JP7651107B2 - Rock bolt and its manufacturing method - Google Patents

Description

The present invention relates to rock bolts used, for example, to support tunnel spaces, and to a method for manufacturing the same.

In a typical tunnel, as shown in Figures 13 and 14, sprayed concrete 102 is poured along the tunnel excavation surface 101, and rock bolts 104 are cast radially from the sprayed concrete 102 into the surrounding ground 103. Each rock bolt 104 is fixed to the ground 103 with an anchoring material 105, and a nut 108 is fitted onto the male thread 107 at the rear end so that the inserted bearing plate 106 is in close contact with the sprayed concrete 102. The tunnel space 110 is supported by an arch structure 109 constructed in the ground 103 surrounding the tunnel by the radially cast rock bolts 104.

The rock bolts 104, which are driven into and fixed in the natural ground 103, support the arch structure 109 so that it does not break by resisting the force F that the natural ground 103 tries to push out with the tensile axial force T generated in the rock bolts 104. In order for the rock bolts 104 to function in this way, it is important that the rock bolts 104 are firmly fixed in the natural ground 103 in a state where they have the required pull-out resistance. Furthermore, it is also necessary that the rock bolts 104 do not break and that nuts are tightened on the rock bolts 104 so that the support plate 106 is in close contact with the sprayed concrete 102.

Patent Document 1 also proposes a rock bolt in which a plate fixing member made of a circular flat steel plate is integrally joined to the rear end of the rock bolt, and a support plate is inserted into the shaft of the rock bolt. This rock bolt is installed by pushing it into an insertion hole in the ground, and is installed in the ground by pressing the support plate with the plate fixing member. Therefore, it is possible to omit the work of attaching the support plate by tightening a nut when installing the rock bolt. Furthermore, the rock bolt in Patent Document 1 is said to be able to prevent damage to the waterproof sheet laid to cover the support plate, because the thickness of the plate fixing member that protrudes from the support plate to the inside of the tunnel is slight.

JP 2005-314993 A

In the meantime, in order to confirm that the rock bolt 104 driven into the natural ground 103 as described above has been driven in a state where it has the required pull-out strength, a pull-out test is performed according to the specifications for construction management. In the pull-out test for the nut-tightened rock bolt 104, the nut 108 pressing the support plate 106 is removed, a tension bar is connected to the male thread 107 at the rear end of the rock bolt 104 via a coupling, and the tension bar is inserted into the center hole ram and loaded with a hydraulic jack to apply a tensile force to the rock bolt and measure whether it will come out until the specified pull-out strength is reached. After confirming that it will not come out until the specified pull-out test, the test device consisting of the coupling, tension bar, center hole ram, and hydraulic jack is removed from the rock bolt 104, and the nut 108 pressing the support plate 106 is re-tightened to the male thread 107 of the rock bolt 104.

This type of pull-out test is usually performed on a sample of all rock bolts 104 driven into the natural ground 103, but even if it is performed on sampled rock bolts 104, it is quite a time-consuming task to remove the nuts 108 from the rock bolts 104 and then re-tighten them to return them to their original state. In addition, in a configuration in which the male threads 107 at the rear ends of the rock bolts 104 protrude into the inside of the tunnel, there is another problem in that if a waterproof sheet is laid inside the tunnel to cover the support plate 106, there is a risk that the waterproof sheet will be damaged, or it becomes necessary to take separate measures to prevent damage.

In addition, the rock bolt in Patent Document 1 has a plate fixing member in the form of a simple flat steel plate that is integrally joined to the rear end to hold down the support plate, making it difficult to conduct a pull-out test. Also, if a bent part is formed at the corner of the support plate by bending it toward the ground, as in the second embodiment of Patent Document 1, there is a risk that if the rock bolt were to protrude into the inside of the tunnel, the bent part would get caught on the waterproof sheet laid to cover the support plate, damaging the waterproof sheet.

The present invention has been proposed in consideration of the above problems, and aims to provide a rock bolt and a manufacturing method thereof that can easily perform a pull-out test without the need to remove and re-tighten the nut when performing the pull-out test. Another aim of the present invention is to provide a rock bolt and a manufacturing method thereof that can prevent damage to the waterproof sheet.

