JPH0932452A - Earth anchor construction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent gravel from spitting out of a leading casing as earth and sand when extending the casing in drilling a borehole in the highly pressurized ground of a sand or gravel layer. SOLUTION: A casing 12 provided at its end with a bit 11 is made to advance into the ground while being rotated, and an inside feedwater pipe 15 is also advanced so that a water spout 16 at the end of the pipe 15 is located inwards of the end bit 11 along the direction of its axis, thereby constantly forming a consolidated part 17 of the ground inside the end of the casing 12. The consolidated part 17 is gradually broken and fluidized by water ejected from the water spout 16 at the end of the feedwater pipe 15, and is discharged to the outside through a space around the outer periphery of the feedwater pipe. The casing 12 and the feedwater pipe 15 are advanced in synchronism with the fluidization rate of the consolidated part 17. When a borehole of a predetermined length for an earth anchor is formed, the feedwater pipe is removed from the inside of the casing, and concrete is packed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of constructing an earth anchor, and more particularly to a method of forming an earth anchor for a mountain retaining support.

[0002]

2. Description of the Related Art In recent years, an earth anchor construction method has been often used as a support for a mountain cleat associated with large-scale excavation. There are various construction methods for this earth anchor construction method. Among them, the single pipe drilling method is the main anchor method under pressure (groundwater pressure).

In this single pipe drilling excavation method, as shown in FIG. 2, a cylindrical casing 2 having a bit 1 at its tip is rotated for excavation, and a pump (not shown) is inserted into the casing 2. ) Was used to eject water from the bit 1 at the tip of the casing, and the drilling water was discharged through the overditch 3 around the outside of the casing 2.

[0004]

The above-mentioned conventional single pipe drilling method is effective and effective in the ground where the pressure is low. However, in the single pipe drilling method, there is a problem that the outflow of earth and sand cannot be stopped when the sand layer or gravel layer is encountered under high pressure due to the large amount of excess excavation because the ground fluidity is extremely high. Therefore, the single pipe drilling method is not often used under high pressure. Further, even if the pressure is low, it is not often used when the ground is a sand layer or a gravel layer.

Therefore, a ground anchor construction method using a double pipe type drilling excavator in which no outflow of sediment occurs even when the pressure is large or the ground is a sand layer or a gravel layer has been considered. As shown in FIG. 3, this double-pipe type drilling excavator has a cylindrical casing 5 having a bit 4 at its tip.
And a water supply pipe 6 arranged on the central axis of the casing 5 and installed such that a tip opening 6a for injecting water is located on substantially the same plane as the tip bit 4 of the casing 5.
It is composed of and.

A closed end plate 7 is connected to the rear end of the casing 5, and a muddy water discharge pipe 8 is formed in the closed end plate 7. The water supply pipe 6 extends through the closed end plate 7 to the outside and is connected to a water supply source (not shown) such as a water supply pump.

According to the earth anchor construction method using such a double pipe type drilling excavator, the casing 5 is rotated to excavate the ground G with the bit 4 at the tip, and the water pipe 6 is cut into the cut soil. Water sprayed from the tip opening 6a is sprayed into muddy water, and this muddy water is taken out by a muddy water discharge pipe 8 provided in the closed end plate 7 at the rear end of the casing 5, thereby substantially carrying out earth and sand. . Generally, the earth anchor has a length of about 20 m to 30 m, and a plurality of casings are added to drill a drilling hole having a predetermined length. After the drilling of a predetermined length is formed in this way, the drilling excavator is removed and concrete is filled to form a ground anchor.

According to the earth anchor construction method using such a double pipe type hole excavator, naturally, unlike the single pipe type, there is no spouting of earth and sand around the casing, and the sand layer or gravel layer is used for excavating holes. Is possible. However, in the conventional ground anchor construction method using the double pipe type drilling excavator, when the sand layer or the gravel layer of high pressure is encountered, for example, when the closed end plate 7 is removed when the casing 5 is added, Since the pressure is high, there is a problem that the gravel becomes blown out from the open end portion of the preceding casing 5 and is not easily stopped.

