JP2012077509A - Expansion steel pipe lock bolt, manufacturing method thereof, and natural ground reinforcing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an expansion steel pipe lock bolt, which easily produces a sufficient frictional resistance to reliably reinforce natural ground, even such as soft bedrock, fractured bedrock, unconsolidated natural ground which are difficult to produce sufficient frictional resistance by expansion of a steel pipe.SOLUTION: When pressurized fluid is injected to a hollow steel pipe 2 to be inserted to a bored hole 31, the steel pipe 2 is allowed to expand so that an expansion steel pipe lock bolt 1 is anchored to natural ground 30 by peripheral surface friction with a hole wall 32. The expansion steel pipe lock bolt 1 is provided with the hollow steel pipe 2 of which surface has a plurality of regularly-arranged protrusions 5, preferably made from a steel plate material having a tensile strength of 400 to 510 N/mmand an elongation equal to or greater than 20%, having a striped pattern on the surface.

Description

  The present invention relates to, for example, an expansion type steel pipe lock bolt used for reinforcing a natural ground from a pit during tunnel excavation, a tip receiving work, a mirror reinforcing work, a manufacturing method thereof, and a natural ground reinforcing method.

  Conventionally, in order to reinforce a natural ground and suppress deformation and collapse when excavating a tunnel, a method of placing a lock bolt as a support member of the natural ground has been performed. For example, Patent Documents 1 and 2 describe the expansion-type steel pipe rock bolts when it is necessary to ensure early fixation in soft rock grounds to cracked rocks or when it is affected by the securing of spring water. Is used.

  This expansion-type steel pipe lock bolt pressurizes and injects fluid without a grout material, compresses the natural ground on the peripheral surface of the hole wall with the expansion pressure of the steel pipe, and combines the friction force on the surface of the steel pipe and the natural ground stress. Reinforce together. In the expansion type steel pipe lock bolt, the load resistance is demonstrated at an early stage.

In addition, in order to prevent the top end from peeling off during tunnel excavation of cracked rock, etc., the expansion-type steel pipe lock bolt is designed to increase the load bearing capacity by increasing the binding force due to the expansion pressure around the hole wall and the frictional force. It is also used for ground support in the long mirror reinforcement work for the purpose of restraining the front receiving work to constrain the natural ground and the pushing behavior in front of the face.

  As shown in FIG. 8 (a), the cross-sectional shape of the expandable steel pipe lock bolt 100 inserted into the hole drilled in the natural ground is a steel pipe with a reduced outer diameter with a smooth outer peripheral surface. It has the shape which has the recessed part 101 bent by. When the expansion type steel pipe lock bolt 100 is used, as shown in FIG. 8A, the expansion type steel pipe lock bolt 100 having the concave portion 101 bent along the axial direction is drilled in the natural ground 200. Into the hole 201.

And as shown in FIG.8 (b), both ends of the expansion type steel pipe lock bolt 100 are closed, and high-pressure injection water W is injected into the inside from an injection port provided at one end of the mouth side, The expansion type steel pipe lock bolt 100 bent by the pressure of the injected water is expanded. As a result, the size of the recess 101 is reduced, and the surface of the expandable steel pipe lock bolt 100 is brought into close contact with the hole wall 202 and fixed to the natural ground 200 by friction resistance.

If the natural ground 100 is, for example, hard rock, the contact stress f due to the hard rock is converted as restraint pressure after the expansion pressure is removed by the high-pressure injection water W, and as shown in FIG. Large frictional resistance can be ensured.

Japanese Patent Publication No. 2-520 Japanese Patent Publication No.2-5238

  By the way, since the above-mentioned expansion type steel pipe lock bolt 100 is formed with a steel pipe having a smooth surface as shown in FIG. 9, when the natural ground 200 is a hard rock, the contact stress is determined from the expansion pressure. However, when the natural ground 200 is a soft or unconsolidated natural ground, the pressure applied to the natural ground 200 by the expansion pressure of the steel pipe is a hole wall. The contact stress of the drilled hole wall 202 is not converted as a restraint pressure, for example, the ground mountain 200 of the hole wall 202 is deformed by the expansion pressure due to the expansion pressure, and sufficient frictional resistance cannot be ensured. . In the case where axial stress is generated in the expandable steel pipe lock bolt 100 due to the deformation of the natural ground 200, the reliability of the drawing strength is also impaired.

