JP3855198B2

JP3855198B2 - Seismic reinforcement structure for pile foundation structures

Info

Publication number: JP3855198B2
Application number: JP2002329071A
Authority: JP
Inventors: 英之真野
Original assignee: Shimizu Corp
Current assignee: Shimizu Corp
Priority date: 2002-11-13
Filing date: 2002-11-13
Publication date: 2006-12-06
Anticipated expiration: 2022-11-13
Also published as: JP2004162362A

Description

【０００１】
【発明の属する技術分野】
本発明は杭基礎構造物の耐震補強構造に係り、既設あるいは新設の構造物の杭基礎に対して鉛直荷重の増加を生じさせることなく、地震時に既設杭に作用する水平力を低減させることのできる杭基礎構造物の耐震補強構造に関する。
【０００２】
【従来の技術】
高架橋の橋脚の杭基礎構造等では、設計当初の構造物重量及び地震時荷重に対して十分な耐力と靱性が確保できるように構造設計が行われ、基礎フーチングの寸法、杭径、本数等の諸元が決定されているが、供用後に従前より厳しく耐震設計基準が改正されたり、上部工の増設等により設定荷重が増加した場合、杭基礎構造における所要の地震時耐力等の確保が困難となる場合がある。
【０００３】
このような場合に対して既設構造物基礎では既存構造に付加するかたちで各種の耐震補強が行われている。図１４〜図１６は従来の基礎構造物の耐震補強構造の一例を示した一部断面図である。図１４は、既設フーチング５０の外周を囲むように増設フーチング５１を一体化させた増し杭構造による耐震補強構造の一例を示している。この増し杭構造では、既設杭５２と同等耐力の新設杭５３を打設するとともに、杭頭を固定するための増設フーチング５１が既設フーチング５０の側面に多数のアンカー筋等のせん断負担材５４を介して一体的に接合されている。これにより既設部に加え、新設杭５３及び一体的に拡幅されたフーチング５０，５１により鉛直荷重、地震時の水平荷重を負担するようになっている。
【０００４】
図１５は、増設フーチング５１の下方の地中部に、既設杭５２の杭頭周囲を囲むように地中連続壁５５を造成した耐震補強構造の一例を示している。この耐震補強構造では同図に示したように、既設杭５２を囲むように、増設フーチング５１と一体的に造成された地中連続壁５５が地震時に作用する水平方向力を負担し、地中連続壁５５で囲まれた地盤内に位置する既設杭５２の杭頭への水平方向力の作用を低減できるようになっている。
【０００５】
これらの耐震補強構造例では、構造物に作用する水平力を新設杭や地中連続壁に伝達するため、杭や地中連続壁を既存のフーチングと剛結する必要があるため、多数のアンカー等を介して拡幅部の増設フーチングを既設フーチングに一体化させる必要があり、煩雑な増設工事を要する。また、増設フーチングによる基礎平面が拡幅されるため、土地の制限を受ける場合がある。さらに新設杭、地中連続壁の施工に、大型の施工機械が必要となり、特に高架橋下などのように工事のための架空制限を受ける場所では適切な施工ができないこともある。また、図１５に示した地中連続壁では、地中連続壁が構造上十分な鉛直支持力を有しないため、耐震補強工の重量分だけ既設杭の軸力が増加し過度な応力状態が生じるという問題もある。
【０００６】
これに対して、十分な水平方向支持力と鉛直支持力とを備えた耐震補強構造の例として既設フーチング６０の周囲に、大径の地盤改良体６２を造成するとともに、この地盤改良体６２内に既製杭６３を打設した複合杭を施工し、それらの杭頭を増設フーチング６１で固定し、増設フーチング６１を既設フーチング６０に一体化させることで、水平方向、鉛直方向に十分な支持力が得られる耐震補強構造が提案されている（図１６，たとえば特許文献１参照）。
【０００７】
【特許文献１】
特開２００２−１８８１５７公報（第４頁の記載）
【０００８】
【発明が解決しようとする課題】
ところで、上述の先行技術文献情報に開示された耐震補強構造は、図１６に示したように、既設フーチングの外周に高圧噴射撹拌工法によって造成された大径の改良体内に既製杭を打設することで、既製杭の鉛直支持力を改良体で負担するようにしたので、新設杭を支持層まで到達させることなく、鉛直支持力を負担できるようにしている。このため、改良体頭部、既製杭頭部の固定を行うために十分剛性の高い増設フーチングを既設フーチングと一体的に構築する必要がある。既設フーチングの周囲に施工される改良体、既製杭、及び増設フーチングとが一体となった耐震補強構造とする各部材を施工し、さらにそれぞれを一体化させる多くの施工工程を要する。また、高架下等においては既製杭の長さ等の制限を受けるため、施工できないケースもあり得る。
【０００９】
そこで、本発明の目的は上述した従来の技術が有する問題点を解消し、簡易な耐震補強構造により既設フーチングの杭基礎に作用する地震時水平方向力の負担低減を図れるようにした杭基礎構造物の耐震補強構造を提供することにある。
【００１０】
【課題を解決するための手段】
上記目的を達成するために、本発明は杭基礎構造物に作用する地震時水平力を負担する水平変位抑止枠構造を、前記杭基礎構造物のフーチングの外周面を囲むように構築した杭基礎構造物の耐震補強構造であって、前記水平変位抑止枠構造は、立壁部が前記フーチングと前記水平変位抑止枠構造との境界面に形成された、鉛直方向の面外せん断力の伝達を絶縁する絶縁層を介して構築された擁壁構造からなり、前記立壁部と一体構築された底版の下面と地盤面との底面摩擦により地震時水平方向力に抵抗することを特徴とする。
【００１１】
また、他の発明として、本発明は杭基礎構造物に作用する地震時水平力を負担する改良ブロック体を、前記杭基礎構造物のフーチングの外周面の地盤を囲むように、所定深度までの２重鋼矢板で包囲し、該区画された地盤内を地盤改良して造成した杭基礎構造物の耐震補強構造であって、前記改良ブロック体は、前記フーチングとの境界面に形成された、鉛直方向の面外せん断力の伝達を絶縁する絶縁層を介して構築され、前記改良ブロック体の底面と地盤面との境界面摩擦により地震時水平方向力に抵抗することを特徴とする。
