JP3765000B2 - Ground improvement foundation method for soft ground. - Google Patents

Ground improvement foundation method for soft ground. Download PDF

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JP3765000B2
JP3765000B2 JP05855298A JP5855298A JP3765000B2 JP 3765000 B2 JP3765000 B2 JP 3765000B2 JP 05855298 A JP05855298 A JP 05855298A JP 5855298 A JP5855298 A JP 5855298A JP 3765000 B2 JP3765000 B2 JP 3765000B2
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foundation
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ground improvement
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JPH11256563A (en
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清 山下
芳雄 平井
毅 山田
正昭 加倉井
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Takenaka Corp
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Description

【０００１】
【発明の属する技術分野】
この発明は、広域の地盤沈下を生ずるような未圧密状態の粘性土、又は構造物の荷重により過大な圧密沈下を発生する正規圧密状態ないしそれに近い状態にある軟弱な粘性土が厚く堆積し、堅固な支持層が深い地盤条件（以下、この条件を前提として軟弱地盤と称する。）の下で或る程度重量が大きい構造物を構築するにあたり、地盤沈下や地震等に対して安全性が高い地盤改良基礎工法の技術分野に属する。
【０００２】
【従来の技術】
従来、構造物の基礎は、杭を使用せずに荷重を基礎版から直接地盤へ伝える直接基礎と、杭を使用した杭打ち基礎に大別され、両者の併用型も知られている。軟弱地盤における直接基礎の一態様として構造物直下の地盤を改良した地盤改良基礎を採用することも公知に属する（例えば特開昭６１ー１５１３２６号公報の第４図、又は本願の図６を参照）。
【０００３】
更に具体的に説明すると、特開平８ー４９２４５号公報には、杭打ち基礎であって、杭の複数本を包含する地盤改良体を液状化発生のおそれがある地層よりも深く造成した構成の液状化抑止基礎構造が記載されている。
特開昭６１ー１５１３２６号公報には、フローティング工法であって、不同沈下を防止するために摩擦杭を造成し、該摩擦杭の上端に設けたヨークから地中梁を吊る不同沈下修正方法が記載されている。
【０００４】
特許第２６４５８９９号公報には、液状化する可能性がある地盤上に建てる構造物の杭打ち基礎工法であって、表層地盤中に平面形状が格子状の難透水性壁構造体を地盤改良体として造成し、前記格子の中に支持層に届く支持杭を構築した高水平耐力杭基礎工法が記載されている。
【０００５】
【本発明が解決しようとする課題】
軟弱地盤上に構造物を構築する場合には、軽微な構造物を除いて、通常は支持杭基礎が採用される。しかし、支持層の深さが地下５０ｍを超えるような場合には、支持杭が長くなることに起因する工事費の増大が大きな問題になる。また、広域の地盤沈下を無視できない場合には、負の摩擦力に対処するために、より大径の杭を採用するか、杭本数を増やすか、負の摩擦力低減対策を施した杭を採用する等々の対処が必要となり、一層のコストアップとなる。
【０００６】
杭を使用しない基礎工法としては、構造物の重量に見合う重量の土を掘削して構造物重量とバランスさせるフローティング基礎が採用される。しかし、構造物重量が大きいと掘削深さを大きくする必要があるから、地下が深い建物以外には適用性に乏しい。
重量が或る程度まで大きい構造物の構築においては、図６のように構造物２の直下地盤を改良して地盤改良基礎１を造成し、根入れ深さＨによる排土重量を考慮して直接基礎としての支持力を確保する。その上で、過大な圧密沈下に伴う不同沈下に対しては、構造物２とベース３（建物基礎）との間にジャッキアップ装置４を設置して対処する直接基礎工法が実施されている。しかし、この直接基礎形式では、構造物２とベース３との間にジャッキアップ装置４の保守、点検用の空間５を確保しなければならず、この空間５を確保する為の地下躯体の構築にかなりな費用がかかる。図６の地盤１５は表層が埋土層で、その下に粘土層７が在り、更に深い位置に砂礫層（支持層）６が在る場合を示している。
【０００７】
同様な既往技術として、図７Ａに例示したように支持層６が地下２０ｍ〜３０ｍ程度に浅い地盤の場合には、同支持層６に到達する地盤改良基礎１を造成する。逆に図７Ｂに例示したように支持層６が地下５０ｍ以上も深い地盤の場合には、支持層６には届かないが、有害な不同沈下に対する抵抗力を十分に発揮する深さまで地盤改良した地盤改良基礎１を造成する直接基礎工法が実施されている。
【０００８】
