Hangzhou foundation structure

Abstract

To reinforce horizontal resistance of a foundation pile in which horizontal force and bending moment act on a pile head, in a liquefaction ground in which horizontal resistance of the side face of a ground improvement body cannot be expected.SOLUTION: A pile foundation structure includes a foundation pile 2 for supporting a structure constructed on a liquefaction ground G1, and a ground improvement body 3 formed around the foundation pile 2, wherein the ground improvement body 3 is provided in the state where the lower end of the ground improvement body 3 is embedded in a non-liquefaction layer G2 positioned below the liquefaction ground G1, a shaft part of the foundation pile 2 is provided with a deviation stopper part 21 of an uneven shape functioning as a deviation stopper between the ground improvement body 3 and the shaft part thereof, and at least a part of the deviation stopper part 21 is arranged in a region of the shaft part forming a compressive truss T between the bottom part of the ground improvement body 3a and at least the part thereof.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pile foundation structure. [Background technology]

[0002] Conventionally, pile foundation structures equipped with foundation piles that support structures built on the ground are subject to large horizontal forces during major earthquakes, and therefore require strict performance requirements in terms of both displacement and stress. For this reason, many structural and construction methods have been proposed that combine foundation pile construction methods and ground improvement methods, which are originally separate construction methods, with the aim of improving the horizontal bearing capacity of foundation piles.

[0003] For example, a method is known in which a soil improvement body is formed around the foundation pile, thereby increasing the diameter of the composite pile consisting of the pile and the soil improvement body, thereby improving the horizontal bearing capacity. This type of pile foundation structure utilizes the horizontal resistance characteristics of the ground, and by increasing the pile diameter of the composite pile and increasing the horizontal reaction area, it is possible to increase the horizontal bearing capacity of the pile, suppress deformation, and reduce the stress generated in the pile.

[0004] In response to this, there is known a pile foundation structure that comprises foundation piles and soil improvement bodies formed around the foundation piles, and that provides horizontal pressure resistance by expanding the diameter of the foundation structure itself with the improvement bodies, as shown in Patent Documents 1 and 2. In this case, the depth direction length of the improvement bodies is made shorter than the length of the foundation piles, and they are concentrated in the upper part, which contributes more to horizontal resistance, thereby limiting the range of ground improvement and reducing costs. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-065579 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-066010 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in conventional pile foundation structures such as those described in Patent Documents 1 and 2, horizontal resistance performance is improved by providing an improvement body around the foundation pile, i.e., the lateral resistance of the improvement body is utilized. This conventional technology is intended for cases where the ground around the foundation pile or improvement body has a certain strength, and is based on the assumption that horizontal resistance can be exerted. Therefore, in liquefied ground, the horizontal resistance of the ground may be lost or significantly reduced during liquefaction, resulting in a risk of not being able to provide horizontal resistance and thus failing to function as a pile foundation structure that can achieve the objectives of this technology. As such, in conventional pile foundation structures, improvement bodies are installed in the hope of providing horizontal pressure resistance, and this function is not fully ensured in liquefied ground, so there is room for improvement in this regard.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a pile foundation structure that can strengthen the horizontal resistance of foundation piles, where horizontal forces and bending moments act on the pile heads, in liquefied ground where horizontal resistance cannot be expected on the sides of the ground improvement body. [Means for solving the problem]

[0008] In order to achieve the above object, the pile foundation structure according to the present invention comprises foundation piles supporting a structure constructed on liquefied ground, and a ground improvement body formed around the foundation piles, The foundation piles are buried in the liquefied ground and a non-liquefied layer located below the liquefied ground, and are provided in a state where they penetrate the non-liquefied layer and reach the supporting layer, The ground improvement body is such that the lower end of the ground improvement body is Non-liquefiable layer The foundation pile is installed in a state where it is embedded in the ground, and the shaft portion of the foundation pile is provided with a shear stopper having an uneven shape that functions as a shear stopper between the foundation pile and the ground improvement body, and at least a part of the shear stopper is arranged in a region of the shaft portion that forms a compression truss between the foundation pile and the bottom of the ground improvement body. The area where the anti-slip portion is provided in the shaft portion includes, on the outer circumferential surface of the foundation pile, at least the area from the intersection with the shaft portion in the compression truss to the bottom of the improved body. It is characterized by the following.

[0009] According to the pile foundation structure of the present invention, a shear stopper with a concave-convex shape is provided on the shaft of the foundation pile, and a ground improvement body is present in the area where a compression truss is formed due to this shear stopper. This allows horizontal forces acting on the foundation pile to be transmitted from the shear stopper to the bottom of the ground improvement body through the ground improvement body formed around the foundation pile. The horizontal forces transmitted to the bottom of the ground improvement body can then be resisted by the bearing reaction force of the bottom of the ground improvement body, which is embedded in the non-liquefaction layer. Therefore, since the present invention utilizes the bearing reaction force of the non-liquefaction layer, excellent horizontal resistance can be achieved by the bearing reaction force of the bottom of the ground improvement body, even when liquefied ground is liquefied during an earthquake. In this way, with this invention, even in a liquefied layer where horizontal resistance cannot be expected from the sides of the ground improvement body, the horizontal resistance of foundation piles, where horizontal forces and bending moments act on the pile head, can be strengthened by utilizing the bearing reaction force at the bottom of the improvement body.

[0010] Furthermore, in the pile foundation structure of the present invention, it is expected that the bearing reaction force at the bottom of the improvement body will resist the horizontal force of the foundation pile. In other words, with this invention, it is no longer necessary to rely on the horizontal resistance of the side of the improvement body to resist the horizontal force of the foundation pile, so the cross-sectional area (outer diameter) of the part of the ground improvement body where the compression truss is not formed can be reduced to the minimum necessary, thereby slimming it down. Slimming the ground improvement body makes it possible to suppress the flow force acting on the foundation pile during liquefaction. In this way, the volume of the ground improvement body can be reduced, leading to cost savings.

[0011] In the pile foundation structure of the present invention, it is preferable that the compression truss formation angle, which is the inclination angle with the bottom of the improved body to form the compression truss, is in the range of 30 to 60 degrees, and that at least a portion of the anti-slip portion is arranged in an area below the height at which the intersection between the compression truss passing through the outer edge of the bottom of the improved body and the shaft of the foundation pile is located.

[0012] In this case, by setting the compression truss angle, which is the inclination angle formed by the compression truss, in the range of 30 to 60 degrees, it is possible to form a sufficient compression truss in the ground improvement body and reliably obtain the horizontal resistance effect due to the bearing reaction force at the bottom of the improvement body. Therefore, even if it is not possible to set the compression truss angle to the general 45 degrees due to site conditions, construction equipment, etc., it is possible to reliably form a compression truss in the ground improvement body.

[0013] In addition, in the pile foundation structure according to the present invention, the compression truss forming angle may be 45 degrees.

