JP6711006B2 - Settling prevention structure for linear structures - Google Patents

Settling prevention structure for linear structures Download PDF

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JP6711006B2
JP6711006B2 JP2016033078A JP2016033078A JP6711006B2 JP 6711006 B2 JP6711006 B2 JP 6711006B2 JP 2016033078 A JP2016033078 A JP 2016033078A JP 2016033078 A JP2016033078 A JP 2016033078A JP 6711006 B2 JP6711006 B2 JP 6711006B2
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ground improvement
linear structure
upper ground
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秀樹 永井
秀樹 永井
大 永礼
大 永礼
俊一 樋口
俊一 樋口
一紀 加藤
一紀 加藤
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Obayashi Corp
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本発明は、液状化層を有する地盤の表層もしくは地表上に敷設された線状構造物の沈下抑止構造および線状構造物の沈下抑止構造の構築方法に関する。 TECHNICAL FIELD The present invention relates to a subsidence suppressing structure for a linear structure laid on the surface of the ground having a liquefaction layer or on the ground surface, and a method for constructing a subsidence suppressing structure for a linear structure.

従来より、液状化層を有する地盤上に構造物を構築する場合において、地震発生時に地盤の液状化現象が生じて構造物に有害な沈下が生じることを防止するべく、構造物直下の地盤改良が実施されている。 Conventionally, when constructing a structure on the ground that has a liquefaction layer, the ground improvement directly below the structure is prevented in order to prevent the liquefaction phenomenon of the ground from occurring and the harmful subsidence of the structure when an earthquake occurs. Is being implemented.

例えば、特許文献１には、拡径頭部を備えた固結体を上方地盤から液状化層を貫通して非液状化層まで到達させ、拡径頭部の上面にて建造物と上方地盤を支持することにより、噴砂現象を防止するとともに沈下を抑止する構成が開示されている。しかし、特許文献１では、例えば構造物が線状構造物である場合に、固結体をどのような構成のものとするのかについて、具体的な検討がなされていない。 For example, in Patent Document 1, a solid body having a diameter-expanding head is made to penetrate from the upper ground to the non-liquefied layer through the liquefaction layer, and the building and the upper ground are provided on the upper surface of the diameter-expansion head. It is disclosed that the structure supports the sand spray phenomenon and suppresses the settlement by supporting the. However, in Patent Document 1, for example, when the structure is a linear structure, no specific examination is made as to what kind of structure the solidified body has.

一般に、線状構造物を液状化層を有する地盤の表層もしくは地表上に構築する際には、線状構造物に大きな残留沈下や不等沈下が生じることのないよう、液状化層の層厚が薄い場合には、線状構造物下の全延長に対して浅層混合処理工法や中層混合処理工法等にてセメント系固化材を用いた地盤改良を施し、液状化対策を行っている。 Generally, when constructing a linear structure on the surface of the ground having a liquefaction layer or on the surface of the ground, the layer thickness of the liquefaction layer should be adjusted so that large residual settlement or uneven settlement does not occur in the linear structure. If the soil is thin, ground improvement using cement-based solidifying material is applied to the entire extension under the linear structure by shallow layer mixing treatment method or middle layer mixing treatment method, and liquefaction measures are taken.

一方で、液状化層の層厚が厚く深度約２０ｍ程度に至るような場合、同じく線状構造物下の全延長に対してセメント系固化材にて地盤改良を施すには高価な深層混合処理工法を採用せざるを得ず、多大な施工費を要することとなる。このため、例えば特許文献２で示すようなサンドコンパクションパイル工法を採用し、線状構造物下の全延長に対して地盤改良を施している。サンドコンパクションパイル工法は、地盤に対して強制的に砂杭を打設して柱状改良体を構築することにより、周辺地盤を締め固める工法であり、液状化防止に有効な工法である。 On the other hand, when the liquefaction layer is thick and reaches a depth of about 20 m, it is expensive to perform ground improvement with cement-based solidifying material for the entire extension under the linear structure, which is an expensive deep layer mixing process. There is no choice but to use the construction method, which requires a large construction cost. Therefore, for example, a sand compaction pile method as shown in Patent Document 2 is adopted, and the ground is improved for the entire extension under the linear structure. The sand compaction pile method is a method of compacting the surrounding ground by constructing a columnar improved body by forcibly placing sand piles on the ground and is an effective method for preventing liquefaction.

特開平８−３１１８６０号公報JP-A-8-31860 特開２００７−３０９０９１号公報JP, 2007-309091, A

しかし、地盤改良工法にサンドコンパクションパイル工法を採用すると、その効果を得るためには線状構造物直下の地盤だけでなく、その両側部の一定範囲の地盤にも地盤改良を施す必要が生じる。このため、敷地確保が煩雑であるとともに、経済性にも劣る。 However, if the sand compaction pile method is adopted as the ground improvement method, it is necessary to improve the ground not only directly under the linear structure but also within a certain range on both sides of the ground structure in order to obtain the effect. Therefore, securing the site is complicated and economically inferior.

