JP7687594B2 - Construction method of steel-reinforced ground improvement body, insertion jig, and steel-reinforced ground improvement body - Google Patents

Description

The present invention relates to a construction method for steel-reinforced ground improvement bodies, an insertion jig, and steel-reinforced ground improvement bodies.

Retaining walls are known in which reinforcing bars are embedded in columnar ground improvement bodies (see, for example, Patent Documents 1 and 2). Retaining walls are also known in which reinforcing steel materials such as reinforcing bars are embedded in columnar ground improvement bodies (soil cement columns) (see, for example, Patent Documents 3 and 4).

JP 2001-182055 A JP 2020-033822 A Japanese Unexamined Patent Publication No. 3-191113 JP 2020-033821 A

In the technology disclosed in Patent Document 4, a steel rod with a male thread formed on its outer periphery is used as the reinforcing steel material. This steel rod is inserted into the columnar ground improvement body by a feed screw mechanism. As a result, the technology disclosed in Patent Document 4 makes it possible to insert lightweight reinforcing steel materials such as steel rods into the ground improvement body.

However, there is room for further improvement in order to efficiently insert reinforcing steel into columnar ground improvement structures.

Taking the above facts into consideration, the present invention aims to efficiently insert reinforcing steel into columnar ground improvement bodies.

The construction method of the steel-reinforced ground improvement body of the first embodiment comprises a dropping process in which a rod-shaped or wire-shaped reinforcing steel having a hooking portion that hooks onto the lower end of a hollow member attached to a steel member is inserted into the hollow member and, with the upper part of the reinforcing steel held by the steel member, the steel member is dropped into the unhardened columnar ground improvement body, and a lifting process in which, with the hold of the upper part of the reinforcing steel by the steel member released, the steel member and the hollow member are lifted up from the unhardened columnar ground improvement body.

According to the construction method of the steel-reinforced ground improvement body of the first aspect , the rod-shaped or wire-shaped reinforcing steel has a hook portion that can be hooked onto the lower end of the hollow member attached to the steel frame member. Then, in the dropping step, the reinforcing steel is inserted into the hollow member, and the steel frame member is dropped into the columnar ground improvement body before hardening while the upper part of the reinforcing steel is held by the steel frame member.

Next, in the lifting process, the steel members and hollow members are lifted up from the columnar ground improvement body before hardening, with the upper part of the reinforcing steel material being released from the steel members. This leaves the reinforcing steel material buried (left behind) inside the columnar ground improvement body.

In this way, in the present invention, by dropping the reinforcing steel material together with the steel frame members into the columnar ground improvement body before hardening in the dropping process, the reinforcing steel material can be inserted into the columnar ground improvement body more efficiently than when only the reinforcing steel material is dropped into the columnar ground improvement body before hardening.

In addition, by holding the upper part of the reinforcing steel material with the steel frame member and hooking the hook part of the reinforcing steel material on the lower end of the hollow member, the reinforcing steel material is prevented from shifting out of position relative to the steel frame member when the steel frame member and the reinforcing steel material are dropped into the columnar ground improvement body before hardening. As a result, it is possible to prevent the reinforcing steel material from shifting out of position relative to the columnar ground improvement body.

The second aspect of the construction method for a steel-reinforced ground improvement body is the same as the first aspect of the construction method for a steel-reinforced ground improvement body, in which the hollow member is a hollow tube extending in the material axial direction of the steel member, and the hook portion, when hooked onto the lower end of the hollow tube, blocks the opening on the lower end side of the hollow tube.

According to the construction method of the steel-reinforced ground improvement body of the second aspect , the hollow member is a hollow tube extending in the axial direction of the steel frame member. A reinforcing steel material is inserted into this hollow tube. In addition, with the reinforcing steel material inserted into the hollow tube, a hook portion of the reinforcing steel material is hooked onto the lower end of the hollow tube. In this state, the opening on the lower end side of the hollow tube is closed by the hook portion.

This prevents unhardened soil (soil cement, etc.) from flowing into the opening at the lower end of the hollow pipe when the steel frame members, hollow pipe, and reinforcing steel are dropped into the unhardened columnar ground improvement body during the dropping process. As a result, adhesion of the reinforcing steel to the inner surface of the hollow pipe via the unhardened soil is prevented.

