TW202039969A - Pile foundation and construction method of pile foundation - Google Patents

Abstract

A pile foundation includes: a pile that supports a towering structure and that extends along a vertical direction, a pile top projecting further upward than the ground; and ground improvement body provided in the pile in a state where the pile is driven into the ground, at least a part of which is in close contact with the inner peripheral surface of the pile.

Description

Pile foundation and construction method of pile foundation

The present disclosure relates to a pile foundation and a construction method of the pile foundation.

Japanese Patent Laid-Open No. 2003-293938 discloses a structure in which a wind power generation device is constructed on a hollow single pile foundation. On the other hand, Japanese Patent Application Laid-Open No. 57-161224 discloses a foundation pile in which cylindrical concrete is clamped on the inner peripheral surface of the lower end of the steel pipe pile to increase the end surface area of the lower end of the steel pipe.

However, as a construction method for pile foundations such as single pile foundations, there is known a construction method in which piles are directly driven into the ground by striking. By driving the pile into the ground, the front-end blocking effect can increase the supporting force, and the construction can be completed in a short time. However, when the pile diameter is large, a sufficient front end occlusion effect cannot be obtained, and a large supporting force cannot be obtained. On the other hand, as described in Japanese Patent Application Laid-Open No. 57-161224, when the area of the end face of the lower end of the pile increases, it is difficult for the pile to drive into the ground, which reduces work efficiency.

The present disclosure takes the above facts into consideration, and its purpose is to provide a pile foundation and a construction method of pile foundation that can increase the supporting force of the pile while ensuring work efficiency.

The pile foundation of the first aspect has: a pile extending in a vertical direction to support a tower-like structure, and the pile head of the pile protrudes upward than the ground, and the lower end of the pile is open; and a ground improvement body, It is installed in the pile with the pile driven into the ground, and at least a part of the ground improvement body is in close contact with the inner peripheral surface of the pile.

In the pile foundation of the first aspect, in the state where the pile is driven into the ground, a ground improvement body is provided in the pile. Moreover, at least a part of this ground improvement body is in close contact with the inner peripheral surface of the pile. Thereby, the part where the pile and the ground improvement body are in close contact improves the frictional force of the inner peripheral surface of the pile, and can further increase the supporting force of the pile.

In addition, since the supporting force can be increased without increasing the thickness of the pile itself, it is possible to drive the pile into the ground by striking.

The pile foundation of the second aspect is in the first aspect, in which sand and soil intrude into the pile, and the ground improvement body is arranged between the inner peripheral surface of the pile and the sand.

In the pile foundation of the second aspect, compared to the case where the whole sand is used as the ground improvement, the construction period can be shortened by providing the ground improvement between the inner peripheral surface of the pile and the sand.

The pile foundation of the third aspect is in the second aspect, and when the cross section of the pile is viewed from the axial direction, the ground improvement body is provided at a plurality of places along the inner circumferential surface of the pile.

In the pile foundation of the third aspect, the construction period can be shortened compared to the case where the ground improvement body is provided along the entire circumference of the inner peripheral surface of the pile.

The pile foundation of the fourth aspect is in the second aspect or the third aspect, and the ground improvement body is formed only in a part of the sand in the axial direction of the sand entering the pile.

The pile foundation of the fifth aspect is the first aspect. When the cross section of the pile is viewed from the axial direction, the ground improvement body is installed in the entire area of the pile.

In the pile foundation of the fifth aspect, the entire inner rigidity of the pile can be improved by the ground improvement body.

The pile foundation of the sixth aspect is in any one of the first aspect to the fifth aspect, and the inner peripheral surface of the pile near the pile head is provided with supporting the ground from above Improved support member.

In the pile foundation of the sixth aspect, since the ground improvement body is supported from above by the supporting member, the pile and the ground improvement body can be integrated more closely.

The pile foundation of the seventh aspect has: a pile that extends in a vertical direction to support a tower-shaped structure, and the pile head of the pile protrudes upward than the ground, and the lower end of the pile is open; and a supporting member, which is provided On the inner peripheral surface of the pile near the pile head, at least a part of the sand that has entered the inside of the pile is supported from above.

