JP2016196803A - Improved ground and ground improving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground improving method superior in resistance force against a vertical force/horizontal force, superior in permeability and easy-to work at a low cost.SOLUTION: The improved ground includes: plural hexagonal units 2 which are disposed in the ground so that six cylindrical improvement columns 10 which has a circular face in cross section are positioned at a vertex of a regular hexagon respectively in plain view; and a not-improved part 3 which is formed in the plural hexagonal units 2. The side faces of the neighboring improvement columns 10 constituting a hexagonal unit 2 make a linear contact with each other, and the side faces of the neighboring improvement columns 10 in the neighboring hexagonal units 2 make a linear contact with each other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an improved ground and a ground improvement method.

  There is known a ground improvement method for forming a plurality of columnar improved pillars in the ground by mixing and stirring cement-based solidified material and earth and sand with a stirring blade. The improved column body in the ground improvement method is formed, for example, in a range of approximately 0.6 to 2 m in diameter and approximately 2 to 20 m in length. The ground improvement method is generally classified into four types, that is, a pile type improvement method, a block type improvement method, a wall type improvement method, and a lattice type improvement method, depending on the arrangement method of the improved pillars.

  The pile-type improvement method is a method in which a plurality of improvement columns are arranged apart from each other. The pile-type improved construction method is easy to construct and has a low improvement rate of about 10 to 30%, and is an economical method. However, since the improved column bodies are independent one by one, when a large horizontal force is applied, the improved column bodies may tilt in a chain manner. In other words, the pile-type improvement method is effective as an increase in bearing capacity against vertical loads of structures and measures against land subsidence, but is not effective as a countermeasure against horizontal forces and liquefaction during earthquakes. In addition, an improvement rate means the ratio of the total plane cross-sectional area of the improvement column body with respect to the surface area of improvement object ground.

  The block-type improved construction method is effective as a countermeasure against liquefaction because it has resistance against both vertical force and horizontal force because the improved pillars are placed in an overlapping manner, and there is almost no unmodified part. . However, the block type improvement has a problem that the improvement rate becomes 78.5% or more and the construction cost increases. Moreover, when the improvement rate becomes large, there is a problem that the ground to be improved is poor in water permeability and hinders the penetration of rainwater.

  The wall type improved construction method is a construction method in which improved pillars are continuously arranged in a wall shape only in a direction in which a horizontal force acts. In the wall-type improved construction method, an unimproved portion is generated at a predetermined interval in a direction orthogonal to the continuous wall-type arrangement, and liquefaction may occur due to the unmodified portion.

  The lattice improvement method is a method in which the improved columns are arranged so as to have a lattice shape (square in a plan view) in plan view, and adjacent improved columns are overlapped by about 20 cm. According to the grid type improvement method, even if the improvement rate is reduced to about 50%, the rigidity of the entire grid can be increased and the horizontal force can be countered. Further, by keeping the relationship between the width and depth of the lattice within a certain range, liquefaction of the unimproved portion surrounded by each lattice can also be prevented (see Patent Document 1).

JP 2013-2078 A

  From the viewpoint of resistance to vertical and horizontal forces, economy, and water permeability, the conventional ground improvement method has many advantages. However, in the grid type improvement method, it is necessary to overlap adjacent improvement columns, and if one or more days elapse after construction of one improvement column, the improvement column is solidified to a certain degree of strength. Therefore, there is a problem that this overlap construction becomes difficult. When overlapping the solidified improved columns, a large construction machine with a large output is required. As a result, construction in a confined place becomes difficult and noise increases.

  The present invention was created in order to solve such problems, and provides a ground improvement method that is excellent in resistance to vertical force and horizontal force, economical efficiency and water permeability of the ground to be improved, and has high workability. For the purpose.

  In order to solve the above problems, the present invention provides a plurality of hexagonal units arranged in the ground so that the centers of the six improved circular pillars having a circular cross section are located at the apexes of a regular hexagon in plan view, An unimproved portion formed inside the hexagonal unit, and the side surfaces of the adjacent improved pillars constituting the hexagonal unit are in line contact with each other, and among the adjacent hexagonal units, The side surfaces of the adjacent improved pillars are in line contact with each other.

  In addition, the present invention provides a plurality of hexagonal units that are arranged in the ground so that the centers of the six improved circular pillars having a circular cross section are positioned at the apexes of the regular hexagon in plan view, and each has an unimproved portion inside. Including the step of forming individual pieces, wherein in the step, the side surfaces of the adjacent improved column bodies constituting the hexagonal unit are brought into line contact with each other, and the adjacent improved hexagonal units are adjacent to each other. The side surfaces are brought into line contact with each other.

  According to such a configuration, the improvement rate is approximately 60%, the construction cost can be reduced, and the economy is excellent. Moreover, the resistance with respect to a vertical force and a horizontal force can be raised by making the some hexagonal unit which exhibits a regular hexagon line-contact, although the improvement rate is low. Moreover, since an improved column is not provided inside each hexagonal unit, the unimproved portion inside each hexagonal unit has a water permeability function. Moreover, the unreformed part which arises between each hexagonal unit also has a water-permeable function. Moreover, since it is only necessary to bring the side surfaces of the improved pillars into line contact, it can be easily constructed. Furthermore, it is not necessary to cut the side surfaces of the improved pillars, and even a small construction machine can be used, so that construction can be performed even in a narrow field.

