JP5351720B2 - Ground improvement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soil improvement construction method for allowing a worker to evaluate the effect of restraining ground soil properly in advance, decide a shape and arrangement of rational improving body, and then construct the improving body with reduced cost. <P>SOLUTION: In this soil improving construction method, such improving body 1 that restrains deformation of the ground when receiving load and being deformed is arranged and constructed in the ground. If stress of the soil to be improved in a case of filling construction is increased, the effect of restraining the soil deformation being different depending on the shape and arrangement of the improving body 1 is obtained as a variation of stress of the ground soil by a finite element method in advance. In addition, a variation of strength or rigidity of the ground soil to be caused by the variation of the stress is obtained based on the variation of the stress. After the shape and the arrangement of the improving body tending to increase this variation are decided, this improving body is constructed. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a ground improvement method for constructing or creating an improved body in the ground.

  As a method for constructing or creating an improved body in the ground, there is a method of stirring and mixing the ground soil and the solidified material, but the present invention is not particularly limited as to a specific method for creating the improved body.

  The conventional ground improvement method for constructing or creating an improved body in the ground roughly applies the following methods such as the composite ground method and the structural method as methods for determining the arrangement. These methods do not consider the effect of the ground proposed in the present invention and restrained by an improved body or the like.

  The composite ground method is a method in which the strength of the improved body and the strength of the ground soil are weighted averages based on the improvement rate or the like according to the following formula (1) and handled as a composite ground having an average strength of the entire ground. Such a construction method including the formula (1) is described in Non-Patent Document 1, for example.

The structural method keeps the strength of the ground as it is and shares the main external force with the improved body. The strength depends on the tensile force and compressive force acting, and the safety factor as a structure (usually 3) This is a method that considers

Deep Mixing Processing Method Manual Editorial Committee, “Depth Mixed Processing Method Design and Construction Manual Revised Version”, Published by Public Works Research Center, March 2004, P80-83

  By the way, in the conventional ground improvement method that creates an improved body in the ground, although the ground is restrained by the improved body, the ground is restrained by the improved body and cannot be freely deformed, so the strength and rigidity increase. However, the effect of restraining the ground proposed in the present invention is not taken into consideration. As a result, the shape and arrangement of a more rational improvement body for exhibiting the restraining effect are not considered.

  Such a ground improvement method that does not consider the effect of restraining the ground by the improved body has the following problems.

  For example, comparing a small number of improved bodies with high strength in the ground and a large number of slightly improved bodies with a lower strength, the average strength of the entire ground (strength as a composite ground) is the same. If so, the design safety factor is the same despite the fact that there is a difference in effect.

  In addition, ground soil that is restrained from free deformation by the improved body has greater rigidity and strength due to the reaction force of the improved body when the average stress of the foundation ground increases, such as in the construction of embankments. However, it is underestimated for its contribution to the suppression and stability of ground soil because it is designed using strength deformation characteristics in a state where the ground soil can be freely deformed without considering its restraining effect.

  As a result, there are cases where the design is excessively safe, or the shape and arrangement of the improved body are not appropriate, and there is a tendency for uneconomic design and construction to be performed.

  On the other hand, when the average stress of the foundation ground decreases as in excavation work, the strength and rigidity decrease as the stress decreases. If the improved body is properly arranged to constrain the deformation of the ground, the reaction force generated in the improved body can reduce the decrease in strength and rigidity. In addition, the decrease in strength and rigidity is large.

  The conventional ground improvement design method does not consider the restraining effect of the ground due to the improved body as described above. There are concerns that it may not be appropriate and problems may arise.

  The present invention was made to solve such problems, and provides a ground improvement method for constructing an improved body under a more suitable arrangement by appropriately evaluating the restraining effect of the ground soil. Moreover, it aims at providing a low-cost and safe ground improvement method by obtaining a rational shape, arrangement and strength of the improved body.

  In order to solve the above-mentioned problems and achieve the object, the invention described in this document is a ground improvement method for constructing an improved body in the ground, and grasps in advance the restraining effect of ground deformation obtained by construction of the improved body. The improvement body is constructed with the shape and arrangement of the improvement body in consideration of the restraining effect of the ground deformation.

More specifically, the invention described in claim 1 is a ground improvement method for constructing an improved body in the ground, and the ground obtained by construction of the improved body when stress of the improved ground such as embankment construction increases. In order to grasp the restraint effect of deformation in advance, the restraint effect of ground deformation, which differs depending on the shape and arrangement of the improved body, is evaluated in advance as a change in ground soil stress by the finite element method. The improvement body is constructed with the shape and arrangement of the improvement body in which at least one of the changes in rigidity tends to increase.
The invention described in claim 2 is based on the ground improvement method described in claim 1, and obtains the constraint effect of ground deformation that varies depending on the shape and arrangement of the improved body as a change in ground soil stress by the finite element method. Based on the change in stress, at least one of the changes in the strength and rigidity of the ground soil caused by the change in the stress is obtained, and the improvement in which at least one of the changes tends to increase The improved body is constructed with the shape and arrangement of the body.
The invention described in claim 3 is based on the ground improvement method described in claim 2, and the change in the stress of the ground soil obtained by the finite element method is the restraining effect of the improved body when the ground receives a load. Therefore, it is characterized in that it is at least one of a direct stress and a shear stress generated as a reaction force.