【００１２】
このとき、前記絶縁層は、前記改良ブロック体と前記フーチングとの境界面に打設された鋼矢板の前記フーチング側に施された樹脂被覆とすることが好ましい。
【００１５】
【発明の実施の形態】
以下、本発明の杭基礎構造物の耐震補強構造の一実施の形態について、添付図面を参照して説明する。図１は既設構造物としての橋脚基礎のフーチングの外周に構築された本発明の耐震補強構造の一部を切欠いて示した斜視図で、図２は同正面図及び平面図である。図１において、既設構造物１は、本実施の形態では、縦横に等間隔をあけて打設された９本の杭２（図２（ｂ）参照）と、この杭２の杭頭を固定してなる平面視して矩形形状をなす鉄筋コンクリート製の基礎フーチング（既設フーチング）３と、この既設フーチング３上に一体的に立設された鉄筋コンクリート柱４とからなる。そしてこの既設構造物１の基礎フーチング３の外周を囲んでに耐震補強構造が構築されている。なお、以下の説明では既設構造物１の基礎フーチング３の耐震補強を例に説明を行っているが、新設構造物の基礎フーチングに本発明の耐震補強構造を適用することも有効であることは言うまでもない。
【００１６】
耐震補強構造は、図１に示したように耐震補強の対象となる既設杭基礎構造物１の基礎フーチング３の外周を取り囲むように構築された基礎水平変位抑止枠構造１０と、該基礎水平変位抑止枠構造１０と既設フーチング３との間に形成された絶縁層２０とから構成されている。
【００１７】
本実施の形態による基礎水平変位抑止枠構造１０は、図１，図２に示したような断面形がＬ型をなす鉄筋コンクリート製の擁壁構造１１からなる。立壁１２の前面は、既設フーチング３の外周面に面し、その高さはフーチング厚さに等しく、所定の底版長さを有する。また既設フーチング３の外周面を完全に囲むように設けられている。なお、立て壁１２の高さと底版１３の長さとは基礎水平変位抑止枠構造１０の目標抵抗値により適宜設定され、その断面形状が決定される。すなわち、基礎水平変位抑止枠構造１０が、図１に示したような擁壁構造１１である場合には、その立壁１２の高さおよび底版１３の底面積を、耐震補強構造において必要とされる水平抵抗力に応じて適宜に設定すればよい。すなわち、大きな水平抵抗力を必要とする場合には底版１３の底面積を広くするか、立壁１２の高さを高くすればよい。
【００１８】
絶縁層２０は、基礎水平変位抑止枠構造１０の立壁１２の前面と既設フーチング３の側面との間の全面に形成された、両部材間での鉛直方向の面外せん断力の伝達を絶縁することを意図して設けられた要素である。したがって、基礎水平変位抑止枠構造１０の自重はその底版１３のみで支持され、既設構造物１の杭２には伝達されない構造になっている。絶縁層２０は本実施の形態では、アスファルト充填層からなり、このアスファルト充填層は鉛直方向に生じる両部材間の位相変位を完全に吸収できる変形能力を期待できる。絶縁層２０を構成する絶縁材料としては、アスファルト等の瀝青材料の充填材料の他、せん断変形性が十分大きい各種ゴム系材料、ゴム系エラストマー等の弾性部材を既設フーチング３の側面に固着するようにして絶縁層２０を形成するようにしてもよい。
【００１９】
これら基礎水平変位抑止枠構造１０と絶縁層２０を施工する手順の一例としては、まず基礎水平変位抑止枠構造１０の底版１３の施工範囲を考慮して決定された既設フーチング３の周囲の地盤の所定範囲で掘削する。このとき地盤状態に応じて土留め工等を施し、掘削空間の確保を図ることが好ましい。次いで既設フーチング３の外周面に絶縁層２０を施工する。この絶縁層２０の施工は、絶縁材料の相違によっては既設フーチング３との間に所定幅（厚さ）の空隙を設けて擁壁構造１１を構築し、その後、空隙に絶縁材料を充填することもできる。擁壁構造１１は現場施工の鉄筋コンクリート構造としてもよいし、プレキャストコンクリート製品を搬入して全体をＰＣ鋼材等を用いて一体構造とさせることもできる。最終的に掘削土を再利用して擁壁構造１１の背面部分を埋戻して埋戻し土１５と擁壁構造１１とを一体化させ、基礎水平変位抑止枠構造１０を完成させる。
【００２０】
ここで、図２（ａ）を参照して、地震時における基礎水平変位抑止枠構造１０の作用について説明する。基礎水平変位抑止枠構造１０としては、上述の擁壁構造１１とその背面の底版１３上の埋戻し土１５を合わせたものが相当する。すなわち、地震時に既設構造物に水平方向力が作用すると、既設フーチング３の側面で対向する擁壁構造１１の立壁１２を押圧する。このとき擁壁構造１１の底版１３の底面と地盤との間には所定の摩擦力が生じ、この摩擦力の分だけ杭２が負担する水平方向力が低減される。すなわち既設の杭２の耐力を越えた分の水平方向力の負担が可能となり、既設杭基礎構造物１の耐震性が向上する。基礎水平変位抑止枠構造１０としての擁壁構造１１の底面に作用する摩擦力の限界値は、砂地盤では擁壁構造１１の自重と埋戻し土１５の重量の和に摩擦係数を乗じたものとなる。粘性土地盤では、地盤の粘着力と摩擦力の小さい方で決まる。
【００２１】
図３は、上述した耐震補強構造において、基礎水平変位抑止枠構造１０の底面摩擦が負担する水平荷重と、既設フーチングの杭が負担する水平荷重とを比較した解析結果である。同図に示したように、基礎水平変位抑止枠構造１０の底面摩擦は、既設杭に比べ、一般に小さな変位で発揮されるので、既設杭に作用する水平方向力を効率的に低減できる。また基礎水平変位抑止枠構造１０を、既設フーチング３の外周全体を囲むように構築することにより、枠構造と既設基礎とが乖離することなく、安定した耐震性能を発揮できる。
【００２２】
［基礎水平変位抑止枠構造の断面形状］
以上述べたように、基礎水平変位抑止枠構造１０としてその作用を十分発揮させるためには、基礎水平変位抑止枠構造１０としての鉛直荷重を十分大きくすることと、その底面と地盤面との間で十分大きな底面摩擦を確保することが重要である。図４各図は、基礎水平変位抑止枠構造の断面形状として、想定される各種断面形状を示した断面図である。図１で示したような擁壁構造１１の断面（図４（ａ））では、擁壁構造１１の重量と底版１３上の埋戻し土１５の土被り重量の和が鉛直荷重となり、摩擦係数μを考慮して底面摩擦が決定される。
