JPH062333A - Expanded anchor method - Google Patents

Abstract

(57) [Abstract] [Purpose] A bottom expansion anchoring method that enables small-diameter drilling and large-diameter bottom expansion in a soft layer. [Structure] The drilling pipe is a double pipe, and the anchor hole 16 is drilled by the bit 14 at the tip of the outer pipe 12-O to a predetermined position of the anchor free length L. Then, the inner pipe 12-I is extended from the tip of the outer pipe 12-O, and while being rotated, high-pressure water is jetted from the nozzle 18 on the side face of the inner pipe tip to perform bottom drilling to the anchor fixing position LO. Then, the high-pressure water is switched to cement milk, and the cement milk is sprayed to grout the anchor fixing portion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bottom expanding anchor construction method for expanding an anchor hole bottom of a mountain retaining wall.

[0002]

2. Description of the Related Art Mountain retaining walls are provided to prevent the collapse of earth and sand. The mountain retaining wall has a structure with excellent water stopping property so as to bear the water pressure of the spring water (groundwater) contained in the ground on the back side. Then, based on data such as soil surveys, the water level of spring water contained in the ground on the back side is assumed, and the water pressure of spring water acting on the mountain wall is calculated to design the mountain wall.

An anchor is provided to stabilize the ground behind the Yamadome wall. The anchor is a hole drilling machine (boring machine) on the mountain retaining wall, and the anchor material such as PC steel stranded wire is inserted and fixed in the anchor hole.
The tensile force is transmitted to the ground to obtain the required yield strength and stabilize the ground.

Here, after the PC steel strand is inserted into the anchor hole, cement milk (also called cement paste)
Such grout material is injected into the anchor hole to fix the PC steel strand to the ground at the bottom of the anchor hole (fixing part). Then, use the jack to tighten the tip (outer end) of the PC steel strand,
The anchor is fixed on the anchor plate and the anchor head, and the anchor is installed.

According to the anchor, the tensile force generated by tensioning the PC steel wire is transmitted to the ground to obtain the required yield strength and the ground is stabilized. Here, in order to strengthen the ground, it is sufficient to increase the tensile force generated in the anchor, that is, the yield strength of the anchor, and the yield strength of the anchor can be increased by the following procedure. Make large holes in the anchor holes to increase the peripheral area. Strengthen the ground by injecting strong materials.

By making a large hole in the anchor hole, it is possible to set a wide friction area between the PC steel wire and the ground. However, since it takes a long time to drill holes and the anchor construction cost tends to be high,
The method of strengthening the ground, which is not often used, is generally adopted.

Ground reinforcement is usually referred to as ground improvement,
It is roughly divided into three methods: chemical injection method, high-pressure jet method, and mixing and stirring method.

[0008]

In the chemical solution injection method, a mixed solution prepared by drilling holes from the surface of the ground and mixing cement glass with a chemical such as water glass is injected into a wide area to improve the ground, and to improve the ground. An anchor is constructed by drilling a predetermined anchor hole. With this method, groundwater can be stopped in a wide area and the ground is strengthened to some extent, but it is inevitable in places with a lot of underground water. In addition, it is strengthened sequentially from the voids where the mixed solution easily enters, and it is difficult to specify the strengthening range.

In the high-pressure jet method, first, a hole is drilled from the surface of the earth, and water is jetted laterally from the anchor hole to the ground at a pressure of 200 to 400 Kg / square cm to scrape the periphery of the anchor hole bottom. Then, high pressure cement milk of about 200-400 Kg / square cm is injected and injected to form a cement cylinder (bulb), and the fixing part of the PC steel strand is connected and fixed to a part of this cylinder. It With this method, a cement cylinder can be accurately formed at a target position. However, the construction must be performed over a wide area, and not only the cost is high, but also a large amount of muddy water is generated, the treatment of mud drainage is troublesome, and the surroundings are easily soiled.

In the mixing and stirring method, one or a few augers are drilled from the ground surface to a predetermined position, and the cement milk is stirred at a predetermined position while pouring. Further, there is also a case where a single auger is used to drill a hole from the surface of the earth, and the powder cement is pressure-fed and mixed with the water in the ground. With this method, the ground can be strengthened at the desired location, and mud drainage is small. However, not only the cost must be increased over a wide area, but also the auger machine is large in size, the construction cost is high, and the construction cannot be performed in a narrow place.