[0014] By using this configuration, the compression truss formation angle can be set to 45 degrees, which ensures the formation of a compression truss that can transmit the horizontal force acting on the foundation pile from the anti-slip section to the bottom of the improved body, thereby obtaining a horizontal resistance effect due to the bearing reaction force at the bottom of the improved body.

[0015] In addition, in the pile foundation structure according to the present invention, the ground improvement body may be characterized in that the outer diameter of the top of the improvement body is equal to or smaller than the outer diameter of the bottom of the improvement body.

[0016] This configuration does not rely too much on the horizontal resistance of the sides of the soil improvement body to withstand the horizontal force acting on the foundation piles, and therefore the cross-sectional area (outer diameter) of the soil improvement body installed in liquefied ground can be kept small, making it possible to slim down the soil improvement body. This also makes it possible to suppress the flow force of the liquefied ground that the foundation piles receive during liquefaction.

[0017] In addition, in the pile foundation structure according to the present invention, the ground improvement body may be a multi-stage columnar body whose outer diameter increases from top to bottom.

[0018] In this case, by making the ground improvement body a multi-stage columnar body and making the outer diameter of the top of the improvement body the smallest, the bearing reaction force at the bottom of the improvement body can be secured and the flow force of the liquefied ground that the foundation piles experience during liquefaction can be suppressed. In addition, in the present invention, the volume of the ground improvement body can be reduced by slimming down the cross-sectional shape of the upper part of the ground improvement body, thereby reducing costs.

[0019] In addition, the pile foundation structure of the present invention may be characterized in that at least a portion of the anti-slip portion is arranged in an area below the height at which the intersection between the compression truss passing through the inner corner of the step portion of the multi-stage columnar body facing the foundation pile and the shaft portion of the foundation pile is located.

[0020] In this case, a compression truss can be efficiently formed in the ground improvement body consisting of multi-stage columnar bodies, ensuring the bearing reaction force at the bottom of the improvement body and suppressing the flow force of the liquefied ground that the foundation piles experience during liquefaction.

[0021] In addition, in the pile foundation structure according to the present invention, the ground improvement body may be a cone-shaped body whose outer diameter gradually increases from top to bottom.

[0022] In this case, since the shape of the ground improvement body consisting of the cone-shaped body is similar to the triangular part of the ground improvement body in which the compression truss is formed, the ground improvement range can be reduced to match the inclination angle of the compression truss, thereby reducing costs.

[0023] In addition, in the pile foundation structure according to the present invention, the foundation piles may be steel pipe piles.

[0024] In this case, since the foundation piles are steel pipe piles, the anti-slip portions can be easily installed and formed.

[0025] In the pile foundation structure according to the present invention, the foundation pile may be a stepped steel pipe or a dimpled steel pipe.

[0026] In this case, by using stepped or dimpled steel pipes, the shear stopper provided on the shaft of the foundation pile is formed in a recessed state, which ensures the integrity of the pile outer surface and the soil improvement body by adhesion, and the horizontal resistance effect of the bearing reaction force at the bottom of the improvement body can be fully obtained. Furthermore, in the present invention, when the inner surface of the steel pipe of the foundation pile is filled with a filler material such as concrete, the adhesion between the inner surface of the steel pipe and the filler material ensures unity, thereby further increasing the horizontal resistance of the foundation pile. Furthermore, in the case of dimpled steel pipes, which have dimples on the steel pipe, even if the steel pipe has depressions and no filler material is filled inside, it can exhibit compression and bending performance equivalent to that of straight steel pipe piles, and can exhibit excellent effects.

[0027] In addition, the pile foundation structure according to the present invention may be characterized in that the anti-slip portion is formed as a recess on the outer peripheral surface of the foundation pile.

[0028] In this case, the recessed shear stopper installed on the shaft of the foundation pile ensures unity between the outer surface of the pile and the ground improvement body, and the bearing reaction force at the bottom of the improvement body provides horizontal resistance. Also, if the inner surface of the foundation pile is filled with concrete or other filler, the adhesion between the inner surface of the pile and the filler ensures unity, making it possible to further increase the horizontal resistance of the foundation pile. Furthermore, by forming the slippage prevention portion as a recess, excellent workability and ease of construction of the pile can be achieved.

[0029] In addition, in the pile foundation structure according to the present invention, the displacement preventing portion may be formed by a weld bead fixed to the outer peripheral surface of the foundation pile.

[0030] In this case, the convex portion can be easily formed by providing a weld bead on the outer peripheral surface of the pile, thereby providing excellent workability and ease of construction of the pile.

[0031] In addition, in the pile foundation structure according to the present invention, the anti-slip portion may be formed by rolling on the outer peripheral surface of the foundation pile.

[0032] In this case, the anti-slip portion provided on the shaft of the foundation pile can be efficiently processed into a stable shape by spiral rolling formed on the outer surface of the pile on the manufacturing line during manufacturing. [Effects of the Invention]

[0033] According to the pile foundation structure of the present invention, the horizontal resistance of foundation piles, in which horizontal forces and bending moments act on the pile head, can be strengthened in liquefied ground where horizontal resistance cannot be expected on the sides of the ground improvement body. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a vertical cross-sectional view showing a pile foundation structure according to a first embodiment of the present invention. [Figure 2] 1(a) to 1(c) are diagrams showing an example of a displacement stopper for a foundation pile. [Figure 3] FIG. 2 is a diagram for explaining the horizontal force transmission mechanism of the pile foundation structure of FIG. 1. [Figure 4] FIG. 4 is an enlarged view of a main part of FIG. 3. [Figure 5] 10(a) and 10(b) are diagrams for explaining the range of the compression truss forming angle. [Figure 6] 1(a) and 1(b) are diagrams showing a construction procedure of a first construction method for a pile foundation structure. [Figure 7] 6(a) to 6(c) are diagrams showing the construction procedure of the first construction method for the pile foundation structure following FIG. 6(b). [Figure 8] 1(a) and 1(b) are diagrams showing a construction procedure of a first construction method for a pile foundation structure. [Figure 9] 8(a) to 8(c) are diagrams showing the construction procedure of the second construction method for the pile foundation structure following FIG. 8(b). [Figure 10] FIG. 10 is a vertical cross-sectional view showing the pile foundation structure according to the second embodiment. [Figure 11]FIG. 10 is a vertical cross-sectional view showing the pile foundation structure according to the third embodiment. [Figure 12] FIG. 10 is a vertical cross-sectional view showing a pile foundation structure according to a fourth embodiment. [Figure 13] FIG. 10 is a vertical cross-sectional view showing the pile foundation structure according to the fifth embodiment. [Figure 14] 14 is a diagram showing an example of a displacement stopper for a foundation pile of the pile foundation structure shown in FIG. 13. FIG. [Figure 15] 15(a) is a side view showing an example of a displacement stopper of a foundation pile of the pile foundation structure shown in FIG. 13, and FIG. 15(b) is a cross-sectional view taken along line AA shown in FIG. 15(a). [Figure 16] FIG. 10 is a vertical cross-sectional view showing a pile foundation structure having a modified anti-slip portion. [Figure 17] 17(a) and 17(b) are horizontal cross-sectional views showing the displacement stopper of the foundation pile shown in FIG. 16. DETAILED DESCRIPTION OF THE INVENTION

[0035] Hereinafter, a pile foundation structure according to an embodiment of the present invention will be described with reference to the drawings.