The lock bolt of the present invention is characterized in that it is made of a steel bar and has a head, the diameter of which is larger than that of the shank, formed integrally with the shank by hot forging on the rear side of the shank in the pouring direction, the head has forging flows formed by hot forging that are continuous with the shank, the front end face of the head is a flat surface provided so as to be able to press a support plate that is fitted onto the shank, and a recess is provided circumferentially on the outer periphery of the head which can engage with a protrusion formed on a pull-out test coupler.
According to this, when performing a pull-out test on a rock bolt, the convex part of the pull-out test coupler can be engaged with the concave part on the outer circumference of the head, and the pull-out test of the rock bolt can be easily performed without the need to remove and re-tighten the nut. In addition, since the bolt can be installed by simply pushing it into the ground without the need for tightening the nut, the labor required for driving the rock bolt can be reduced. In addition, since the rock bolt can be configured without forming a part that protrudes outward from the head, damage to the waterproof sheet that is laid to directly or indirectly cover the head of the rock bolt can be prevented.

The lock bolt of the present invention is characterized in that the recess is a recessed groove provided around the outer periphery of the head.
This eliminates the need to position the recess in the head of the lock bolt and the protrusion of the pull-out test coupler in the circumferential direction, making it easier to perform a pull-out test on the rock bolt.

The lock bolt of the present invention is characterized in that the peripheral edge of the rear end of the head is formed in a rounded shape.
According to this, by making the peripheral edge of the rear end of the head of the rock bolt round, it is possible to more reliably prevent damage to the waterproof sheet that is laid so as to directly or indirectly cover the head of the rock bolt. The form in which the peripheral edge of the rear end of the head is rounded includes a shape in which the peripheral edge of the head is chamfered by R-chamfering, a hemispherical shape, or a shape close to a hemispherical shape such as a warhead shape.

The rock bolt structure of the present invention is characterized in that a bearing plate is fitted onto the shaft portion of the rock bolt of the present invention, and the corners of the bearing plate are chamfered with a radius.
According to this, by forming the corners of the support plate with a radiused chamfer, damage to the waterproof sheet that is laid to directly or indirectly cover the head of the rock bolt and the support plate can be more reliably prevented.

The manufacturing method of the lock bolt of the present invention is a method of manufacturing a lock bolt of the present invention, characterized in that it comprises a first step of forming a head having a larger diameter than the shank by hot forging at one end of a steel bar having the outer shape and outer circumferential size of the shank, and a second step of rotating the steel bar with the head formed thereon and pressing a groove cutting tool against a predetermined position on the rotating head to form a recessed groove on the outer periphery of the head.
This allows the head of the rock bolt to be made from the same material as the shaft, and also allows the head to have a material structure with a homogenous internal structure and high toughness, with grain flows formed by hot forging that continue from the shaft. This makes it possible to obtain a rock bolt that exhibits high strength and high yield strength over its entire length. Furthermore, the hot forging process allows the rock bolt of the present invention to be manufactured quickly and inexpensively.

The method of installing a rock bolt of the present invention is a method of installing a rock bolt of the present invention, characterized in that it comprises a first step of extrapolating a support plate from the tip side of the shaft portion of the rock bolt, and a second step of driving the rock bolt into the ground by pressing the support plate against the ground with the front end surface of the head.
This eliminates the need to tighten the nuts until the support plate is in close contact with the ground or sprayed concrete, and the rock bolt can be installed simply by moving it in a pushing motion, making construction work easier.