In the pile foundation of the seventh aspect, a supporting member is provided on the inner circumferential surface of the pile near the pile head, and the supporting member supports at least a part of the sand that has entered the pile from above. By providing the supporting member in this way, when the pile is driven into the ground, the sand and soil in the pile can be compressed by the supporting member, and the front end blocking effect can be obtained.

In the eighth aspect of the pile foundation, in the seventh aspect, the supporting member is an annular flange extending radially inward from the inner circumferential surface of the pile.

In the pile foundation of the eighth aspect, the annular flange can be used to compress the sand in the pile. In addition, since the upper and lower spaces of the flange are connected, it is possible to put medicines and the like into the sand and soil to improve the ground after the pile is driven.

In the ninth aspect of the pile foundation, in the seventh aspect, the support member is a disc-shaped member that closes the lower end of the pile head.

In the pile foundation of the ninth aspect, the vertical force can be transmitted to the entire sand and soil in the pile by the disc-shaped member.

The pile foundation of the tenth aspect is in any one of the seventh aspect to the ninth aspect, and a filling material is filled between the sand entering the pile and the supporting member.

In the pile foundation of the tenth aspect, the sand and the supporting member can be integrated with the filling material.

The pile foundation of the eleventh aspect is attached to any one of the first aspect to the tenth aspect. A floor is provided on the ground, and the floor is fixed on the pile head so as to act on the pile The force is transmitted to the site.

In the pile foundation of the eleventh aspect, even when an external force is input in the direction in which the pile falls, at least a part of the external force can be transmitted to the ground via the floor, and the resistance of the pile to the horizontal force can be ensured.

The pile foundation of the twelfth aspect is in any one of the first aspect to the eleventh aspect, and the tower-shaped structure constitutes the foot of the wind power generator.

In the pile foundation of the twelfth aspect, even when a moment in the tilting direction is applied to the pile due to a heavy object such as a wind turbine, the pile can be prevented from falling over by increasing the supporting force of the pile.

The construction method of the pile foundation of the thirteenth aspect has the following steps: driving a pile with an open lower end into the ground so that the pile head of the pile protrudes above the ground; and in the sand entering the inside of the pile, at least The sandy soil near the inner peripheral surface of the pile is improved on the ground.

In the construction method of the pile foundation of the thirteenth aspect, by performing ground improvement on at least the sand near the inner peripheral surface of the pile, the ground improvement body can be brought into close contact with the inner peripheral surface of the pile. Thereby, the frictional force of the inner peripheral surface of the pile can be increased, and the supporting force of the pile can be increased. In addition, compared with the method of pile construction after cutting the ground, the work efficiency can be ensured by driving the pile into the ground.

As described above, according to the pile foundation and the construction method of the pile foundation of the present disclosure, it is possible to improve the supporting force of the pile while ensuring work efficiency.

>First Embodiment> The pile foundation 10 of the first embodiment will be described with reference to the drawings. As shown in FIG. 1, the pile foundation 10 of this embodiment is a foundation supporting a wind power generator 12.

The wind power generator 12 includes a foot (tower) 14 that is a tower-shaped structure extending from the pile foundation 10 in a vertical direction; and a windmill 16 provided at the upper end of the foot 14. In addition, the windmill part 16 includes a nacelle 18, a hub 20 and blades 22.

The diameter of the leg portion 14 of the wind turbine generator 12 gradually decreases upward, and the lower end of the leg portion 14 is connected to the pile foundation 10. In addition, a nacelle 18 constituting the windmill unit 16 is rotatably attached to the upper end of the leg portion 14, and a generator and an amplifier (not shown) are housed in the nacelle 18.

The nacelle 18 is connected to the hub 20 via a rotor shaft (not shown). In addition, blades 22 as a plurality of rotating wings are attached to the hub 20. In this embodiment, as an example, three blades 22 are attached to the peripheral surface of the hub 20.

The legs 14 of the wind power generator 12 as described above are supported by the pile foundation 10. Here, the pile foundation 10 of this embodiment includes a substantially cylindrical pile 24.