[0036] (First embodiment) The pile foundation structure 1 of this embodiment shown in Figure 1 is a structure that makes it possible to efficiently strengthen the horizontal resistance of the foundation piles 2, which are subjected to horizontal forces and bending moments acting on the pile heads, of the foundation structure of a structure (not shown) constructed on liquefiable ground G1 consisting of a soft layer such as a sandy layer that is at risk of liquefaction. In this embodiment, a non-liquefaction layer G2 is present below the liquefaction ground G1, and a supporting layer (not shown) is further present below the non-liquefaction layer G2.

[0037] The pile foundation structure 1 includes foundation piles 2 that support a structure constructed on liquefied ground G1, and soil improvement bodies 3 formed around the foundation piles 2.

[0038] The foundation piles 2 are steel pipe piles such as stepped steel pipes 2A and 2B shown in Figures 2(a) and 2(b) and dimpled steel pipes 2C shown in Figure 2(c). The foundation piles 2 may be cast-in-place piles or precast piles. The foundation piles 2 may be made of reinforced concrete (concrete piles) or steel. However, the use of steel pipe piles has the advantage that it is easier to install (form) the unevenness of the shear stopper 21 described below.

[0039] The stepped steel pipe 2A shown in Figure 2(a) extends in a circumferential direction perpendicular to the pipe axis O, and has circumferential grooves 21a recessed from the outer circumferential surface 2a of the pile, spaced apart in the pipe axial direction. The stepped steel pipe 2B shown in Figure 2(b) is inclined in a direction intersecting the pipe axis O in side view, and has inclined grooves 21b recessed from the outer circumferential surface 2a of the pile, spaced apart in the pipe axial direction. The dimpled steel pipe 2C shown in Figure 2(c) has a plurality of recessed grooves 21c on the outer circumferential surface 2a of the pile, spaced apart in the circumferential and pipe axial directions. The circumferential groove 21a, the inclined groove 21b, and the recessed groove 21c are recesses formed during the manufacturing of the steel pipe, and correspond to the slippage prevention portion 21 described later.

[0040] As shown in FIG. 1, the foundation piles 2 are buried in liquefied ground G1 and non-liquefied layer G2, and are driven into the ground after penetrating the non-liquefied layer G2 to reach the supporting layer. The foundation piles 2 are installed perpendicular to the ground surface using, for example, a pile driver (not shown), and are driven into the ground by penetrating the ground. Since the foundation piles 2 configured in this manner reach the supporting layer, the supporting layer can withstand vertical forces via the foundation piles 2, and the foundation piles 2 have sufficient strength in the vertical direction. In other words, the vertical load of the structure can be supported by the foundation piles 2. Furthermore, during an earthquake, part of the horizontal force that the foundation pile 2 receives from the structure and the liquefied ground G1 is transmitted to the non-liquefied layer G2 through the embedded portion 3c (bottom portion 3a of the improvement body) of the ground improvement body 3, as described below, and is borne by the non-liquefied layer G2.

[0041] The ground improvement body 3 is installed over almost the entire area of ​​the liquefied ground G1 in the vertical direction, with its lower end (bottom 3a of the improvement body) embedded in the non-liquefied layer G2 located below the liquefied ground G1. The ground improvement body 3 is a multi-stage columnar body with an outer diameter that increases from top to bottom. The ground improvement body 3 in this embodiment is a single-stage columnar body. In other words, the outer diameter of the top 3b of the improvement body near the ground surface is smaller than the outer diameter of the bottom 3a of the improvement body.

[0042] The ground improvement body 3 is formed around the foundation pile 2, for example, by solidifying soil and sand with a cement-based solidifying agent such as cement milk. The ground improvement body 3 has a two-tiered structure with a cylindrical lower columnar body 31 located below approximately the center in the height direction, and a cylindrical upper columnar body 32 located above the lower columnar body 31 and with a smaller diameter than the lower columnar body 31. The outer diameter of the upper columnar body 32 is set to be at least larger than the outer diameter of the foundation pile 2. The improvement body bottom portion 3a, which is the lower part of the lower columnar body 31, is embedded in the non-liquefaction layer G2 to a predetermined thickness as described above.

[0043] In this way, the ground improvement body 3 has a large diameter at its bottom (lower columnar body 31), and is structured to maximize the bearing reaction force F2 at the bottom. In addition, the upper part of the improvement body (upper columnar body 32) has a smaller diameter than the lower columnar body 31, and the width (diameter) of the improvement body is reduced. As a result, the ground improvement body 3 can be structured to be resistant to the flow force of the ground without impeding the slip-through phenomenon in which liquefied ground G1 flows between the foundation piles 2 even during liquefaction.

[0044] The ground improvement body 3 is formed in a specified ground area by digging up the soil around the foundation pile 2 with the excavation blades 41 of the excavation rod 4 (see Figures 6(b) and 7(b)) when driving the foundation pile 2 into the ground, and then mixing the excavated soil with cement milk and solidifying it.

[0045] In this way, in the pile foundation structure 1 of this embodiment, the ground improvement body 3 solidified with cement milk is formed in the liquefied ground G1 and non-liquefaction layer G2 around the foundation pile 2. The pile foundation structure 1 has high rigidity because the ground improvement body 3 is reinforced with an outer diameter larger than that of the foundation pile 2, and the horizontal force acting on the foundation pile 2 can be sufficiently resisted by the ground improvement body 3 embedded in the non-liquefaction layer G2. The mechanism of load transfer (load transfer mechanism) acting on the pile foundation structure 1 at this time will be described in detail later.

[0046] 3 and 4, the pile outer surface 2a of the shaft of the foundation pile 2 is provided with a shear stopper 21 having an uneven shape that has a shear stop function between the ground improvement body 3 and the pile outer surface 2a, within a certain range from the bottom of the ground improvement body 3. At least a part of the shear stopper 21 is arranged in the compression truss formation area Ta where a compression truss T is formed between the pile outer surface 2a of the shaft of the foundation pile 2 and the ground improvement body bottom 3a.

