JP5014759B2 - Ground improvement method - Google Patents

Description

The present invention relates to a ground improvement method for reducing the consolidation settlement of soft ground.

In soft ground such as peat ground and cohesive ground, when embankment is constructed on this soft ground, the soft ground, which is the foundation ground, is sunk due to the load of embankment and the like. In some cases, the amount of subsidence predetermined for the ground was exceeded.
Conventionally, for example, a pile type improved construction method has been used as a construction method for reducing the consolidation settlement of such soft ground. In this construction method, as shown in FIG. 10 , a cement-based or lime-based solidified material is supplied into the soft ground 1 and mixed and stirred to harden the solidified material and soft soil in the soft ground 1. A pile-shaped solidified body (improved body) 101 is formed, and this pile-shaped solidified body 101 is formed so as to be scattered at a plurality of predetermined intervals in the soft ground that is the object, and the improved ground 100 is obtained. It is a construction method that reduces consolidation settlement of soft ground. According to this construction method, the load of the embankment 102 and the like constructed on the soft ground 1 is more shared by the plurality of pile-shaped solid bodies (improved bodies) 101 formed in the soft ground 1, so that the soft ground The consolidation settlement can be reduced.

  In the pile type improvement method, in order to obtain the settlement amount (S) of the soft ground (improved ground 100) improved by the solidified body (improved body), first, the stress reduction coefficient is expressed by the following formula (1). It is necessary to calculate (β).

上記式（１）において、βは、応力低減係数であり、ｎは、応力分担比（固化体（改良体）の圧密降伏応力（Ｐ_ｃ）と改良地盤の平均圧密圧力（＝Ｐ_ｏ＋ΔＰ／２）の比と、固化体（改良体）と元の軟弱地盤の体積圧縮係数の比（応力分担比の逆数）との関係図からの求められる値）である。また、ａ_ｐは、改良率（固化体（改良体）の地表面における面積（断面積；Ｓ_Ａ）と、盛土の荷重全体が掛かる地盤（改良地盤）全体の面積（Ｓ_Ｂ）との比（Ｓ_Ａ／Ｓ_Ｂ））である。
上記式（１）によって算出した応力低減係数（β）に基づいて、固化体（改良体）によって改良された軟弱地盤（改良地盤１００）の沈下量（Ｓ）は、次に示す式（２）によって、算出する。

In the above formula (1), β is a stress reduction coefficient, and n is a stress sharing ratio (consolidation body (improved body) consolidation yield stress (P _c ) and improved ground average consolidation pressure (= P _o + ΔP / 2) and the relationship between the volume compression coefficient ratio of the solidified body (improved body) and the original soft ground (reciprocal of the stress sharing ratio). In addition, _ap is the ratio between the improvement rate (the area (cross-sectional area; S _A ) of the solidified body (improved body) on the ground surface and the area (S _B ) of the entire ground (improved ground) on which the entire embankment load is applied. (S _A / S _B )).
Based on the stress reduction coefficient (β) calculated by the above formula (1), the subsidence amount (S) of the soft ground (improved ground 100) improved by the solidified body (improved body) is expressed by the following formula (2): To calculate.

In the pile type improvement method, in order for the consolidation settlement of the soft ground (improved ground) improved by the solidified body (improved body) to fall below the allowable settlement amount range, the settlement amount of the improved ground (S) Must be set smaller than the allowable settlement amount (Sa) (S <Sa). In order to reduce the subsidence amount (S) of the improved ground, it is necessary to reduce the stress reduction coefficient (β) of the improved ground based on the above formula (2). Based on the formula (1), the improvement rate (a _p ) is the ratio of the area (cross-sectional area) of the solidified body (improved body) on the ground surface to the total area of the ground (improved ground) to which the entire load such as embankment is applied. ) Should be set large. Usually, the improvement rate (a _p ) in the pile type improvement method is set to about 10 to 90%, preferably about 30 to 80%.
In the pile type improvement method, the safety factor (F _s ) of the solidified body (improved body) is calculated by the following formula (3).