The invention according to claim 4 is based on the ground improvement construction method according to claim 3, and at least one of the changes in strength and rigidity of the ground soil caused by the change in stress is an embankment construction or the like. When the stress of the improved ground increases, it is an increase of at least one of the strength and rigidity of the ground soil caused by the sum of the direct stress and the shear stress.
As described above, the inventions described in claims 1 to 4 assume a case where the stress of the improved ground such as embankment increases, while the following claims 5 to 5 are assumed. In 8, it is assumed that the stress of the improved ground such as excavation decreases.
That is, in the ground improvement method for constructing the improved body in the ground, the invention described in claim 5 has the effect of restraining the ground deformation obtained by the construction of the improved body when the stress of the improved ground such as excavation decreases. In order to grasp in advance, the restraint effect of ground deformation that varies depending on the shape and arrangement of the improved body is evaluated in advance as a change in ground soil stress by the finite element method, and among the changes in the strength and rigidity of the ground soil caused by this stress change The improvement body is constructed with the shape and arrangement of the improvement body that can suppress at least one of the reductions.
The invention described in claim 6 is based on the ground improvement method described in claim 1, and obtains the restraining effect of ground deformation that varies depending on the shape and arrangement of the improved body as a change in ground soil stress by the finite element method. Based on the change in the stress, the shape of the improved body that can determine the change in at least one of the changes in the strength and rigidity of the ground soil caused by the change in the stress and can suppress the decrease in at least one of the changes. And the improved body is constructed with the arrangement.
The invention described in claim 7 is based on the ground improvement method described in claim 6, and the change in the stress of the ground soil determined by the finite element method is the effect of restraint by the improved body when the ground receives a load. Therefore, it is characterized in that it is at least one of a direct stress and a shear stress generated as a reaction force.
The invention described in claim 8 is based on the ground improvement method described in claim 7, and at least one of the changes in strength and rigidity of the ground soil caused by the change in stress is caused by excavation or the like. When the stress of the improved ground is reduced, it is intended to compensate for at least one of the decrease in strength and rigidity of the ground soil caused by the sum of the direct stress and shear stress.

  The changes in the strength and rigidity of the ground soil mentioned here are caused by the sum of stresses generated by the improved body in the position where the soil is constrained, that is, the sum of the direct stress and shear stress. The change in strength and rigidity can be obtained (expressed) by the following equation (2).

The intensity change described above can be obtained based on the following equations (3) and (4).

S = Rs × Si (3)
Rs = 1 + αΔσ ^p + βΔτ ^q (4)
here,
S: Strength of ground soil changed by restraining deformation Si: Ground soil strength before restraining deformation Rs: Rate of change of strength Δσ: Change of direct stress Δτ: Change of shear stress α, β, p , Q: The shape that constrains the ground, and a coefficient determined by the strength of the improved body. To obtain it more simply, it can be obtained by the following formula (7), which is an extension of the composite ground strength formula.
Sc = Sp × a _P + κ · r _S · Ss (1−a _P ) (7)
here,
Sc: Combined ground strength considering deformation restraint effect Sp: Strength of improved body a _P : Improvement rate Ss: Strength of ground soil before restraint deformation κ: Fracture Strength Reduction Rate r _S : Coefficient Considering Restraint Effect Similarly, the rigidity change described above can be obtained based on the following equations (5) and (6).

E = Re × Ei (5)
Re = 1 + γΔσ ^r + κΔτ ^s (6)
here,
E: Deformation coefficient representing the rigidity of the ground soil changed by restraining deformation Ei: Deformation coefficient representing the rigidity of the ground soil before restraining deformation Re: Stiffness change rate Δσ: Change in direct stress Δτ: Shear Stress change γ, κ, r, s: The shape that constrains the ground, and the coefficient determined by the rigidity of the improved body, can be obtained easily by the following equation (8) that is an extension of the compound ground strength equation: .

Ec = Ep × a _P + κ · r _S · Es (1−a _P ) (8)
here,
Ec: Composite ground deformation coefficient in consideration of the restraining effect of deformation Ep: Deformation coefficient of improved body a _P : Improvement rate Es: Deformation coefficient of ground soil before constraining deformation κ: Corresponds to the destruction of the improved body Reduction rate r _S of the fracture strength of the original ground: a coefficient considering the restraining effect. The invention according to claim 9 is based on the ground improvement method according to any one of claims 1 to 8, and the shape of the improved body is It is characterized by being cylindrical.

