state of the improved body, direct water permeability cannot be evaluated.
[0005]
From the above (1), (2), and (3), the measurement methods (A) and (B) are not applied as a water-impervious evaluation technique for the entire ground improvement body (artificial bottom). Thus, the problem of the ground improvement construction method is that its water-impervious performance evaluation method has not been established.
[0006]
The present invention solves the above-mentioned problems of the prior art, and provides a water impermeability evaluation method for ground that can be applied not only to artificial ground and other ground improvement bodies but also to water impermeability evaluation of other pillar grounds. For the purpose. In the following explanation, the ground means an artificial bottom of the deadline wall in the ground or its deadline wall (that is, a side wall), and is used to mean improved ground, non-improved ground, other impermeable bodies, and the like. .
[0007]
[Means for Solving the Problems]
Aqueous Evaluation barrier of the ground according to the present invention, the water passing holes of the observation pipe close to the surface of the ground to be measured is disposed, shielding of the ground to measure the ground of impermeability by the water level changes in the observation pipe In the water evaluation method, the observation pipes are installed at a plurality of points on the ground, and the water impermeability of the ground is evaluated based on the difference in the water level change curves of the respective observation pipes.
In addition, the present invention provides an overall and / or local distribution of the ground from the planar distribution of hydraulic conductivity calculated from the water level change curves of the plurality of observation pipes arranged at the water-impervious evaluation point of the ground. It is characterized by evaluating water impermeability.
Further, the present invention is characterized in that a water leakage location is specified from a difference in water level change or a difference in water permeability coefficient between the plurality of observation pipes.
Further, the present invention is characterized in that the ground is a bottom of a closed wall in the ground.
Further, the present invention is characterized in that the observation pipe is given an initial water level higher than the groundwater level outside the closed wall in the ground, and the present invention is characterized in that the ground is made of an improved body. To do.
[0008]
According to the first invention , since the water level in the observation pipe changes in proportion to the outflow of water penetrating the ground, simply measuring this water level change makes it easy to block the ground without the need for complicated equipment or construction. Aqueous property can be evaluated.
[0009]
In addition, according to the first to sixth inventions, the application of the principle premised on the first half of the first invention can easily identify the water-imperviousness at multiple points of the ground without requiring complicated equipment and construction, It becomes possible to easily perform the quality control of the water shielding performance of the ground.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a basic principle diagram of the present invention. An underground continuous wall 2 having a predetermined depth is constructed from the ground surface 1, and an artificial bottom 3 having a predetermined thickness is constructed below the underground continuous wall 2. ing. The artificial bottom plate 3 may have a water channel 4 penetrating vertically due to a defect or the like, and water leakage from the water channel 4 may occur. A plurality of observation pipes 5 are inserted at predetermined intervals inside the underground continuous wall 2 as means for detecting the location where the water channel 4 is generated.
[0011]
Layers such as silt / clay layer 6 and sand / silt layer 7 are deposited on the inner layer of the underground continuous wall 2, and the observation pipe 5 is inserted through these layers, and the upper end 8 of the pipe is the surface of the earth. 1, the pipe tip 10 reaches the upper surface 11 of the artificial bottom board 3. As understood from FIG. 1, when a plurality of observation pipes 5 are inserted into the underground continuous wall 2, the groundwater in the underground continuous wall 2 is higher than the groundwater level 13 of the ground 12 around the underground continuous wall 2. In a state where the position is high, the initial water level 14 in the pipe is lowered to the water level lowering position 15 over time due to the outflow of water from the water channel 4 of the artificial bottom board 3. Moreover, the water level in the observation pipe 5 a where the pipe tip 10 is directly above or close to the water path 4 is the fastest, and the water level in the observation pipe 5 is farther from the water path 4. It can be seen that the rate of decrease is slower than the rate of decrease of the water level of the observation pipe 5 directly above the water path.
[0012]
Therefore, by measuring the decrease rate of the groundwater level in each of the plurality of observation pipes 5 and calculating the permeability coefficient of each part of the artificial bottom board 3, the groundwater permeability location, that is, the location where the water channel 4 is located. Can be specified.