Also in the above formula (3), in order to increase the safety factor (F _s ) of the solidified body (improved body), when the design standard strength (q _uck ) of the solidified body (improved body) is a fixed value, It is necessary to set a large improvement rate (a _p ).
However, in order to increase the improvement rate (a _p ), it is necessary to increase the area (cross-sectional area) of the solidified body (improved body) on the ground surface, and as one method, the solidified body (improved body) itself As another method, it is necessary to increase the number of solidified bodies (improved bodies) to be formed on the soft ground that is the area to be improved, both methods increase the amount of construction soil, increase the number of processes, Since the construction period was long and the cost was increased, it was not economically preferable.
On the other hand, when the design standard strength (q _uck ) of the solidified product (improved product) is increased and the safety factor is increased without setting the improvement rate ( _ap ) large, the solidified product (improved product) Since the area (cross-sectional area) on the ground surface is not large, as a result, the space between the solidified body (improved body) and the solidified body (improved body) becomes wider, and the stress due to the loading load is the design stress sharing. The soft ground existing in the part between the solidified body (improved body) and the solidified body (improved body) is not settled according to the ratio and sinks due to the load such as embankment constructed on the soft ground, and the solidified body ( There was a problem that unevenness was formed on the surface of the soft ground (improved ground) improved by the improved body, resulting in uneven settlement.

As a method of reducing consolidation settlement of the soft ground without setting a large improvement rate, first, a bank is formed on the soft ground, and then a prefabricated pile is formed in the vertical direction across the soft ground and the bank. Further, a solidified layer is formed on the embankment and the ready-made pile, a pavement is constructed on the solidified layer, and the load applied to the soft ground is transferred to the soft ground via the ready-made pile. There has been proposed a method for transmitting to a high-quality ground in the deep part of the ground (Patent Document 1). In this method, the improvement rate by the ready-made pile is set so as not to exceed 10%.
JP 2003-268790 A

However, although the method described in Patent Document 1 sets the improvement rate to be small so that the improvement rate by the ready-made pile does not exceed 10%, the consolidation settlement of the soft ground is reduced. In addition to forming embankments on the ground and placing ready-made piles, a solidified layer must be further formed on the embankments and ready-made piles, and pavement must be built on the solidified layers. There were many, construction period became long, and construction cost increased.
Therefore, an object of the present invention is to provide a ground improvement method capable of reducing the increase in the number of processes, materials, and the like as much as possible, and economically reducing consolidation settlement of soft ground.

As a result of intensive studies to solve the above problems, the present inventor supplied the solidified material into the soft ground in the process of penetration and extraction of the mixed stirring attachment into the soft ground, mixed and stirred, A pile-shaped solidified portion forming step for forming a pile-shaped solidified portion made of the solidified material and soft soil and having a substantially rectangular cross section in the horizontal direction is separate from the positions of penetration and extraction in this pile-shaped solidified portion forming step. In the process of penetration and extraction of the mixing and stirring attachment into the soft ground, the solidified material is supplied into the soft ground and mixed and stirred so as to be connected to the periphery of the upper part of the pile-shaped solidified portion. And an expanded solidified portion forming step of forming the solidified portion made of the solidified material and soft soil integrally with the pile-shaped solidified portion so as to protrude in a horizontal direction by a specific length from the pile-shaped solidified portion. by ground improvement method, including While the area on the ground surface of the ground improvement body can be expanded at the expansion and solidification part, the improvement rate of the ground improvement body can be set to a large value, while increasing the construction period and increasing the materials etc. as much as possible, It has been found that the consolidation settlement of soft ground can be reduced economically, and the present invention has been completed.

