JP3468503B2 - Ground anchor with restraint - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground anchor in which the stress transmitted from a load bearing body to a grout is averaged in the length direction.

[0002]

2. Description of the Related Art In conventional ground anchors,
The length is determined on the assumption that the tension force acting on the load bearing body or the pressure bearing body is evenly transmitted to the ground in the length direction of the fixing portion.

However, in reality, as shown in FIG. 6, the tension force is not evenly transmitted from the load bearing body or pressure bearing body (bearing plate) of the fixing portion to the peripheral grout and the ground, and the tip of the anchor becomes maximum. , The stress distribution decreases as it goes to the anchor head. As described above, since an excessively large compressive stress locally acts on the grout of the fixing long portion, the stress at the tip portion sometimes exceeds the allowable compressive strength as illustrated.

Further, as shown in FIG. 7, the distribution of the adhesion stress of the tension material embedded in the grout is such that the boundary between the free length portion and the fixing length portion of the tension material becomes the maximum and decreases as it goes to the tip side.
At the cutting edge, no adhesive stress was applied and the entire length was not used effectively. Due to this local concentrated stress, cracks were formed in the grout, and the cracks sometimes progressed, leading to the anchor body coming out or the tendon material coming out.

For this reason, in Japanese Utility Model Publication No. 4-37956, as shown in FIG. 5, the tip side of the anchor is enlarged and excavated to form a taper shape, and the stress acting on the grout is uniformly distributed in the length direction of the fixing portion. Thus, the compressive strength of the grout is set to be equal to or lower than that, and a steel sheath having irregularities on the outer periphery is embedded in the grout.

In addition, Japanese Utility Model Laid-Open No. 4-89125, Japanese Patent Laid-Open No. 7-89125.
As described in No. 127057, it has been proposed to surround the tension member near the load bearing body with a conical or drum-shaped coil spring to reinforce the grout. (See FIGS. 7 and 8)

[0007]

However, expanding the diameter of the tip of the anchor requires a special bit for expanding the diameter, and a general-purpose drill bit cannot be used. The drilling efficiency is poor and it is not economical. Further, in the method of drilling with the diameter-expanding bit only when the diameter-expanding hole of the tip portion is used, it is necessary to prepare two kinds of bits, and it is troublesome to replace the bit. Reinforcement with coil springs is because the springs are not continuous but have a gap,
The grout may not have sufficient restraint effect and may not be able to withstand great tension.

Therefore, in the present invention, the stress of the ground anchor is evenly distributed over the entire length of the fixing length portion, local excessive stress is prevented from being generated, the fixing length portion can be shortened, and the workability is improved. It provides a good ground anchor.

[0009]

[Means for Solving the Problems] A tension member including an unbonded portion is inserted into a restraint body, and a high-strength filler is filled in the restraint body to integrate the tension member and the restraint body into a load-bearing body. As a result, the stress is distributed evenly in the longitudinal direction of the load bearing body. Specifically, the restraint body is a steel pipe having a rigidity of 1.2 mm or more, and the compressive strength of the filler is preferably 500 kg / cm ² or more. Further, it is possible to disperse the stress by providing uneven ribs on the outer circumference of the steel pipe.

[0010]

[Function] When the tension material inserted in a restraint body such as a steel pipe is used, the compressive strength of the filler constrained around the circumference is
The rigidity is increased in proportion to 2.5 to 4 times that of the unconstrained case, so that the adhesive strength of the tension material and the filler material is increased, and the restraint body and the tension material are firmly integrated into a load-bearing body. Becomes Furthermore,
The stress of the filler is dispersed in the lengthwise direction to the unbonded portion by the restraint body and is averaged, so that the crack of the filler and further the crack of the grout of the ground anchor are prevented. The concavo-convex ribs of the restraint body disperse the compressive stress and the shear stress and transmit them to the grout around the load bearing body evenly and reliably.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to the drawings. FIG. 1 is an embodiment of the ground anchor of the present invention. In the tension material 1, a wire 11 made of unbonded PC steel is bent to make a U-turn, and a polyethylene sheath of a constant length portion of the U-turn portion 12 is removed to expose the wire of PC steel. The plurality of U-turned PC steel strands 11 are bound by holding spacers (not shown) at intervals between the PC steel strands and appropriately arranging them.

Since the spacing is maintained by the spacers, the entire circumference of each PC steel stranded wire is in contact with the filler 3, and each P
Adhesive force with the filler can be expected for the C steel stranded wire. The U-turn PC stranded wire may have the same length, or the arrangement can be changed by changing the length and shifting the fixing position in the restraint body. In the example of FIG. 1, U-turn PC steel strands 11 having substantially the same length are arranged in a cage. Figure 2
In the above example, the PC stranded wires are arranged in parallel with each other in the steel pipe 41 while keeping the intervals with spacers.