In addition, when the tunnel is excavated in cracked rock mass and unconsolidated ground, it is also possible to prevent contact from the expansion pressure when it is installed on hard rock. The stress is exerted as a restraining force, and a sufficient receiving effect of the front ground can be secured. However, when the ground 200 is a soft or unconsolidated ground, the ground of the hole wall is deformed by the expansion pressure of the steel pipe. Uniform contact stress is not converted as restraint pressure, and sufficient restraint force of the front ground cannot be secured, and the effect of suppressing peeling of the top end portion is impaired. Similarly, in the case of natural ground reinforcement to a long mirror reinforcing work by connecting a single pipe or a plurality of pipes, similarly, the restraining force cannot be ensured and the effect is impaired.

The present invention has been made in view of the above problems, and it is easy to provide sufficient frictional resistance even in a natural ground where it is difficult to ensure a frictional resistance due to the expansion of a steel pipe such as a soft rock, a cracked rock, and an unconsolidated ground. It is an object of the present invention to provide an expansion-type steel pipe lock bolt, a manufacturing method thereof, and a natural ground reinforcement construction method that can secure the natural ground securely.

In the expandable steel pipe lock bolt of the present invention, fluid is pressurized and injected into a hollow steel pipe inserted into a drilled hole, and the hollow steel pipe is expanded and fixed to a natural ground by peripheral friction with a hole wall. In the expansion type steel pipe lock bolt, a plurality of protrusions are regularly provided on the surface of the hollow steel pipe.
According to this configuration, by a plurality of protrusions regularly provided on the surface of the hollow steel pipe, even in a natural ground where it is difficult to ensure frictional resistance due to the expansion of the steel pipe such as soft rock, cracked rock, unconsolidated ground, Sufficient frictional resistance can be easily secured, and the natural ground can be reinforced reliably.

The expansion type steel pipe lock bolt of the present invention is made of a steel plate having a hollow steel pipe formed with a plate thickness of 2.1 to 2.3 mm, a tensile strength of 400 to 510 N / mm ² and an elongation of 20% or more, A striped pattern is formed on the surface.
According to this structure, the sufficient expansion | swelling of a hollow steel pipe and a striped pattern can ensure more sufficient friction resistance, and can reinforce the reinforcement of a natural ground.

In the method of manufacturing an expandable steel pipe lock bolt of the present invention, a fluid is pressurized and injected into a hollow steel pipe inserted into a drilled hole, and the hollow steel pipe is expanded to produce a natural ground due to peripheral surface friction with the hole wall. In the manufacturing method of the expansion type steel pipe rock bolt to be fixed, a step of regularly forming a plurality of protrusions on the surface side by rolling using a steel plate having a tensile strength of 400 to 510 N / mm ² and an elongation of 20% or more as a raw material And bending the rolled steel sheet to form an electric resistance steel pipe having an outer diameter of 57 to 76.3 mm, and roll forming the electric resistance steel pipe to reduce the outer diameter to 40 to 55 mm to form a hollow steel pipe. And a process.
According to this configuration, it is possible to easily and accurately manufacture an expandable steel pipe lock bolt that can easily ensure a sufficient frictional resistance and can reliably reinforce the natural ground.

The natural ground reinforcement method of the present invention is a natural ground reinforcement method using the expansion type steel pipe rock bolt of the present invention, in which a mortar is filled in a hole drilled in the natural ground and a hollow having the plurality of regular protrusions. A steel pipe is inserted, and fluid is pressurized and injected into the hollow steel pipe in the hole.
According to this configuration, it is possible to easily ensure sufficient frictional resistance even in rocks where it is difficult to ensure frictional resistance due to the expansion of steel pipes, such as soft rocks, cracking rocks, and unconsolidated grounds. The natural ground can be reinforced, and the combined use of mortar can further enhance the natural ground reinforcing effect.

In the natural ground reinforcement method of the present invention, the length of the hollow steel pipe of the expansion type steel pipe lock bolt is 3 m to 8 m, and the hollow steel pipe is connected to form a reinforcing pipe having a length of 6 m to 20 m. And the fluid is pressurized and injected into the reinforcing tube to be expanded.
According to this configuration, even with natural ground reinforcement such as a long mirror reinforcement for connecting a plurality of hollow steel pipes, sufficient frictional resistance can be easily ensured, and natural ground reinforcement can be achieved.