The ground reinforcement structure of the present invention is a ground reinforcement structure in which the rock bolt of the present invention is driven, and is characterized in that the rock bolt is driven into the ground with a support plate having rounded chamfered corners and inserted onto the shaft portion interposed between the front end surface of the head and the ground or the surface to be poured of sprayed concrete, and a waterproof sheet is laid so as to directly or indirectly cover the head, the peripheral edge of which at the rear end is formed in a rounded shape.
According to this, when a pull-out test is performed on a rock bolt that has been driven into a natural ground reinforcement structure, the convex part of the pull-out test coupler can be engaged with the concave part on the outer periphery of the head of the rock bolt, and the pull-out test of the rock bolt can be easily performed without the need to remove and re-tighten the nut. In addition, since the rock bolt can be installed by simply pushing it into the natural ground without the need for tightening the nut, the labor required for the installation work of the rock bolt can be reduced. In addition, since the rock bolt can be configured without forming a part that protrudes outward from the head of the rock bolt, damage to the waterproof sheet that is laid so as to directly or indirectly cover the head of the rock bolt can be prevented. Furthermore, the rounded chamfering of the corners of the support plate and the rounded shape of the periphery of the head of the rock bolt can more reliably prevent damage to the waterproof sheet.

The pull-out test method of the present invention is a pull-out test method for a rock bolt in a ground reinforcement structure in which the rock bolt of the present invention is driven into the ground and a support plate extrapolated to the shaft is interposed between the front end surface of the head and the ground or the poured surface of sprayed concrete, and is characterized in that it comprises a first step of engaging the convex portion of the pull-out test coupler with the concave portion formed on the outer periphery of the head of the rock bolt in a driven state and connecting the rock bolt and a tension rod via the pull-out test coupler, and a second step of applying a force in the pull-out direction to the head via the tension rod and determining the pull-out strength of the rock bolt.
According to this, when a pull-out test is performed on a rock bolt that has been driven into a natural ground reinforcement structure, the convex part of the pull-out test coupler can be engaged with the concave part on the outer periphery of the head of the rock bolt, making it possible to easily perform a pull-out test on the rock bolt without the need to remove and retighten the nut. In addition, after the pull-out test is completed, the rock bolt can be easily restored to its original state by simply removing the pull-out test coupler from the head of the rock bolt, making it unnecessary to retighten the nut.

The pull-out test method of the present invention is characterized in that the pull-out test coupler is composed of a bottomed tubular portion arranged on the lock bolt side and a male threaded portion arranged on the tension rod side, the convex portion being engaged with the concave portion on the inner circumference of the bottomed tubular portion, the pull-out test coupler is divided into a pair of halves in the axial direction, the convex portion of the pull-out test coupler is engaged with the concave portion of the head by fitting together the pair of halves, and the male threaded portion formed by fitting together the pair of halves is screwed into the female threaded portion formed at the tip of the tension rod.
According to this, the male threaded portion of the pull-out test coupler can be screwed into the female threaded portion of the tension rod to engage the convex portion of the pull-out test coupler with the concave portion of the head of the lock bolt, making it possible to connect the lock bolt and tension rod via the pull-out test coupler inexpensively and efficiently.

The pull-out test method of the present invention is characterized in that the pull-out test coupler is composed of a cylinder formed by joining a pair of axially divided halves together, and an outer fitting casing that is fitted around the joined pair of halves to maintain the shape of the cylinder, the inner circumference of the cylinder is formed with the convex portion that engages with the concave portion, and a reduced diameter portion is formed on the tension rod side of the cylinder, the pair of halves are joined together so that the convex portion engages with the concave portion of the head, and the large diameter portion formed at the tip of the tension rod is engaged in the pull-out direction by the reduced diameter portion, and the outer fitting casing is externally fitted from the tension rod side to maintain the shape of the cylinder formed by the pair of halves.
With this, by simply externally fitting the outer casing onto the pair of halves, the convex portion of the pull-out test coupler can be engaged with the concave portion of the head of the lock bolt, and the large diameter portion of the tension rod can be engaged in the pull-out direction, making it possible to connect the lock bolt and tension rod via the pull-out test coupler inexpensively and efficiently.

The lock bolt of the present invention makes it possible to easily perform a pull-out test without the need to remove and retighten the nut.