[0047] The anti-slip section 21 installed on the outer surface 2a of the pile shaft of the foundation pile 2 has the function of transmitting the load from the uneven portion of the anti-slip section 21 to the ground improvement body 3 when a horizontal force F1 or bending moment M acts on the foundation pile 2. The shear stopper 21 is arranged in an area below the height of the intersection P between the compression truss T and the shaft of the foundation pile 2, where the inclination angle (compression truss angle θ) formed with the bottom 3a of the improved body is 60 degrees or less. The compression truss angle θ is preferably in the range of 30 to 60 degrees, and more preferably 45 degrees (see Figure 5(a)). Here, the compression truss T1 shown in Figure 5(a) has a θ of 45 degrees, the compression truss T2 has a θ of 60 degrees, and the compression truss T3 has a θ of 30 degrees.

[0048] The displacement preventing portion 21 is formed as a depression on the outer peripheral surface 2a of the foundation pile 2 as shown in FIGS. 2(a) to 2(c) described above.

[0049] Next, the load transfer mechanism of the pile foundation structure 1 of this embodiment will be specifically described with reference to FIGS. Inside the ground improvement body 3, the load transmitted from the shaft of the foundation pile 2 and the shear stopper 21 installed on its surface (outer periphery of the pile 2a) is transmitted to the bottom 3a of the improvement body and is supported by the bearing reaction force (symbol F2) in the ground of the non-liquefaction layer G2. At this time, a compression truss T is formed inside the ground improvement body 3 sandwiched between the foundation pile 2 and the bottom 3a of the improvement body. The formation of this compression truss T allows for efficient load transmission. Furthermore, because the load transmission associated with the compression truss T is based on compressive stress, load is transmitted reliably even to a ground improvement body 3 that does not have tensile strength.

[0050] Here, the symbols shown in FIG. 3 are as follows: r o : Radius of foundation pile 2 R B : Radius of the bottom part 3a of the improved body R t : Radius of improved body top 3b ΔR: Radius of the embedded part 3c of the ground improvement body 3 into the non-liquefaction layer G2 (ΔR = R B -r o ) h: Height of ground improvement body 3 (be careful with the definition, not the total length) l: The depth direction length where the anti-slip portion 21 is installed (formed) (= the length from the intersection point P described above to the bottom portion 3a of the improved body) θ: Compression truss forming angle (tanθ=l / ΔR) d e :Depth of embedment of ground improvement body 3 into non-liquefaction layer G2

[0051] As shown in Figure 4, it is preferable that the compression truss T has an inclination angle (compression truss forming angle θ) of 45 degrees with respect to the bottom 3a of the improved body to be formed. In other words, when the compression truss forming angle θ of the compression truss T is 45 degrees, at least the length range 1 in the depth direction of the shaft portion where the shear stopper 21 is formed (the length from the intersection point P where the compression truss T passing through the outer edge 3d of the bottom 3a of the improved body intersects with the shaft portion of the foundation pile 2 to the bottom 3a of the improved body) is equivalent to the radial length ΔR of the embedded portion 3c of the ground improvement body 3 into the non-liquefaction layer G2. Furthermore, for example, when the compression truss angle θ is between 45 and 60 degrees and passes through the outer edge 3d of the bottom 3a of the improved body, the intersection P at the shaft of the foundation pile 2 is located above the intersection P at the compression truss angle θ of 45 degrees, so the upper limit position of the range in which at least a part of the shear stopper 21 is provided is also above the upper limit position when the compression truss angle θ is 45 degrees. In other words, the length range 1 in the depth direction of the shaft in which the shear stopper 21 is formed becomes larger.

[0052] The shear stopper 21 may be provided in an area above the installation range (shear stopper functional area 21A) determined by the compression truss forming angle θ of the compression truss T. For example, even if the transmission function of resisting the horizontal force acting on the foundation pile 2 by the compression truss T with the bearing reaction force of the bottom part 3a of the improvement body does not work, the shear stopper 21 can be provided outside the shear stopper functional area 21A in order to exert a shear stop function with the ground improvement body 3 or to provide a shear stop function with the concrete filled inside the foundation pile 2.

[0053] The range of the compression truss T formed by the shear stopper 21 is certainly included in the ground improvement body 3. Geometrically, this requires a ground improvement body 3 with a range (radially outward) larger than the triangular portion defined by the bottom 3a of the improvement body, the shear stopper functional area 21A at the shaft of the foundation pile 2, and the inclined line of the compression truss T connecting the outer edge 3d of the bottom 3a of the improvement body and the shaft of the foundation pile 2.

[0054] As shown in Figures 5(a) and (b), the compression truss forming angle θ is generally 45 degrees, and the shape and size of the ground improvement body 3 are set based on this. Furthermore, it is better to limit the compression truss forming angle θ to the range of 30 to 60 degrees as necessary based on the site conditions, construction equipment, etc. Outside this angle, the compression truss T will not be formed sufficiently and will not be effective.

[0055] Figure 5(b) shows an example in which the height of the lower columnar body 31 is small. In this case, the compression truss T passes through the inner corner 33a of the step 33 of the multi-stage columnar soil improvement body 3, facing the foundation pile 2, and is placed in an area below the height of the intersection P with the shaft of the foundation pile 2. In Figure 5(b), the compression truss T1 (solid line in Figure 5(b)) passing through the outer edge 3d of the bottom 3a of the improvement body and the inner corner 33a has a compression truss forming angle θ of 45 degrees. The 60-degree compression truss T2 (chain double-dashed line in Figure 5(b)) passing through the outer edge 3d of the bottom 3a of the improvement body is not entirely included in the soil improvement body 3, so part of the compression truss T2 is located outside the soil improvement body 3. As a result, the horizontal force that the foundation pile 2 receives at this compression truss T2 is not transmitted to the bottom 3a of the improvement body.

[0056] Next, two construction examples (first construction method and second construction method) will be described as construction methods for the above-mentioned pile foundation structure 1. The first construction method will be described with reference to Figures 6(a), (b) and 7(a) to (c). The first construction method is a post-pile construction method.

[0057] First, as shown in Fig. 6(a), the drilling rod 4 is placed above ground at the construction site. The drilling rod 4 includes a rod 40, a drilling blade 41 that is disposed at the lower end of the rod 40 and is expandable and contractible in diameter, and a stirring blade 42 that is disposed above the drilling blade 41.

[0058] Next, as shown in FIG. 6(b), the rod 40 is rotated to excavate the ground by rotating the drilling blade 41 and the mixing blade 42. In this first embodiment, the soil improvement body 3 is a multi-stage columnar body formed of an upper columnar body 32 and a lower columnar body 31. Therefore, excavation is performed in the region of the upper columnar body 32 with the drilling blade 41 and the mixing blade 42 contracted to a predetermined length, and in the region of the lower columnar body 31 with the drilling blade 41 and the mixing blade 42 expanded to a larger diameter than in the region of the upper columnar body 32. Then, after the drilling rod 4 has excavated to a depth at which it is embedded in the non-liquefaction layer G2, the drilling rod 4 is pulled up while cement milk is poured into the surrounding area from a pouring outlet (not shown) provided at the lower end of the drilling rod 4 and stirred and mixed with the excavated soil and sand. As a result, a ground improvement body 3 of a predetermined shape (a multi-stage columnar body in the first embodiment) is constructed, as shown in Figure 7(a), in which the bottom part 3a of the improvement body forms an embedded part 3c embedded in the non-liquefaction layer G2.

