JP2010255247A - Soil improving construction method and soil improving structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soil improving construction method which makes a replacing thickness smaller than a replacing thickness by a conventional mattress construction method, and a soil improving structure which exerts high strength even if reduced in thickness to be thinner than a conventional mattress structure. <P>SOLUTION: The soil improving construction method includes a lower layer forming process of laying a lower layer reinforcing material formed of a geotextile, an intermediate layer forming process of laying a honeycomb-like solid reinforcing material on the lower layer reinforcing material, the solid reinforcing material having a plurality of consecutively formed cells with open tops, and filling the cells with a filler to form an intermediate layer, and an upper layer forming process of laying an upper layer reinforcing material formed of the geotextile on the intermediate layer. The soil improving construction method is carried out to lay the soil improving structure having the lower layer reinforcing material, the intermediate layer, and the upper layer reinforcing material on the surface layer or the base layer of the soil. The soil improving structure is manufacturing by the soil improving construction method. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a ground improvement method that can reinforce a soft ground and a structure for ground improvement.

  When installing houses, retaining walls, etc. on soft ground, or embedding pipes, etc. in soft ground, the mattress construction method can be used to reinforce the ground under these structures. It was. With the mattress method, artificially created ground (hereinafter referred to as “mattress-like structure”) made by wrapping medium filling material made of crushed stone etc. with geotextile is laid on the surface or base layer of the soft foundation ground. Thus, the load applied from above (hereinafter referred to as “upload”) is dispersed by the shear resistance exerted by the mattress-like structure to increase the supporting force of the foundation ground.

  As a technique related to the mattress construction method described above, for example, in Patent Document 1, a geotextile is laid in a mold standing on a soft ground, and the peripheral portion of the geotextile is erected upward into a surface layer material accommodating portion. Disclosed is a construction method in which an improved surface layer is constructed by filling a cement-based slurry and then bending and coating the peripheral edge onto the surface of the cement-based slurry, fixing the opposing peripheral edges together, and curing the cement-based slurry. Has been.

Japanese Patent Laid-Open No. 11-140859

  Including the construction method disclosed in Patent Document 1, the effect of reinforcing the soft ground has been obtained even with the conventional mattress construction method. However, in order to obtain a sufficient reinforcing effect by the conventional mattress method, it is necessary to produce a large (thick) mattress-like structure. When such a large mattress-like structure is used, it is necessary to dig a large hole for embedding the mattress-like structure. That is, in the conventional mattress method, the thickness of the ground to be replaced by the mattress-like structure (hereinafter sometimes referred to as “replacement thickness”) is large.

  Therefore, the present invention provides a ground improvement method capable of reducing the replacement thickness as compared with the conventional mattress method, and a ground improvement structure capable of exhibiting high strength even when made thinner than the conventional mattress-like structure. It is an issue to provide.

  The present invention will be described below. In addition, in order to make an understanding of this invention easy, the reference sign of an accompanying drawing is attached in brackets, However, This invention is not limited to the form of drawing.

  In the first aspect of the present invention, a lower layer forming step (S1) in which a lower layer reinforcing material (1) made of geotextile is laid, and a plurality of cells (21) having an open top are continuously formed on the lower layer reinforcing material. An intermediate layer forming step (S2) for laying the formed honeycomb three-dimensional reinforcing material (20) and filling the cells with the filling material (22) to form the intermediate layer (2); A ground improvement structure (10) having a lower layer reinforcing material, an intermediate layer, and an upper layer reinforcing material, comprising an upper layer forming step (S3) for laying an upper layer reinforcing material (3) made of geotextile on the layer. Is a ground improvement method for laying on the surface or base layer of the ground (100).

  In the present invention, “a honeycomb-shaped three-dimensional reinforcing material in which a plurality of cells having upper openings are continuously formed” means that, when installed horizontally, a plurality of cells having at least upper openings are continuously arranged in the horizontal direction. It means that the cross-sectional shape in the horizontal direction has a honeycomb structure. In the present invention, the type of geotextile used for the lower layer reinforcing material and the upper layer reinforcing material is not particularly limited, and the lower layer reinforcing material and the upper layer reinforcing material may be composed of different types of geotextiles, Things can also be used. Therefore, in the present invention, the term “reinforcing material” may be used simply to include the lower layer reinforcing material and the upper layer reinforcing material.

