JP2009002007A - Soil improving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an effective and proper soil improving method which can bring about an excellent improvement effect even at a low improvement rate by improving a static compaction effect brought about by a plastic gel. <P>SOLUTION: A ground material composed of the plastic gel is statically pressurized and injected into the ground to be improved, so that the original ground can be peripherally pushed open to become solid and an improved body can be formed by the solidification of the grout material. In that case, many improved piles are formed by being disposed in a state that peripheral surfaces of them are brought at least into contact with one another, so that the integral improved body can be formed of all the improved piles. A wall-shaped improved wall 10 or an improved block in a lattice shape in a plan view is suitably used as the improved body. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a ground improvement method for soft ground and sand ground, and more particularly to a ground improvement method belonging to the category of static compaction methods.

As this type of ground improvement method, sand compaction pile method and rod compaction pile method are well known, but in recent years, static compaction method using plastic gel as shown in Patent Documents 1 and 2 has been developed. It is in the mood to spread widely as a preventive measure against lateral flow and liquefaction of sand ground.
This is because a plastic gel mainly composed of fly ash or cement bentonite is used as a grout material to be injected into the ground, and the surrounding ground is grounded by the injection pressure by statically injecting it into the ground. The main objective is to form a pile-like improved pile by consolidation of the grout material, while gradually expanding and compacting.
JP 2003-105745 A JP 2006-257281 A

In the above method, the injection holes for injecting the plastic gel as the grout material are formed in the target ground in a pattern of square array or equilateral triangle array (staggered array), and therefore a large number of improved piles finally formed The arrangement pattern is also a square arrangement or an equilateral triangle arrangement as it is, but such an arrangement pattern may not always provide a sufficient improvement effect.
Therefore, in order to obtain a sufficient improvement effect in the above construction method, it is necessary to increase the improvement rate sufficiently by narrowing the interval between the injection holes, which increases the construction cost and the construction period, so there is room for improvement in that respect. Is what is left.

  In view of the above circumstances, the present invention can further improve the static compaction effect by the plastic gel, so that an excellent improvement effect can be obtained even at a low improvement rate, thereby reducing the construction cost and the construction period. The purpose is to provide an effective and appropriate ground improvement method.

  The present invention statically injects a grout material composed of a plastic gel into the ground to be improved, thereby spreading and solidifying the original ground around the ground, and an improved body by solidifying the grout material. It is a ground improvement method to be formed, and by forming a large number of improved piles side by side with their peripheral surfaces at least in contact with each other, an integral wall-like or block-like improved body is formed over the improved piles. It is a feature.

In the present invention, by forming a large number of improved piles arranged in one direction, an improved wall having a wall shape on one side is formed as a whole, and the improved walls are spaced from each other within a region to be improved. In this case, it is preferable to form a plurality in a state of being arranged substantially in parallel.
In addition, it is also preferable to form an improved block in which a plurality of improved piles are arranged in two directions orthogonal to each other so that the improved walls in the two directions are orthogonal to each other to form a lattice shape in plan view. is there.
Based on the improvement rate determined by the thickness and spacing of the improved wall, the volume strain generated at the center position between the improved walls is calculated by the improvement, and the post-improvement is calculated based on the volume strain and the gap ratio before the improvement. By calculating the gap ratio of the ground, it is possible to calculate and evaluate the N value of the improved ground based on the gap ratio.

  According to the ground improvement method of the present invention, a large number of improved piles are integrated to form an improved body in the form of an improved wall or improved block, compared to a conventional general method in which the improved piles are simply arranged independently. If the improvement rate is the same, the improvement effect can be greatly improved. Therefore, the improvement rate required to obtain the equivalent improvement rate is sufficiently small, and in any case, the improvement rate is lower than the conventional method. The improvement effect which is excellent in the rate can be obtained, and it is possible to reduce the construction cost and the construction period required for the ground improvement.