[0059] Next, as shown in Figure 7(b), a foundation pile 2, which has a shear stopper 21 pre-installed in a predetermined area on the outer circumferential surface 2a of the pile, is driven into the constructed ground improvement body 3. Specifically, the foundation pile 2 is penetrated into the ground improvement body 3 and the ground below the ground improvement body 3 until the tip of the foundation pile 2 reaches the bearing layer (see Figure 7(c)). The foundation pile 2 is extended to a predetermined length depending on the driving length. As shown in Figure 7(c), by driving the foundation pile 2 to a predetermined depth, the shear stopper 21 of the foundation pile 2 is also positioned at a predetermined height. This completes the construction. By installing the foundation piles 2 in this manner, the foundation piles 2 can obtain vertical bearing capacity, and furthermore, the surrounding area of ​​the foundation piles 2 in the liquefied ground G1 is covered by the ground improvement body 3, thereby constructing a pile foundation structure 1 that transmits the horizontal force acting on the foundation piles 2 to the bottom 3a of the ground improvement body 3.

[0060] Next, the second construction method will be described with reference to Figures 8(a), (b) and 9(a) to (c). The second construction method is a simultaneous pile construction method.

[0061] First, as shown in Figure 8(a), a drilling rod 4 equipped with a foundation pile 2, which has a shear stopper 21 already installed in a predetermined area on the outer circumferential surface 2a of the pile, is installed above ground at the construction site. The configuration of the drilling rod 4 is the same as that used in the first construction method described above. The foundation pile 2 is set at a position above the mixing blade 42, with the rod 40 inserted inside the pile. The drilling blade 41 and mixing blade 42 can pass inside the foundation pile 2 when their diameters are reduced.

[0062] Next, as shown in FIG. 8(b), the drilling rod 4 equipped with the foundation pile 2 is rotated to rotate the drilling blade 41 and the mixing blade 42 to excavate the ground. In this first embodiment, the soil improvement body 3 is a multi-stage columnar body formed of an upper columnar body 32 and a lower columnar body 31. Therefore, in the region of the upper columnar body 32, the drilling blade 41 and the mixing blade 42 are excavated with their diameters reduced to a predetermined length, and in the region of the lower columnar body 31, the drilling blade 41 and the mixing blade 42 are excavated with their diameters expanded to a greater extent than in the region of the upper columnar body 32, to a depth at which they are embedded in the non-liquefaction layer G2. At this time, as the drilling rod 4 penetrates the ground, the foundation pile 2 also penetrates into the excavated ground.

[0063] In the second construction method, simultaneously with excavation using the drilling rod 4, cement milk is poured into the surrounding area from a pouring outlet (not shown) provided at the lower end of the drilling rod 4 and stirred and mixed with the excavated soil and sand, thereby constructing a ground improvement body 3 of a predetermined shape (in the first embodiment, a multi-stage columnar body) in which the bottom 3a of the improvement body is embedded in the non-liquefaction layer G2 to form an embedded portion 3c, as shown in Figure 9(a). Next, while leaving the foundation pile 2 penetrated into the ground together with the drilling rod 4 in place, the drilling rod 4 with the drilling blades 41 and the stirring blades 42 reduced in diameter is passed through the inside of the foundation pile 2 and pulled out to the ground.

[0064] Next, as shown in Figure 9(b), the foundation pile 2, which has a shear stopper 21 pre-installed in a predetermined area on the outer circumferential surface 2a of the pile, is driven into the further constructed ground improvement body 3 and the non-liquefaction layer G2 below it. Specifically, the foundation pile 2 is penetrated into the ground improvement body 3 and the ground below the ground improvement body 3 until the tip of the foundation pile 2 reaches the bearing layer (see Figure 9(c)). The foundation pile 2 is extended to the predetermined length depending on the driving length. As shown in Figure 9(c), by driving the foundation pile 2 to the predetermined depth, the shear stopper 21 of the foundation pile 2 is also positioned at a predetermined height. This completes the construction. By installing the foundation piles 2 in this manner, the foundation piles 2 can obtain vertical bearing capacity, and furthermore, the surrounding area of ​​the foundation piles 2 in the liquefied ground G1 is covered by the ground improvement body 3, thereby constructing a pile foundation structure 1 that transmits the horizontal force acting on the foundation piles 2 to the bottom 3a of the ground improvement body 3.

[0065] Next, the operation of the above-described pile foundation structure 1 will be described in detail with reference to the drawings. As shown in Figure 2, in the pile foundation structure 1 according to this embodiment, a shear stopper 21 with a concave-convex shape is provided on the shaft of the foundation pile 2. The soil improvement body 3 is present within the area where the compression truss T is formed due to this shear stopper 21. This allows the horizontal force acting on the foundation pile 2 to be transmitted from the shear stopper 21 to the bottom 3a of the improved body via the soil improvement body 3 formed around the foundation pile 2. The horizontal force transmitted to the bottom 3a of the improved body can then be resisted by the bearing reaction force of the bottom 3a of the improved body, which is embedded in the non-liquefaction layer G2. Therefore, in this embodiment, the bearing reaction force of the non-liquefaction layer G2 is utilized, and therefore, excellent horizontal resistance can be achieved due to the bearing reaction force of the bottom 3a of the improved body, even when the liquefied ground G1 is liquefied during an earthquake. In this way, in this embodiment, even in a liquefied layer where horizontal resistance cannot be expected from the sides of the ground improvement body 3, the horizontal resistance of the foundation pile 2, where horizontal forces and bending moments act on the pile head, can be strengthened by utilizing the bearing reaction force of the bottom 3a of the improvement body.

[0066] Furthermore, in this embodiment, it is expected that the bearing reaction force of the bottom 3a of the improvement body will resist the horizontal force of the foundation pile 2. In other words, in this embodiment, it is no longer necessary to expect the bearing reaction force of the side surface of the improvement body to resist the horizontal force of the foundation pile 2, so the cross-sectional area (outer diameter) of the part of the ground improvement body 3 where the compression truss T is not formed can be reduced to the minimum necessary, thereby slimming it down. If the ground improvement body 3 is slimmed down, it will be possible to suppress the flow force acting on the foundation pile 2 during liquefaction. In this way, the volume of the ground improvement body 3 can be reduced, and costs can be reduced.

