JP7048936B2 - Self-drilling lock bolt and ground reinforcement method using it - Google Patents

Description

The present invention is a self-perforated lock bolt and a self-perforated lock bolt that is driven into the ground while being perforated by a perforating bit attached to the tip in a soft ground where the perforated hole wall is not self-supporting and it is difficult to insert the lock bolt. Regarding the reinforcement method of the ground using.

Conventionally, as a support using a lock bolt, after drilling from the mirror surface or wall surface of the face toward the ground with a drill jumbo equipped with a drilling rod, the drilling rod is pulled out and the lock bolt is inserted in the drilling. It is known to prevent displacement and loosening of the ground by inserting it and filling the surroundings with grout material to integrate it with the ground, and to reinforce the ground around the tunnel.

In addition, in the case of collapsible ground where there is a risk of hole wall collapse when the drilling rod is pulled out, it is difficult to insert the lock bolt into the drilling after pulling out the drilling rod, so a drilling bit at the tip. A self-drilled lock bolt may be used in which the lock bolt is driven into the ground while drilling the ground, and the rod used for drilling is used as it is as a lock bolt for reinforcement. This self-drilling lock bolt work was performed by drilling the ground with a drill jumbo using a hollow lock bolt with a drilling bit attached to the tip, and then injecting grout material from the rear end of the lock bolt. The grout material passes through the drilling bit and is filled and solidified in the drilling.

When excavating a tunnel in a soft ground, if it is difficult for the face to stand on its own and the face is unstable, an auxiliary method may be used to stabilize the ground in front of the face by driving a mirror bolt into the face. In this construction method, since the mirror bolts that have been driven in are excavated when the face is excavated, the material of the mirror bolts is a glass fiber reinforced resin (so that it does not interfere with the excavation of the face and can be cut relatively easily. Glassfiber Reinforced Plastic, GRP or GFRP) is often used. The GRP lock bolt is superior in corrosion resistance to steel bolts and is lightweight at about 1/4 in weight, so that it is excellent in workability and can be easily cut by a cutter bit or the like during tunnel excavation. Because of its advantages, it is widely used not only as mirror bolts but also as other lock bolts such as lock bolts radially placed on the wall surface of a tunnel.

As the lock bolt made of fiber reinforced resin, for example, in Patent Document 1 below, in a support member for bedrock in which a drilling crown is attached to the tip side and the base end side is connected to a drilling machine or an injection machine. Self-perforation in which threaded portions are formed on the outer periphery of both ends of a fiber-reinforced cured resin rod having linear glass fibers and spiral glass fibers oriented in the longitudinal direction of the pipe within the wall thickness of the pipe made of the cured resin. Bolt is disclosed.

Further, as an auxiliary method for assisting a defective ground with a mirror bolt, for example, in Patent Document 2 below, a tubular reinforcing material is placed in the ground, and the internal space of the tubular reinforcing material that has been placed or is being placed is used. A construction method in which an expandable cement-based solidifying material is injected, and the solidifying material is leached into the ground around the tubular reinforcing material to expand and solidify, thereby increasing the pressure in the ground and reinforcing the ground. Is disclosed.

Japanese Unexamined Patent Publication No. 9-184400 Japanese Patent Application Laid-Open No. 2003-321992

However, the conventional self-drilling GRP lock bolt is a GRP when a large load is applied at the time of drilling due to impact such as impact or rotation when drilling with a drill jumbo in a relatively hard ground or a ground mixed with gravel. There was a drawback that defects such as breakage and breakage of the manufactured lock bolts were likely to occur. Therefore, in the techniques described in Patent Documents 1 and 2, when a self-drilling lock bolt made of GRP is used, the impact energy acting on the tip portion provided with the drilling bit is not absorbed and the drill jumbo drifter and lock are used. Since the concentration is concentrated on the joint end with the bolt, the lock bolt is liable to break or break.

Therefore, a main object of the present invention is to provide a self-perforated lock bolt capable of preventing breakage or breakage of the lock bolt at the time of drilling, and a method for reinforcing the ground using the self-perforated lock bolt.

In order to solve the above problem, the present invention according to claim 1 comprises a hollow lock bolt provided with a drilling bit at the tip, and the lock bolt is composed of a fiber reinforced resin lock bolt and a steel lock bolt. A self-drilling lock bolt that is axially connected by a sleeve .
A self-perforated lock bolt characterized in that the steel lock bolt is connected to the rear end of the fiber-reinforced resin lock bolt having a perforated bit at the tip thereof is provided.