The pile 24 is formed of a steel pipe, extends in a vertical direction as an axial direction, and is provided substantially coaxially with the leg 14 of the wind power generator 12. In addition, except for the pile head 24A provided on the upper part of the pile 24, the other parts are driven into the site 26 by the striking method. Here, in this embodiment, since it is the pile foundation 10 of the offshore wind power generator 12, the pile 24 is driven into the seabed, and the pile 24 is driven from the ground 26 to about 4 to 6 times the diameter of the pile 24 depth. In this embodiment, as an example, a pile 24 having a pile diameter of 5 to 9 m is used, and it is driven from the ground 26 to a depth of about 30 m.

As shown in FIG. 2A, the upper end and the lower end of the pile 24 are open, and the pile 24 is driven into the ground 26 by the hammering method, so that the sand S enters the inside of the pile 24. In addition, by driving the pile 24 into the ground 26, the surface of the sand S in the pile 24 will be located below the surface of the ground 26.

Here, in a state where the pile 24 is driven into the ground 26, a ground improvement body 28 is provided in the pile 24. As shown in FIG. 2B, at least a part of the ground improvement body 28 is in close contact with the inner peripheral surface 24B of the pile 24, and the ground improvement body 28 of this embodiment is provided between the inner peripheral surface 24B of the pile 24 and the sandy soil S.

(Construction method of pile foundation) Next, an example of the construction method of the pile foundation 10 of this embodiment is demonstrated. First, the pile 24 is driven into the site 26 to a predetermined depth by using the striking method. At this time, the pile 24 is driven so that the pile head 24A protrudes more upward than the ground 26. If such a blow construction method is adopted, the site 26 is not limited to a sand ground or a relatively loose gravel site, and the pile 24 can be constructed (driving) even in soft rock.

Next, the sandy soil S near the inner peripheral surface 24B of the pile 24 among the sandy soil S entering the inside of the pile 24 is ground improvement. Specifically, in the inner peripheral surface 24B of the pile 24 or the inside of the pile 24, a plurality of injection holes are formed along the axial direction of the steel pipe, and improved materials such as chemicals or cement particles are injected into these injection holes from the upper part of the pile 24. The ground improvement body 28 is formed by injection. As another method, a drill hole may be excavated from the upper part of the pile 24, and a ground improvement material such as cement may be injected through a method such as mixing blades or spraying to form the ground improvement body 28. The construction of the pile foundation 10 is performed in this way.

(effect) Next, the function of this embodiment will be explained.

In the pile foundation 10 of the present embodiment, at least a part of the ground improvement body 28 is in close contact with the inner peripheral surface 24B of the pile 24. Thereby, the frictional force of the inner peripheral surface 24B of the pile 24 in the part where the pile 24 and the ground improvement body 28 are in close contact is improved. Therefore, the supporting force of the pile 24 can be increased.

In particular, if the diameter of the pile 24 is a large diameter, the front end blocking effect cannot be sufficiently obtained, and a large supporting force cannot be obtained. However, with the structure of this embodiment, a large supporting force can be obtained. This effect will be described with reference to the schematic diagram of the pile shown in FIG. 10.

Figure 10A shows a small diameter pile 100. The diameter of the pile 100 is, for example, 1 m in diameter. When the pile 100 is driven into the site 26 by the percussion method, a pressure influence circle with load is formed by the front end blocking effect. It is worth mentioning that the surrounding area T of the pile 100 is soil disturbed by the impact of the pile 100. As a result, the visible cross-sectional area of the surface of the pile 100 increases, and the supporting force of the pile 100 increases.

On the other hand, Fig. 10B shows a large-diameter pile 102. The diameter of the pile 102 is 5-9 m in diameter, for example. When the pile 102 is driven into the ground 26 by the percussion method, the extent to which the sand in the surrounding area T of the pile 102 is disturbed mainly depends on the ground. In addition, the sand and soil in the radial center portion of the pile 102 is far away from the peripheral surface of the pile 102 and will not be disturbed. Therefore, a pressure influence circle of linear load is formed, and compared with the small-diameter pile 100, it is impossible to expect an increase in the supporting force due to the occlusion effect of the front end.