【００２３】
このとき基礎水平変位抑止枠構造として十分な鉛直荷重を得るためには、たとえば図４（ｂ）に示したような矩形断面形状の中実重量構造１８とすることが好ましい。この場合にも中実重量構造構造１８は、その内側面が絶縁層２０を介してフーチング３の外周面を囲むように構築されている。この中実重量構造１８は、自重が擁壁構造１１の重量と底版１３上の埋戻し土１５の土被り重量の和より大きくなるので、中実重量構造１８の底面１８ａと地盤面との摩擦は、擁壁構造１１（図４（ａ））底版１３の底面１３ａと地盤面との摩擦より大きくなる。
【００２４】
また、既設杭構造物に対して、設置される基礎水平変位抑止枠構造の水平方向力の負担が十分見込まれるならば、図４（ｃ），（ｄ）に示したようなスラブ構造１９を基礎水平変位抑止枠構造１０として採用することもできる。この場合、図４（ｃ）に示したスラブ構造１９では、埋戻し土１５の重量との和により鉛直荷重が決定するが、スラブ構造１９の底面１９ａと地盤面との摩擦が十分とれることが明らかな場合には地表面位置にスラブ構造１９を設置し、スラブ構造１９のみによることも可能である（図４（ｄ））。このように、基礎水平変位抑止枠構造の断面形状は、地盤面との間の摩擦により得られる目標抵抗が満たされることを前提に、種々の断面形状、寸法とすることができる。
【００２５】
基礎水平変位抑止枠構造１０としての擁壁構造１１は、地震時に既設構造物から作用する水平方向力に対して地盤面に対して所定の摩擦抵抗を発揮し、既設フーチング３を囲む枠体構造として一様に剛体変位するような剛性を有する必要がある。そのため、上述したＬ型擁壁において立壁１２の剛性が不足するおそれがある場合には立壁１２の背面に控え壁１６を設けることが好ましい（図５（ａ））。また、十分な剛性を確保するためには、上方が開放された箱形断面１７とし、内部に埋戻し土１５を充填する断面形状とすることが好ましい。
【００２６】
［底面摩擦の増加、水平変位の拘束手段］
図６各図は基礎水平変位抑止枠構造１０の底面摩擦の増加を図るための構成を示している。図６（ａ）は基礎水平変位抑止枠構造１０の一実施の形態としての擁壁構造１１において、その底版１３下の地盤面に割栗石３０を敷設し、底版１３との摩擦増加を図った例を示している。図６（ｂ）は、擁壁構造１１の底版１３との境界地盤に地盤改良層３１を設け、底版１３の底面にせん断キーとしての突起１３ｂを形成して地盤面に対するせん断抵抗を増加させるようにした例を示している。上述の構成により底面摩擦の増加を図ることにより、既設フーチング３の杭２の水平抵抗負担分を大幅に低減することができる。また、地震時に既設フーチング３を介して擁壁構造１１に加わる水平方向力による基礎水平変位抑止枠構造１０の変位を積極的に拘束する手段として、図７各図に示した構成を採用することもできる。すなわち、図７（ａ）は擁壁構造１１の底版１３下に短杭３２を打設し、短杭の杭頭を底版１３に固定した構造を示している。この場合、短杭３２が鉛直荷重を支持して底面摩擦が減少しないように、杭周面に摩擦低減処理を行うことが好ましい。図７（ｂ）は比較的低い立壁１２を有する擁壁構造１１とし、底版１３からその下部の地盤にかけてアンカーボルト３３を所定の傾角で打設し、各アンカーボルト３３に水平方向分力を負担させるようにした例を示している。なお、地震力作用時には、擁壁構造１１から外周に向けて打設されたアンカーボルト３３のうち、引張材として作用する方向に位置するアンカーボルト３３が有効に機能する。
【００２７】
図８は、既設フーチング３と擁壁構造１１との間に形成される絶縁層２０の変形例を示している。以上の説明では絶縁層２０には変形性能の高い絶縁材料が充填されるとしたが、この既設フーチング３と擁壁構造１１との離隔を十分にとり、その隙間部分に砕石２１を密に充填し、水平方向に関しては押しつぶされる砕石２１間の噛み合うことにより水平方向力が伝達され、鉛直方向には所定のせん断面で砕石２１の噛合いが解放した状態で鉛直方向荷重の絶縁が達成される。
【００２８】
図９，図１０は基礎水平変位抑止枠構造１０の他の発明として、上述の擁壁構造１１に代えて既設フーチング３の外周を囲むように区画された範囲に改良体ブロック３５を造成し、この改良体ブロック３５で水平抵抗力を発揮させるようにした例を示している。すなわち、この基礎水平変位抑止枠構造１０では、既設フーチング３の外周を掘削せずに、既設フーチング３の外周を２重締切工のように、所定の深度まで鋼矢板３６，３７で包囲し、２重に囲まれた地盤内を地盤改良することで改良体ブロック３５が造成されている。この改良体ブロック３５の底面３５ａと原地盤の間の境界面で摩擦作用が発揮される。このとき図１０に示したように、既設フーチング３の側面に沿って打設される内側鋼矢板３６のフーチング接触面側には絶縁層２０として機能する樹脂被覆２２等を施し、鉛直方向の摩擦を低減することが好ましい。また既設フーチング３の周囲に薄い非改良層を残す方法も可能である。
【００２９】
［参考例１］
図１１は、参考例として地盤沈下の恐れがない場所で、擁壁構造１１の底面積を拡幅せずに底面摩擦を増加させるために、鉛直グラウンドアンカー３８を併用した施工例を示している。このとき、アンカー定着部３８ａは支持層５に到達するようにすることが好ましく、導入アンカー力を調整することにより、アンカー頭部３８ｂを支持する枠体構造３９の底面３９ａと地盤面との底面摩擦の適宜調整することができる。
【００３０】
［参考例２］
図１２，図１３は既設構造物が構築された敷地において、一部に本発明を適用することを想定した参考例を示している。両図は、構造物の一部が敷地境界等に隣接し、地下構造物の構築余裕がない場合を想定した基礎水平変位抑止枠構造１０の施工例を示している。図１３は図１２の平面図であるが、既設構造物のフーチングの一辺Ａが敷地境界Ｌに接しているため、一辺Ａでは擁壁構造１１の立壁１２のみが構築され、その分、他の擁壁構造１１の底版１３の底面積を増加させることにより、基礎水平変位抑止枠構造１０としての全底面積を確保している。
【００３１】
【発明の効果】
以上に述べたように、本発明によれば、比較的簡易に構築できる基礎水平変位抑止枠構造が地震時の水平方向力を十分負担することできるため、既設構造物の杭基礎に対して鉛直荷重の増加を生じさせることなく、地震時に既設杭に作用する水平力を低減させることのできるという効果を奏する。