Therefore, during the lifting process, when the steel members and hollow members are lifted from the columnar ground improvement body before hardening, the reinforcing steel material is prevented from being lifted together with the hollow members. This allows the reinforcing steel material to be more reliably embedded (left in place) inside the columnar ground improvement body.

The construction method for a steel-reinforced ground improvement body of the third aspect is the construction method for a steel-reinforced ground improvement body of the first or second aspect, wherein the hook portion tapers away from the lower end of the hollow member.

According to the construction method of the steel-reinforced ground improvement body of the third aspect , the hook portion tapers away from the lower end of the hollow member. This makes it easier to drop the reinforcing steel into the columnar ground improvement body before hardening in the dropping step. Therefore, the reinforcing steel can be inserted into the columnar ground improvement body more efficiently.

The insertion jig of the fourth aspect comprises a steel frame member which holds the upper part of a rod-shaped or wire-shaped reinforcing steel material having a hooking portion and is dropped into the columnar ground improvement body before hardening together with the reinforcing steel material, and a hollow member which is attached to the steel frame member and has the hooking portion hooked to its lower end with the reinforcing steel material inserted.

According to the insertion jig of the fourth aspect , the steel frame member holds the upper part of the rod-shaped or wire-shaped reinforcing steel material having a hook portion, and is dropped into the columnar ground improvement body together with the reinforcing steel material before hardening. A hollow member is attached to this steel frame member. The reinforcing steel material is inserted into the hollow member. In this state, the hook portion of the reinforcing steel material is hooked onto the lower end of the hollow tube.

Here, by dropping the steel frame members together with the reinforcing steel into the columnar ground improvement body before hardening, the reinforcing steel can be inserted into the columnar ground improvement body more efficiently than when only the reinforcing steel is dropped into the columnar ground improvement body before hardening.

In addition, by holding the upper part of the reinforcing steel material with the steel member and hooking the hook part of the reinforcing steel material on the lower end of the hollow member, the reinforcing steel material is prevented from shifting out of position relative to the steel member when the steel member and the reinforcing steel material are dropped into the columnar ground improvement body before hardening. As a result, it is possible to prevent the reinforcing steel material from shifting out of position relative to the columnar ground improvement body.

The steel-reinforced ground improvement body of the fifth aspect comprises a columnar ground improvement body, and a rod-shaped or wire-shaped reinforcing steel material having a hook portion at the bottom and embedded in the columnar ground improvement body.

The steel-reinforced ground improvement body of the fifth aspect comprises a columnar ground improvement body and rod-shaped or wire-shaped reinforcing steel embedded in the columnar ground improvement body.

Here, the reinforcing steel has a hook at the bottom. This hook increases the pull-out resistance of the reinforcing steel. Therefore, the reinforcing effect of the columnar ground improvement body using the reinforcing steel can be improved.

When embedding reinforcing steel in a columnar ground improvement body, for example, the reinforcing steel is inserted into a hollow member attached to a steel frame member, the hook portion of the reinforcing steel is hooked onto the lower end of the hollow member, and the upper portion of the reinforcing steel is held by the steel frame member. In this state, the steel frame member is dropped into the columnar ground improvement body before hardening.

Next, with the steel member releasing the upper part of the reinforcing steel material, the steel member and hollow member are pulled up from the columnar ground improvement body before hardening. This leaves the reinforcing steel material buried (left in place) inside the columnar ground improvement body.

By hooking the hook portion of the reinforcing steel material onto the lower end of the hollow member in this way, the reinforcing steel material is prevented from shifting out of position relative to the steel member when the steel member and reinforcing steel material are dropped into the columnar ground improvement body before hardening. As a result, it is possible to prevent the reinforcing steel material from shifting out of position relative to the columnar ground improvement body.

As described above, according to the present invention, reinforcing steel can be efficiently inserted into columnar ground improvement bodies.

