JP2019011629A - Pile foundation structure - Google Patents

Abstract

To provide a pile foundation structure in which a function for lessening the displacement of a pile with respect to flow force at the time of liquefaction is included separately from a function for supporting a structure by pile.SOLUTION: A pile foundation structure 10 for supporting an above-ground pier (structure) 1 is provided in a ground X, the pile foundation structure 10 comprising a plurality of piles 11, a restraint body 20, and a connection body 40. The plurality of piles 11 are provided in the ground X, and their lower ends 11b reach a support layer Xb and their pile heads 11a are coupled to the structure. The restraint body 20 is provided within the ground X so as to surround the plurality of piles 11 above the support layer Xb. The connection body 40 includes a ground anchor 30, a first end 31a of which is fixed to the restraint body 20, and a fixing member 32 of which is fixed to the support layer Xb.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pile foundation structure.

  As a viaduct pier used for structures such as roads and railways, a structure called a multi-column pier having a plurality of columns is known. As an example, a multi-column pier having a three-dimensional structure in which a plurality of steel pipes and the like are used as pillars and these pillars are connected to each other by a horizontal member or an oblique member. Generally, the pier is supported on the ground by a foundation. When the ground is solid, a reinforced concrete plate called a footing that directly contacts the ground may be used. However, for example, when the ground is soft, a pile foundation is often employed.

  Examples of the pile used for the pile foundation structure include a steel pipe pile or a PHC (Pretensioned Spun High-strength Concrete) pile. For example, Patent Document 1 describes a structure in which a steel pipe column and a steel pipe pile are connected in the vertical direction in a multi-column pier and footing is omitted. In this structure, one steel pipe pile is connected to one steel pipe column of a multi-column pier, and the load from the superstructure and the pier is directly transmitted to the pile foundation without using the footing ( 1 pillar 1 pile structure) is adopted.

JP 2008-303598 A

  In the pile foundation structure described in Non-Patent Document 1 described above, the fluid force generated with liquefaction during an earthquake is taken into consideration, and resistance performance against the fluid force is studied. In order to suppress the displacement of the pile with respect to the fluid force at the time of liquefaction, for example, it is conceivable to make the pile thick. However, increasing the thickness of the pile exceeds the original function required for the pile (supporting function for structures such as bridge piers), so such a pile foundation structure is not reasonable.

  An object of this invention is to provide the pile foundation structure with which the function for suppressing the displacement of a pile with respect to the fluid force at the time of liquefaction is provided separately from the support function of the structure by a pile.

  The present invention is a pile foundation structure that is provided on the ground and supports the structure on the ground, and is provided on the ground, the lower end reaches the support layer, and a plurality of structures in which the structure is coupled to the pile head A pile, a restraint provided in the ground so as to surround a plurality of piles above the support layer, and a connected body having an upper end fixed to the restraint and a lower end fixed to the support layer It is characterized by providing.

  According to this pile foundation structure, since a restraint body provided so as to surround a plurality of piles and a connecting body for connecting the restraint body to the support layer are provided, a fluid force acts during liquefaction. Even in this case, the displacement of the pile is restrained by the restraint body, and the displacement of the pile is suppressed. The restraint body and the connection body are provided separately from the structure support function of the pile. That is, the function for suppressing the displacement of the pile against the fluid force at the time of liquefaction is provided separately from the function of supporting the structure by the pile. Thus, according to the function-separated type pile foundation structure, it is not necessary to thicken the pile for countermeasures against fluid force at the time of liquefaction, which is reasonable.

  The restraint may have a frame shape surrounding the whole of the plurality of piles. In this case, even when a plurality of piles move during liquefaction, the displacement of these piles is suppressed by the frame-like restraint. Further, the frame-like restraint body can be constructed even after the pile is placed or before the pile is placed. Thus, according to the frame-shaped restraint body, the degree of freedom of the construction procedure is enhanced, and any pile foundation can be targeted.

  The plurality of piles may be provided with a connecting member that connects the plurality of piles. In this case, the piles are connected by a connecting member and can move together when liquefied. And the displacement of a pile is suppressed by the frame-shaped restraint body.