  In the ground improvement method of the first aspect of the present invention, the upper layer reinforcing material and the lower layer reinforcing material are preferably made of a geotextile having particularly strong tensile strength in the triaxial direction.

  In the present invention, “a geotextile having particularly strong strength in the triaxial direction” means that, when laid horizontally, it has a particularly strong tensile strength in the triaxial direction in the horizontal plane, resulting in strength in all directions (360 degrees). This means a geotextile having a truss structure that has a pseudo structure. As a specific example of this geotextile, there can be mentioned Geogrit disclosed in JP-A-2004-44374.

  In the ground improvement method of the first aspect of the present invention, the height H of the ground improvement structure (10) can be determined by the following equation (1).

ここに、

here,

である。
（ただし、ｑ_ａ：地盤改良用構造物下の地盤の許容支持力、γ_２：中間層の単位体積質量、Ｋｐ：受働土圧係数、φ_２：中間層のせん断抵抗角、γ_１：地盤改良用構造物が敷設される地盤の単位体積質量、Ｄｆ：地表から地盤改良用構造物の上面までの深さ、Ｂ：地盤改良用構造物に上載荷重が加えられる部分を長方形と見なした場合の該部分の一辺の長さ、Ｌ：地盤改良用構造物に上載荷重が加えられる部分を長方形と見なした場合の該部分のＢに直交する方向の辺の長さ、Ｔ_Ｄ：補強材の設計強度、θ：補強材の許容伸びに対する変位角、ｑ：上載荷重）

It is.
(Where q _a : allowable bearing capacity of the ground under the ground improvement structure, γ ₂ : unit volume mass of the intermediate layer, Kp: passive earth pressure coefficient, φ ₂ : shear resistance angle of the intermediate layer, γ ₁ : ground Unit volume mass of the ground where the improvement structure is laid, Df: Depth from the ground surface to the top surface of the ground improvement structure, B: The portion where the overload is applied to the ground improvement structure was considered as a rectangle L: length of one side of the portion, L: length of a side in a direction perpendicular to B of the portion when a portion to which an overload is applied to the ground improvement structure is regarded as a rectangle, T _D : reinforcement Design strength of material, θ: displacement angle relative to allowable elongation of reinforcing material, q: load on top)

  When a conventional mattress-like structure is installed horizontally, the mattress-like structure has strong strength in two axial directions (one direction and a direction perpendicular to the direction in a plane parallel to the horizontal plane). Therefore, it was thought that the overload could be distributed in those directions. Therefore, the stress distribution in the mattress-like structure due to the overload is calculated on a vertical plane (two-dimensional) parallel to either of the two axial directions.

  On the other hand, in the ground improvement method of the present invention, as will be described in detail later, when the ground improvement structure of the present invention obtained by the method is installed horizontally, the ground improvement structure is parallel to the horizontal plane. Since it is possible to have strong strength in almost all directions within a smooth surface, it is considered that the overload can be dispersed in all directions. Therefore, the stress distribution in the ground improvement structure due to the overload can be considered in three dimensions, that is, a two-dimensional plane parallel to the horizontal plane and a height dimension. Therefore, the height H necessary for the ground improvement structure can be obtained by an expression that three-dimensionally considers the stress distribution in the ground improvement structure as in the above formula (1).

  The second aspect of the present invention relates to a lower layer reinforcing material (1) made of geotextile, a honeycomb-shaped three-dimensional reinforcing material (20) in which a plurality of cells (21) having an open top are continuously formed, and filling the cells. The ground improvement structure (10) in which the intermediate layer (2) having the intermediate filling material (22) and the upper layer reinforcing material (3) made of geotextile are laminated in this order.

  In the ground improvement structure according to the second aspect of the present invention, the upper layer reinforcing material and the lower layer reinforcing material are preferably made of a geotextile having particularly strong tensile strength in the triaxial direction.

  According to the present invention, a ground improvement method capable of reducing the replacement thickness as compared with the conventional mattress method, and a ground improvement structure capable of exhibiting high strength even if made thinner than the conventional mattress-like structure. Can be provided.