1A is a left side view of a lock bolt according to a first embodiment of the present invention, FIG. 1B is a front view thereof, FIG. 1C is a right side view thereof, and FIG. 4A and 4B are perspective explanatory views illustrating the attachment of a pull-out test jig to the rock bolt of the first embodiment. 4A is a plan view of a bearing plate that is extrapolated to the rock bolt of the first embodiment, and FIG. 5A to 5E are process explanatory diagrams illustrating a manufacturing process of the lock bolt of the first embodiment. 5A to 5D are process explanatory diagrams illustrating the installation process of the rock bolt of the first embodiment. FIG. 1 is a schematic explanatory diagram of a tunnel constructed using a natural ground reinforcement structure in which rock bolts of the first embodiment are installed. FIG. 7 is an explanatory diagram illustrating a fixing mechanism of the rock bolt of the first embodiment in the example of the tunnel of FIG. 6 . FIG. 2 is a partial cross-sectional view illustrating a pull-out test on a rock bolt in a natural ground reinforcement structure in which the rock bolt of the first embodiment is driven. 5A is a left side view of a lock bolt according to a second embodiment of the present invention, FIG. 5B is a front view thereof, FIG. 5C is a right side view thereof, and FIG. 5D is an enlarged front view of the periphery of the head portion thereof. 13A and 13B are perspective explanatory views illustrating the attachment of a pull-out test jig of another example to the rock bolt of the second embodiment. 6A to 6E are process explanatory diagrams illustrating a manufacturing process of the lock bolt of the second embodiment. FIG. 11 is a partial cross-sectional view illustrating a pull-out test on a rock bolt in a natural ground reinforcement structure in which the rock bolt of the second embodiment is driven. A schematic diagram of a typical tunnel under construction. FIG. 2 is an explanatory diagram illustrating a typical fixing mechanism of a rock bolt.

[Lock bolt of the first embodiment]
1 and 2, a lock bolt 1 according to a first embodiment of the present invention is made of a deformed steel bar, which is a metal material or a steel bar material, and a generally conical sword tip 12 is formed at the tip in the driving direction of a shaft portion 11, which has the shape of a deformed steel bar. A head portion 13 having a larger diameter than the shaft portion 11 is formed on the rear side in the driving direction of the shaft portion 11, and the head portion 13 is formed in a generally cylindrical shape that protrudes outward from the outer periphery of the shaft portion 11, and a peripheral corner portion 15 of a rear end face 14 of the generally cylindrical head portion 13 is rounded.

The head 13 is provided so that the front end surface 16 at the tip of the head 13 can press the support plate 2 (described later) that is fitted onto the shaft 11, and the outer diameter of the head 13 is larger than the insertion hole 21 of the shaft 11 formed in the support plate 2. In this embodiment, the front end surface 16 of the head 13 is a flat surface. In addition, a recess is provided in the circumferential direction on the outer periphery of the head 13 that can engage with a protrusion of the pull-out test coupler 6 (described later), and in this embodiment, a recess is provided around the outer periphery of the head 13 in the form of a groove 17.

Furthermore, in the lock bolt 1 of this embodiment, the head 13 and the shaft 11 are integrally formed, and the head 13 is integrally formed on the rear side of the shaft 11 by hot forging using, for example, a high-tensile deformed steel bar specified in JIS G3112. In other words, in the lock bolt 1 of this embodiment, the head 13 and the shaft 11 are integrally formed from the same high-tensile metal material.

The support plate 2, which is inserted onto the shaft 11 of the rock bolt 1 and forms a rock bolt structure together with the rock bolt 1, is a generally rectangular plate in the example shown in FIG. 3, with each corner 22 being chamfered with a radius. An insertion hole 21 into which the shaft 11 of the rock bolt 2 is inserted is formed in the approximate center of the support plate 2 in a plan view, and the diameter of the insertion hole 21 is larger than the outer diameter of the shaft 11 and smaller than the outer diameter of the head 13.

In the case of manufacturing the rock bolt 1 of this embodiment in which the head 13 is integrally formed on the rear side of the shaft 11 by hot forging, a rod-shaped metal material or bar steel material having the outer shape and outer peripheral size of the shaft 11 is used as the raw material, for example, the deformed steel bar 1m shown in FIG. 4(a) is used. The deformed steel bar 1m is preferably a high-tensile deformed steel bar, and more preferably a high-tensile deformed steel bar specified in JIS G3112.