  According to the present invention, it is possible to easily ensure sufficient frictional resistance even in a natural ground where it is difficult to ensure frictional resistance due to expansion of a steel pipe such as soft rock, cracked rock, unconsolidated ground, etc. A natural mountain can be reinforced. That is, by providing a projection-like rough surface shape on the surface of the hollow steel pipe, even in a soft ground, the rough surface shape bites into the hole wall, increasing the friction resistance and adhesion between the hole wall and the steel pipe surface, The rough surface shape functions as the pulling strength.

  And even in soft ground conditions from soft rock to unconsolidated ground, as a support member, the required frictional resistance can be obtained on the surface of the hollow steel pipe and the hole wall surface due to expansion pressure, ensuring sufficient pulling strength can do. In addition, even when used as a receiving work that restrains the front ground at the top of the tunnel during tunnel excavation and prevents peeling, etc., sufficient adhesion of the peripheral surface of the hole wall necessary for restraining the front ground is sufficiently secured. It is preferable to use a mortar filling between the surface of the rough hollow steel pipe surface that comes into contact with the hole wall, and to further improve the friction resistance with the hole wall and the adhesion between the surface of the hollow steel pipe, The restraint force of the front ground can be increased. In addition, sufficient frictional resistance can be easily ensured even by natural ground reinforcement such as a long mirror reinforcement work connecting a plurality of hollow steel pipes.

(A) is the side view before expansion which shows the state inserted in the hole which perforated the expansion type steel pipe lock bolt of embodiment by this invention, (b) is before expansion of the expansion type steel pipe lock bolt inserted in the hole. Partial enlarged view. (A) is a side view showing a state in which the expansion type steel pipe lock bolt of the embodiment according to the present invention has expanded in a hole drilled, and (b) is a partially enlarged view showing a state in which the expansion type steel pipe lock bolt has expanded in the hole. Figure. (A) is an enlarged view showing a striped pattern on the surface of a hollow steel pipe used for the expandable steel pipe lock bolt of the embodiment according to the present invention, and (b) is a striped pattern on the surface of the hollow steel pipe used for the expandable steel pipe lock bolt. Explanatory drawing which shows stripe height. Explanatory drawing which shows the stress state of the natural ground after pressure expansion which used the expansion type steel pipe lock bolt of embodiment as a support member. (A) is a cross-sectional view of a state in which the expansion type steel pipe lock bolt of the embodiment is used as a support member of a natural ground reinforcement work, and (b) shows the stress state of the natural ground after pressure expansion used as a support member. Illustration. (A) is a cross-sectional view showing a state in which the expansion-type steel pipe lock bolt of the embodiment is used as a pre-receiving work, and (b) is a vertical cross-section showing a stress state of a natural mountain after pressure expansion used as a pre-receiving work. Figure. (A) is a cross-sectional view showing a state in which the expansion-type steel pipe lock bolt of the embodiment is used as a mirror reinforcement, and (b) is a longitudinal cross-section showing a stress state of a natural mountain after pressure expansion used as a mirror reinforcement. Figure. (A) is sectional drawing before the expansion which shows the state inserted in the hole which perforated the conventional expansion type steel pipe lock bolt, (b) is sectional drawing which shows the state which the conventional expansion type steel pipe lock bolt expanded in the hole (C) is sectional drawing which shows the state which received the contact stress after the conventional expansion type steel pipe lock bolt expanded in the hole. (A) is explanatory drawing which shows the stress state of the natural ground after the pressure expansion used as a conventional supporting member.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  As shown in FIGS. 1 to 4, the expandable steel pipe lock bolt 1 of the present embodiment is configured such that a fluid is pressurized and injected into a hollow steel pipe 2 inserted into a hole 31 drilled in a natural ground 30. The hollow steel pipe 2 is inflated and fixed to the natural ground 30 by the peripheral surface friction with the hole wall 32, and the hollow steel pipe 2 has a concave portion 21 bent inward from one place in the circumferential direction, such as the center upper end of the illustrated example. It has become. A sealing sleeve 3 is provided at the tip of the hollow steel tube 2, and a water injection sleeve 4 is provided at the mouth end of the hollow steel tube 3, both ends thereof are closed, and a plurality of protrusions 5 are formed on the surface thereof. It is provided regularly.