しかし、地盤改良基礎１の場合には、不同沈下により地盤改良体の内部に過大なせん断応力、引張応力が発生し、同地盤改良体に亀裂が生じ、更には地震時の付加応力により地盤改良体を破壊に至らしめるおそれもある。よって，図７Ａの場合は例外として、図７Ｂのように支持層６が深い条件下では、地盤改良基礎１は、構造物２の鉛直荷重及び水平力を負担し支持する働きに加えて、不同沈下を防ぐ働きの分を加算した深さまでの地盤改良を要求される。よって、施工費が増大し工期が長引く問題がある。
【０００９】
直接基礎形式で支持できる構造物２の荷重は不同沈下量からきまり、その値は通常地盤の許容支持力よりもかなり小さい値となる。よって或る程度重量が大きい構造物の構築は難しいという問題もある。
従って、本発明の目的は、図７Ｂのように支持層が深い軟弱地盤上に構造物を構築するにあたり地盤改良基礎を採用すること、その場合に地盤沈下や地震等に対する安全性が高く、しかも地盤改良基礎を割合に浅く安価に短工期で施工できる地盤改良基礎工法を提供することである。
【００１０】
本発明の異なる目的は、地盤改良基礎の不同沈下を防ぐ杭を補完的に採用した杭併用型の地盤改良基礎工法を提供することである。
【００１１】
【課題を解決するための手段】
上記の課題を解決するための手段として、請求項１記載の発明に係る軟弱地盤における地盤改良基礎工法は、
支持層６が深い軟弱地盤１５上に構築される構造物２の直接基礎工法において、
構造物直下の地盤を根入れ深さＨまで掘削し、更にその直下地盤を構造物２の鉛直荷重及び水平力を負担し支持する強度及び規模で改良した地盤改良基礎１を造成し、構造物２の基礎スラブ２ａを前記根入れ深さＨを底面とするフローティング基礎として前記地盤改良基礎１との境界面を一体化して構築すること、
構造物２の前記根入れ深さＨに基づく排土重量を上回る構造物２の荷重を地盤に伝達させ前記地盤改良基礎１の沈下を防止する荷重補完用の杭体１０を、前記地盤改良基礎１の範囲内に、杭頭部を前記構造物２の基礎スラブ２ａと結合して造成し併用することをそれぞれ特徴とする。
【００１２】
【発明の実施の形態及び実施例】
請求項１に記載した発明に係る軟弱地盤における地盤改良基礎工法は、軟弱地盤１５の上に構築される構造物の直接基礎工法（フローティング基礎工法）として実施される。
具体的には、図１及び図２に例示したように、構造物２の直下地盤を改良した地盤改良基礎１を、構造物２の鉛直荷重及び水平力を負担し支持する強度及び規模で造成する。構造物２の根入れ深さＨを基礎底面とするフローティング基礎として実施される。前記フローティング基礎の底面下に例えば深層混合処理工法などにより固結状態の地盤改良基礎（地盤改良体）１を造成する。この地盤改良基礎１の平面的な形状、大きさ、垂直方向の断面積（改良深さ）などは次のように条件づける。
【００１３】
地盤改良基礎１の平面形状と大きさは、構造物２の全荷重を支持地盤（支持土層）へ伝達するのに十分な大きさ、形状とする。通例、構造物２の平面形状と略相似形状で少し大きいものとなる。地盤改良基礎１の垂直断面積とその下端深さは、前記平面積の大きさを考慮しつつ、構造物２の荷重に対して、軟弱地盤１５の許容支持力が上回る下端深さとする。
【００１４】
次に、この地盤改良基礎１の圧密沈下の原因となる、フローティング基礎の根入れ深さＨに基づく排土重量を上回る構造物２の荷重は、荷重補完用に設けた杭群１０を通じて地盤に伝達させる。図１では杭群１０を圧密層１１を貫通してその下の非圧密層１２に届く深さまで構築した実施例を示している。図２は非圧密層がない場合で、支持層６には届かないものの、補完するべき荷重を伝達可能であるように杭群１０を十分に深く（長く）構築した例を示している。各杭１０の杭頭部は基礎スラブ２ａと結合する。
【００１５】
杭群１０を施工するための準備として、地盤改良基礎１の改良施工に際しては同地盤改良基礎１内部の杭１０を打設するべき位置に、予め杭１０の外径よりも少し大径で孔状の未改良部を残しておき、杭用孔の掘削を容易ならしめる。杭１０は、地盤改良基礎１の範囲内において、同地盤改良基礎１に圧密沈下（不同沈下）の発生が懸念される場所へ集中的に配置してその働きの効率化を図ることが有益であり、杭の設計、施工に自在性がある。
上述のように構成して、構造物２の荷重のうち根入れ深さＨの排土重量に相当する荷重は、フローティング基礎の基礎スラブ２ａから地盤改良基礎１を通じて直接軟弱地盤１５へ伝達させる。そして、前記排土重量を超える荷重は、地盤改良基礎１に併用した杭群１０を通じて地盤へ伝達する。従って、構造物２の荷重が排土重量よりもかなり大きい場合でも、杭群１０の併用によって地盤に過大な圧密沈下は発生せず、沈下量は弾性変形の範囲、又はそれに近い値となるため、不同沈下も小さい値となる。その結果、地盤改良基礎１に発生するせん断応力、引張応力も小さくなり、ひび割れが生ずることもなく、地盤改良基礎１自体が持つ高い曲げ、せん断剛性を構造物２のフローティング基礎２ａの剛性の一部として長期的に利用できる。
【００１６】
従ってまた、図３に全体像を示し、図４Ａ，Ｂに部分詳細を示したように、地盤改良基礎１とフローティング基礎（基礎躯体）との境界面に、図４Ａに示したコッター１３、或いは図４Ｂに示したようなスタッド１４を設けて地盤改良基礎１とフローティング基礎とを一体化することにより、基礎は全体として地盤改良基礎１の下端を底面とする剛性の高いベタ基礎として挙動することになり、不同沈下がより小さく安定性が高い基礎を実現できる。
【００１７】