When processing this deformed steel bar 1m by hot forging, for example, a die 31 and a punch 32 as shown in Figures 4(a) and (b) are used. The die 31 is configured by combining a pair of forging dies, such as an upper and lower pair, and the shape of the die 31 formed by combining the pair of forging dies has an insertion hole 311 formed with a diameter approximately the same as the outer diameter of the deformed steel bar 1m, and an internal space 312 formed to communicate with the insertion hole 311 and open on the opposite side to the insertion hole 311. The internal space 312 has a shape and size that approximately corresponds to the outer shape of the approximately cylindrical head 13. The punch 32 is formed to approximately correspond to the shape and size of the internal space 312, and can be inserted into the internal space 312 from the opening side.

Then, the highly heated deformed steel bar 1m is inserted into the insertion hole 311 and placed in the die space 312 of the die 31, with one end of the deformed steel bar 1m protruding from the die space 312 by a predetermined length on the opposite side to the insertion hole 311 (see FIG. 4(a)). After that, the punch 32 is slightly inserted into the die space 312 from the protruding side of the deformed steel bar 1m, and hot forging is performed by crushing the deformed steel bar 1m in the die space 312, and a head 13m1, which is the original shape of the approximately cylindrical head 13 with a larger diameter than the shaft 11m, is integrally formed on the rear side, which is one end of the shaft 11m of the deformed steel bar 1m (see FIG. 4(b)). After the head 13m1 is formed, the punch 32 is withdrawn and the pair of forging dies that make up the die 31 are opened and removed, and unnecessary burrs BU are removed as necessary from the deformed steel bar 1m with the head 13m1 formed (see Figure 4 (c)).

Then, the deformed steel bar 1m on which the head 13m1 is formed is rotated using a lathe or the like, and the groove cutting tool 33 is pressed against a predetermined position of the rotating head 13m1 to form a concave groove 17 on the outer periphery of the head 13m1, and in this embodiment, the R chamfering tool 34 is pressed against the rear end corner of the rotating head 13m1 to chamfer the peripheral corner of the rear end face of the head 13m1 (see FIG. 4(d)). Then, a substantially conical tip 12 is separately formed at the tip of the deformed steel bar 1m by hot forging or the like, to obtain the lock bolt 1 of this embodiment (see FIG. 4(e)). Note that the hot forging when forming the lock bolt 1 of this embodiment by hot forging may be any appropriate method within the scope of the present invention, and it is also possible to use, for example, free forging hot forging without using a forging die.

As an example of a lock bolt 1 in which a roughly cylindrical head 13 is integrally formed by hot forging on the rear side of the shaft 11, the rock bolt 1 made of 1 m of deformed steel bar SD345 with a nominal diameter of 22 mm and D22, as specified in JIS G3112, has a tensile strength of 133.5 kN. This exceeds the standard strength (tensile load 122 kN) of an existing nut-tightened lock bolt with a threaded portion made of deformed steel bar SD345 with a nominal diameter of 24 mm and D25, as specified in JIS G3112, and allows for size reduction. Note that the strength of a lock bolt with a threaded portion is determined by the threaded portion, but the lock bolt 1 of this embodiment does not have a threaded portion, and in addition, the shaft 11 and head 13 are integrally formed by hot forging, making it possible to exhibit high tensile strength.

Next, the construction process of the rock bolt 1 of this embodiment will be described. When constructing the rock bolt 1, as shown in Figures 5 (a) and (b), the support plate 2 having the insertion hole 21 is inserted from the tip side in the casting direction onto the shaft 11 of the rock bolt 1. The process of inserting the shaft 11 of the rock bolt 1 into the insertion hole 21 of the support plate 2 can be performed in any suitable manner. For example, the support plate 2 is held by a holding mechanism provided near the tip of the guide cell 41 of the rock bolt driving device, and the rear end of the rock bolt 1 is held by a push-in type driving machine 42 that slides along the guide cell 41 as described below, and the driving machine 42 is advanced to insert the shaft 11 of the rock bolt 1 into the insertion hole 21 of the support plate 2 held in a predetermined position by the holding mechanism (see Figures 5 (a) to (c)). The bearing plate 2 does not have to be moved closer to the head 13 of the rock bolt 1, but is placed near the tip of the shaft 11 and inserted. Also, a hole 52 is formed in advance in the natural ground 50, or in the natural ground 50 and the sprayed concrete 51, and a fixing material 53 such as mortar is poured into the hole 52 (see Figure 7).