  The restraint may have a flat plate shape including a plurality of holes through which the plurality of piles are inserted. In this case, since each pile is surrounded by the restraint body, the displacement of each pile is suppressed by the restraint body. The connecting member that connects the piles can be omitted.

  The coupling body includes a fixing member which is a lower end portion fixed to the support layer, and a steel material including a first end which is an upper end portion fixed to the restraining body and a second end connected to the fixing member. You may have an anchor. When a coupling body has a ground anchor, it can resist the tensile force (pulling-out force) at the time of liquefaction by the ground anchor.

  The ground has a flow direction in the lateral flow associated with liquefaction during an earthquake, and the connecting body is provided at a downstream portion in the flow direction of the restraint body and supports at least one of the downstream portions. You may have two piles. When a pile body is provided on the downstream side in the flow direction, the pile body can resist the compressive force (pushing force) during liquefaction.

  According to the present invention, the function for suppressing the displacement of the pile with respect to the fluid force at the time of liquefaction is provided separately from the function of supporting the structure by the pile. There is no need to thicken.

It is a figure showing a pile foundation structure concerning a 1st embodiment of the present invention. It is a plane sectional view of the pile foundation structure of FIG. It is a figure which shows the pile foundation structure which concerns on 2nd Embodiment of this invention. It is a figure which shows the pile foundation structure which concerns on 3rd Embodiment of this invention. It is a plane sectional view of the pile foundation structure of FIG. It is a top view which shows the modification of a restraint body. It is a figure which shows the pile foundation structure which concerns on the modification of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

  With reference to FIG. 1, the pile foundation structure 10 which concerns on 1st Embodiment is demonstrated. As shown in FIG. 1, the pile foundation structure 10 is provided on a relatively soft ground X and supports the pier 1 that is a structure on the ground. The pier 1 supports a viaduct provided for a ground structure such as a road or a railway. The pier 1 is, for example, a steel pipe assembled pier (or a multi-column pier) having a plurality of steel pipe columns 2. A plurality of (for example, four) cylindrical steel pipe columns 2 are erected in parallel on the ground X. The plurality of steel pipe columns 2 are arranged so as to be aligned in the bridge axis direction and the bridge axis perpendicular direction. In addition, the number and arrangement | sequence of the some steel pipe pillar 2 are not restricted to this aspect.

  Two adjacent steel pipe columns 2 are connected by a horizontal connecting member 3 extending in the horizontal direction. The horizontal connecting material 3 is made of a steel plate, and is joined to the two steel pipe columns 2 by, for example, welding. The horizontal connecting material 3 may be provided obliquely with respect to the horizontal direction. The horizontal connecting material 3 may be omitted. The upper end of the pier 1 is connected to the superstructure. A pile foundation structure 10 is connected to the lower end of the pier 1, that is, the lower end 2 a of the steel pipe column 2. The structure supported by the pile foundation structure 10 is not limited to the pier 1. The structure supported by the pile foundation structure 10 may be a building, for example.

  The pile foundation structure 10 has a plurality of (for example, four) piles 11, and these piles 11 are provided so as to reach the support layer Xb of the ground X. The plurality of piles 11 provided in the ground X are spaced apart in the horizontal direction, and are provided so that their axes are parallel to each other. In the pier 1 and the pile foundation structure 10, both the axis of the steel pipe column 2 and the axis of the pile 11 may extend in the vertical direction. The pile 11 is a steel pipe pile, for example. As the pile 11, a steel pipe soil cement pile having higher rigidity than a normal steel pipe pile may be used. By using a steel pipe soil cement pile, the number of piles 11 can be minimized. The pile 11 may be a PHC pile or the like.