That is, the present invention provides the following [1] to [ 3 ].
[1] Using a construction machine having a mixing and stirring attachment for discharging the solidified material and mixing and stirring the soft soil and the solidified material , the solidified material is supplied into the soft ground, mixed and stirred, and the solidified material and A ground improvement method that reduces consolidation settlement of soft ground by a ground improvement body made by hardening soft soil,
(A) In the process of penetration and extraction of the mixed stirring attachment into the soft ground, the solidified material is supplied into the soft ground, mixed and stirred, and the pile-shaped solidified portion composed of the solidified material and soft soil is formed. A pile-shaped solidified part forming step to be formed;
(B) In the process of penetration and extraction of the mixed stirring attachment into the soft ground at a position different from the position of penetration and extraction in the pile-shaped solidified part forming step (A), the pile-shaped solidified part The solidified material is supplied into the soft ground so as to be connected to the periphery of the upper portion of the slab, mixed and stirred, and the expanded solidified portion composed of the solidified material and the soft soil is integrally formed with the pile-shaped solidified portion. A solidified portion forming step;
Only containing and horizontal cross-section of the pile-like coated portion has a substantially rectangular shape, if the length of one side of the substantially rectangular cross section is a, the larger coated portion is the pile-like solidified portion The ground improvement construction method characterized in that the length (L) of the solidified portion projecting in the horizontal direction is 0.7a to 1.5a .
In [2] the expansion solidified portion forming process (B), the vertical length of the enlarged coated portion (enlarged solidified portion depth: H) is such that a 0.7 L ~ 1.5 L, the larger coated portion The ground improvement construction method according to the above [1] to be formed.
[3] In the expanded solidified portion forming step (B), the expanded solidified portion is formed so that the length (enlarged solidified portion depth: H) in the vertical direction of the expanded solidified portion is 1 to 3 m. The ground improvement construction method according to [1] or [2].

The present invention is connected to the periphery of the upper part of the pile-shaped solidified part formed in the soft ground, and since the enlarged solidified part is formed integrally with the pile-shaped solidified part, the area on the ground surface of the ground improvement body (In addition, the area on the ground surface of the ground improvement body is not limited to the upper surface forming the same surface as the ground surface of the soft ground, but also includes the area (cross-sectional area) near the ground surface of the soft ground) While the improvement rate of the ground improvement body can be set large, only the upper part of the ground improvement body is enlarged and the whole ground improvement body is not enlarged, so the amount of construction soil and the number of ground improvement bodies The increase can be suppressed as much as possible, the increase in cost can be prevented, and the consolidation settlement of the soft ground can be reduced economically.The present invention is an expansion solidification connected around the upper part of the pile-shaped solidification part of the ground improvement body. Depending on the part, set a large improvement rate of the ground improvement body Therefore, compared with the case where the ground improvement body is formed only with the pile-shaped solidified part, the number of ground improvement bodies formed in the soft ground can be reduced, and the ground improvement body The construction period can be shortened with the reduction of the set number.
When reducing the number of ground improvement bodies to be set, it is necessary to increase the amount of solidification material supplied to the soft ground and increase the strength of the ground improvement body so that the design standard strength is satisfied with a small number. Even when the addition amount of the solidifying material is increased, the number of ground improvement bodies set is smaller, the number of constructions is reduced and the construction period can be shortened, so that the cost for the entire construction can be reduced.

Hereinafter, the ground improvement method of the present invention will be described with reference to the drawings.
FIG. 1 is a flowchart showing an example of the ground improvement method according to the present invention. FIG. 2 is a diagram showing an example of a construction machine used when the ground improvement method of the present invention is applied to a middle layer improvement method having a maximum improvement depth of about 10 m from the ground surface. FIG. 3 is a process diagram showing an outline when the ground improvement method of the present invention is applied to the intermediate layer improvement method.

The ground improvement method of the present invention uses a construction machine having a mixing stir attachment for discharging solidified material and mixing and stirring soft soil and solidified material, supplying the solidified material into the soft ground, mixing and stirring A ground improvement method for reducing consolidation settlement of soft ground by means of a ground improvement body obtained by hardening the solidified material and soft soil, wherein (A) the process of penetration and extraction of the mixed stirring attachment into the soft ground among supplies solidified material soft in the ground, are stirred together, the pile-like solidified portion forming step of forming a pile-like coated portion consisting of the solidified material and soft soil, (B) the pile-like solidified portion In the process of penetration and extraction of the mixed stirring attachment into the soft ground at a position different from the position of penetration and extraction in the forming step (A), it is connected to the periphery of the upper part of the pile-shaped solidified portion. In soft ground The solidifying material supply, stirred together, the enlarged coated portion consisting of the solidified material and soft soil, saw including an enlarged solidified portion forming step of forming integrally with said pile-like solidified portion, and the pile-like solidified The horizontal cross-section of the portion is substantially rectangular, and when the length of one side of the substantially rectangular cross-section is a, the length of the enlarged solidified portion projecting horizontally from the pile-shaped solidified portion (enlarged) This is a ground improvement method with a solidified part overhang length (L) of 0.7a to 1.5a .