The object of the present invention is to solve the above-mentioned conventional problems. Even when excavating a hole in a high pressure ground of a sand layer or a gravel layer, the preceding casing is added when the casing is replenished. The purpose is to provide a method of constructing an earth anchor that prevents gravel from becoming sand and blowing out.

[0010]

The present invention is a ground anchor construction method, and is configured as follows in order to solve the above-mentioned technical problems. That is, according to the earth anchor construction method of the present invention, the casing having a bit at the tip is rotated to advance in the ground, and the water pipe arranged in this casing is also water jetting opening at the tip during the advance of the casing. Are forwarded together so as to be located axially inward of the tip bit of the casing to constantly form a consolidating part of the ground inside the tip of the casing, and water is discharged from the water ejection opening at the tip of the water pipe. Jetting,
Spraying on the inner surface of the consolidating portion to sequentially collapse and fluidize, and fluidized mud water is discharged to the outside through the outer space of the water pipe in the casing, thus forming a hole. At this time, if necessary, the casing and the water supply pipe are replenished to form a ground anchor drilling hole of a predetermined length, and then the water supply pipe is removed from the inside of the casing and filled with concrete.

According to the earth anchor construction method of the present invention thus constructed, since the tip of the casing projects from the water ejection opening position at the tip of the water pipe, a hole is formed in the ground while rotating the casing. Meanwhile, when water is ejected from the water supply pipe and the earth and sand are discharged from the muddy water extraction pipe provided in the closed end plate, a compacted portion is formed inside the tip of the casing.

Therefore, even in the case of excavating a hole in a gravel layer under a high pressure, when the casing is replenished, the gravel which is about to be blown out by the groundwater pressure is blocked by the consolidating portion. Therefore, the casing is replenished without blowing out the gravel from the preceding casing.

After that, when the drilled holes are formed to a predetermined length,
The casing and the water pipe are removed, and the drill hole is filled with concrete to form the earth anchor.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The ground anchor construction method of the present invention will now be described in more detail with reference to the embodiments shown in the drawings. FIG. 1 shows a drilling excavator 10 used in a ground anchor construction method according to an embodiment of the present invention. The boring machine 10 includes a cylindrical casing 12 having a bit 11 provided at its tip and rotatably supported.

A closed end plate 13 is detachably connected to the rear end portion of the casing 12, and a muddy water discharge pipe 14 is provided on the closed end plate 13. A water supply pipe 15 is arranged inside the casing 12 along the longitudinal axis thereof, and a tip of the water supply pipe 15 is opened for ejecting water to form a water ejection opening 16. This water pipe 1
5 is connected to an external water feed pump (not shown) through the closed end plate 13.

The casing 12 has a water pipe 1 at its tip.
5 is projected from the tip of the water, that is, the position of the water ejection opening 16, and a compacted portion 17 of the ground is formed inside the tip of the casing 12.

The earth anchor construction method of the present invention, which is carried out by using the boring machine 10 thus constructed, will be described below. In order to form an earth anchor, for example, in a ground G of a gravel layer, a casing 12 having a bit 11 at its tip
Rotate to move forward. And the casing 12
Water pipe 15 arranged in this casing 12 during forward movement of
Is also advanced so that the water ejection opening 16 at its tip is located axially inward of the tip bit 11 of the casing 12.

As a result, since the water ejection opening 16 which is the tip of the water supply pipe 15 arranged in the casing 12 is located rearward of the tip bit 11 of the casing 12, that is, inward in the axial direction, inside the tip of the casing 12. The clogged gravel is in a compacted state.

The compacted portion 17 clogged inside the tip of the casing 12 is fluidized by the water jetted from the water jetting opening 16 which is the tip of the water pipe 15, and is gradually broken from the surface thereof. It is discharged from the muddy water discharge pipe 14 through the outer peripheral space.