  Each pile 11 has an upper part 11d including a pile head part 11a to which the lower end part of each steel pipe column 2 is coupled, and a lower end 11b reaching the support layer Xb of the ground X. The lower end 2a of each steel pipe column 2 is connected to each pile head 11a, and thereby the pile foundation structure 10 is connected to the steel pipe column 2. The pier 1 and the pile foundation structure 10 have a so-called one-column / one-pile structure. The upper part 11d of the pile 11 is a part above the middle part of the entire length of the pile 11, for example. For example, the ground X includes a liquefied layer Xd that can flow at the time of an earthquake in the upper part near the pier 1. The liquefied layer Xd may be formed in a region corresponding to the upper portion 11d of the pile 11 or may be formed in a region partially overlapping with the upper portion 11d. The liquefied layer Xd may be formed below the upper part 11 d of the pile 11.

  In the pile foundation structure 10, between the adjacent piles 11, the connection member 12 extended horizontally is provided. Pile heads 11 a of the plurality of piles 11 are connected by a plurality of connecting members 12. The connecting member 12 may be provided at the upper part 11d of the pile 11 and below the pile head part 11a. The connecting member 12 is made of, for example, a steel material. The connecting member 12 functions as an underground beam, for example. The pile heads 11 a (upper portions 11 d) of the plurality of piles 11 are integrated by a connecting member 12 that connects the plurality of piles 11. The shape of the connecting member 12 is not limited to a shape extending horizontally. The connecting member 12 may have a brace shape extending obliquely. Thus, the structure in which the pile heads 11a of the plurality of piles 11 are coupled by the coupling member 12 is a pile foundation structure in which the footing is omitted.

  The pile foundation structure 10 includes a restraining body 20 provided in the ground X so as to surround the upper portions 11d of the plurality of piles 11, and a connecting body 40 that connects the restraining body 20 and the support layer Xb. By providing these restraining bodies 20 and connecting bodies 40, the pile foundation structure 10 can suppress fluctuations of the plurality of piles 11 within a predetermined range when a liquefaction phenomenon occurs during an earthquake.

  The restraint body 20 is provided above the support layer Xb. The restraint body 20 may be positioned in the liquefied layer Xd of the ground X, may be positioned so as to overlap the liquefied layer Xd, or may be positioned above the liquefied layer Xd. The position (that is, the depth) of the restraint 20 can be set in consideration of the bending moment distribution of the pile 11. That is, the restraining body 20 is provided at a position where the maximum value of the bending moment of the pile 11 becomes small. The restraint body 20 may be provided so as to surround the pile head portion 11a.

  The configuration of the restraining body 20 will be described in more detail. As shown in FIGS. 1 and 2, the restraining body 20 has a frame shape surrounding the entire plurality of piles 11 in plan view. The restraining body 20 has a rectangular frame shape. In other words, the restraining body 20 has a square shape in plan view. The restraint body 20 includes an inner peripheral surface 21 that faces the plurality of piles 11, and the plurality of piles 11 are disposed on the inner peripheral side of the restraint body 20. For example, a gap (gap) is formed between the inner peripheral surface 21 of the restraining body 20 arranged on the outside of the four piles 11 and each pile 11.

  The restraining body 20 may be made of hollow concrete having a rectangular cross section. The restraint 20 is a light structure that floats in the ground X when it liquefies. The restraint body 20 has a relatively small specific gravity with respect to the ground X (liquefied layer Xd) at the time of liquefaction, and is configured to float without sinking when liquefied. In addition, the restraint body 20 is buried in the ground X and is stationary at a normal time when no earthquake occurs. The restraining body 20 is a hollow box made of steel or concrete, and it is preferable that the apparent specific gravity be as small as possible than the specific gravity of the liquefied layer Xd.

  The gap between the restraint 20 and the pile 11 can be set according to the deformation performance of the pile 11. For example, the gap is set larger than the allowable displacement in the pile 11. A cushioning material such as rubber or sponge may be sandwiched between the restraining body 20 and the pile 11.

  The connecting body 40 has four ground anchors 30 that connect the restraining body 20 and the support layer Xb. Each ground anchor 30 includes a steel material 31 in which a first end 31 a as an upper end portion is fixed to the restraining body 20, and a fixing member 32 as a lower end portion connected to a second end 31 b of the steel material 31. The fixing member 32 is fixed to the support layer Xb.