5(c), the rear end of the rock bolt 1 is held by a push-in type driving machine 42 that slides along a guide cell 41, and the driving machine 42 is advanced toward the natural ground 50, and the rock bolt 1 is pushed into the drilled hole 52 into which the fixing material 53 has been injected, starting from the tip side where the sword point 12 is formed. The rock bolt 1 is pushed in until the front end surface 16 of the head 13 presses the bearing plate 2 against the natural ground 50, and the bearing plate 3 is interposed between the front end surface 16 of the head 13 and the natural ground 50 or the surface to be poured of the sprayed concrete 51 (the surface of the natural ground 50 or the surface of the sprayed concrete 51), and the rock bolt 1 is driven into the natural ground 50 (see FIG. 5(d)). In the natural ground reinforcement structure constructed in this construction process, the bearing plate 2, which has a rounded corner 22 and is fitted onto the shaft 11, is interposed between the front end surface 16 of the roughly cylindrical head 13 and the natural ground 50 or the surface to which the sprayed concrete 51 is poured, and the rock bolt 1 is driven into the natural ground 10 in a state in which the bearing plate 2 can receive the pushing force when the natural ground 50 pushes out.

An example of a tunnel with a natural ground reinforcement structure constructed by the above construction process is shown in Figures 6 and 7. In this example, sprayed concrete 51 is poured along the tunnel excavation surface 54, and rock bolts 1 are cast radially from the sprayed concrete 51 into the surrounding natural ground 50. Each rock bolt 1 is fixed to the natural ground 50 with an anchoring material 53, and the front end surface 16 of the roughly cylindrical head 13 is pressed against the support plate 2 so that the inserted support plate 2 is in close contact with the sprayed concrete 51. The tunnel space 56 is supported by an arch structure 55 constructed in the natural ground 50 around the tunnel by the radially cast rock bolts 1.

Furthermore, in this example, a sheet-like cushioning material 57 such as nonwoven fabric is laid to cover the generally cylindrical head 13 with chamfered corners 15 on the periphery of the rear end face 14 of the rock bolt 1 that protrude into the inside of the tunnel, and the support plate 2 with chamfered corners 22, and a waterproof sheet 58 is laid so as to be layered on the inside of the cushioning material 57. In other words, the waterproof sheet 58 is laid to indirectly cover the generally cylindrical head 13 with chamfered corners 15 on the periphery of the rear end face 14, and the support plate 2 with chamfered corners 22. The cushioning material 57 and the waterproof sheet 58 are laid, for example, by fixing the cushioning material 57 to the sprayed concrete 51 with fasteners 571 such as anchors or nails and laying it along the inner surface of the sprayed concrete 51, and by fixing the cushioning material 57, the waterproof sheet 58, which is fixed to the cushioning material 57 at scattered fixing parts and laid over the cushioning material 57, is laid along the inner surface of the sprayed concrete 51. 59 shown in the figure is the covering concrete.

In this natural ground reinforcement structure with the waterproof sheet 58 laid, the bearing plate 2 installed on the natural ground 50 protrudes from the surface of the sprayed concrete 51 by, for example, a thickness of 9 to 12 mm, and furthermore, the roughly cylindrical head 13 protrudes from the surface of the bearing plate 2 inside the tunnel by, for example, a height of about 30 mm, and the buffer material 57 and waterproof sheet 58 are laid to cover these. However, since the installation pitch of the rock bolts 1 in the tunnel circumferential direction is more than 1 m apart, the actual buffer material 57 and waterproof sheet 58 are laid in a state with less unevenness than the schematic example in Figure 6. It is also possible to lay the waterproof sheet 58 so that it directly covers the roughly hemispherical head 13 and bearing plate 2 without laying the buffer material 57.

