JP2818102B2 - Ground anchor structure - 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 structure for fixing a ground structure, a retaining wall and the like to the ground.

[0002]

2. Description of the Related Art So-called ground anchors for stabilizing the ground are broadly divided into temporary anchors corresponding to temporary structures and permanent anchors corresponding to permanent structures.
Further, two types of permanent anchors are used, a tension type anchor and a compression type anchor, depending on the condition of the ground and the type of structure.

[0003] The difference between the tension type anchor and the compression type anchor will be briefly described. As shown in FIG. 6 (a), the tension type anchor has a fixed length L1 of an anchor cable 50 with a capsule 51 and a free length. The portion L2 is connected to the sheath tube 52.
And the anchor cable 50 and the capsule 51 are integrated with the grout material 53 filled in the capsule 51, and the anchor cable 50 is pulled.

On the other hand, as shown in FIG. 7 (a) or FIG. 8 (a), the compression-type anchor includes a load-bearing body 54, which is a pressure-resistant member made of a steel pipe or the like, and is provided on the underground side of the fixing length L1. At least one anchor cable 50 is attached to one or more of the ends, and a plurality of anchor cables 50 are attached thereto. The anchor cable 50 and the load-bearing body 54 are covered with the sheath tube 52, and the load-bearing body 54 and the sheath tube 52 are free-length. In this structure, the sheath cable 52 is integrated with the grout material 53 or the like while the portion L2 is left, and the anchor cable 50 is pulled. 6 to 8, reference numeral 55 denotes an anchor hole, and reference numeral 56 denotes a grout material filled in the anchor hole 55.

[0005]

In the above-mentioned tension type anchor, as shown in FIG. 6 (b), when the anchor cable 50 is pulled, stress concentrates on the boundary between the fixing length portion L1 and the free length portion L2. As a result, a local tensile stress is applied to the grout material 56 around the boundary, and cracks occur. When this crack occurs, although the stress is once released, the tensile force is maintained, so that the crack continues to propagate toward the underground end of the fixing length portion L1, and cracks are sequentially generated. That is, it is inevitable that cracks occur at a plurality of locations of the grout material 56. Therefore, the grout material 56 cannot be regarded as an anticorrosion material, and thus covers the capsule 51. Also, due to the occurrence of cracks in the grout material 56,
Since the peripheral frictional resistance is lower than when the fixing length L1 is short, even if the fixing length L1 is long, the transmission of the tensile stress is not efficient.

In the case of a compression type anchor, FIG.
As shown in FIG. 8B and FIG. 8B, a compressive stress is applied to the grout material 56 so that no crack is generated.
If a plurality of load bearing members 54 are used as shown in FIG.
It has the advantages that the load of the load on the ground can be reduced and construction is possible even on soft ground. However, since the load-bearing body 54 is made of steel, it has elasticity (Young's modulus ratio), and the elasticity of the load-bearing body 54 is naturally larger than that of the grout material 56. Is transmitted only for a short distance (for example, about 1.2 meters), and the compressive stress applied to the grout material 56 is significantly uneven (uneven). Therefore, when the calculated fixing length is as long as 6 to 10 meters, there is a problem that the theoretical fixing length cannot be calculated at the time of design. However, the actually functioning fixing length L1 is shorter than the theoretical length.

As described above, in both the tension type and the compression type anchor structures, a problem occurs because the stress distribution is concentrated on a part of the fixing length portion L1. In FIG. 6B, P1 is a tensile stress, and FIG.
8 (b) and FIG. 8 (b), P2 is a curve showing the distribution of compressive stress.

The present invention has been made in view of the above circumstances, and is intended to correct the non-uniformity of the stress distribution observed in the above-described tension type and compression type anchor structures, that is, to achieve a uniform stress distribution. Accordingly, it is an object of the present invention to provide a ground anchor structure capable of efficiently introducing a load.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and is provided for a stress transmitting material such as a PC steel rod inserted into an anchor hole excavated and formed in a target ground. A plurality of fixed length portions, which are fixed to each other at an interval from the underground end to the ground surface end of the stress transmitting material and rigidly connected as a whole via the stress transmitting material. Are provided, and the anchor cables are engaged for each of the load-bearing bodies, and the plurality of anchor cables pulled out to the ground surface along the stress-transmitting material are tensioned, so that the stress transmitting material is inserted into the anchor hole. And grout material filled so as to adhere to both the load-bearing body, the anchor body composed of the stress transmitting material and the load-bearing body is fixed to the target ground, among the plurality of load-bearing bodies,
The one located on the ground surface side is characterized in that a passage hole is provided to allow the passage of the anchor cable engaged with the load bearing body located on the ground side.