本発明は、かかる課題に鑑みなされたものであって、その主な目的は、液状化層を有する地盤の表層もしくは地表上に構築する線状構造物の沈下を防止することが可能な、線状構造物の沈下抑止構造および線状構造物の沈下抑止構造の構築方法を提供することである。 The present invention has been made in view of the above problems, and its main purpose is to prevent the subsidence of a linear structure constructed on the surface or the surface of the ground having a liquefaction layer, It is an object of the present invention to provide a method for constructing a settlement suppressing structure for a linear structure and a settlement suppressing structure for a linear structure.

上記目的を達成するため、本発明の線状構造物の沈下抑止構造は、液状化層を有する地盤の表層もしくは地表上に敷設される線状構造物の沈下抑止構造であって、前記線状構造物を支持するセメント系固化材による上部地盤改良体と、該上部地盤改良体を支持するセメント系固化材による複数の地盤改良杭と、を備え、前記上部地盤改良体は、前記線状構造物の長さ方向に延在し、幅と比較して高さが同一もしくは大きい矩形状の断面を有する長尺体からなり、前記上部地盤改良体の断面の高さは、前記地盤改良杭の配置間隔と前記上部地盤改良体に作用する鉛直荷重とを設定したうえで、鉛直荷重に対して前記上部地盤改良体に生じる最大垂直応力度を算定し、最大垂直応力度と前記上部地盤改良体の材料の引張強度との関係から決定されており、前記地盤改良杭は、少なくとも杭先端部が前記液状化層より下方に位置する非液状化層に支持されることを特徴とする。また、本発明の線状構造物の沈下抑止構造は、液状化層を有する地盤の表層もしくは地表上に敷設される線状構造物の沈下抑止構造であって、前記線状構造物を支持するセメント系固化材による上部地盤改良体と、該上部地盤改良体を支持するセメント系固化材による複数の地盤改良杭と、を備え、前記上部地盤改良体は、前記線状構造物の長さ方向に延在し、幅と比較して高さが同一もしくは大きい矩形状の断面を有する長尺体からなり、前記地盤改良杭は、前記線状構造物の両側部近傍に等間隔配置または千鳥配置となるように設けられ、少なくとも杭先端部が前記液状化層より下方に位置する非液状化層に支持されることを特徴とする。さらに、本発明の線状構造物の沈下抑止構造は、前記上部地盤改良体と前記地盤改良杭に跨るように、ズレ止めが配置されることを特徴とする。 In order to achieve the above object, the subsidence prevention structure for a linear structure according to the present invention is a subsidence prevention structure for a linear structure laid on the surface of the ground having a liquefaction layer or on the ground surface, wherein the linear An upper ground improvement body made of a cement-based solidifying material for supporting a structure, and a plurality of ground improvement piles made of the cement-based solidifying material for supporting the upper ground improved body, wherein the upper ground improved body is the linear structure. Extending in the length direction of the object, consisting of an elongated body having a rectangular cross section whose height is the same as or larger than the width, the height of the cross section of the upper ground improvement body is After setting the arrangement interval and the vertical load that acts on the upper ground improvement body, calculate the maximum vertical stress degree that occurs in the upper ground improvement body with respect to the vertical load, the maximum vertical stress degree and the upper ground improvement body It is determined from the relationship with the tensile strength of the material, and at least the tip of the soil improvement pile is supported by the non-liquefaction layer located below the liquefaction layer. Further, the subsidence prevention structure for a linear structure according to the present invention is a subsidence prevention structure for a linear structure laid on the surface of the ground having a liquefaction layer or on the ground surface, and supports the linear structure. An upper ground improvement body made of cement-based solidifying material; and a plurality of ground improvement piles made of cement-based solidifying material supporting the upper ground improved body; The elongated ground having a rectangular cross-section extending to the same height as the width of the linear structure, and the ground improvement piles are arranged at equal intervals or in a staggered arrangement in the vicinity of both sides of the linear structure. It is characterized in that at least the tip of the pile is supported by the non-liquefied layer located below the liquefied layer. Further, the subsidence prevention structure for a linear structure according to the present invention is characterized in that a shift stopper is arranged so as to straddle the upper ground improvement body and the ground improvement pile.

上述する本発明の線状構造物の沈下抑止構造によれば、上部地盤改良体が非液状化層に支持された複数の地盤改良杭にて支持されることから、地震時に地盤の液状化現象が発生しても、上部地盤改良体に有害な沈下を生じることがない。このため、上部地盤改良体に支持される線状構造物は、地震時にも残留沈下や不等沈下を生じることなく常時の健全な状態を維持することが可能となる。 According to the subsidence prevention structure for a linear structure of the present invention described above, since the upper ground improvement body is supported by the plurality of ground improvement piles supported by the non-liquefaction layer, the ground liquefaction phenomenon during an earthquake Even if the occurrence occurs, harmful subsidence does not occur in the upper ground improvement body. Therefore, the linear structure supported by the upper ground improvement body can maintain a normal sound state without causing residual settlement or uneven settlement even during an earthquake.

