Construction method of steel-reinforced ground improvement body, insertion jig, and steel-reinforced ground improvement body

Abstract

To efficiently insert a reinforcement steel material into a column-shaped ground improvement body.SOLUTION: A construction method of a steel reinforced ground improvement body includes: a dropping step of inserting into a hollow pipe 50 a bar-shaped reinforcement steel material 24 with a cap 26 hooked on a lower end 50L of the hollow pipe 50 attached on a steel frame member 40 and dropping the steel frame member 40 into a column-shaped ground improvement body 22 prior to cure in a state where an upper part of the reinforcement steel material 24 is held by the steel frame member 40; and a lifting step of lifting up the steel frame member 40 and the hollow pipe 50 from the column-shaped ground improvement body 22 prior to cure in a state where holding of the upper part of the reinforcement steel material 24 by the steel frame member 40 is released.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a construction method of a steel-reinforced ground improvement body, an insertion jig, and a steel-reinforced ground improvement body.

Background Art

[0002] There is known a retaining wall in which a reinforcing cage is embedded in a columnar ground improvement body (see, for example, Patent Documents 1 and 2). Further, there is known a retaining wall in which reinforcing steel materials such as reinforcing bars are embedded in a columnar ground improvement body (soil-cement column body) (see, for example, Patent Documents 3 and 4).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technique disclosed in Patent Document 4, a steel bar having a male thread formed on the outer peripheral surface is used as the reinforcing steel material. This steel bar is inserted into the columnar ground improvement body by a feed screw mechanism. Thereby, in the technique disclosed in Patent Document 4, a reinforcing steel material such as a light-weight steel bar can be inserted into the ground improvement body.

[0005] However, there is still room for further improvement in order to efficiently insert the reinforcing steel material into the columnar ground improvement body.

[0006] In consideration of the above facts, an object of the present invention is to efficiently insert a reinforcing steel material into a columnar ground improvement body.

Means for Solving the Problem

[0007] According to the first aspect The construction method of the steel-reinforced ground improvement body includes inserting a rod-shaped or linear reinforcing steel bar having a hooking portion that hooks on the lower end of a hollow member attached to a steel frame member into the hollow member, and while holding the upper portion of the reinforcing steel bar by the steel frame member, dropping the steel frame member into a columnar ground improvement body before hardening; and a pulling-up step of pulling up the steel frame member and the hollow member from the columnar ground improvement body before hardening with the holding of the upper portion of the reinforcing steel bar by the steel frame member released.

[0008] The first aspect According to the construction method of the steel-reinforced ground improvement body according to this, the rod-shaped or linear reinforcing steel bar has a hooking portion that is hooked on the lower end of a hollow member attached to a steel frame member. And in the dropping step, the reinforcing steel bar is inserted into the hollow member, and while holding the upper portion of the reinforcing steel bar by the steel frame member, the steel frame member is dropped into the columnar ground improvement body before hardening.

[0009] Next, in the pulling-up step, with the holding of the upper portion of the reinforcing steel bar by the steel frame member released, the steel frame member and the hollow member are pulled up from the columnar ground improvement body before hardening. Thereby, the reinforcing steel bar is embedded (left remaining) inside the columnar ground improvement body.

[0010] Thus, in the present invention, in the dropping step, by dropping the reinforcing steel bar together with the steel frame member into the columnar ground improvement body before hardening, as compared with the case of dropping only the reinforcing steel bar into the columnar ground improvement body before hardening, the reinforcing steel bar can be efficiently inserted into the columnar ground improvement body.

[0011] Also, while holding the upper portion of the reinforcing steel bar by the steel frame member and hooking the hooking portion of the reinforcing steel bar on the lower end of the hollow member, when dropping the steel frame member and the reinforcing steel bar into the columnar ground improvement body before hardening, displacement of the reinforcing steel bar with respect to the steel frame member is suppressed. As a result, displacement of the reinforcing steel bar with respect to the columnar ground improvement body can be suppressed.

[0012] According to the second aspect The construction method of the steel-reinforced ground improvement body is According to the first aspect In the construction method of the steel-reinforced ground improvement body, the hollow member is a hollow pipe extending in the material axis direction of the steel frame member, and the hanging portion closes the opening on the lower end side of the hollow pipe while being hooked to the lower end of the hollow pipe.

[0013] The second aspect According to the construction method of the steel-reinforced ground improvement body according to, the hollow member is a hollow pipe extending in the material axis direction of the steel frame member. Reinforcing steel is inserted into this hollow pipe. Further, with the reinforcing steel inserted into the hollow pipe, a hanging portion of the reinforcing steel is hooked to the lower end of the hollow pipe. In this state, the opening on the lower end side of the hollow pipe is closed by the hanging portion.