In the method of making a large hole in the anchor hole, the hole is drilled as a whole, that is, with a large diameter from the beginning to the end. Therefore, the drilling time is long and the drilling cost is high. become. On the other hand, if the anchor hole is not largely drilled as a whole and only the bottom portion (fixing portion) of the anchor hole is widely drilled, the required friction area can be obtained without lengthening the drilling time. Can be secured.

In the method of widening only the bottom portion of the anchor hole (bottom expanding anchor method), the bit at the tip of the drilling pipe of the drilling machine is laterally pushed out by the load or water pressure from the upper portion and pushed out. The bottom of the anchor hole is expanded with a bit for drilling.
Further, the bit may be pushed laterally and drilled by rotation in a predetermined direction (for example, left rotation).

In the conventional bottom expansion anchoring method in which the bit is laterally protruded and drilled, a small-scale bottom expansion can be carried out relatively easily. However, the following are pointed out as drawbacks. A large amount of protrusion cannot be obtained, and it is difficult to drill a large-diameter bottom hole in a small-diameter anchor hole. When anchoring in a soft layer, the bottom part may collapse and the PC steel wire may not be inserted to the intended depth.

The present invention is an anchor having a small diameter in a soft layer.
The purpose of the present invention is to provide a bottom-enlarged anchoring method that enables bottom-drilling of large-diameter holes.

[0015]

In order to achieve this object, according to the bottom expanding anchor method according to the present invention, the hole forming pipe is a double pipe, and the bit at the tip of the outer pipe is used to position the anchor free length at a predetermined position. Drill an anchor hole up to. Then, extend the inner pipe from the outer pipe tip, jet high-pressure water from the nozzle on the side of the inner pipe tip, and perform bottom drilling to the anchor fixing position,
The high-pressure water is switched to cement milk, and the cement milk is sprayed to grout the anchor fixing section.

[0016]

Embodiments of the present invention will now be described in detail with reference to the drawings.

As shown in FIG. 1, in the anchor-bottoming method according to the present invention, the boring pipe 12 of the boring machine includes an inner pipe 12-I and an outer pipe.
It is a double tube with 12-O. As you can see from Figure 1 (A),
First, the anchor hole 16 is drilled to the predetermined position of the anchor free length portion L by the bit 14 at the tip of the outer pipe 12-O.

The bit 17 is attached to the tip of the inner tube 12-I, and one to several nozzles 18 are provided on the side surface of the tip of the inner tube 12-I. Therefore, as shown in FIG. 1 (B), if the inner pipe 12-I is extended from the tip of the outer pipe 12-O and high-pressure water is jetted from the nozzle 18 while rotating the inner pipe, the anchor hole 16 is cut. A hole is made and the bottom is expanded.

When the bottom hole is drilled by high pressure water to the anchor fixing position (scheduled depth) LO, cement milk (cement paste) is injected and jetted in place of the high pressure water, and the anchor fixing portion Grouting is performed to form a cylinder (bulb) of cement on the bottom of the anchor. here,
The injection of cement milk may be performed while pulling up the inner pipe 12-I.

Then, the inner pipe 12-I is pulled out and collected. After recovering the inner pipe 12-I, a normal anchor process is performed. That is, an anchor material such as PC steel wire is inserted into the anchor hole 16 and the PC steel wire is fixed with a grout, and then the outer pipe 12-O is extracted and recovered. Then, the PC steel stranded wire is tensioned with a jack and fixed with an anchor plate and an anchor head.

In the present invention, after the anchor hole 16 is drilled to some extent by the bit 14 of the outer pipe 12-O, high-pressure water is jetted to expand the bottom, and the anchor hole 16 is filled with high-pressure water from the beginning to the end. Not drilled. Therefore, a large amount of muddy water is not generated, mud drainage is relatively easily treated, and the surrounding pollution can be prevented. In addition, it is not necessary to discharge the sediment from the bottom of the ground to the outside.

Further, by adjusting the position of the nozzle 18 by advancing and retracting the inner pipe 12-I, the position and length of the expanded bottom portion can be freely set, and the cement cylinder can be accurately molded at a desired position. Further, the position and length of the expanded bottom portion can be adjusted by adjusting the diameter and flow rate of the nozzle.

Furthermore, since most of the anchor holes 16 are drilled by the outer pipe 12-O, it is possible to easily drill a small diameter and also to easily enlarge a large diameter bottom by hydraulic pressure. That is, according to the present invention, it is possible to widen the bottom of a large diameter anchor hole.