また、上部地盤改良体は地盤改良杭にて支持される簡略な構造であるため、上部地盤改良体に作用する鉛直荷重が決まると、地盤改良杭の配置間隔によって上部地盤改良体の断面高さを設定できる。したがって、上部地盤改良体が破壊しない程度の断面高さを確保しつつ、地盤改良杭の配置間隔を大きく取ることにより、地盤改良杭の数量を減らすことができるため、地盤改良杭に深層混合処理工法を採用した際にも、コストを大幅に削減することが可能となる。 In addition, since the upper ground improvement body has a simple structure supported by the ground improvement piles, once the vertical load acting on the upper ground improvement body is determined, the cross-sectional height of the upper ground improvement body is determined by the arrangement interval of the ground improvement piles. Can be set. Therefore, it is possible to reduce the number of ground improvement piles by increasing the arrangement interval of the ground improvement piles while ensuring a cross-sectional height that does not destroy the upper ground improvement body. Even when the construction method is adopted, the cost can be significantly reduced.

さらに、上部地盤改良体と地盤改良杭は、セメント系固化材による地盤改良体を採用している。これにより、砂杭を採用する場合のように線状構造物の両側部に余改良部を設ける必要がないため、沈下抑止構造を無駄のないスリムな構造とすることが可能となる。 Furthermore, the upper ground improvement body and the ground improvement pile adopt the ground improvement body made of cement-based solidifying material. As a result, unlike the case where the sand pile is adopted, it is not necessary to provide extra improvement portions on both sides of the linear structure, and thus it is possible to make the settlement suppressing structure a lean and lean structure.

また、大規模地震が発生した際にも、地盤改良杭に対する上部地盤改良体の水平方向のズレを抑止し、より安全な構造とすることが可能となる。 Further , even when a large-scale earthquake occurs, it is possible to suppress the horizontal displacement of the upper ground improvement body with respect to the ground improvement pile, and to provide a safer structure.

そして、上部地盤改良体と地盤改良杭は、それぞれ地盤深度に適した異なる地盤改良工法より構築されるため、施工性を大幅に向上できるとともにコストを低減でき、沈下抑止構造を経済的に構築することが可能となる。 Since the upper ground improvement body and the ground improvement pile are constructed by different ground improvement methods suitable for the soil depth, respectively, the workability can be greatly improved, the cost can be reduced, and the subsidence prevention structure can be economically constructed. It becomes possible.

本発明によれば、地震発生時に液状化現象が生じる可能性を有する地盤に線状構造物を構築しても、経済的かつ無駄のない構造ながら、確実に線状構造物の有害な沈下を防止することが可能となる。 According to the present invention, even if a linear structure is constructed on the ground where a liquefaction phenomenon may occur when an earthquake occurs, it is possible to reliably prevent harmful subsidence of the linear structure while maintaining an economical and lean structure. It becomes possible to prevent it.

本発明における線状構造物の沈下抑止構造の概略を示す図である。It is a figure which shows the outline of the settlement suppression structure of the linear structure in this invention. 本発明における地震発生時の上部地盤改良体の転倒に対する安定検討を示す図である。It is a figure which shows the stability examination with respect to the fall of the upper ground improvement body at the time of the earthquake occurrence in this invention. 本発明における地震発生時の地盤改良杭における断面検討を示す図である。It is a figure which shows the cross-section examination in the ground improvement pile at the time of earthquake occurrence in this invention. 本発明における線状構造物の沈下抑止構造を施工する手順を示す図である。It is a figure which shows the procedure of constructing the settlement suppression structure of the linear structure in this invention. 本発明における線状構造物の沈下抑止構造の他の事例を示す図である。It is a figure which shows the other example of the settlement suppression structure of the linear structure in this invention.

本発明の線状構造物の沈下抑止構造は、液状化層を有する地盤において地震発生時に液状化現象が生じた場合にも、地盤の表層もしくは地表に敷設された線状構造物に残留沈下や不等沈下を生じさせることなく健全な状態を維持するものである。 The subsidence prevention structure for a linear structure according to the present invention has a feature that even when a liquefaction phenomenon occurs in a ground having a liquefaction layer when an earthquake occurs, residual subsidence or a subsidence in a linear structure laid on the surface layer of the ground or on the ground surface. It maintains a healthy condition without causing uneven settlement.