[0013]
FIG. 2 shows a simplified principle of the measurement method described in FIG. That is, the artificial bottom plate (ground improvement body) 3 is as if the bottom of the container, and the observation pipe 5 is considered as the peripheral wall of the container, and the initial water level 14 in the container, that is, in the observation pipe 5 is outside the container, that is, outside the underground continuous wall 2. 2, and when the artificial bottom plate 13 has a water channel 4 and the water channel 4 communicates with the inside and outside of the container, the initial water level 14 in the container is time as shown in the graph curve of FIG. It decreases with the progress of and approaches the groundwater level 13 outside the underground continuous wall. Therefore, the water permeability coefficient of each observation pipe 5 is calculated from the rate of decrease of the initial water level in the container at this time, and the location of the water channel 4 can be specified based on the calculated coefficient.
[0014]
A measurement sequence in the case where the water channel 4 of the artificial bottom board 3 is specified by the method shown in FIG. 1 will be described.
(1) An observation pipe 5 is installed on the artificial bottom board 3 for which the water-imperviousness is to be evaluated. A strainer portion (perforation) is processed in the tip portion 10 of the observation pipe 5. As the initial water level 14, a higher water level than the underground continuous wall groundwater level 13 is given in the observation pipe 5.
(2) Due to the difference in water level between the inside and outside of the underground continuous wall, water penetrates into the artificial bottom board 3, and the water level in the observation pipe 5 gradually decreases with time from the principle shown in FIG. The water permeability coefficient (cm / sec) can be calculated from this water level reduction curve.
{Circle around (3)} That is, if a plurality of observation pipes 5 are arranged in a plane, the hydraulic conductivity around the pipe can be obtained from the water level lowering speed of each pipe. In particular, in the observation pipe 5 arranged in the vicinity of the water path 4, the water level lowering speed becomes faster than the other pipes, so that the hydraulic conductivity is calculated to be large.
(4) From the planar distribution of the hydraulic conductivity measured by each observation pipe 5, the overall and local water shielding properties of the artificial bottom board 3 can be directly evaluated.
[0015]
There are two observation methods for the initial water level 14 of the observation pipe 5.
(1A) If the underground continuous wall 2 is higher than the groundwater level of the surrounding ground due to the construction of the artificial bottom, observe it as it is.
(1B) When the difference between the water level in the underground continuous wall 2 and the water level outside the continuous wall is small, water is injected into the observation pipe 5 to cause a water level difference between the inside and outside of the continuous wall, and the water level inside the pipe Observe the decline.
[0016]
[Example]
Specific examples of the present invention will be described.
In the present invention, a plurality of measurement points on the artificial bottom board 3 are determined at random, and a method of obtaining a permeability coefficient from a change in water level in an observation pipe provided at each measurement point can be considered as a kind of on-site permeability test.
[0017]
Specifically, the construction procedure of the observation pipe 5 is as follows.
(1) An observation pipe is installed in a drilling hole excavated for construction of an improved body (that is, an artificial bottom) or newly drilled by boring. The material of the observation pipe is not particularly limited as long as it is relatively hard.
(2) A hole is made in the peripheral wall of the tip of the observation pipe, and a mesh is wound around the observation pipe to prevent clogging at the tip of the observation pipe due to the flow of earth and sand from the excavation hole wall. To do).
(3) The installation depth of the observation pipe shall be the depth at which the pipe strainer part is directly above the artificial bottom plate for which water-imperviousness is to be evaluated.
(4) After installing the pipe, when pulling out the casing, cement milk is filled around the pipe so that there is no water around the pipe. At this time, a sealing material is wound around the strainer portion so that the cement milk does not rotate (described later with reference to FIG. 3).
(5) If there is a silt or clay layer (imperviously permeable layer) as shown in Fig. 1 on the artificial bottom plate, water leakage around the observation pipe will be more reliably prevented, so the artificial bottom plate will be more tightly sealed. Can be evaluated.