FIG. 2 is a cross-sectional plan view showing a steel-reinforced ground improvement body according to one embodiment. FIG. 2 is a vertical cross-sectional view showing the construction process of the steel-reinforced ground improvement body shown in FIG. 1. This is a cross-sectional view taken along line 3-3 in Figure 2. FIG. 3 is an enlarged elevational view of the cap shown in FIG. 2 . 5A is a cross-sectional view taken along line 5-5 in FIG. 4, and FIG. 5B is a cross-sectional view corresponding to FIG. 5A, showing a state in which the reinforcing steel material and the cap have been moved radially relative to the hollow tube. This is a cross-sectional view taken along line 6-6 in Figure 2. FIG. 3 is a vertical cross-sectional view showing a state in which the insertion jig shown in FIG. 2 is laid on the ground. FIG. 2 is a vertical cross-sectional view showing the construction process of the steel-reinforced ground improvement body shown in FIG. 1. FIG. 2 is a cross-sectional plan view showing a modified example of a steel-reinforced ground improvement body according to one embodiment. FIG. 2 is a cross-sectional plan view showing a modified example of a steel-reinforced ground improvement body according to one embodiment. 11A is a plan cross-sectional view showing a modified example of the holder in one embodiment, and FIG. 11B is a cross-sectional view taken along line 11B-11B in FIG. 11A.

Below, one embodiment will be described with reference to the drawings.

(Steel reinforcement ground improvement body)
Fig. 1 shows a steel-reinforced ground improvement body 20 according to this embodiment. The steel-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 Fig. 1, an insertion jig 30, which will be described later, is shown by a two-dot chain line.

(Columnar improved body)
The columnar ground improvement bodies 22 are connected in the ground in a wall-like manner, for example, to form an earth retaining wall 10. An underground space (including the indoor space of the underground structure) 12 is formed on one side in the thickness direction of the earth retaining wall 10. Therefore, earth pressure P acts on the earth retaining wall 10 from the other side in the thickness direction (the side opposite to the underground space 12).

In addition, the arrow P shown appropriately in each figure indicates the direction of earth pressure acting on the retaining wall 10 (columnar ground improvement body 22) and the thickness direction of the retaining wall 10. Furthermore, the arrow W indicates the width direction of the retaining wall 10 (columnar ground improvement body 22).

The columnar ground improvement body 22 is formed, for example, from hardened soil cement. Specifically, the columnar ground improvement body 22 is created by injecting a cement-based hardening material such as cement milk into the ground from the tip of an excavation auger while excavating the ground with the excavation auger. The excavated soil and the cement-based hardening material are then stirred and mixed underground, and the formed soil cement is allowed to harden, thereby creating the columnar ground improvement body 22.

(Reinforcing steel)
A plurality of reinforcing steel materials 24 are embedded inside the columnar ground improvement body 22. The plurality of reinforcing steel materials 24 are formed of bar-shaped steel materials such as reinforcing bars and steel bars, and are embedded along the axial direction (up-down direction) of the columnar ground improvement body 22. As shown in Fig. 2, these reinforcing steel materials 24 are dropped into the columnar ground improvement body 22 (soil cement) before hardening together with steel members 40 described later.

As shown in FIG. 1, the multiple reinforcing steel materials 24 are spaced apart in the width direction of the columnar ground improvement body 22. The multiple reinforcing steel materials 24 are also buried closer to the side on which the earth pressure P acts (the side opposite the underground space 12) than the center of the columnar ground improvement body 22. This allows the multiple reinforcing steel materials 24 to efficiently bear the bending caused by the earth pressure P.

In addition, from the viewpoint of increasing adhesion (integrity) with the columnar ground improvement body 22, the reinforcing steel material 24 is preferably a deformed reinforcing bar or a deformed steel rod. Furthermore, the reinforcing steel material 24 is not limited to a rod-shaped steel material such as a reinforcing bar, but may be a linear steel material such as a PC steel wire.

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 so as to taper away from the reinforcing steel material 24. In other words, the cap 26 is formed so as to taper away from the lower end 50L of the hollow tube 50 when attached to the reinforcing steel material 24 inserted inside the hollow tube 50 described below.

