JPH0413497B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a ground anchor for anchoring above-ground structures, mountain retaining walls, etc. to the ground.

(Conventional technology) Ground anchors are ground anchors that are made by drilling a hole in the ground with a boring machine, etc., inserting a tensile steel material into the hole, and then injecting grout around it to resist pulling force. It is a structure.

The basic structure of a ground anchor is, as shown in Figure 2, an anchor head b that fixes the anchor to a ground structure a or a mountain retaining wall, a tensile steel member c that transmits tensile force, and a tensile steel member c. The anchor body d is provided to transmit the tensile force of the anchor body d to the surrounding ground.

When this ground anchor is used in a permanent structure, rust prevention of tensile steel becomes a particular problem. Therefore, in consideration of rust prevention and stress transmission, Figures 3 to 5 are
A ground anchor as shown in the figure was proposed and put into practical use.

In the ground anchor shown in Fig. 3, a tensile steel member 1 is protected by a corrugated sheath 2, and the stress applied to the tensile steel member 1 is transmitted by adhesion to internal grout 3 within the corrugated sheath 2, and the tensile force is is tensile steel material 1 → internal grout 3 → corrugated sheath 2
→External grout 5 between corrugated sheath 2 and anchor hole 4 →Transmitted to surrounding ground.

In the figure, 6 is a sheath at the free length above the anchoring part of the tensile steel material 1, and 7 is a waterproof tape between the sheath 6 and the corrugated sheath 2.

In both the internal grout and the external grout, the anchor is called a tension anchor because force is transmitted from a portion close to the head and tensile stress is generated inside the grout.

In the ground anchor shown in FIG. 4, a fixing plate 8 is fixed to the bottom of a corrugated sheath pipe 2 installed for rust prevention, and the lower end of the tensile steel member 1 is fixed to the fixing plate 8, and is applied to the tensile steel member 1. The tensile force is directly transmitted to the anchoring plate 8, and from the anchoring plate 8, it is transmitted as compressive force to the corrugated sheath pipe 2, internal grout 3, and external grout 5, and is further transmitted to the ground, and is called a compression type anchor. has been done.

In the figure, reference numeral 9 denotes a bottom waterproofing section of the corrugated sheath tube 2.

The ground anchor shown in Fig. 5 has an upper part 1a unbonded from the middle of the corrugated sheath 2 of the tensile steel
It is constructed from PC steel wire and is a combination of tension type and compression type anchors. Note that parts in the figure that are equivalent to the ground anchors shown in FIGS. 2 and 3 are given the same reference numerals.

(Problems to be Solved by the Invention) In the above-mentioned conventional ground anchor, when attempting to transmit the tensile force applied to the tensile steel material by the adhesive force with the grout, the grout length must be made very long, Furthermore, if the restraining force around the grout is small, there is a problem that the anchor body grout will split and the tensile steel material will be pulled out.

In order to increase the restraint force on the grout, it has been expected to use a corrugated sheath, which is conventionally used for rust prevention, but the corrugated sheath does not have a sufficient grout restraint effect.

(Means for Solving the Problems) The present invention was proposed in order to solve these problems, and the present invention has been proposed in order to solve these problems. The anchor hole is surrounded by a conical sheath tube whose diameter gradually increases as the anchor hole increases, and an internal grout and an external grout are filled inside the sheath tube and between the sheath tube and the anchor hole, respectively. This relates to ground anchors.

(Function) Since the ground anchor according to the present invention is configured as described above, a tensile force is applied to the tensile steel material, and the lower end of the tensile steel material is inserted into the conical sheath pipe for rust prevention of the tensile steel material. When a tensile force is transmitted to the internal grout, the internal grout receives a force that causes it to pull upward.

Since the sheath tube is formed into a conical shape whose diameter gradually increases as it goes downward, when the sheath tube is subjected to a pulling force by the internal clout, this force is applied to the tensile steel material. This is the tightening force that restrains the

Further, the external grout between the anchor hole and the sheath pipe is strongly pressed against the outer circumferential ground by the wedge action of the conical sheath pipe that is subjected to the pulling force as described above.

(Effects of the Invention) As described above, in the ground anchor according to the present invention, the sheath pipe surrounding the lower end of the tensile steel material inserted into the anchor hole is formed into a conical sheath whose diameter gradually increases as it goes downward. By forming the tube into a tube, when a tensile force is applied to the tensile steel material, the conical sheath tube generates a clamping force that restrains the tensile steel material in the grout in the sheath pipe, as described above, so that the tensile steel material is The adhesion between the steel and the grout is increased by the confining force of the grout, and therefore, tensile steel can be expected to have a high pull-out strength with a short bond length.

Further, since the external grout between the sheath pipe and the anchor hole is pressed against the external ground by the wedge effect of the conical sheath pipe, the pull-out shearing resistance between the anchor and the outer circumferential ground increases.

(Example) The present invention will be described below with reference to an example shown in FIG.

11 is an anchor hole drilled in the ground 12, and 13 is inserted into the same anchor hole 11.
It is a tensile steel material made of stranded PC steel wire or the like, and its lower end is surrounded by a steel conical sheath tube 14 whose diameter gradually increases as it goes downward.

A high-strength internal mortar 15 is filled in the conical sheath tube 14, and an external mortar 15 is placed between the sheath tube 14 and the inner peripheral surface of the anchor hole 11.
6 is loaded.

In the figure, 17 is a sheath tube surrounding the upper free length portion of the tensile steel wire 13.

Since the illustrated embodiment is configured as described above, when a tensile force is applied to the tensile steel member 13 and this force is transmitted to the internal grout 15, the internal grout 15 receives a force that causes it to be pulled upward. .

However, since the sheath pipe 14 is formed into a conical shape whose diameter gradually increases as it goes downwards, when the grout 15 receives a pulling force, it will generate a tightening force p that restrains the tensile steel member 13. Become.

As is well known, the adhesive strength between the steel wire and the grout increases with the restraining force of the grout, so according to the above embodiment, the tensile steel material 13 can be expected to have a large pull-out strength with a short adhesive length. .

Further, the conical sheath tube 14 has an external grout 1
6, and the same external grout 16
is pressed against the outer circumferential ground 12 with a strong pressing force q, and the pull-out shearing resistance between the ground 12 and the anchor increases.

In addition, if the surrounding ground is soft, external grout 1
6 will split, so it is important to inject the grout into solid ground with sufficient pressure.

[Brief explanation of drawings]

Fig. 1 is a vertical sectional view showing an embodiment of the ground anchor according to the present invention, Fig. 2 is a joint sectional view showing an outline of the ground anchor, and Figs. It is a joint sectional view showing each example of a ground anchor. 11... Anchor hole, 12... Ground, 13
... Tensile steel material, 14 ... Conical sheath pipe, 15
...Internal mortar, 16...External mortar.

Claims (1)

[Claims] 1. A tensile steel material inserted into an anchor hole drilled in the ground is surrounded by a conical sheath pipe whose diameter gradually increases as it goes downward, and the sheath pipe and the anchor are A ground anchor characterized by having internal grout and external grout filled between each hole.