しかも、地盤改良基礎１とフローティング基礎２ａとの境界面が一体化されると、地震時の構造物２の慣性力に対しては、基礎に生ずる水平力及びある程度の大きさの引き抜き力についても、フローティング基礎２ａから地盤改良基礎１へ確実に伝達され、更に地盤改良基礎１の底面及び側面を介して地盤へ伝達させて処理出来る。
【００１８】
従って、杭群１０に関しては、基本的に水平抵抗を期待しなくてもよく、小径の杭でこと足りる。但し、地震時の地盤の水平変位により杭体が破壊しないように、杭材には靭性が大きいものを使用するなどして対処する。また、杭群１０は構造物２の重量の一部を地盤改良基礎１より下方の地盤へ伝達することのみを目的としているものであり、支持力としては考慮されない。それ故に通常の杭基礎の杭体に比較して安全率を小さく見込めるので、杭の仕様は支持杭に比して直径が小さく、長さも短いものでこと足りる。
【００１９】
広域の地盤沈下が生ずる場合には、本発明の基礎形式は地盤と共に沈下するので、支持杭基礎において不可避である、地表面からの構造物２の抜け上がりを防ぐこともでき、地盤面との段差を生じないから、機能面からも有利である。
本発明の基礎工法は、既往の地盤改良直接基礎、例えば図６又は図７Ｂに示す基礎工法と比較すると、より大きな重量の構造物２の基礎として適用できる。また、構造物２の荷重分布が極端に偏って不均一な場合には、その荷重分布に応じて杭群１０の配置を工夫することにより自在に対処でき適用範囲が広い。
【００２０】
そして、本発明の基礎工法は、支持層６が深い場合には、既往の地盤改良直接基礎に比較して工事費がはるかに安価で、経済的に短工期で施工することができる。
図５はモデルによる比較の計算例を示す。その前提条件として、支持層６は地下５０ｍの位置に在り、その上の表層はＮ値が０〜１程度の軟弱粘性地盤である。構造物２の平面形状は３０ｍ×６０ｍの長方形であり、その重量は１０トン／ｍ2の大きさである。根入れの深さＨが２．５ｍであるとき、既往の地盤改良直接基礎による場合には、左図のように地盤改良基礎１の深さは１０ｍにも達する。これが本発明の基礎工法によれば、地盤改良基礎１の深さは半分の５ｍで足りる。使用した杭１０は直径が６０ｃｍ、長さが３０ｍ、本数は６６本である。このような杭群１０の施工を含めても、本発明は２５〜４０％のコストダウンを達成出来る。
【００２１】
因みに、本発明の基礎工法が有利な条件は、次の通りである。
（１）軟弱地盤における構造物２の建設であること。
（２）支持層が地下４０ｍ〜５０ｍ以上に深いこと。杭打ち基礎に対しての有利性である。
（３）構造物２の根入れが２ｍ以上に深いこと。従って、構造物２に地下室がある場合は更に有利である。
（４）構造物２の重量が７〜８トン／ｍ２以上に大きいこと。
【００２２】
【発明の効果】
本発明に係る軟弱地盤における地盤改良基礎工法によれば、支持層が深い軟弱地盤上に地盤改良基礎を採用して構造物を構築する場合に、地盤沈下や地震等に対する安全性が高く、しかも地盤改良基礎を浅く安価に短工期で施工できる。
構造物の根入れが深く、構造物の重量が大きい場合の基礎工法として広く実施出来るのである。
【図面の簡単な説明】
【図１】本発明に係る地盤改良基礎工法の実施例を示した立面図である。
【図２】本発明に係る地盤改良基礎工法の異なる実施例を示した立面図である。
【図３】本発明に係る地盤改良基礎工法の異なる実施例を示した立面図である。
【図４】ＡとＢは本発明に係る地盤改良基礎工法におけるフローティング基礎と地盤改良基礎との一体化手段の例を示した部分拡大図である。
【図５】本発明に係る地盤改良基礎工法と既往の地盤改良直接基礎工法との費用見積もりの計算例のモデル図である。
【図６】従来の地盤改良基礎工法の例を示した立面図である。
【図７】ＡとＢは従来の地盤改良基礎工法の例を示した立面図である。
【符号の説明】
１５ 軟弱地盤
２ 構造物
１ 地盤改良基礎
１０ 杭[0001]
BACKGROUND OF THE INVENTION
This invention is a thick pile of unconsolidated viscous soil that causes land subsidence in a wide area, or normal compacted state that generates excessive consolidation subsidence due to the load of the structure or soft viscous soil in a state close thereto, Highly safe against ground subsidence, earthquakes, etc. when constructing a structure that is somewhat heavy under the ground conditions where the solid support layer is deep (hereinafter referred to as soft ground assuming this condition) It belongs to the technical field of foundation improvement foundation method.
[0002]
[Prior art]