The invention described in claim 10 is characterized in that the shape of the improved body is a flat cylindrical shape on the premise of the ground improvement method according to any one of claims 1-8.
The invention described in claim 11 is based on the ground improvement method according to any one of claims 1 to 8, and the shape of the improved body is a cylindrical one that is gradually expanded in the depth direction. It is characterized by that.

  According to the invention described in claims 1, 2, and 5, 6, the improvement effect in consideration of the restraining effect of the ground deformation obtained in advance by grasping the restraining effect of the ground deformation obtained by the construction of the improvement body. Because the improved body is constructed with the shape and arrangement of the above, it is possible to design and construct a more rational improved body considering the constraining effect of the ground, which was difficult in the past, and obtain a much higher improvement effect .

  That is, by using the ground improvement method based on the new concept proposed in the present invention, the conventional design method tends to become excessive when the average stress increases and becomes dangerous when the average stress decreases. The design and construction of the ground improvement method can be carried out more rationally.

  In particular, it is possible to rationally determine the shape, arrangement, and strength of a preferred improved body, which has been difficult when the restraining effect is not considered, and as a result, the shape and arrangement of the improved body can be made without waste. Therefore, infrastructure development in soft ground areas, which tend to be costly, can be implemented more economically, and there are effects such as effective use of construction investment and a great economic effect on the local community.

  According to the third and seventh aspects of the invention, paying attention to the change in stress that varies depending on the shape, arrangement, or strength of the improved body, the ground receives the load for the change in the ground soil stress determined by the finite element method. There is an advantage that the calculation method is simple because at least one of the direct stress and the shear stress generated as a reaction force due to the restraining effect by the improved body is used.

  According to the fourth and eighth aspects of the present invention, at least one of the changes in the strength and rigidity of the ground soil caused by the change in the stress is converted into the ground soil caused by the sum of the direct stress and the shear stress. Therefore, the calculation method is simplified and the reliability of the calculation result is increased.

  According to the ninth aspect of the present invention, a ground improvement method having a higher restraining effect can be provided by arranging the improved body in a cylindrical shape so as to restrain the ground.

  According to the invention described in claim 10, the improved body is improved in a low-cost and high-constraint effect by arranging the improved body in a flat cylindrical shape so as to restrain the ground. Can provide.

  According to the eleventh aspect of the present invention, the shape of the improved body is a cylindrical shape whose diameter is gradually expanded in the depth direction, and is arranged so as to restrain the ground. Will further improve.

It is explanatory drawing which calculates | requires increase of the intensity | strength of soil and rigidity when load, such as embankment, is added, (a) is a vertical cross-sectional explanatory drawing, (b) is a plane explanatory drawing of the figure (a). It is explanatory drawing which calculates | requires the increase in the intensity | strength of soil and rigidity when load, such as a side movement, is applied, (a) is a vertical cross-sectional explanatory drawing, (b) is a plane explanatory drawing of the figure (a). It is plane explanatory drawing which shows the example of the improved body arrange | positioned so that soil may be restrained. It is a three-dimensional explanatory drawing which shows the example which arrange | positions a shallow mixed process layer on the upper part of the improved body arrange | positioned so that soil may be restrained. (A)-(c) is a plane explanatory view which shows the example which arrange | positions an improved body in the direction which resists earth pressure when an uneven earth pressure is applied. It is a figure which shows the example which arrange | positions the improved body which expanded the diameter of the lower part side by side, (a) is the solid explanatory drawing, (b) is sectional explanatory drawing of the figure (a). It is a figure which shows the example of calculation of the improvement effect at the time of using a flat cylindrical improvement body, (a) is a three-dimensional explanatory drawing at the time of providing a shallow mixed process layer, (b) is the improvement similar to FIG. 3D is a three-dimensional explanatory view of the body alone, and FIG. 3C is a three-dimensional explanatory view when a banking body is provided on the shallow mixed treatment layer of FIG. It is plane explanatory drawing which shows the example which arrange | positions a cylindrical improvement body in zigzag form. It is plane explanatory drawing which shows the example which arrange | positions a cylindrical improvement body in a grid | lattice form. (A), (b) is a plane explanatory view showing the example which arranged the cylindrical improvement object so that it may not contact mutually. It is explanatory drawing which shows the example whose improvement body arrange | positioned so that the ground may be restrained may be arch shape seeing planarly. (A)-(d) is explanatory drawing which shows the other example which the improvement body arrange | positioned so that the ground may be restrained may be arch shape seeing planarly. (A)-(c) is explanatory drawing which shows the evaluation result in a centrifugal model test. It is a figure which shows the example in the case of excavating a recessed part adjacent to a columnar improvement area | region, (a) is the solid explanatory drawing, (b) is the plane explanatory drawing. Similarly, it is a figure which shows the example in the case of excavating a recessed part near a columnar improvement area | region, (a) is the solid explanatory drawing, (b) is the plane explanatory drawing. It is a figure which shows the example in the case of excavating a recessed part in the area | region pinched | interposed into the composite improvement body, (a) is the solid explanatory drawing, (b) is the plane explanatory drawing. It is a figure which shows the example in the case of excavating a recessed part near a composite improvement body, (a) is the solid explanatory drawing, (b) is the plane explanatory drawing.