本実施の形態では、線状構造物として表層中に埋設された地中埋設管を事例とし以下に図１〜図５を参照して説明するが、必ずしもこれに限定されるものではなく、線状構造物は地表上に敷設されるものであってもよい。また、線状構造物は、上下水道管等の地中埋設管に限定されるものではなく、共同溝、暗渠、盛土構造物等、線状をなす構造物であればいずれであってもよい。 In the present embodiment, an underground buried pipe buried in the surface layer as a linear structure will be described as an example with reference to FIGS. 1 to 5 below, but the present invention is not limited to this, and The structure may be laid on the surface of the earth. Further, the linear structure is not limited to underground pipes such as water and sewer pipes, and may be any linear structure such as common ditch, underdrain, embankment structure and the like. ..

図１（ａ）、（ｂ）で示すように、表層１１、液状化を生じる可能性がある液状化層１２、及び液状化を生じる可能性が低い非液状化層１３を有する地盤１０には、表層１１に線状構造物１が埋設されており、線状構造物１は上部地盤改良体２１と複数の地盤改良杭２２よりなる沈下抑止構造２に支持されている。 As shown in FIGS. 1A and 1B, the ground 10 having a surface layer 11, a liquefaction layer 12 that may cause liquefaction, and a non-liquefaction layer 13 that has a low possibility of liquefaction The linear structure 1 is embedded in the surface layer 11, and the linear structure 1 is supported by a subsidence prevention structure 2 including an upper ground improvement body 21 and a plurality of ground improvement piles 22.

上部地盤改良体２１は、図１（ａ）で示すように、線状構造物１およびこれを埋設する埋戻し土３を支持可能な構造を有し、その形状は線状構造物１の長さ方向に延在する断面視矩形状の長尺体よりなり、断面は幅ｗと比較して断面高さｈが同一もしくは大きくなるよう形成されている。そして、表層１１から液状化層１２に至る深さまで地盤１０を掘削し、セメント系固化材と撹拌・混合して固化することにより構築されるもので、バックホウをベースマシンとして作業可能な浅層混合処理工法もしくは中層混合処理工法にて構築される。つまり、上部地盤改良体２１における下面の最深度は、中層混合処理工法にて作業可能な深さとなる。 As shown in FIG. 1A, the upper ground improvement body 21 has a structure capable of supporting the linear structure 1 and the backfill soil 3 in which the linear structure 1 is embedded. The cross-section is formed of a rectangular elongated body extending in the depth direction, and the cross-section is formed so that the cross-section height h is the same as or larger than the width w. Then, it is constructed by excavating the ground 10 to a depth from the surface layer 11 to the liquefaction layer 12 and stirring and mixing with a cement-based solidifying material to solidify, and a shallow layer mixing that can work with a backhoe as a base machine. It is constructed by the processing method or middle layer mixing processing method. That is, the maximum depth of the lower surface of the upper ground improvement body 21 is the depth at which the middle layer mixing processing method can be used.

一方、下部地盤改良杭２２は、図１（ｂ）で示すように、載置される態様で上方に配置される上部地盤改良体２１を支持可能な構造を有し、上部地盤改良体２１の軸線方向に間隔を有して複数が配置されている。そして、上部地盤改良体２１の下面が位置する深さから非液状化層１３に至る深さまで地盤１０を掘削し、セメント系固化材と撹拌・混合して固化することにより構築されるもので、深層混合処理工法にて構築される。本実施の形態では、図１（ｂ）で示すように、１軸型の混合処理機を採用しソイルセメント柱を構築している。 On the other hand, as shown in FIG. 1( b ), the lower ground improvement pile 22 has a structure capable of supporting the upper ground improvement body 21 arranged above in a mounted manner. Plural pieces are arranged at intervals in the axial direction. Then, it is constructed by excavating the ground 10 from a depth where the lower surface of the upper ground improvement body 21 is located to a depth reaching the non-liquefied layer 13, and stirring and mixing with a cement-based solidifying material to solidify. It is constructed by the deep mixing method. In the present embodiment, as shown in FIG. 1B, a uniaxial type mixing processor is adopted to construct a soil cement column.

このような構成の上部地盤改良体２１および下部地盤改良杭２２は、液状化層１２を有する地盤１０中に構築されるため、地震の発生により地盤１０に液状化現象が生じた際には主働土圧と動水圧が側圧として作用する。そこで、上部地盤改良体２１および下部地盤改良杭２２を設計する際には、以下の検討を行っている Since the upper ground improvement body 21 and the lower ground improvement pile 22 having such a configuration are constructed in the ground 10 having the liquefaction layer 12, they are mainly used when the ground 10 undergoes a liquefaction phenomenon due to the occurrence of an earthquake. Working earth pressure and hydraulic pressure act as lateral pressure. Therefore, when designing the upper ground improvement body 21 and the lower ground improvement pile 22, the following studies are conducted.

