JP2020051064A - Ground improvement composite pile foundation, independent footing foundation combined with ground improvement composite pile, and method of designing independent footing foundation combined with ground improvement composite pile - Google Patents

Abstract

To provide a ground improvement composite pile foundation with improved horizontal resistance, an independent footing foundation combined with a ground improvement composite pile, and a method of designing the independent footing foundation combined with the ground improvement composite pile.SOLUTION: A ground improvement composite pile foundation 1A comprises: an improved body 7 provided on a surface layer part of a ground 11 and formed of soil and sand of the surface layer part and a solidifying material mixed and stirred with the soil and sand; and one or more piles 9 sunk inside the improved body 7. The surface layer part of the ground 11 is composed of a clay ground. When an outside diameter of the pile 9 is Dp and a distance from the center of the pile 9 to an outer edge of the improved body 7 or a polygon circumscribing the improved body 7 is Lpi, the distance Lpi satisfies the relationship represented by the following formula: 2.6Dp<Lpi<3.4Dp.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a ground improvement composite pile foundation, an independent footing foundation combined with a ground improvement composite pile, and a method of designing an independent footing foundation combined with a ground improvement composite pile.

  2. Description of the Related Art Conventionally, ground improvement has been performed to increase the supporting force of soft ground and to suppress settlement. For example, the ground improvement disclosed in Patent Literature 1 is to construct a soil cement composite pile on soft ground. In constructing the soil cement composite pile, a solidified material such as cement milk is poured into the ground while stirring and mixing to form a soil cement column (improved body) on the ground. Is inserted. A cylindrical prefabricated pile having a diameter larger than the outer diameter of the prefabricated pile with blades is connected to the upper end of the prefabricated pile with blades, and the outer diameter of the soil cement column is enlarged at the outer periphery of the cylindrical prefabricated pile. According to the soil-cement composite pile, a large-diameter cylindrical ready-made pile is provided, and the outer diameter of the soil-cement pillar is expanded at the outer periphery of the cylindrical ready-made pile, so that the cylindrical ready-made pile and the outer periphery of the soil-cement pillar are integrated. And the horizontal resistance is improved.

JP 2003-96770 A

  When a horizontal force acts on a pile, the ground around the pile becomes plastic and rises, and the horizontal resistance of the pile decreases. At this time, it is considered that the uplift of the ground is caused by a slip line propagating obliquely upward from a portion of the pile located at the boundary depth between the plastic region I and the plastic region II in the ground. The horizontal resistance of the pile depends on the shearing force acting on the slip surface, and the shearing force is related to the internal friction angle φ and the adhesive force c. It is thought that the horizontal resistance of the pile can be increased if possible.

  On the other hand, Patent Document 1 discloses only setting the outer diameter of the soil cement column so that the pile and the soil cement column behave integrally with each other in order to increase the horizontal resistance of the pile. It does not disclose that the slip line is generated diagonally upward from the pile portion located at the boundary depth between the plastic zone I and the plastic zone II of the ground, and does not disclose increasing the viscosity (adhesive strength) of the slip line. .

  In view of the above circumstances, an object of at least one embodiment of the present invention is to improve a ground improvement composite pile foundation with improved horizontal resistance, an independent footing foundation combined with a ground improvement composite pile, and an independent footing foundation combined with a ground improvement composite pile. Another object of the present invention is to provide a design method.

(1) The ground improvement composite pile foundation according to at least one embodiment of the present invention includes:
Provided on the surface layer of the ground, an improved body composed of a solidified material that is agitated and mixed with the earth and sand of the surface layer and the earth and sand,
And one or more piles sunk inside the improved body,
The surface layer of the ground is constituted by clay ground,
When the outer diameter of the pile is Dp, and the distance from the center of the pile to the outer edge of the improved body or a polygon circumscribing the improved body is Lpi,
The distance Lpi is given by the following equation:
2.6Dp <Lpi <3.4Dp
Satisfies the relationship indicated by.

Cohesive soil-based soils are characterized by a small internal friction angle φ and an adhesive force c, and are generally considered to have an internal friction angle φ ≒ 0. Therefore, in clay ground (including clay-based ground), The boundary depth between I and the plastic zone II is at most about 2.5 times the outer diameter Dp of the pile, and the slip line propagates obliquely upward at an angle of 45 degrees from the boundary depth. For this reason, the range in which the slip line reaches on the surface of the ground is a range of about 6 Dp around the pile.
In consideration of this, in the above configuration (1), the distance Lpi from the center of the pile to the outer edge of the improved body or the polygon circumscribing the improved body is set to be more than 2.6 Dp and less than 3.4 Dp. As a result, substantially the entire area of the slip line propagating from the boundary depth passes through the improved body, and the viscosity of the slip line and thus the shearing force can be increased. As a result, the occurrence of slip lines is suppressed, and the horizontal resistance of the pile can be increased.

(2) The ground improvement composite pile foundation according to at least one embodiment of the present invention includes:
Provided on the surface layer of the ground, an improved body composed of a solidified material that is agitated and mixed with the earth and sand of the surface layer and the earth and sand,
And one or more piles sunk inside the improved body,
A distance from the center of the pile to an outer edge of the improved body or a polygon circumscribing the improved body is set based on a boundary depth between the plastic region I and the plastic region II in the ground.

  According to the above configuration (2), the distance from the center of the pile to the outer edge of the improved body or the polygon circumscribing the improved body is set based on the boundary depth between the plastic region I and the plastic region II. Substantially the entirety of the slip line propagating therefrom can pass through the improved body. As a result, it is possible to increase the viscosity and thus the shearing force of the slip line, suppress the occurrence of the slip line, and increase the horizontal resistance of the pile.

(3) In some embodiments, in the above configuration (1) or (2),
It further includes a ground surface reinforcing layer that covers the surface of the surrounding ground around the improved body.

If the pile and the improved body have a high degree of integration and the strength difference between the surrounding ground and the improved body is large, slip lines may occur in the surrounding ground of the improved body, and the surrounding ground may be deformed to lower the horizontal resistance.
In this regard, according to the above configuration (3), by covering the surface of the surrounding ground with the ground surface reinforcing layer, deformation of the surrounding ground can be suppressed, and the horizontal resistance of the pile can be increased.

(4) In some embodiments, in any one of the configurations (1) to (3),
The surface of the improved body further includes an improved body surface reinforcing layer.

  According to the above configuration (4), by providing the improved body surface reinforcing layer, deformation of the improved body can be suppressed, and the horizontal resistance of the pile can be further increased.

(5) In some embodiments, in the above configuration (4),
The improved body surface reinforcing layer is constituted by a metal plate,
The apparatus further includes a projection provided integrally with the plate and buried inside the improved body or at a boundary between the improved body and the surrounding ground around the improved body.
According to the above configuration (5), by providing the protrusion, the deformation of the improved body can be suppressed, and the horizontal resistance of the pile can be increased.