  In addition, it is preferable that the vertical shear force generated at the contact portion between the side surfaces of the adjacent improved column bodies is set to be equal to or less than the frictional resistance force generated at the contact portion during an earthquake.

  According to such ground improvement method, the resistance against vertical force and horizontal force can be further increased.

  According to the ground improvement method according to the present invention, it is excellent in resistance to vertical force / horizontal force, economical efficiency and water permeability, and it is possible to improve workability.

It is a schematic plan view which shows the improved ground which concerns on 1st embodiment of this invention. It is a top view which shows the hexagonal unit which concerns on 1st embodiment. It is a side view which shows the two improvement pillar bodies which concern on 1st embodiment. It is a graph which shows the relationship between lattice space | interval / improvement depth, and the excess pore water pressure of the original ground in a lattice. It is a stress figure concerning a lattice type improvement construction method. It is a stress figure of the ground improvement construction method concerning a first embodiment. It is a construction (improvement) area side cross-sectional schematic diagram for demonstrating the calculation method of a perpendicular direction shear force and a frictional resistance force. (A) is a table | surface which shows the seismic intensity K calculated | required from the liquefied layer thickness h and the non-liquefied layer thickness d, (b) is a graph corresponding to Fig.8 (a). It is an effect | action figure of the lattice type improved construction method with respect to a vertical direction shear force. It is an effect | action figure of the ground improvement construction method which concerns on 1st embodiment with respect to a perpendicular direction shear force. (A) is a sectional side view of the experimental apparatus, (b) is a plan view of the experimental apparatus, and (c) is a side view showing an improved column for experiments. It is a figure which shows Example 1, (a) is a top view, (b) is a sectional side view. It is a figure which shows the comparative example 1, (a) is a top view, (b) is a sectional side view. It is a figure which shows Example 2, (a) is a top view, (b) is a sectional side view. It is a figure which shows the comparative example 2, (a) is a top view, (b) is a sectional side view. It is a schematic plan view which shows the improved ground which concerns on 2nd embodiment of this invention.

[First embodiment]
A first embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the improved ground 1 according to the present embodiment includes a plurality of hexagonal units 2, unimproved portions 3 and 3 ′, and a plurality of auxiliary improved pillars 4 arranged in the construction zone Z. Is built. Although the shape and size of the construction zone Z are not particularly limited, in the present embodiment, a rectangular shape is exhibited. In the construction zone Z of the present embodiment, for example, when the diameter Φ of the improved column 10 is 1.0 m, the horizontal dimension a is 12.0 m and the vertical dimension b is 10.57 m (about 130 m ² ).

  As shown in FIG. 2, the hexagonal unit 2 is composed of six improved pillars 10. Each improved column 10 has a cylindrical shape. The center of the improved column 10 is arranged so that the regular hexagonal apex is located. As shown in FIG. 3, the diameter Φ and the length H of the improved column 10 are appropriately set within a range where the diameter Φ is approximately 0.6 to 2.0 m and the length H is approximately 2.0 to 20 m, for example. The

  One side of the virtual regular hexagon of the hexagonal unit 2 of the present embodiment has the same dimension as the diameter Φ of the improved column 10. The peripheral surfaces (side surfaces) of the adjacent improved column bodies 10 and 10 are in line contact with each other. As shown in FIG. 3, the hexagonal unit 2 is embedded at a predetermined depth D from the ground G. The depth D is set as appropriate.

  In this embodiment, since the diameter Φ of the improved column 10 is set to 1.0 m, 14 hexagonal units 2 are arranged in the construction area Z. The improvement rate of the improved ground 1 of this embodiment is 63.7%.

As shown in FIG. 3, the diameter Φ and the length H of the improved column 10 are the horizontal force P ₂ (the hydrodynamic pressure, the weight of the construction zone Z, and the inertial force of the upper load) when a predetermined upper load is applied. The vertical shearing force τ _v generated at the contact part (line contact part) between the improved pillars 10 and 10 adjacent to each other due to the friction generated at the contact part by the horizontal force P ₁ (earth pressure from the surroundings). Set to be less than the resistance.

  The material of the improved column 10 is not particularly limited as long as it exhibits a predetermined compressive strength with respect to a vertical force and a horizontal force, but in this embodiment, a cement-based solidifying material and earth and sand are used. Although the manufacturing method of the improved column 10 is not particularly limited, in the present embodiment, the cemented solid material is injected into the ground, and the underground soil and cement solidified material are mixed and stirred with a stirring blade. doing. The improved column 10 can be formed using a known construction machine. The construction machine mainly includes, for example, a rod provided with a plurality of stirring blades, a driving unit that rotationally drives the rod, and a vehicle body that holds the rod and the driving unit.

  As shown in FIG. 1, the adjacent hexagonal units 2 and 2 are arranged so as to be in line contact with each other. Here, when distinguishing a plurality of hexagonal units 2, they are referred to as hexagonal units 2A, 2B, 2C,. One improved column 10 of the hexagonal unit 2A is disposed so as to be in line contact with one improved column 10 of another hexagonal unit 2B adjacent to the hexagonal unit 2A. At this time, the centers of the improved pillars 10 and 10 that are in line contact are located on a line connecting the center of the hexagonal unit 2A and the center of the hexagonal unit 2B.