上部地盤改良体２１を設計する際には、地震が発生し地盤１０に液状化現象が生じた場合を想定した転倒に対する安定検討を行う。具体的には、図２で示すように、地震の発生により地盤１０に液状化現象が生じた状態において上部地盤改良体２１に作用する主働土圧Ｅａ、上部地盤改良体の慣性力Ｈおよび液状化層１２の動水圧Ｐｄの３つの荷重より地盤改良杭２２の天端における地震時発生モーメントΣＭｏを算定し、上部地盤改良体２１の受動土圧による限界モーメントΣＭｒに対して、所定の安全率以上であることを確認する。 When designing the upper ground improvement body 21, a stability study against a fall is performed assuming an earthquake and a liquefaction phenomenon on the ground 10. Specifically, as shown in FIG. 2, the active earth pressure Ea acting on the upper ground improvement body 21, the inertial force H of the upper ground improvement body, and the liquid state when the ground 10 is liquefied due to the occurrence of an earthquake. An earthquake generated moment ΣMo at the top of the soil improvement pile 22 is calculated from the three loads of the dynamic water pressure Pd of the stratified layer 12, and a predetermined safety factor is obtained for the critical moment ΣMr of the upper soil improvement body 21 due to the passive earth pressure. Confirm that the above.

なお、上部地盤改良体２１は複数の地盤改良杭２２にのみ支持される簡略な構造であるため、断面については連続梁式により、上部地盤改良体２１に作用する鉛直荷重に対して上部地盤改良体２１の発生応力度を算出し、上部地盤改良体２１の材料の許容応力度以下であることを確認する。なお、上部地盤改良体２１に作用する鉛直荷重は、少なくとも線状構造物１および埋戻し土３の重量を含む上載荷重と上部地盤改良体２１の自重を足し合わせたものである。 Since the upper ground improvement body 21 has a simple structure that is supported only by a plurality of ground improvement piles 22, the continuous beam type is used for the cross section to improve the upper ground improvement body against the vertical load acting on the upper ground improvement body 21. The generated stress level of the body 21 is calculated, and it is confirmed that the stress level is equal to or lower than the allowable stress level of the material of the upper ground improvement body 21. The vertical load acting on the upper ground improvement body 21 is the sum of the overlaid load including at least the weight of the linear structure 1 and the backfill soil 3 and the own weight of the upper ground improvement body 21.

一方、地盤改良杭２２を設計する際には、梁ばねモデルにて地震が発生し地盤１０に液状化現象が生じた場合を想定した断面検討を行う。沈下抑止構造２の変形は地盤１０の変形に追従するが、両者は剛性が異なるためその変位に齟齬が生じ、これにより地盤改良杭２２は、地盤１０から反力を受けることとなる。そこで、図３で示すように、上部地盤改良体２１および地盤改良杭２２と地盤１０との間に地盤ばねを設け、断面を梁要素でモデル化する。 On the other hand, when designing the ground improvement pile 22, a cross-sectional study is performed assuming a case where an earthquake occurs and a liquefaction phenomenon occurs in the ground 10 in the beam spring model. The deformation of the subsidence prevention structure 2 follows the deformation of the ground 10, but since the two have different rigidity, there is a discrepancy in the displacement, and the ground improvement pile 22 receives a reaction force from the ground 10. Therefore, as shown in FIG. 3, a ground spring is provided between the upper ground improvement body 21, the ground improvement pile 22 and the ground 10, and the cross section is modeled by a beam element.

また、地震の発生により地盤１０に液状化現象が生じた状態において水平方向に作用する側圧として、埋戻し土３、線状構造物１、上部地盤改良体２１および地盤改良杭２２の慣性力Ｈ１〜Ｈ４と、液状化層１２の動水圧Ｈ５と、主働土圧Ｈ６とを考慮する。そして、地震時における地盤改良杭２２の発生応力度を算出し、地盤改良杭２２の材料の許容応力度以下であることを確認する。 In addition, as a lateral pressure that acts in the horizontal direction when the ground 10 is liquefied due to the occurrence of an earthquake, the backfill soil 3, the linear structure 1, the upper ground improvement body 21, and the inertial force H1 of the ground improvement pile 22 are used. -H4, the hydraulic pressure H5 of the liquefaction layer 12, and the active earth pressure H6 are considered. Then, the generated stress level of the ground improvement pile 22 at the time of an earthquake is calculated, and it is confirmed that the stress level is equal to or lower than the allowable stress level of the material of the ground improvement pile 22.