As described above, in the mode shown in FIG. 10B, the frictional force of the inner peripheral surface of the pile 102 cannot be exceeded to exert the front-end blocking effect, and it is considered that this front-end blocking effect is substantially equal to the frictional force of the inner peripheral surface of the pile 102. Here, the friction force per unit area of the inner peripheral surface of the pile 102 is set to τ, the radius of the inner peripheral surface of the pile 102 is set to r _in , and the height of the sand invading the pile 102 is set to h, then the total The frictional force F is calculated by the following formula (1).

・・・(1)(Formula 1)

···(1)

On the other hand, if the front end supporting force of the inner peripheral surface of the pile of sand to 102 P, the supporting force per unit area is set to p _in, and P p _in the relation having the formula (2).

・・・(2)(Equation 2)

···(2)

As described above, when the front end blocking effect is equal to the frictional force of the inner peripheral surface of the pile 102, the front end supporting force P is equal to the total frictional force F. Therefore, the following formula (3) holds.

・・・(3)(Equation 3)

・・・(3)

The following formula (4) is derived from the formula (3).

・・・(4)(Equation 4)

・・・(4)

Understood the above formula (4), the radius r of the inner circumferential surface of the per unit area of the inner peripheral surface 102 of the supporting force of the pile and the pile 102 p _in the _in inverse proportion. That is, the larger the diameter of the pile 102, the smaller the supporting force of the tip.

On the other hand, according to equation (4), even if the pile 102 has a large diameter, by increasing the friction force τ, the supporting force of the tip can be ensured. Here, in the present embodiment, as shown in FIGS. 2A and 2B, the frictional force of the inner peripheral surface 24B of the pile 24 is increased by bringing the ground improvement body 28 and the inner peripheral surface 24B of the pile 24 into close contact. Thereby, even in the case of using a large-diameter pile 24, the supporting force of the pile 24 can be increased.

In addition, in this embodiment, since the thickness of the pile 24 itself is not thickened and the supporting force can be increased, the pile 24 can be driven into the ground 26 by a blow. That is, there is no need to perform pile construction after cutting the ground 26. Therefore, it is possible to increase the supporting force of the pile 24 while ensuring work efficiency. In particular, when the pile foundation 10 is constructed on the sea, as shown in the present embodiment, by using the structure in which the ground improving body 28 increases the supporting force, the small pile 24 can be used, and the specifications of the transportation ship can be reduced. Therefore, the cost of construction can be reduced.

Furthermore, in this embodiment, compared with the case where the whole sand S is used as a ground improvement body, by providing the ground improvement body 28 between the inner peripheral surface 24B of the pile 24 and the sand and soil S, the construction period can be shortened.

It is worth mentioning that, in the present embodiment, as shown in FIG. 2B, the ground improvement body 28 is provided on the inner peripheral surface 24B of the pile 24 throughout the entire circumference, but it is not limited to this. For example, the structure of the modified example shown in FIG. 3 may be adopted.

(Modification) As shown in FIG. 3A, similar to the present embodiment, the pile 24 constituting the pile foundation 30 of this modification example is driven into the ground 26 by the hammering method except for the pile head 24A provided on the upper part.

Here, as shown in FIG. 3B, in a state where the pile 24 is driven into the ground 26, a ground improvement body 28 is provided in the pile 24. The ground improvement body 28 is provided between the inner peripheral surface 24B of the pile 24 and the sand S. In addition, when the cross-section of the pile 24 is viewed from the axial direction, the ground improvement bodies 31 are provided at a plurality of intervals along the inner peripheral surface 24B of the pile 24. In this modification, grounds are provided at five places at intervals along the inner peripheral surface 24B. Improved body 31.

As described above, in this modification, the frictional force can be increased in the portion where the ground improvement body 31 and the inner peripheral surface 24B of the pile 24 are in close contact. In addition, compared to the case where the ground improvement bodies are provided over the entire circumference along the inner peripheral surface 24B of the pile 24, the ground improvement bodies 31 are provided at intervals along the inner peripheral surface 24B of the pile 24, and the construction period can be shortened.