[0067] Furthermore, in this embodiment, by setting the compression truss forming angle θ, which is the inclination angle formed by the compression truss T, in the range of 30 to 60 degrees, the compression truss T can be sufficiently formed in the ground improvement body 3, and the horizontal resistance effect due to the bearing reaction force of the bottom part 3a of the improvement body can be reliably obtained. Therefore, even if it is not possible to set the compression truss forming angle θ to 45 degrees, which is the general value, due to conditions such as site conditions and construction equipment, the compression truss T can be reliably formed in the ground improvement body 3. In particular, by setting the compression truss formation angle θ to 45 degrees, it is possible to reliably form a compression truss T that can transmit the horizontal force acting on the foundation pile 2 from the anti-slip section to the bottom 3a of the improved body, thereby obtaining a horizontal resistance effect due to the bearing reaction force of the bottom 3a of the improved body.

[0068] Furthermore, in this embodiment, the outer diameter of the top 3b of the soil improvement body 3 is equal to or smaller than the outer diameter of the bottom 3a of the soil improvement body, so the horizontal force acting on the foundation piles 2 is not excessively expected to be borne by the horizontal resistance of the side surface 3e of the soil improvement body 3. This makes it possible to slim down the cross-sectional area (outer diameter) of the soil improvement body 3 installed in the liquefied ground G1 by keeping it small. This makes it possible to suppress the flow force of the liquefied ground G1 that the foundation piles 2 receive during liquefaction.

[0069] In addition, in this embodiment, the ground improvement body 3 is made into a multi-stage columnar body, and the outer diameter of the top part 3b of the improvement body is made the smallest, thereby ensuring the bearing reaction force of the bottom part 3a of the improvement body and suppressing the flow force of the liquefied ground G1 that the foundation pile 2 receives during liquefaction. In this embodiment, the cross-sectional shape of the upper part of the ground improvement body 3 is made slimmer, which makes it possible to reduce the volume of the improvement body and lower costs.

[0070] Moreover, in this embodiment, the compression truss T passes through the inner corner of the step of the multi-stage columnar body facing the foundation pile 2, and is placed in an area (slip-stop functional area 21A) below the height at which the intersection with the shaft of the foundation pile 2 is located. This allows the compression truss T to be efficiently formed in the ground improvement body 3 consisting of the multi-stage columnar body, ensures the bearing reaction force of the bottom part 3a of the improvement body, and suppresses the flow force of the liquefied ground G1 that the foundation pile 2 receives during liquefaction.

[0071] Furthermore, in this embodiment, since the foundation piles 2 are steel pipe piles, the displacement preventing portions 21 can be easily installed and formed.

[0072] In addition, in this embodiment, by adopting stepped steel pipes 2A, 2B (see Figures 2(a) and (b)) or dimpled steel pipe 2C (see Figure 2(c)), the anti-slip portion 21 provided on the shaft of the foundation pile 2 is formed in a recessed state. Therefore, the adhesion between the outer peripheral surface 2a of the pile and the ground improvement body 3 can ensure unity, and the effect of horizontal resistance due to the bearing reaction force of the bottom part 3a of the improvement body can be fully obtained.

[0073] In addition, in this embodiment, when a filler material such as concrete is filled into the inner surface of the steel pipe of the foundation pile 2, the adhesion between the inner surface of the steel pipe and the filler material ensures integrity, and the horizontal resistance of the foundation pile 2 can be further increased. Furthermore, in the case of dimpled steel pipe 2C (see Figure 2(c)), which has dimples on the steel pipe, even though it has depressions and no filler is filled inside the steel pipe, it can exhibit compression and bending performance equivalent to that of a straight steel pipe pile, thereby demonstrating excellent effects. In this embodiment, by forming the slippage prevention portion 21 as a recess, excellent workability and ease of construction of the pile can be obtained.

[0074] In the pile foundation structure 1 according to the present embodiment described above, the horizontal resistance of the foundation pile 2, in which horizontal forces and bending moments act on the pile head, can be strengthened in liquefied ground G1 where horizontal resistance cannot be expected on the side of the ground improvement body 3.

[0075] (Second embodiment) As shown in Figure 10, the pile foundation structure 1A according to the second embodiment has a columnar structure in which the shape of the ground improvement body 3A is a constant outer diameter throughout the entire depth direction. That is, the outer diameter of the top portion 3b of the ground improvement body 3A is approximately the same as the outer diameter of the bottom portion 3a of the ground improvement body 3A. In this case, too, the ground improvement body 3A has an embedded portion 3c embedded in the non-liquefaction layer G2.

[0076] The foundation pile 2 has the same configuration as that of the first embodiment described above. That is, the pile outer surface 2a of the shaft of the foundation pile 2 is provided with a shear stopper 21 having an uneven shape that functions to prevent shear between the ground improvement body 3A and the pile outer surface 2a and within a certain range from the bottom of the ground improvement body 3A. At least a portion of the shear stopper 21 is arranged in the compression truss formation region Ta where a compression truss T is formed between the pile outer surface 2a and the bottom 3a of the ground improvement body 3A.

[0077] The dotted line of the compression truss T shown in FIG. 10 is a line at which the compression truss forming angle θ at the outer edge 3d of the improved body bottom 3a of the ground improvement body 3A is 45 degrees. In the second embodiment, on the pile outer surface 2a of the foundation pile 2, a shear stopper 21 is provided in the region (slip stopper functional region 21A) from the intersection P of the compression truss T with the shaft of the foundation pile 2 to the improved body bottom 3a. Note that the shear stopper 21 only needs to be provided in at least a part of the shear stopper functional region 21A of the foundation pile 2, and is not limited to being provided throughout the entire shear stopper functional region 21A, and may be arranged intermittently in the vertical direction. Furthermore, as described above, the shear stopper 21 may also be provided in a region other than the shear stopper functional region 21A (here, the region above the shear stopper functional region 21A).

[0078] In the pile foundation structure 1A according to the second embodiment, an embedded portion 3c is formed in the ground improvement body 3A, which is embedded in the non-liquefaction layer G2, and a shear stop portion 21 is provided on the foundation pile 2, so that a bearing reaction force F2 is obtained from the bottom 3a of the improvement body by the compression truss T, and the horizontal force F1 acting on the foundation pile 2 can be borne by the non-liquefaction layer G2.

[0079] On the other hand, in the pile foundation structure 1A according to the second embodiment, the upper cross section of the soil improvement body 3 is not reduced in diameter as in the pile foundation structure 1 according to the first embodiment described above. In other words, since a large cylindrical soil improvement body 3A exists on top of the liquefied ground G1, there is a possibility that the ground between the foundation piles 2 will hinder the slip-through phenomenon during liquefaction compared to when the upper cross section is small as in the first embodiment described above, and the structure is more susceptible to the flow force of the ground.

[0080] (Third embodiment) As shown in FIG. 11, the pile foundation structure 1B according to the third embodiment has a configuration in which soil improvement bodies 3B made of columnar bodies are provided only in the lower part of the liquefied ground G1 in the depth direction. In other words, the ground improvement body 3B is equivalent to the configuration in which the upper columnar bodies 32 (see Figure 1) of the first embodiment described above are omitted and only the lower columnar bodies 31 are provided, and the outer diameter of the top part 3b of the ground improvement body and the outer diameter of the bottom part 3a of the ground improvement body are approximately the same. In this case, the ground improvement body 3B also has an embedded part 3c embedded in the non-liquefaction layer G2.