Specifically, the cap 26 is formed into a truncated cone shape using metal or resin, etc., and its bottom surface 26A is fixed to the lower end of the reinforcing steel material 24 by welding, adhesive, etc. This makes it easier to drop the cap 26 and the reinforcing steel material 24 into the columnar ground improvement body 22 before hardening, which will be described later. In addition, the cap 26 is formed so as to hook onto the lower end 50L of the hollow tube 50, as will be described later.

The hollow tube 50 is an example of a hollow member. The cap 26 is an example of a hook portion.

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

2 and 3, the insertion jig 30 includes a steel member 40, a number of hollow tubes 50, and a number of retainers 60. In the following explanation, unless otherwise specified, each component of the insertion jig 30 will be explained based on the state in which the material axis direction of the steel member 40 is the up-down direction (vertical direction).

(Steel frame members)
The steel frame member 40 holds the multiple reinforcing steel materials 24 and functions as a weight for dropping these reinforcing steel materials 24 into the unhardened columnar ground improvement body 22. The steel frame member 40, together with the multiple reinforcing steel materials 24, is dropped into the unhardened columnar ground improvement body 22 and temporarily embedded inside the columnar ground improvement body 22 along the axial direction of the columnar ground improvement body 22. The steel frame member 40 is then pulled out of the unhardened columnar ground improvement body 22.

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

(hollow tube)
As shown in Fig. 1, the steel member 40 is dropped into the columnar ground improvement body 22 with its width direction being the width direction of the retaining wall 10 (columnar ground improvement body 22). As shown in Fig. 2, a plurality of hollow tubes 50 are attached to one surface of the web 44 of the steel member 40.

The hollow tubes 50 extend in the axial direction of the steel member 40 and are arranged from the bottom to the top of the steel member 40. The upper end side of the web 44 of the steel member 40 is used as an attachment space for attaching the vibrator 80 described below.

As shown in FIG. 3, the hollow tubes 50 are, for example, cylindrical tubes made of metal. The hollow tubes 50 are arranged along the material axis of the steel frame member 40 and spaced apart in the width direction of the steel frame member 40 (the direction in which the pair of flanges 42 face each other). These hollow tubes 50 are attached to the surface of the web 44 by welding. The symbol M indicates weld metal.

5A , the inner diameter B of the hollow tube 50 is larger than the diameter _D1 of the reinforcing steel material 24. The reinforcing steel material 24 is inserted inside the hollow tube 50. The inner diameter B of the hollow tube 50 is also smaller than the diameter _D2 of the bottom surface 26A of the cap 26.

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 (hereinafter also referred to as the "lower end opening") 52 on the lower end 50L side of the hollow tube 50 is blocked by the cap 26. Therefore, when the insertion jig 30 is inserted into the columnar ground improvement body 22 before hardening, soil cement is prevented from flowing into the lower end opening 52 of the hollow tube 50.

When the reinforcing steel material 24 is 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. As a result, the reinforcing steel material 24 and the cap 26 move radially relative to the hollow tube 50 within the range of the gap G, and there is a possibility that the lower end opening 52 of the hollow tube 50 will be opened.

5(B), in this embodiment, the size of the cap 26 is set so that the lower end opening 52 of the hollow tube 50 will not be opened even if the cap 26 is displaced radially from the concentricity of the hollow tube 50. Specifically, the diameter D _2/2 of the bottom surface 26A of the cap 26 is set to exceed the inner diameter B of the hollow tube 50 minus the diameter D _1/2 of the reinforcing steel material 24 (D _2/2 >B-D _1/2 ).

(Holding tool)
2, with the cap 26 hooked onto the lower end 50L of the hollow tube 50, the upper end 24U of the reinforcing steel material 24 protrudes from an opening on the upper end side of the hollow tube 50 (hereinafter also referred to as the "upper end opening"). In addition, a holder 60 is provided on the upper part of the hollow tube 50.

As shown in FIG. 6, the retainer 60 has a pair of screw members 62. The pair of screw members 62 are screwed into screw holes 54 formed on both radial sides of the outer circumferential surface of the hollow tube 50. The pair of screw members 62 clamp the upper part of the reinforcing steel material 24 from both radial sides, so that the upper part of the reinforcing steel material 24 is removably held to the steel frame member 40 via the hollow tube 50.