  In the ground improvement method of the present invention, the improvement effect can be quantitatively determined only by determining the form and improvement rate of the improved body, using a simple calculation formula or a simple chart that can be created based on the calculation formula. It is possible to evaluate and to easily determine the improvement rate necessary to obtain a desired improvement effect.

1 to 2 show a first embodiment of the present invention. This is an application example when the ground improvement method of the present invention is implemented as a countermeasure for preventing lateral flow with respect to the ground behind the revetment 1.
That is, when the revetment 1 is damaged and collapses or tilts to the sea side during a major earthquake, a lateral flow occurs in which the ground behind it flows toward the sea side. Since serious damages such as collapse, inclination, and damage to the support pile 3 are assumed, the ground improvement is performed on the ground between the revetment 1 and the structure 2 in the first embodiment, and FIG. By forming a plurality of wall-shaped improved walls 10 as shown in FIG. 2 at a predetermined interval, even if the revetment 1 breaks down, side walls are prevented from being generated by the improved walls 10, thereby The structural safety and reliability of 2 and the support pile 3 are ensured.

  The ground improvement method of the first embodiment is based on a static compaction method by statically injecting a grout material made of plastic gel into the original ground as shown in Patent Documents 1 and 2. However, in the conventional method, a large number of improved piles are simply formed in a square or equilateral triangular arrangement pattern at intervals, whereas in this embodiment, a large number of improved piles are provided as shown in FIG. The piles 5 are formed side by side in a state where at least the peripheral surfaces are in contact with each other to form a wall-like improved wall 10 of one surface as a whole, and the improved walls 10 are spaced at a predetermined interval. A plurality are formed in a state of being arranged in a substantially parallel state.

  In this case, the conventional process can be used as it is for the process of forming the individual improved piles 5 (static compaction process by pressure injection of grout material). For example, as shown in FIG. What is necessary is just to press-inject the grout material which consists of plastic gel by inserting the injection | pouring pipe | tube 6 in it. However, in the conventional construction method, the injection interval is set so that each improved pile 5 is formed independently, but in this embodiment, the injection is performed so that their peripheral surfaces are at least in contact with each other or are somewhat overlapped. The interval will be set closely.

Further, the order of formation of the large number of improved piles 5 may be appropriate. For example, the improved piles 5 may be formed one by one sequentially from one side portion of the improved wall 10 to be formed to the other side portion. One or several piles 5 may be alternately formed at a time, and finally all may be made continuous. Of course, if possible, a large number of improved piles 5 may be formed together at one time.
Moreover, in the formation of each improved pile 5 (static compaction process by each improved pile 5), it may be performed sequentially from the deep part toward the surface layer part, and the surface layer part may precede the deep part as necessary. Anyway.
Further, if necessary, as shown in FIG. 2 (a), other improved piles 5 may be formed at appropriate intervals between the improved walls 10 so that the compacting effect between the improved walls 10 can be achieved. Can be further increased.

As described above, a large number of the improved piles 5 are continuously and integrally formed so as to be in contact with each other to form the wall-like improved wall 10, so that the entire improved wall 10 functions as an underground wall to the ground. In addition to obtaining the reinforcing effect, by providing the improved walls 10 in substantially parallel, the original ground left between them is also effectively compacted from the improved walls 10 on both sides and is naturally consolidated and solidified. .
As a result, an excellent compaction effect on the entire original ground can be obtained, and even if the improvement rate is not so large as described later, that is, the thickness of the improvement wall 10 is small, the interval between the improvement walls 10 is large. However, a sufficient ground improvement effect is obtained, and an excellent lateral flow prevention effect and liquefaction prevention effect are obtained.

