JPH06306858A - Ground anchor - Google Patents

Abstract

PURPOSE:To make a stick-cut between the hardening material of an anchor long part and the peripheral ground so as not to occur by letting compressive force act on this anchor long part. CONSTITUTION:Plural pieces of tension materials 1 are divided into some tension material groups different in length in some pieces, while the number of pieces of tension materials 1 constituting the longest tension material group is made most numerous, and in proportion as becoming shorter, the number of pieces of the tension materials 1 constituent in order is made to be lessened. These tension materials 1 are bundled in one, inserting it into sheaths 4 and 5, and the bundle is inserted into a bored hole 6 made in the ground. A hardening material 7 is poured into the inside and outside of these sheaths 4 and 5, hardening it. Tension takes place at each tension material group, and thereby the largest tensible force is imparted to the longest tension material 1a, and the reduced tensible force is given to these tension materials 1b and 1c becoming shortened in order.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground anchor used for fixing a structure on the ground and the like, and more particularly to a ground anchor which is less likely to be cut off from the ground and is highly reliable.

[0002]

2. Description of the Related Art A ground anchor has been developed which is inserted into a hole drilled in the ground and fixed therein. The structure of this ground anchor is as shown in FIG. That is,
A part of the tensile material a such as a steel strand is covered with an unbonded sheath b to form a free length portion A, and the other part is a fixed length portion B where the surface of the steel strand is exposed. A plurality of the tensile members a are bundled, the free length portion A is passed through the straight sheath c, and the fixing length portion B is passed through the deformed sheath d which is made of steel and has an uneven peripheral surface. First, the fixing long portion B side is passed through a hole e drilled in the ground. In this state, a hardening material f such as cement milk is injected into and out of the sheaths c and d to fix the fixing portion of the ground anchor.

The tensile material a, which has been exfoliated from the ground anchor, is a hardened material f injected into the deformed sheath d.
Adhere to. The hardened material f injected into the outer periphery of the deformed sheath d adheres to the ground g around the inner wall of the drilled hole e. When a tension is applied to this anchor, that is, the tension member a, this tension acts on the anchoring portion of the anchor. In response to this tension, the tensile material a and the hardened material f around the tensile material a have an adhesive stress τ.
Due to c, the hardened material f and the ground g around it are resisted by their frictional resistance force τs. Such a ground anchor is called a tension type. That is, the tension force acts on the fixing long portion B as a tensile force for extending the fixing long portion B.

[0004]

The problem with the above ground anchor is the lack of adhesion between the hardening material f and the ground g around it. As described above, when a tensile force is applied to the tensile material, a frictional resistance force τs is generated between the hardened material f and the surrounding ground g. This resistance is likely to increase in accordance with the tension and is evenly generated over the entire length of the fixing length portion B, but it does not actually occur as designed. Figure 4
The lower part shows the frictional resistance force τ in the conventional anchor.
It is a distribution map of s. When the tension is increased, the resistance does not increase, but the frictional resistance moves from A to C in the figure toward the bottom of the drilled hole.

The cause of this is as described above.
This is because the tension applied to the ground anchor acts as a tensile force on the entire length of the fixing long portion B, so that the hardened material f and the surrounding ground g are cut off from each other. That is, since the fixing length B is extended by the tensile force, the hardening material f and the surrounding ground g
Will no longer be attached, and a large frictional resistance τs will no longer occur. FIG. 5 shows the displacement of the frictional resistance τs between the hardened material f and the ground g. As the tension is increased, the frictional resistance τs increases to some extent. However, when the force exceeds a certain level, the frictional resistance force τs drops significantly. This is because the fixing length portion B is stretched due to the tension force, and the adhesion breakage occurs between the hardened material f and the ground g that are stretched accompanying it. As a result, the resistance has dropped to 50-60% of the peak value. When such a drop occurs, the frictional resistance generation portion sequentially moves toward the back in order to counter the tension force at the back portion where the adhesion failure has not yet occurred. That is, this means that it is extremely difficult for the tension type to generate a frictional resistance force over the entire length of the fixing length portion B.