[0018]
A process of creating the strainer portion 16 at the tip 10 of the observation pipe 5 will be described with reference to FIGS. As shown in FIG. 3 (A), a large number of small holes 17 having a diameter of about 20 mm are cut out from the lower end of a polyvinyl chloride observation pipe 5 having an outer diameter of 76 mm and an inner diameter of 65 mm to a length of about 1000 mm from the lower end of the pipe. A PVC cap 18 is fitted. As shown in FIG. 3 (B), a mesh material 19 of 60 mesh is wound around the pipe in a double-cut manner over the small hole 17. As shown in FIG. 3C, the linen 20 is wound around the mesh material 19 with a winding number wire. Thus, winding the mesh material 19 and the linen 20 around the pipe in the strainer portion 16 more completely prevents clogging of the earth and sand in the small holes 17, smoothes the inflow of groundwater, and improves the measurement accuracy. Because.
[0019]
In order to further prevent clogging of earth and sand into the small holes 17, a water-swellable sealing material 21 having a predetermined width and a predetermined thickness is provided on the outer periphery of the observation pipe 5 on the upper side of the winding portion of the linen 20 at a predetermined interval. Wrap it in three steps. Further, an inverted conical receiving member 22 such as a commercially available shampoo hat is attached to the upper side of the water-swellable sealing material 21. The receiving member 22 has an inverted conical portion 23 which is bent in a zigzag direction in the horizontal 360 ° direction, the lower cylindrical body 24 is fitted to the observation pipe 5 and the outer periphery thereof is fastened by a wire 25 for observation. Fix to the outer periphery of the pipe 5.
[0020]
Therefore, when the strainer portion 16 of the observation pipe 5 having the above-described configuration is inserted into a casing previously inserted into the excavation hole and the gap between the hole wall and the observation pipe 5 is filled with cement milk while the casing is pulled out, the cement milk Is first received by the inverted conical portion 23 of the receiving member 22 having a shampoo hat shape, and is spread so as to contact the inner peripheral wall of the excavation hole, thereby preventing the cement milk from falling downward. In the unlikely event that the cement milk falls outside the receiving member 22, it is received by the three-stage water-swellable sealing material 21, and is prevented from dropping downward, so that it is surely prevented from entering the strainer portion 16. .
[0021]
As described above, since the small holes 17 of the strainer portion 16 are provided with a plurality of clogging prevention means, the small holes 17 are not clogged, and the groundwater naturally flows into the small holes 17 and more strictly. In addition, the water barrier property of the artificial bottom board 3 can be evaluated. FIG. 4 shows an outline of the distal end portion of the observation pipe 5 and its installation depth. As can be seen from the figure, the strainer 16 at the end of the pipe is placed as close as possible to the surface of the improved body construction part (that is, the artificial bottom board 3), so that the water channel 4 and the observation pipe 5 are in close communication with each other. Therefore, it is possible to accurately react the outflow of groundwater from the water channel 4 as a drop in the water level in the observation pipe 5, so that more accurate measurement is possible. it can. In relation to this, at a position above the strainer section 16, the gap between the observation pipe 5 and the excavation hole wall after the casing is pulled out is filled with cement milk 26, so that the strainer section around the pipe. The water channel leading to 16 is reliably prevented. Thereby, it is possible to accurately react the amount of water flowing from the water channel 4 of the artificial bottom board 3 as a drop in the water level 14 in the pipe, and to perform highly accurate measurement.
[0022]
Next, as a specific observation example, the results of the evaluation of the water-imperviousness of the improved body by the method of the present invention in an actual site where the improved body construction is applied to the artificial bottom part of the underground continuous wall are shown in FIG. Referring to FIG.
[0023]
FIG. 5 shows the installation position of the observation pipe on the improved body construction section inside the underground continuous wall 2 of the illustrated dimensions, and FIGS. 6 (A) and 6 (B) show the installation depth and the underground continuous wall. The water level outside (natural ground) is shown. In FIG. 5, a partially overlapped circled portion 27 indicates a construction range of one improved body. Also, the positions of the ten observation pipes are indicated by ● and indicated by No1 to No10. In the No. 1 observation pipe installation position, a hatched range 28 is an unimproved portion (that is, a portion having a water channel).