It is a flowchart which shows the process with which the ground improvement construction method of this invention is equipped. It is a figure which shows roughly the perpendicular direction cross section of the structure for ground improvement of this invention. It is a top view which shows roughly a part of geotextile which can be used for an upper layer reinforcing material and a lower layer reinforcing material. It is a figure which shows roughly the intensity | strength of the geotextile shown in FIG. It is a perspective view which shows roughly the attitude | position before the expansion | deployment of the honeycomb-shaped solid reinforcement material which can be used for this invention. FIG. 6 is a perspective view schematically showing a posture of the honeycomb-shaped three-dimensional reinforcing material shown in FIG. 5 during expansion. It is the schematic which shows three-dimensionally the stress distribution when an overlay load is applied to the structure for ground improvement of this invention. It is a figure for demonstrating the idea that the dead weight of the structure for ground improvement is offset by the pressing embankment effect with the surrounding ground.

  The above-described operation and gain of the present invention will be clarified from embodiments for carrying out the invention described below.

  FIG. 1 is a flowchart showing steps provided in the ground improvement method of the present invention. FIG. 2 is a diagram schematically showing a vertical section of the ground improvement structure of the present invention. Hereinafter, the present invention will be described in detail based on embodiments with reference to FIGS. 1 and 2 and appropriate drawings. However, the present invention is not limited to these embodiments.

  As shown in FIG. 1, the ground improvement method of the present invention includes a lower layer forming step S1, an intermediate layer forming step S2, and an upper layer forming step S3. By passing through these steps, the ground improving method of the present invention is provided. A structure 10 (hereinafter sometimes referred to as “mattress 10”) can be obtained.

  Each step provided in the ground improvement method of the present invention will be described in detail below.

(Lower surface forming step S1)
Step S <b> 1 is a step of laying a lower layer reinforcing material 1 made of geotextile on the bottom surface of a depression formed on the ground 100 or on the surface layer portion of the ground 100, as shown in FIG. 2.

  Although the geotextile constituting the lower layer reinforcing material that can be used in the present invention is not particularly limited, the mesh opening as shown in FIG. 3 has a substantially triangular shape and has a particularly strong tensile strength in the triaxial direction. As a result, it is preferable to use a geotextile having a truss structure that has a pseudo strength in all directions (360 degrees) (for example, Geogrit disclosed in JP-A-2004-44374). (This is sometimes called “truss structural reinforcement”). FIG. 3 is a top view schematically showing a part of the geotextile that can be used for the upper layer reinforcing material and the lower layer reinforcing material.

  FIG. 4 shows the strength of the geotextile shown in FIG. In FIG. 4, concentric circles indicate strength, numbers on the outside of the outermost circle indicate directions (angles) having strength, and broken lines indicate the tensile strength of the geotextile. As shown in FIG. 4, the geotextile shown in FIG. 3 has a particularly strong strength in three axial directions (0 ° -180 °, 60 ° -240 °, and 120 ° -300 °). 360 degrees).

(Intermediate layer forming step S2)
In step S2, a honeycomb-shaped three-dimensional reinforcing material 20 in which a plurality of cells 21, 21,... Having upper openings are continuously formed is laid on the lower layer reinforcing material 1, and the cells 21, 21,. In this process, the intermediate layer 2 including the honeycomb three-dimensional reinforcing material 20 and the intermediate filler 22 is formed by filling the intermediate filler 22.

  First, the configuration of the honeycomb-shaped three-dimensional reinforcing material 20 will be described with reference to FIGS. 5 and 6. FIG. 5 is a perspective view schematically showing a posture before expansion of the honeycomb-shaped three-dimensional reinforcing material 20 that can be used in the present invention, and FIG. 6 is a posture of the honeycomb-shaped three-dimensional reinforcing material 20 shown in FIG. FIG.

  The honeycomb-shaped three-dimensional reinforcing material 20 includes a plurality of cells 21, 21,... Opened at the top, and the cells 21, 21,. It is comprised by couple | bonding in the coupling | bond part 24 provided in (4). The honeycomb three-dimensional reinforcing material 20 can be easily transported by placing the cells 21, 21,... In a closed position as shown in FIG. 5 during transportation, and the arrows shown in FIG. By pulling and expanding in the direction of V, the cells 21, 21,... Can be opened as shown in FIG.

  As shown in FIG. 6, the intermediate layer 2 is formed by spreading the honeycomb three-dimensional reinforcing material 20 and then filling the cells 21, 21,. As the filling material 22, what is used for the conventional mattress construction method can be used, without being specifically limited. Specifically, in addition to gravel materials such as crushed stone, locally generated soil such as sand and clay can be used.