[0014] Thereby, in the dropping step, when dropping the steel frame member, the hollow pipe, and the reinforcing steel into the columnar ground improvement body before hardening, the inflow of the ground (soil cement, etc.) before hardening into the opening on the lower end side in the hollow pipe is suppressed. As a result, the adhesion of the reinforcing steel to the inner peripheral surface of the hollow pipe via the ground before hardening is suppressed.

[0015] Therefore, in the pulling-up step, when pulling up the steel frame member and the hollow member from the columnar ground improvement body before hardening, the pulling up of the reinforcing steel together with the hollow member is suppressed. Therefore, the reinforcing steel can be more reliably embedded (left) inside the columnar ground improvement body.

[0016] According to the third aspect The construction method of the steel-reinforced ground improvement body is The first aspect or According to the second aspect In the construction method of the steel-reinforced ground improvement body, the hanging portion tapers as it moves away from the lower end of the hollow member.

[0017] The third aspectAccording to the construction method of the steel-reinforced ground improvement body according to the present invention, the engaging portion tapers as it moves away from the lower end of the hollow member. As a result, in the dropping process, it becomes easier to drop the reinforcing steel into the columnar ground improvement body before hardening. Therefore, the reinforcing steel can be inserted more efficiently into the columnar ground improvement body.

[0018] According to the fourth aspect The insertion jig includes an iron frame member that holds the upper part of a rod-shaped or linear reinforcing steel having an engaging portion and is dropped into the columnar ground improvement body before hardening together with the reinforcing steel, and a hollow member that is attached to the iron frame member and has the engaging portion hooked at the lower end in a state where the reinforcing steel is inserted.

[0019] The fourth aspect According to the insertion jig according to the present invention, the iron frame member holds the upper part of a rod-shaped or linear reinforcing steel having an engaging portion and is dropped into the columnar ground improvement body before hardening together with the reinforcing steel. A hollow member is attached to this iron frame member. The reinforcing steel is inserted into the hollow member. In this state, the engaging portion of the reinforcing steel is hooked at the lower end of the hollow tube.

[0020] Here, by dropping the iron frame member together with the reinforcing steel into the columnar ground improvement body before hardening, the reinforcing steel can be inserted more efficiently into the columnar ground improvement body compared to the case of dropping only the reinforcing steel into the columnar ground improvement body before hardening.

[0021] Also, by holding the upper part of the reinforcing steel with the iron frame member and hooking the engaging portion of the reinforcing steel at the lower end of the hollow member, when dropping the iron frame member and the reinforcing steel into the columnar ground improvement body before hardening, displacement of the reinforcing steel with respect to the iron frame member is suppressed. As a result, displacement of the reinforcing steel with respect to the columnar ground improvement body can be suppressed.

[0022] According to the fifth aspect The steel-reinforced ground improvement body includes a columnar ground improvement body and a rod-shaped or linear reinforcing steel having an engaging portion at the lower part and buried in the columnar ground improvement body.

[0023] The fifth aspect According to the steel-reinforced ground improvement body according to , it includes columnar ground improvement bodies and rod-shaped or linear reinforcing steel bars embedded in the columnar ground improvement bodies.

[0024] Here, the reinforcing steel bar has a hooking portion at the lower part. This hooking portion enhances the pull-out resistance of the reinforcing steel bar. Therefore, the reinforcing effect of the columnar ground improvement body by the reinforcing steel bar can be enhanced.

[0025] Also, when embedding the reinforcing steel bar in the columnar ground improvement body, for example, with the reinforcing steel bar inserted into a hollow member attached to a steel frame member, hook the hooking portion of the reinforcing steel bar to the lower end of the hollow member, and hold the upper part of the reinforcing steel bar by the steel frame member. In this state, drop the steel frame member into the columnar ground improvement body before hardening.

[0026] Next, with the holding of the upper part of the reinforcing steel bar by the steel frame member released, pull up the steel frame member and the hollow member from the columnar ground improvement body before hardening. As a result, the reinforcing steel bar is embedded (left remaining) inside the columnar ground improvement body.

[0027] By hooking the hooking portion of the reinforcing steel bar to the lower end of the hollow member in this way, when dropping the steel frame member and the reinforcing steel bar into the columnar ground improvement body before hardening, the displacement of the reinforcing steel bar relative to the steel frame member is suppressed. As a result, the displacement of the reinforcing steel bar relative to the columnar ground improvement body can be suppressed.

Effect of the Invention

[0028] As described above, according to the present invention, the reinforcing steel bar can be efficiently inserted into the columnar ground improvement body.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0030] Hereinafter, one embodiment will be described with reference to the drawings.