Conventionally, the foundation of a structure is roughly divided into a direct foundation that transmits a load directly from the foundation plate to the ground without using a pile, and a pile foundation that uses a pile, and a combination type of both is also known. It is also known to employ a ground improvement foundation obtained by improving the ground directly under the structure as one aspect of the direct foundation in soft ground (see, for example, FIG. 4 of Japanese Patent Laid-Open No. 61-151326 or FIG. 6 of the present application). ).
[0003]
More specifically, Japanese Patent Application Laid-Open No. 8-49245 discloses a pile foundation and a ground improvement body including a plurality of piles, which is constructed deeper than a formation that may cause liquefaction. The liquefaction deterrent basic structure is described.
Japanese Patent Application Laid-Open No. 61-151326 discloses a floating construction method, in which a friction pile is formed to prevent uneven settlement, and a non-uniform settlement correction method in which an underground beam is hung from a yoke provided at the upper end of the friction pile. Are listed.
[0004]
Japanese Patent No. 2645899 discloses a pile driving foundation method for a structure to be built on the ground that may be liquefied, and a ground improvement body having a lattice-shaped non-permeable wall structure in the surface layer ground. As described above, a high horizontal strength pile foundation method is described in which a support pile that reaches the support layer is constructed in the lattice.
[0005]
[Problems to be solved by the present invention]
When constructing structures on soft ground, support pile foundations are usually adopted except for minor structures. However, when the depth of the support layer exceeds 50 m underground, an increase in the construction cost due to the longer support pile becomes a big problem. If land subsidence in a wide area cannot be ignored, a pile with a larger diameter, increased number of piles, or a measure with negative frictional force reduction measures should be used to deal with negative frictional forces. It is necessary to take measures such as hiring, which further increases the cost.
[0006]
As a foundation method that does not use piles, a floating foundation that excavates soil with a weight that matches the weight of the structure and balances it with the weight of the structure is adopted. However, if the structure weight is large, it is necessary to increase the excavation depth.