  Further, the other improved column body 10 of the hexagonal unit 2A is arranged so as to be in line contact with one improved column body 10 of another hexagonal unit 2C adjacent to the hexagonal unit 2A. At this time, the centers of the improved pillars 10 and 10 that are in line contact are located on a line connecting the center of the hexagonal unit 2A and the center of the hexagonal unit 2C.

In this way, the hexagonal unit 2A is in line contact with the other hexagonal units 2B, 2C, 2D, 2E, 2F, and 2G arranged radially around the periphery. In other words, the hexagonal units 2B, 2C, 2D, 2E, 2F, and 2G are arranged with a phase around the hexagonal unit 2A by 60 °. Furthermore, the hexagonal units 2B, 2C, 2D, 2E, 2F, and 2G are in line contact with the hexagonal unit 2 on the outer side. That is, by arranging the hexagonal units 2 in this way, the planar shape connecting the centers of three adjacent hexagonal units 2 (for example, hexagonal units 2A, 2B, 2C) becomes a regular triangle, and the construction zone Z A honeycomb structure is formed as a whole.

  The unimproved portion 3 is a portion corresponding to the original ground. That is, the unimproved portion 3 is a region that is not improved inside the hexagonal unit 2 (region surrounded by the six improved pillars 10). Further, as shown in FIG. 1, the region surrounded by the three adjacent hexagonal units 2, 2, 2 also becomes the unimproved portion 3 ′. The unimproved portion 3 ′ also has the same shape as the unimproved portion 3 inside the hexagonal unit 2.

  The size of the unimproved part 3 is “lattice spacing / improvement depth and excess of ground in the lattice” in the model vibration test of the ground improved in the grid type (Ground improvement design guideline for architectural foundation: written by the Architectural Institute of Japan) The graph of “Relationship of pore water pressure” (see FIG. 4) can be derived for reference.

  For example, when the diameter Φ of the improved column 10 is set to 1.0 m and the length is set to 4.0 m, as shown in FIG. 2, the interval L between the unimproved portions 3 is approximately 1.0 m, and the depth H The (liquefied layer thickness h) is 4.0 m. Therefore, L / H (h) is 0.25. As shown in FIG. 4, in order to prevent liquefaction from occurring, it is necessary to set the maximum excess interval water pressure ratio to 0.5 or less. Therefore, it is preferable that the value of L / H (h) is 0.95 or less. In this embodiment, since L / H (h) is set to 0.5 to 0.05, liquefaction can be prevented.

  A plurality of auxiliary improvement pillars 4 are arranged between the outer edge of the construction zone Z and the hexagonal unit 2. The auxiliary improved column 4 is an improved column that fills the space between the outer edge of the construction zone Z and the hexagonal unit 2. By providing the auxiliary improvement pillar body 4, the resistance with respect to the horizontal force and the vertical force of the improvement ground 1 can be raised more. The auxiliary improvement pillar 4 is formed with the same material as the improvement pillar 10, and is formed with the same construction method. Adjacent auxiliary improvement pillars 4 are in line contact with each other. Moreover, it arrange | positions so that the improvement pillar 10 and the auxiliary | assistant improvement pillar 4 of the adjacent hexagonal unit 2 may also be in line contact. A plurality of auxiliary improvement pillars 4 are arranged between the construction zone Z and the hexagonal unit 2 as necessary. In the present embodiment, 19 auxiliary improved pillars 4 are arranged, for example.

  Next, the ground improvement construction method according to the present embodiment will be described. The ground improvement method according to the present embodiment performs a preparation process, a honeycomb structure forming process, and an auxiliary improved column forming process.

  The preparation step is a step of forming a mark at a planned position where the improved pillar 10 is formed on the ground G (see FIG. 3). In the preparation step, a mark is formed at each vertex of the virtual regular hexagon.

The honeycomb structure forming step is a step of forming a plurality of hexagonal units 2 in the ground. In the honeycomb structure forming step, the six improved pillars 10 are formed by using the construction machine described above, and one hexagonal unit 2 is formed. The improved column 10 is formed so that the center of the improved column 10 is located at the apex of the virtual regular hexagon. The diameter Φ and the length H of the improved column 10 are the vertical directions that act on the contact portions of the adjacent improved columns 10 and 10 by the horizontal force P ₂ when a predetermined overload is applied as shown in FIG. taking into account the frictional resistance force generated at the contact portion by shearing force tau _v and a horizontal force P _1, the value of L / H (h) as liquefaction countermeasure can be determined in consideration.

Then, a plurality of hexagonal units 2 are formed around the hexagonal unit 2. One of the improved column bodies 10 of the adjacent hexagonal units 2 and 2 is brought into line contact with the other improved column body 10 so that the plurality of hexagonal units 2 form a honeycomb structure as a whole. In the honeycomb structure forming step, it is not always necessary to form each hexagonal unit 2, and it is sufficient that a plurality of hexagonal units 2 are finally formed to form a honeycomb structure.

  The auxiliary improvement pillar body formation process is a process of forming a plurality of auxiliary improvement pillar bodies 4 in the gap between the outer edge of the construction zone Z and the hexagonal unit 2. The improved ground 1 is formed by the above.