The hollow steel pipe 2 is made of a steel plate having a tensile strength of 400 to 510 N / mm ² and an elongation of 20% or more, and is formed with a plate thickness of 2.1 to 2.3 mm. The protrusions 5 on the surface are preferably formed at the same time when the steel plate material is rolled.

As shown in FIG. 3, it is preferable to form the protrusions 5 having a substantially elliptical shape in plan view in a striped pattern so that the major axis directions are alternated. In the example of FIG. 3B, the height (stripe height) of the protrusion 5 is 1.0 to 2.0 mm, the pitch between the protrusions 5 and 5 (stripe pitch) is 20 mm, and the plate thickness (ground thickness) other than the protrusion 5 portion. ) It is formed with 2.1 to 2.3 mm. When the fringe height is high, a large frictional resistance is ensured, but the fringe height of the protrusion 5 is preferably 1 to 2 mm in consideration of processing in a reduced diameter. The hollow steel pipe 2 is formed by bending a rolled steel plate to form an ERW steel pipe having an outer diameter of 57 to 76.3 mm, and roll forming the ERW steel pipe to reduce the outer diameter to 40 to 55 mm to form a hollow steel pipe. It is preferable.

  The expansion type steel pipe lock bolt 1 is inserted into a hole 31 drilled in a natural ground 30 as shown in FIG. As shown in FIG. 1 (b), the expansion type steel pipe lock bolt 1 is reduced in diameter and formed in a circular outer periphery, and is bent from the upper end of the center inward along the inner diameter of the pipe, so that the recess 21 is deeply inside. It is formed in the cross-sectional shape which protrudes. The hole 31 has, for example, an outer diameter of the hole wall 32 of 55 mm and a perforation length of 4 m, and the expandable steel pipe lock bolt 1 has an outer diameter of 45 mm and a length of 4 m, for example.

  The water injection side sleeve 4 at the end of the mouth is formed with an injection port for high-pressure injection water W. The injection water W is injected from this injection port to pressurize and expand the expandable steel pipe lock bolt 1, thereby forming the recess 21. The expansion type steel pipe lock bolt 1 is enlarged so that the size of the steel pipe is reduced, and is fixed to the hole wall 32 of the rock mass of the natural ground 30 as shown in FIG. 2 (a) and 2 (b) show a state in which the hollow steel pipe 2 is expanded and brought into contact with the hole wall 32 in a state where the expandable steel pipe lock bolt 1 is fixed to the hole wall 32 after the pressure expansion. The shape of the protrusion 5 bites into and closely adheres, and even in a soft ground, the biting force of the protrusion 5 on the surface of the hollow steel pipe 2 into the hole wall surface is largely secured.

  Here, Table 1 shows the results of a pull-out test assuming that the expandable steel pipe lock bolt 1 is sandy land. A conventional pull-out test based on a ground condition assuming a sandy soil for the expansion steel pipe lock bolt 100 having a smooth surface and the expansion steel pipe lock bolt 1 having a striped pattern on the surface according to the present embodiment is an unconsolidated sand. In order to reproduce the state where the expansion type steel pipe rock bolts 1 and 100 are in close contact with the hole wall of the pebble land, it is performed by the state of the sand gel by the penetration of the water glass solution type that minimizes the influence of the adhesive force by the injection material It was.

  As shown in the numerical values of Table 1, the expansion type steel pipe lock bolt 1 shows about five times the adhesion force of the conventional expansion type steel pipe lock bolt 100. As a result of the pull-out test, the conventional expansion-type steel pipe lock bolt 100 with a smooth surface is 72 kN (18 × 4 m), and the required pull-out strength (190 kN) is insufficient. In the case of the bolt 1, the result that the required 190 kN or more (97.8 × 4 m) can be sufficiently secured is obtained.

  Next, the case where the expansion type steel pipe lock bolt 1 is used as a support member will be described. FIG. 4 shows the stress state of the natural ground 30 after the shot concrete 6 and the steel support 7 are installed in the tunnel space T after tunnel excavation, and the expandable steel pipe lock bolt 1 is installed as a pattern bolt. Yes. In the case where the natural ground 30 is a soft natural ground, it is impossible to secure an early pulling strength with a normal rock bolt. Therefore, the expandable steel pipe lock bolt 1 is installed as a support member during tunnel excavation. The expansion type steel pipe lock bolt 1 is filled with high-pressure injection water W from the injection port of the water injection side sleeve 4, and the expansion type steel pipe lock bolt 1 is fixed to the pressurized and expanded hole wall 32. The protrusion 5 having a striped pattern bites into and comes into close contact with the hole wall 32 at the time of expansion in which the cross-sectional shape expands and comes into contact.