(6) In some embodiments, in the above configuration (5),
The protrusion is configured to block a slip line propagating obliquely upward from a portion of an outer peripheral surface of the pile located at a boundary depth between the plastic region I and the plastic region II in the ground.
According to the configuration (6), the occurrence of a slip line is suppressed by the projection, and the horizontal resistance of the pile can be increased.

(7) In some embodiments, in the above configuration (5) or (6),
The plate has one or more through holes.
According to the above configuration (7), the improved body before hardening enters the through-hole of the plate, and then hardens, thereby increasing the integrity of the plate and the improved body. For this reason, the deformation of the improved body can be further suppressed by the plate, and the horizontal resistance of the pile can be increased.

(8) In some embodiments, in any one of the configurations (5) to (7),
The plate is joined to the pile.
According to the above configuration (8), the deformation and displacement of the pile are transmitted to the improved body via the plate, whereby the deformation and displacement of the pile are suppressed, so that the horizontal resistance of the pile can be further increased. .

(9) In some embodiments, in any one of the configurations (1) to (8),
Inside the improved body, having a protrusion attached to the pile,
The protrusion is disposed so as to block a slip line that propagates obliquely upward from a portion of the outer peripheral surface of the pile located at a boundary depth between the plastic region I and the plastic region II in the ground.
According to the above configuration (9), the occurrence of a slip line is suppressed by the projection, and the horizontal resistance of the pile can be increased.

(10) The ground improvement composite pile combined independent footing foundation according to at least one embodiment of the present invention includes:
A ground improvement composite pile foundation according to any one of the above configurations (1) to (9),
A footing that is arranged on the pile and the improved body and is made of concrete,
Assuming that the bottom area of the footing is Af and the surface area of the improved body is Ai, the following formula:
0.8Ai ≦ Af ≦ 1.2Ai
Satisfies the relationship indicated by.

  According to the configuration (10), since the footing is provided over substantially the entire surface of the improved body, deformation of the improved body can be suppressed by the footing, and the horizontal resistance of the pile can be increased. Further, since the footing is provided over substantially the entire surface of the improved body, the vertical load from the upper structure can be directly borne by the improved body. Therefore, it is not necessary to transmit the vertical load of the upper structure to the improved body via the pile, so that the pile head joint structure can be simplified and a pile having a low compressive strength can be used.

(11) A method for designing an independent footing foundation combined with a ground improvement composite pile according to at least one embodiment of the present invention includes:
Provided on the surface layer of the ground, an improved body composed of a solidified material that is agitated and mixed with the earth and sand of the surface layer and the earth and sand,
One or more piles sunk inside the improved body;
The footing, which is arranged on the pile and the improved body and is made of concrete, comprising: a ground improvement composite pile combined independent footing foundation combined with a soil layer in which the surface layer of the ground is made of clay ground,
When the outer diameter of the pile is Dp, and the distance from the center of the pile to the outer edge of the improved body or a polygon circumscribing the improved body is Li,
The distance Lpi is given by the following equation:
2.6Dp <Lpi <3.4Dp
The outer diameter Dp of the pile and the distance Lpi are set so as to satisfy the relationship represented by
Assuming that the bottom area of the footing is Af and the surface area of the improved body is Ai, the following formula:
0.8Ai ≦ Af ≦ 1.2Ai
The bottom area Af of the footing and the surface area Ai of the improved body are set so as to satisfy the relationship expressed by:

According to the above configuration (11), the propagation from the boundary depth is performed by setting the distance Lpi from the center of the pile to the outer edge of the improved body or the polygon circumscribing the improved body to be more than 2.6 Dp and less than 3.4 Dp. Substantially the entire area of the slip line passes through the improved body, and the viscosity of the slip line and thus the shear force can be increased. As a result, the occurrence of slip lines is suppressed, and the horizontal resistance of the pile can be increased.
Further, according to the configuration (11), since the footing is provided over substantially the entire surface of the improved body, deformation of the improved body can be suppressed by the footing, and the horizontal resistance of the pile can be increased. . Further, since the footing is provided over substantially the entire surface of the improved body, the vertical load from the upper structure can be directly borne by the improved body. Therefore, it is not necessary to transmit the vertical load of the upper structure to the improved body via the pile, so that the pile head joint structure can be simplified and a pile having a low compressive strength can be used.

(12) A method for designing an independent footing foundation combined with a ground improvement composite pile according to at least one embodiment of the present invention includes:
Provided on the surface layer of the ground, an improved body made of a solidified material that is agitated and mixed with the earth and sand of the surface layer,
One or more piles sunk inside the improved body;
The footing, which is arranged on the pile and the improved body and is made of concrete, comprising: a ground improvement composite pile combined independent footing foundation design method comprising:
Based on the boundary depth of the plastic zone I and the plastic zone II in the ground, set the distance from the center of the pile to the outer edge of the improved body or a polygon circumscribing the improved body,
Assuming that the bottom area of the footing is Af and the surface area of the improved body is Ai, the following formula:
0.8Ai ≦ Af ≦ 1.2Ai
The bottom area Af of the footing and the surface area Ai of the improved body are set so as to satisfy the relationship expressed by:

According to the above configuration (12), the distance from the center of the pile to the outer edge of the improved body or the polygon circumscribing the improved body is set based on the boundary depth between the plastic region I and the plastic region II. Substantially the entirety of the slip line propagating therefrom can pass through the improved body. As a result, it is possible to increase the viscosity and thus the shearing force of the slip line, suppress the occurrence of the slip line, and increase the horizontal resistance of the pile.
According to the above configuration (12), since the footing is provided over substantially the entire surface of the improved body, deformation of the improved body can be suppressed by the footing, and the horizontal resistance of the pile can be increased. . Further, since the footing is provided over substantially the entire surface of the improved body, the vertical load from the upper structure can be directly borne by the improved body. Therefore, it is not necessary to transmit the vertical load of the upper structure to the improved body via the pile, so that the pile head joint structure can be simplified and a pile having a low compressive strength can be used.

  According to at least one embodiment of the present invention, a ground improvement composite pile foundation with improved horizontal resistance, an independent footing foundation combined with a ground improvement composite pile, and a method of designing an independent footing foundation combined with a ground improvement composite pile are provided. .