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

(Installation process)
First, a description will be given of the attachment process for attaching the reinforcing steel material 24 to the insertion jig 30. Fig. 7 shows a state in which the steel frame member 40 of the insertion jig 30 is laid on the ground.

In this state, the reinforcing steel material 24 is inserted from the upper end side into the lower end openings 52 of the multiple hollow tubes 50, and the cap 26 provided at the lower end of the reinforcing steel material 24 is hooked onto the lower end 50L of the hollow tube 50. As a result, the lower end openings 52 of the hollow tubes 50 are blocked by the cap 26.

Next, as shown in FIG. 6, the upper part of the reinforcing steel material 24 is held by a holder 60 provided at the upper part of the hollow tube 50. Specifically, a 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 material 24 is sandwiched between the pair of screw members 62 from both sides. In this way, the reinforcing steel material 24 is held by the pair of screw members 62.

(Positioning process)
Next, a description will be given of a process for positioning the reinforcing steel material 24 relative to the columnar soil improvement body 22. Fig. 2 shows the columnar soil improvement body 22 (soil cement) formed in the ground before hardening.

A steel plate 70 is laid on top of the columnar ground improvement body 22. A circular through hole 72 is formed in the center of the steel plate 70, and the columnar ground improvement body 22 is exposed from this through hole 72. A pair of guide members 74 are installed on the outer periphery of the steel plate 70. Note that the steel plate 70 may be provided as needed and can be omitted. Also, the number of guide members 74 does not necessarily need to be two; one will suffice.

The pair of guide members 74 are formed, for example, from H-shaped steel. The pair of guide members 74 are arranged approximately parallel to each other on both sides of the columnar ground improvement body 22. Furthermore, the pair of guide members 74 are arranged with the guide surfaces of the respective flanges 74A facing each other.

In this state, a vibrator 80 such as a vibrator hammer is attached to the upper end of the web 44 of the steel member 40. Then, the steel member 40 is raised and lifted up by a crane (not shown) and the lower end of the steel member 40 is inserted between the flanges 74A (guide surfaces) of a pair of guide members 74. This positions the steel member 40 relative to the columnar ground improvement body 22, and positions the multiple reinforcing steel members 24 relative to the columnar ground improvement body 22. At this time, the verticality of the steel member 40 is appropriately adjusted.

(Dropping process)
Next, a description will be given of the dropping process in which the insertion jig 30 and the reinforcing steel material 24 are dropped into the columnar ground improvement body 22 before hardening. In the dropping process, as described above, with the insertion jig 30 positioned relative to the columnar ground improvement body 22, a vibrator 80 such as a vibrator hammer attached to the upper end side of the web 44 of the steel member 40 is operated, and the steel member 40 is vibrated in the vertical direction by the vibrator 80.

As a result, the insertion jig 30 and the reinforcing steel material 24 are dropped (driven) into the interior of the columnar ground improvement body 22 before hardening while being guided by a pair of guide members 74. In addition, the lower end opening 52 of each hollow tube 50 is blocked by the cap 26 of the reinforcing steel material 24. This prevents soil cement from flowing into the interior of the hollow tube 50 from the lower end opening 52 of the hollow tube 50.

Next, when the lower end of the steel member 40 reaches a predetermined depth, the vibrator 80 is stopped. Note that the retainers 60 installed at the top of each hollow tube 50 are not lowered into the columnar ground improvement body 22 but are left exposed above ground.

(Pulling up process)
Next, a description will be given of the pulling-up process for pulling up the insertion jig 30 from the unhardened columnar ground improvement body 22. In the pulling-up process, first, the holding of the reinforcing steel material 24 by the holding device 60 is released as shown in Fig. 6. Specifically, the pair of screw members 62 attached to the upper part of each hollow tube 50 is loosened, and the clamping of the upper part of the reinforcing steel material 24 by the pair of screw members 62 is released.