上述した構成の線状構造物１の沈下防止構造は、線状構造物１を支持する上部地盤改良体２１の下面が液状化層１２に接しているものの、上部地盤改良体２１に作用する鉛直荷重のすべてを地盤改良杭２２に伝達する構造としている。また、非液状化層１３に支持される地盤改良杭２２は、許容鉛直支持力を算定するにあたり、地震の発生時において液状化層１２における摩擦抵抗力が大幅に低下することを考慮し、液状化層１２の許容杭周面摩擦力を考慮しない。したがって、許容鉛直支持力は、非液状化層１３における許容杭周面摩擦力と許容杭先端支持力から算定することとした。なお、非液状化層１３は、図示しないが支持層を含むものである。 In the subsidence prevention structure of the linear structure 1 having the above-described configuration, the lower surface of the upper ground improvement body 21 supporting the linear structure 1 is in contact with the liquefaction layer 12, but the vertical structure acts on the upper ground improvement body 21. All the loads are transmitted to the ground improvement pile 22. In addition, the ground improvement pile 22 supported by the non-liquefaction layer 13 has a liquid resistance in consideration of the fact that the frictional resistance force in the liquefaction layer 12 is significantly reduced when an earthquake occurs when calculating the allowable vertical bearing capacity. The permissible pile peripheral frictional force of the chemical conversion layer 12 is not considered. Therefore, the allowable vertical supporting force is calculated from the allowable pile peripheral surface frictional force in the non-liquefaction layer 13 and the allowable pile tip supporting force. The non-liquefied layer 13 includes a support layer (not shown).

これにより、地震の発生により地盤１０に液状化現象が生じた場合にも、上部地盤改良体２１と下部地盤改良杭２２よりなる沈下抑止構造２はその影響を受けることがない。このため、上部地盤改良体２１に支持される線状構造物１も残留沈下や不等沈下等の有害な沈下を生じることなく、健全な状態を維持することが可能となる。 As a result, even if the ground 10 is liquefied due to the occurrence of an earthquake, the subsidence prevention structure 2 including the upper ground improvement body 21 and the lower ground improvement pile 22 is not affected. Therefore, the linear structure 1 supported by the upper ground improvement body 21 can be maintained in a healthy state without causing harmful subsidence such as residual subsidence or unequal subsidence.

こうして設計した上部地盤改良体２１および下部地盤改良杭２２よりなる沈下抑止構造２の施工手順は、以下のとおりである。 The construction procedure of the subsidence prevention structure 2 including the upper ground improvement body 21 and the lower ground improvement pile 22 designed in this way is as follows.

まず、図４（ａ）で示すように、地盤中に間隔を設けて複数の地盤改良杭２２を深層混合処理工法にて構築する。次に、図４（ｂ）で示すように、地盤改良杭２２の上面と少なくとも接するようにして上部地盤改良体２１を、浅層混合処理工法もしくは中層混合処理工法にて構築し、複数の地盤改良杭２２および上部地盤改良体２１を固化させる。この後、図４（ｃ）で示すように、線状構造物１を敷設し、表層１１の上面まで埋戻し土３により埋戻しを行う。 First, as shown in FIG. 4( a ), a plurality of ground improvement piles 22 are constructed by a deep layer mixing treatment method with a space provided in the ground. Next, as shown in FIG. 4(b), the upper ground improvement body 21 is constructed by the shallow layer mixing treatment method or the middle layer mixing treatment method so as to be at least in contact with the upper surface of the ground improvement pile 22 and The improvement pile 22 and the upper ground improvement body 21 are solidified. After that, as shown in FIG. 4C, the linear structure 1 is laid and backfilled with the backfill soil 3 to the upper surface of the surface layer 11.

また、既設の線状構造物１に対して沈下抑止構造２を設けようとする場合には、図５（ａ）で示すように、線状構造物１の両側部近傍に等間隔配置または千鳥配置となるように複数の地盤改良杭２２を打設した後、例えば、線状構造物１の両側部より線状構造物１の直下に、斜め・曲がり・水平方向の制御が可能な自在ボーリングを用いた地盤改良工法にて上部地盤改良体２１を構築するとよい。 In addition, when the subsidence prevention structure 2 is to be provided to the existing linear structure 1, as shown in FIG. After driving a plurality of ground improvement piles 22 so as to be arranged, for example, a free boring capable of oblique, bending, and horizontal control directly below the linear structure 1 from both sides of the linear structure 1. It is advisable to construct the upper ground improvement body 21 by a ground improvement method using.

なお、上部地盤改良体２１の断面高さｈは、地盤改良杭２２の配置間隔と上部地盤改良体２１に作用する鉛直荷重とを設定したうえで、鉛直荷重に対して上部地盤改良体２１に生じる最大垂直応力度を算定し、最大垂直応力度と上部地盤改良体２１の材料の引張強度との関係から決定できる。したがって、本実施の形態では、地表面から上部地盤改良体２１の上面までの深さと上部地盤改良体２１の断面高さｈとを足し合わせた地盤１０中の深度、つまり上部地盤改良体２１の下面の深度位置が、浅層混合処理工法もしくは中層混合処理工法等にて構築できる深さに収まるよう、地盤改良杭２１の配置間隔を調整している。 The sectional height h of the upper ground improvement body 21 is set to the upper ground improvement body 21 against the vertical load after setting the arrangement interval of the ground improvement piles 22 and the vertical load acting on the upper ground improvement body 21. The maximum vertical stress level that occurs can be calculated and determined from the relationship between the maximum vertical stress level and the tensile strength of the material of the upper ground improvement body 21. Therefore, in the present embodiment, the depth in the ground 10 obtained by adding the depth from the ground surface to the upper surface of the upper ground improvement body 21 and the sectional height h of the upper ground improvement body 21, that is, the upper ground improvement body 21 The arrangement interval of the ground improvement piles 21 is adjusted so that the depth position of the lower surface is within the depth that can be constructed by the shallow layer mixing treatment method or the middle layer mixing treatment method.