[0081] The foundation pile 2 has the same configuration as that of the first embodiment described above. That is, the outer peripheral surface 2a of the shaft of the foundation pile 2 is provided with a shear stopper 21 having an uneven shape that functions to prevent shear between the shaft and the ground improvement body 3B, within a certain range from the bottom of the ground improvement body 3B. At least a portion of the shear stopper 21 is arranged in the compression truss formation region Ta where a compression truss T is formed between the shaft and the bottom 3a of the ground improvement body 3B. In FIG. 11, the shear stopper 21 is provided over almost the entire area of ​​the shaft of the foundation pile 2 that contacts the ground improvement body 3B.

[0082] The dotted line of the compression truss T1 shown in Figure 11 is a line at the outer edge 3d of the improved body bottom 3a of the ground improvement body 3B where the compression truss forming angle θ is 45 degrees. In the third embodiment, on the pile outer surface 2a of the foundation pile 2, a shear stopper 21 is provided in the region (slip stopper functional region 21A) from the intersection P of the compression truss T with the shaft of the foundation pile 2 to the improved body bottom 3a. Note that the shear stopper 21 only needs to be provided in at least a part of the shear stopper functional region 21A of the foundation pile 2, and is not limited to being provided throughout the entire shear stopper functional region 21A, and may be arranged intermittently in the vertical direction. Furthermore, as described above, the shear stopper 21 may also be provided in regions other than the shear stopper functional region 21A.

[0083] In the pile foundation structure 1B according to the third embodiment, an embedded portion 3c is formed in the ground improvement body 3B, which is embedded in the non-liquefaction layer G2, and a slip prevention portion 21 is provided on the foundation pile 2, so that a bearing reaction force is obtained from the bottom 3a of the improvement body by the compression truss T, and the horizontal force acting on the foundation pile 2 can be borne by the non-liquefaction layer G2.

[0084] Furthermore, since the pile foundation structure 1B of the third embodiment does not have an upper columnar body 32 like the pile foundation structure 1 of the first embodiment described above, ground improvement work above the liquefied ground G1 is not required, thereby enabling further cost reductions.

[0085] (Fourth embodiment) A pile foundation structure 1C according to the fourth embodiment shown in FIG. 12 is configured to include a soil improvement body 3C in the form of a cone-shaped column whose outer diameter gradually increases from top to bottom. The ground improvement body 3C is provided over almost the entire area of ​​the liquefied ground G1 in the vertical direction, as in the first embodiment described above, with its lower end (the bottom part 3a of the improvement body) embedded in the non-liquefied layer G2. That is, the outer diameter of the top part 3b of the improvement body near the ground surface of the ground improvement body 3C is smaller than the outer diameter of the bottom part 3a of the improvement body.

[0086] The foundation pile 2 has the same configuration as in the above-described embodiment. That is, the outer peripheral surface 2a of the shaft of the foundation pile 2 is provided with a shear stopper 21 having an uneven shape that functions to prevent shear between the ground improvement body 3C and the pile 2, within a certain range from the bottom of the ground improvement body 3C. At least a portion of the shear stopper 21 is arranged in the compression truss formation region Ta where a compression truss T is formed between the pile 2 and the bottom 3a of the ground improvement body 3B.

[0087] The dotted line of the compression truss T shown in FIG. 12 is a line at which the compression truss forming angle θ at the outer edge 3d of the improved body bottom 3a of the ground improvement body 3C is 45 degrees. In the fourth embodiment, on the pile outer surface 2a of the foundation pile 2, a shear stopper 21 is provided in the region (slip stopper functional region 21A) from the intersection P of the compression truss T with the shaft of the foundation pile 2 to the improved body bottom 3a. Note that the shear stopper 21 only needs to be provided in at least a part of the shear stopper functional region 21A of the foundation pile 2, and is not limited to being provided throughout the entire shear stopper functional region 21A, and may be arranged intermittently in the vertical direction. Furthermore, as described above, the shear stopper 21 may also be provided in a region other than the shear stopper functional region 21A (here, the region above the shear stopper functional region 21A).

[0088] In the pile foundation structure 1C according to the fourth embodiment, an embedded portion 3c is formed in the ground improvement body 3C, which is embedded in the non-liquefaction layer G2, and a shear stopper portion 21 is provided on the foundation pile 2, so that a bearing reaction force F2 is obtained from the bottom 3a of the improvement body by the compression truss T, and the horizontal force F1 acting on the foundation pile 2 can be borne by the non-liquefaction layer G2.

[0089] Furthermore, in the pile foundation structure 1B of the fourth embodiment, as with the pile foundation structure 1 of the first embodiment described above, the cross-sectional area of ​​the upper part of the ground improvement body 3C is small and the diameter is reduced, so that the ground improvement work above the liquefied ground G1 can be reduced, thereby reducing costs.

[0090] Furthermore, in the pile foundation structure 1C according to the fourth embodiment, the soil improvement body 3C has a cone shape, so that construction can be carried out efficiently while gradually expanding the diameter by a constant amount during construction. Furthermore, in this embodiment, the shape of the ground improvement body 3C consisting of a cone-shaped body is similar to the triangular part of the ground improvement body 3C in which the compression truss T is formed, so the ground improvement range can be reduced to match the compression truss formation angle θ, thereby reducing costs.

[0091] (Fifth embodiment) Next, as shown in Figure 13, the pile foundation structure 1D according to the fifth embodiment is configured such that the uneven-shaped anti-slip portion 22 provided on the shaft of the foundation pile 2 in the first embodiment above protrudes outward from the outer circumferential surface 2a of the pile. The shape of the ground improvement body 3 is a multi-stage columnar body, as in the first embodiment. That is, the ground improvement body 3 is provided with its lower end (the bottom portion 3a of the improvement body) embedded in the non-liquefaction layer G2. The foundation pile 2 has the same configuration as that of the first embodiment except for the displacement stopper 22, and reaches a supporting layer (not shown).

[0092] The dotted line of the compression truss T shown in Figure 13 is a line where the compression truss forming angle θ at the outer edge 3d of the improved body bottom 3a of the ground improvement body 3 is 45 degrees. The shear stopper 22 is provided on the pile outer surface 2a of the foundation pile 2 in the area (shear stopper functional area 22A) from the intersection P of the compression truss T1 with the shaft of the foundation pile 2 to the improved body bottom 3a. Note that the shear stopper 22 only needs to be provided in at least a part of the shear stopper functional area 22A of the foundation pile 2, and is not limited to being provided throughout the entire shear stopper functional area 22A, and may be arranged intermittently in the vertical direction. Furthermore, as described above, the shear stopper 22 may also be provided in areas other than the shear stopper functional area 22A (here, the area above the shear stopper functional area 22A).

