Generally, when a steep excavation hole is formed in a digging or foundation work at a civil engineering and construction field, to prevent an earth wall falling down toward the excavation hole, an earth anchor method is widely used. The earth anchor method is explained as follows.
As shown in FIG. 1, big stakes such as H-beams are driven into a ground and a designated ground is excavated, and then earth plates are inserted between the big stakes, and thus an earth wall 1 is formed.
Subsequently, boring is performed through the earth wall 1 at a predetermined slanted angle, then an anchor body 3 is driven into the boring portion 2, then grouting is performed for a fixed anchor length Lb, and thus the anchor body 3 is fixed. Generally, the anchor body 3 is divided into a free length La and the fixed anchor length Lb with respect to a portion at which a virtual collapse line (which is represented by a dashed line in FIG. 1) meets the boring portion, and the virtual collapse line is set by a design standard according to a soil between an edge of a bottom surface 6 of the excavation hole and the ground. A first grouting is generally performed for the fixed anchor length Lb.
When curing for the grouting is completed, a tension force is applied to the free length La of the anchor body 3 and the anchor body 3 is fixed into a bracket 10 which is installed at a girder 4 of the earth wall 1. To do this, the free length La of the anchor body 3 is passed through a through portion formed at the bracket 10 and then is fixed using a cone 5 having a diameter more than the through portion.
After the anchor body 3 is fixed into the bracket 10, a second grouting is performed for a remaining portion of the boring portion 2, and thus construction is completed. Accordingly, a tension force of the anchor body 3 counters with an earth pressure and supports the earth wall 1.
The present invention relates to a bracket applying the tension force to the free length La of the anchor body 3 and fixing the anchor body 3 in the earth anchor method.
FIG. 2 is a perspective view illustrating one example of a bracket 10 widely used in the prior art. The bracket 10 includes two side plates 11 each having about triangular shape, and a pressure bearing plate 12 which is installed on the same inclined sides of the two side plates 11 and couples the two side plates 11 and includes a through portion 12a, through which the anchor body 3 is withdrawn, at a center portion of the pressure bearing plate 12.
However, for the bracket 10, because the tension force of the anchor body 3 is distributed through the pressure bearing plate 12 and the both side plates 11, a case frequently occurs in construction that the pressure bearing plate 12 warps and the side plates 11 are deformed.
Further, as shown in FIG. 1, because the bracket 10 is supported by the girder 4, to fix the bracket 10, it is necessary that the side plates of the bracket 10 are welded to the girder 4. Accordingly, it takes much time to install and disjoint the bracket 10, and due to the welding, damages to the girder 4 may be unavoidable.
Recently, to resolve these problems, new type of brackets have been put on the market. For example, FIGS. 3 and 4 are perspective and exploded perspective views, respectively, of a bracket 50 described in Korean Issued Patent No. 441619.
The bracket 50 includes a main supporting material 20, an auxiliary supporting material 40, a guide material 30 fixed between the main supporting material 20 and the auxiliary material 40.
The main supporting material 20 includes two side plates 21, a pressure bearing plate 23 welded to upper portions of the same inclined sides 21a of the both side plates 21 and having a through portion 24, and base plates 22a and 22b spaced apart from each other and fixed to lower portions of the side plates 21.
The auxiliary supporting material 40 has a bent shape at a predetermined angle at a center of the auxiliary supporting material 40 and is fixed between the both side plates 21 of the main supporting material 20. The guide material 30 has about cylindrical shape, and one end of the guide material 30 is fixed to the pressure bearing plate 23 of the main supporting material and the other end of the guide material 30 is fixed to the auxiliary supporting material 40.
Because the auxiliary supporting material 40 and the guide material 30 distributes a tension force of an anchor body applied to the main supporting material 20, the bracket 50 endures a tension force more than the bracket described in FIG. 2. As shown in FIG. 5, even though a real tension direction of the anchor body 3 is not equal to a reference tension angle of the bracket 50, a free length of the anchor body 3 is withdrawn through the guide material 30, and it can be prevented to some extent to prevent the anchor body interfering with the through portion 24 and the girder 4.
However, as shown in FIG. 5, when the real tension direction of the anchor body 3 is not equal to the reference tension angle of the bracket 50, it is unavoidable that the anchor body 3 is severely bent and withdrawn through the guide material 30 and the through portion.
When the anchor body 3 is bent, a force in a different direction from the tension direction of the anchor body 3 is applied, and as a result, it is inevitable that the tension force applied to the anchor body 3 is distributed. Accordingly, to apply a tension force according to a design standard to the anchor body 3, a tension force more than that in a normal situation should be applied in consideration of distribution of a tension force. This means that the bracket 50 should have a more supporting force, and works as a limitation to losing weight and minimizing size of the bracket 50.
Recently, to resolve these problems, an earth anchor bracket has been suggested in which an arch-shaped curved portions are formed at inclined sides of both side plates and a pressure bearing plate is moved along the curved portions.
When the curved portion is formed in the earth anchor bracket, because the pressure bearing plate can be moved according to an installation angle of the anchor body, even though the anchor body is not bent, it is possible to maintain tension direction of the anchor body perpendicular to the pressure bearing plate.
To obtain this effect, a boring portion formed at a earth wall to insert the anchor body is bored exactly at a center of curvature of the arch-shaped curved portion of the earth anchor bracket.
However, in a real construction field, a case occurs much that the boring portion is deviated from a reference position. Accordingly, even though the pressure bearing plate is moved along the arch-shaped curved portion, it is difficult to maintain the tension direction of the anchor body perpendicular to the pressure bearing plate.
When the tension direction of the anchor body is not maintained perpendicularly to the pressure bearing plate, because a horizontal force as well as a perpendicular force is applied to the pressure bearing plate, the ground plate is moved along the curved portion of the earth anchor bracket and, for the moving, deformation of the pressure bearing plate occurs.