It is a schematic diagram for explaining the ground improvement composite pile foundation concerning at least one embodiment of the present invention, and the upper structure supported by the ground improvement composite pile foundation. It is a schematic fragmentary sectional view for explaining a ground improvement composite pile foundation. It is a schematic plan view of a ground improvement composite pile foundation. It is a figure for explaining deformation of the ground when a horizontal force acts on a pile head. It is a graph which shows the relationship between undrained shear strength and boundary depth in a clay ground. (A) and (b) are each a schematic plan view of a ground improvement composite pile foundation according to another embodiment of the present invention. It is a schematic fragmentary sectional view of the ground improvement composite pile foundation concerning other embodiments of the present invention. It is a schematic fragmentary sectional view of the ground improvement composite pile foundation concerning other embodiments of the present invention. It is a figure for explaining an operation effect of an improved body surface reinforcement layer. It is a schematic fragmentary sectional view of the ground improvement composite pile foundation concerning other embodiments of the present invention. It is a schematic fragmentary sectional view of the ground improvement composite pile foundation concerning other embodiments of the present invention. It is a schematic fragmentary sectional view of the ground improvement composite pile foundation concerning other embodiments of the present invention. It is a schematic fragmentary sectional view of the ground improvement composite pile foundation concerning other embodiments of the present invention. It is a schematic fragmentary sectional view of the ground improvement composite pile foundation concerning other embodiments of the present invention. It is a schematic fragmentary sectional view of the ground improvement composite pile foundation concerning other embodiments of the present invention. It is a schematic fragmentary sectional view of the ground improvement composite pile foundation concerning other embodiments of the present invention. It is a schematic plan view of the ground improvement composite pile foundation concerning other embodiment of this invention. FIG. 18 is a schematic partial sectional view of a pile and a plate constituting the ground improvement composite pile foundation of FIG. 17. It is a schematic plan view of the ground improvement composite pile foundation concerning other embodiment of this invention. FIG. 20 is a schematic partial sectional view of a pile and a plate constituting the ground improvement composite pile foundation of FIG. 19. It is a schematic fragmentary sectional view for explaining an independent footing foundation combined with a ground improvement composite pile according to another embodiment of the present invention. It is a flowchart which shows the rough procedure of the design method of the independent footing foundation combined with ground improvement composite pile of FIG. 23 is a diagram for explaining the design method in FIG. 22. FIG. It is a schematic fragmentary sectional view of the ground improvement composite pile foundation concerning other embodiments of the present invention. It is a graph which shows the relationship between N value and boundary depth Zpc in sandy ground. It is a graph which shows the relationship between internal friction angle (phi) in sandy ground, and boundary depth Zpc.

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention thereto, but are merely illustrative examples. Absent.
For example, the expression representing a shape such as a square shape or a cylindrical shape not only represents a shape such as a square shape or a cylindrical shape in a strictly geometrical sense, but also an uneven portion or a chamfer as long as the same effect can be obtained. A shape including a part and the like is also represented.

FIG. 1 is a schematic diagram for explaining a ground improvement composite pile foundation (hereinafter, also simply referred to as a pile foundation) 1 according to at least one embodiment of the present invention, and an upper structure 5 supported by the pile foundation 1. It is. FIG. 2 is a schematic partial sectional view for explaining a pile foundation 1A which is an example of the pile foundation 1. FIG. 3 is a schematic plan view of the pile foundation 1A.
The upper structure 5 is, for example, an S-structure (steel frame) middle and low-rise building, and has a height of about 3 to 4 floors. The upper structure 5 is used, for example, as a store, a warehouse, a factory, a gymnasium, or the like.

As shown in FIGS. 1 to 3, the ground improvement composite pile foundation 1 </ b> A includes an improved body 7 and one or more piles 9.
The improved body 7 is provided on a surface portion of the ground 11, and is composed of soil and sand of the surface portion and a solidified material mixed with the soil and agitated. In addition, the surface part of the ground 11 means the surface side of the ground. The improved body 7 is formed by injecting a solidifying material while stirring the surface layer portion and hardening the solidifying material. For example, the solidifying material is cement milk, and the improved body 7 is soil cement. Soil cement, for example, has a compressive strength of 200 kN / ^{m 2} or more 5000kN / ^{m 2} or less. The improved body 7 has, for example, a cylindrical shape, but may have a prismatic shape as shown by a two-dot chain line in FIG.

  One or more piles 9 are submerged inside the improved body 7. The pile head 9 a of the pile 9 projects from the surface of the improved body 7. On the other hand, the tip (lower end) 9 b of the pile 9 is located inside the improved body 7. The stake 9 has, for example, a hollow cylindrical shape or a rectangular cylindrical shape, but may be solid. The pile 9 is, for example, a concrete pile such as a PRC pile (prestressed concrete pile) or a PHC pile (high-strength prestressed concrete pile), or a steel pipe pile. The pile 9 has, for example, an outer diameter of 50 mm or more and 500 mm or less, and preferably has an outer diameter of 300 mm or less.

  The surface layer of the ground 11 is made of clay ground. The clay ground is a ground mainly composed of silt having a particle diameter of 0.074 mm or less or clay having a particle diameter of 0.005 mm or less, but may contain some sand. That is, the “clay ground” in the present specification includes a clay-based ground.

In the ground improvement composite pile foundation 1A, when the outer diameter of the improved body 7 centering on the pile 9 is Di and the outer diameter of the pile 9 is Dp, the following equation is used.
5.2Dp <Di <6.8Dp
Is satisfied.
In the case where the improved body 7 has a prismatic shape, the outer diameter Di of the improved body 7 about the pile 9 refers to the diameter of a circle inscribed in the improved body 7 about the pile 9. Similarly, when the pile 9 has a prismatic shape, the outer diameter Dp of the pile 9 refers to the diameter of a circle inscribed in the pile 9.

In other words, in the ground-improved composite pile foundation 1A, the outer diameter of the pile 9 is Dp, and from the center of the pile 9 to the outer edge of the improved body 7 or a polygon circumscribing the improved body 7 in plan view. Where Lpi is the distance of
2.6Dp <Lpi <3.4Dp
Is satisfied.

  In the pile foundation 1, the head of the pile 9 (pile head 9 a) protrudes from the improved body 7, and the pile head 9 a is surrounded by a block-shaped footing 13 made of concrete. The footing 13 is partially provided on the improved body 7, and is configured to transmit the vertical load of the upper structure 5 to the pile 9. On the footing 13, a column (steel frame) 15 of the upper structure 5 is erected.

  FIG. 4 is a diagram for explaining deformation of the ground when a horizontal force acts on the pile head. FIG. 5 is a graph showing the relationship between the undrained shear strength Cu and the boundary depth Zpc in the clay ground. The boundary depth Zpc indicates the depth of the boundary between the plastic region I and the plastic region II, and is standardized by the outer diameter of the pile. Accordingly, the actual boundary depth can be obtained by multiplying the boundary depth Zpc by the outer diameter of the pile.