  Hereinafter, more specific embodiments of the ground improvement method according to the present invention will be described. However, although the embodiment of the present invention shows the most preferable form, the present invention is not limited to this.

  For example, the improved body described here is constructed by mixing ground soil and cement or cement-based solidified material such as cement and mixing it, as well as pushing ground and sand into the ground and replacing it with ground soil. Includes crushed stone and sand columns. In addition, the method for construction or construction of the improved body may be either a mechanical stirring mixing method in which the solidified material is discharged into a soft ground and stirred and mixed, or a high pressure jet stirring method in which the solidified material is rotated and injected at high pressure. Specific means and methods for constructing or constructing the body are not limited to specific ones.

  In the ground improvement method for constructing an improved body in the ground, the present invention is applied after determining the arrangement, shape and strength of the improved body so as to effectively restrain the deformation of the ground caused by a change in load. The method is as described above.

  When the ground receives a change in load, the deformation of the ground soil to be deformed is restricted by arranging an improved body. At that time, the change of the soil soil caused by the improved body in the position to restrain the soil is regarded as the change of shear stress and the change of the direct stress, and the change of the strength and rigidity of the soil caused by the sum of the stress is changed. Obtaining and evaluating the restraint effect of the ground by the improved body as the strength and deformation characteristics of the ground soil, and determining the placement, shape and strength of the improved body and constructing it, it can be a rational ground improvement method. it can.

  For example, as shown in FIGS. 1A and 1B, when a load F such as the embankment body 3 is applied to a plurality of cylindrical improvement bodies 1 and an unimproved portion 2 that is the ground between them, In the design and construction method, there is an example in which settlement calculation is performed assuming a ratio of stresses shared by the ground soil of the improved body 1 and the unimproved portion 2. Conventionally, the strength of the unimproved portion 2 is not changed as the strength of the ground soil before the improved body 1 is created.

  On the other hand, in the present invention, as shown in FIG. 1, when a load F such as the embankment body 3 is applied, the change in the direct stress caused by the deformation restraint of the ground soil is represented by Δσ, and the above formulas (3) to (6) ) To determine changes in strength and rigidity of ground soil. In addition, (DELTA) S in FIG.1 (b) shows the intensity | strength change of ground soil, (DELTA) E shows the rigidity change of a ground soil, respectively.

  By this, the restraint effect of the ground soil by the improved body 1 is evaluated as a change in the strength and deformation characteristics of the ground soil, and the shape and arrangement of the improved body 1 for ground improvement are determined in consideration of this. Reasonable ground improvement can be performed by appropriately evaluating the restraining effect of the ground soil.

  In addition, as shown in FIGS. 2A and 2B, when a load IF such as lateral movement due to uneven earth pressure is applied for the embankment body 3 on the abutment 4 side, for example, deformation of the ground soil A change in shearing stress caused by restraint is expressed by Δτ, and a change in strength and rigidity of the ground soil is obtained from the above formulas (3) to (8).

  Thus, rational design and construction are possible by appropriately evaluating the change in stress due to restraint and reflecting this in the change in strength and rigidity of the ground soil. Moreover, since the effect of the restraint which changes with arrangement | positioning of the improvement body 1 is evaluated, the more rational shape, arrangement | positioning, and intensity | strength of the improvement body 1 can be determined.

  Further, for example, as shown in FIG. 3, when the improved body 11 arranged to constrain the ground soil is a flat hollow cylindrical shape (a planar shape is substantially flat oval or flat oval), Thus, the change in the direct stress caused by the deformation restriction of the ground soil of the improved body 11 arranged in a cylindrical shape is represented by Δσ, and the change in the strength and rigidity of the ground soil is obtained from the equations (3) to (8). Thus, for a vertical load, the method of surrounding in a cylindrical shape as shown in FIG. 3 is reasonable, but if the unimproved portion 2a surrounded by the improved body 11 is too large, the restraining effect decreases. Further, if the improved body 11 arranged so as to constrain the ground soil is a cylinder, there is no particular limitation such as a perfect circle, an ellipse, a square, a triangle, etc. Even if the axial cross-sectional area of the cylinder is the same , May be different, and so on. Further, in the case of an elliptical shape or a flat shape, it is not always necessary to have a closed loop shape as shown in FIG. 3, and even if one end or both ends in the long side direction are open, there is little influence on the restraining effect. is there.