  Next, the operation of the improved ground 1 according to this embodiment with respect to the horizontal shear force will be described. First, with reference to FIG. 5, the operation of the square unit 20 of the lattice type improvement method as a comparative example will be described. As shown in FIG. 5, the square unit 20 of the lattice type improvement method is arranged side by side so that the centers of a plurality of columnar improvement column bodies 30 are positioned on the sides of the virtual square in plan view. Yes. Adjacent improved column bodies 30 overlap each other by about 20 cm. For example, the wrap part E is formed when the improved column bodies 30A and 30B overlap, and the wrap part F is formed when the improved column bodies 30A and 30C overlap. The interior of the square unit 20 is an unimproved portion 23.

With respect to the action of the horizontal shearing force, in the conventional square unit 20, for example, when a horizontal force P ₀ (P ₀ = P ₁ + P ₂ ) is applied to the improved column 30A of the square unit 20, the lap portions E and F The improved column body 30A is prevented from shifting in the X direction by the horizontal shear resistance forces τ _E and τ _F.

Next, with reference to FIG. 6, the effect | action of the hexagonal unit 2 which concerns on this embodiment with respect to a horizontal direction shear force is demonstrated. In FIG. 6, the six improved pillars 10 are distinguished by attaching 10a, 10b, 10c, 10d, 10e, and 10f. As shown in FIG. 6, in the hexagonal unit 2 according to the present embodiment, for example, when a horizontal force P ₀ acts on the improved column body 10a, the reaction force Pb is received from the improved column body 10b adjacent to the improved column body 10a. The reaction force Pc is received from the improved column 10c adjacent to the improved column 10a. Similarly to the improved column body 10a, when the horizontal force P ₀ acts on the improved column body 10 in the other improved column bodies 10a, the reaction force is generated from the other two adjacent improved column bodies 10 and 10. Receive. As a result, even if a horizontal force P ₀ is applied to the improved column 10, a reaction force against the horizontal force P ₀ is applied, so that each improved column 10 is displaced (here, the improved column 10 a is X Can be prevented.

That is, according to the improved ground 1 of the present embodiment (hexagonal unit 2), an improved pillar 10, 10 to each other, which are arranged in contact with each other at the apex of the virtual regular hexagon arched action effect with respect to the horizontal force P ₀ ( The horizontal compressive force is transmitted toward the center of each improved column body 10 by the wedge effect), and the horizontal direction shear force in the contact portion between the improved column bodies 10 and 10 is improved. Since it does not act (substantially close to zero), it is not necessary to overlap the improved column bodies 10 and 10 with each other.

  According to the improved ground 1 described above, the improvement rate is approximately 60%, the construction cost can be reduced, and the economy is excellent. In addition, since a honeycomb structure is constructed by a plurality of hexagonal units 2 having a regular hexagonal shape (because the hexagonal units 2 and 2 are in line contact with each other), the vertical force and horizontal force are low, although the improvement rate is low. Can increase the resistance against. Moreover, since the improved column body 10 is not provided inside each hexagonal unit 2, the unimproved portion 3 inside each hexagonal unit 2 has a water permeability function. Further, the unimproved portion 3 ′ generated between the adjacent hexagonal units 2 and 2 also has a water permeability function.

  Moreover, according to this embodiment, since it is only necessary to make the improvement column bodies 10 and 10 line-contact, it can construct easily. That is, since it is not necessary to overlap the improved column bodies 10, 10, it is not necessary to cut a part of the improved column body 10. As a result, even a small construction machine can be used, and construction can be performed even in a narrow field.

Moreover, in this embodiment, since L / H (h) of the unimproved portion 3 is set to 0.5 to 0.05, liquefaction can be prevented. In the present embodiment, the vertical shearing force τ _v generated at the contact portion of the adjacent improved column bodies 10 and 10 due to the horizontal force P ₂ (the dynamic hydraulic pressure, the weight of the construction zone Z, and the inertial force of the loading load) is The diameter Φ and the length H of the improved column 10 are set so that the force P ₁ (earth pressure from the surroundings) is equal to or less than the frictional resistance force generated in the contact portion. Thereby, the resistance with respect to a horizontal force can be raised more. Moreover, in construction, by making the diameter Φ of the improved column body 10 larger than the design value, for example, by 5 to 10%, the construction error can be absorbed and the improved column bodies 10 and 10 can be brought into line contact with each other reliably. it can. Further, the term “regular hexagon” in the claims does not mean a “regular hexagon” in a mathematical sense due to a design error, but includes a substantial hexagon.

Next, a method for calculating the vertical shear force and the frictional resistance will be described in detail with reference to FIG. In the ground improvement by the solidification method using a cement-based solidifying material, the vertical shearing force is generated at the center of the construction zone Z and becomes the largest when the surrounding ground is liquefied during an earthquake. When the maximum vertical shear force (kN / m) per 1 m of the section depth on the side of the enforcement area is τ _vmax , the maximum vertical shear force τ _vmax is obtained by the following equation (1).