In the invention according to claim 1, since the fiber-reinforced resin lock bolt and the steel lock bolt are connected in the axial direction by the sleeve, the ground is relatively hard or the ground is mixed with gravel. Even if an impact force such as impact or rotation acts during drilling with a drill jumbo, the impact energy is absorbed and relaxed by the excellent yield strength of the steel lock bolt, and the lock bolt can be prevented from breaking or breaking. That is, even when the drilling bit comes into contact with a relatively hard ground or gravel due to axial displacement or torsional deformation of the steel lock bolt, a strong impact such as impact or rotation from the drill jumbo occurs. Since the energy can be absorbed and buffered by the steel lock bolt portion, damage to the fiber reinforced resin lock bolt can be prevented.

Further, in the self-drilling lock bolt according to the present invention, since the use of the steel lock bolt is limited to a part, the fiber reinforced resin lock bolt portion has excellent corrosion resistance, and the weight of the entire lock bolt can be reduced. It has excellent properties and can be easily cut during tunnel excavation even when used as a mirror bolt or a lock bolt that will be cut in future tunnel widening excavation.

In the present invention , the steel lock bolt is connected to the rear end of the fiber reinforced resin lock bolt by the sleeve. In this embodiment, by fixing the steel lock bolt portion to the drifter of the drill jumbo, the steel lock bolt is placed on the portion where the impact force such as impact or rotation from the drill jumbo at the base end directly exerts a large force. Due to the location, the excellent yield strength of the steel lock bolts will more reliably prevent breakage and breakage of the fiber reinforced resin lock bolts.

The present invention according to claim 2 comprises a hollow lock bolt provided with a perforated bit at the tip, and the lock bolt is such that a fiber reinforced resin lock bolt and a steel lock bolt are axially connected by a sleeve. It is a self-drilling lock bolt
The fiber reinforced resin lock bolt is connected to the rear end of the tip side steel lock bolt provided with a drilling bit at the tip, and the rear end side steel lock bolt is connected to the rear end of the fiber reinforced resin lock bolt. Self-drilling lock bolts characterized by being connected are provided.

In the invention according to claim 2 , the fiber-reinforced resin lock bolt is connected to the rear end of the tip-side steel lock bolt by the sleeve, and the fiber-reinforced resin lock bolt is connected to the rear end of the fiber-reinforced resin lock bolt by the sleeve. A steel lock bolt on the rear end side is connected. This embodiment is particularly suitable for use as a long lock bolt having a total length of more than 4 m, and the tip side steel lock bolt provided with a drilling bit is connected to the tip of the fiber reinforced resin lock bolt. Therefore, even if the drilling bit comes into contact with a hard ground or gravel and a large impact force acts on the tip portion, the impact force is absorbed and relaxed by the steel lock bolt on the tip side, which has excellent proof stress. It will be possible to prevent breakage and breakage of lock bolts made of fiber reinforced resin.

As the present invention according to claim 3 , in the sleeve, the bond length of the fiber-reinforced resin lock bolt is longer than the bond length of the steel lock bolt. Is provided.

In the invention according to claim 3 , in order to prevent the fiber-reinforced resin lock bolt in the sleeve from being damaged and to secure a predetermined tensile strength, the bond length of the fiber-reinforced resin lock bolt in the sleeve is relatively set. It's long.

According to the fourth aspect of the present invention, in each of the fiber-reinforced resin lock bolt and the steel lock bolt, a male screw portion is formed on the outer surface of at least the portion to which the sleeve is bonded, and the male screw portion is formed on the inner surface of the sleeve. The self-drilling lock bolt according to any one of claims 1 to 3 , wherein a screwable female thread portion is formed is provided.

In the invention according to claim 4 , the fiber-reinforced resin lock bolt is screwed to one end of the sleeve, and the steel lock bolt is screwed to the other end, so that the fiber-reinforced resin lock bolt and the steel lock are screwed together. It is a structure in which bolts are connected. Therefore, the two can be easily connected and the workability is improved.