In this way, in a tunnel ground reinforcement structure equipped with rock bolts 1 driven and fixed into the ground 50 and bearing plates 2, the force F that the ground 50 tries to push out is supported by the bearing plates 2, and is resisted by the axial force T in the tensile direction generated in the rock bolts 1, thereby supporting the arch structure 55 so that it does not break (see Figure 7).

Next, an example of a pull-out test for the rock bolt 1 of this embodiment will be described. When a pull-out test is performed on the rock bolt 1 in a state where it is cast in a natural ground reinforcement structure, for example, sprayed concrete 51 is cast along the surface of the natural ground 50, the rock bolt 1 is cast into a drilled hole 52 drilled in the natural ground 50 and the sprayed concrete 51, and the rock bolt 1 is fixed by an anchoring material 53 in the drilled hole 52, and the bearing plate 2 inserted on the shaft 11 is interposed between the front end surface 16 of the head 13 and the surface to which the sprayed concrete 51 is cast. In this ground reinforcement structure, the convex strip 63 corresponding to the convex portion of the pull-out test coupler 6 is engaged with the concave groove 17 corresponding to the concave portion formed on the outer periphery of the head 13 of the cast rock bolt 1, and the rock bolt 1 and the tension rod 71 are connected via the pull-out test coupler 6 (see Figures 8 and 2).

The pull-out test coupler 6 used in this example is composed of a bottomed tubular portion 61 arranged on the lock bolt 1 side and a male threaded portion 62 arranged on the tension rod 71 side, and a convex rib 63 corresponding to a convex portion that engages with a concave groove 17 corresponding to a concave portion of the lock bolt head 13 is formed on the inner circumference of the bottomed tubular portion 61. Furthermore, the pull-out test coupler 6 is configured by fitting together a pair of axially split halves 60, 60, and the bottomed tubular portion 61, male threaded portion 62, and convex rib 63 are respectively formed when the half-split portions 601, 602, and 603 of the pair of halves 60, 60 are fitted together.

Then, the pair of halves 60 are fitted together at the head 13 of the rock bolt 1 driven into the natural ground 50 to form the pull-out test coupler 6, and the protruding strip 63 is engaged with the concave groove 17 of the head 13. Furthermore, the male threaded portion 62 of the pull-out test coupler 6 formed by fitting the pair of halves 60 together is screwed relatively into the female threaded portion 711 formed at the tip of the tension rod 71, and the shape of the pull-out test coupler 6 formed by fitting the pair of halves 60 together is stably held by the screwing of the male threaded portion 62 and the female threaded portion 711, and the rock bolt 1 and tension rod 71 are connected via the pull-out test coupler 6.

In the example of Figure 8, a base plate 721 of a roughly cap-shaped pull-out test reaction pedestal 72 is provided so as to be placed on the support plate 2 that is in contact with the sprayed concrete 51 by being pressed by the front end surface 16 of the head 13 of the rock bolt 1, and the head 13 of the rock bolt 1 and the pull-out test coupler 6 are arranged inside the pull-out test reaction pedestal 72. A tension rod 71 is inserted into the pull-out test reaction pedestal 72 from a through hole, and the female threaded portion 711 at the tip of the tension rod 71 is screwed into the male threaded portion 62 of the pull-out test coupler 6.

A center hole jack 73 and a pull-out test measuring plate 74 are fitted to the portion of the tension rod 71 that protrudes from the pull-out test reaction base 72 on the side opposite the ground 50, and a pull-out test holding nut 75 is screwed onto the tension rod 71 to restrict movement of the pull-out test measuring plate 74 on the side opposite the ground 50.