  The steel material 31 is a stranded wire made of PC steel (piano wire), for example. The first end 31a of each steel material 31 is fixed at, for example, the four corner positions of the restraining body 20. The steel material 31 is provided so as to spread radially from the restraining body 20 toward the support layer Xb (so as to form a hypotenuse of a quadrangular pyramid). A known wedge fixing may be used as a fixing form of the steel material 31 to the restraining body 20. As a connection form of the steel material 31 to the fixing member 32, a known wedge fixing may be used. Further, the fixing member 32 may be fixed to the support layer Xb using a known placement method. The ground anchor 30 including the steel material 31 and the fixing member 32 is configured to withstand a predetermined tensile force (pulling force).

  Then, the construction method (construction method) of the pile foundation structure 10 is demonstrated. First, the restraining body 20 is installed at a predetermined position in the ground X. Next, a plurality of piles 11 are driven in a predetermined arrangement to reach the support layer Xb. Various methods such as Nakabori method, embedding method, impact method, press-fitting method, and a combination of these methods can be applied to placing the pile 11. At this time, the pile 11 may be driven using the restraint body 20 installed in advance as a guide. Prior to placing the piles 11, the piles 11 may be coupled together by the connecting members 12, or the connecting members 12 may be attached after the placing of the piles 11. Furthermore, the steel pipe pillar 2 is couple | bonded with the pile foundation structure 10 (each pile 11 in this embodiment), and the pier 1 is constructed | assembled. In the construction method of the pile foundation structure 10, the restraint body 20 may be constructed after the pile 11 is driven, or the restraint body 20 may be constructed before the pile 11. Thus, by selecting a construction procedure freely, the pile foundation structure 10 of the present embodiment can be applied as, for example, seismic reinforcement for an existing pile foundation.

  According to the pile foundation structure 10 of the present embodiment, the restraint body 20 provided so as to surround the plurality of piles 11 and the connecting body 40 that connects the restraint body 20 to the support layer Xb are provided. Even when a fluid force is applied during liquefaction (see the flow direction D shown in FIG. 1), the displacement of the pile 11 is restrained by the restraining body 20, and the displacement of the pile 11 is suppressed. The restraint body 20 and the connection body 40 are provided separately from the structure support function of the pile 11. That is, the function for suppressing the displacement of the pile 11 with respect to the fluid force during liquefaction is provided separately from the function of supporting the pier 1 by the pile 11. Thus, according to the function-separated type pile foundation structure 10, it is not necessary to thicken the pile 11 for the countermeasure against the fluid force at the time of liquefaction, and it is reasonable.

  According to the pile foundation structure 10, even when a plurality of piles 11 are moved during liquefaction, the displacement of these piles 11 is suppressed by the frame-shaped restraining body 20. Further, the frame-like restraining body 20 can be constructed relatively easily even after the pile 11 is placed or before the pile 11 is placed. Thus, according to the frame-shaped restraint body 20, the freedom degree of a construction procedure is raised and can make all pile foundations object.

  The piles 11 are connected by a connecting member 12 and integrated. The plurality of piles 11 can move together during liquefaction. And the displacement of the pile 11 is suppressed by the frame-shaped restraining body 20.

  When the coupling body 40 includes the ground anchor 30, the ground anchor 30 can resist the tensile force (pulling force) during liquefaction.

  Next, a pile foundation structure according to the second embodiment will be described with reference to FIG. The difference between the pile foundation structure 10A of the second embodiment and the pile foundation structure 10 of the previous embodiment is that a part of the four ground anchors 30 (for example, two) is replaced with a pile body 35. It is a point provided with 40 A of coupling bodies. In this pile foundation structure 10A, the direction of lateral flow accompanying liquefaction during an earthquake is considered. Depending on the ground X, the flow direction D of the lateral flow may be specified. When the flow direction D is specified, at least one pile body 35 that supports the downstream portion may be provided in the downstream portion (the right portion in the drawing) of the restraining body 20 in the flow direction D. .