[0010]

According to the present invention, the compressive stress and the tensile stress are simultaneously and uniformly transmitted to the stress transmitting member from the plurality of load-bearing members mounted on the stress transmitting member at regular intervals in a state where the anchor cable is tensioned. As a result, a tension load is applied to the grout material in the anchor hole without applying tension to the stress transmitting material as a result. As a result, compressive stress and tensile stress are evenly distributed over the entire fixing length portion of the anchor body to give an evenly distributed load, and the fixing length portion functions effectively.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a permanent anchor structure obtained by the method of the present embodiment, where reference symbol G denotes an object ground to be earthed, 1 is an earth retaining wall provided on the surface of the object ground G, and 2 is an object ground G. Anchor hole formed by excavation, 3 is an anchor cable inserted into the anchor hole up to the bottom of the hole, 4 is a load bearing member, 5 is a PC steel rod (stress transmitting material) on which the load bearing member 4 is mounted, and 6 is an anchor. Grout material filled in the holes,
The anchor body 7 of the present embodiment is constituted by the load-bearing body 4, the PC steel bar 5, and the grout material 6.

According to this anchor structure, the ground-side end of the anchor cable 3 passes through the pedestal 8 and the anchor head 9 applied to the retaining wall 1, and is tensioned by a jack (not shown). By engaging the wedge 10 attached to the outer periphery of the protruding end of the cable 3 with the anchor head 9, earth retaining of the target ground G is achieved. An end of the anchor cable 3 protruding from the anchor head 9 is covered with an oil cap 11.

As shown in FIG. 3, the anchor cable 3 is an unbonded PC strand made of a PC steel stranded wire 3a, and the surface thereof is covered with a CD sheath 12 which is a corrugated tube, subjected to anticorrosion treatment, and provided inside. Is filled with grease 3b, and a cylindrical compression ring 13 is fixed to one end of the grease 3b. In the case of the present embodiment, six anchor cables 3 are used.

The load-bearing body 4 is made of, for example, ductile cast iron and has a surface subjected to anticorrosion treatment by galvanization.
As shown in FIG. 5 and FIG. 5, a plurality (three in this case) of support members 22 and a pair of cable members are arranged on a cylindrical shaft body 21 from one end side (right side in FIG. 4) which is an end on the ground surface side. Joint 23
Are integrally formed. The supporting body 22 has a flange shape coaxial with the shaft body 21, and when viewed from the side,
One end surface is formed with a flat bearing surface 22a orthogonal to the shaft body 21, and the other end surface is a tapered surface 22b having a gradually decreasing diameter.
It has become. A plurality (eight in this case) of U-shaped grooves 24 that are open to the outer peripheral side are formed at a plurality of locations (eight in this case) equally spaced around the circumference. Each groove 24
Are formed so as to be aligned in a straight line in parallel with the shaft body 21 over the three supporting members 22. The cable engaging portion 23
The supporting body 22 is formed in a substantially fan shape having the same outer diameter as the supporting body 22, and is disposed at a position different from the shaft body 21 by an angle of 180 degrees. The cable engaging portion 23 has an anchor cable 3
Is formed in parallel with the shaft 21. The cable insertion hole 25 is coaxially positioned on an extension of the set of (three) grooves 24 of the supporting members 22 aligned in a straight line. A screw is formed on the inner peripheral surface of the shaft body 21. A pilot cap 26 is fitted to the underground end of the shaft 21.

The load-bearing body 4 having the above structure is mounted on one PC steel bar 5 having a predetermined length. The PC steel bar 5 is coated with a resin material such as epoxy over the entire surface, and a screw is formed on the entire peripheral surface thereof. The load-bearing body 4 is screwed into the screw in the same direction. Thus, a total of three PC steel bars 5 are arranged and mounted at both ends and the center of the steel bar 5. P
Since the load-bearing body 4 is screwed into the C-steel bar 5 and mounted,
There is an advantage that the load bearing member 4 can be mounted at an arbitrary position on the PC steel bar 5. Here, the first load-bearing body 4A, the second load-bearing body 4B, and the third load-bearing body 4C are arranged in this order from the underground end.

The anchor cables 3 are inserted into the respective cable insertion holes 25 of the pair of cable engaging portions 23 of each load-bearing body 4 from the underground side of the anchoring cable 3 from the end where the compression ring 13 is not fixed. Then, the compression ring 13 is engaged with the cable engaging portion 23. Each anchor cable 3 is pulled out to the ground side along the PC steel rod 5 and has a load-bearing body 4 corresponding to the extending direction.
Is passed through the groove 24 of the supporting body 22 at the position shown in FIG. Two anchor cables 3 are engaged with the three load-bearing members 4. In order to prevent interference between the anchor cables 3 that are extended by being engaged with the respective load-bearing members 4, the load-bearing members 4 rotate around the axis. Are shifted in phase.