The present invention according to claim 5 is a ground reinforcement method using the self-drilling lock bolt according to any one of claims 1 to 4 .
The self-drilling lock bolt is placed in the ground, and the grout material is injected through the hollow portion of the fiber-reinforced resin lock bolt and the steel lock bolt, and the grout material permeates into the ground to reinforce the ground. A method of reinforcing the ground using a self-drilling lock bolt, which is characterized by the fact that it is used, is provided.

As described in detail above, according to the present invention, it is possible to provide a self-drilled lock bolt that prevents the lock bolt from breaking or being damaged during drilling, and a method for reinforcing the ground using the self-drilled lock bolt.

It is a vertical sectional view which shows the excavation procedure of a tunnel. It is a cross-sectional view of a tunnel. It is a side view which shows the self-drilling lock bolt 1 which concerns on this invention. It is an enlarged sectional view which shows the sleeve 6 part of the self-drilling lock bolt 1. (A) to (E) are cross-sectional views showing the construction procedure of the ground reinforcement method using the self-perforated lock bolt 1 according to the present invention. It is a cross-sectional view which shows the construction procedure (1) of a tunnel. It is a cross-sectional view which shows the construction procedure (2) of a tunnel. It is a side view which shows the self-drilling lock bolt 1A which concerns on another form example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

As shown in FIGS. 1 and 2, the self-drilling lock bolt 1 according to the present invention includes a lock bolt that is inserted and placed in the tunnel wall surface in the direction of the tunnel radial direction during tunnel excavation, and a ground in front of the face. It can be used as a mirror bolt to be inserted and placed toward a mountain, and can also be used as a support member for reinforcement of a wall surface such as a revetment or a slope. The self-perforated lock bolt 1 is particularly preferable when the perforated hole wall does not stand on its own and is placed on a soft ground where it is difficult to insert the lock bolt. It can also be used for good ground. This document describes in detail the case where it is used for tunnel excavation.

As shown in FIGS. 3 and 4, the self-perforated lock bolt 1 according to the present invention is composed of a hollow lock bolt 3 having a perforated bit 2 at the tip, which is opposite to the tip provided with the perforated bit 2. The lock bolt 3 at the base end on the side is fixed to the drifter of the drill jumbo so that the lock bolt 3 is driven into the ground while punching the ground with the drilling bit 2 while applying impact and rotation. Is.

The lock bolt 3 has a structure in which a fiber reinforced resin lock bolt 4 and a steel lock bolt 5 are axially connected by a sleeve 6. That is, the lock bolt 3 is divided into a fiber reinforced resin lock bolt 4 and a steel lock bolt 5 in the axial direction, and these are connected in the axial direction by the sleeve 6.

The fiber-reinforced resin lock bolt 4 and the steel lock bolt 5 are each made of a hollow substantially circular tube body, and hollow portions 4a and 5a penetrating both ends along the axial direction are formed in the axial core portion. .. In the connecting portion by the sleeve 6, both hollow portions 4a and 5a communicate with each other. The outer diameter of the fiber-reinforced resin lock bolt 4 and the outer diameter of the steel lock bolt 5 are formed to be substantially the same, and the diameter (inner diameter) of the hollow portion 4a of the fiber-reinforced resin lock bolt 4 and steel. The diameter (inner diameter) of the hollow portion 5a of the lock bolt 5 is formed to be substantially the same as the diameter (inner diameter).

The fiber-reinforced resin lock bolt 4 is composed of a fiber-reinforced resin impregnated with a thermosetting resin and then cured. The thermosetting resin can be arbitrarily selected as long as it is used for the fiber reinforced resin, and examples thereof include unsaturated polyester resin, vinyl ester resin, epoxy resin, polyamide resin and phenol resin. be able to. Further, the fiber used for the fiber-reinforced resin can be arbitrarily selected, and examples thereof include glass fiber, carbon fiber, and Kepler fiber. In particular, it is preferable to use glass fiber.

It is preferable that each of the fiber-reinforced resin lock bolt 4 and the steel lock bolt 5 has a male threaded portion formed on the outer surface of at least the portion to which the sleeve 6 is bonded. It is desirable that the male threaded portion is formed over the entire length of the lock bolts 4 and 5. It is preferable that the fiber-reinforced resin lock bolt 4 and the steel lock bolt 5 have threads of the same shape having the same pitch and the like. As a result, the same workability as that of the conventional lock bolt can be obtained, and the workability of the connection by the sleeve 6 is also improved.