  The ground improvement method of the present invention can be performed using a general construction machine 20 having a main body such as a backhoe as shown in FIG. The construction machine 20 shown in FIG. 2 has a mixed stirring attachment 22 provided with a stirring blade 22a attached to the tip of an arm 21a of a backhoe 21 that is a main body of the construction machine 20.

[(A) Pile-shaped solidified part forming step]
As shown in FIGS. 1 and 3, the pile-shaped solidified portion forming step (A) moves the construction machine to a predetermined position of the soft ground 1 to be constructed (in FIG. 3, the main body of the construction machine). The backhoe is not shown.), A setting step (a) for setting the mixing and stirring attachment 22 at a predetermined position, and the stirring blade 22a is rotated while discharging the solidifying material from the tip of the mixing and stirring attachment 22, thereby While mixing and stirring soft soil, the stirring and penetration step (b) for penetrating the mixed stirring attachment 22 to a predetermined depth in the soft ground 1, and the stirring blade 22a while discharging the solidified material from the tip of the mixed stirring attachment 22 Is rotated, and the mixing / stirring attachment 22 is pulled out from the penetration hole 2 while mixing and stirring the solidified material and soft soil, and the formation of the pile-shaped solidified portion 3 is completed.
In addition, as a method of discharging the solidified material from the mixed stirring attachment, a method of discharging the solidified material only when the mixed stirring attachment penetrates may be used, or a method of discharging the solidified material only at the time of drawing may be used. .

[(B) Expanded solidified portion forming step]
As shown in FIG.1 and FIG.3, an expansion solidification part formation process (B) is a pile-shaped solidification in the position connected around the upper part of the pile-shaped solidification part 3 formed in the pile-shaped solidification part formation process (A). Move the construction machine or the mixing and stirring attachment 22 so as to be integrated with the part 3 to form an enlarged solidified part, and set the mixing and stirring attachment 22 at a predetermined position. In the setting step (d), while the solidified material is discharged from the tip of the mixed stirring attachment 22, the stirring blade 22a is rotated to mix and stir the solidified material and soft soil, and the mixed stirring attachment 22 is moved to the soft ground 1 The stirring blade 22a while discharging the solidification material from the tip of the mixing / stirring attachment 22 and the stirring / penetrating step (e) that penetrates from the ground surface to a depth less than the depth at which the pile-shaped solidified portion 3 is formed. Times And mixing and stirring the solidified material and soft soil, and including a stirring / pulling step (f) of pulling out the mixed stirring attachment 22 from the penetration hole 2, curing the mixed and stirred mixture of the solidified material and soft soil, The formation of the solidified portion 3 and the enlarged solidified portion 4a integrated with the periphery of the upper portion of the pile-shaped solidified portion 3 is completed.
In FIG. 3, after the enlarged solidified portion 4 a is formed, another enlarged solidified portion 4 b is formed at a position opposite to the pile-shaped solidified portion 3 to complete the ground improvement body 5.

  The order of the pile-shaped solidified portion forming step (A) and the enlarged solidified portion forming step (B) may be as described above, forming the pile-shaped solidified portion first, and then forming the enlarged solidified portion, An enlarged solidified part may be formed first, and then a pile-shaped solidified part may be formed.

As the solidifying material to be added to the soft ground, slurry-like cement, cement solidifying material, quicklime, etc. can be usually used.
The above-mentioned solidified material is, for example, a solidified material of a predetermined specification (usually in the form of a slurry) manufactured at a solidified material slurry manufacturing plant, with a predetermined pressure and flow rate from the solidified material slurry manufacturing plant. By feeding to a part, it can supply in a soft ground from the front-end | tip part of a mixing stirring attachment.

  As shown in FIG. 3, the pile-shaped solidified portion 3 of the ground improvement body 5 may be formed so as to be grounded on the high-quality ground 103 having a firm support force, and the pile-shaped solidified portion is grounded on the high-quality ground. The pile-shaped solidified portion may be formed so as to float in the soft ground (not shown).