3 to 4 show a second embodiment of the present invention. This is to improve the ground for preventing lateral flow with respect to the original ground between the revetment 1 and the structure 2 as in the first embodiment, but in the first embodiment, a plurality of walls are provided. In the second embodiment, a lattice-like improvement block 20 is formed instead of the parallel improvement wall 10.
That is, as shown in FIG. 4, the improved block 20 of the second embodiment has a large number of improved piles 5 arranged side by side in two directions orthogonal to each other and formed as a whole in a plan view lattice shape. The improved wall 10 of the first embodiment is integrally formed in a state where a plurality of the improved walls 10 are combined in an orthogonal state (in the case of FIG. 3A, four in each of the vertical and horizontal directions). In this case, if necessary, another improved pile 5 may be provided in the grid of the lattice as shown in FIG.
According to this, not only a more excellent reinforcing effect on the original ground can be obtained by the robust grid-like improvement block 20 in which the two-direction improvement walls 10 are combined vertically and horizontally, but it is left in the grid of the grid. The original ground is also compacted from the surroundings and naturally becomes sufficiently solid, so even if the improvement rate is sufficiently low, that is, without increasing the thickness of the improvement wall 10 in both directions, the grid area is also made very small. Even if it does not, the outstanding improvement effect with respect to the whole original ground is acquired.

Next, a design method for carrying out the ground improvement method by forming the improved wall 10 and the improved block 20 and a method for evaluating the ground improvement effect by the method will be described with reference to FIGS.
This method is based on the method for evaluating the compaction effect in the sand compaction pile method already proposed by the applicant (see Japanese Patent Application Laid-Open No. 10-237856), and between the improved walls corresponding to the form of the improved body. The improvement effect corresponding to the form of the improved body is estimated by calculating the density increase after the improvement by paying attention to the volume strain generated in the above.

(1) Improvement rate and volumetric strain of the ground As shown in FIG. 5 (a), the radius of the improved pile 5 is R ₀ and the effective thickness of the improved wall 10 is d.
2R ₀ · d = πR ₀ ²
From the relationship
d = πR _0/2
And
Further, if the interval (distance between centers) of the improved walls 10 is A, the improvement rate δ in that case is δ = d / A
Represented as:
In that case, the volume strain ε _ν generated at the center position between the improved walls 10 due to the improvement is ε _ν = d / (A−d) = δ / (1−δ).
Represented as:
Further, in the case of the lattice-like improved block 20 as shown in FIG. 5B, the effective thickness in both directions is d,
d = πR _0/2
And Also, assuming that the interval in one direction (center distance) is A and the interval in the orthogonal direction (same) is B, the improvement rates δ _A and δ _{B in} both directions are δ _A = d / A, respectively.
δ _B = d / B
In this case, the volume strain ε _{ν at} the center position between the improved walls 10 in both directions (that is, the center position of the lattice mesh) is ε _ν = δ _A / (1-δ _A ) + δ _B / (1-δ _B )
It becomes.
For reference, when the improved piles 5 are independently arranged in a square pattern as usual, the radius of each improved pile 5 is set to R ₀ and the center position of the square arrangement from the center as shown in FIG. When the distance to the _{R m,} the improvement ratio _{δ δ = (R 0 / R} m) 2
And the average volume strain ε _ν is ε _ν = R ₀ ² / (R _m ² −R ₀ ² ) = δ / (1-δ)
It is.

(2) Increase in N value due to improvement When N value of the ground before improvement is N, and N _a is a corrected N value that corrects the effects of the effective upper loading pressure σ _v ′ and fine grain content F _c of the ground, The corrected N value N _a is obtained by equation (1).
ΔN _{f in the} equation (1) is a correction value of the N value for the fine particle content F _c , which can be determined with reference to the simple liquefaction determination method of the building foundation structure design guideline.

From the corrected N value N _a obtained by the equation (1), the relative density D _r of the ground before improvement and the gap ratio e ₀ of the ground before improvement are obtained by a series of equations shown as the equation (2), Based on the gap ratio e ₀ and the volumetric strain ε _ν , the improved ground gap ratio e ₀ ′ is obtained. The volume strain ε _ν here is obtained based on the improvement rate δ when the improved wall 10 is formed, and is obtained corresponding to the improvement rates δ _A and δ _B in both directions when the improved block 20 is formed. Is.
From the result, the improved relative density D _r ′ of the ground and the corrected N value N _a ′ after the improvement are sequentially obtained by back calculation, and from the result, the improved N value N ′ by the formula (1) ′. Can be requested.