<The second embodiment> Next, the pile foundation 32 of the second embodiment will be described with reference to FIGS. 4A and 4B. It is worth mentioning that the same components as those in the first embodiment are given the same reference numerals, and descriptions are omitted as appropriate.

As shown in FIG. 4A, the pile 24 constituting the pile foundation 32 of the present embodiment is the same as that of the first embodiment. Except for the pile head 24A, the other parts of the pile 24 are driven into the site 26 by the strike method.

Here, a ground improvement body 33 is provided inside the pile 24. When at least a part of the ground improvement body 33 is in close contact with the inner peripheral surface 24B of the pile 24 and the cross section of the pile 24 is viewed from the axial direction, the ground improvement body 33 of this embodiment is installed in the entire area within the pile 24.

In addition, a flange 34 is provided on the inner peripheral surface 24B of the pile 24 as a support member that supports the ground improvement body 33 from above, and partitions the inner space of the pile 24 up and down. The flange 34 is made of metal, is disposed near the pile head 24A, and is joined (fixed) to the inner peripheral surface 24B of the pile 24 by welding or the like.

In addition, the flange 34 extends radially inward from the inner peripheral surface 24B of the pile 24 and is formed in a ring shape. As shown in FIG. 4B, a substantially circular opening 34A is formed in the radial center portion of the flange 34. Therefore, the ground improvement body 33 has a structure exposed to the pile head 24A side through the opening 34A.

Here, an example of the construction method of the pile foundation 32 of this embodiment is demonstrated. First, the flange 34 is joined to the inner peripheral surface 24B of the pile 24. Then, the pile 24 with the flange 34 is driven into the site 26 to a predetermined depth by using the striking method. At this time, the pile head 24A protrudes above the ground 26.

Next, ground improvement is performed on the entire sandy soil that has entered the pile 24 to form a ground improvement body 33. The construction of the pile foundation 10 is performed in this way.

(effect) Next, the function of this embodiment will be explained.

In the pile foundation 32 of this embodiment, the rigidity of the whole inside of the pile 24 can be improved by the ground improvement body 33 provided in the whole area of the pile 24. In addition, since the ground improvement body 33 is supported from above by the flange 34, the pile 24 and the ground improvement body 33 can be integrated more closely.

In addition, in this embodiment, since the flange 34 is formed in a ring shape, the sand and soil in the pile 24 can be compressed by the flange 34. In addition, since the upper and lower spaces of the flange 34 communicate, after the pile 24 is driven, a chemical or the like can be put into sand and soil to improve the ground. The other functions are the same as in the first embodiment.

<The third embodiment> Next, the pile foundation 40 of the third embodiment will be described with reference to FIGS. 5A and 5B. It is worth mentioning that the same components as those in the first embodiment are given the same reference numerals, and descriptions are omitted as appropriate.

As shown in FIG. 5A, the pile 24 which comprises the pile foundation 40 of this embodiment is the same as that of 1st Embodiment. Moreover, except for the pile head 24A, the other parts of the pile 24 are driven into the site 26 by the striking method.

In addition, in a state where the pile 24 is driven into the ground 26, a ground improvement body 28 is provided in the pile 24. The ground improvement body 28 is provided between the inner peripheral surface 24B of the pile 24 and the sand S.

Here, in this embodiment, a floor 42 is provided on the pile head 24A of the pile 24, and the floor 42 includes a base 42A and a triangular plate 42B.

The base 42A is formed with the axial direction (vertical direction) of the pile 24 as the thickness direction, and is installed on the ground 26. In addition, as shown in FIG. 5B, the base 42A has a substantially circular shape concentric with the pile 24 in a plan view. In addition, in this embodiment, as an example, the base 42A is formed of steel material and is fixed to the peripheral surface of the pile head 24A. As a method of fixing the base 42A to the pile head 24A, in addition to welding, a method of mechanically tightening with bolts, nuts, or the like may be used.