【図面の簡単な説明】
【図１】本発明による杭基礎構造物の耐震補強構造の一実施の形態を示した斜視図。
【図２】本発明の杭基礎構造物の耐震補強構造の一例を示した正面図、平面図。
【図３】本発明の耐震補強構造の底面摩擦と既設杭の水平荷重の負担の関係を示したグラフ。
【図４】基礎水平変位抑止枠構造の断面形状例を示した部分横断面図。
【図５】基礎水平変位抑止枠構造の変形例を示した部分断面図。
【図６】絶縁層の変形例を示した部分断面図。
【図７】擁壁構造の底版の底面摩擦の増加方法について示した部分断面図。
【図８】擁壁構造の底版の底面摩擦の増加方法について示した部分断面図。
【図９】基礎水平変位抑止枠構造の変形例を示した部分断面図。
【図１０】図９に示した基礎水平変位抑止枠構造の平面図。
【図１１】基礎水平変位抑止枠構造の変形例（アンカー）を示した部分断面図。
【図１２】基礎水平変位抑止枠構造の変形例（境界隣接時）を示した部分断面図。
【図１３】図１２に示した基礎水平変位抑止枠構造及び敷地境界を併示した平面図。
【図１４】従来の耐震補強構造（増し杭方式）の一例を示した部分断面図。
【図１５】従来の耐震補強構造（連壁方式）の一例を示した部分断面図。
【図１６】従来の耐震補強構造（複合杭方式）の一例を示した部分断面図。
【符号の説明】
１既設構造物
２杭
３既設フーチング（基礎フーチング）
１０基礎水平変位抑止枠構造
１１擁壁構造
１２立壁
１３底版
１５埋戻し土
１８中実重量構造
１９スラブ構造
２０絶縁層
３５改良体ブロック[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a seismic reinforcement structure for a pile foundation structure, which reduces the horizontal force acting on an existing pile during an earthquake without causing an increase in vertical load on the pile foundation of an existing or new structure. The present invention relates to a seismic reinforcement structure for a pile foundation structure that can be made.
[0002]
[Prior art]
In the pile foundation structure of the viaduct pier, the structural design is performed so that sufficient strength and toughness can be secured against the initial structure weight and earthquake load, and the dimensions of the foundation footing, the pile diameter, the number, etc. Although the specifications have been determined, if the seismic design standards are revised more severely than before after operation, or if the set load increases due to the addition of superstructure, it is difficult to ensure the required seismic strength in the pile foundation structure. There is a case.
[0003]
In such a case, various seismic reinforcements are carried out on the existing structure foundation in addition to the existing structure. 14 to 16 are partial cross-sectional views showing an example of a conventional seismic reinforcement structure for a foundation structure. FIG. 14 shows an example of a seismic reinforcement structure with an additional pile structure in which the extension footing 51 is integrated so as to surround the outer periphery of the existing footing 50. In this increased pile structure, a new pile 53 having the same proof strength as that of the existing pile 52 is placed, and an additional footing 51 for fixing the pile head is provided with a shear bearing material 54 such as many anchor bars on the side of the existing footing 50. Are joined together. Thus, in addition to the existing portion, the new pile 53 and the integrally widened footings 50 and 51 bear a vertical load and a horizontal load during an earthquake.