As described above, the PC steel rod 5 on which the three load-bearing members 4 with which the two anchor cables 3 are engaged is mounted.
Each load-bearing body 4 is inserted into the anchor hole 2 with the end on the underground side, that is, the pilot cap 26 side facing the underground side. An anticorrosion cover (not shown) that covers the compression ring 13 is fitted to the end of the load-bearing body 4 on the side where the pilot cap 26 is mounted.

The anchor structure according to the present embodiment has been described above. According to this anchor structure, as described above, the ground-side end of the anchor cable 3 is passed through the pedestal 8 and the anchor head 9 applied to the retaining wall 1. Nervous with a jack not shown
In this state, the wedge 10 attached to the outer periphery of the protruding end of the anchor cable 3 is engaged with the anchor head 9 so that the target ground G is earthed. In this anchor structure, as shown in FIG. 1, a portion where the compressive stress is transmitted from the foreground on the underground side to the grout material 6 by the third load bearing member 4 </ b> C (from the third load bearing member 4 </ b> C slightly to the surface side) Is set as the fixing length portion L1, and the portion from the fixing length portion L1 to the anchor head 9 is set as the free length portion L2.

In the anchoring length L1 of the anchor structure in a state where the anchor cable 3 is tensioned and anchored, the first, second and third load bearing members 4A, 4B, 4
The following effects are produced by C.

Each of the load bearing members 4A, 4B and 4C transmits a tensile stress or a compressive stress to the grout material 6 or the PC steel bar 5, and shows a distribution state of the transmitting force of the tensile stress or the compressive stress in FIG. Pointing at.

First, the most advanced first load-bearing body 4A on the underground side
Transmits only the compressive stress to the ground surface directly to the grout material 6 and applies a compressive stress to the ground surface side along the length direction of the PC steel rod 5. Next, the second load bearing member 4B
Similarly transmits the compressive stress to the ground surface directly to the grout material 6 and applies a tensile stress to the PC steel bar 5 in the underground portion from itself, and further transmits the PC steel rod in the ground surface portion to itself. 5 is given a compressive stress. Next, the third load bearing member 4C
Similarly transmits the compressive stress toward the ground surface directly to the grout material 6 and also applies a tensile stress to the partial PC steel bar 5 on the ground side, that is, almost the entire length of the PC steel bar 5 from itself.

When the compressive stress and the tensile stress act as described above, between the first load bearing member 4A and the second load bearing member 4B, and between the second load bearing member 4B and the third load bearing member 4C, A compressive stress and a tensile stress are generated at the same time, and both are combined to generate a stress on the ground surface side (the free length portion L2 side). Here, the tensile stress applied to the PC steel bar 5 is offset by the compressive stress. As a result, the load (tension) is hardly applied to the PC steel bar 5 itself, but the load is transmitted to the grout material 6. That is, a compressive stress is applied to the PC steel bar 5 and at the same time, a tensile stress having the same magnitude is applied to the PC steel bar 5 and the entire tensile stress is transmitted to the grout material 6 by maintaining the state. Therefore, the PC steel bar 5 is completely integrated with the grout material 6 without elongation, so that the so-called peripheral friction resistance generated between the PC steel bar 5 and the grout material 6 is maximized.

In summary, the compressive stress generated by the first to third load bearing members 4A, 4B, 4C is generated by the tensile force generated from the second and third load bearing members 4B, 4C via the PC steel bar 5. The tension is offset by the stress, and as a result, a tension load is applied to the grout material 6 in a state where no tension is applied to the PC steel bar 5 (a state in which no elongation occurs). As a result, the stress, which is the compressive stress and the tensile stress, is evenly distributed over the entire fixing length L1, that is, an evenly distributed load is applied to the fixing length L1, and the fixing length L1 functions effectively. I do.

Accordingly, a structure in which the conventional tension-type anchor and the compression-type anchor are combined is obtained, and the disadvantages of these conventional types are eliminated. That is, stress is not concentrated on the boundary between the fixing length portion L1 and the free length portion L2, and the occurrence of cracks due to the application of local tensile stress to the grout material 6 around the boundary is suppressed. Therefore, crack propagation to the underground side is less likely to occur in the grout material 6. As a result, the grout material 6 having no crack can be regarded as an anticorrosion material, and the fixing length L1
This eliminates the need to cover the capsule, and the anchor life can be set longer. In this way, the disadvantages of the tension anchor are solved.