[0031] (Steel Material-Reinforced Ground Improvement Body) In FIG. 1, a steel material-reinforced ground improvement body 20 according to the present embodiment is shown. The steel material-reinforced ground improvement body 20 includes a columnar ground improvement body 22 and a plurality of reinforcing steel materials 24 embedded in the columnar ground improvement body 22. In addition, in FIG. 1, an insertion jig 30 described later is shown by a two-dot chain line.

[0032] (Columnar Improvement Body) The columnar ground improvement body 22 is, for example, connected in a wall shape in the ground and constitutes a retaining wall 10. A subterranean space (including the indoor space of an underground structure) 12 is formed on one side in the thickness direction of the retaining wall 10. Therefore, earth pressure P acts on the retaining wall 10 from the other side in the thickness direction (the side opposite to the subterranean space 12).

[0033] Note that the arrow P appropriately shown in each figure indicates the acting direction of the earth pressure on the retaining wall 10 (columnar ground improvement body 22) and the thickness direction of the retaining wall 10. Further, the arrow W indicates the lateral width direction of the retaining wall 10 (columnar ground improvement body 22).

[0034] The columnar ground improvement body 22 is formed of, for example, hardened soil cement. Specifically, the columnar ground improvement body 22 is formed by injecting a cement-based hardening material such as cement milk from the tip of an excavation auger while excavating the ground with the excavation auger. Then, the excavated soil and the cement-based hardening material are agitated and mixed in the ground, and the formed soil cement is hardened, whereby the columnar ground improvement body 22 is constructed.

[0035] (Reinforcing steel) A plurality of reinforcing steels 24 are embedded inside the columnar ground improvement body 22. The plurality of reinforcing steels 24 are formed of bar-shaped steel materials such as reinforcing bars and steel bars, and are embedded along the axial direction (vertical direction) of the columnar ground improvement body 22. As shown in FIG. 2, these reinforcing steels 24 are dropped into the columnar ground improvement body 22 (soil cement) before hardening together with a steel frame member 40 described later.

[0036] As shown in FIG. 1, the plurality of reinforcing steels 24 are arranged at intervals in the lateral width direction of the columnar ground improvement body 22. Further, the plurality of reinforcing steels 24 are embedded closer to the acting side of the earth pressure P (the side opposite to the underground space 12) with respect to the center of the columnar ground improvement body 22. Thereby, the plurality of reinforcing steels 24 are enabled to efficiently bear the bending due to the earth pressure P.

[0037] Note that the reinforcing steel 24 is preferably a deformed reinforcing bar or a deformed steel bar from the viewpoint of enhancing the adhesion (integrality) with the columnar ground improvement body 22. Further, the reinforcing steel 24 is not limited to bar-shaped steel materials such as reinforcing bars, and may be, for example, a linear steel material such as a PC steel wire.

[0038] As shown in FIG. 4, a cap 26 is provided at the lower end of the reinforcing steel material 24. The cap 26 is formed to taper as it moves away from the reinforcing steel material 24. In other words, the cap 26 is formed to taper as it moves away from the lower end 50L of the hollow pipe 50 in a state where it is attached to the reinforcing steel material 24 inserted into the hollow pipe 50 described later.

[0039] Specifically, the cap 26 is formed in a frustum shape by metal, resin, or the like, and its bottom surface 26A is fixed to the lower end of the reinforcing steel material 24 by welding, adhesion, or the like. This makes it easier to drop the cap 26 and the reinforcing steel material 24 into the columnar ground improvement body 22 before hardening described later. Further, the cap 26 is formed so as to be caught by the lower end 50L of the hollow pipe 50 as described later.

[0040] Note that the hollow pipe 50 is an example of a hollow member. Further, the cap 26 is an example of a catching portion.

[0041] (Insertion jig) Next, the configuration of the insertion jig used in the construction method of the steel material-reinforced ground improvement body according to the present embodiment will be described.

[0042] As shown in FIGS. 2 and 3, the insertion jig 30 includes a steel frame member 40, a plurality of hollow pipes 50, and a plurality of holders 60. In the following description, unless otherwise specified, each component of the insertion jig 30 will be described based on a state where the material axis direction of the steel frame member 40 is the vertical direction (axial direction).

[0043] (Steel frame member) The steel frame member 40 functions as a weight for dropping the plurality of reinforcing steel materials 24 into the columnar ground improvement body 22 before hardening while holding the plurality of reinforcing steel materials 24. The steel frame member 40, together with the plurality of reinforcing steel materials 24, is dropped into the columnar ground improvement body 22 before hardening and is temporarily embedded along the axial direction of the columnar ground improvement body 22 inside the columnar ground improvement body 22. Thereafter, the steel frame member 40 is pulled out from the columnar ground improvement body 22 before hardening.