In order to prevent such adhesion breakage, a load-dispersion type ground anchor has been developed. In this method, the length of each tension member is changed so as not to cause sticking breakage, and the position of the fixing long portion in the drilling hole is shifted to distribute the load due to the tension force.
However, such a load-dispersed anchor has a problem that the load concentrates only on the tensile member having a short length. That is, since each tensile member is made of steel, a load is applied to the tensile member, so that elongation occurs in the tensile member. This elongation is large when the length of the tensile member is long, and small when it is short. When tension members of different lengths are simultaneously tensioned with the same force, the shortest tension member first reaches the elongation limit. That is, only the shortest tensile material reaches the limit of elongation, and the other tensile materials have room for elongation. From now on, the load acting on the shortest tensile material will be larger than the others. This is the same phenomenon as when a rubber rope that allows elongation and a steel rope that only has a small elongation are tensioned at the same time, only the steel rope receives a large tension force and the rubber rope bears only a small amount for the elongation. If the tension exceeds this limit, only the load acting on the shortest tensile member is significantly increased, and as a result, the breaking load is exceeded and the breaking occurs.

The present invention has been made in order to solve the above problems, and it is unlikely that the anchoring long portion of a tension type ground anchor will be easily cut off from the ground, and the tensile material will not break. The purpose is to provide a highly reliable ground anchor.

[0008]

A ground anchor according to the present invention relates to a so-called dispersion type anchor in which a fixing long portion of a tension member is displaced in a longitudinal direction to disperse a portion where a fixing force acts. is there. That is, the plurality of tensile members are divided into several groups. The free length portion of each tensile member is passed through an unbonded sheath or the like to prevent adhesion with the curing material and allow free elongation, and the tip is peeled off to form a fixing length portion that adheres to the curing material. The length of the constructed tension member group is different for each group, and the fixing length portion is shifted for each group and arranged in the fixing sheath. When the fixing long portions are offset, it is preferable that the distance between the fixing positions is 1.5 to 3 m, and the length from the fixing position of the shortest tension material group to the ground surface is 6 m.

At this time, the number of the tensile members constituting each tensile member group is changed, the number of the tensile member group having the longest length is set to the maximum, and the number of each tensile member group is reduced as the length becomes shorter. Reduce sequentially. For example, if the total number of tensile members is 6, the longest tensile member group consists of 3 tensile members, the next longest tensile member group consists of 2 tensile members, and the shortest tensile member group consists of 1 Constitute. This is inserted into a drilled hole in the ground, a hardening material such as cement milk is injected into the inside and outside of the sheath, and the fixing long portion of the tensile material is adhered to the hardening material to fix it. In the drill hole, the longest anchorage length of the tension material is located on the bottom side of the drill hole, and the next longest tension material anchorage length is located on the ground side and in the drill hole. Become.

A tension force is applied to each tension member fixed as described above. Since tension members have different lengths depending on the group, there is a difference in elongation when tensioned.When tensioned together, a large load acts only on the shortest tension member. Do it. That is, if there are three tension material groups, each tension material group is separately tensioned by the jack to give a predetermined tension force, and finally the same tension force is applied to all the tension material groups. At this time, the tension applied to each tension material group is changed. First, a tensile force of about 60% of the breaking load is applied to the longest tensile material group, and to a tensile material group having a longer length than that, about 10% is sequentially applied to each tensile material group in the order of decreasing length. It is preferred to reduce the tension by%.

[0011]

Function: For example, assuming that the breaking load of each tensile member is 60%, the six tensile members are divided into three tensile member groups, the longest tensile member group is three, and the next longest tensile member group is two. , The shortest tension material group is made into one and each tension material is given the desired tension force. Then, a total load of 30 tons is applied to the longest tensile material group, a total load of about 17 tons is applied to the next longest tensile material group, and a total load of about 7 tons is applied to the shortest tensile material group. In other words, in terms of the total length of the anchored long portion B of the anchor, it means that the acting tension force gradually increases toward the bottom side of the drilled hole. This is a state in which the portion of the fixing long portion B located on the shallow side on the ground side is always pushed up by the portion located on the bottom side. That is, the compressive force acts on the entire length of the fixing long portion B, and the anchor is different from the conventional ground anchor called the tension type. In other words, in the conventional tension type anchor, tensile force acts so that part of the fixing length part expands and the adhesive is cut off between the hardened material and the ground. Is less likely to occur. In addition, in the dispersion type in which the fixing length portion is shifted along the entire length of the drilled hole, the load of the tensile member is dispersed over the entire length, but in addition to this, the anchor where the compressive force acts on the entire fixing length portion B is less likely to cause attachment breakage, It can be expected that a large amount of frictional resistance will be obtained.