[0004]
FIG. 15 shows an example of the seismic reinforcement structure in which the underground continuous wall 55 is formed in the underground part below the extension footing 51 so as to surround the pile head periphery of the existing pile 52. In this seismic reinforcement structure, as shown in the figure, the underground continuous wall 55 formed integrally with the extension footing 51 so as to surround the existing pile 52 bears the horizontal force acting during the earthquake, The action of the horizontal force on the pile head of the existing pile 52 located in the ground surrounded by the continuous wall 55 can be reduced.
[0005]
In these seismic reinforcement structural examples, the horizontal force acting on the structure is transmitted to the new pile and underground continuous wall, so the pile and underground continuous wall must be rigidly connected to the existing footing. It is necessary to integrate the extension footing of the widened portion with the existing footing via the like, and a complicated extension work is required. In addition, because the foundation plane is widened by extension footing, it may be subject to land restrictions. Furthermore, large construction machines are required for the construction of new piles and underground continuous walls, and appropriate construction may not be possible especially in places subject to aerial restrictions for construction, such as under a viaduct. Moreover, in the underground continuous wall shown in FIG. 15, since the underground continuous wall does not have a sufficient vertical support force in structure, the axial force of the existing pile increases by the weight of the seismic reinforcement work, and an excessive stress state is generated. There is also a problem that arises.
[0006]
On the other hand, a large-diameter ground improvement body 62 is formed around the existing footing 60 as an example of an earthquake-proof reinforcement structure having sufficient horizontal support force and vertical support force. By constructing composite piles with ready-made piles 63 installed on them, fixing the pile heads with the extension footings 61, and integrating the extension footings 61 with the existing footings 60, sufficient support in the horizontal and vertical directions Has been proposed (see FIG. 16, for example, Patent Document 1).
[0007]
[Patent Document 1]
JP 2002-188157 A (described on page 4)
[0008]
[Problems to be solved by the invention]
By the way, as shown in FIG. 16, the seismic reinforcement structure disclosed in the above-mentioned prior art document information places a ready-made pile in a large-diameter improved body constructed by a high-pressure jet stirring method on the outer periphery of an existing footing. Thus, since the vertical support force of the ready-made pile is borne by the improved body, the vertical support force can be borne without causing the new pile to reach the support layer. For this reason, in order to fix the improved body head and the pre-made pile head, it is necessary to construct an extension footing having a sufficiently high rigidity integrally with the existing footing. A number of construction steps are required to construct each member having an earthquake-proof reinforcement structure in which an improved body, an existing pile, and an extension footing that are constructed around an existing footing are integrated, and further to integrate them. In addition, there may be cases in which construction cannot be performed under an overpass or the like because the length of a ready-made pile is limited.
[0009]
Accordingly, an object of the present invention is to solve the problems of the conventional technology described above, and a pile foundation structure capable of reducing the burden of horizontal force during an earthquake acting on the pile foundation of an existing footing by a simple seismic reinforcement structure. The object is to provide a seismic reinforcement structure for objects.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a pile foundation in which a horizontal displacement restraining frame structure bearing a horizontal force acting on a pile foundation structure is constructed so as to surround the outer peripheral surface of the footing of the pile foundation structure. An anti-seismic reinforcement structure for a structure, wherein the horizontal displacement restraining frame structure is configured to insulate vertical out-of-plane shear force transmission in which a standing wall portion is formed at a boundary surface between the footing and the horizontal displacement restraining frame structure. It comprises a retaining wall structure constructed through an insulating layer, and resists horizontal force during an earthquake due to bottom surface friction between the bottom surface of the bottom plate and the ground surface constructed integrally with the standing wall portion.
[0011]
As another invention, the present invention provides an improved block body that bears an earthquake horizontal force acting on a pile foundation structure, up to a predetermined depth so as to surround the ground of the outer peripheral surface of the footing of the pile foundation structure. It is a seismic reinforcement structure of a pile foundation structure that is surrounded by a double steel sheet pile and is improved by improving the inside of the partitioned ground , wherein the improved block body is formed at the interface with the footing, It is constructed through an insulating layer that insulates transmission of vertical out-of-plane shear force, and resists horizontal force during earthquakes by friction between the bottom surface of the improved block body and the ground surface.
[0012]
At this time, it is preferable that the insulating layer is a resin coating applied to the footing side of a steel sheet pile placed on the boundary surface between the improved block body and the footing.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an earthquake-proof reinforcement structure for a pile foundation structure according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view showing a part of the seismic reinforcement structure of the present invention constructed on the outer periphery of the footing of the pier foundation as an existing structure, and FIG. 2 is a front view and a plan view of the same. In FIG. 1, the existing structure 1 fixes nine piles 2 (see FIG. 2B) placed at equal intervals in the vertical and horizontal directions and the pile heads of the piles 2 in this embodiment. The base footing (existing footing) 3 made of reinforced concrete having a rectangular shape in plan view, and the reinforced concrete column 4 erected integrally on the existing footing 3 are formed. And the earthquake-proof reinforcement structure is constructed surrounding the outer periphery of the foundation footing 3 of the existing structure 1. In the following description, the earthquake-proof reinforcement of the foundation footing 3 of the existing structure 1 is described as an example. However, it is effective to apply the earthquake-proof reinforcement structure of the present invention to the foundation footing of the new structure. Needless to say.