[0044] As shown in FIG. 3, the steel frame member 40 is formed of an H-shaped steel. The steel frame member 40 has a pair of flanges 42 facing each other and a web 44 connecting the pair of flanges 42.

[0045] (Hollow pipe) As shown in FIG. 1, the steel frame member 40 is dropped into the columnar ground improvement body 22 with the lateral direction of the steel frame member 40 being the lateral direction of the retaining wall 10 (columnar ground improvement body 22). As shown in FIG. 2, a plurality of hollow pipes 50 are attached to one surface of the web 44 of the steel frame member 40.

[0046] The plurality of hollow pipes 50 extend in the material axis direction of the steel frame member 40 and are arranged from the lower part to the upper part of the steel frame member 40. Note that the upper end side of the web 44 of the steel frame member 40 is a mounting space for mounting a vibrator 80 described later.

[0047] As shown in FIG. 3, the plurality of hollow pipes 50 are, for example, cylindrical pipes made of metal. The plurality of hollow pipes 50 are arranged along the material axis direction of the steel frame member 40 and are spaced apart in the lateral direction of the steel frame member 40 (the facing direction of the pair of flanges 42). These hollow pipes 50 are attached to the surface of the web 44 by welding. Note that the symbol M indicates the welding metal.

[0048] As shown in FIG. 5(A), the inner diameter B of the hollow pipe 50 is larger than the diameter D of the reinforcing steel material 24 1 The reinforcing steel material 24 is inserted into the hollow pipe 50. Also, the inner diameter B of the hollow pipe 50 is smaller than the diameter D of the bottom surface 26A of the cap 26 2

[0049] ​As a result, with the reinforcing steel material 24 inserted inside the hollow tube 50, the cap 26 is hooked onto the lower end 50L of the hollow tube 50, and the opening on the lower end 50L side of the hollow tube 50 (hereinafter also referred to as the "lower end opening") 52 is blocked by the cap 26. Therefore, when inserting the insertion jig 30 into the columnar ground improvement body 22 before hardening, the inflow of soil cement into the lower end opening 52 of the hollow tube 50 is suppressed.

[0050] Here, with the reinforcing steel material 24 arranged concentrically with the hollow tube 50, a gap G is formed between the outer peripheral surface of the reinforcing steel material 24 and the inner peripheral surface of the hollow tube 50. Therefore, within the range of the gap G, the reinforcing steel material 24 and the cap 26 move radially with respect to the hollow tube 50, and thus the lower end opening 52 of the hollow tube 50 may be opened.

[0051] As a countermeasure in this embodiment, as shown in FIG. 5(B), the size of the cap 26 is set so that the lower end opening 52 of the hollow tube 50 is not opened even if the cap 26 is displaced radially from concentricity with the hollow tube 50. Specifically, the diameter D of the bottom surface 26A of the cap 26 2 / 2 is set to exceed the inner diameter B of the hollow tube 50 - the diameter D of the reinforcing steel material 24 1 / 2 (D 2 / 2 > B - D 1 / 2).

[0052] (Holder) As shown in FIG. 2, with the cap 26 hooked onto the lower end 50L of the hollow tube 50, the upper end portion 24U of the reinforcing steel material 24 protrudes from the opening on the upper end side of the hollow tube 50 (hereinafter also referred to as the "upper end opening"). Further, a holder 60 is provided on the upper part of the hollow tube 50.

[0053] As shown in Fig. 6, the retainer 60 has a pair of screw members 62. The pair of screw members 62 are respectively tightened into screw holes 54 formed on both radial sides of the outer peripheral surface of the hollow tube 50. By sandwiching the upper part of the reinforcing steel member 24 from both sides in the radial direction with this pair of screw members 62, the upper part of the reinforcing steel member 24 is detachably held by the steel frame member 40 via the hollow tube 50.

[0054] (Construction method of steel-reinforced ground improvement body) Next, an example of the construction method of the steel-reinforced ground improvement body according to this embodiment will be described.

[0055] (Mounting process) First, the mounting process of attaching the reinforcing steel member 24 to the insertion jig 30 will be described. Fig. 7 shows a state in which the steel frame member 40 of the insertion jig 30 is laid on the ground.

[0056] In this state, the reinforcing steel member 24 is inserted into the lower end openings 52 of the plurality of hollow tubes 50 from the upper end side, and the cap 26 provided at the lower end portion of the reinforcing steel member 24 is hooked on the lower end 50L of the hollow tube 50. Thereby, the lower end opening 52 of the hollow tube 50 is blocked by the cap 26.