The method for manufacturing the fiber-reinforced resin lock bolt 4 is not particularly limited, and a generally known method can be appropriately selected. As an example of this, the filamentous fibers are integrally wound and tightened in a spiral shape at intervals in the outer peripheral axis direction on the surface of a rod-shaped long fibrous fiber impregnated with a thermosetting resin and continuous in the length direction. It can be created by forming a spiral concave groove portion by the raised and tightened filamentous fiber portion and forming a convex mountain portion between the intervals between the adjacent concave groove portions, and then curing the thermosetting resin. can. The rod-shaped long fibrous fiber is a long-fiber fiber that has been cured into a rod by a thermosetting resin. As the long fibers, the fibers listed as the above-mentioned fiber reinforced resin can be used, and among them, glass fibers are particularly preferable. Further, the filamentous fiber is a fiber used for forming a concave groove portion and a convex mountain portion by winding it around a long fibrous fiber and tightening it. For example, vinylon, tetron, kepler, nylon. , Glass yarn, glass roving and the like can be used.

As the steel lock bolt 5, a conventionally known steel lock bolt can be used as it is.

The sleeve 6 that connects the fiber-reinforced resin lock bolt 4 and the steel lock bolt 5 is a steel coupling member that connects the ends of both lock bolts 4 and 5 in a state of being abutted in the axial direction. , Forming a hollow circular tube with both ends open. On the inner surface of the sleeve 6, a female screw portion into which the male screw portion of the fiber reinforced resin lock bolt 4 and the steel lock bolt 5 can be screwed is formed. As a result, the fiber-reinforced resin lock bolt 4 is screwed in from one end of the sleeve 6, and the steel lock bolt 5 is screwed in from the other end, whereby the fiber-reinforced resin lock bolt 4 and the steel lock bolt are screwed in. 5 can be connected.

The length of the sleeve 6 is arbitrary, but is preferably 100 to 500 mm, preferably 100 to 300 mm.

As shown in FIG. ₄ , in the sleeve 6, the bond lengths L4 and L5 of the fiber-reinforced resin lock bolt 4 and the steel lock bolt ₅ may be the same, but the fiber-reinforced resin lock bolt may be the same. It is preferable that the bond length L ₄ of 4 is longer than the bond length L ₅ of the steel lock bolt 5 (L ₄ > L ₅ ). As a result, damage to the fiber-reinforced resin lock bolt 4 can be reduced, and a predetermined tensile strength can be secured in the sleeve 6. The bond lengths L ₄ and L ₅ are the lengths at which the lock bolts 4 and 5 fit into the sleeve 6, and the end edge of the fiber reinforced resin lock bolt 4 and the steel lock bolt 5 in the sleeve 6 are used. By arranging the bolts so as to be abutted against each other, the total length of the combined lengths of the two is substantially the same as the total length of the sleeve 6.

In order to improve the adhesion between the sleeve 6 and the lock bolts 4 and 5, the gap between the inner surface of the sleeve 6 and the outer surface of the fiber reinforced resin lock bolt 4 and the steel lock bolt 5 is filled with a filler. Is preferable.

In the self-drilling lock bolt 1 of the embodiment shown in FIG. 3, a steel lock bolt 5 is connected to the rear end of the fiber reinforced resin lock bolt 4 having a drilling bit 2 at the tip thereof via the sleeve 6. There is. That is, the fiber reinforced resin lock bolt 4 is arranged on the tip end side, and the steel lock bolt 5 is arranged on the base end side, and these are connected by the sleeve 6. The drilling bit 2 is attached to the tip of the fiber-reinforced resin lock bolt 4, and the rear end side of the steel lock bolt 5 is fixed to the drifter of the drill jumbo.

When the self-drilling lock bolt 1 is set in the drifter of the drill jumbo, only the steel lock bolt 5 portion on the proximal end side is fixed, and the fiber reinforced resin lock bolt 4 portion is arranged in front of the drifter.

The length (L1) of the steel lock bolt 5 is formed to be a length necessary for absorbing and mitigating the impact energy on the proximal end side in addition to the length for fixing to the drifter of the drill jumbo. It is preferably about 1 m. The total length of the self-drilling lock bolt 1 is arbitrarily set depending on the situation, but since it is generally about 3 to 4 m, it is adjusted by the length of the fiber-reinforced resin lock bolt 4 and is made of the fiber-reinforced resin. The lock bolt 4 is longer than the length (L1) of the steel lock bolt 5.