[0016]
As shown in FIG. 1, the seismic reinforcement structure includes a foundation horizontal displacement restraining frame structure 10 constructed so as to surround the outer periphery of the foundation footing 3 of the existing pile foundation structure 1 to be subjected to the earthquake reinforcement, and the foundation horizontal displacement. The insulating frame 20 is formed between the restraining frame structure 10 and the existing footing 3.
[0017]
A basic horizontal displacement restraining frame structure 10 according to the present embodiment includes a reinforced concrete retaining wall structure 11 having an L-shaped cross section as shown in FIGS. The front surface of the standing wall 12 faces the outer peripheral surface of the existing footing 3, the height of which is equal to the footing thickness, and has a predetermined bottom plate length. Further, it is provided so as to completely surround the outer peripheral surface of the existing footing 3. The height of the standing wall 12 and the length of the bottom slab 13 are appropriately set according to the target resistance value of the basic horizontal displacement restraining frame structure 10, and the cross-sectional shape thereof is determined. That is, when the foundation horizontal displacement suppression frame structure 10 is the retaining wall structure 11 as shown in FIG. 1, the height of the standing wall 12 and the bottom area of the bottom plate 13 are required in the seismic reinforcement structure. What is necessary is just to set suitably according to a horizontal resistance force. That is, when a large horizontal resistance force is required, the bottom area of the bottom plate 13 may be increased or the height of the standing wall 12 may be increased.
[0018]
The insulating layer 20 is formed on the entire surface between the front surface of the standing wall 12 and the side surface of the existing footing 3 of the basic horizontal displacement restraining frame structure 10 and insulates transmission of the vertical out-of-plane shear force between the two members. It is an element provided with the intention. Therefore, the weight of the foundation horizontal displacement restraining frame structure 10 is supported only by the bottom plate 13 and is not transmitted to the pile 2 of the existing structure 1. In this embodiment, the insulating layer 20 is composed of an asphalt filling layer, and this asphalt filling layer can be expected to have a deformability capable of completely absorbing the phase displacement between both members generated in the vertical direction. As an insulating material constituting the insulating layer 20, in addition to a bitumen filling material such as asphalt, various rubber materials having a sufficiently large shear deformation property, and elastic members such as a rubber elastomer are fixed to the side surface of the existing footing 3. Thus, the insulating layer 20 may be formed.
[0019]
As an example of a procedure for constructing the foundation horizontal displacement restraining frame structure 10 and the insulating layer 20, first, the ground around the existing footing 3 determined in consideration of the construction range of the bottom slab 13 of the foundation horizontal displacement restraining frame structure 10. Excavate within a predetermined range. At this time, it is preferable to secure an excavation space by applying earth retaining work or the like according to the ground condition. Next, the insulating layer 20 is applied to the outer peripheral surface of the existing footing 3. The construction of the insulating layer 20 is to construct a retaining wall structure 11 by providing a gap having a predetermined width (thickness) with the existing footing 3 depending on the difference in the insulating material, and then filling the gap with the insulating material. You can also. The retaining wall structure 11 may be an on-site reinforced concrete structure, or a precast concrete product may be carried in and the entire structure may be made into an integrated structure using PC steel or the like. Finally, the excavated soil is reused to backfill the back surface portion of the retaining wall structure 11 so that the backfill soil 15 and the retaining wall structure 11 are integrated to complete the foundation horizontal displacement restraining frame structure 10.
[0020]
Here, with reference to Fig.2 (a), the effect | action of the foundation horizontal displacement suppression frame structure 10 at the time of an earthquake is demonstrated. The basic horizontal displacement restraining frame structure 10 corresponds to a combination of the retaining wall structure 11 described above and the backfill soil 15 on the bottom plate 13 on the back surface thereof. That is, when a horizontal force acts on an existing structure during an earthquake, the standing wall 12 of the retaining wall structure 11 facing the side surface of the existing footing 3 is pressed. At this time, a predetermined frictional force is generated between the bottom surface of the bottom plate 13 of the retaining wall structure 11 and the ground, and the horizontal force borne by the pile 2 is reduced by this frictional force. That is, it becomes possible to bear the horizontal force that exceeds the proof strength of the existing pile 2, and the earthquake resistance of the existing pile foundation structure 1 is improved. The limit value of the friction force acting on the bottom surface of the retaining wall structure 11 as the foundation horizontal displacement restraining frame structure 10 is obtained by multiplying the sum of the weight of the retaining wall structure 11 and the weight of the backfill soil 15 by the friction coefficient in the sand ground. It becomes. In the viscous ground, it is determined by the smaller of the adhesion and frictional forces of the ground.
[0021]
FIG. 3 is an analysis result comparing the horizontal load borne by the bottom friction of the foundation horizontal displacement restraining frame structure 10 and the horizontal load borne by the existing footing pile in the above-described seismic reinforcement structure. As shown in the figure, since the bottom friction of the foundation horizontal displacement restraining frame structure 10 is generally exhibited with a small displacement compared to the existing pile, the horizontal force acting on the existing pile can be efficiently reduced. Further, by constructing the foundation horizontal displacement restraining frame structure 10 so as to surround the entire outer periphery of the existing footing 3, stable earthquake resistance performance can be exhibited without the frame structure and the existing foundation separating.
[0022]
[Cross-sectional shape of basic horizontal displacement restraint frame structure]
As described above, in order to sufficiently exert the action as the foundation horizontal displacement restraining frame structure 10, it is necessary to increase the vertical load as the foundation horizontal displacement restraining frame structure 10 sufficiently between the bottom surface and the ground surface. It is important to ensure a sufficiently large bottom friction. 4 is a cross-sectional view showing various assumed cross-sectional shapes as the cross-sectional shape of the basic horizontal displacement restraining frame structure. In the cross section of the retaining wall structure 11 as shown in FIG. 1 (FIG. 4A), the sum of the weight of the retaining wall structure 11 and the weight of the earth covering 15 of the backfill soil 15 on the bottom slab 13 is a vertical load, and the friction coefficient. The bottom friction is determined considering μ.