Since the bottom is expanded by the high pressure water, the ground at the bottom of the anchor hole 16 is unlikely to collapse. Therefore, even when the anchor hole 16 is drilled in the soft layer, the PC steel wire can be inserted up to the expanded bottom portion of the anchor hole without being hindered by the collapse of the ground.

Do not stop at the free length part L, and go beyond the free length part to the planned fixing position (planned depth) LO with the outer tube 12-O and anchor hole 16
May be drilled. In this case, after drilling to the planned depth LO,
After pulling up the outer pipe 12-O to the free length part L, while rotating the inner pipe 12-I, high pressure water is jetted from the nozzle 18 to perform bottom drilling. Then, instead of high-pressure water, cement milk is sprayed to form a cylinder (bulb) of cement. Then, after pulling out and collecting the inner pipe 12-I, the PC steel wire is inserted into the anchor hole 16, and after pulling out and collecting the outer pipe 12-O, the PC steel wire is strained and fixed. Needless to say.

The nozzle 18 around the inner pipe 12-I may be a hole itself provided in the inner pipe, or the inner diameter of the hole provided in the inner pipe is 2.7 to
It may be configured with a nozzle of about 3.0 mm. Cement milk is, for example, 60 liters / minute, 200-300 Kg
It is jetted at / cm 2.

After the outer pipe 12-O is drilled to the planned depth Lo, the injection of high pressure water is omitted, the outer pipe is pulled up to the position of the free length L, and the cement milk is injected from the inner pipe 12-2. If
The ground is prevented from peeling off due to mud drainage, and the bottom anchor can be easily formed even in the soft layer. In this method, since cutting by high water pressure is omitted, the bottom expanding function is reduced, but the generation of muddy water can be further reduced.

The above-mentioned embodiments are intended to explain the present invention, and are not intended to limit the present invention at all, and all modifications and alterations made within the technical scope of the present invention are also included in the present invention. It goes without saying that it will be done.

[0029]

As described above, the expanded bottom anchor of the present invention.
According to the construction method, since the anchor holes are not drilled with high pressure water from the beginning to the end, a large amount of muddy water is prevented. Therefore, the mud drainage can be treated relatively easily, and the expanded bottom anchor can be formed without contaminating the surroundings. In addition, it is not necessary to discharge the sediment from the bottom of the ground to the outside.

By adjusting the position, diameter and flow rate of the nozzle, the position and length of the expanded bottom portion can be set freely, and the cylinder (bulb) of cement can be accurately molded to the desired position.

Since most of the anchor holes are drilled by the outer pipe, small-diameter holes can be easily drilled, and the large-diameter bottoms can be easily expanded by water pressure, so that the small-diameter anchor holes can be widened. It will be possible.

Since the bottom is expanded by high-pressure water, the ground at the bottom part of the anchor is unlikely to collapse, and even when the anchor hole is drilled in the soft layer, the anchor material such as PC steel wire collapses the ground. Can be inserted up to the bottom of the anchor hole without being hindered by

[Brief description of drawings]

FIG. 1 is a schematic process drawing showing a bottom expanding anchor construction method of the present invention.

[Explanation of symbols]

 12 Drilling pipe of drilling machine 12-I Drilling pipe outer pipe 12-O Drilling pipe inner pipe 14 Outer pipe tip bit 16 Anchor hole 17 Inner pipe bit 18 Inner pipe nozzle L Anchor free Expected depth of long LO anchor

Claims (2)

[Claims] 1. A boring machine for boring an outer hole of a double-hole boring pipe to an anchor free wall to a predetermined position of an anchor free length in an outer pipe, and extending an inner pipe from the outer pipe, While rotating, high pressure water is jetted from the nozzle on the peripheral surface of the inner pipe to expand the anchor hole to drill holes in the fixing part.Instead of high pressure water, the cement milk is jetted from the nozzle while the inner pipe A bottom-anchored construction method in which the machine is rotated to grout to the upper part of the fixing unit. 2. An outer pipe of a double-drilled pipe of a drilling machine, an anchor hole is drilled in a mountain retaining wall to a predetermined anchor depth, and the outer pipe is pulled up to an anchor free length portion, and an inner pipe While rotating, the high-pressure water is sprayed from the nozzle on the peripheral surface of the inner pipe to expand the anchor hole, and instead of high-pressure water, cement milk is sprayed from the nozzle to grout the bottom anchor method.