  Further, from the viewpoint of improving the drainage of the intermediate layer 2, it is preferable to provide a plurality of holes 25 in the strip material 23 as appropriate.

  The honeycomb-shaped three-dimensional reinforcing material is self-supporting by spreading. Therefore, the ground improvement construction method of the present invention can be constructed without installing a frame that is necessary when the conventional mattress construction method is constructed. That is, in the ground improvement construction method of the present invention, the work of installing and removing the mold is not necessary. Further, each cell of the honeycomb-shaped three-dimensional reinforcing material restrains the filling material, so that the intermediate layer exhibits high strength. Therefore, the ground improvement structure of the present invention can exhibit high strength even if it is thinner than a conventional mattress-like structure.

  In addition, the honeycomb-shaped three-dimensional reinforcing material used in the present invention can be selected to have an appropriate height according to the use situation. Also, a plurality of honeycomb-shaped three-dimensional reinforcing materials can be laid in piles.

(Upper surface forming step S3)
Step S <b> 3 is a step of laying an upper layer reinforcing material 3 made of geotextile on the intermediate layer 2. Since the same material as the lower layer reinforcing material 1 can be used as the upper layer reinforcing material 3, the description thereof is omitted.

(Mattress 10)
The mattress 10 can be obtained through the steps S1 to S3 described above. The mattress 10 uses a lower layer reinforcing material 1 and an upper layer reinforcing material 3 having pseudo strength in all directions in a horizontal plane when laid horizontally, and is formed in a honeycomb shape between the lower layer reinforcing material 1 and the upper layer reinforcing material 3. The intermediate layer 2 having the three-dimensional reinforcing material 20 and the filling material 22 can be provided. By adopting such a configuration, the mattress 10 has a strong strength in all directions in the horizontal plane when laid horizontally, so that the overload can be dispersed with high efficiency. Therefore, even if it is thinner (lower in height) than a conventional mattress-like structure, high strength can be exhibited. In the ground improvement structure of the present invention, for example, the thickness can be about 30 cm.

  As described above, since the ground improvement structure of the present invention can be made thinner than the conventional mattress-like structure, the ground improvement method of the present invention has a smaller replacement thickness than the conventional mattress method. can do.

  When the mattress 10 is installed horizontally, the size of the horizontal surface can be appropriately selected according to the size of the object to be installed on the mattress 10 and the necessary height is determined by the method described below. can do.

(How to find the height H required for the mattress 10)
As for the height of the mattress 10, the height of the intermediate layer 2 is dominant. Therefore, the height of the mattress 10 can be set to an appropriate height by selecting an appropriate height of the honeycomb-shaped three-dimensional reinforcing material 20 used for the intermediate layer 2. When a plurality of honeycomb-shaped three-dimensional reinforcing materials 20 are laid in piles, the height of the mattress 10 can be set to an appropriate height by setting the total height to an appropriate height.

  A method of obtaining the height H necessary for the mattress 10 will be described with reference to FIG. FIG. 7 is a schematic diagram three-dimensionally showing the stress distribution in the mattress 10 due to the overload applied to the mattress 10.

  As described above, the mattress 10 obtained by the ground improvement method of the present invention can have strength in all directions on a horizontal plane when laid horizontally. Therefore, the loading load can be dispersed in all directions. Therefore, as shown in FIG. 7, the stress distribution in the ground improvement structure 10 due to the overload can be considered in three dimensions, that is, a two-dimensional plane parallel to a horizontal plane and a height dimension.

A single arrow in FIG. 7 indicates the direction in which the stress acts. The meaning of the characters shown in FIG. 7 will be described. q is an upper load, p is a distributed pressure on the lower surface of the mattress 10, B is a length of one side of the portion when the upper load is applied to the mattress 10 as a rectangle, and L is an upper load on the mattress 10. The length of the side in the direction perpendicular to B of the portion when the portion to which is added is regarded as a rectangle, q _a is the allowable bearing force of the ground 100 under the mattress 10, and Df is from the ground surface to the upper surface of the mattress 10 depth, H is the mattress 10 height, T _D design strength of the reinforcement, z is depth from the upper surface of the mattress 10, a, b is that each of the upper surface of the mattress 10, c, d, respectively It means a point on the lower surface side of the mattress 10.