In the construction of a structure whose weight is large to a certain extent, the foundation foundation 1 is created by improving the direct foundation board of the structure 2 as shown in FIG. Secure support as a direct basis. On top of that, a direct foundation method is implemented in which a jack-up device 4 is installed between the structure 2 and the base 3 (building foundation) to deal with the uneven settlement due to excessive consolidation settlement. However, in this direct foundation type, a space 5 for maintenance and inspection of the jack-up device 4 must be secured between the structure 2 and the base 3, and construction of an underground structure for securing this space 5 is required. It costs a lot of money. The ground 15 in FIG. 6 shows a case where the surface layer is a buried soil layer, the clay layer 7 exists below it, and the gravel layer (support layer) 6 exists at a deeper position.
[0007]
As a similar past technique, as illustrated in FIG. 7A, when the support layer 6 is a ground having a shallow depth of about 20 m to 30 m, the ground improvement foundation 1 that reaches the support layer 6 is created. Conversely, as illustrated in FIG. 7B, in the case where the support layer 6 is deeper than 50 m underground, the support layer 6 does not reach, but the ground has been improved to a depth that sufficiently exhibits the resistance to harmful unsettled settlement. A direct foundation method for constructing the ground improvement foundation 1 is being implemented.
[0008]
However, in the case of the ground improvement foundation 1, excessive shear stress and tensile stress are generated inside the ground improvement body due to the unsettled settlement, the ground improvement body is cracked, and further, the ground improvement is caused by the additional stress during the earthquake. There is also a risk of destroying the body. Therefore, in the case of FIG. 7A, under the condition that the support layer 6 is deep as shown in FIG. 7B, the ground improvement foundation 1 is not limited in addition to the function of bearing and supporting the vertical load and horizontal force of the structure 2. It is required to improve the ground to a depth that adds the amount of work to prevent settlement. Therefore, there is a problem that the construction cost increases and the construction period is prolonged.
[0009]
The load of the structure 2 that can be directly supported by the foundation type is determined by the amount of uneven settlement, and its value is considerably smaller than the allowable bearing capacity of the normal ground. Therefore, there is also a problem that it is difficult to construct a structure that is somewhat heavy.
Therefore, the object of the present invention is to adopt a ground improvement foundation when constructing a structure on soft ground with a deep support layer as shown in FIG. 7B, and in that case, it is highly safe against ground subsidence and earthquakes. The purpose is to provide a ground improvement foundation method that can be constructed in a short period of time at a low cost with a shallow ground improvement foundation.
[0010]
Another object of the present invention is to provide a pile improvement type ground improvement foundation method that complementarily employs a pile that prevents uneven settlement of the ground improvement foundation.
[0011]
[Means for Solving the Problems]
As means for solving the above problems, the ground improvement foundation method in the soft ground according to the invention of claim 1 is:
In the direct foundation method of the structure 2 in which the support layer 6 is constructed on the deep soft ground 15,
Excavate the ground directly under the structure to a depth of depth H, and further create a ground improvement foundation 1 that is improved in strength and scale to support and support the vertical load and horizontal force of the structure 2 Constructing the foundation slab 2a of 2 as a floating foundation having the root depth H as the bottom and integrating the boundary surface with the ground improvement foundation 1 ;
The pile body 10 for loading supplement to prevent subsidence of the load of the structure 2 above the earth removal weight based on the embedment depth H of the structure 2 is transmitted to the ground the soil improvement foundation 1, the ground improvement foundation 1 is characterized in that a pile head is combined with the foundation slab 2a of the structure 2 and used together.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The ground improvement foundation method for soft ground according to the first aspect of the present invention is implemented as a direct foundation method (floating foundation method) for a structure constructed on the soft ground 15.
Specifically, as illustrated in FIG. 1 and FIG. 2, the ground improvement foundation 1 improved from the direct foundation board of the structure 2 is formed with a strength and scale that bears and supports the vertical load and horizontal force of the structure 2. To do. This is implemented as a floating foundation having a depth of penetration H of the structure 2 as a base bottom surface. A ground improvement foundation (ground improvement body) 1 in a solidified state is formed under the bottom surface of the floating foundation by, for example, a deep mixing treatment method. The planar shape, size, vertical cross-sectional area (improvement depth), etc. of the ground improvement foundation 1 are conditioned as follows.
[0013]
The planar shape and size of the ground improvement foundation 1 are set to a size and shape sufficient to transmit the entire load of the structure 2 to the supporting ground (supporting soil layer). Usually, the structure 2 is a little larger than the planar shape of the structure 2. The vertical cross-sectional area and the lower end depth of the ground improvement foundation 1 are set to a lower end depth that exceeds the allowable supporting force of the soft ground 15 with respect to the load of the structure 2 in consideration of the size of the flat area.