The length in the vertical direction of the expanded solidified portion (expanded solidified portion depth: H) is substantially equal to the length of the expanded solidified portion protruding from the pile-shaped solidified portion in the horizontal direction (extended solidified portion protruding length: L). Is preferably 0.7L to 1.5L, and more preferably 0.8L to 1.2L with respect to the extended solidified portion overhang length (L).
For example, when the expanded solidified portion overhang length (L) is 1 to 3 m, the expanded solidified portion depth (H) is preferably 0.7 to 4.5 m, more preferably 0.8 to 3.6 m, More preferably, it is 1-3m.
When the expanded solidified portion depth (H) is less than 0.7 L with respect to the expanded solidified portion overhang length (L), the expanded solidified portion becomes thin. An excessive bending moment or shear stress is generated in the enlarged solidified portion, and the joint portion between the pile-shaped solidified portion and the enlarged solidified portion is easily broken. If the expanded solidified portion depth (H) exceeds 1.5L, the expanded solidified portion depth (H) becomes too large with respect to the expanded solidified portion overhang length (L). It does not have a well-balanced size with respect to the extended solidified portion overhang length (L), which is economically undesirable.

  In addition, since an expansion solidification part is normally formed using the same thing as the mixing stirring attachment which forms a pile-shaped solidification part, the cross section (horizontal direction cross section) which cut the pile-shaped solidification part in the horizontal direction is substantially When the length of one side of the rectangular shape is a, the length that the expanded solidified portion projects horizontally from the pile-shaped solidified portion (enlarged solidified portion overhang length: L) is a pile shape The length is substantially equal to the length a of one side of the solidified portion, specifically 0.7a to 1.5a.

  The example shown in FIGS. 1 and 3 is an example in which the ground improvement method of the present invention is applied to the middle layer improvement method in which the depth of improvement by the ground improvement body is about 10 m from the ground surface. Not only the middle layer improvement method, but also the shallow layer improvement method and the deep layer improvement method can be applied.

  In the example shown in FIGS. 2 and 3, a mixed stirring attachment 22 provided with a stirring blade 22 a is attached to the tip of an arm 21 a of a backhoe 21 that is a main body of a general construction machine 20. By rotating the stirring blade 22a in the vertical direction, the solidified material and the soft soil are mixed and stirred, the mixture of the solidified material and the soft soil is hardened, and the pile-shaped solidified portion having a substantially rectangular cross section in the horizontal direction and an enlargement An example of forming a solidified portion is shown.

Next, the ground improvement body formed by the ground improvement construction method of the present invention (hereinafter also referred to as the ground improvement body of the present invention) will be described.
The ground improvement body of the present invention is a ground improvement body for reducing consolidation settlement of soft ground, which is a hardened body of a mixture of soft soil and solidified material constituting the soft ground, and is a pile-shaped hardened body A pile-shaped solidified portion, and an enlarged solidified portion integrated with the pile-shaped solidified portion, which is a hardened body connected to the periphery of the upper portion of the pile-shaped solidified portion.

FIG. 4 is a perspective view showing a first embodiment of the ground improvement body of the present invention, and FIG. 5 is a front view of the ground improvement body. The ground improvement body shown in FIG.4 and FIG.5 has the same form as the ground improvement body demonstrated in FIG. 3, The same code | symbol was attached | subjected about the part which is common in FIG.
As shown in FIGS. 4 and 5, the ground improvement body 5 includes a pile-shaped solidified portion 3 having a substantially rectangular cross section in the horizontal direction and a hardened structure connected to the upper portions of the two opposite side surfaces of the pile-shaped solidified portion 3. The body has two enlarged solidified portions 4a and 4b having a substantially rectangular cross section in the horizontal direction.
The length that the expanded solidified portions 4a and 4b project from the pile-shaped solidified portion 3 in the horizontal direction (enlarged solidified portion projected length: L) is the length of one side of the pile-shaped solidified portion 3 whose horizontal cross section is substantially rectangular. When the thickness is a, the length is substantially equal to the length a of one side of the pile-shaped solidified portion 3, and is specifically 0.7a to 1.5a. Further, the length in the vertical direction (enlarged solidified portion depth: H) of the enlarged solidified portions 4a and 4b is preferably substantially equal to the extended solidified portion overhang length (L), preferably 0.7L to It is 1.5L, More preferably, it is 0.8L-1.2L.