このような施工方法にて構築される上部地盤改良体２１と地盤改良杭２２は、それぞれ地盤深度に適した異なる地盤改良工法より構築された、セメント系固化材による地盤改良体が採用されることとなる。これにより、施工性を大幅に向上できるとともにコストを低減できるだけでなく、サンドコンパクションパイル工法を採用する場合に必要となる余改良部を線状構造物１の両側部に設ける必要がないため、沈下抑止構造２を経済的で無駄のないスリムな構造とすることが可能となる。 For the upper ground improvement body 21 and the ground improvement pile 22 constructed by such a construction method, the ground improvement body made of a cement-based solidifying material, which is constructed by different ground improvement methods suitable for the ground depth, is adopted. Becomes As a result, not only the workability can be greatly improved and the cost can be reduced, but also it is not necessary to provide the over-improved portions required when the sand compaction pile method is adopted on both sides of the linear structure 1, so that the settlement It is possible to make the deterrent structure 2 economical and lean in structure.

また、上部地盤改良体２１が破壊しない程度の断面高さｈを確保しつつ、地盤改良杭２１の配置間隔を大きく取ることにより、地盤改良杭２１の数量を減らすことができるため、地盤改良杭２１に深層混合処理工法を採用した際にも、コストを大幅に削減することが可能となる。 In addition, the number of ground improvement piles 21 can be reduced by increasing the arrangement interval of the ground improvement piles 21 while ensuring the sectional height h to the extent that the upper ground improvement body 21 is not destroyed. Even when the deep-layer mixing processing method is adopted for 21, the cost can be significantly reduced.

さらに、上部地盤改良体２１と下部地盤改良杭２２はともにセメント系固化材を用いた地盤改良体であることから、上部地盤改良体２１の下面と下部地盤改良杭２２の杭頭部とによりなる接触部には摩擦力もしくは接着力が生じる。したがって、地震の発生に伴う水平力の作用により、両者が水平方向に相対移動する挙動を示した場合にも、その挙動に抵抗して上部地盤改良体２１と下部地盤改良杭２２の位置ズレを防止できる。 Furthermore, since both the upper ground improvement body 21 and the lower ground improvement pile 22 are ground improvement bodies using the cement-based solidifying material, they are composed of the lower surface of the upper ground improvement body 21 and the pile head of the lower ground improvement pile 22. A frictional force or an adhesive force is generated at the contact portion. Therefore, even when both of them show a relative relative movement in the horizontal direction due to the action of the horizontal force due to the occurrence of the earthquake, the upper ground improvement body 21 and the lower ground improvement pile 22 are displaced from each other by resisting the behavior. It can be prevented.

なお、本発明の線状構造物１の沈下抑止構造２は、上記実施形態に限定されるものではなく、本発明の趣旨を逸脱しない範囲で、種々の変更が可能であることはいうまでもない。 The subsidence prevention structure 2 for the linear structure 1 of the present invention is not limited to the above embodiment, and it goes without saying that various modifications can be made without departing from the spirit of the present invention. Absent.

例えば、本実施の形態では、地盤改良杭２２に１軸型の混合処理機を採用したが、必ずしもこれに限定されるものではない。例えば、２軸型や３軸型の混合処理機を採用して複数本のソイルセメント柱にて１つの地盤改良杭２２を構築してもよいし、また、ソイルセメント柱の連続方向を上部地盤改良体２１の幅方向もしくは軸線方向のいずれに向けてもよい。 For example, in the present embodiment, the uniaxial type mixing processor is adopted as the ground improvement pile 22, but the present invention is not necessarily limited to this. For example, one soil improvement pile 22 may be constructed with a plurality of soil cement columns by adopting a two-axis type or three-axis type mixing processing machine, or the continuous direction of the soil cement columns may be the upper ground. The improvement body 21 may be oriented in either the width direction or the axial direction.

また、本実施の形態では、上部地盤改良体２１の上面に線状構造物１を載置するように敷設しているが、必ずしもこれに限定されるものではなく、上部地盤改良体２１と線状構造物１との間に埋戻し土３や設置架台が介装されてもよいことは言うまでもない。 Further, in the present embodiment, the linear structure 1 is laid so as to be placed on the upper surface of the upper ground improvement body 21, but the present invention is not necessarily limited to this, and the upper ground improvement body 21 and the line It goes without saying that the backfill soil 3 and the installation frame may be interposed between the structure 1 and the structure 1.