[0057] Next, as shown in Fig. 6, the upper part of the reinforcing steel member 24 is held by the retainer 60 provided on the upper part of the hollow tube 50. Specifically, the pair of screw members 62 attached to the upper part of the hollow tube 50 are tightened, and the upper part of the reinforcing steel member 24 is sandwiched from both sides between the pair of screw members 62. Thereby, the reinforcing steel member 24 is held by the pair of screw members 62.

[0058] (Positioning process) Next, the positioning process of the reinforcing steel member 24 with respect to the columnar ground improvement body 22 will be described. Fig. 2 shows the columnar ground improvement body 22 (soil cement) before hardening formed in the ground.

[0059] On the improved columnar ground 22, a steel plate 70 is laid. A circular through-hole 72 is formed in the central part of the steel plate 70, and the improved columnar ground 22 is exposed from this through-hole 72. On the outer peripheral part of this steel plate 70, a pair of guide members 74 are installed. Note that the steel plate 70 may be provided as necessary and can be omitted. Also, the guide members 74 are not necessarily required to be two in number, and one may be sufficient.

[0060] The pair of guide members 74 are formed of, for example, H-shaped steel. Also, the pair of guide members 74 are arranged substantially parallel to both sides of the improved columnar ground 22. Further, the pair of guide members 74 are arranged with the guide surfaces of the respective flanges 74A facing each other.

[0061] In this state, a vibratory hammer 80 or the like is attached to the upper end side of the web 44 of the steel frame member 40. Then, while lifting the steel frame member 40 by a crane or the like (not shown), the lower end side of the steel frame member 40 is inserted between the flanges 74A (guide surfaces) of the pair of guide members 74. Thereby, the steel frame member 40 is positioned with respect to the improved columnar ground 22, and a plurality of reinforcing steel bars 24 are positioned with respect to the improved columnar ground 22. At this time, the verticality of the steel frame member 40 is appropriately adjusted.

[0062] (Falling-in process) Next, the falling-in process of dropping the insertion jig 30 and the reinforcing steel bars 24 into the improved columnar ground 22 before hardening will be described. In the falling-in process, as described above, with the insertion jig 30 positioned with respect to the improved columnar ground 22, the vibratory hammer 80 or the like attached to the upper end side of the web 44 of the steel frame member 40 is operated, and the steel frame member 40 is vibrated in the vertical direction by the vibratory hammer 80.

[0063] As a result, the insertion jig 30 and the reinforcing steel material 24 are dropped (driven) into the inside of the columnar ground improvement body 22 before hardening while being guided by the pair of guide members 74. Further, the lower end opening 52 of each hollow tube 50 is blocked by the cap 26 of the reinforcing steel material 24. Thereby, the inflow of the soil cement into the hollow tube 50 from the lower end opening 52 of the hollow tube 50 is suppressed.

[0064] Next, when the lower end portion of the steel frame member 40 reaches a predetermined depth, the vibrator 80 is stopped. The retainer 60 provided at the upper portion of each hollow tube 50 is left exposed on the ground without being dropped into the inside of the columnar ground improvement body 22.

[0065] (Pull-up process) Next, a pull-up process of pulling up the insertion jig 30 from the columnar ground improvement body 22 before hardening will be described. In the pull-up process, first, as shown in FIG. 6, the holding of the reinforcing steel material 24 by the retainer 60 is released. Specifically, the pair of screw members 62 attached to the upper portion of each hollow tube 50 are loosened, and the clamping of the upper portion of the reinforcing steel material 24 by the pair of screw members 62 is released.

[0066] Next, as shown in FIG. 8, the vibrator 80 is operated, and the insertion jig 30 is pulled up while vibrating the upper end side of the steel frame member 40. As a result, the insertion jig 30 is pulled out from the columnar ground improvement body 22 before hardening, and a plurality of reinforcing steel materials 24 are left (embedded) inside the columnar ground improvement body 22.

[0067] Further, the insertion jig 30 is pulled up while vibrating the upper end side of the steel frame member 40 by the vibrator 80. As a result, the soil cement flows into the hole formed in the columnar ground improvement body 22 as the insertion jig 30 is pulled up, the hole is filled, and the soil cement is compacted. Therefore, the soil cement easily adheres to the reinforcing steel material 24.

[0068] Thereafter, by hardening the columnar ground improvement body 22, the steel material-reinforced ground improvement body 20 is formed.

[0069] In addition, when reusing the insertion jig 30, after washing away the soil cement adhering to the insertion jig 30 with the insertion jig 30 lying on the ground, the above attachment process is performed.