  In the soft ground condition, in the soft ground condition, the contact stress f is not easily converted from the expansion pressure c as a restraint pressure, and the frictional resistance g as the required pulling strength cannot be obtained. By expanding the cross-sectional shape into the hole wall 32 at the time of expansion, the strip-shaped protrusion 5 is bitten and brought into close contact, thereby obtaining a large frictional resistance g by the expandable steel pipe lock bolt 1 and ensuring an early pulling strength. . K in the figure is the stress of the natural ground.

FIG. 5 (a) is a cross-sectional view of the state in which the expansion-type steel pipe lock bolt 1 of the embodiment is used as a support member (pattern bolt) for natural ground reinforcement, and FIG. The stress state of the natural ground after pressurization expansion used as a support member of an end is shown. Due to the influence of the loosened region 8 associated with tunnel excavation, the stress k of the natural ground acts on the inner space side of the tunnel, but the reinforcing effect of the lock bolt is exerted by the large frictional resistance g of the expandable steel pipe lock bolt 1.

  Next, in the cracked rock mass and unconsolidated ground, the conventional steel expansion rock bolt with a smooth surface is used as a receiving work 9 for restraining the front ground at the top of the tunnel to prevent peeling. The case where the expansion type steel pipe lock bolt 1 whose surface by 100 and the surface by this embodiment are striped pattern shape is used is demonstrated. In this example, mortar filling for improving adhesion is used in combination, and the excavation cycle after installing the first receiving work 9 becomes early, and the adhesion strength of the mortar at the time of weak age is affected.

The test results are shown in Table 2. The mortar is cured after 12 hours, and the adhesive strength at that time is the test result. As shown in Table 2, the conventional steel pipe bolt 100 having a smooth surface in the pull-out test result at the time of weak age has an adhesion of 0.19 N / mm ² , and the expansion steel pipe lock bolt 1 has 0 .. Adhesive strength of 50 N / mm ² or more can be secured, and a sufficient effect of improving adhesive strength is obtained.

FIG. 6 (a) is a cross-sectional view of the front receiving work 9 in the tunnel space T, which is installed as a front receiving work 9 with an expansion-type steel pipe lock bolt 1 having a length of 3 m at a distance of 60 cm in a 120 ° range of the top end. ing. In the figure, 6 is shotcrete, 7 is a steel support, and 8 is a loosened region. 6B shows the stress state of the natural ground 30 at the time of tunnel excavation of the receiving work 9, and since the bending stress and the axial stress are acting on the expandable steel pipe lock bolt 1, the soft ground In the mountains, the adhesion strength as a binding force is inferior, and it is necessary to secure the frictional resistance g and adhesion strength between the front receiving member and the peripheral surface of the hole wall. Therefore, it is preferable that the surface of the rough hollow steel pipe 2 to be in contact with the hole wall 32 by a means such as filling mortar in the hole 31 in advance before the expansion type steel pipe lock bolt 1 is placed. In addition, mortar filling is used in combination with the frictional resistance g and adhesion of the expandable steel pipe lock bolt 1 to increase the restraint force of the ground in front of the face.

Further, as shown in FIG. 7, for example, as shown in FIG. 7, the expansion type steel rock bolt 1 of the present embodiment has insufficient peripheral surface adhesion due to a steel tube having a smooth peripheral surface even when used as a reinforcing tube of a mirror reinforcement work 10. It is possible to compensate, and the striped projection 5 is bitten into the hole wall 32 so as to be brought into close contact therewith, thereby obtaining a large frictional resistance g by the expandable steel pipe lock bolt 1 and securing an early pulling strength. In the cross-sectional view of the mirror reinforcement work 10 in FIG. 7 (a), an expansion type steel pipe lock bolt 1 having a length of 6m is installed in the range at 1.5m intervals in the mirror part to which the shotcrete 6 is applied. Yes. The vertical cross-sectional view of FIG. 7B shows the stress state of the natural ground of the face mirror part 11 during the tunnel excavation of the mirror reinforcement work 10, and an excellent axial stress acts on the expandable steel pipe lock bolt 1. ing. In the loose region 8 of the soft ground, the adhesion strength as a restraining force is inferior, so it is necessary to secure the frictional resistance g between the mirror reinforcing member and the peripheral surface of the hole wall, and the frictional resistance g of the expandable steel pipe lock bolt 1 is improved. Thus, the binding force of the ground in front of the face can be increased.