Further, the elasticity (Young's modulus ratio) of each of the load-bearing bodies 4A, 4B, 4C and the PC steel rod 5 can be almost ignored by the canceling action of the compressive stress and the tensile stress (in particular, in this case, the long PC steel The effect of neglecting the Young's modulus ratio of the rod 5 is remarkable).
The transmission distance of the compressive stress of A, 4B and 4C becomes longer than before. That is, it is possible to effectively transmit the compressive stress to the grout material 6, so that the entire fixing length L1 can be set short and the theoretical fixing length L1 can be calculated at the time of design. . in this way,
The disadvantages of compression anchors are solved. The fixing length L
Since 1 effectively functions, it can be applied to softer ground than in the past, and the construction can be made safer.

Further, the anchor cable 3 is made of the CD sheath 12 and the grout material 6, and the PC steel rod 5 is made of a resin such as epoxy coated on itself and the grout material 6.
Each of them has a double anticorrosion treatment and is therefore satisfactory as a permanent anchor structure.
Since stress is applied to the grout material 6 in a state where no elongation occurs in the C steel bar 5, the Young's modulus ratio of the PC steel bar 5 can be neglected, so that the crack is not generated in the grout material 6. I have. Therefore, it can be said that it is not necessary to cover the anchor cable and the load-bearing body with the capsule, and it is not necessary to use an anchor cable made of a new material having excellent corrosion resistance.

[0027]

As described above, according to the anchor structure of the present invention, the anchoring length portion set in the stress transmitting material such as the PC steel rod inserted into the anchor hole excavated and formed in the target ground has the above-mentioned structure. A plurality of load-bearing bodies are fixedly attached to each other at an interval from the underground end of the stress transmitting material toward the ground surface end and rigidly connected as a whole via the stress transmitting material. An anchor cable is engaged for each load-bearing body, and the plurality of anchor cables pulled out to the ground surface along the stress transmitting material are tensioned, so that the anchor holes adhere to both the stress transmitting material and the load-bearing body. The grout material filled as described above, the anchor body composed of the stress transmitting material and the load bearing member is fixed to the target ground, and among the plurality of load bearing members, those located more on the ground side, Earth Characterized in that the passage hole to permit passage of anchor cable to be engaged in the load body located on the side is provided, each load from the anchor cable
The compressive stress transmitted to the body and each load bearing
With the tensile stress generated in the stress transmitting member by rigid connection
Both are transmitted to the ground and the stress peaks are averaged. I
Therefore, the tension type and compression type anchor structure have
Disadvantages are eliminated and uniform load introduction is realized
In addition, it is necessary to extend the life of the anchor and secure the construction.
It has the effect that it can be done.

[Brief description of the drawings]

FIG. 1 is a side view of one embodiment of the present invention.

FIG. 2 is a stress distribution diagram of an anchor structure according to one embodiment.

FIG. 3 is a side view illustrating a configuration of an anchor cable.

FIG. 4 is a side view of the load bearing member.

FIG. 5 is a cross-sectional view of the load bearing member.

6 (a) is a side view of a conventional tension type anchor structure, and FIG. 6 (b) is a stress distribution diagram.

FIGS. 7A and 7B are a side view and a stress distribution diagram, respectively, of a conventional compression-type anchor structure having one load-bearing body.

8A is a side view and FIG. 8B is a stress distribution diagram of a conventional compression-type anchor structure having a plurality of load-bearing bodies.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Earth retaining wall 2 Anchor hole 3 Anchor cable 4 (4A, 4B, 4C) Load-bearing body 5 PC steel rod (stress transmitting material) 6 Grout material 7 Anchor body G Target ground

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) E02D 5/80

Claims (1)

(57) [Claims] 1. An anchoring portion set in a stress transmitting material such as a PC steel rod inserted into an anchor hole excavated and formed in a target ground, from an underground end of the stress transmitting material to a ground surface side. edge
Are fixed to each other at an interval toward
Several load-bearing bodies rigidly connected as a whole via stress transmitting materials
An anchor cable is engaged for each of the load bearing members, and the plurality of anchor cables drawn to the ground surface along the stress transmitting member are tensioned, so that the stress transmitting member and the load bearing member are inserted into the anchor holes. The grout material filled so as to adhere to both, the anchor body composed of the stress transmitting material and the load-bearing body is fixed to the target ground, and among the plurality of load-bearing bodies, it is located closer to the surface of the ground.
Are engaged with a load-bearing body located more underground
A ground anchor structure having a passage hole that allows passage of an anchor cable .