When the area of the pile-like solidified portion 3 of the ground improvement body 5 shown in FIGS. 4 and 5 is 1.5 m × 1.5 m, for example, the overhang length (L) of the enlarged solidified portions 4a and 4b is 1.0 to 4.5 m, and the expanded solidified portion depth (H) is preferably 1.0 to 4.5 m.
For example, the area of the pile-shaped solidified portion 3 of the ground improvement body 5 is 1.5 m × 1.5 m, the expanded solidified portion overhang length (L) of the expanded solidified portions 4a and 4b is 1.0 m, and the expanded solidified portion depth When (H) is 1.0 m, the area on the ground surface of the ground improvement body 5 is 5.25 m ² (= the cross-sectional area of the horizontal cross section of the pile-shaped solidified portion (1.5 m × 1.5 m = 2. 25 m ² ) + the cross-sectional area (1.0 m × 1.5 m × 2 = 3.0 m ² ) of the horizontal cross section of the enlarged solidified portion, and the ground improvement body 5 is formed only by the pile-shaped solidified portion 3 Compared to the area of 2.25 m ^{2 on} the ground surface, the area of the ground improvement body on the ground surface becomes larger, and the area of the ground improvement body on the ground surface and the area of the entire ground on which the entire load of the embankment is applied Since the improvement rate that is the ratio can be set to a large value, Or economically than when increasing the number of ground improvement body, it is possible to reduce the consolidation settlement of soft ground by embankment like. According to the ground improvement body 5 of this invention, it is also possible to set an improvement rate to 50% or more.
In addition, although only one enlarged solidified portion may be formed on one of the upper side portions of the pile-shaped solidified portion, the overlay load such as the embankment on the improved ground is not evenly applied to the pile-shaped solidified portion, Since the load tends to be eccentric with respect to the pile-shaped solidified portion or the expanded solidified portion due to the overload, and the joint portion between the pile-shaped solidified portion and the expanded solidified portion is easily broken, the expanded solidified portion is the pile-shaped solidified portion. It is preferable to form at least two at opposite positions with respect to.

Next, another example of the ground improvement body of the present invention will be described.
FIG. 6 is a perspective view showing a second embodiment of the ground improvement body of the present invention, and FIG. 7 is a front view of the ground improvement body. As shown in FIGS. 6 and 7, the ground improvement body 7 is connected to a pile-shaped solidified portion 8 having a substantially rectangular cross section in the horizontal direction, and all side surfaces of the pile-shaped solidified portion 8 and upper portions of corner portions. The hardened body has eight enlarged solidified portions 9a to 9h having a substantially rectangular cross section in the horizontal direction. The extended solidified portion overhang length (L ₁ ) of each of the enlarged solidified portions 9a to 9h is a length substantially equal to the length a of one side of the pile-shaped solidified portion 8 having a substantially rectangular cross section in the horizontal direction. Is 0.7a to 1.5a. The length in the vertical direction of the expanded solidified portion 8 (expanded solidified portion depth: H ₁ ) is preferably substantially equal to the extended solidified portion overhang length (L ₁ ), preferably 0.7 L ₁ to 1. a .5L _1, more preferably 0.8L ₁ ~1.2L _1.