  When the expansion steel lock bolt 1 is connected as a reinforcement pipe or the like of the mirror reinforcement work 10, for example, the length of the hollow steel pipe 2 of the expansion steel pipe lock bolt 1 is set to 3 m to 8 m, and the hollow steel pipe 2 is connected. It is preferable to form a reinforcing pipe having a length of 6 m to 20 m by connecting through a pipe, inserting the reinforcing pipe into the hole 31, and injecting a fluid into the reinforcing pipe for expansion.

[Modifications of Embodiment, etc.]
In addition to the configurations of the inventions and embodiments, the invention disclosed in the present specification includes those specified by changing these partial configurations to other configurations disclosed in the present specification, or these configurations. Also included are those specified by adding other configurations disclosed in the specification, or those obtained by deleting these partial configurations to the extent that partial effects can be obtained and specifying them as higher-level concepts. Is also included.

  For example, the shape of the protrusion 5 in the above embodiment is a substantially elliptical shape in plan view, but is not limited thereto, and may be a substantially polygonal shape in plan view, a substantially circular shape in plan view, or the like. Further, the arrangement of the protrusions 5 is not limited to the striped pattern, and is appropriate as long as it is a regular arrangement.

DESCRIPTION OF SYMBOLS 1,100 ... Expansion type steel pipe lock bolt 2 ... Hollow steel pipe 21, 101 ... Recess 3 ... Sealing side sleeve
4 ... Water injection side sleeve 5 ... Protrusion 6 ... Spring concrete 7 ... Steel support 8 ... Loose area 9 ... Picking work 10 ... Mirror reinforcement work 11 ... Face mirror part 30, 200 ... Mt. 31, 31 ... 201 Hole 32 202 ... hole wall c ... expansion pressure f ... contact stress g ... friction resistance k ... mountain stress W ... injected water T ... tunnel space

Claims (5)

In an expandable steel pipe lock bolt in which fluid is pressurized and injected into a hollow steel pipe inserted into a drilled hole, and the hollow steel pipe is expanded and the peripheral surface friction with the hole wall is fixed to a natural ground.
An expansion type steel pipe lock bolt, wherein a plurality of protrusions are regularly provided on the surface of the hollow steel pipe. The hollow steel pipe is formed with a plate thickness of 2.1 to 2.3 mm,
The expansion type steel pipe rock bolt according to claim 1, wherein a steel plate having a tensile strength of 400 to 510 N / mm ² and an elongation of 20% or more is used as a raw material, and a striped pattern is formed on the surface. In a method for producing an expandable steel pipe lock bolt in which a fluid is pressurized and injected into a hollow steel pipe inserted into a drilled hole, and the hollow steel pipe is expanded and the peripheral surface friction with a hole wall is fixed to a natural ground.
A step of forming a plurality of protrusions regularly on the surface side by rolling, using a steel sheet having a tensile strength of 400 to 510 N / mm ² and an elongation of 20% or more,
Bending the rolled steel sheet to form an ERW steel pipe having an outer diameter of 57 to 76.3 mm;
Forming the hollow steel pipe by roll forming the electric resistance steel pipe and reducing the outer diameter to 40 to 55 mm;
A method for producing an expandable steel pipe lock bolt, comprising: A natural ground reinforcement method using the expansion type steel pipe lock bolt according to claim 1,
A ground made by filling a mortar into a hole drilled in a natural ground and inserting a hollow steel pipe having the plurality of regular protrusions, and injecting a fluid into the hollow steel pipe in the hole for expansion. Mountain reinforcement method. The length of the hollow steel pipe of the expandable steel pipe lock bolt is 3 m to 8 m,
The hollow steel pipe is connected to form a reinforcing pipe having a length of 6m to 20m and inserted into the hole,
The ground reinforcement method according to claim 4, wherein a fluid is pressurized and injected into the reinforcement pipe.

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