In the self-perforated lock bolt 1 according to the present embodiment, the perforated bit 2 is attached to the tip of the fiber-reinforced resin lock bolt 4. The perforated bit 2 can be mounted without limitation by using known means, for example, the male screw portion provided on the outer surface of the fiber reinforced resin lock bolt 4 is provided on the hollow inner surface behind the perforated bit 2. This can be done by screwing the female threaded portion (not shown).

The inside of the drilling bit 2 is provided with a through hole that opens toward the tip and communicates with the hollow portion 4a of the fiber-reinforced resin lock bolt 4, and is rearward through the hollow portion of the lock bolt 3 during self-drilling. By ejecting air or water sent from the end through the through hole of the perforation bit 2 from the opening at the tip, rapid perforation can be performed and the self-perforation lock bolt 1 is driven into the ground. After that, the grout material fed from the rear end through the hollow portion of the lock bolt 3 is discharged from the opening at the tip through the through hole of the perforation bit 2, so that the grout material can be reliably filled in the perforation. can.

A procedure for reinforcing the ground using the self-drilling lock bolt 1 having the above configuration will be described. First, as shown in FIG. 1, a ground is excavated to form a tunnel space 10, and a spraying material 11 such as mortar or concrete supplied from a concrete mixer truck 12 is sprayed on the wall surface of the tunnel space 10. After spraying, the self-drilling lock bolt 1 is driven into the ground by the drill jumbo 14.

As shown in FIG. 5A, the self-drilling lock bolt 1 is driven by attaching the steel lock bolt 5 portion on the rear end side of the self-drilling lock bolt 1 to the drifter 15 of the drill jumbo 14. While applying impact and rotation by 14, a drilling bit 2 provided at the tip forms a drilling in the ground, and a lock bolt 3 (fiber reinforced resin lock bolt) led by the drilling bit 2 and integrally mounted. 4 and a steel lock bolt 5) are placed in the perforation.

When the self-drilling lock bolt 1 is placed in the ground, the drifter 15 of the drill jumbo 14 is removed from the self-drilled lock bolt 1 as shown in FIG. 5 (B), and the hollow portion 5a at the rear end of the lock bolt is removed. The injection adapter 16 is screwed into the opening of the hole, and the gap between the self-drilling lock bolt 1 at the mouth of the perforation and the ground is closed with the coking material 17.

Next, as shown in FIG. 5C, the tip of the injection device 18 for feeding the injection material 19 for ground reinforcement is connected to the injection adapter 16, and the hollow portions 4a and 5a of the lock bolt 3 and the drilling bit 2 are connected. The injection material 19 is press-fitted into the perforation through the perforation (FIG. 5 (D)).

As shown in FIG. 5 (E), the injection material 19 penetrates into the ground around the perforation through the voids and cracks in the ground, and reinforces a certain range of the ground around the perforation. As the injection material 19, known materials can be used without limitation, and for example, water glass type, cement type, or urethane type may be used.

Explaining the effect of the self-perforated lock bolt 1, the self-perforated lock bolt 1 has a structure in which the fiber-reinforced resin lock bolt 4 and the steel lock bolt 5 are axially connected by the sleeve 6. Therefore, even if an impact force such as impact or rotation acts during drilling with the drill jumbo 14 in a relatively hard ground or a ground mixed with gravel, the impact energy is due to the excellent yield strength of the constituent lock bolt 5. Is absorbed and relaxed, and breakage or breakage of the lock bolt 3 can be prevented. That is, even when the drilling bit 2 comes into contact with a relatively hard ground or gravel due to axial displacement or torsional deformation of the steel lock bolt 5, the drill jumbo 14 hits or rotates. Since the strong impact energy of the rock bolt 4 can be absorbed and mitigated, damage to the fiber-reinforced resin lock bolt 4 can be prevented.

Further, in the self-drilling lock bolt 1 according to the present invention, since the steel lock bolt 5 is limited to a part, the fiber reinforced resin lock bolt 4 portion has excellent corrosion resistance and the weight of the entire lock bolt can be reduced. It has excellent workability and can be easily cut when excavating a tunnel even when used as a mirror bolt or a lock bolt that will be cut in the future.