Here, in Formula (1), the width (m) of the construction zone Z shown in FIG. 7 is B, the liquefied layer thickness (m) is h, the non-liquefied layer thickness (m) is d, and the width of the overlay (M) is l, weight above groundwater level in construction zone Z (kN / m) is W ₁ = γ _t dB, unit volume weight (kN / m ³ ) is γ _t , weight below groundwater level in construction zone Z Let (kN / m) be W ₂ = γ _{t ′} hB, and the unit volume weight in water (kN / m ³ ) be γ _t ′. Further, the upper mounting load (kN / m) Q = ql , load the (kN / ^{m 2)} q per unit area, the main働土pressure _{(kN / m) P aH =} (1/2) k a γ t d ^2, the main働土pressure coefficient <1 _{k a,} Passive earth pressure (kN / m) to _{P PH = (1/2) k p} γ t d 2, Passive earth pressure coefficient> 1 _{k p,} during liquefaction The earth pressure (kN / m) is set to P _OH = k _O ((1/2) γ _{t ′} h ² + γ _t dh), k _O = 1.0. Furthermore, the dynamic water pressure (kN / m) is set to P _DH ≈ (7/8) · (π / 4) · (γ _w + RU · γ _t ') Kh ² , and the unit volume weight of water (10 kN / m ³ ) is set to γ. _w , excess pore water pressure ratio (1.0) is RU, inertial force (kN / m) is KQ, KW ₁ , KW ₂ , seismic intensity K used in design is K = α _max / g, ground surface maximum horizontal acceleration (gal ) Is α _max and gravity acceleration (980 gal) is g. In addition, it is preferable to set the seismic intensity K in the range of 0.15-0.36. In this embodiment, for convenience of explanation, 1 tf / m ² is converted to 10 kN / m ² and 1 tf / m ³ is converted to 10 kN / m ³ .

6 / B ² in the formula (1) is the reciprocal of the flat section coefficient per 1 m of the construction area depth. M in the formula (1) is a moment centering on the lower end of the central portion of the construction zone Z shown in FIG. 7, and the moment M is obtained by the following formula (2).

Horizontal force _{P 1} is determined by the following formula (3).

Horizontal force _{P 2} is calculated by the following formula (4).

In the present embodiment, the resistance force against the maximum vertical shear force τ _vmax is a frictional resistance force generated at the contact portion between the adjacent improved column bodies 10 and 10 due to the horizontal force P ₁ (earth pressure from the surroundings). The size of the frictional resistance force f (kN / m) per 1 m of the section depth on the construction area is a value obtained by multiplying the horizontal force P ₁ = P _aH + P _OH by the friction coefficient μ between the improved column bodies 10 and 10, that is, It is calculated | required by Formula (5).

  Regarding the friction coefficient μ, the road earthwork guideline adopts μ = 0.5 for hard clay.

In order to stabilize the construction zone Z during an earthquake (during liquefaction), the frictional resistance force f must be greater than or equal to the maximum vertical shear force τ _vmax . That is, it is necessary to satisfy the relationship of f / τ _vmax ≧ 1.0.

As an example, the following numerical values are substituted into the equations (1) and (5), and the relationship between the liquefied layer thickness h and the non-liquefied layer thickness d and the seismic intensity K is determined as f = τ _vmax . , (B). The numerical values to be substituted here are B = 15 m, γ _t = 18 kN / m ³ , γ _t ′ = 10 kN / m ³ , q = 10 kN / m ² , l = 10 m, Q = 100 kN / m, k _a = 0. 41, k _p = 2.46 (φ25 °), and k _o = 1.0. Moreover, any value of 2 m, 4 m, 6 m, 8 m, 10 m, and 20 m is substituted for the liquefied layer thickness h, and any of 1 m, 2 m, 3 m, and 4 m is assigned to the non-liquefied layer thickness d. A numerical value was substituted.

The graph shown in FIG. 8B represents four line graphs for each non-liquefied layer thickness d of 1 m to 4 m. Each broken line indicates a boundary (a line of f = τ _vmax ) where the frictional resistance force f and the maximum vertical shear force τ _vmax are equal.

That is, in the region where the seismic intensity K is larger than the broken line, the frictional resistance force f is smaller than the maximum vertical shear force τ _vmax (f <τ _vmax ), and in the region where the seismic intensity K is smaller than the broken line, the frictional resistance force f is It means that it is larger than the maximum vertical shear force τ _vmax (f> τ _vmax ). For example, in the case where the liquefaction layer thickness h is 2 m and the non-liquefaction layer thickness d is 4 m, the seismic intensity K = 0.399 (391 gal). The maximum vertical shear force τ _vmax becomes equal. In addition, the frictional resistance force f is smaller than the maximum vertical shear force τ _vmax for earthquakes with a seismic intensity greater than the above numerical value, and the frictional resistance force f is maximum vertical for an earthquake with a seismic intensity smaller than the above numerical value. It becomes larger than the directional shear force τ _vmax .

Here, as a guideline for the seismic intensity K, for example, K = 0.15 to 0.20 (150 gal to 200 gal) is recommended for damage limit examination in the architectural foundation structure design guidelines (edited by the Architectural Institute of Japan, August 10, 2004). K = 0.36 (350 gal) is recommended for studying the ultimate limit. When these values are compared with the values shown in Fig. 8 (a), the damage limit study values are satisfied in all cases, and the ultimate limit study values are also satisfied in some cases. I understand that. This _proves that in many cases, it can be resisted by the frictional resistance force f generated at the contact portion of the adjacent improved column bodies 10 and 10 with respect to the maximum vertical shearing force τ _vmax .