[0070] Here, the construction method of the steel-reinforced ground improvement body according to the present embodiment is not limited to the above procedure and can be appropriately changed. For example, in the present embodiment, in the pulling-up process, the holding of the reinforcing steel 24 by the holder 60 was released. However, the holder 60 only needs to hold the reinforcing steel 24 so that the reinforcing steel 24 does not fall from the insertion jig 30. After the reinforcing steel 24 lands on the columnar ground improvement body 22 before hardening, it is not necessarily required to hold the reinforcing steel 24.

[0071] Therefore, for example, in the dropping process, after the reinforcing steel 24 lands on the columnar ground improvement body 22, the holding of the reinforcing steel 24 by the holder 60 may be released, and then the reinforcing steel 24 may be further dropped into the columnar ground improvement body 22 before hardening.

[0072] In addition, in the present embodiment, the holder 60 is not dropped into the columnar ground improvement body 22. However, after releasing the holding of the reinforcing steel 24 by the holder 60, the upper end portions of the holder 60 and the reinforcing steel 24 may be dropped into the columnar ground improvement body 22 before hardening.

[0073] In addition, in the present embodiment, in the dropping process and the pulling-up process, the steel frame member 40 was vibrated by the vibrator 80. However, the vibrator 80 only needs to vibrate the steel frame member 40 as necessary and can be appropriately omitted.

[0074] (Effect) Next, the effects of the present embodiment will be described.

[0075] As described above, in the present embodiment, in the dropping step, the reinforcing steel material 24 is dropped into the columnar ground improvement body 22 before hardening together with the insertion jig 30. Thereby, in the present embodiment, the reinforcing steel material 24 can be efficiently inserted into the columnar ground improvement body 22 as compared with the case where only the reinforcing steel material 24 is dropped into the columnar ground improvement body 22 before hardening.

[0076] Further, the reinforcing steel material 24 is inserted into a hollow tube 50 attached to the steel frame member 40. The upper portion of the reinforcing steel material 24 is held by a holder 60 provided at the upper portion of the hollow tube 50. Thereby, when the insertion jig 30 is lifted by a crane or the like, the fall of the reinforcing steel material 24 is suppressed.

[0077] Furthermore, by inserting the reinforcing steel material 24 into the hollow tube 50, when the steel frame member 40 is vibrated by a vibrator 80, the reinforcing steel material 24 is prevented from flailing. Also, when the steel frame member 40 and the reinforcing steel material 24 are dropped into the columnar ground improvement body 22 before hardening, the displacement of the reinforcing steel material 24 with respect to the steel frame member 40 is suppressed. As a result, the displacement of the reinforcing steel material 24 with respect to the columnar ground improvement body 22 can be suppressed.

[0078] Also, a cap 26 is provided at the lower end portion of the reinforcing steel material 24. By hooking this cap 26 on the lower end 50L of the hollow tube 50, when the steel frame member 40 and the reinforcing steel material 24 are dropped into the columnar ground improvement body 22 before hardening, the displacement of the reinforcing steel material 24 with respect to the steel frame member 40 is further suppressed.

[0079] Also, the lower end opening 52 of the hollow tube 50 is closed by a cap 26 provided at the lower end portion of the reinforcing steel material 24. Thereby, in the dropping step, when the insertion jig 30 and the reinforcing steel material 24 are dropped into the columnar ground improvement body 22 before hardening, the inflow of the unhardened soil cement into the lower end opening 52 inside the hollow tube is suppressed. As a result, the adhesion of the reinforcing steel material 24 to the inner peripheral surface of the hollow tube 50 via the unhardened soil cement is suppressed.

[0080] Therefore, when the steel frame member 40 and the hollow pipe 50 are lifted from the columnar ground improvement body 22 before curing in the lifting process, it is suppressed that the reinforcing steel material 24 is lifted together with the hollow pipe 50. Therefore, the reinforcing steel material 24 can be more reliably embedded (left) in the columnar ground improvement body 22 before curing.

[0081] Here, as shown in FIG. 5(B), when the reinforcing steel material 24 and the cap 26 move in the radial direction with respect to the hollow pipe 50, the lower end opening 52 of the hollow pipe 50 may be opened. In particular, in the present embodiment, as described above, while vibrating the upper end side of the steel frame member 40 with the vibrator 80, the insertion jig 30 and the reinforcing steel material 24 are dropped into the columnar ground improvement body 22 before curing. Therefore, it is easy for the reinforcing steel material 24 and the cap 26 to move in the radial direction with respect to the hollow pipe 50.