Assuming that the load q is dispersed within the mattress 10 at a dispersion angle α, the distribution pressure on the lower surface of the mattress 10 having a height H is p, and the load dispersion effect of the mattress 10 (hereinafter referred to as “mattress effect”) is M. if _E, overburden load, since the sum of the load and the mattress effect M _E after dispersion, the following formula (2) is satisfied.
qBL = p (B + 2Htanα) (L + 2Htanα) + M _E (2)

When the allowable bearing capacity of the ground 100 of the lower mattress 10 is q _a, the sum of its own weight gamma _{2 H} distribution pressure p and mattress 10 of mattress 10 lower surface (gamma ₂ the unit volume weight of the intermediate layer 2.) Is q if equal to _a, so that the following equation (3).
p + γ ₂ H = q _a (3)

However, when actually excavating the ground 100 and installing the mattress 10 at a depth of (Df + H) from the ground surface at the site where the ground improvement method of the present invention is actually performed, the term of γ ₂ H in the formula (3) Is not considered approximately. This is because the self-weight γ ₂ H of the mattress 10 is a force γ ₁ H (γ ₁ is a unit of the ground 100) that acts due to the pressing embankment effect with the ground 100 around the position where the mattress 10 is embedded, as shown in FIG. This is because it is offset by (volume mass). For this reason, an approximate value as shown in the following formula (4) can be adopted as this correction.

p≈q _a (4)

Here, if the dispersion angle alpha = 45 °, following from the equation (2) and (4), consider the difference between the load after dispersion and overburden load is mattress effect M _E, the mattress effect M _E1 It can be obtained by the equation (5).
M _E1 = qBL−q _a × (B + 2H) (L + 2H) (5)

On the other hand, the mattress effect M _E can also be considered as follows. When the mattress 10 receives a bending stress due to the load q, it is considered that a compressive force is generated on the upper portion of the mattress 10 and a tensile force is generated on the lower portion, the intermediate layer 2 resists the compressive force, and the reinforcing material resists the tensile force. That is, the shear resistance of the intermediate layer 2 S, when the tensile resistance of the reinforcing material is T, the mattress effect M _E is considered to be the sum of the tensile shear strength of the intermediate layer and the reinforcing material, mattress The effect M _E2 can be obtained from the following equation (6).

M _E2 = S + T (6)

First, consider the tensile resistance T of the reinforcing material. When the tensile resistance of the lower layer reinforcing material is _Tunder , and the tensile resistance of the _upper layer reinforcing material is Tupper, each is obtained by the following equation.
T _under = 2T _D1 × 2 (7)
T _upper = 2T _D2 × 2 (8)
Here, T _D1 is the design strength of the lower layer reinforcing material, and T _D2 is the design strength of the upper layer reinforcing material.
The design strength T _D of the reinforcing member is the sum of the design strength of the design strength and the upper reinforcement of the lower reinforcement Considering the safety factor,
ΣT _D = T _under + T _upper (9)
It can be expressed. Or
T = ΣT _D × sin θ (10)
It can be expressed.
Here, θ is a displacement angle with respect to the allowable elongation of the lower layer reinforcing material or the upper layer reinforcing material.
The above formulas (7) and (8) are for the case where a truss structure reinforcing material is used for the lower layer reinforcing material and the upper layer reinforcing material, and two directions (in a plane parallel to the horizontal plane) When a tensor having strong strength in the direction orthogonal to the direction is used, the tensile resistance is halved.

Next, it is assumed that the shear resistance S of the intermediate layer 2 is exerted on the surfaces of ac and bd where the load is dispersed. On these surfaces, the vertical stress in the ground due to the load q can be regarded as 0, and the vertical stress σv is expressed by the following equation (11).
σv = γ ₁ Df + γ ₂ z (11)

Here, for the sake of simplicity, assuming that the shear resistance on the ac and bd planes can be evaluated on a vertical plane passing through the midpoint of those planes, S is calculated by the following equation (12).
S = (2∫K · σv · tanφ ₂ · dz) × 2 (12)

Here, φ ₂ is the shear resistance angle of the intermediate layer 2, and K is the earth pressure coefficient at the position of the depth z in the mattress 10. The horizontal force becomes a variable depending on the depth because when the bending deformation occurs in the mattress 10, it is compressed at the upper part and is pulled at the lower part. For this reason, the following is considered.