  In FIG. 4, the shallow mixed processing layer 5 is arranged on the upper part of the flat hollow cylindrical improvement body 11 similar to that in FIG. 3 arranged so as to constrain the ground soil. As described above, when the cylindrical improved body 11 is covered with the shallow mixing processing board (layer) 5, the ground soil inside the improved body 11, that is, the unreformed part 2 a has a place to move. Therefore, an extremely high restraining effect is obtained, and settlement and deformation are effectively suppressed.

  FIG. 5 shows an improvement similar to that of FIG. 3 in the direction of resisting earth pressure when a load IF of lateral movement due to uneven earth pressure is applied to the cylindrical improvement body 11 arranged so as to restrain the ground soil. In this example, the bodies 11 are arranged side by side. That is, (a), (b), and (c) of FIG. 5 are examples of improved patterns for increasing the soil restraining effect when a load IF of lateral movement due to uneven earth pressure is applied. (A) is an independent arrangement type in which the adjacent improvement bodies 11, 11 are separated from each other and independent from each other, (b) is a continuous arrangement type in which the adjacent improvement bodies 11, 11 are in contact with each other, (c). Is a staggered arrangement type in which improved bodies 11, 11.. With this arrangement, the ground soil to be deformed by the uneven earth pressure, that is, the unmodified soils 2 and 2a is constrained, and at the same time, the improved body 11 generates a compressive stress and generates a tensile stress. Can be suppressed. Moreover, although not shown in figure, it is high including the soil inside the improved body 11 (unmodified soil 2a) by giving the shallow layer mixing processing board 5 to the upper part of the improved body 11 similarly to FIG. Demonstrate the settlement.

  Further, as shown in FIG. 6B, when the load F of the embankment body 3 or the like is large, as shown in FIG. 6A, the planar shape of the improved body 21 is the same as that of FIG. Based on the premise, the taper shape (substantially truncated elliptical cone shape) with the lower diameter expanded in a skirt shape is shown by an arrow P so that the diameter gradually increases in the depth direction. Thus, unimproved ground soil is pushed into the improved body 21, and the restraining effect of the unimproved portion 2a can be further enhanced. Furthermore, as shown in the figure, by arranging the shallow mixed treatment layer 5 in the upper part of the improved body 21 as in FIG. It becomes a substantially sealed state, and the restraining effect of the unimproved portion 2 can be further enhanced. In addition, WF of Fig.6 (a) has shown the flow of groundwater.

  Next, a calculation example of the constraint effect of the ground soil is shown below in the embodiment of FIG.

-Conditions of embankment body 3 and improved body 11 Height of embankment body 3: 8 m
Shape of improved body 11: flat cylindrical shape
(1.5m shallow mixed processing layer 5 is placed on top of the improved body)
In this case, the soil soil has a shear strength of 30 kN / m ² , a Young's modulus representing rigidity of 1 MN / m ² , an improvement rate ap = 18%, an improved body strength of 500 kN / m ² , and a deformation coefficient of 60 MN / m ² . and m ^2.

  In the conventional design method, the average strength S of the composite ground is calculated without considering the change in strength of the ground soil of the unimproved portion due to the constraint effect, and is as follows.

S = 500 × 0.18 + 30 × (1−0.18)
= 114.6 kN / m ²
Similarly, a deformation coefficient E representing rigidity is as follows.

E = 60 × 0.18 + 1 × (1−0.18)
= 11.62 MN / m ²
On the other hand, here, changes in the direct stress σ and the shear stress τ were calculated using the three-dimensional finite element method shown in FIG. (A) shows the state of the ground before embankment, (b) shows the flat cylindrical improvement body 11, and (c) shows the situation where the embankment is loaded.

The internal stress constrained by the improved body 11 in this calculation example is
・ Average value of change in direct stress Δσ = 11.6 kN / m ²
・ Average value of shear force Δτ = 0.5kN / m ²
It becomes.

Here, if α = 0.04, β = 0.1, p = 1, q = 1,
Rs = 1 + αΔσ ^p + βΔτ ^q
= 1 + 0.04 × (11.6) ¹ + 0.1 × (0.5) ¹
= 1.52
It becomes.

This increases the strength by 52% over the conventional design method. Therefore, the shear strength of the soft layer constrained by the improved body increases to 30 × 1.52 = 45.6 kN / m ² .

When the average strength of the composite ground is calculated using the shear strength, the strength is as follows. The strength is increased by about 10% from the strength of 114.6 kN / m ² of the conventional design method.

S = 500 × 0.18 + 45.6 × (1−0.18)
= 127.4kN / m ²
Similarly, regarding the rate of change in stiffness, if γ = 0.15, κ = 0.05, r = 0.5, s = 0.5,
Re = 1 + γΔσ ^r + κΔτ ^s
= 1 + 0.15 × (11.6) ^0.5 + 0.05 × (0.5) ^0.5
= 1.55
Thus, the rigidity is increased by 55%.