さらに、例えば図５（ｂ）で示すように、上部地盤改良体２１の下面と下部地盤改良杭２２の杭頭部とによりなる接触部にＨ形鋼等の鋼材よりなるズレ止め４を埋設すると、大規模地震が発生した際にも両者の位置ズレを確実に抑制することが可能となる。 Further, for example, as shown in FIG. 5(b), if a slip stopper 4 made of a steel material such as H-section steel is embedded in the contact portion formed by the lower surface of the upper ground improvement body 21 and the pile head of the lower ground improvement pile 22. Even in the event of a large-scale earthquake, it is possible to reliably suppress the positional deviation between the two.

１ 線状構造物
２ 沈下抑止構造
２１ 上部地盤改良体
２２ 地盤改良杭
３ 埋戻し土
４ ズレ止め
１０ 地盤
１１ 表層
１２ 液状化層
１３ 非液状化層 1 linear structure 2 subsidence prevention structure 21 upper ground improvement body 22 ground improvement pile 3 backfill soil 4 displacement prevention 10 ground 11 surface layer 12 liquefaction layer 13 non-liquefaction layer

Claims (3)

液状化層を有する地盤の表層もしくは地表上に敷設される線状構造物の沈下抑止構造であって、
前記線状構造物を支持するセメント系固化材による上部地盤改良体と、該上部地盤改良体を支持するセメント系固化材による複数の地盤改良杭と、を備え、
前記上部地盤改良体は、前記線状構造物の長さ方向に延在し、幅と比較して高さが同一もしくは大きい矩形状の断面を有する長尺体からなり、
前記上部地盤改良体の断面の高さは、前記地盤改良杭の配置間隔と前記上部地盤改良体に作用する鉛直荷重とを設定したうえで、鉛直荷重に対して前記上部地盤改良体に生じる最大垂直応力度を算定し、最大垂直応力度と前記上部地盤改良体の材料の引張強度との関係から決定されており、
前記地盤改良杭は、少なくとも杭先端部が前記液状化層より下方に位置する非液状化層に支持されることを特徴とする線状構造物の沈下抑止構造。 A subsidence suppressing structure for a linear structure laid on the surface of the ground having a liquefaction layer or on the ground surface,
An upper ground improvement body by a cement-based solidifying material that supports the linear structure, and a plurality of ground improvement piles by the cement-based solidifying material that supports the upper ground improving body,
The upper ground improvement body extends in the lengthwise direction of the linear structure, and is composed of an elongated body having a rectangular cross-section with the same or large height as compared with the width ,
The height of the cross section of the upper ground improvement body is the maximum that occurs in the upper ground improvement body with respect to the vertical load after setting the arrangement interval of the ground improvement pile and the vertical load acting on the upper ground improvement body. The vertical stress is calculated and determined from the relationship between the maximum vertical stress and the tensile strength of the material of the upper ground improvement body,
At least the tip of the ground improvement pile is supported by a non-liquefaction layer located below the liquefaction layer, wherein the structure for suppressing settlement of linear structures is provided. 液状化層を有する地盤の表層もしくは地表上に敷設される線状構造物の沈下抑止構造であって、
前記線状構造物を支持するセメント系固化材による上部地盤改良体と、該上部地盤改良体を支持するセメント系固化材による複数の地盤改良杭と、を備え、
前記上部地盤改良体は、前記線状構造物の長さ方向に延在し、幅と比較して高さが同一もしくは大きい矩形状の断面を有する長尺体からなり、
前記地盤改良杭は、前記線状構造物の両側部近傍に等間隔配置または千鳥配置となるように設けられ、少なくとも杭先端部が前記液状化層より下方に位置する非液状化層に支持されることを特徴とする線状構造物の沈下抑止構造。 A subsidence suppressing structure for a linear structure laid on the surface of the ground having a liquefaction layer or on the ground surface,
An upper ground improvement body by a cement-based solidifying material supporting the linear structure, and a plurality of ground improvement piles by a cement-based solidifying material supporting the upper ground improving body,
The upper ground improvement body extends in the lengthwise direction of the linear structure, and is composed of an elongated body having a rectangular cross-section with the same or larger height than the width ,
The ground improvement piles are provided in the vicinity of both side portions of the linear structure so as to be arranged at equal intervals or in a staggered arrangement, and at least the tip of the pile is supported by the non-liquefaction layer located below the liquefaction layer. A subsidence prevention structure for linear structures characterized by the following. 請求項１または２に記載の線状構造物の沈下抑止構造において、
前記上部地盤改良体と前記地盤改良杭に跨るように、ズレ止めが配置されることを特徴とする線状構造物の沈下抑止構造。 In settlement-inhibiting structure of the linear structure as claimed in claim 1 or 2,
A subsidence prevention structure for a linear structure, wherein a shift stopper is arranged so as to straddle the upper ground improvement body and the ground improvement pile.
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