[0093] The protruding anti-slip portion 22 may be, for example, a weld bead 22a fixed to the outer circumferential surface 2a of the foundation pile 2 as shown in Fig. 14. In this case, the protruding portion can be easily formed by providing the weld bead 22a on the outer circumferential surface 2a of the pile, thereby providing excellent workability and ease of construction of the pile.

[0094] 15(a) and (b), protrusions 22b may be formed by rolling on the outer circumferential surface 2a of the foundation pile 2. Forming the protrusion-shaped anti-slip portion 22 using such a rolling production line makes it possible to efficiently provide an anti-slip portion in a stable shape on the shaft portion of the foundation pile 2. Note that the reference numeral 22c (the line between the protrusions 22b located in the center in the axial direction) in FIGS. 15(a) and (b) indicates the weld line when the foundation pile 2 is manufactured using a steel plate having the protrusions 22b formed by rolling.

[0095] Furthermore, other protruding anti-slip portions 22 may be formed by bending reinforcing bars, round steel bars, flat steel bars, etc. into a ring shape and placing them on the outer surface 2a of the foundation pile 2 and fastening them by welding or the like.

[0096] 16 and 17(a) and (b), in a modified pile foundation structure 1D, it is also possible to use, as another protruding shear stopper 22, a plurality of perforated steel plates 23 extending along the axial direction on the outer peripheral surface 2a of the foundation pile 2 and spaced apart in the circumferential direction. The perforated steel plates 23 are configured such that a plurality of through holes 23a (for example, four in FIG. 17(a) and eight in FIG. 17(b)) are arranged in a strip-shaped steel plate in the extension direction. The perforated steel plates 23 are arranged so that the central axes of the through holes 23a are oriented in a direction perpendicular to the axial direction of the foundation pile 2, and the plate surface of the steel plate is radial to the foundation pile 2.

[0097] Although the embodiment of the pile foundation structure according to the present invention has been described above, the present invention is not limited to the above embodiment and can be modified as appropriate within the scope of the invention.

[0098] For example, the outer diameter, length, and material of the foundation pile 2 can be set appropriately according to conditions such as ground conditions and the load of the structure to be supported.

[0099] In addition, in the above-mentioned embodiments, examples of the shape of the ground improvement body include a multi-stage columnar body, a columnar body with one cross section, and a cone-shaped columnar body, and examples of the uneven-shaped anti-slip portion formed on the shaft of the foundation pile include a depression, a welded bead, a protrusion formed by rolling, and a perforated steel plate, but it is possible to appropriately set combinations of ground improvement bodies of various shapes and anti-slip portions of foundation piles of various configurations.

[0100] In the other embodiments except for the third embodiment described above, the soil improvement bodies 3, 3A, 3C, and 3D are configured to be provided over the entire area up to above the liquefied ground G1, but this is not a limitation. That is, like the soil improvement body 3B in the third embodiment described above, there may be a portion above the liquefied ground G1 where no soil improvement body is formed.

[0101] Furthermore, the shape of the ground improvement body is not limited to the above-mentioned embodiment. For example, the ground improvement body 3 consisting of multi-stage columnar bodies in the first embodiment has a shape in which a single stage 33 consisting of a lower columnar body 31 and an upper columnar body 32 is formed, but two or three or more stages may be formed.

[0102] In addition, the components in the above-described embodiments can be replaced with well-known components as appropriate, without departing from the spirit of the present invention. [Explanation of symbols]

[0103] 1, 1A~1D pile foundation structure 2 Foundation piles 2a Pile outer surface 2A, 2B stepped steel pipe 2C Dimpled Steel Pipe 21, 22 Stopper 21A, 22A Anti-slip functional area 21a Circumferential groove 21b Slant groove 21c groove 22a Weld bead 22b protrusion 23 Perforated steel plate 3, 3A~3D ground improvement body 3a Improved bottom part 3b Improved body top 3c Root section 31 Hypocolumnar 32 Upper columnar body G1 Liquefied ground G2 Non-liquefiable layer T compression truss Ta compression truss forming region

Claims

1. Foundation piles that support a structure constructed on liquefied ground; A ground improvement body formed around the foundation pile, The foundation piles are buried in the liquefied ground and a non-liquefied layer located below the liquefied ground, and are provided in a state where they penetrate the non-liquefied layer and reach the supporting layer, The ground improvement body is provided with the lower end of the ground improvement body embedded in the non-liquefaction layer, The shaft portion of the foundation pile is provided with an uneven-shaped anti-slip portion that functions as an anti-slip portion between the foundation pile and the ground improvement body, At least a part of the shear stopper is disposed in the region of the shaft portion that forms a compression truss between the shaft portion and the bottom of the ground improvement body, A pile foundation structure characterized in that the area in which the anti-slip portion is provided in the shaft portion includes at least the area on the outer surface of the foundation pile from the intersection with the shaft portion in the compression truss to the bottom of the improved body.

2. The compression truss forming angle, which is the inclination angle with the bottom of the improved body for forming the compression truss, is in the range of 30 to 60 degrees, The pile foundation structure described in claim 1, characterized in that at least a portion of the anti-slip portion is arranged in an area below the height at which the intersection between the compression truss passing through the outer edge of the bottom of the improvement body and the axis of the foundation pile is located.

3. The pile foundation structure according to claim 2, wherein the compression truss forming angle is 45 degrees.

4. The pile foundation structure according to any one of claims 1 to 3, characterized in that the outer diameter of the top of the ground improvement body is equal to or smaller than the outer diameter of the bottom of the ground improvement body.

5. 5. The pile foundation structure according to claim 1, wherein the ground improvement body is a multi-stage columnar body whose outer diameter increases from top to bottom.

6. The pile foundation structure described in claim 5, characterized in that at least a portion of the anti-slip portion is arranged in an area below the height at which the intersection between the compression truss passing through the inner corner of the step portion of the multi-stage columnar body facing the foundation pile and the axis of the foundation pile is located.

7. 5. The pile foundation structure according to claim 1, wherein the ground improvement body is a cone-shaped columnar body whose outer diameter gradually increases from top to bottom.

8. The pile foundation structure according to any one of claims 1 to 7, wherein the foundation piles are steel pipe piles.

9. 9. The pile foundation structure according to claim 8, wherein the foundation pile is a stepped steel pipe or a dimpled steel pipe.

10. The pile foundation structure according to any one of claims 1 to 8, wherein the anti-slip portion is formed as a recess on the outer peripheral surface of the foundation pile.

11. 9. The pile foundation structure according to claim 1, wherein the anti-slip portion is formed by a weld bead fixed to the outer peripheral surface of the foundation pile.

12. The pile foundation structure according to any one of claims 1 to 8, wherein the anti-slip portion is formed by rolling on the outer peripheral surface of the foundation pile.

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