When the deformation coefficient representing rigidity is evaluated by the same evaluation method as the strength, it becomes as follows, and the deformation coefficient increases by about 4% from the deformation coefficient of 11.62 MN / m ^{2 of the} conventional design method.

E = 60 × 0.18 + 1.55 × (1−0.18)
= 12.071MN / m ²
As described above, when the strength evaluation method of the present invention is applied to the ground soil of an unimproved portion, even if the conventional composite ground design method is used, the strength increases by about 10%, and the rigidity increases by about 4%. The ground evaluation will increase. As described above, the strength of the improved body and the amount of arrangement (improvement rate) can be reduced, and the cost can be reduced. In addition, it is possible to provide a ground improvement method that is more rational than the above calculation example by the shape and arrangement of the improved body that efficiently restrains the ground.

  The three cases shown in FIGS. 13A to 13C are subjected to a centrifugal model experiment under an acceleration of 80 G, and in order to examine the influence of the difference in the restraining effect due to the arrangement and shape of the improved body on the deformation, The behavior was evaluated by the same three-dimensional finite element method as in FIG. The quantity of ground improvement is the same. FIG. 13A shows a case of so-called columnar improvement similar to FIG. 1, in which a large number of cylindrical improvement bodies 1 are arranged on the ground below the embankment body 3. (B) of the figure shows a case of so-called wall-like improvement, in which two underground wall-like improvement bodies 101 standing upright on the ground below the embankment body 3 are arranged at a predetermined distance. (C) of the same figure is the case of what is called cylindrical improvement similar to FIG. 3, and the flat cylindrical improvement body 11 is arrange | positioned in the ground under the embankment body which abbreviate | omitted illustration. In any case, the embankment body 3 is constructed after the height of the embankment body 3 is 10 m and the 1 m shallow mixed processing layer 5 is disposed on each of the improved bodies 1, 101, 11.

  As a result, when the improved body 1 or 101 has a columnar shape and a wall shape as shown in FIGS. 13A and 13B, the restraint effect is almost the same, and the settlement at the bottom position of the embankment body 3 occurs. The amount was about 80 cm. On the other hand, when the improved body 11 was flat as shown in FIG. 13C, it was found that the amount of settlement at the bottom portion of the embankment body 3 was reduced to about 60 cm. That is, even if the number of ground improvement was the same, it was confirmed that the countermeasure effect differs depending on the shape of the improved body.

  This result can be interpreted as an increase of about 50% in the rigidity of the ground soil surrounded by a flat cylindrical improvement body, and in addition to demonstrating the calculation example shown above. Don't be.

  FIG. 8 is an example in which a plurality of hollow cylindrical improvement bodies 31 arranged to constrain the ground soil are arranged in a staggered manner so as to contact each other. It is an arrangement in which the ground soil is effectively restrained and tensile stress is not easily generated in the improved body 31, and the reference improvement rate is 44%. For example, since the cement-based improved body 31 has a lower tensile strength than compression, it is desirable to arrange the improved body 31 that generates as little tensile stress as possible in order to sufficiently exert the effect of restraining the ground soil. The arrangement in FIG. 8 meets this requirement, and in addition to the unimproved portion 31a inside each hollow cylindrical improvement body 31, a gap formed between the improvement bodies 31 and 31 in contact with each other. Since the same restraining force also acts on the unimproved portion 2, the tensile stress generated in the improved body 31 becomes very small. In this case, as in the case of FIG. 4, the effect is further increased if the structure is such that the shallow mixed processing layer 5 is covered.

  FIG. 9 is an example in which a plurality of hollow cylindrical improvement bodies 31 arranged to constrain the ground soil are arranged in a rectangular shape or a lattice shape. It is an arrangement in which the ground soil is effectively restrained and tensile stress is not easily generated in the improved body 31, and the reference improvement rate is 38.5%. As described above, the arrangement shown in FIG. 9 has the same effect as the arrangement shown in the zigzag form in FIG. As in the case of FIG. 8, the outward direct stress Δσ similar to the unimproved portion 31 a inside the improved body 31 is also generated in the ground soil of the unimproved portion 2.

  (A) and (b) of FIG. 10 are based on the arrangement of FIG. 8 or 9 and are arranged such that the hollow cylindrical improvement bodies 31 and 31 do not contact each other. In this case, a similar effect is exhibited, but since the effect of restraint on the ground soil outside the cylinder of the improved body 31 is reduced, the overall reinforcing effect is slightly reduced. In the arrangement where the cylindrical improvement body 31 does not contact, when the distance between the improvement bodies 31 and 31 is 2 m, the reference improvement rate is 23% to 27%.