Next, as shown in FIG. 8, the vibrator 80 is operated to vibrate the upper end side of the steel member 40 while the insertion jig 30 is raised. As a result, the insertion jig 30 is pulled out of the columnar ground improvement body 22 before hardening, and multiple reinforcing steel members 24 are left (embedded) inside the columnar ground improvement body 22.

The insertion jig 30 is then raised while vibrating the upper end of the steel member 40 with the vibrator 80. As a result, as the insertion jig 30 is raised, the soil cement flows into the holes formed in the columnar ground improvement body 22, filling the holes and compacting the soil cement. This makes it easier for the soil cement to adhere to the reinforcing steel material 24.

Then, the columnar ground improvement body 22 is hardened to form the steel-reinforced ground improvement body 20.

When reusing the insertion jig 30, the soil cement adhering to the insertion jig 30 is washed away while the insertion jig 30 is laid flat on the ground, and then the above-mentioned installation process is carried out.

The construction method of the steel-reinforced ground improvement body according to this embodiment is not limited to the above procedure and can be modified as appropriate. For example, in this embodiment, the retention of the reinforcing steel material 24 by the retention tool 60 is released during the lifting process. However, the retention tool 60 only needs to retain the reinforcing steel material 24 so that the reinforcing steel material 24 does not fall from the insertion tool 30, and does not necessarily need to retain the reinforcing steel material 24 after the reinforcing steel material 24 lands on the columnar ground improvement body 22 before hardening.

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

In addition, in this embodiment, the retaining device 60 is not dropped into the inside of the columnar ground improvement body 22. However, after the retention of the reinforcing steel material 24 by the retaining device 60 is released, the upper end of the retaining device 60 or the reinforcing steel material 24 may be dropped into the columnar ground improvement body 22 before hardening.

In addition, in this embodiment, the steel frame member 40 is vibrated by the vibrator 80 during the dropping process and the pulling process. However, the vibrator 80 only vibrates the steel frame member 40 as necessary, and can be omitted as appropriate.

(effect)
Next, the effects of this embodiment will be described.

As described above, in this embodiment, in the dropping process, the reinforcing steel material 24 is dropped together with the insertion jig 30 into the columnar ground improvement body 22 before hardening. As a result, in this embodiment, the reinforcing steel material 24 can be inserted into the columnar ground improvement body 22 more efficiently than in the case where only the reinforcing steel material 24 is dropped into the columnar ground improvement body 22 before hardening.

The reinforcing steel material 24 is inserted into a hollow tube 50 attached to the steel frame member 40. The upper part of the reinforcing steel material 24 is held by a holder 60 provided at the upper part of the hollow tube 50. This prevents the reinforcing steel material 24 from falling when the insertion jig 30 is hoisted by a crane or the like.

Furthermore, by inserting the reinforcing steel material 24 into the hollow tube 50, the reinforcing steel material 24 is prevented from moving wildly when the steel member 40 is vibrated by the vibrator 80. In addition, when the steel member 40 and the reinforcing steel material 24 are dropped into the columnar ground improvement body 22 before hardening, the positional deviation of the reinforcing steel material 24 relative to the steel member 40 is suppressed. As a result, the positional deviation of the reinforcing steel material 24 relative to the columnar ground improvement body 22 can be suppressed.

A cap 26 is provided at the lower end of the reinforcing steel material 24. By hooking this cap 26 onto the lower end 50L of the hollow tube 50, the positional deviation of the reinforcing steel material 24 relative to the steel member 40 is further suppressed when the steel member 40 and the reinforcing steel material 24 are dropped into the columnar ground improvement body 22 before hardening.

The lower end opening 52 of the hollow tube 50 is closed by a cap 26 attached to the lower end of the reinforcing steel material 24. This prevents unhardened soil cement from flowing into the lower end opening 52 inside the hollow tube when the insertion jig 30 and the reinforcing steel material 24 are dropped into the unhardened columnar ground improvement body 22 during the dropping process. As a result, the reinforcing steel material 24 is prevented from adhering to the inner surface of the hollow tube 50 via the unhardened soil cement.