As shown in FIG. 4, when a horizontal force acts on the pile head, the soil in the plastic region I is pushed by the pile on the front side (front side) in the direction of the horizontal force, and a slip line is generated. As a result, the soil in the plastic zone I sinks along with the deformation of the pile on the rear side (rear side) in the horizontal force acting direction.
On the other hand, even if the pile is deformed by the horizontal force, the soil in the plastic zone II on the front side of the horizontal force only moves around to the side of the pile and moves rearward due to the overburden pressure. And does not move upward.
Therefore, in order to suppress deformation of the ground around the pile due to horizontal force, it is important to improve the plastic region I, and for that purpose, it is important to grasp the depth of the plastic region I.

  As shown in FIG. 5, in the clay ground, the boundary depth between the plastic region I and the plastic region II is about 2.5 times the outer diameter Dp of the pile at the maximum, and the slip line is 45 degrees from the boundary depth. At an angle of. For this reason, the range in which the slip line reaches on the surface of the ground is a range of about 6 Dp around the pile.

  In consideration of this, in the above configuration, the outer diameter Di of the improved body 7 is set to be more than 5.2 Dp and less than 6.8 Dp, in other words, the outer edge of the improved body 7 or the outer periphery of the improved body 7 is circumscribed from the center of the pile 9. The distance Lpi to the polygon is set to be more than 2.6 Dp and less than 3.4 Dp. As a result, substantially the entire area of the slip line 16a propagating from the boundary depth passes through the improved body 7, and the viscosity at the slip line 16a and thus the shearing force can be increased. As a result, the occurrence of the slip line 16a is suppressed, and the horizontal resistance of the pile 9 can be increased.

  If the outer diameter Di of the improved body 7 is too large, the improvement range is widened, and the working time and cost are increased. Therefore, the outer diameter Di of the improved body 7 is preferably as close as possible to 6 Dp. Therefore, the outer diameter Di of the improved body 7 is preferably set to be more than 5.6 Dp and less than 6.4 Dp, and more preferably set to be more than 5.8 Dp and less than 6.2 Dp. In other words, distance Lpi is preferably set to be more than 2.8 Dp and less than 3.2 Dp, and more preferably set to be more than 2.9 Dp and less than 3.1 Dp.

  Hereinafter, other embodiments of the present invention will be described. However, the same or similar configurations as those of the above-described embodiments will be denoted by the same names or reference numerals, and description thereof will be omitted or simplified.

FIG. 6A is a schematic plan view of a ground improvement composite pile foundation 1B according to another embodiment of the present invention. The improved body 7 of the ground improvement composite pile foundation 1B is configured by a plurality of improved bodies 7a, 7b, 7c, 7d. As described above, the improved body 7 may adopt a lap arrangement (for example, a pile type, a wall type, or a block type) in which a plurality of the improved types 7a to 7d are arranged so as to partially overlap. Alternatively, a non-wrap arrangement in which the plurality of improved bodies 7a to 7d are in contact with or apart from each other (for example, a pile arrangement or a tangent arrangement) may be employed. And in the case of a lap arrangement | positioning or an overlap arrangement | positioning, the number of the improved bodies 7a-7d which comprise the improved body 7 is not limited to four, What is necessary is just two or more.
A pile 9 is laid in each of the improved bodies 7a, 7b, 7c, 7d, and the following equation is provided between the outer diameter Dp of the pile 9 and the outer diameter Di of each of the improved bodies 7a, 7b, 7c, 7d.
5.2Dp <Di <6.8Dp
The relationship indicated by is established.

In other words, in the ground improvement composite pile foundation 1B, the outer diameter of the pile 9 is set to Dp in consideration of the case where the plurality of improved bodies 7a to 7d constitute one improved body 7, When the distance from the center of the pile 9 to the outer edge of the improved body 7 or a polygon circumscribing the improved body 7 in plan view is Lpi, the following formula is used:
2.6Dp <Lpi <3.4Dp
Is satisfied.
When a plurality of piles 9 are laid in the improved body 7, the center interval Lc between the piles 9 is set to, for example, 2.0 Dp or more and 2.5 Dp or less, but is not limited thereto.

  FIG. 6B is a schematic plan view of a ground improvement composite pile foundation 1B 'according to another embodiment of the present invention. The improved body 7 of the ground improvement composite pile foundation 1B 'is constituted by a plurality of improved bodies 7e, 7f, 7g, 7h. In the improved body 7 of the ground-improved composite pile foundation 1B ', the overlap area of the improved bodies 7e to 7h is smaller in plan view than the overlap area of the improved bodies 7a to 7d in the improved body 7 of the ground-improved composite pile foundation 1B. As described above, the outer diameter Di and the position of the improved bodies 7e to 7h are determined. That is, as shown in FIG. 6A, when the center interval Lc is 2.0 Dp or more and 2.5 Dp or less and the pile 9 is arranged at the center of each of the improved bodies 7 a to 7 d, the overlapping of the improved bodies 7 a to 7 d is performed. Although the area is increased, as shown in FIG. 6B, if the centers of the improved bodies 7e to 7h are shifted with respect to the pile 9, the size of the improved body 7 as a whole is substantially the same. Also, the outer diameter Di of each of the improved bodies 7e to 7h can be reduced.

Also in the ground improvement composite pile foundation 1B ', when the outer diameter of the pile 9 is Dp, and the distance from the center of the pile 9 to the outer edge of the improved body 7 or a polygon circumscribing the improved body 7 is Lpi in plan view. And the following formula:
2.6Dp <Lpi <3.4Dp
Is satisfied.
On the other hand, in the ground improvement composite pile foundation 1B ', the following formula is provided between the outer diameter Dp of the pile 9 and the outer diameter Di of each of the improved bodies 7e to 7f.
5.2Dp <Di <6.8Dp
It is not necessary that the relationship represented by is always established. That is, when the center of the pile 9 is deviated from the center of each of the improved bodies 7e to 7f in the lap arrangement, it is sufficient that 2.6 Dp <Lpi <3.4 Dp is satisfied, and 5.2 Dp <Di <6. It does not need to be .8 Dp.

FIG. 7 is a schematic partial sectional view of a ground improvement composite pile foundation 1C according to another embodiment of the present invention.
As shown in FIG. 7, the ground improvement composite pile foundation 1C is different from the ground improvement composite pile foundation 1A in that the ground improvement composite pile foundation 1C further includes a ground surface reinforcement layer 17 covering the surface of the peripheral ground 11a around the improvement body 7. .

If the pile 9 and the improved body 7 are highly integrated and the difference in strength between the surrounding ground 11a and the improved body 7 is large, a slip line 16b occurs in the surrounding ground 11a of the improved body 7 and the surrounding ground 11a is deformed to cause horizontal resistance. May decrease.
In this regard, according to the above configuration, by covering the surface of the peripheral ground 11a with the ground surface reinforcing layer 17, the deformation of the peripheral ground 11a can be suppressed, and the horizontal resistance of the pile 9 can be increased.