FIG. 8 is a plan view of the improved ground obtained by improving the soft ground by the ground improved body shown in FIG. 7, and FIG. 9 is a vertical sectional view showing a schematic configuration of the improved ground. In addition, the example shown in FIG. 9 has shown the ground improvement body 7 of the bottoming system which made the pile-shaped solidification part 8 ground to the quality ground 103. FIG.
As shown in FIGS. 8 and 9, when the ground improvement body 7 is composed only of the pile-shaped solidified portion 8, the cross-sectional area (am × am) of the horizontal section of the pile-shaped solidified portion 8 and the entire improved ground are The improvement rate, which is a ratio with the shared area (Dm × Dm) for sharing the load such as embankment, is a ² / D ² × 100%. On the other hand, since the area (dm × dm, d = a + 2L ₁ ) of the ground improvement body 7 on the ground surface of the ground improvement body 7 having the enlarged solidified portions 9a to 9h increases, the improvement rate of the ground improvement body 7 (D ² / D ² × 100%) can be set larger than the improvement rate (a ² / D ² × 100%) when the ground improvement body 7 is composed only of the pile-shaped solidified portion 8. The consolidation settlement of the improved ground 100 obtained by improving the soft ground 1 with the ground improvement body 7 can be reduced. According to the ground improvement body 7 of the present invention, the improvement rate can be set as large as 50 to 100%.
For example, when applying the ground improvement method of the present invention to the middle layer improvement method and forming the pile-shaped solidified portion 8 having a horizontal sectional area of 1.5 m × 1.5 m, the expanded solidified portion depth (H ₁ It is preferable to form enlarged solidified portions 9a to 9h having a length of 1.0 to 1.5 m and an extended solidified portion overhang length (L ₁ ) of 1.0 to 1.5 m. In this case, the area of the ground improvement body 7 on the ground surface can be set to 3.5 m × 3.5 m to 4.5 m × 4.5 m.

[Example 1]
The ground improvement body 5 shown in FIG.4 and FIG.5 was formed using the ground improvement construction method and construction machine shown in FIGS. First, in the pile-shaped solidified portion forming step (A), the horizontal cross-section is approximately 1.5 m × 1 on the soft ground including the cohesive soil having a depth of 6.0 m and the horizontal cross-section is rectangular. A 5 m bottomed pile-shaped solidified portion 3 was formed. Next, the enlarged solidified portion forming step (B) is connected to the upper portion of the pile-shaped solidified portion 3 and the enlarged solidified portion overhanging length L is 1.0 m at a position facing the pile-shaped solidified portion 3 as the center. Two enlarged solidified portions 4a and 4b having a solidified portion depth H of 1.0 m and a horizontal cross section of a substantially rectangular shape were formed.
Next, for the improvement target area of 1000 m ² , the total improvement soil amount required when the improvement rate is 50%, when using the ground improvement body (Example 1) having the expanded solidification part of the present invention, A comparison was made when using a ground improvement body that does not have a conventional expanded solidified part.
(When having an enlarged solidified part)
The area of the ground surface portion of the improved body was 5.25 m ² (1.5 m × 3.5 m). The number of necessary improved bodies is 1000 m ² × 50% ÷ 5.25 m ² ≈96, and the amount of improved soil per one is 1.5 m × 1.5 m × 6.0 m + 2 × (1.0 m × 1 .0m × 1.5m) = 16.5m ^3, and the total modified soil weight was 96 × 16.5m ³ = 1584m ^3.
(When there is no enlarged solidification part)
The area of the ground surface portion of the improved body was 2.25 m ² (1.5 m × 1.5 m). The number of necessary improved bodies is 1000 m ² × 50% ÷ 2.25 m ² ≈223, and the amount of improved soil per one is 1.5 m × 1.5 m × 6.0 m = 13.5 m ³ the total modified soil weight was 223 × 13.5m ³ = 3010.5m ^3.
From the above, when the improved body having the enlarged solidified portion of the present invention is used, the total amount of improved soil required to ensure the same improvement rate is compared with that when the improved body having no conventional expanded solidified portion is used. As a result, it was reduced to about half, and the soft ground could be improved economically.