Therefore, in the pulling-up process, when the steel frame member 40 and the hollow pipe 50 are pulled up from the columnar ground improvement body 22 before hardening, the reinforcing steel material 24 is prevented from being pulled up together with the hollow pipe 50. Therefore, the reinforcing steel material 24 can be more reliably embedded (left in place) in the columnar ground improvement body 22 before hardening.

Here, as shown in FIG. 5(B), if the reinforcing steel material 24 and the cap 26 move radially relative to the hollow tube 50, there is a possibility that the lower end opening 52 of the hollow tube 50 will be opened. In particular, in this embodiment, as described above, the upper end side of the steel member 40 is vibrated by the vibrator 80 while the insertion jig 30 and the reinforcing steel material 24 are dropped into the columnar ground improvement body 22 before hardening. Therefore, the reinforcing steel material 24 and the cap 26 are likely to move radially relative to the hollow tube 50.

To address this issue, in this embodiment, the diameter D1 of the bottom surface 26A of the cap 26 is set so that the lower end opening 52 of the hollow tube 50 will not open even if the reinforcing steel material 24 and cap 26 move radially relative to the hollow tube 50. More specifically, the diameter _D2 / ₂ of the bottom surface 26A of the cap 26 is set to exceed the inner diameter B of the hollow tube 50 - the diameter _D1 /2 of the reinforcing steel material 24 ( _D2 /2>B- _D1 /2).

This makes it possible to more reliably prevent unhardened soil cement from flowing into the lower end opening 52 in the hollow tube 50 when the insertion jig 30 and reinforcing steel material 24 are dropped into the unhardened columnar ground improvement body 22 during the dropping process.

Furthermore, the cap 26 is formed in a truncated cone shape that tapers away from the lower end 50L of the hollow tube 50. This makes it easier to drop the reinforcing steel material 24 into the columnar ground improvement body 22 before it hardens during the dropping process. Therefore, the reinforcing steel material 24 can be inserted into the columnar ground improvement body 22 more efficiently.

Moreover, by providing a 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 reinforcing steel material 24 on the columnar ground improvement body 22 can be improved.

(Modification)
Next, a modification of the above embodiment will be described.

In the above embodiment, as shown in FIG. 1, multiple reinforcing steel materials 24 are arranged at intervals in the width direction of the retaining wall 10 and are embedded closer to the side on which the earth pressure P acts (the side opposite the underground space 12) with respect to the center of the columnar ground improvement body 22. However, the embedding position of the reinforcing steel materials 24 relative to the columnar ground improvement body 22 can be changed as appropriate.

For example, in the modified example shown in FIG. 9, multiple reinforcing steel members 24 are embedded on both sides of the thickness direction (arrow P direction) of the columnar ground improvement body 22. In this case, for example, the insertion jig 30 is dropped twice into the columnar ground improvement body 22 before hardening.

For example, in the modified example shown in FIG. 10, multiple reinforcing steel members 24 are arranged in two rows in the width direction of the retaining wall 10. The multiple reinforcing steel members 24 in each row are arranged at intervals in the thickness direction of the retaining wall 10. These reinforcing steel members 24 are inserted, for example, into multiple hollow tubes 50 attached to both sides of the web 44 of the steel member 40. Furthermore, the steel member 40 is dropped into the columnar ground improvement body 22 before hardening, with the width direction being the thickness direction of the retaining wall 10.

In the modified example shown in FIG. 10, a 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 manner, the reinforcing steel material 24 can be buried in the outer periphery of the columnar ground improvement body 22. Although not shown in the figure, the hollow tube 50 can also be attached to the inner surface of the flange 42 of the steel frame member 40.

In addition, in the above embodiment, multiple reinforcing steel members 24 are embedded in the columnar ground improvement body 22. However, at least one reinforcing steel member 24 can be embedded in the columnar ground improvement body 22.

In the above embodiment, the reinforcing steel material 24 is held by clamping it from both radial sides with a pair of screw members 62 of the retainer 60. However, for example, as shown in FIG. 11(A), multiple screw holes 54 may be formed on the front side of the hollow tube 50 (the side opposite the steel frame member 40), and multiple screw members 62 may be screwed into these screw holes 54 to press the reinforcing steel material 24 against the inner surface on the back side of the hollow tube 50, thereby holding the reinforcing steel material 24.