[0082] As a countermeasure in the present embodiment, even if the reinforcing steel material 24 and the cap 26 move in the radial direction with respect to the hollow pipe 50, the diameter D of the bottom surface 26A of the cap 26 is set so that the lower end opening 52 of the hollow pipe 50 is not opened. 1 More specifically, the diameter D of the bottom surface 26A of the cap 26 2 / 2 is set to exceed the inner diameter B of the hollow pipe 50 - the diameter D of the reinforcing steel material 24 1 / 2) (D 2 / 2 > B - D 1 / 2).

[0083] Thereby, in the dropping process, when the insertion jig 30 and the reinforcing steel material 24 are dropped into the columnar ground improvement body 22 before curing, it is possible to more reliably suppress the inflow of the uncured soil cement into the lower end opening 52 in the hollow pipe 50.

[0084] Furthermore, the cap 26 is formed in a frustum shape that tapers as it moves away from the lower end 50L of the hollow pipe 50. Thereby, in the dropping process, it becomes easier to drop the reinforcing steel material 24 into the columnar ground improvement body 22 before curing. Therefore, the reinforcing steel material 24 can be inserted into the columnar ground improvement body 22 more efficiently.

[0085] Moreover, by providing the cap 26 at the lower end of the reinforcing steel material 24, the pull-out resistance of the reinforcing steel material 24 can be increased. Therefore, the reinforcing effect of the columnar ground improvement body 22 by the reinforcing steel material 24 can be enhanced.

[0086] (Modification example) Next, a modification example of the above embodiment will be described.

[0087] In the above embodiment, as shown in FIG. 1, a plurality of reinforcing steel materials 24 are arranged at intervals in the lateral width direction of the retaining wall 10, and are buried closer to the side where the earth pressure P acts (the side opposite to the underground space 12) with respect to the center of the columnar ground improvement body 22. However, the embedding position of the reinforcing steel material 24 with respect to the columnar ground improvement body 22 can be appropriately changed.

[0088] For example, in the modification example shown in FIG. 9, a plurality of reinforcing steel materials 24 are buried on both sides in the thickness direction (arrow P direction) of the columnar ground improvement body 22. In this case, for example, the insertion jig 30 is dropped in twice with respect to the columnar ground improvement body 22 before hardening.

[0089] Also, for example, in the modification example shown in FIG. 10, a plurality of reinforcing steel materials 24 are arranged in two rows in the lateral width direction of the retaining wall 10. The plurality of reinforcing steel materials 24 in each row are arranged at intervals in the thickness direction of the retaining wall 10. These reinforcing steel materials 24 are inserted into a plurality of hollow tubes 50 attached to both surfaces of the web 44 of the steel frame member 40, for example. Further, the steel frame member 40 is dropped into the columnar ground improvement body 22 before hardening with the lateral width direction as the thickness direction of the retaining wall 10.

[0090] Also, in the modification example shown in FIG. 10, the hollow tube 50 is attached to the outer surface of the flange 42 of the steel frame member 40. By attaching the hollow tube 50 to the outer surface of the flange 42 in this way, the reinforcing steel material 24 can be buried in the outer peripheral portion of the columnar ground improvement body 22. Although not shown, the hollow tube 50 can also be attached to the inner surface of the flange 42 of the steel frame member 40.

[0091] In the above-described embodiment, a plurality of reinforcing steel materials 24 are embedded in the columnar ground improvement body 22. However, at least one reinforcing steel material 24 can be embedded in the columnar ground improvement body 22.

[0092] In the above-described embodiment, the reinforcing steel material 24 is held by sandwiching the reinforcing steel material 24 from both sides in the radial direction by a pair of screw members 62 of the holder 60. However, for example, as shown in FIG. 11(A), a plurality of screw holes 54 are formed on the front side (the side opposite to the steel frame member 40) of the hollow tube 50, and the reinforcing steel material 24 is pressed against the inner peripheral surface on the back side of the hollow tube 50 by a plurality of screw members 62 screwed into these screw holes 54, whereby the reinforcing steel material 24 may be held.

[0093] By forming the screw holes 54 on the front side of the hollow tube 50 in this way, it becomes easier to screw the screw members 62 into the screw holes 54. Further, as shown in FIG. 11(B), by shifting the screw holes 54 (see FIG. 11(A)) and the screw members 62 in the vertical direction, it becomes even easier to screw the screw members 62 into the screw holes 54.

[0094] The holder 60 of the above-described embodiment has a pair of screw members 62. However, the holder is not limited to a pair of screw members, and may be, for example, a nut member placed (engaged) on the upper end of the hollow tube 50. The reinforcing steel material 24 is detachably held by the nut member by screwing a screw portion provided at the upper end portion of the reinforcing steel material 24 into the nut member.