In addition, e _max and e _min in the formula (2) are the maximum sand gap ratio and the minimum sand gap ratio, respectively, and these values are preferably obtained from the in-situ collected soil. with F _c (3) can be obtained by expression.

In addition, α in the equation (2) is a parameter that takes into account the effect that the improvement effect is reduced because the ground is lifted by the ground improvement in sand with a lot of fine particles, and is obtained by the equation (4).

(3) Chart for design and evaluation A chart as shown in FIG. 6 can be created from the result of the above calculation, and a design for determining the improvement rate δ by using the chart, and an improvement based thereon The effect can be easily evaluated.
The chart shown in FIG. 6 shows the amount of increase in the correction N value due to the improvement (increase amount ΔNa relative to the correction N value Na of the ground), using the improvement rate δ and the fine particle content Fc as parameters for each form of improvement. It is shown. All the charts shown are applied when the improvement rate δ is 15%, (a) is applied to the improved wall 10, (b) is applied to the improved block 20, (C) is applied when the independent improved piles 5 are arranged in a square for reference.
From this chart, when the improvement rate δ is set to 15%, for example, when the correction N value Na of the ground is 15 and the fine particle content Fc is 10%, as shown in FIG. In the case of the improved wall 10, the increase amount of the N value is 44, and as shown in (b), the increase amount of the N value is 70 in the case of the improved block 20.
On the other hand, when the independent improved piles 5 are simply arranged in a square by the conventional method, the increase amount of the N value is only 28 as shown in (c), and even if the improvement rate δ is the same, the improvement effect can be obtained. It turns out that a big difference arises.

  As described above, according to the ground improvement method of the present invention, a large number of improved piles 5 are integrated to form an improved body in the form of improved wall 10 or improved block 20, so that the improved piles 5 are simply spaced apart. Compared to the conventional general arrangement method that is arranged independently, if the improvement rate is equivalent, the improvement effect can be remarkably improved. Therefore, the improvement rate necessary to obtain the equivalent improvement rate is sufficiently small. In any case, even if the improvement rate is low compared with the conventional method, an excellent improvement effect can be obtained, and the construction cost and the construction period required for ground improvement can be reduced.

  Further, in the ground improvement method of the present invention, the improvement effect (increase in N value) is quantitatively evaluated using only the above calculation formula or chart only by determining the improvement rate for each form of the improved body. Therefore, the improvement rate necessary for obtaining a desired improvement effect can be easily determined using the above-described arithmetic expression or chart.

Although the embodiments of the present invention have been described above, the above embodiments are merely suitable examples, and the present invention is not limited to the above embodiments.
For example, in the above embodiment, only the wall-like improvement wall 10 and the lattice-like improvement block 20 are exemplified as the improvement body in the present invention, but the improvement body in the present invention has many improvements by the grout material made of plastic gel. As long as the piles are integrally formed in a wall shape or a block shape, the form of the improved body is arbitrary as long as it is formed, and various forms other than those shown in the above embodiment are conceivable, and particularly improved As the form of the block 20, for example, those shown in FIGS.
The improved blocks 21 and 22 shown in FIG. 7 and FIG. 8 are both formed by surrounding the periphery in a box shape by the two-way improvement wall 10 and forming only the one-way improvement wall 10 inside thereof (in other words, FIG. 3 9 is simplified by partially omitting the internal improvement wall 10 from the grid-like improvement block 20 shown in FIG. 9), and the improvement block 23 shown in FIG. 9 is a main improvement wall 10 and an orthogonal direction to support it. 10 provided with a plurality of buttress-like improved walls 10 and the one shown in FIG. 10 are a plurality of improved piles arranged in a hexagonal shape to form a honeycomb-like improved block 24 as a whole.