[0024]
FIG. 6 shows the installation depth of the observation pipe 5, its initially set water level, and the water level outside the underground continuous wall 2 (in the natural ground). In addition, the artificial bottom base (ground improvement body) 3 is provided on the first sand layer 29, and the first silt layer 30, the second sand layer 31, and the second silt layer 32 are sequentially deposited on the first sand layer 29. It is a mutual layer 33 of a silt layer. Further, the initial installation water level is about G · L-7.5 m, the water level of the first sand layer 29 is about G · L-12.0 m, and the water level of the second sand layer 31 is about −6.5 m. The depth from the ground surface 1 to the lower surface of the artificial ground 3 is 57.5 m, the size of the artificial ground 3 is 17.4 × 12.4 m, and other dimensions are as illustrated. Further, the observation pipe 5 includes a plurality of pipes connected to each other by a joint 34 to form an observation pipe 5 having a strainer portion 16 of 1 m and an upper portion of about 50 m. A pressure-type water level sensor 35 is inserted into the observation pipe 5, and a lead wire 36 derived therefrom is led to the strain amplifier.
[0025]
When constructing the artificial bottom wall of the underground continuous wall, the observation means shown in Fig. 4 and Fig. 5 are used to observe No1 to No10 when there is a water channel (unimproved part) around the observation pipe installation position in the previous figure No1. FIG. 7 and FIG. 8 show the results obtained by performing measurement at the pipe installation position and measurement at the No. 1 to No. 10 observation pipe installation positions in the state after completion of the improved body that blocks the unimproved portion. In FIG. 7, the water level change in the pipe arrange | positioned to each No1-No10 in the state in which the water bottom 4 exists in the artificial bottom board 3 is shown. As can be seen from the figure, the No. 2 and No. 9 pipes that are close to No. 1 draw almost the same water level lowering curve, but the No. 3, No. 4, No. 7, and No. 6 pipes that are distant from No. 1 have gentle water level lowering curves.
[0026]
FIG. 8 shows a change in the water level in the pipes arranged at No. 1 to No. 10 in the state where there is no water channel 4 in the artificial bottom board 3. As can be seen from the figure, after the improvement, that is, in the state where there is no water channel 4, all of the pipes No. 1 to No. 10 have almost the same water level lowering curve.
[0027]
FIG. 9 shows the hydraulic conductivity obtained from the water level lowering curves of the observation pipes at the positions No1 to No10. That is, in the same figure, in No1-No10, the result which calculated | required the hydraulic conductivity from the water level in a pipe is shown about the state which has a simulated water channel in the artificial bottom board 3, and the state after completion of improvement body construction. The horizontal axis is the distance from No1 on the unmodified part to each pipe, and the vertical axis is the hydraulic conductivity. As can be seen from the figure, the permeability coefficient of each point after the improvement body is almost constant, and the improvement coefficient can be evaluated as k = 4.5 × 10 ⁻⁷ cm / sec. Moreover, when the result in the state with the simulated water path around No1 is seen, it can be seen that the permeability coefficient in the vicinity of No1 is increased and the location of the water path is captured.
[0028]
From the measurement results of the two cases with the above-mentioned water path and after completion of the improved body (without the water path), if there is no water path, the overall permeability coefficient of the improved body can be obtained and the water impermeability can be evaluated. it can. In the case where there is a water channel, it is understood that the location of the water channel can be specified because the hydraulic conductivity around the water channel shows a large value. The permeability coefficient is calculated from the state where there is an unimproved portion and the change in the water level in the pipe after the improvement, and the theoretical formula is the same as the formula in a general permeability test.
[0029]
In addition, although the above-mentioned embodiment demonstrated the artificial bottom board of the underground continuous wall, this invention is applicable not only to the improved ground but to the evaluation of the water-imperviousness of the non-improved normal ground and the stratum. For example, the wall that cuts off the upper part of the artificial bottom plate may be a mountain retaining wall that is cut off by a sheet pile, an SMW column wall, or the like instead of the underground continuous wall. Furthermore, the present invention can also be applied to the evaluation of the water barrier property of the side wall. In that case, if the observation pipe is arranged along the side wall (if there are a plurality of the pipes, several places in the depth direction or the horizontal direction), the water impermeability of the side wall can be evaluated. Furthermore, the inside of the partition closed by the artificial bottom plate and the side wall is not limited to the formation, but may be filled with water or muddy water, and in that case, the water shielding property of the artificial bottom plate and the side wall can be evaluated. .