  The outer diameter Dr of the ground surface reinforcing layer 17 is preferably more than 5.2 times and less than 6.8 times the outer diameter Di of the improved body 7. If it is increased, the area of the ground surface reinforcing layer 17 becomes too large. On the other hand, according to FIG. 5, if the boundary depth Zpc is set to 1.5, the undrained shear strength Cu can cover a range of 0.625 (a range of 0.1 in terms of N value). . Assuming that the boundary depth Zpc is 1.5, the outer diameter of the reach of the slip line 16b is four times (4Di) the outer diameter Di of the improved body 7 around the pile 9. In consideration of this point, the outer diameter Dr of the ground surface reinforcing layer 17 is preferably set to be four times or more and less than 6.8 times the outer diameter Di of the improved body 7.

In some embodiments, the ground surface reinforcement layer 17 is made of concrete 17a or asphalt.
According to the above configuration, by forming the ground surface reinforcing layer 17 with concrete 17a or asphalt, deformation of the surrounding ground 11a can be suppressed and the horizontal resistance of the pile 9 can be increased with a simple configuration.

FIG. 8 is a schematic partial cross-sectional view of a ground improvement composite pile foundation 1D according to another embodiment of the present invention.
As shown in FIG. 8, the ground improvement composite pile foundation 1 </ b> D differs from the ground improvement composite pile foundation 1 </ b> A in further including an improved body surface reinforcing layer 19 covering the surface of the improved body 7. The improved body surface layer 19 is provided so as to surround the pile head 9 a and is in close contact with the surface of the improved body 7.

According to the above configuration, by providing the improved body surface reinforcing layer 19, the deformation of the improved body 7 can be suppressed, and the horizontal resistance of the pile 9 can be further increased.
Here, FIG. 9 is a diagram for explaining the function and effect of the improved body surface reinforcing layer 19. As shown in FIG. 9, when a large horizontal force acts on the pile head 9a, the pile head 9a moves forward in the direction in which the horizontal force acts, and a gap is created behind. Further, a crack is formed at an angle of 30 to 40 degrees from the side of the pile 9 toward the front. When a crack or a gap is generated in this way, the rearward side of the improved body 7 in the direction of action of the horizontal force cannot suppress the displacement of the pile 9 in the horizontal direction.

  In this regard, if the improved body surface reinforcing layer 19 is provided, it is possible to prevent the improved body 7 from rising due to slippage. Further, in the vicinity of the ground surface that contributes most to the horizontal resistance, the integration of the pile 9 and the improved body 7 can be enhanced, and the deformation of the pile 9 can be suppressed. At this time, even if a gap or a crack is generated, the rear side of the improved body 7 in the direction of the horizontal force contributes to the suppression of the deformation of the pile 9 by providing the improved body surface reinforcing layer 19. it can. As a result, even when the improved body surface reinforcing layer 19 is provided, the damage to the improved body 7 can be reduced even with a repeated load such as an earthquake motion. Thus, by providing the improved body surface reinforcing layer 19, the deformation of the improved body 7 can be suppressed, and the horizontal resistance of the pile 9 can be further increased.

10 to 12 are schematic partial cross-sectional views of ground improvement composite pile foundations 1E to 1G according to another embodiment of the present invention.
As shown in FIGS. 10 to 12, the ground improvement composite pile foundation 1 </ b> E to 1 </ b> G includes a ground improvement composite pile foundation 1 </ b> C or a ground improvement composite It is different from pile foundation 1D.
According to the above configuration, the provision of both the ground surface reinforcing layer 17 and the improved body surface reinforcing layer 19 can further increase the horizontal resistance of the pile 9.

In some embodiments, the improved body surface reinforcing layer 19 is configured by a metal plate (steel plate) 19a as illustrated in FIGS. 8 and 10, and is configured by a reinforced concrete 19b as illustrated in FIG. As shown in FIG. 12, it is constituted by concrete 19c or is constituted by asphalt.
According to the above configuration, by forming the improved body surface reinforcing layer 19 from a metal plate 19a, reinforced concrete 19b, concrete 19c or asphalt, the deformation of the improved body 7 is suppressed with a simple structure, and the pile 9 Horizontal resistance can be increased.

FIG. 13 is a schematic partial cross-sectional view of a ground improvement composite pile foundation 1H according to another embodiment of the present invention.
As shown in FIG. 13, the ground-improved composite pile foundation 1H differs from the ground-improved composite pile foundation 1A and the like in that a protrusion 21 attached to the pile 9 is provided inside the improved body 7. The protrusion 21 is disposed so as to block the slip line 16a that propagates obliquely upward from a portion of the outer peripheral surface of the pile 9 located at the boundary depth between the plastic region I and the plastic region II in the ground 11. .
According to the above configuration, the occurrence of the slip line 16 a is suppressed by the projection 21, and the horizontal resistance of the pile 9 can be increased.

In some embodiments, the protrusion 21 includes an annular, C-shaped, tubular, or helical metal member.
According to the above configuration, since the protrusion 21 includes an annular, C-shaped, cylindrical, or spiral metal member, the occurrence of the slip line 16a is suppressed with a simple configuration, and the horizontal resistance of the pile 9 is reduced. Can be enhanced.

FIG. 14 is a schematic partial cross-sectional view of a ground improvement composite pile foundation 1J according to another embodiment of the present invention.
As shown in FIG. 14, the ground improvement composite pile foundation 1J is different from the ground improvement composite pile foundation 1D shown in FIG. 8 in that the ground improvement composite pile foundation 1J further includes a projection 23 provided integrally with the plate 19a. The protrusion 23 extends in the vertical direction, and is buried inside the improved body 7 or at a boundary between the improved body 7 and the surrounding ground 11a.
According to the above-described configuration, the provision of the projections 23 increases the integration between the improved body 7 and the plate 19a. In addition, the provision of the projections 23 reliably prevents the slip line 16a from passing through the improved body 7 and reaching the surface of the surrounding ground 11a. As a result, deformation of the improved body 7 can be suppressed, and the horizontal resistance of the pile 9 can be increased.

FIG. 15 is a schematic partial cross-sectional view of a ground improvement composite pile foundation 1K according to another embodiment of the present invention.
As shown in FIG. 15, the ground improvement composite pile foundation 1K includes a plurality of protrusions 23 provided integrally with the plate 19a, and the protrusions 23 are embedded in the improved body 7 as shown in FIG. It is different from the ground improvement composite pile foundation 1D. According to the above configuration, the provision of the plurality of protrusions 23 enhances the integration between the improved body 7 and the plate 19a. In addition, the provision of the plurality of protrusions 23 reliably prevents the slip line 16a from passing through the improved body 7 and reaching the surface of the surrounding ground 11a. As a result, deformation of the improved body 7 can be suppressed, and the horizontal resistance of the pile 9 can be increased.