[Example 2]
The ground improvement body 7 shown in FIG.6 and FIG.7 was formed using the ground improvement construction method and construction machine shown in FIGS. First, by the pile-shaped solidified portion forming step (A), the horizontal cross section has a substantially rectangular shape on the soft ground including the viscous soil having a depth of 6.0 m, and the cross sectional area of this cross section is 1.5 m × 1.5 m. The bottomed pile-shaped solidified portion 8 was formed. Next, by the enlarged solidified portion forming step (B), the solidified portion overhanging length L ₁ is 1.5 m and the enlarged solidified portion depth H ₁ is connected to all side surfaces and the upper corners of the pile-shaped solidified portion 8. Eight expanded solidified portions 9a to 9h having a horizontal cross section of approximately 1.5 mm were formed.
Next, the case of using relative improvement target area 1000 m ^2, the total modified soil amount necessary when the improvement ratio of 50%, soil improvement material having a larger coated portion of the present invention (Example 2), A comparison was made when using a ground improvement body that does not have a conventional expanded solidified part.
(When having an enlarged solidified part)
The area of the ground surface portion of the improved body was 20.25 m ² (4.5 m × 4.5 m). The number of necessary improved bodies is 1000 m ² × 50% ÷ 20.25 m ² ≈25, and the amount of improved soil per one is 1.5 m × 1.5 m × 6.0 m + 8 × (1.5 m × 1 .5m × 1.5m) = 40.5m ^3, and the total modified soil weight was 25 × 40.5m ³ = 1012.5m ^3.
(When there is no enlarged solidification part)
The area of the ground surface portion of the improved body was 2.25 m ² (1.5 m × 1.5 m). The number of necessary improved bodies is 1000 m ² × 50% ÷ 2.25 m ² ≈223, and the amount of improved soil per one is 1.5 m × 1.5 m × 6.0 m = 13.5 m ³ the total modified soil weight was 223 × 13.5m ³ = 3010.5m ^3.
From the above, when the improved body (Example 2) having the expanded solidified portion of the present invention is used, the total amount of improved soil required to ensure the same improvement rate is the improved body having no conventional expanded solidified portion. Compared to when it was used, it was significantly reduced to about 1/3, and the soft ground could be improved economically.

It is a flowchart which shows an example of the ground improvement construction method of this invention. It is a figure which shows schematic structure of an example of the construction machine used for the ground improvement construction method of this invention. It is process drawing which shows an example of the ground improvement construction method of this invention. It is a perspective view which shows 1st embodiment of the ground improvement body of this invention. It is a front view of the ground improvement body shown in FIG. It is a perspective view which shows 2nd embodiment of the ground improvement body of this invention. It is a front view of the ground improvement body shown in FIG. It is a top view of the improved ground improved by the ground improvement body shown in FIG. It is sectional drawing of the perpendicular direction which shows schematic structure of the improved ground shown in FIG. It is explanatory drawing which shows schematic structure of the improved ground by the conventional pile type improvement construction method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Soft ground 2 Penetration hole 3 Pile solidification part 4a, 4b Expansion solidification part 5 Ground improvement body 6 Penetration hole 7 Ground improvement body 8 Pile solidification part 9a-9h Expansion solidification part 20 Construction machine 21 Backhoe 21a Arm 22 Mixed stirring attachment 22a Stirring blade 100 Improved ground 101 Solidified body (improved body)
102 Filling 103 Good quality ground

Claims (3)

Using a construction machine having a mixing stir attachment for discharging the solidified material and mixing and stirring the soft soil and the solidified material , the solidified material is supplied into the soft ground, mixed and stirred, and the solidified material and the soft soil are removed. A ground improvement method that reduces consolidation settlement of soft ground by a ground improvement body that has been hardened,
(A) In the process of penetration and extraction of the mixed stirring attachment into the soft ground, the solidified material is supplied into the soft ground, mixed and stirred, and the pile-shaped solidified portion composed of the solidified material and soft soil is formed. A pile-shaped solidified part forming step to be formed;
(B) In the process of penetration and extraction of the mixed stirring attachment into the soft ground at a position different from the position of penetration and extraction in the pile-shaped solidified part forming step (A), the pile-shaped solidified part The solidified material is supplied into the soft ground so as to be connected to the periphery of the upper portion of the slab, mixed and stirred, and the expanded solidified portion composed of the solidified material and the soft soil is integrally formed with the pile-shaped solidified portion. A solidified portion forming step;
Only containing and horizontal cross-section of the pile-like coated portion has a substantially rectangular shape, if the length of one side of the substantially rectangular cross section is a, the larger coated portion is the pile-like solidified portion The ground improvement construction method characterized in that the length (L) of the solidified portion projecting in the horizontal direction is 0.7a to 1.5a . In the expansion solidified portion forming process (B), the vertical length of the enlarged coated portion (enlarged solidified portion depth: H) is such that a 0.7 L ~ 1.5 L, to form an enlarged solidified portion claims Item 1. Ground improvement method according to item 1.   The expanded solidified portion is formed so that a length (enlarged solidified portion depth: H) in the vertical direction of the expanded solidified portion is 1 to 3 m in the expanded solidified portion forming step (B). The ground improvement method described.

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