  FIG. 11 shows an example in which improvement bodies 41 having a substantially semicircular or arched shape in plan view are arranged side by side in a direction to resist earth pressure when a load IF such as lateral movement is applied as an uneven earth pressure. . When uneven earth pressure is applied by a retaining wall or the like, if the arch-like improved body 41 is arranged in a direction that resists earth pressure, the generation of tensile stress in the improved body 41 is suppressed.

  FIG. 12 shows that when the load IF such as lateral movement is applied as an uneven earth pressure, the open side of the arch-shaped improvement body 41 is extended or released in order to further increase the restraining effect of the ground soil. It is the example made into the improvement body arrangement | positioning which closed the side. Specifically, FIG. 4A shows an independent arrangement of an arch-shaped improvement body 41 with the open side extended by a straight wall body 6, and FIG. Each open side is extended by a wall body 6. Further, FIG. 6 (c) shows that the open side of the independently arranged arch-shaped improvement body 41 is extended by the wall body 6, and another arch-shaped improvement body is also provided between the wall bodies 6 and 6. The entire improved body is closed looped by placing 51, and FIG. 6D is a continuous arrangement instead of the independent arrangement of FIG.

  According to the arrangement shown in FIG. 12, it is possible to expect further improvement in the restraining effect of the ground soil as compared with the arrangement of FIG. 11.

For example, as shown in FIGS. 14 (a) and 14 (b), a plurality of cylindrical improvement bodies 1 and an unimproved portion 2 that is the ground between them are adjacent or close to each other, and the adjacent region is defined as a recess 102. When a substantially vertical excavation as shown in FIG. 5A is performed in order to dig into a groove shape, DD deformation occurs in the direction of the excavation portion in the recess 102, and the stress of the adjacent ground decreases. Thereby, the strength and rigidity of the ground of the unimproved portion 2 are lowered.
In the current design / construction method, since the strength / rigidity is generally evaluated as a composite ground, the above-mentioned phenomenon is not assumed, and the strength of the unmodified part 2 is the same as before the improvement body 1 is created. The strength of the ground soil remains unchanged. For this reason, the strength and rigidity of the unimproved portion 2 are overestimated, and it is highly possible that the design is a so-called dangerous side.

  On the other hand, in the present invention, as shown in FIGS. 14A and 14B, assuming that DD deformation is caused by excavation in the recess 102, the change of the direct stress caused by the deformation restraint of the ground soil is expressed as Δσ. And the changes in the strength and rigidity of the ground soil are obtained from the above formulas (3) to (8). Note that ΔS in FIG. 14B indicates a change in the strength of the ground soil, and ΔE indicates a change in the stiffness of the ground soil.

By this, the restraint effect of the ground soil by the improved body 1 is evaluated as a change in the strength and deformation characteristics of the ground soil, and the shape and arrangement of the improved body 1 for ground improvement are determined in consideration of this. Reasonable ground improvement can be performed by appropriately evaluating the restraining effect of the ground soil.
For example, as shown in FIGS. 15A and 15B, a region adjacent to or close to the unimproved soil 2 including a plurality of cylindrical improvement bodies 1 is excavated in a groove shape as a recess 103 having a slope 103a. The situation is similar for so-called cut work.

16 (a) and 16 (b) show a preferred ground improvement form in the case of excavating the recess 102 almost vertically as in FIG. Here, as an improved body, in addition to the upright wall body 104, a plurality of in-line cylindrical improvement bodies 104 are arranged side by side on the back side of the wall body 104 to form a composite type improvement body. The incomplete cylindrical improvement body 105 can be understood as having a shape obtained by dividing the flat cylindrical improvement body 11 shown in FIG. 3 into two in the major axis direction. As a result, a portion surrounded by the wall body 104 and the incomplete cylindrical improvement body 105 becomes a closed space and is completely restrained. As a result, it is possible to perform rational ground improvement that appropriately evaluates the restraining effect of the ground soil.
In this case, in addition to the case where a part of the space surrounded by the wall body 104 and the incomplete cylindrical improvement body 105 is open and not a so-called complete closed space, an incomplete cylinder other than the wall body 104 is used. Even if the portion of the shape improvement body 105 is cylindrical, quadrangular, triangular, or the like, it is possible to correctly evaluate the effect of restraint and perform appropriate design and construction.

17 (a) and 17 (b) show a preferred ground improvement form in the case of so-called cut work for excavating into a groove shape as the concave portion 103 having the inclined surface 103a, as in FIG. Here, as an improved body, a slanted wall body 106 that is inclined so as to be substantially parallel to the inclined surface 103a and a substantially vertical upright wall body 104 are combined, and both upper ends thereof are butted together to form a composite improved body. . As is clear from the figure, the portion surrounded by the inclined wall body 106 and the upright wall body 104 is constrained with an incomplete closed space. As a result, it is possible to perform rational ground improvement that appropriately evaluates the restraining effect of the ground soil.
In this case, it goes without saying that a corresponding effect can be expected even if a space is formed between the upper ends of the slanted wall body 106 and the upright wall body 104. Further, if necessary, a plurality of slanted wall bodies 106 may be superposed.
Further, when a plurality of incomplete cylindrical improvement bodies 105 similar to those in FIG. 16 are arranged in parallel on the back side of the upright wall body 104, the restraining effect is further enhanced. Further, even if the cylindrical improvement body 105 has a cylindrical shape, a quadrangular prism shape, a triangular prism shape, or the like, the effect of restraint can be correctly evaluated and appropriate design and construction can be performed as in the case of FIG.