When an increase in load occurs due to an unexpected situation in the anchor to which tension is applied as described above, the anchors are dispersed and act on each tension member. However, as described above, the tensile material having a short length has a smaller elongation than the tensile material having a long length, and therefore the rate of increase in load is larger than that of the long material. Due to an unexpected situation, the tension of the longest tension material is 10%.
While increasing, for example, the second longest tensile material will increase 10% by number, and the third longest tensile material will increase by 20 %%.
In other words, the increase rate of the load is high due to the small elongation, and even if there is a difference in the tension force given in advance, the load that the shorter tensile member bears is the load that the longer tensile member bears as the load increases. It will be 80%. Finally, when the load carried by the longest tensile material becomes 80% of the breaking load, the load acting on other tensile materials also becomes close to 80%. As a result, almost even loads are applied to all of the plurality of tension members. When the load is increased more than this, the short tensile member receives a larger load, so the elongation deformation becomes large, and a large difference in load does not occur for each tensile member. There is no problem. The relationship between the elongation of this tensile member and the load is shown in the graph of FIG.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on an embodiment shown in the drawings. In the figure, 1 is a tension member, the free length portion is passed through an unbonded sheath 2 of polyethylene, and the fixing length portion 3 is left bare. The sixteen tension members as described above are divided into three tension member groups, and the lengths are made different for each tension member group. The longest tension material group is composed of three tension materials 1a, the next longest tension material group is composed of two tension materials 1b, and the shortest tension material group is composed of one tension material 1c. The tension members 1 are bundled and passed through the fixing sheath 4. As the fixing sheath 4, a deformed sheath made of stainless steel having an uneven surface is used. Since the tension material 1 has a different length for each tension material group, the fixing length portion 3 in the fixing sheath 4 is sequentially displaced. That is, the longest tension material group is located at the end of the fixing sheath 4, and as the tension material group becomes shorter, the fixing long portions 3 are sequentially displaced and arranged in the sheath 4. In the experiments described below, the length Lp from the end of the fixed length portion 3 of each tension member group to the end of another tension member group is 2 to 3 m, and the length Lf from the end of the free length portion to the ground is 6 It was set to ~ 7 m. The free length portion of the tension member 1 is arranged in a straight sheath 5 made of synthetic resin.

The one constructed as described above is inserted into the drilled hole 6 excavated in the ground. In this state, the longest tensile member 1 is located on the innermost side of the excavation hole 6, and as it becomes shorter, it is sequentially located on the ground side. Sheath 4 in this state
Inject cement milk, which is the hardening material 7, into and out of 5 and harden it. The fixing long portion 3 of the stripped tensile member 1 adheres to the hardening material 7, and the hardening material 7 injected into the outer periphery of the fixing sheath 4 adheres to the peripheral surface of the sheath 4 and the inner surface of the drilled hole 6 to form the fixing long portion. B
Is established.

Tension is applied to the ground anchor as described above. The tension force is applied separately to the tensile member groups having different lengths. The tensile load of 30 tons is given to the three longest tensile material groups, and 60% of the breaking load of each tensile material is set to 10 tons. Tensile force of about 16.6 tons gives 40% of the breaking load to the shortest tensile member group, resulting in total tension of 6.6 tons. That is, the tension force that acts on the bottom side of the drilled hole 6 is large over the entire length of the fixing length portion B, and the compression force that pushes up from the bottom side to the ground side acts. This makes it difficult for the hardened material 7 and the surrounding ground to become detached from each other. Further, since the tension member 1 is displaced in the fixing sheath 4, the load due to the tension force is dispersed over the entire length of the fixing length B,
The frictional resistance τs can be obtained from the entire length. Moreover, even if an unexpected load is generated and a difference in elongation occurs due to the difference in the length of the tensile member 1, about 80% of the breaking load acts on all the tensile members 1, and some of the tensile members 1 It does not work either. The following table 1 shows the numerical values obtained by the experiment in which this was performed.