A plurality of triangular plates 42B are provided on the upper surface side of the base 42A. Eight triangular plates 42B are provided at equal intervals along the circumferential direction of the pile 24. In addition, as shown in FIG. 5A, each triangular plate 42B is formed in a substantially triangular shape so as to form a linear portion in the direction of the pile 24 and the direction of the base 42A.

The lower end surface of the triangular plate 42B extends along the base 42A in the radial direction of the pile 24 and is fixed to the upper surface of the base 42A. In addition, the side surface of the triangular plate 42B located on the center side of the pile 24 extends in the vertical direction along the pile head 24A, and is fixed to the aforementioned pile head 24A. As a method of fixing the above-mentioned triangular plate 42B to the base 42A and the pile head 24A, it is the same as the base 42A. In addition to welding, a mechanical fastening method such as bolts and nuts may also be used.

As described above, the floor 42 is provided on the ground 26 and fixed to the pile head 24A. Therefore, the external force acting on the pile 24 is transmitted to the ground 26 via the floor 42.

(effect) Next, the function of this embodiment will be explained.

In the pile foundation 40 of the present embodiment, even when an external force is input in the direction in which the pile 24 falls, at least a part of the external force can be transmitted to the ground 26 via the floor 42, and the horizontal force of the pile 24 can be ensured. resistance. In addition, the floor 42 can suppress the erosion of the seabed surface. The other functions are the same as in the first embodiment.

<The fourth embodiment> Next, the pile foundation 50 of the fourth embodiment will be described with reference to FIGS. 6A and 6B. It is worth mentioning that the same reference numerals are given to the same structures as in the second embodiment, and the descriptions are appropriately omitted.

As shown in FIG. 6A, with respect to the structure of the second embodiment, in the pile foundation 50 of this embodiment, the floor 42 described in the third embodiment is installed. Specifically, a ground improvement body 33 is provided inside the pile 24, and this ground improvement body 33 is provided in the entire area of the pile 24 when the cross section of the pile 24 is viewed from the axial direction.

In addition, the inner peripheral surface 24B of the pile 24 is provided with a flange 34. The flange 34 is arranged near the pile head 24A, and is joined to the inner peripheral surface 24B of the pile 24 by welding or the like.

In addition, a floor 42 is provided on the pile head 24A of the pile 24, and a base 42A and a triangular plate 42B constituting the floor 42 are fixed to the pile head 24A.

(effect) Next, the function of this embodiment will be explained.

In the pile foundation 50 of the present embodiment, as in the third embodiment, even when an external force is input in the direction in which the pile 24 falls, at least a part of the external force can be transmitted to the ground 26 via the floor 42. Ensure the resistance of the pile 24 to horizontal forces. The other functions are the same as in the first embodiment.

<The fifth embodiment> Next, the pile foundation 60 of the fifth embodiment will be described with reference to FIGS. 7A and 7B. It is worth mentioning that the same components as those in the first embodiment are given the same reference numerals, and descriptions are omitted as appropriate.

As shown in FIG. 7A, the pile 24 which comprises the pile foundation 70 of this embodiment is the same as that of 1st Embodiment. Moreover, except for the pile head 24A, the other parts of the pile 24 are driven into the site 26 by the striking method.

Here, a disc-shaped member 62 is provided on the inner peripheral surface 24B of the pile 24 as a support member that supports the sand and soil S from above while partitioning the inner space of the pile 24 up and down. The disc-shaped member 62 is arranged near the pile head 24A, and the peripheral edge portion of the disc-shaped member 62 is joined (fixed) to the inner peripheral surface 24B of the pile 24 by welding or the like.

In addition, a filling material 64 is filled between the sand S entering the inside of the pile 24 and the disc-shaped member 62. As the filler 64, for example, mortar, concrete, fiber reinforced concrete, gypsum, cement slurry, fiber reinforced resin, etc. can be used. In addition, the sand S and the disc-shaped member 62 are integrated by the filler 64.

(effect) Next, the function of this embodiment will be explained.

In the pile foundation 60 of this embodiment, a disc-shaped member 62 is provided on the inner peripheral surface 24B of the pile 24 near the pile head 24A, and this disc-shaped member 62 supports the sand and soil S entering the pile 24 from above. By providing the disc-shaped member 62 in this way, when the pile 24 is driven into the ground 26, the sand and soil S in the pile 24 can be compressed by the disc-shaped member 62, and the front end blocking effect can be obtained.