Examples of the lock bolt to be cut in the future include rock bolts used for tunnel widening excavation shown in FIG. 6 and two parallel tunnel excavations shown in FIG. 7. The example shown in FIG. 6 is a case of excavating a wall surface with the widening of a tunnel, and the example shown in FIG. 7 excavates a tunnel following a position adjacent to the preceding tunnel in parallel with the preceding tunnel. It is a case. As described above, by using the self-drilling lock bolt 1 according to the present invention as the lock bolt to be cut in the future, the portion of the fiber reinforced resin lock bolt 4 can be easily cut at the time of tunnel excavation, so that the tunnel can be excavated quickly. Is possible.

[Examples of other forms]
Next, the self-drilling lock bolt 1A according to another embodiment will be described with reference to FIG. The self-drilled lock bolt 1A has a fiber-reinforced resin lock bolt 4 connected to the rear end of a tip-side steel lock bolt 5A having a drilling bit 2 at the tip by the sleeve 6, and the fiber-reinforced resin. A steel lock bolt 5B on the rear end side is connected to the rear end of the lock bolt 4 by the sleeve 6. That is, by adding the tip side steel lock bolt 5A between the fiber reinforced resin lock bolt 4 and the drilling bit 2 of the self-drilling lock bolt 1 according to the embodiment shown in FIG. 3 above, the fiber reinforced resin Steel lock bolts 5A and 5B are arranged on both the front end side and the rear end side of the lock bolt 4.

As the tip side steel lock bolt 5A and the rear end side steel lock bolt 5B, the same steel lock bolt 5 used for the self-drilling lock bolt 1 according to the embodiment shown in FIG. 3 is used. be able to.

The self-drilling lock bolt 1A according to the present embodiment is particularly suitable for use as a long lock bolt having a total length exceeding 4 m, and the drilling bit 2 hits a relatively hard ground or gravel at the time of drilling and the tip portion thereof. Even when the impact or rotation energy acting on the bolt suddenly increases, the strength of the steel lock bolt 5A on the tip side can prevent the lock bolt 4 made of fiber reinforced resin from breaking or breaking.

1 ... Self-drilling lock bolt, 2 ... Drilling bit, 3 ... Lock bolt, 4 ... Fiber reinforced resin lock bolt, 4a ... Hollow part, 5 ... Steel lock bolt, 5a ... Hollow part, 6 ... Sleeve, 10 ... Tunnel Space, 11 ... spray material, 12 ... concrete mixer car, 13 ... sprayer, 14 ... drill jumbo, 15 ... drifter, 16 ... injection adapter, 17 ... caulking material, 18 ... injection device, 19 ... injection material

Claims (5)

It consists of a hollow lock bolt with a drilling bit at the tip, and the lock bolt is a self-drilling lock bolt in which a fiber-reinforced resin lock bolt and a steel lock bolt are axially connected by a sleeve. ,
A self-perforated lock bolt characterized in that the steel lock bolt is connected to the rear end of the fiber-reinforced resin lock bolt provided with a perforated bit at the tip . It consists of a hollow lock bolt having a drilling bit at the tip, and the lock bolt is a self-drilling lock bolt in which a fiber-reinforced resin lock bolt and a steel lock bolt are axially connected by a sleeve.
The fiber reinforced resin lock bolt is connected to the rear end of the tip side steel lock bolt provided with a drilling bit at the tip, and the rear end side steel lock bolt is connected to the rear end of the fiber reinforced resin lock bolt. Self-drilling lock bolts characterized by being connected. The self-perforated lock bolt according to any one of claims 1 and 2 , wherein in the sleeve, the bond length of the fiber-reinforced resin lock bolt is longer than the bond length of the steel lock bolt. In each of the fiber-reinforced resin lock bolt and the steel lock bolt, a male screw portion is formed on the outer surface of at least the portion to which the sleeve is bonded, and a female screw portion into which the male screw portion can be screwed is formed on the inner surface of the sleeve. The self-drilling lock bolt according to any one of claims 1 to 3 . A method for reinforcing a ground using the self-drilling lock bolt according to any one of claims 1 to 4 above.
The self-drilling lock bolt is placed in the ground, and the grout material is injected through the hollow portion of the fiber-reinforced resin lock bolt and the steel lock bolt, and the grout material permeates into the ground to reinforce the ground. A method of reinforcing the ground using self-drilling lock bolts, which is characterized by the fact that it is used.

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