  8 (a) and 8 (b), it is assumed that the lower end of the improved pillar 10a is not embedded in the lower non-liquefied layer. Since the numerical value of the seismic intensity K shown in a) and (b) is increased, the application range of the present invention is expanded.

  Next, the effect | action of the improved ground 1 which concerns on this embodiment with respect to a perpendicular direction shear force is demonstrated. First, with reference to FIG. 9, the effect | action of the rounded square unit 50 of the lattice type | formula improvement method used as a comparative example is demonstrated. The tangential square unit 50 of the lattice type improvement method is different from the square unit 20 shown in FIG. 5 in that adjacent improvement column bodies 60 and 60 are in line contact with each other without overlapping.

As described in FIG. 3, in the tangent square unit 50, for example, when a horizontal force P ₀ (P ₀ = P ₁ + P ₂ ) is applied to the improved column body 60 </ _b > A, the horizontal force P ₂ (dynamic pressure and construction area) The vertical direction shearing force τ _v is generated at the contact portion between the adjacent improved column bodies 60A and 60B due to the weight of Z and the inertial force of the loading load), and the horizontal force P ₁ (periphery) toward the center of the tangential square unit 50 Frictional resistance is generated at the contact portions of the adjacent improved column bodies 60, 60 due to the earth pressure from However, the Se'en quadrangular unit 50, not in the relationship of allocation is improved pillar 60 with each other by the horizontal force P ₁ is clamped to each other toward the center of Se'en quadrangular unit 50. In other words, since the force which digs in between the improvement pillars 60 and 60 which adjoin each improvement pillar body 60 does not act mutually, the improvement pillar body 60 becomes easy to shift | deviate by an earthquake motion. In particular, the improved column body 60 located at the center of each side of the virtual square is easily displaced. When such a shift occurs, the frictional resistance does not work at all, and thus it is necessary to overlap the improved column bodies 60 and 60 with each other.

Next, with reference to FIG. 10, the effect | action of the hexagonal unit 2 which concerns on this embodiment with respect to a perpendicular direction shear force is demonstrated. As described in FIG. 3, in the hexagonal unit 2 according to the present embodiment, for example, when a horizontal force P ₀ (P ₀ = P ₁ + P ₂ ) acts on the improved column body 10 b, the horizontal force P ₂ (dynamic water pressure and Due to the weight of the construction zone Z and the inertial force of the mounted load), a vertical shearing force τ _v is generated at the contact portion of the adjacent improved column bodies 10b and 10d, and a horizontal force P ₁ (periphery) toward the center of the hexagonal unit 2 Frictional resistance is generated at the contact portions of the adjacent improved column bodies 10 and 10 due to the earth pressure from the ground. In the hexagonal unit 2, the improved column bodies 10 are arranged to be fastened to each other toward the center of the hexagonal unit 2 by the horizontal force P ₁ . In other words, since each of the improved column bodies 10 interacts with a force that bites between the adjacent improved column bodies 10, 10, each improved column body 10 is displaced by the wedge effect even when subjected to earthquake motion. Can be prevented. Thereby, in the hexagonal unit 2 which concerns on this embodiment, since frictional resistance acts reliably, it is not necessary to make the improvement column bodies 10 and 10 overlap.

Next, with reference to FIGS. 11-15, the effect of the improved ground (hexagon unit) of this invention is demonstrated in detail by an Example and a comparative example.
<Experimental equipment, improved pillar>
First, with reference to FIGS. 11A to 11C, the experimental apparatus 100 and the improved column 200 used in this experiment will be described.
The experimental apparatus 100 includes a box-shaped acrylic tank 110 opened upward, a sponge 120 installed on the inner surface of the acrylic tank 110, and an outer side installed across the bottom surface of the acrylic tank 110 and the inner surface of the sponge 120. A PVC sheet 130. Inside the outer PVC sheet 130, water-containing sand 140 is laid. An inner PVC sheet 150 is installed on the sand 140. On the inner PVC sheet 150, a loading body 160 is placed. The load body 160 is composed of sand, iron powder, and an iron rectangular parallelepiped, and is stacked in this order from the lower side. The periphery of the inner PVC sheet 150 is bent upward and faces the outer PVC sheet 130 with a gap 170 therebetween. In this experiment, when the sand 140 is liquefied by applying vibration, sand is generated from the gap 170, so that the occurrence of liquefaction can be easily confirmed. The iron rectangular parallelepiped of the load-bearing body 160 is provided with a mark that becomes a measurement point P (see the broken-line circle shown in FIG. 11B) for measuring the amount of settlement. A plurality of measurement points P are arranged in parallel at equal intervals in the vertical and horizontal directions of the acrylic tank 110.