[0095] Further, without using a holder, the upper portion of the reinforcing steel material 24 may be welded to the upper end portion of the hollow tube 50 or the steel frame member 40, whereby the reinforcing steel material 24 is held by the steel frame member 40. In this case, the holding of the reinforcing steel material 24 by the steel frame member 40 is released by cutting the welded portion and the upper portion of the reinforcing steel material 24.

[0096] In the above-described embodiment, the hollow tube 50 extends from the lower part to the upper part of the steel frame member 40. However, for example, a short hollow tube (lower hollow tube) may be attached to the lower part of the steel frame member 40, and a short hollow tube (upper hollow tube) may be attached to the upper part of the steel frame member 40, and the reinforcing steel material 24 may be inserted into these lower hollow tube and upper hollow tube.

[0097] In the above-described embodiment, the hollow member is the hollow tube 50. However, the hollow member may be, for example, a plurality of ring-shaped members that are attached at intervals in the material axis direction of the steel frame member 40 and into which the reinforcing steel material 24 is inserted. In this case, a cap 26 is hooked on the lower end of the lowermost ring-shaped member among the plurality of ring-shaped members.

[0098] In the above-described embodiment, the cap 26 is formed in a frustum of a cone shape. However, the shape of the cap 26 can be changed as appropriate, and for example, a tapered shape such as a conical shape, a frustum of a pyramid shape, or a pyramid shape may be used. Further, the cap 26 is not limited to a tapered shape, and for example, a cylindrical shape or a polygonal column shape may be used.

[0099] Furthermore, the hooking portion is not limited to the cap 26 that closes the lower end opening 52 of the hollow tube 50. The hooking portion only needs to be able to be hooked on at least the lower end 50L of the hollow tube 50, and for example, a U-shaped hook or the like may be used.

[0100] In the above-described embodiment, the cap 26 is provided at the lower end portion of the reinforcing steel material 24. However, the cap 26 is not limited to the lower end portion of the reinforcing steel material 24, and for example, it may be provided at the lower part of the reinforcing steel material 24.

[0101] In the above-described embodiment, the steel frame member 40 is formed of H-shaped steel. However, the steel frame member 40 is not limited to H-shaped steel, and for example, it may be round steel pipe, square steel pipe, C-shaped steel, or the like.

[0102] In addition, in the above-described embodiment, the retaining wall 10 is constituted by the steel-reinforced ground improvement body 20. However, the steel-reinforced ground improvement body 20 is not limited to the retaining wall 10, and for example, it may constitute a lattice-shaped ground improvement body or the like that is formed in a lattice shape in plan view and suppresses the liquefaction of the liquefied layer.

[0103] As described above, one embodiment of the present invention has been described. However, the present invention is not limited to such an embodiment, and one embodiment and various modifications may be used in appropriate combination, and of course, the present invention can be implemented in various modes without departing from the gist of the present invention.

Explanation of Reference Numerals

[0104] 20 Steel-reinforced ground improvement body 22 Columnar ground improvement body 24 Reinforcing steel 26 Cap (hanging portion) 30 Insertion jig 40 Steel frame member 50 Hollow pipe (hollow member) 50L Lower end (lower end of hollow member) 52 Opening (opening on the lower end side of hollow member)

Claims

1. Insert a rod-shaped or wire-shaped reinforcing steel bar having a hooking portion that catches on the lower end of a hollow member attached to a steel frame member into the hollow member, and while holding the upper portion of the reinforcing steel bar in the holding portion of the steel frame member, a dropping step of dropping the steel frame member into a columnar ground improvement body before hardening; A pulling-up step of pulling up the steel frame member and the hollow member from the columnar ground improvement body before hardening with the holding of the upper portion of the reinforcing steel bar by the holding portion released; A construction method of a steel bar-reinforced ground improvement body comprising the above.

2. The hollow member is a hollow pipe extending in the material axis direction of the steel frame member, The hooking portion closes the opening on the lower end side of the hollow pipe while being hooked on the lower end of the hollow pipe, The construction method of the steel bar-reinforced ground improvement body according to Claim 1.

3. The hooking portion tapers as it moves away from the lower end of the hollow member, The construction method of the steel bar-reinforced ground improvement body according to Claim 1 or Claim 2.

4. A steel frame member that holds the upper portion of a rod-shaped or wire-shaped reinforcing steel bar having a hooking portion in a holding portion and is dropped into a columnar ground improvement body before hardening together with the reinforcing steel bar; A hollow member attached to the steel frame member and having the hooking portion hooked on the lower end with the reinforcing steel bar inserted therein; An insertion jig comprising the above.

Images