[0016]

[Table 1]

According to the above table, when the distance Lp between the fixing positions of each tension member group is set to 3 m and the length Lf from the fixing position of the shortest tension member 4c to the ground is 6 m,
The load acting on each of the tensile members 1a, 1b, 1c is approximately 80% of the breaking load. In the above examples, the tensile member 1 was divided into three tensile member groups, but the number of the tensile member groups and the number of each of the tensile members 1 constituting the tensile member group are arbitrary, and the tensile members constituting the tensile member groups located at a shallow position are used. The number of the material 1 may be smaller than that of the tensile material 1 located at a deeper position than that.

[0018]

The present invention has been made to solve the above problems, and the following effects can be obtained. The tension material is divided into tension material groups of different lengths, and the anchoring length part is slid and anchored in the sheath. Therefore, the load is distributed over the anchor anchoring length part, and the friction resistance force is obtained from the entire length. You can Since the number of tensile material groups that settle in the back of the drilling hole was set to be larger than the number of tensile material groups that settled in a shallower depth, the load that acts on the drilling hole becomes larger at the back of the drilling hole and pushes upward from the back. The compressive force acts on the hardened material and the hardened material and the surrounding ground are less likely to be cut off. The deeper the hole is, the deeper the surrounding ground is stable and firm, and even if it is a distributed anchor, it anchors a large amount of tension material at a deep position.This anchor improves the problems of the distributed type itself. And make the load-distributed anchor even more reliable. The tension force is changed for each tension material group with different length, and the tension force of short tension material is made small beforehand, so even if an unexpected situation occurs after that and the load increases, the tension force acting on each tension material. Since the load is almost equalized, the load is not concentrated on a part of the tensile material and the adhesion with the hardened material is not broken or the tensile material is not broken. Since it is a simple structure that only changes the tension applied, it simplifies the design, calculation, and construction, ensures that its function is demonstrated, and improves the reliability of the anchor.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a ground anchor according to the present invention.

FIG. 2 is a stress diagram showing the action of the tension force.

FIG. 3 is a distribution diagram of a frictional resistance force between a hardened material and a surrounding ground.

FIG. 4 is a distribution diagram of a conventional ground anchor and frictional resistance force.

FIG. 5 is a graph showing the adhesion stress between the hardened material and the surrounding ground.

FIG. 6 is a graph showing elongation and load of a tensile member.

[Explanation of symbols]

 A Free length part B Fixing length part 1 Tensile material 2 Unbonded sheath 3 Tensile material Fixing length part 4 Fixing sheath 5 Straight sheath 6 Drilling hole 7 Hardening material

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[Procedure amendment]

[Submission date] January 29, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

[0016]

[Table 1]

Claims (4)

[Claims] 1. A plurality of tension members each having a fixed length portion which is exposed at a tip end thereof are divided into several groups, and the length of the tension members is made different for each group, and the tension members having different lengths. The number of the tension material group with the longest length in the anchor that slides the fixing length part for each group and arranges it in the sheath, positions it inside the drilling hole, and fills the hardening material inside and outside the sheath to fix it. The tensile force given to each tensile material group as the length is shortened, and the tensile force is given to each tensile material group as the length is shortened. The ground anchor characterized by reducing. 2. A plurality of tensile members are divided into at least two tensile member groups, the longest tensile member group is constituted by 1/3 to 2/3 of the total number of tensile members, and then the length is set. 2. The ground according to claim 1, wherein the long tensile material is composed of 1/4 to 2/4 of the total number of tensile materials, and the number is gradually reduced as the length is shortened. anchor. 3. The distance between the fixing positions of each tension member group is 1.5.
2. The ground anchor according to claim 1, wherein the length of the tension member group having the shortest length from m to 3 m is 6 m from the fixing position to the ground surface. 4. A tensile material group having the longest length is given a tension force of about 60% of the breaking load of the tensile material, and a tensile material having a length shorter than that is applied in order of decreasing length. The ground anchor according to claim 1, wherein the tension is reduced by about 10% of the breaking load for each group.