  This invention is a lower-cost ground improvement method in which the restraint effect of the ground soil by the improved body constructed in the ground is appropriately evaluated in advance, and the shape, arrangement and strength of the improved body are determined and applied. is there.

1 ... Improved body 2 ... Unmodified part (ground soil)
2a ... Unmodified part (ground soil)
DESCRIPTION OF SYMBOLS 3 ... Embankment body 5 ... Shallow mixed processing layer 11 ... Improved body 21 ... Improved body 31 ... Improved body 31a ... Unmodified part 41 ... Improved body 51 ... Improved body F ... Embankment load IF ... Load such as lateral movement WF ... Groundwater flow Δσ: Changes in direct stress caused by deformation restraint of ground soil Δτ: Changes in shear stress caused by restraint deformation of ground soil ΔS: Change in strength of ground soil ΔE: Change in stiffness of ground soil

Claims (11)

In the ground improvement method of building an improved body in the ground,
When stress of improved ground such as embankment construction increases,
In order to grasp in advance the restraint effect of ground deformation obtained by the construction of the improved body, the restraint effect of ground deformation that differs depending on the shape and arrangement of the improved body is evaluated in advance as a change in soil soil stress by the finite element method,
A ground improvement construction method characterized by constructing the improved body with the shape and arrangement of the improved body in which at least one of the changes in strength and rigidity of the ground soil caused by the change in stress tends to increase. In the ground improvement construction method according to claim 1,
While obtaining the constraint effect of ground deformation that varies depending on the shape and arrangement of the improved body as a change in the stress of the ground soil by the finite element method,
Based on the change in the stress, obtain the change in at least one of the changes in the strength and rigidity of the ground soil caused by the change in the stress,
A ground improvement construction method characterized by constructing the improved body with the shape and arrangement of the improved body in which at least one of the changes tends to increase. In the ground improvement construction method according to claim 2,
The change in the ground soil stress obtained by the finite element method is at least one of a direct stress and a shear stress generated as a reaction force due to the restraining effect of the improved body when the ground receives a load. A ground improvement method characterized by In the ground improvement construction method according to claim 3,
The change in at least one of the changes in strength and rigidity of the ground soil caused by the change in stress is the ground caused by the sum of the direct stress and shear stress when the stress in the improved ground such as embankment construction increases. A ground improvement method characterized by an increase in at least one of the increase in soil strength and rigidity. In the ground improvement method of building an improved body in the ground,
When the stress of improved ground such as excavation decreases,
In order to grasp in advance the restraint effect of ground deformation obtained by the construction of the improved body, the restraint effect of ground deformation that differs depending on the shape and arrangement of the improved body is evaluated in advance as a change in soil soil stress by the finite element method,
A ground improvement construction method characterized by constructing the improved body with the shape and arrangement of the improved body capable of suppressing a decrease in at least one of the changes in strength and rigidity of the ground soil caused by the change in stress. In the ground improvement construction method according to claim 1,
While obtaining the constraint effect of ground deformation that varies depending on the shape and arrangement of the improved body as a change in the stress of the ground soil by the finite element method,
Based on the change in the stress, obtain the change in at least one of the changes in the strength and rigidity of the ground soil caused by the change in the stress,
The ground improvement construction method characterized by constructing the said improved body with the shape and arrangement | positioning of the improved body which can suppress the fall of this at least any one. In the ground improvement construction method according to claim 6,
The change in the ground soil stress obtained by the finite element method is at least one of a direct stress and a shear stress generated as a reaction force due to the restraining effect of the improved body when the ground receives a load. A ground improvement method characterized by In the ground improvement construction method according to claim 7,
The change in at least one of the changes in strength and rigidity of the ground soil caused by the change in the stress is the ground soil generated by the sum of the direct stress and shear stress when the stress in the improved ground such as excavation decreases. A ground improvement method that compensates for at least one of the decrease in strength and rigidity of the ground. In the ground improvement construction method in any one of Claims 1-8,
A ground improvement construction method characterized in that the shape of the improved body is cylindrical. In the ground improvement construction method in any one of Claims 1-8,
A ground improvement method characterized in that the improved body has a flat cylindrical shape. In the ground improvement construction method in any one of Claims 1-8,
A ground improvement method characterized in that the shape of the improved body is a cylindrical one whose diameter is gradually expanded in the depth direction.

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