[0014]
Then, causing the ground improvement foundation 1 of consolidation settlement, the load of the structure 2 above the earth removal weight, based on the embedment depth H of the floating foundation, the ground through pile group 10 provided for loading complement Communicate. FIG. 1 shows an embodiment in which the pile group 10 is constructed to a depth reaching the non-consolidated layer 12 through the consolidated layer 11. FIG. 2 shows an example in which the pile group 10 is constructed sufficiently deep (long) so that a load to be complemented can be transmitted, although it does not reach the support layer 6 in the case where there is no non-consolidated layer. The pile head of each pile 10 is combined with the foundation slab 2a.
[0015]
As a preparation for constructing the pile group 10, a hole having a slightly larger diameter than the outer diameter of the pile 10 in advance at the position where the pile 10 inside the ground improvement foundation 1 should be placed when the ground improvement foundation 1 is improved. The unmodified part of the shape is left and the excavation of the hole for the pile is made easy. Within the range of the ground improvement foundation 1, the piles 10 are beneficially arranged on the ground improvement foundation 1 at a place where the occurrence of consolidation subsidence (dissimilar subsidence) is a concern, and it is beneficial to improve the efficiency of the work. Yes, there is flexibility in the design and construction of piles.
With the configuration described above, the load corresponding to the soil removal weight of the penetration depth H among the loads of the structure 2 is directly transmitted to the soft ground 15 from the foundation slab 2a of the floating foundation through the ground improvement foundation 1. And the load exceeding the said earth removal weight is transmitted to the ground through the pile group 10 used together with the ground improvement foundation 1. Therefore, even when the load of the structure 2 is considerably larger than the weight of the soil, excessive consolidation settlement does not occur in the ground by the combined use of the pile group 10, and the amount of settlement becomes a range of elastic deformation or a value close thereto. , Non-uniform settlement is also a small value. As a result, the shear stress and tensile stress generated in the ground improvement foundation 1 are also reduced, and cracks are not generated. The high bending and shear rigidity of the ground improvement foundation 1 itself is one of the rigidity of the floating foundation 2a of the structure 2. Can be used in the long term as a department.
[0016]
Therefore, as shown in FIG. 3 and the partial details in FIGS. 4A and B, the cotter 13 shown in FIG. 4A or the boundary surface between the ground improvement foundation 1 and the floating foundation (foundation) By providing the stud 14 as shown in FIG. 4B and integrating the ground improvement foundation 1 and the floating foundation, the foundation as a whole behaves as a solid base having high rigidity with the lower end of the ground improvement foundation 1 as the bottom surface. Therefore, it is possible to realize a foundation with less uneven settlement and high stability.
[0017]
In addition, when the boundary surface between the ground improvement foundation 1 and the floating foundation 2a is integrated, the horizontal force generated on the foundation and the pulling force of a certain size are also applied to the inertial force of the structure 2 during the earthquake. The ground can be reliably transmitted from the floating foundation 2a to the ground improvement foundation 1, and further transmitted to the ground via the bottom and side surfaces of the ground improvement foundation 1.
[0018]
Therefore, with respect to the pile group 10, it is not necessary to basically expect horizontal resistance, and a small-diameter pile is sufficient. However, in order to prevent the pile body from being destroyed due to the horizontal displacement of the ground during an earthquake, it is necessary to use a pile material with high toughness. Moreover, the pile group 10 is only for the purpose of transmitting a part of the weight of the structure 2 to the ground below the ground improvement foundation 1, and is not considered as a supporting force. Therefore, since the safety factor can be expected to be smaller than the pile body of a normal pile foundation, it is sufficient that the specification of the pile is smaller in diameter and shorter than the support pile.
[0019]
When a wide area of land subsidence occurs, the foundation type of the present invention subsidizes with the ground, so that it is inevitable in the support pile foundation, it is possible to prevent the structure 2 from coming off from the ground surface. Since no step is produced, it is advantageous from the functional aspect.
The foundation construction method of the present invention can be applied as a foundation for a structure 2 having a larger weight as compared with a conventional ground improvement direct foundation, for example, the foundation construction method shown in FIG. 6 or 7B . Moreover, when the load distribution of the structure 2 is extremely biased and uneven, it can be dealt with freely by devising the arrangement of the pile group 10 according to the load distribution, and the application range is wide.