  In the above embodiment, the ground improvement method according to the present invention is applied as a side flow prevention measure against the back ground of the revetment. However, the present invention is not only a side flow prevention measure, for example, around buildings or buildings. It is effective as a countermeasure for the ground directly below, and is widely applicable to various ground improvements for various purposes such as measures for preventing liquefaction and subsidence of soft ground, measures for strengthening bearing capacity, and prevention of deformation due to anchoring during underground excavation. Needless to say.

1 shows a first embodiment of a ground improvement method according to the present invention. It is a figure showing an improvement wall same as the above. The 2nd Embodiment of the ground improvement construction method of this invention is shown. It is a figure which shows an improvement block same as the above. It is explanatory drawing about the improvement rate and volume strain by each improvement body formed in this invention and the conventional ground improvement construction method. It is a chart which shows the improvement effect by each improvement body same as the above. It is a figure which shows other embodiment of this invention. It is a figure which shows other embodiment same as the above. It is a figure which shows other embodiment same as the above. It is a figure which shows other embodiment same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Revetment 2 Structure 3 Support pile 5 Improved pile 6 Injection pipe 10 Improved wall (improved body)
20 Improved blocks (improved)
21-24 Improved block (improved)

Claims (5)

Ground improvement to form an improved body by solidifying the grout material by statically injecting the grout material made of plastic gel into the ground to be improved by pressing and spreading the ground to the periphery. Construction method,
A ground improvement construction method characterized in that a large number of improved piles are formed side by side so that their peripheral surfaces are in contact with each other, thereby forming an integrated wall-like or block-like improved body in the whole of the improved piles. The ground improvement method according to claim 1,
By forming a large number of improved piles side by side in a state where their peripheral surfaces are at least in contact with each other, an improved wall having a wall shape of one surface is formed as a whole, and the improved walls are arranged in the improvement target region. A ground improvement construction method characterized in that a plurality of them are formed in a state of being arranged substantially parallel to each other at a predetermined interval. The ground improvement method according to claim 1,
An improved block in which a large number of improved piles are arranged side by side in two directions orthogonal to each other with their peripheral surfaces at least in contact with each other, so that the improved walls in the two directions are orthogonal to each other and form a planar view lattice shape The ground improvement construction method characterized by forming. The ground improvement method according to claim 2 or 3,
Based on the improvement rate determined by the thickness and spacing of the improved walls, the volume strain generated at the center position between the improved walls is calculated by the improvement, and the ground after the improvement is calculated based on the volume strain and the gap ratio before the improvement. A ground improvement construction method characterized by calculating a gap ratio of the ground and calculating and evaluating an N value of the ground after improvement based on the gap ratio. The ground improvement construction method according to claim 4, wherein the N value of the ground after the improvement is calculated and evaluated by the following formula.

Here, N, N ′: N value of ground before and after improvement N _a , N _a ′: Correction N value of ground before and after improvement
σ _ν ': Effective upper pressure
ΔN _f : Correction by fine grain D _r , D _r ': Relative density of ground before and after improvement e ₀ , e ₀ ': Ground ratio before and after improvement e _max , e _min : Maximum sand and minimum gap ratio
α: Volume increase rate due to ground swell
α = 0.00158 × F _c ^1.389
F _c : Fine grain content
ε _ν : Volume strain generated at the center between improved walls
(In the case of an improved wall in one direction)
ε _ν = δ / (1-δ)
δ: Improvement rate
δ = d / A
d: Effective thickness of the improved wall
d = πR _0/2
R ₀ : radius of improved pile
A: Distance between improved walls (center distance between improved walls)
(In the case of a grid-like improved block with improved walls in two orthogonal directions)
[epsilon] _v = {[delta] _A / (1- [delta] _A )} + {[delta] _B / (1- [delta] _B )}.
δ _A , δ _B : Improvement rate in two directions
δ _A = d / A
δ _B = d / B
d: Effective thickness of improved wall in two directions
d = πR _0/2
R ₀ : radius of improved pile
A, B: Distance between improved walls in two directions (center distance between improved walls)

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