FIG. 16 is a schematic partial cross-sectional view of a ground improvement composite pile foundation 1L according to another embodiment of the present invention.
As shown in FIG. 16, the ground improvement composite pile foundation 1L includes a plurality of protrusions 23 provided integrally with the plate 19a, and the ground improvement shown in FIG. It is different from composite pile foundation 1K. For example, as the distance from the stake 9 increases, the length of the protrusion 23 increases.
According to the above configuration, the provision of the plurality of protrusions 23 enhances the integration between the improved body 7 and the plate 19a. In addition, the provision of the plurality of protrusions 23 reliably prevents the slip line 16a from passing through the improved body 7 and reaching the surface of the surrounding ground 11a. As a result, deformation of the improved body 7 can be suppressed, and the horizontal resistance of the pile 9 can be increased.

In some embodiments, the protrusion 23 is formed of a cylindrical or square metal tube, a round bar or a deformed reinforcing bar, or a flat bar.
According to the above configuration, the protrusion 23 is formed of a cylindrical or square metal tube, a round bar or a deformed reinforcing bar, a flat bar, or the like. Resistance can be increased.

FIG. 17 is a schematic plan view of a ground improvement composite pile foundation 1M according to another embodiment of the present invention.
As shown in FIG. 17, the ground improvement composite pile foundation 1M differs from the ground improvement composite pile foundation 1D shown in FIG. 8 in that the plate 19a has one or more through holes 25.
According to the above configuration, the improved body 7 before hardening enters the through hole 25 of the plate 19a and then hardens, whereby the plate 19a and the improved body 7 come into close contact with each other, and the plate 19a and the improved body 7 are integrated. The nature becomes high. Therefore, the deformation of the improved body 7 can be further suppressed by the plate 19a, and the horizontal resistance of the pile 9 can be increased.

FIG. 18 is a schematic partial cross-sectional view of the pile 9 and the plate 19a used in the ground improvement composite pile foundation 1M. As shown in FIG. 18, the plate 19a and the pile 9 are joined to each other. For example, when joining the plate 19a to the concrete pile 9 by welding, a metal reinforcing band 27 may be provided on the pile head 9a, and the plate 19a may be welded to the reinforcing band 27.
According to the above configuration, since the deformation and displacement of the pile 9 are transmitted to the improved body 7 via the plate 19a, the deformation and displacement of the pile 9 are suppressed, so that the horizontal resistance of the pile 9 is further increased. Can be.

  The pile 9 in FIG. 18 is a PRC pile, and is a hollow and cylindrical concrete portion 29, end plates 31 disposed at both ends of the concrete portion 29, and a concrete portion 29 provided between the end plates 31. A penetrating PC steel rod 33 is provided. The reinforcing bands 27 cover the outer peripheral surfaces of both ends of the concrete portion 29. Further, a pile code 35 indicates a welded portion (fillet welded portion).

FIG. 19 is a schematic plan view of a ground improvement composite pile foundation 1N according to another embodiment of the present invention. FIG. 20 is a schematic partial cross-sectional view of the pile 9 and the plate 19a used in the ground improvement composite pile foundation 1N along the line XX-XX in FIG.
As shown in FIGS. 19 and 20, the ground improvement composite pile foundation 1 </ b> N has a point that a gap 37 is provided between the pile 9 and the plate 19 a while the pile 9 and the plate 19 a are joined to each other. This is different from the ground improvement composite pile foundation 1M shown in FIG.
According to the above configuration, the improved body 7 before hardening enters the through holes 25 and the gaps 37 of the plate 19a and then hardens, whereby the plate 19 and the improved body 7 come into close contact with each other, and the plate 19a and the improved body 7 Is more integrated. Therefore, the deformation of the improved body 7 can be further suppressed by the plate 19a, and the horizontal resistance of the pile 9 can be increased.

  FIG. 21 is a schematic plan view of an independent footing foundation (hereinafter also simply referred to as a footing foundation) 3 used in combination with a ground improvement composite pile according to another embodiment of the present invention. The footing foundation 3 includes a footing 13 provided over substantially the entire surface of the improved body 7 together with the ground improvement composite pile 1A. The footing 13 is made of concrete and surrounds the pile head 9 a protruding from the surface of the improved body 7. For example, the pile head 9 a protrudes from the surface of the improved body 7 with a length of 50 mm to 150 mm, and is surrounded by the footing 13. Therefore, the horizontal force acting on the upper structure 5 is configured to act on the pile 9 via the footing 13.

  On the other hand, the footing 13 has a block shape and is configured to transmit the vertical load of the upper structure 5 over the entire area of the improved body 7. In other words, the footing foundation 3 differs from the pile foundation 1 in function in that the vertical load of the upper structure 5 is not supported by the pile 9 but is supported by the improved body 7. Therefore, the bottom area of the footing 13 is substantially equal to the surface area of the improved body 7. For example, when the bottom area of the footing 13 is Af and the surface area of the improved body 7 is Ai, the bottom area Af is 0% of the surface area Ai. 0.8 to 1.2 times (0.8 Ai ≦ Af ≦ 1.2 Ai), preferably 0.9 to 1.1 times, more preferably 0.95 to 1.05 times It is as follows. The surface area Ai of the improved body 7 also includes the area of the portion where the pile 9 is laid, that is, the surface area of the pile 9. On the footing 13, a column (steel frame) 15 of the upper structure 5 is erected.

  Further, according to the above configuration, since the footing 13 is provided over substantially the entire surface of the improved body 7, the deformation of the improved body 7 can be suppressed by the footing 13, and the horizontal resistance of the pile 9 is increased. be able to. Further, since the footing 13 is provided over substantially the entire surface of the improved body 7, the vertical load from the upper structure 5 can be directly applied to the improved body 7. For this reason, it is not necessary to transmit the vertical load of the upper structure 5 to the improved body 7 via the pile 9, so that the pile head joint structure can be simplified and a pile having a low compressive strength can be used as the pile 9. It becomes possible. The reason why the pile head joint structure can be simplified is that, for example, the pull-out force is hardly applied to the target middle and low-rise building. For example, the pile head 9a is attached to the footing 13. This means that the pile head 9a and the footing 13 are not connected by a reinforcing bar or the like. Further, according to the above configuration, it is not necessary to provide a protrusion on the pile 9 in order to transmit the vertical load of the pile 9 to the improved body 7. However, as will be described later, a protrusion for blocking the slip line 16a may be provided on the pile 9 instead of transmitting the vertical load to the improved body 7.