[0023]
At this time, in order to obtain a sufficient vertical load as the basic horizontal displacement restraining frame structure, for example, a solid weight structure 18 having a rectangular cross section as shown in FIG. 4B is preferable. Also in this case, the solid weight structure 18 is constructed such that the inner surface surrounds the outer peripheral surface of the footing 3 with the insulating layer 20 interposed therebetween. Since the solid weight structure 18 has its own weight larger than the sum of the weight of the retaining wall structure 11 and the covering weight of the backfill soil 15 on the bottom slab 13, the friction between the bottom surface 18a of the solid weight structure 18 and the ground surface. Is larger than the friction between the bottom surface 13a of the bottom slab 13 and the ground surface (FIG. 4 (a)).
[0024]
Moreover, if the load of the horizontal force of the foundation horizontal displacement suppression frame structure to be installed is expected sufficiently with respect to the existing pile structure, the slab structure 19 as shown in FIGS. It can also be employed as the basic horizontal displacement restraining frame structure 10. In this case, in the slab structure 19 shown in FIG. 4 (c), the vertical load is determined by the sum of the weight of the backfill soil 15, but the friction between the bottom surface 19a of the slab structure 19 and the ground surface may be sufficiently taken. If it is clear, it is possible to install the slab structure 19 at the ground surface position and use only the slab structure 19 (FIG. 4D). As described above, the cross-sectional shape of the basic horizontal displacement restraining frame structure can have various cross-sectional shapes and dimensions on the assumption that the target resistance obtained by friction with the ground surface is satisfied.
[0025]
The retaining wall structure 11 as the foundation horizontal displacement restraining frame structure 10 exhibits a predetermined frictional resistance against the ground surface against a horizontal force acting from an existing structure during an earthquake, and surrounds the existing footing 3. It is necessary to have rigidity so that the rigid body is uniformly displaced. Therefore, when there is a possibility that the rigidity of the standing wall 12 is insufficient in the L-shaped retaining wall described above, it is preferable to provide the retaining wall 16 on the back surface of the standing wall 12 (FIG. 5A). Moreover, in order to ensure sufficient rigidity, it is preferable to set it as the box-shaped cross section 17 by which upper direction was open | released, and it is set as the cross-sectional shape with which the backfill soil 15 is filled inside.
[0026]
[Increasing bottom friction, restraining means of horizontal displacement]
Each figure of FIG. 6 has shown the structure for aiming at the increase in the bottom friction of the basic | foundation horizontal displacement suppression frame structure 10. FIG. FIG. 6A shows a retaining wall structure 11 as one embodiment of the basic horizontal displacement restraining frame structure 10, in which a cracked stone 30 is laid on the ground surface under the bottom slab 13 to increase friction with the bottom slab 13. An example is shown. In FIG. 6B, a ground improvement layer 31 is provided on the boundary ground between the retaining wall structure 11 and the bottom slab 13, and a protrusion 13b as a shear key is formed on the bottom surface of the bottom slab 13 so as to increase the shear resistance to the ground surface. An example is shown. By increasing the bottom friction with the above-described configuration, the horizontal resistance share of the pile 2 of the existing footing 3 can be significantly reduced. Further, as a means for positively restraining the displacement of the basic horizontal displacement restraining frame structure 10 due to the horizontal force applied to the retaining wall structure 11 through the existing footing 3 during an earthquake, the configuration shown in each figure of FIG. 7 is adopted. You can also. That is, FIG. 7A shows a structure in which a short pile 32 is driven under the bottom plate 13 of the retaining wall structure 11 and the pile head of the short pile is fixed to the bottom plate 13. In this case, it is preferable to perform a friction reducing process on the circumferential surface of the pile so that the short pile 32 supports the vertical load and the bottom friction is not reduced. FIG. 7B shows a retaining wall structure 11 having a relatively low standing wall 12, and anchor bolts 33 are driven at a predetermined inclination angle from the bottom plate 13 to the lower ground, and a horizontal component force is applied to each anchor bolt 33. The example which made it do is shown. In addition, the anchor bolt 33 located in the direction which acts as a tension | pulling material among the anchor bolts 33 driven toward the outer periphery from the retaining wall structure 11 functions effectively at the time of a seismic-force action.
[0027]
FIG. 8 shows a modification of the insulating layer 20 formed between the existing footing 3 and the retaining wall structure 11. In the above description, the insulating layer 20 is filled with an insulating material having a high deformation performance. However, the existing footing 3 and the retaining wall structure 11 are sufficiently separated, and the crushed stone 21 is tightly filled in the gap portion. In the horizontal direction, the horizontal force is transmitted by meshing between the crushed stones 21 to be crushed, and in the vertical direction, the insulation of the vertical load is achieved in a state where the mesh of the crushed stones 21 is released at a predetermined shear surface.