  For example, in the restraint body 20, two ground anchors 30 similar to those in the first embodiment are provided at two corners on the upstream side in the flow direction D, and at the two corners on the downstream side in the flow direction D, Two pile bodies 35 are provided. The upper end portion 35a of the pile body 35 is fixed to the restraining body 20, and the lower end portion 35b of the pile body 35 is fixed to the support layer Xb. The pile body 35 may be a PHC pile or a steel pipe pile. During an earthquake, the ground anchor 30 is located on the pulling side, and the pile body 35 is located on the pushing side.

  According to the pile foundation structure 10 </ b> A, as in the pile foundation structure 10, the displacement of the pile 11 is restrained by the restraining body 20, and the displacement of the pile 11 is suppressed. A function for suppressing displacement of the pile 11 with respect to the fluid force during liquefaction is provided separately from the function of supporting the pier 1 by the pile 11. According to the function-separated pile foundation structure 10A, it is not necessary to thicken the pile 11 in order to prevent the fluid force at the time of liquefaction, which is reasonable. Furthermore, a pile body 35 is provided on the downstream side in the flow direction D. The pile body 35 can resist the compressive force (pushing force) at the time of liquefaction.

  Then, with reference to FIG. 4 and FIG. 5, the pile foundation structure which concerns on 3rd Embodiment is demonstrated. The difference between the pile foundation structure 10B of the third embodiment and the pile foundation structure 10 of the first embodiment is that, in addition to the four ground anchors 30, the pile foundation structure 10 </ b> B further includes a connection body 40 </ b> B provided with eight ground anchors 30. is there. As shown in FIGS. 4 and 5, the steel materials 31 of the eight ground anchors 30 are longer than the steel materials 31 of the four ground anchors 30. More specifically, three fixing members 32 are provided at four locations in the support layer Xb, as in the first embodiment. The ground anchor 30 including the long steel material 31 extends from a certain location in the support layer Xb to a corner adjacent to the corner of the restraint 20 closest to the location. As a result, the three steel materials 31 extend in different directions from the support layer Xb. The three first ends 31 a are fixed at the four corner positions of the restraining body 20.

  Thus, for example, a total of 12 ground anchors 30 are arranged so as to form a three-dimensional truss in the ground. According to the pile foundation structure 10 </ b> B provided with the connection body 40 </ b> B, the restraint body 20 tries to return to the original position more stably due to the buoyancy generated during liquefaction in the restraint body 20 and the tension generated in the ground anchor 30. As a result, the displacement of the pile 11 can be more reliably restrained. In the first embodiment, when the restraining body 20 itself receives a fluidizing force, the restraining body 20 can be displaced like an idle circle depending on the size of the buoyancy. Therefore, the displacement of the pile 11 may not be sufficiently restrained. According to the pile foundation structure 10B provided with this connection body 40B, even when restraint body 20 itself receives fluidization force, the displacement of restraint body 20 can be suppressed and the displacement of pile 11 can be restrained. In addition, when arrange | positioning the ground anchor 30 in a solid truss shape, the other arrangement | positioning different from the coupling body 40B may be employ | adopted.

  Although the embodiment of the present invention has been described, the present invention is not limited to the above embodiment. For example, the shape and structure of the restraint can be changed as appropriate. As shown in FIG. 6, a pile foundation structure 10 </ b> C having a flat plate-like restraining body 20 </ b> C including a plurality of holes 22 through which each of the plurality of piles 11 is inserted may be used. The diameter of the hole 22 is larger than the diameter of the pile 11. Thus, the restraint 20C surrounds the pile 11 individually. In this case, the gap around each pile 11 formed in the hole 22 may also be set based on the same concept as the gap between the plurality of piles 11 and the restraint body 20. A cushioning material such as rubber or sponge may be sandwiched between the constraint body 20 </ b> C and the pile 11. In the pile foundation structure 10C, each pile 11 is surrounded by the restraining body 20C, so that the displacement of each pile 11 is suppressed by the restraining body 20C. A connecting member that connects the piles 11 can be omitted.