FIG. 22 is a flowchart showing a schematic procedure of a method of designing the footing foundation 3 in FIG. 21 (hereinafter, also simply referred to as a design method). FIG. 23 is a diagram for explaining the design method.
As shown in FIG. 22, the design method includes a ground surface layer determining step S1, an improved body diameter setting step S3, a pile number setting step S5, a pile horizontal resistance determining step S7, an improved body depth setting step S9, and A vertical support force determination step S11 is provided.

In the ground surface layer determining step S1, it is determined whether or not the surface layer of the ground 11 needs to be improved. Specifically, when the surface portion of the ground 11 is clay ground and is soft, it is determined that improvement is necessary.
If improvement is required, an improved body diameter setting step S3 and a pile number setting step S5 are performed.
In the improved body diameter setting step S3, when the outer diameter of the improved body 7 centering on the pile 9 is Di and the outer diameter of the pile 9 is Dp, the following equation is used:
5.2Dp <Di <6.8Dp
The outer diameter Di of the improved body 7 and the outer diameter Dp of the pile 9 are set so as to satisfy the relationship indicated by.

Alternatively, in the improved body diameter setting step S3, when the outer diameter of the pile 9 is Dp, and the distance from the center of the pile 9 to the outer edge of the improved body 7 or a polygon circumscribing the improved body 7 is Lpi in plan view. And the following formula:
2.6Dp <Lpi <3.4Dp
Are set so as to satisfy the relationship represented by the following formula (4): the outer diameter Dp of the pile 9 and the distance Lpi from the center of the pile 9 to the outer edge of the improved body 7 or a polygon circumscribing the improved body 7.

  In the pile number setting step S5, the number n of the piles 9 set in the improved body 7 is appropriately set. When a plurality of piles 9 are laid down in one improved body 7, the center interval Lc of the piles 9 is set to, for example, 2.0 Dp to 2.5 Dp.

After the improved body diameter setting step S3 and the pile number setting step S5, a pile horizontal resistance determining step S7 is performed. In the pile horizontal resistance determination step S7, the horizontal resistance of the pile 9 is determined based on the specifications set in the improved body diameter setting step S3 and the pile number setting step S5.
Specifically, a horizontal load Q / n acting on each pile 9 is given from the footing 13 in consideration of the upper structure 5, and it is determined whether the horizontal displacement amount, the generated bending moment, and the like of the pile 9 are within allowable values. I do. If the amount of horizontal displacement or the generated bending moment exceeds the allowable value, it is determined that the horizontal resistance of the pile 9 is insufficient, and the improved body diameter setting step S3 and the number of piles setting step S5 are performed again.

On the other hand, if the horizontal displacement, the generated bending moment, and the like are within the allowable values, it is determined that the horizontal resistance of the pile 9 is sufficient, and the improved body depth setting step S9 is performed.
In the improved body depth setting step S9, the length Li of the improved body 7 is appropriately set. The length Li of the improved body 7 is set to be equal to or longer than the length (pile length) Lp of the pile 9 (Li ≧ Lp). The pile length Lp is set so that the pile 9 can be regarded as a long pile. Specifically, using the characteristic value β of the pile 9, the pile length Lp is calculated by the following equation:
Lp> 3 / β
Is set to satisfy.
Note that the characteristic value β is expressed by the following equation:
β = (khDp / 4EI) ＾ 0.25
Indicated by The symbols in the formula are as follows.
kh: Horizontal ground reaction force coefficient kh = {. alpha..700N. (Dp)}-0.75
N: N value Dp: Non-dimensional pile diameter (Dimensionless numerical value expressing pile diameter in cm)
ξ: Premium coefficient α: Constant

After the improved body depth setting step S9, a vertical support force determining step S11 is performed. In the vertical support force determination step S11, it is determined whether the vertical support force of the improved body 7 is sufficient.
Specifically, whether the vertical bearing capacity is sufficient is determined by the following equation:
qa = min (q1, q2) ≧ σe = Na / Af
Is determined based on whether or not is established.
The symbols in the formula are as follows.
qa1 = (1/3) · {(qd · Ab + {τdi · hi) / Af}
qa2 = (1/3) · {(Rpu + {τd · hi) / Af}
σe: Improved body vertical stress Na: Long-term column axial force qd: Ultimate vertical bearing capacity of the lower ground (kN / m ² )
Ab: Bottom area of the improved body (m ² )
τdi: Ultimate peripheral friction stress of each layer of the improved body (kN / m ² )
hi: Layer thickness of each layer (m)
ψ: Perimeter length of improved body (m)
Af: Footing bottom area or cross-sectional area of improved body (m ² )
Rpu: Ultimate tip vertical bearing capacity of the improved body (kN / m ² )

That is, it is determined whether or not the vertical stress σe acting on the improved body 7 from the footing 13 can be supported by the improved body 7 and the lower ground of the improved body 7.
When it is determined that the vertical support force of the improved body 7 is insufficient, the pile number setting step S5 is performed again if the setting change of the number of piles is necessary, and if it is unnecessary, the depth setting of the improved body is performed. Step S9 is performed again. On the other hand, when it is determined that the vertical support force of the improved body 7 is sufficient, the design ends.

When the above-mentioned design method is applied to the design method of the independent footing foundation combined with the ground improvement composite pile, when the bottom area of the footing 13 is Af and the surface area of the improved body 7 is Ai, the following formula is used.
0.8Ai ≦ Af ≦ 1.2Ai
The bottom area Af of the footing 13 and the surface area Ai of the improved body are set so as to satisfy the relationship expressed by.

  According to the design method of the ground improvement composite pile foundation described above, the outer diameter Di of the improved body 7 is set to be more than 5.2 Dp and less than 6.8 Dp, or the outer edge of the improved body 7 or the improved body from the center of the pile 9. By setting the distance Lpi to the polygon circumscribing 7 at more than 2.6 Dp and less than 3.4 Dp, substantially the entire area of the slip line 16 a propagating from the boundary depth passes through the improved body, and the slip line 16 a , And thus the shearing force can be increased. As a result, the occurrence of the slip line 16a is suppressed, and the horizontal resistance of the pile 9 can be increased.

  In addition, according to the above-described method for designing an independent footing foundation combined with a ground improvement composite pile, since the footing 13 is provided over substantially the entire surface of the improved body 7, the deformation of the improved body 7 can be suppressed by the footing 13. Thus, the horizontal resistance of the pile 9 can be increased. Further, since the footing 13 is provided over substantially the entire surface of the improved body 7, the vertical load from the upper structure 5 can be directly applied to the improved body 7. Therefore, it is not necessary to transmit the vertical load of the upper structure 5 to the improved body 7 via the pile 9, so that the pile head joint structure can be simplified and the vertical load of the upper structure 5 can be improved through the pile 9. It is not necessary to provide a projection or the like for transmitting to the body 7 on the pile 9, and it is possible to use a pile having a low compressive strength as the pile 9.