[0028]
9 and 10, as another invention of the basic horizontal displacement restraining frame structure 10, an improved body block 35 is formed in a range partitioned so as to surround the outer periphery of the existing footing 3 in place of the retaining wall structure 11 described above. An example is shown in which the horizontal resistance is exerted by the improved body block 35. That is, in this basic horizontal displacement restraining frame structure 10, without digging the outer periphery of the existing footing 3, the outer periphery of the existing footing 3 is surrounded by the steel sheet piles 36 and 37 to a predetermined depth as in a double cut-off work, The improved body block 35 is formed by improving the ground in the ground surrounded by double layers. A frictional action is exhibited at the boundary surface between the bottom surface 35a of the improved body block 35 and the original ground. At this time, as shown in FIG. 10, a resin coating 22 or the like that functions as the insulating layer 20 is applied to the footing contact surface side of the inner steel sheet pile 36 that is driven along the side surface of the existing footing 3, and vertical friction is achieved. Is preferably reduced. A method of leaving a thin non-improved layer around the existing footing 3 is also possible.
[0029]
[Reference Example 1]
FIG. 11 shows a construction example in which a vertical ground anchor 38 is used in combination to increase bottom friction without widening the bottom area of the retaining wall structure 11 in a place where there is no fear of ground subsidence as a reference example . At this time, the anchor fixing portion 38a preferably reaches the support layer 5, and the bottom surface 39a of the frame structure 39 supporting the anchor head 38b and the bottom surface of the ground surface are adjusted by adjusting the introductory anchor force. Friction can be adjusted as appropriate.
[0030]
[Reference Example 2]
12 and 13 show reference examples assuming that the present invention is applied to a part of a site where an existing structure is constructed . Both figures show a construction example of the foundation horizontal displacement restraining frame structure 10 assuming that a part of the structure is adjacent to the site boundary and the like and there is no room for construction of the underground structure. FIG. 13 is a plan view of FIG. 12. However, since one side A of the footing of the existing structure is in contact with the site boundary L, only the standing wall 12 of the retaining wall structure 11 is constructed on one side A. By increasing the bottom area of the bottom plate 13 of the retaining wall structure 11, the entire bottom area as the basic horizontal displacement restraining frame structure 10 is secured.
[0031]
【The invention's effect】
As described above, according to the present invention, the foundation horizontal displacement restraining frame structure that can be constructed relatively easily can sufficiently bear the horizontal force at the time of an earthquake. There is an effect that the horizontal force acting on the existing pile at the time of an earthquake can be reduced without causing an increase in load.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of a seismic reinforcement structure for a pile foundation structure according to the present invention.
FIG. 2 is a front view and a plan view showing an example of a seismic reinforcement structure for a pile foundation structure of the present invention.
FIG. 3 is a graph showing the relationship between the bottom friction of the seismic reinforcement structure of the present invention and the horizontal load of the existing pile.
FIG. 4 is a partial cross-sectional view showing an example of a cross-sectional shape of a basic horizontal displacement restraining frame structure.
FIG. 5 is a partial cross-sectional view showing a modified example of the basic horizontal displacement restraining frame structure.
FIG. 6 is a partial cross-sectional view illustrating a modified example of an insulating layer.
FIG. 7 is a partial cross-sectional view showing a method for increasing bottom friction of a bottom plate having a retaining wall structure.
FIG. 8 is a partial cross-sectional view showing a method for increasing bottom friction of a bottom plate having a retaining wall structure.
FIG. 9 is a partial sectional view showing a modification of the basic horizontal displacement restraining frame structure.
10 is a plan view of the basic horizontal displacement restraining frame structure shown in FIG. 9. FIG.
FIG. 11 is a partial cross-sectional view showing a modified example (anchor) of the basic horizontal displacement restraining frame structure.
FIG. 12 is a partial cross-sectional view showing a modified example (when adjacent to the boundary) of the basic horizontal displacement restraining frame structure.
13 is a plan view illustrating the basic horizontal displacement restraining frame structure and the site boundary shown in FIG.
FIG. 14 is a partial cross-sectional view showing an example of a conventional seismic reinforcement structure (additional pile method).
FIG. 15 is a partial sectional view showing an example of a conventional seismic reinforcement structure (continuous wall system).
FIG. 16 is a partial sectional view showing an example of a conventional seismic reinforcement structure (composite pile method).
[Explanation of symbols]
1 Existing structure 2 Pile 3 Existing footing (foundation footing)
DESCRIPTION OF SYMBOLS 10 Base horizontal displacement suppression frame structure 11 Retaining wall structure 12 Standing wall 13 Bottom plate 15 Backfill soil 18 Solid weight structure 19 Slab structure 20 Insulating layer 35 Improved body block

Claims

An anti-seismic reinforcement structure for a pile foundation structure constructed so as to surround the outer peripheral surface of the footing of the pile foundation structure, a horizontal displacement restraining frame structure that bears a horizontal force during an earthquake acting on the pile foundation structure, The horizontal displacement restraining frame structure is a retaining wall that is constructed through an insulating layer that insulates transmission of vertical out-of-plane shear force, with a standing wall portion formed at the boundary surface between the footing and the horizontal displacement restraining frame structure. An anti- seismic reinforcement structure for a pile foundation structure comprising a structure and resisting a horizontal force during an earthquake due to a bottom friction between a bottom surface of a bottom plate and a ground surface which are integrally constructed with the standing wall portion .

An improved block body that bears an earthquake horizontal force acting on a pile foundation structure is surrounded by a double steel sheet pile up to a predetermined depth so as to surround the ground of the outer peripheral surface of the footing of the pile foundation structure, It is a seismic strengthening structure of pile foundation structure created by improving the ground inside the formed ground, and the improved block body transmits vertical out-of-plane shear force formed at the interface with the footing. An anti-seismic reinforcement structure for a pile foundation structure constructed through an insulating layer that insulates and resists horizontal force during an earthquake due to friction between the bottom surface of the improved block body and the ground surface.

The pile foundation structure according to claim 2, wherein the insulating layer is made of a resin coating applied to the footing side of a steel sheet pile placed on the boundary surface between the improved block body and the footing . Seismic reinforcement structure.