  You may combine the pile body 35 (connecting body 40A) of 10 A of pile foundation structures of 2nd Embodiment, and said restraint body 20C. The number of the ground anchors 30 and the pile bodies 35 which a connection body has can be changed suitably. Only one ground anchor 30 may be provided. Only one pile body 35 may be provided. The ground anchor 30 may not be provided, and only a plurality of pile bodies 35 may be provided. A gap may not be provided between the restraint body and the pile 11.

  You may combine the connection body 40B of the pile foundation structure 10B of 3rd Embodiment, and said restraint body 20C. Any arrangement of the ground anchors 30 forming a three-dimensional truss can be adopted for the restraining body 20C.

  Moreover, the pile foundation which the restraint body 20 surrounds is not restricted to a footingless structure as described above. For example, as shown in FIG. 7, in a pile foundation structure 10 </ b> D in which a frame-like restraint body 20 and a connecting body 40 are applied to a pile foundation including a footing 15 that is a concrete plate provided on a pile head 11 a. There may be. In that case, for example, the restraint 20 surrounds the entire plurality of piles 11 in plan view and also surrounds the footing 15. For example, the inner peripheral surface 21 of the restraining body 20 faces the side surface of the footing 15. A gap (gap) is formed between the inner peripheral surface 21 of the restraining body 20 and the footing 15.

  Any of the above-described connected bodies can also be employed for the pile foundation structure provided with the footing 15. Further, unlike the embodiment shown in FIG. 7, the restraint body 20 may surround the plurality of piles 11 at a location (depth) different from the footing 15 with respect to the pile foundation structure provided with the footing 15. Good.

  In the pile foundation structure of the present invention, the restraining body 20 may be provided for any foundation structure including the plurality of piles 11.

  When there is an existing pile foundation (foundation structure) and a structure, the pile foundation structure of the present invention may be applied to seismic reinforcement to be applied later to the existing pile foundation. In that case, a restraint body and a connection body are constructed later, and a pile foundation structure of the present invention is constructed.

  DESCRIPTION OF SYMBOLS 1 ... Bridge pier, 10 ... Pile foundation structure, 10A, 10B, 10C, 10D ... Pile foundation structure, 11 ... Pile, 11a ... Pile head, 11b ... Lower end, 11d ... Upper part, 12 ... Connecting member, 15 ... Footing, 20 ... restraint body, 20C ... restraint body, 22 ... hole, 30 ... ground anchor, 31 ... steel material, 31a ... first end (upper end), 31b ... second end, 32 ... fixing member (lower end), 35 ... pile Body, 35a ... upper end part, 35b ... lower end part, 40 ... coupling body, 40A, 40B ... coupling body, D ... flow direction, X ... ground, Xb ... support layer, Xd ... liquefaction layer.

Claims (6)

It is a pile foundation structure that is provided on the ground and supports ground structures,
A plurality of piles in which the lower end reaches the support layer and is provided on the ground, and the structure is coupled to the pile head,
Above the support layer, a restraint provided in the ground so as to surround the plurality of piles;
A pile foundation structure comprising: an upper end portion fixed to the restraint body, and a connecting body having a lower end portion fixed to the support layer.   The pile foundation structure according to claim 1, wherein the restraining body has a frame shape surrounding the plurality of piles.   The pile foundation structure according to claim 2, wherein a connection member that connects the plurality of piles is provided on the plurality of piles.   The pile foundation structure according to claim 1, wherein the restraining body has a flat plate shape including a plurality of holes through which the plurality of piles are inserted. The connector is
A fixing member which is the lower end portion fixed to the support layer;
The ground anchor including a steel material including a first end that is the upper end portion fixed to the restraining body and a second end connected to the fixing member. The pile foundation structure according to any one of the above. The ground has a flow direction in lateral flow accompanying liquefaction during an earthquake,
The said connection body has at least 1 pile body which is provided in the downstream part of the said flow direction of the said restraint body, and supports the said downstream part, The any one of Claims 1-5 characterized by the above-mentioned. The pile foundation structure according to one item.

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