The vertical and horizontal dimensions D1, D2 of the acrylic tank 110 were set to 19 cm and 40 cm, respectively. The thickness dimension D3 of the sponge 120 was set to 2 cm. The inner dimension D4 between the pair of facing sponges 120, 120 was set to 36 cm. The height dimension D5 of the sand 140 was set to 15.2 cm. The relative density of sand 140 and water was set to 40 to 50% suitable for the occurrence of liquefaction. The thickness of the sand of the loading body 160 was set to 1 cm, the thickness of the iron powder was set to 2.2 cm, and the vertical and horizontal height dimensions of the iron rectangular parallelepiped were set to 2 cm, 2 cm, and 3 cm, respectively. The loading load of the loading body 160 was set to 3.2 kN / m ² .

The improved pillar body 200 shown in FIG. 11C is a cylindrical body made of soil cement. As the improved column 200, one having a diameter φ of 25 mm, a length H of 150 mm, a density ρt of 1.88 g / cm ³ , and a uniaxial compressive strength qu of 1200 kN / m ² was used.

<Experiment method>
In this experiment method, the experimental apparatus 100 is vibrated in the left-right direction (horizontal direction) with a vibration apparatus (not shown), and the amount of subsidence of the iron cuboid at each measurement point P when liquefaction occurs, and the improved column A deviation of 200 was measured. In this experiment, the vibration frequency was 4 Hz, the half amplitude was 2.5 mm, and the acceleration was 161 gal. In each of Examples 1 and 2, the hexagonal unit 300 was used, and in Comparative Examples 1 and 2, each of the above measurements was performed using a tangential square unit 400. In Example 1 and Comparative Example 1, an experiment was performed in an environment in which the earth pressure in the left and right direction applied to each unit 300 and 400 was equal. In Example 2 and Comparative Example 2, the left and right direction applied to each unit 300 and 400 The experiment was conducted in an environment where the earth pressure of the soil was uneven.

<Example 1>
As shown in FIGS. 12A and 12B, in Example 1, the hexagonal unit 300 was arranged at the center in the left-right direction of the acrylic tank 110. In Example 1, when vibration was performed for 20 seconds, liquefaction started about 1-2 seconds after the start of vibration.
In Example 1, the settlement amount of the measurement point P located inside the hexagonal unit 300 was 2 mm to 3 mm, and the settlement amount of the measurement point P located outside the hexagonal unit 300 was 3 mm to 16 mm. The broken line Y1 shown in FIG. 12 (b) schematically shows the state of settlement, and the amount of settlement was relatively small. In Example 1, the left and right direction shift of the improved column 200 did not occur.

<Comparative Example 1>
As shown in FIGS. 13A and 13B, in Comparative Example 1, the tangent square unit 400 is arranged in the center of the acrylic tank 110 in the left-right direction. In Comparative Example 1, when excitation was performed for 15 seconds, liquefaction started about 1-2 seconds after the start of excitation.
In Comparative Example 1, the settlement amount of the measurement point P located inside the tangent square unit 400 is 3 mm to 4 mm, and the settlement amount of the measurement point P located outside the tangent square unit 400 is 3 mm to 26 mm. became. A broken line Y2 shown in FIG. 13B schematically shows a sinking situation. The broken line Y2 is located below the broken line Y1 shown in FIG. That is, the amount of settlement in Comparative Example 1 was larger than the amount of settlement in Example 1. In the first comparative example, among the improved column bodies 200, those having no other improved column bodies 200 adjacent to the inside in the leftmost and right columns are displaced by about 5 mm toward the center of the tangential square unit 400 (FIG. 13). (See the white arrow in (a), the broken line in FIG. 13 (b)).

<Example 2>
As shown in FIGS. 14A and 14B, in Example 2, the hexagonal unit 300 was arranged eccentrically on the right side of the acrylic tank 110. In the hexagonal unit 300, the earth pressure on the left side is larger than the earth pressure on the right side with respect to the hexagonal unit 300. In Example 2, when excitation was performed for 13 seconds, liquefaction started about 4 to 5 seconds after the start of excitation.
In Example 2, the settlement amount of the measurement point P located inside the hexagonal unit 300 was 2 mm, and the settlement amount of the measurement point P located outside the hexagonal unit 300 was 3 mm to 16 mm. A broken line Y3 shown in FIG. 14 (b) schematically shows the state of settlement, and the amount of settlement was relatively small. In Example 2, the left and right direction shift of the improved column 200 did not occur.

<Comparative example 2>
As shown in FIGS. 15A and 15B, in Comparative Example 2, the tangent square unit 400 is eccentrically arranged on the right side of the acrylic tank 110. The earth pressure on the left side of the tangent square unit 400 is greater than the earth pressure on the right side of the tangent square unit 400. In Comparative Example 2, when excitation was performed for 13 seconds, liquefaction started about 4 to 5 seconds after the start of excitation.
In Comparative Example 2, the settlement amount of the measurement point P located inside the tangent square unit 400 is 3 mm to 4 mm, and the settlement amount of the measurement point P located outside the tangent square unit 400 is 4 mm to 17 mm. became. A broken line Y4 shown in FIG. 15B schematically shows a sinking situation. The broken line Y4 is located below the broken line Y3 shown in FIG. That is, the amount of settlement in Comparative Example 2 was larger than the amount of settlement in Example 2. In Comparative Example 2, the columns without the other improved column 200 adjacent to the right side in the leftmost and center rows of the improved column 200 are shifted to the right by about 7 to 10 mm (the white arrow in FIG. 15A). , See the broken line in FIG.