The tension material 1 is inserted into a steel pipe 41 having an uneven rib 42 on the outer peripheral surface thereof, including the unbonded portion 13, and is filled with grout having a compressive strength of 500 kg / cm ² to be hardened. Was integrated into a load-bearing body 4.
The filling material 3 may be filled when the tension material 1 is inserted into the steel pipe in a factory or the like, or may be filled and hardened on the ground before inserting and installing the ground anchor in the boring hole in the field.

When a PC steel stranded wire whose surface is coated with epoxy resin is used, the tension member 1 is protected by the grout, the steel pipe, the filler, and the coating film, so that high corrosion resistance and durability can be obtained. . The concrete PC stranded wire is JIS G
3536 SWPR7B φ12.7 mm, φ15.
The length is 2 mm or the like, and the PC stranded wire (SC strand: trade name) obtained by unwinding the PC stranded wire and coating the strands with an epoxy resin coating or the like and having the strands twisted together again has excellent corrosion resistance.

The steel pipe 41 has a wall thickness of 1.2 to 3.5 mm, is rigid, and is ribbed on the outer peripheral surface, so that the shearing force is dispersed in the longitudinal direction and is reliably transmitted to the surrounding ground. The diameter of the PC steel wire to be inserted depends on the number of PC steel wires to be inserted. If the wall thickness of the steel pipe is thin, the effect of restraining the filler is small, the increase in the compressive strength of the filler is small, and the wall thickness exceeding 3.5 mm causes a cost problem.
A front member (not shown) having a sharp tip is attached to the tip of the steel pipe 41 to facilitate insertion into the boring hole. The ground anchor manufactured in this way is inserted into the boring hole drilled in the ground, and the compressive strength 2 is applied to the outside of the load bearing body 4.
The ground anchor is installed in the ground by injecting grout of about 0 to 350 kg / cm ² .

The transmission mechanism of the tensile force acting on the ground anchor of the present invention will be described. The tensile force acting on the tension member 1 is transmitted from the PC steel wire to the filler 3. Steel pipe 41
Since the filler constrained from being deformed in the lateral direction has a compressive strength that is about 3 to 4 times higher than that in the unconstrained case,
The adhesive force between the PC steel strand 11 and the filling material increases, and the tension material is prevented from coming out.

The filler 3 in the steel pipe 41 and the PC steel strand 11
The adhesive stress distribution of 1 is averaged by the restraining effect of the restraining body as shown in FIG. Further, since the boundary portion between the unbonded portion 13 and the fixing portion of the PC steel stranded wire is inside the steel pipe 41, an excessive compressive stress generated at the boundary is restrained, and the tension material 1 and the steel pipe 41 are integrated into a load bearing capacity. Since it is the body 4, as shown in FIG. 4, the stress is dispersed up to the end of the PC steel wire on the unbonded side, and the stress distribution becomes uniform, so that cracking of the filler is prevented.

Further, since the uneven ribs 42 on the outer periphery of the steel pipe 41 disperse the load and transmit the load to the grout and the surrounding ground evenly in the longitudinal direction of the load bearing body 4, the stress generated in the grout is an allowable compressive strength. It becomes the following.

[0019]

According to the present invention, the fracture surface of the conventional ground anchor is moved to the restraining area in the load bearing body to prevent the occurrence of local overstress, and the uneven ribs on the outer periphery of the load bearing body are subjected to compressive stress and shear stress. Since it is transmitted while being averaged to the grout around the load-bearing body while being dispersed, the compressive stress received by the filler inside the restraint body and the stress transmitted to the grout around the load-bearing body are also averaged below the allowable compressive strength of the grout. Dispersed in. Further, since the filler is restrained by the restraint body such as a steel pipe, the adhesive strength between the tension member and the filler is increased. Since the load-bearing body of the present invention is obtained by inserting the PC steel wire into the steel pipe and integrating it with the filler, the structure is simple, the cost is low, and the manufacturing is easy.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a sectional view of another embodiment of the present invention.

FIG. 3 is a distribution diagram of adhesion stress between a PC stranded wire and a filler.

FIG. 4 is a stress distribution diagram that acts on the grout.

FIG. 5 is a stress distribution diagram of a ground anchor whose tip has an enlarged diameter.

FIG. 6 is a stress distribution diagram of a conventional compression type ground anchor.

FIG. 7 is a stress distribution diagram of a conventional tensile type ground anchor.

FIG. 8 A conventional ground anchor reinforced with a conical coil spring.

FIG. 9 is a conventional ground anchor reinforced with a drum coil spring.

[Explanation of symbols]

1 tension material 11 PC steel stranded wire 12 U turn part 13 Unbond Department 3 Filling material 4 load-bearing body 41 Restraint (steel pipe) 42 uneven rib

Claims (2)

(57) [Claims] 1. A restraint body in which a tensioning material including an unbonded portion is inserted into a restraint body made of a steel pipe having an uneven rib formed on the surface, and a boundary portion between the unbonded portion and the fixing portion is located in the steel pipe. And the tension material are integrated with the filler, and the compressive strength of the filler is greater than that of the ground anchor grout, and the compressive strength is 500.
A ground anchor that is at least kg / cm ² . 2. The ground anchor according to claim 1, wherein the tendon is U-turned.