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

The retainer 60 in the above embodiment has a pair of screw members 62. However, the retainer is not limited to a pair of screw members, and may be, for example, a nut member that is placed (engaged) on the upper end of the hollow tube 50. The threaded portion provided on the upper end of the reinforcing steel material 24 is screwed into this nut member, whereby the reinforcing steel material 24 is removably held by the nut member.

In addition, the reinforcing steel material 24 may be held to the steel frame member 40 by welding the upper part of the reinforcing steel material 24 to the upper end of the hollow tube 50 or the steel frame member 40 without using a retainer. In this case, the retention of the reinforcing steel material 24 by the steel frame member 40 is released by cutting the welded portion or the upper part of the reinforcing steel material 24.

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

In the above embodiment, the hollow member is a hollow tube 50. However, the hollow member may be, for example, a plurality of ring-shaped members attached at intervals in the axial direction of the steel frame member 40 and into which the reinforcing steel member 24 is inserted. In this case, the cap 26 is hooked onto the lower end of the lowest ring-shaped member among the plurality of ring-shaped members.

In the above embodiment, the cap 26 is formed in a truncated cone shape. However, the shape of the cap 26 can be changed as appropriate, and may be, for example, a tapered shape such as a cone shape, a truncated pyramid shape, or a pyramid shape. In addition, the cap 26 is not limited to a tapered shape, and may be, for example, a cylindrical shape or a polygonal prism shape.

Furthermore, the hooking part is not limited to the cap 26 that closes the lower end opening 52 of the hollow tube 50. The hooking part may be anything that can be hooked at least to the lower end 50L of the hollow tube 50, and may be, for example, a U-shaped hook.

In addition, in the above embodiment, the cap 26 is provided at the lower end of the reinforcing steel material 24. However, the cap 26 is not limited to being provided at the lower end of the reinforcing steel material 24, and may be provided, for example, at the lower part of the reinforcing steel material 24.

In the above embodiment, the steel frame member 40 is formed from an H-shaped steel. However, the steel frame member 40 is not limited to an H-shaped steel, and may be, for example, a round steel pipe, a square steel pipe, a C-shaped steel, etc.

In addition, in the above embodiment, the retaining wall 10 is formed 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 may be, for example, a lattice-shaped ground improvement body formed in a plan view to suppress liquefaction of the liquefaction layer.

Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and one embodiment and various modified examples may be used in appropriate combination, and the present invention may of course be embodied in various forms without departing from the spirit of the present invention.

20 Steel-reinforced ground improvement body 22 Columnar ground improvement body 24 Reinforcement steel 26 Cap (hook part)
30 Insertion jig 40 Steel frame member 50 Hollow tube (hollow member)
50L Bottom end (bottom end of hollow member)
52 Opening (opening at the lower end of the hollow member)

Claims (4)

a dropping process in which a rod-shaped or wire-shaped reinforcing steel material having a hook portion that hooks onto the lower end of a hollow member attached to a steel member is inserted into the hollow member, and the steel member is dropped into the columnar ground improvement body before hardening while the upper part of the reinforcing steel material is held by the holding portion of the steel member;
A lifting process in which the steel frame member and the hollow member are lifted up from the columnar ground improvement body before hardening in a state in which the holding of the upper part of the reinforcing steel material by the holding part is released;
A construction method for a steel-reinforced ground improvement body comprising: The hollow member is a hollow tube extending in a material axial direction of the steel frame member,
The hook portion closes an opening on a lower end side of the hollow tube when hooked on the lower end of the hollow tube.
A method for constructing the steel-reinforced ground improvement body according to claim 1. The hook portion tapers away from the lower end of the hollow member.
A method for constructing the steel-reinforced ground improvement body according to claim 1 or 2. A steel member that holds an upper portion of a rod-shaped or wire-shaped reinforcing steel material having a hook portion with a holding portion and is dropped into the columnar ground improvement body before hardening together with the reinforcing steel material;
a hollow member attached to the steel frame member and having the hook portion hooked to a lower end thereof with the reinforcing steel material inserted therein;
An insertion jig comprising: