JPS5827368B2 - Removable earth anchor method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a removable earth anchor construction method that facilitates construction of an earth anchor and removal of its PC steel material.

Earth anchors, which are buried deep underground to maintain earth retaining walls during civil engineering and construction work, are usually constructed by integrating steel with cement milk, and are left in the ground even after the construction work is completed.

Therefore, when newly excavating the part where the earth anchor is buried, the steel material of the anchor that remains buried becomes an obstacle, making it impossible or extremely difficult to excavate.

In order to overcome this drawback, various methods have been proposed for removing embedded steel materials after construction is completed, but these methods involve, for example, melting the sheathing material of the sheathed PC steel material or destroying the surroundings of the steel material. This method was not practical because it was extremely labor intensive and caused damage to the nearby soil.

In view of these points, it is an object of the present invention to provide a removable earth anchor construction method that allows steel materials to be easily removed and does not cause damage to nearby soil.

The present invention is a method for removing a PC steel material while leaving a fixing body at the end of the PC steel material, in which a single fixing body is fixed to the ends of a plurality of PC steel materials, and the fixing body of the PC steel material is preliminarily removed from the vicinity of the fixing body. The tensile strength of the part is reduced by reducing its cross-sectional area, forming a notch, or applying heat treatment, and after being used as an earth anchor, it is added to the PC steel material.
By applying tension to each piece, the pieces are broken at the portions where the tensile strength is lowered, and the prestressed steel material is successively pulled out.

Hereinafter, the present invention will be explained with reference to drawings of embodiments.

Figure 1 shows the state in which the earth anchor is embedded, and the earth anchor 6 that holds the retaining wall 2 is located on the adjacent land 1 of the construction site.
is buried, and the retaining wall 2 is suppressed and held at the upper end of the PC steel material 3 via a bearing plate 61 and an anchor plate 62.

The earth anchor 6 consists of a PC steel material 3 consisting of a plurality of PC @ stranded wires 30, a fixing body 5 provided at the tip thereof, grout milk 60 filled around it, and the PC steel stranded wires and grout. It is composed of a tube 70 for insulation.

W70c! - As the pipe, a polyethylene pipe, a steel pipe such as a spiral sheath, or other pipes capable of preventing infiltration of grout milk can be used.

In this configuration, a plurality of PC steel members 3 are grouped together and a single fixing body 5 is attached to the tip thereof, so that the entire PC steel member 3 is made thin, thereby making it possible to reduce the diameter of the earth anchor polling hole.

Further, the anchoring body 5 is firmly anchored to the PC steel material 3 so that a large tension introducing force can be set when used as an anchor.

In the part of the PC steel stranded wire 3 near the anchoring body 5, a notch 8 is formed in each of the common stranded wires 30 as shown in FIG.
This applies tension to the stranded wire 30, causing it to break at the notch 8 due to stress concentration.

Instead of this steel stranded wire 30, a PC steel material may be used.

To construct this earth anchor, first, notches 8 are formed in each of the steel stranded wires 30 on the ground, and then a plurality of the wires are assembled together and a fixing body 5 is attached to assemble the PC steel material 3.

Next, the tube body 70 is inserted from the tip of the PC steel stranded wire to complete the anchor, and this is inserted into the hole at the construction site, and grout milk 60 is filled in the Pauling company, and after it hardens and becomes strong. Tension is applied to the PC steel material 3 at the anchor plate portion to hold the earth retaining wall 2.

The size and shape of the notch 8 are set so that the PC steel material 3 will not break depending on the tension applied at this time.

When removing the cable after the anchor work is completed, first, the introduction force to the PC steel material 3 is released at the tension fixing end, and tension is applied to each of the steel strands 30 one by one.

At this time, a slightly larger tension is applied to the common stranded wire 30 than the tension shared during use as an anchor, and by this tension the common stranded wire 30 is
It breaks due to stress concentration at the part, and is pulled out one by one.

Therefore, the steel stranded wire 30 will not be broken midway and left in the soil, and the PC steel material can be reliably removed leaving only the fixing body 5 and the portion fixed thereto.

3 and 4 show another embodiment, in which the steel strands 30
breaks one of the strands, thereby reducing the cross-sectional area of the steel wire 30.

Therefore, if a tension exceeding a certain value is applied to the steel stranded wire 30, it will break at that portion.

The drawing shows an example in which only one strand at the center of the stranded wire 30 is broken, but the number of strands to be broken is determined as appropriate from the relationship with the tension force as an anchor and the breaking force during extraction. do it.

In addition, PC steel material (diameter 12.7M) made of 7 steel stranded wires bundled
If the central strand of the stranded wire is broken at the point where the tension is introduced as an anchor, the force applied to the stranded wire will be approximately 77.0OOKP, but the force applied to the stranded wire during pulling will be approximately 16,000 OOKP. 000
Since it can be broken at Ky, the tension force as an anchor is large, and it can be pulled out with a relatively small force.

FIG. 5 shows yet another embodiment, in which the region A of the PC steel material 3 to which the fixing body is attached has been previously heat-treated to weaken its tensile strength.

Therefore, in this case as well, the conventional stranded wire 30 can be broken and removed with a relatively small force, as described above.

As shown in Fig. 6, the effect of heat treatment on the steel stranded wire 30 is that it exhibits the highest tensile strength in so-called bluing treatment at 200 to 300°C, and as the temperature rises above that, the tensile strength decreases. Breaking load can be set by selection.

As explained above, the present invention attaches a single anchoring body to the end of a plurality of PC steel members to form an anchor with a small diameter as a whole, and each steel member reduces the tensile strength near the anchoring body to 1. It is designed so that it can be pulled out one by one, and can exert sufficient tension as an anchor, while also being able to remove the steel material reliably with a small amount of force.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway sectional view showing an embodiment of the present invention with an earth retaining wall held, and Fig. 2 is a side view of the vicinity of the anchorage.
Fig. 3 is a side view showing another embodiment, and Fig. 4 is I of Fig. 3.
A sectional view taken along the line V-IV, FIG. 5 is a side view of the vicinity of the fixing portion showing yet another embodiment, and FIG. 6 is a diagram showing the relationship between heat treatment temperature and tensile strength of steel material. 3... PC steel material, 5... Anchor body, 6... Earth anchor, 8... Notch, 9... Broken part, 10...
Pipe, A... heat treatment area.

Claims (1)

[Claims] I In a method of removing a PC steel material while leaving a fixing body at the end of the PC steel material, a single fixing body is fixed to the end of a plurality of PC steel materials, and the PC! The tensile strength of the l1il material near the anchor is reduced by reducing its cross-sectional area, forming a notch, or applying heat treatment, and after using it as an earth anchor, tension is applied to the PC steel material one by one. This removable earth anchor construction method is characterized in that the prestressed steel material is sequentially pulled out by breaking the prestressed steel material at the portion where the tensile strength is reduced.