At this time, the speed at which the compacted portion 17 is sequentially collapsed from its surface by the water jetted from the water jet opening 16 of the water supply pipe 15 to be fluidized and the speed at which the casing 12 is dug are controlled to be substantially equal. . Therefore, the compacted portion 17 having the predetermined length L always exists inside the tip of the casing 12.

If the compacted portion 17 of the ground is always present inside the tip of the casing 12 in this manner, for example, when a hole is formed in the ground G such as a gravel layer having a high pressure, another casing is used as the preceding casing 12 Closed end plate 13 to add to
Even when the pressure is removed, the groundwater pressure that attempts to enter the casing 12 from the tip is blocked by the consolidating portion 17.

In this way, when the casing 12 and the water supply pipe 15 are added as necessary to form a ground anchor drilling hole of a predetermined length, the water supply pipe 15 is then pulled out from the casing 12 to replace the mortar. I do. Then, after inserting the PC steel wire, the tip bit is cut off, thereby forming a ground anchor. .

Incidentally, the reason why the muddy water is blown out when the casing is replenished in the conventional double pipe type hole excavator as shown in FIG. 3 is inferred from the operation of the hole excavator 10 as described above. Since the tip of the casing 5 which is the outer pipe and the tip of the water pipe 6 which is the inner pipe are configured to be located on substantially the same plane, the space between the inner pipe and the outer pipe is open to the ground. Therefore, it is considered that the groundwater pressure easily enters the casing 5 as soon as the closed end plate 7 connected to the rear end of the casing 5 is removed.

[0024]

EXAMPLE As one example of the earth anchor construction method of the present invention, the length L inside the tip of the casing 12 forming the compacted portion 17, that is, the water ejection opening 1 of the water pipe 15 is shown.
The tip length of the casing 12 protruding from the position 6 depends on the nature of the ground G, but is preferably about 50 cm.

[0025]

As described above, according to the earth anchor construction method of the present invention, the casing having the bit at the tip thereof is moved forward in the ground while rotating, and at the same time, the casing is arranged in the casing during the forward movement of the casing. As for the water pipe, by advancing together, the water ejection opening at the tip of the water pipe is positioned axially inward of the tip bit of the casing,
Since the compacted part of the ground is always formed inside the tip of the casing, for example, when forming a ground hole by forming a hole in the ground such as a gravel layer with high pressure, another casing is used as the preceding casing. Even if the closed end plate is removed for replenishment, the groundwater pressure that tries to enter the casing from the tip is blocked by the consolidating unit, and as a result, muddy water can be prevented from blowing out from the casing.

[Brief description of drawings]

FIG. 1 is a structural explanatory view schematically showing a ground excavation state by a ground anchor construction method according to an embodiment of the present invention.

FIG. 2 is a structural explanatory view schematically showing a conventional single pipe drilling excavator forming an earth anchor.

FIG. 3 is a structural explanatory view schematically showing a conventional double pipe type drilling excavator forming an earth anchor.

[Explanation of symbols]

 G Ground 10 Drilling excavator 11 Bit 12 Casing 13 Closing end plate 14 Mud extraction pipe 15 Water pipe 16 Water ejection opening 17 Consolidation part

Claims (1)

[Claims] 1. A casing having a bit at its tip is rotated to move forward in the ground, and a water pipe arranged in the casing also has a water jet opening at its tip when the casing is moving forward. By advancing together so as to be positioned axially inward from the bit, always forming a consolidation part of the ground inside the tip of the casing, injecting water from the water ejection opening at the tip of the water pipe, Spraying on the inner surface of the and breaking down one after another to fluidize,
Discharging the fluidized muddy water to the outside through the outer space of the water supply pipe in the casing, and when forming a hole in this way, the casing and the water supply pipe are replenished as necessary to have a predetermined length. A method of constructing an earth anchor, which comprises forming a hole for earth anchor, and then removing the water pipe from the inside of the casing and filling with concrete.