FIG. 24 is a schematic partial sectional view of a footing foundation 3 using a ground improvement composite pile foundation 1P according to another embodiment of the present invention.
In the embodiment described above, the surface layer of the ground 11 is clay ground, but the ground improvement composite pile foundation 1P is applied to sandy ground mainly composed of sand. Even if the surface portion of the ground 11 is sandy ground, the outer diameter Di of the improved body 7 centering on the pile 9 may be set based on the boundary depth between the plastic region I and the plastic region II in the ground 11. .
Here, FIG. 25 is a graph showing the relationship between the N value (the number of impacts by the standard penetration test) and the boundary depth Zpc in the sandy ground. FIG. 26 is a graph showing the relationship between the internal friction angle φ and the boundary depth Zpc in a sandy ground. The angle θ of the slip line 16a is given by the following equation:
θ = 45 + φ / 2
Represented by

Therefore, using FIG. 25 and FIG. 26, even in a sandy ground, the boundary depth is determined from the N value, and the angle θ of the slip line 16a is further determined. The range reaching the surface of the ground 11 can be grasped. By setting the range as the improved body 7, the slip line 16a can pass through the improved body 7 over the entire area.
Thus, the outer diameter Di of the improved body 7 centering on the pile 9 is set based on the boundary depth between the plastic region I and the plastic region II in the ground 11, and the slip line 16a propagated from the boundary depth extends over the entire region. If it passes through the improved body 7, the viscosity at the slip line 16a and hence the shearing force can be increased, the occurrence of the slip line 16a can be suppressed, and the horizontal resistance of the pile 9 can be increased.

  Lastly, the present invention is not limited to the above-described embodiment, and includes a modification of the above-described embodiment and a combination thereof.

1,1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1J, 1K, 1L, 1M, 1N, 1P Ground improvement composite pile foundation 3 Ground improvement composite pile combined independent footing foundation 5 Superstructure 7,7a, 7b, 7c, 7d, 7e, 7f, 7g, 7h Improved body 9 Pile 9a Pile head 9b Tip 11 Ground 11a Peripheral ground 13 Footing 15 Column 16a, 16b Slip line 17 Ground surface reinforcing layer 17a Concrete 19 Improved body surface reinforcement Layer 19a Plate 19b Reinforced concrete 19c Concrete 21 Projection 23 Projection 25 Through hole 27 Reinforcement band 29 Concrete part 31 End plate 33 PC steel rod 35 Welded part (fillet welded part)
37 gap

Claims (12)

Provided on the surface layer of the ground, an improved body composed of a solidified material that is agitated and mixed with the earth and sand of the surface layer and the earth and sand,
And one or more piles sunk inside the improved body,
The surface layer of the ground is constituted by clay ground,
When the outer diameter of the pile is Dp, and the distance from the center of the pile to the outer edge of the improved body or a polygon circumscribing the improved body is Lpi,
The distance Lpi is given by the following equation:
2.6Dp <Lpi <3.4Dp
A ground-improved composite pile foundation, which satisfies the relationship shown in (1). Provided on the surface layer of the ground, an improved body composed of a solidified material that is agitated and mixed with the earth and sand of the surface layer and the earth and sand,
And one or more piles sunk inside the improved body,
The distance from the center of the pile to an outer edge of the improved body or a polygon circumscribing the improved body is set based on a boundary depth between the plastic region I and the plastic region II in the ground. Ground improvement composite pile foundation. The ground improvement composite pile foundation according to claim 1 or 2, further comprising a ground surface reinforcing layer that covers a surface of a surrounding ground around the improved body. The ground improvement composite pile foundation according to any one of claims 1 to 3, further comprising an improved body surface reinforcing layer that covers a surface of the improved body. The improved body surface reinforcing layer is constituted by a metal plate,
The projection according to claim 4, further comprising a protrusion provided integrally with the plate and embedded in the inside of the improved body or at a boundary between the improved body and a peripheral ground around the improved body. Ground improvement composite pile foundation. The protrusion is configured to block a slip line propagating obliquely upward from a portion of the outer peripheral surface of the pile located at a boundary depth between the plastic region I and the plastic region II in the ground. The ground improvement composite pile foundation according to claim 5, characterized in that: The ground improvement composite pile foundation according to claim 5, wherein the plate has one or more through holes. The ground improvement composite pile foundation according to any one of claims 5 to 7, wherein the board is joined to the pile. Inside the improved body, having a protrusion attached to the pile,
The protrusion is disposed so as to block a slip line that propagates obliquely upward from a portion of the outer peripheral surface of the pile located at a boundary depth between the plastic region I and the plastic region II in the ground. The ground improvement composite pile foundation according to any one of claims 1 to 8, characterized in that: The ground improvement composite pile foundation according to any one of claims 1 to 9,
A footing that is arranged on the pile and the improved body and is made of concrete,
Assuming that the bottom area of the footing is Af and the surface area of the improved body is Ai, the following formula:
0.8Ai ≦ Af ≦ 1.2Ai
An independent footing foundation combined with a ground improvement composite pile, which satisfies the relationship shown in (1). Provided on the surface layer of the ground, an improved body composed of a solidified material that is agitated and mixed with the earth and sand of the surface layer and the earth and sand,
One or more piles sunk inside the improved body;
The footing, which is arranged on the pile and the improved body and is made of concrete, comprising: a ground improvement composite pile combined independent footing foundation combined with a soil layer in which the surface layer of the ground is made of clay ground,
When the outer diameter of the pile is Dp, and the distance from the center of the pile to the outer edge of the improved body or a polygon circumscribing the improved body is L,
The distance Lpi is given by the following equation:
2.6Dp <Lpi <3.4Dp
The outer diameter Dp of the pile and the distance Lpi are set so as to satisfy the relationship represented by
Assuming that the bottom area of the footing is Af and the surface area of the improved body is Ai, the following formula:
0.8Ai ≦ Af ≦ 1.2Ai
A bottom foot area Af of the footing and a surface area Ai of the improved body are set so as to satisfy the following relationship. Provided on the surface layer of the ground, an improved body composed of a solidified material that is agitated and mixed with the earth and sand of the surface layer and the earth and sand,
One or more piles sunk inside the improved body;
The footing, which is arranged on the pile and the improved body and is made of concrete, comprising: a ground improvement composite pile combined independent footing foundation design method comprising:
Based on the boundary depth of the plastic zone I and the plastic zone II in the ground, set the distance from the center of the pile to the outer edge of the improved body or a polygon circumscribing the improved body,
Assuming that the bottom area of the footing is Af and the surface area of the improved body is Ai, the following formula:
0.8Ai ≦ Af ≦ 1.2Ai
A bottom foot area Af of the footing and a surface area Ai of the improved body are set so as to satisfy the following relationship.

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