[0020]
And when the support layer 6 is deep, the foundation construction method of this invention can be constructed economically in a short construction period because the construction cost is much lower than that of the existing ground improvement direct foundation.
FIG. 5 shows a calculation example of comparison by model. As a precondition thereof, the support layer 6 is at a position of 50 m underground, and the upper surface layer is a soft viscous ground having an N value of about 0 to 1. The planar shape of the structure 2 is a 30 m × 60 m rectangle, and its weight is 10 ton / m 2 . When the depth H of the penetration is 2.5 m, the depth of the ground improvement foundation 1 reaches 10 m as shown in the left figure in the case of the existing ground improvement direct foundation. According to the foundation construction method of the present invention, the depth of the ground improvement foundation 1 is half, ie, 5 m. The used pile 10 has a diameter of 60 cm, a length of 30 m, and the number is 66. Even if construction of such a pile group 10 is included, the present invention can achieve a cost reduction of 25 to 40%.
[0021]
Incidentally, the conditions under which the foundation method of the present invention is advantageous are as follows.
(1) The construction of the structure 2 on soft ground.
(2) The support layer is deep 40 m to 50 m or more underground. This is an advantage over pile foundations.
(3) The depth of the structure 2 is deeper than 2 m. Therefore, it is further advantageous when the structure 2 has a basement.
(4) The weight of the structure 2 is as large as 7-8 ton / m 2 or more.
[0022]
【The invention's effect】
According to the ground improvement foundation method for soft ground according to the present invention, when a structure is constructed by using a ground improvement foundation on a soft ground with a deep support layer, safety against ground subsidence or earthquake is high, and The ground improvement foundation can be constructed shallowly and inexpensively in a short construction period.
It can be widely implemented as a foundation method when the structure is deeply embedded and the weight of the structure is large.
[Brief description of the drawings]
FIG. 1 is an elevational view showing an embodiment of a ground improvement foundation method according to the present invention.
FIG. 2 is an elevational view showing different embodiments of the ground improvement foundation method according to the present invention.
FIG. 3 is an elevational view showing different embodiments of the ground improvement foundation method according to the present invention.
FIGS. 4A and 4B are partially enlarged views showing examples of means for integrating a floating foundation and a ground improvement foundation in the ground improvement foundation construction method according to the present invention. FIGS.
FIG. 5 is a model diagram of a calculation example of cost estimation between the ground improvement foundation method and the existing ground improvement direct foundation method according to the present invention.
FIG. 6 is an elevation view showing an example of a conventional ground improvement foundation method.
FIGS. 7A and 7B are elevation views showing an example of a conventional ground improvement foundation method.
[Explanation of symbols]
15 Soft ground 2 Structure 1 Ground improvement foundation 10 Pile

Claims (1)

支持層が深い軟弱地盤上に構築される構造物の直接基礎工法において、
構造物直下の地盤を根入れ深さまで掘削し、更にその直下地盤を構造物の鉛直荷重及び水平力を負担し支持する強度及び規模で改良した地盤改良基礎を造成し、構造物の基礎スラブを前記根入れ深さを底面とするフローティング基礎として前記地盤改良基礎との境界面を一体化して構築すること、
構造物の前記根入れ深さに基づく排土重量を上回る構造物の荷重を地盤に伝達させ前記地盤改良基礎の沈下を防止する荷重補完用の杭体を、前記地盤改良基礎の範囲内に、杭頭部を前記構造物の基礎スラブと結合して造成し併用することをそれぞれ特徴とする、軟弱地盤における地盤改良基礎工法。In the direct foundation method for structures constructed on soft ground where the support layer is deep,
Excavate the ground directly under the structure to the depth of penetration, and then create a ground improvement foundation with improved strength and scale to support and support the vertical load and horizontal force of the structure. Constructing and integrating the boundary surface with the ground improvement foundation as a floating foundation having the base depth as the bottom ;
The pile body for loading complement the load of the structure above the earth removal weight based on the embedment depth of the structure is transmitted to the ground to prevent subsidence of the ground improvement basis, within the scope of the ground improvement foundation, A ground improvement foundation method in soft ground, characterized in that the pile head is combined with the foundation slab of the structure.
JP05855298A 1998-03-10 1998-03-10 Ground improvement foundation method for soft ground. Expired - Fee Related JP3765000B2 (en)

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