In particular, in this embodiment, since the disk-shaped member 62 can transmit the vertical force to the entire sand and soil S in the pile 24, the supporting force of the pile 24 can be increased.

In addition, in this embodiment, the sand S and the disc-shaped member 62 are integrated by the filler 64. Thereby, compared with the structure in which the filler 64 is not provided, it is not necessary to perform ground improvement on the sand and soil S in the pile 24, that is, the supporting force of the pile 24 can be increased.

The first to fifth embodiments and modification examples have been described above, but they can be implemented in various ways within the scope not departing from the gist of the present disclosure. For example, it is also possible to adopt a configuration in which the above-mentioned embodiments are combined separately. That is, the flange 34 of the second embodiment shown in FIGS. 4A and 4B may be fixed to the pile foundation 10 of the first embodiment shown in FIGS. 2A and 2B. In addition, between the flange 34 of the second embodiment and the floor improvement body 33, the filler 64 of the fifth embodiment shown in FIG. 7A may be provided.

In addition, in the second embodiment and the fourth embodiment described above, the metal flange 34 is provided on the inner peripheral surface 24B of the pile 24, but it is not limited to this. For example, a concrete flange can be provided. In this case, the flange can be poured after the pile 24 is driven into the ground 26. In addition, a filler such as cement slurry may be filled between the flange and the sand or the ground improvement.

In addition, in the above-described embodiment, the pile 24 is formed of a steel pipe, but the material of the pile 24 is not particularly limited, and the pile may be formed of other materials. For example, wood piles or concrete piles made of concrete can be used. In addition, piles formed by combining these materials can also be used.

In addition, in the above-mentioned embodiment, the pile foundation for supporting the leg part 14 of the wind power generator 12 was demonstrated as a tower-shaped structure, but it is not limited to this. That is, it can be applied to pile foundations supporting other tower-shaped structures, and can also be applied to pile foundations supporting tower-shaped structures such as iron towers. In this case, multiple piles can be driven into the site to support tower-like structures such as iron towers.

In addition, in the above-mentioned first embodiment, as shown in FIG. 2, the ground improvement body 28 is formed in the entire axial direction with respect to the sand and soil S entering the inside of the pile 24, but it is not limited to this. For example, the structure shown in FIG. 8 and FIG. 9 may be adopted.

As shown in FIG. 8A, in the pile foundation 70, in a state where the pile 24 is driven into the ground 26, a ground improvement body 28 is provided in the pile 24. Here, the ground improvement body 28 is formed only in a part of the sand in the axial direction in the sand S entering the inside of the pile 24. Moreover, as shown in FIG. 8B, the ground improvement body 28 is provided between the inner peripheral surface 24B of the pile 24 and the sand soil S.

In addition, in the pile foundation 80 shown in FIG. 9A, a ground improvement body 31 is provided in the pile 24, and the ground improvement body 31 is formed only in a part of the sand in the axial direction of the sand S entering the inside of the pile 24. In addition, as shown in FIG. 9B, when the cross-section of the pile 24 is viewed from the axial direction, the ground improvement bodies 31 are provided at a plurality of intervals along the inner peripheral surface 24B of the pile 24. In this modification, they are spaced apart along the inner peripheral surface 24B. Ground improvement bodies 31 are provided at five locations.

10: pile foundation 12: Wind power plant 14: Feet (tower-shaped structure) 24: pile 24A: pile head 24B: inner peripheral surface 26: Site 28: Site Improvement 30: pile foundation 31: Site Improvement 32: pile foundation 33: Site Improvement 34: Flange (support member) 40: pile foundation 42: Floor 50: pile foundation 60: pile foundation 62: Disc-shaped member (support member) 64: filling material 70: pile foundation 80: pile foundation 100: pile 102: pile S: Sand