  When the mattress 10 is subjected to bending stress, a compressive force is generated at the upper part of the mattress 10, so that K = Kp (passive earth pressure coefficient) at z = 0. In addition, a tensile force is generated at the lower portion of the mattress 10, but the reinforcing material that restrains the deformation of the intermediate layer 2 resists the tensile force, so that a tensile force is not generated between the intermediate layers 2. First, K = 0 when z = H. If K changes linearly with depth during this period, it is expressed by the following equation.

K = (1-z / H) Kp
Z = 0 → K = Kp
Z = H → K = 0
Kp = ^tan 2 (45 ° _{+ φ 2/2) (13} )

  Here, when the equations (11) and (13) are substituted into the equation (12) and integrated, the following equation (14) is obtained.

Thus, equation (5) and (14) a When enumeration equation (6) in consideration, the quadratic equation should the height H of the mattress 10 which is determined from the allowable bearing capacity q _a mattress 10 subsoil is shown below (16 ).

From M _E1 = M _E2 ,

  The value of H obtained as a solution of the above equation (16) is a height necessary for the mattress 10, and the height of the mattress 10 may be higher than that value. Therefore, the height H of the mattress 10 is given by the following formula (1).

ここに、

here,

である。

It is.

In the description so far, the required height H of the mattress 10 is calculated. However, when the required height H of the mattress 10 is set to a constant value, the reinforcing material strength T _D is obtained by the following equation (18). req can also be calculated backward.

  Further, in the above formula (18), the stress distribution due to the overload is considered three-dimensionally, but when considered two-dimensionally as in the prior art, the following formula (19) is obtained.

  Although the present invention has been described in connection with the most practical and preferred embodiments at the present time, the present invention is not limited to the embodiments disclosed herein, The present invention can be changed as appropriate without departing from the scope or spirit of the invention that can be read from the claims and the entire specification, and the ground improvement method and the structure for ground improvement accompanying such changes are also within the technical scope of the present invention. It must be understood as included.

DESCRIPTION OF SYMBOLS 1 Lower layer reinforcement material 2 Middle layer 3 Upper layer reinforcement material 10 Structure for ground improvement (mattress)
20 Honeycomb three-dimensional reinforcing material 21 Cell 22 Filling material 23 Strip material 24 Bonding site 25 Hole 100 Ground

Claims (5)

A lower layer forming step of laying a lower layer reinforcing material made of geotextile,
On the lower layer reinforcing material, a honeycomb-shaped three-dimensional reinforcing material in which a plurality of cells having upper openings are continuously formed is laid, and an intermediate layer is formed by filling the cells with a filling material. A layer forming step;
An upper layer forming step of laying an upper layer reinforcing material made of geotextile on the intermediate layer;
A ground improvement construction method comprising laying a ground improvement structure having the lower layer reinforcing material, the intermediate layer, and the upper layer reinforcing material on a surface layer or a base layer portion of the ground. The ground improvement construction method according to claim 1, wherein the upper layer reinforcing material and the lower layer reinforcing material are made of a geotextile having a particularly strong tensile strength in a triaxial direction. The ground improvement construction method according to claim 1 or 2, wherein the height H of the structure for ground improvement is determined by the following formula (1).

here,

It is.
(Where q _a : allowable bearing capacity of the ground under the ground improvement structure, γ ₂ : unit volume mass of the intermediate layer, Kp: passive earth pressure coefficient, φ ₂ : shear resistance angle of the intermediate layer, γ ₁ : ground Unit volume mass of the ground where the improvement structure is laid, Df: Depth from the ground surface to the top surface of the ground improvement structure, B: The portion where the overload is applied to the ground improvement structure was considered as a rectangle L: length of one side of the portion, L: length of a side in a direction perpendicular to B of the portion when a portion to which an overload is applied to the ground improvement structure is regarded as a rectangle, T _D : reinforcement Design strength of material, θ: displacement angle relative to allowable elongation of reinforcing material, q: load on top) A lower layer reinforcement made of geotextile,
A honeycomb-shaped three-dimensional reinforcing material in which a plurality of cells having an open top are continuously formed, and an intermediate layer having a filling material filled in the cells;
An upper layer reinforcement made of geotextile,
A structure for ground improvement, stacked in that order. The structure for ground improvement according to claim 4, wherein the upper layer reinforcing material and the lower layer reinforcing material are made of a geotextile having particularly strong tensile strength in three axial directions.

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