<Summary>
Comparing the experimental results of Example 1 and Comparative Example 1, when the earth pressure applied to each unit 300, 400 is equal, the amount of settlement of the hexagonal unit 300 is the amount of settlement of the tangential square unit 400. Less than the amount proved. Moreover, in the tangent square unit 400, the shift of the improved column 200 due to the earthquake motion (liquefaction) occurs, but in the hexagonal unit 300, the shift of the improved column 200 due to the earthquake motion (liquefaction) does not occur. Proven.
When the experimental results of Example 2 and Comparative Example 2 are compared, the amount of settlement of the hexagonal unit 300 is equal to the tangential square unit 400 even in an environment where the earth pressure in the horizontal direction applied to the units 300 and 400 is not uniform. It was proved to be less than the amount of settlement. Moreover, in the tangent square unit 400, the shift of the improved column 200 due to the earthquake motion (liquefaction) occurs, but in the hexagonal unit 300, the shift of the improved column 200 due to the earthquake motion (liquefaction) does not occur. Proven.

According to Examples 1 and 2 and Comparative Examples 1 and 2 described above, in the contacted square unit 400, the improved column bodies 200 are connected to each other by the horizontal force P ₁ (earth pressure from the surroundings). Since there is no arrangement relationship that is tightened toward the center of each other, and each improved column body 200 does not interact with the force between the adjacent improved column bodies 200, 200, the seismic motion It is inferred that the improved column 200 is displaced. Moreover, since the shift | offset | difference of the improved pillar 200 generate | occur | produces, it is guessed that the amount of settlements also increases.
On the other hand, in the hexagonal unit 300, the improved column bodies 200 are arranged to be fastened to each other toward the center of the hexagonal unit 300 by the horizontal force P _1. It is inferred that the improved column bodies 200 do not shift due to the wedge effect even if they receive an earthquake motion, because forces that bite between the matched improved column bodies 200 and 200 interact with each other. Moreover, since the shift | offset | difference of the improvement pillar 200 does not generate | occur | produce, it is guessed that the amount of settlements also decreases.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. As shown in FIG. 16, the improved ground 41 according to the second embodiment is constructed by including a plurality of hexagonal units 2 and unimproved portions 3 and 5. The improved ground 41 is different from the first embodiment in the arrangement of the hexagonal units 2. Hereinafter, the description will focus on the parts that are different from the first embodiment.

In the construction zone Z of the present embodiment, for example, when the diameter Φ of the improved column 10 is 1.0 m, the horizontal dimension a is 12.0 m and the vertical dimension is 10.96 m (about 130 m ² ). The structure of the hexagonal unit 2 is the same as that of the first embodiment. In the present embodiment, the hexagonal unit 2 is disposed so that the two improved column bodies 10 of the hexagonal units 2 out of the adjacent hexagonal units 2 are in line contact with each other. Of the adjacent hexagonal units 2, 2, the planar shape connecting the centers of a total of four improved pillars 10 that are in line contact with each other has a square shape in plan view. Moreover, it arrange | positions so that the planar shape which ties the center of four adjacent hexagonal units 2 (for example, hexagonal unit 2 (alpha), 2 (beta), 2 (gamma), 2 (delta)) may become a rectangular shape. For example, six auxiliary improved column bodies 4 are arranged in the present embodiment for the same purpose as in the first embodiment.

  Further, an unreformed portion 5 is formed by four adjacent hexagonal units 2. The unimproved portion 5 is a ground that is not improved similarly to the unimproved portion 3, and is a region having a water permeability function. When L / H (h) is set, the value of the long side portion La of the unimproved portion 5 is substituted for L.

  Even with the improved ground 41 according to the second embodiment described above, it is possible to achieve substantially the same effect as the improved ground 1 according to the first embodiment. According to the improved ground 41, the improvement rate is about 60.9%, the construction cost can be reduced, and the economy is excellent. Moreover, since the adjacent hexagonal units 2 and 2 are in line contact with each other, the resistance against vertical force and horizontal force can be increased for a low improvement rate.

DESCRIPTION OF SYMBOLS 1 Improved ground 2 Hexagonal unit 3 Unimproved part 3 'Unimproved part 4 Auxiliary improved pillar 10 Improved pillar Φ Diameter H Length

Claims (3)

A plurality of hexagonal units arranged in the ground so that the centers of the six improved circular pillars are positioned at the apexes of the regular hexagon in plan view;
An unmodified portion formed inside the hexagonal unit,
While the side surfaces of the adjacent improved pillars constituting the hexagonal unit are in line contact with each other,
Of the adjacent hexagonal units, the side surfaces of the adjacent improved pillars are in line contact with each other.   The vertical shearing force generated at the contact portion between the side surfaces of the adjacent improved column bodies during an earthquake is set to be equal to or less than the frictional resistance force generated at the contact portion. Improved ground. Including a step of forming a plurality of hexagonal units each having an unimproved portion inside by arranging them in the ground so that the centers of the six improved circular pillars are located at the apexes of the regular hexagon in plan view. ,
In the process,
While making the side surfaces of the adjacent improved pillars constituting the hexagonal unit line contact each other,
Of the adjacent hexagonal units, the side surfaces of the adjacent improved pillars are brought into line contact with each other.

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