[0030]
【The invention's effect】
As described above, the present invention has the following effects.
(1) The water-imperviousness of various grounds can be easily evaluated only by observing the water level in the observation pipe.
(2) The overall and local water-blocking performance of the ground can be measured simultaneously.
(3) It is only necessary to install the observation pipe close to the surface of the ground.
(4) Since the hydraulic conductivity around each point of the observation pipe installation position can be measured directly and individually, the reliability of the observation results is high.
(5) Since it only measures changes in the water level in the observation pipe, it does not require a complicated measurement system.
(6) The water channel can be identified from the distribution of planar hydraulic conductivity.
(7) No complicated analysis is required for the measurement results.
(8) If sufficient water-imperviousness is recognized by this evaluation technique during the construction of the ground improvement body, additional construction of the subsequent improvement body is unnecessary, and the construction cost of the ground improvement body (artificial bottom) should be reduced. Is possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing the principle of a method for evaluating the water-imperviousness of an artificial bottom board as a ground improvement body of the present invention.
FIG. 2 is a diagram showing the principle of FIG. 1 in a more simplified manner.
FIGS. 3A, 3B, and 3C are explanatory views showing a manufacturing process of a strainer portion at the tip of an observation pipe. FIGS.
FIG. 4 is a schematic diagram showing the relationship between the strainer section at the tip of the observation pipe and the pipe installation depth.
FIG. 5 is an explanatory plan view showing an installation position of an observation pipe.
6A is an explanatory diagram showing the installation depth of the observation pipe and the groundwater level outside the continuous underground wall, and FIG. 6B is a detailed side view of the observation pipe.
FIG. 7 is a graph showing changes in water level in a state where there is a simulated water channel at each observation pipe position of the artificial bottom board.
FIG. 8 is a graph showing a change in water level in a state where there is no water channel at each observation pipe position of the artificial bottom board.
FIG. 9 is a graph showing the water permeability coefficient at each position of the artificial bottom board.
[Explanation of symbols]
1 Ground surface 2 Underground continuous wall 3 Ground improvement body (artificial bottom)
4 Water path 5 Observation pipe 6 Silt, clay layer 7 Sand silt layer 8 Pipe upper end 10 Pipe tip 11 Upper surface 12 Peripheral ground 13 Ground water level 14 Initial water level in pipe 15 Water level lowering position 16 Strainer section 17 Small hole 18 Made of PVC Cap 19 Mesh material 20 Linen 21 Water-swellable seal material 22 Receiving member 23 Inverted conical portion 24 Lower cylindrical body 25 Line 26 Cement milk 27 ○ Illustrated portion 28 Diagonal area 29 First sand layer 30 First silt layer 31 Second Sand layer 32 Second silt layer 33 Mutual layer 34 Joint 35 Pressure type water level sensor 36 Lead wire

Claims

In the method for evaluating water impermeability of a ground , wherein the water passage hole of the observation pipe is disposed close to the surface of the ground to be measured, and the water impermeability of the ground is measured by a change in the water level in the observation pipe, the observation pipe is connected to the ground. A groundwater imperviousness evaluation method characterized in that it is installed at a plurality of points, and the groundwater imperviousness is evaluated by the difference in the water level change curve of each observation pipe .

Evaluating the overall and / or local water-imperviousness of the ground from the planar distribution of hydraulic conductivity calculated from the water level change curves of each of the plurality of observation pipes installed at the water-impervious evaluation point of the ground. The groundwater imperviousness evaluation method according to claim 1, wherein:

Wherein the plurality of respective aqueous Evaluation barrier of the ground according to claim 1, wherein the the difference between the difference or the respective hydraulic conductivity of the water level change to identify the leakage location of the observation pipe.

The ground the claims 1 to an aqueous Evaluation barrier of the ground according to claim 3, characterized in that a closed for wall bottom plate of the ground.

The groundwater imperviousness evaluation method according to claim 4 , wherein an initial water level higher than a groundwater level outside the closed wall in the ground is given to the observation pipe.

The ground imperviousness evaluation method according to any one of claims 1 to 5 , wherein the ground is made of an improved body. "