Fig. 1 is an overall schematic diagram showing a wind power generation device applying the pile foundation of the first embodiment. Figure 2A is an elevational cross-sectional view of the pile foundation of the first embodiment. Fig. 2B is a cross-sectional view showing a state cut along the line 2B-2B of Fig. 2A. Fig. 3A is a vertical cross-sectional view of a pile foundation of a modification of the first embodiment. Fig. 3B is a cross-sectional view showing a state cut along the line 3B-3B of Fig. 3A. Fig. 4A is a vertical sectional view of the pile foundation of the second embodiment. Fig. 4B is a cross-sectional view showing a state cut along the line 4B-4B of Fig. 4A. Fig. 5A is an elevation sectional view of the pile foundation of the third embodiment. Fig. 5B is a cross-sectional view showing a state cut along the line 5B-5B of Fig. 5A. Fig. 6A is an elevation sectional view of the pile foundation of the fourth embodiment. Fig. 6B is a cross-sectional view showing a state cut along the line 6B-6B of Fig. 6A. Fig. 7A is a vertical sectional view of the pile foundation of the fifth embodiment. Fig. 7B is a cross-sectional view showing a state cut along the line 7B-7B of Fig. 7A. Fig. 8A is an elevation sectional view of a pile foundation of another example of the first embodiment. Fig. 8B is a cross-sectional view showing a state cut along the line 8B-8B of Fig. 8A. Fig. 9A is a vertical sectional view of a pile foundation of another example of the first embodiment. Fig. 9B is a cross-sectional view showing the state cut along the line 9B-9B of Fig. 9A. Figure 10A is a schematic diagram showing the pressure influence circle at the front end of the pile, which shows the pressure influence circle of the small diameter pile. Figure 10B is a schematic diagram showing the pressure influence circle at the front end of the pile, which shows the pressure influence circle of the large-diameter pile.

no.

10: pile foundation

24: pile

24A: pile head

26: Site

28: Site Improvement

Claims (13)

A pile foundation having: A pile that extends in a vertical direction to support a tower-shaped structure, and the pile head of the pile protrudes upward than the ground, and the lower end of the pile is open; and A ground improvement body is provided in the pile in a state where the pile is driven into the ground, and at least a part of the ground improvement body is in close contact with the inner peripheral surface of the pile. The pile foundation according to claim 1, wherein the pile has sand and soil intrusion, and the ground improvement body is provided between the inner peripheral surface of the pile and the sand. The pile foundation according to claim 2, wherein, when the cross section of the pile is viewed from the axial direction, the ground improvement body is provided at a plurality of places along the inner circumferential surface of the pile. The pile foundation according to claim 2 or claim 3, wherein the ground improvement body is formed only in a part of the sand in the axial direction of the sand entering the pile. The pile foundation according to claim 1, wherein, when the cross section of the pile is viewed from the axial direction, the ground improvement body is provided in the entire area within the pile. The pile foundation according to any one of claims 1 to 3, wherein a support member that supports the ground improvement from above is provided on the inner peripheral surface of the pile near the pile head. A pile foundation having: A pile that extends in the vertical direction to support a tower-like structure, and the pile head of the pile protrudes upward than the ground, and the lower end of the pile is open; and a support member that is provided near the pile head On the inner peripheral surface of the pile, at least a part of the sand which enters the inside of the pile is supported from above. The pile foundation according to claim 7, wherein the supporting member is an annular flange extending radially inward from the inner circumferential surface of the pile. The pile foundation according to claim 7, wherein the supporting member is a disc-shaped member that closes the lower end of the pile head. The pile foundation according to any one of claim 7 to claim 9, wherein a filling material is filled between the sand and soil entering the inside of the pile and the supporting member. The pile foundation according to any one of claim 1 to claim 3, wherein a floor is provided on the ground, and the floor is fixed on the pile head so that the force acting on the pile is transmitted to the ground. The pile foundation according to any one of claims 1 to 3, wherein the tower structure is configured as a foot of a wind power generator. A construction method of pile foundation has the following steps: Drive a pile with an open lower end into the site so that the pile head of the pile protrudes above the site; and Among the sand that has entered the inside of the pile, at least the sand near the inner peripheral surface of the pile is ground improvement.

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