Then, by applying pressure in the extension direction of the center hole jack 73, a pull-out force is applied to the tension rod 71 via the pull-out test measuring plate 74 and the pull-out test holding nut 75. As a result, a reaction force is obtained from the pull-out test reaction force base 72, and a force in the pull-out direction is applied to the rock bolt 1 from the head 13 via the tension rod 71 and the pull-out test coupler 6. In this way, a pull-out force is applied to the rock bolt 1, and the axial force applied to the rock bolt 1 is calculated from the applied load, and the displacement of the pull-out test measuring plate 74 is measured, thereby recognizing the elongation of the rock bolt 1 and recognizing the pull-out strength of the rock bolt 1. The recognition of the pull-out strength by recognizing the elongation of the rock bolt 1 is preferably performed by a computer device such as a personal computer, smartphone, or dedicated terminal that stores mutual correspondence data in a memory unit, and outputting the data from an output unit.

According to the first embodiment, when performing a pull-out test on the rock bolt 1, the convex rib 63 corresponding to the convex portion of the pull-out test coupler 6 can be engaged with the concave groove 17 corresponding to the concave portion on the outer periphery of the head 13, and the pull-out test on the rock bolt 1 can be easily performed without the need to remove and re-tighten the nut. In addition, since the rock bolt 1 can be installed simply by pushing it into the ground 50 without the need for nut tightening, the labor required for the installation work of the rock bolt 1 can be reduced. In addition, since the rock bolt 1 can be configured without forming a portion that protrudes outward from the head 13, damage to the waterproof sheet 58 that is laid to directly or indirectly cover the head 13 of the rock bolt 1 can be prevented.

In addition, by forming the recess of the head 13 of the rock bolt 1 into a recessed groove 17, it is not necessary to perform the work of positioning the recess of the head 13 of the rock bolt 1 and the protrusion of the pull-out test coupler 6 in the circumferential direction, making it easier to perform a pull-out test on the rock bolt 1. In addition, by chamfering the corners 15 of the roughly cylindrical head 13 of the rock bolt 1, it is possible to more reliably prevent damage to the waterproof sheet 58 that is laid so as to directly or indirectly cover the head 13 of the rock bolt 1. In addition, by forming the corners 22 of the support plate 2 with a chamfered radius, it is possible to more reliably prevent damage to the waterproof sheet 58 that is laid so as to directly or indirectly cover the head 13 of the rock bolt 1 and the support plate 2.

In addition, when manufacturing a rock bolt 1 by forming a head 13 with a larger diameter than the shaft 11 by hot forging at one end of a steel bar having the outer shape and outer circumferential size of the shaft 11 of the rock bolt 1, the head 13 of the rock bolt 1 can be formed from the same material as the shaft 11. In addition, the head 13 can have a material structure with a homogenous internal structure and high toughness with increased viscosity, in which a forging flow line is formed in the head 13 that is continuous with the shaft 11 by hot forging. Therefore, it is possible to obtain a rock bolt 1 that exhibits high strength and high yield strength over its entire length. In addition, the rock bolt 1 can be manufactured quickly and inexpensively by manufacturing it by hot forging. In addition, when a manufacturing process is used in which the deformed steel bar 1m on which the head 13m1 is formed is rotated to form a groove 17 on the outer periphery of the head 13m1 and to chamfer the peripheral corners of the rear end face of the head 13m1, the process of rotating the deformed steel bar 1m on which the head 13m1 is formed can both form the groove 17 on the outer periphery of the head and chamfer the radius of the rear end face of the head, thereby improving the efficiency of the manufacturing process.

In addition, with the method of installing the rock bolt 1 in this embodiment, there is no need to tighten the nuts until the bearing plate 2 is in close contact with the ground 50 or the sprayed concrete 51, and the rock bolt 1 can be installed simply by moving it in a pushing motion, making the installation work easier.

In addition, in a pull-out test of a rock bolt 1 in a ground reinforcement structure in which the rock bolt 1 is driven into the ground 50 and the bearing plate 2 inserted around the shaft 11 is between the front end surface 16 of the head 13 and the ground 50 or the surface to be poured of the sprayed concrete 51, the pull-out test of the rock bolt 1 can be easily performed by simply engaging the protruding strip 63 of the pull-out test coupler 6 with the concave groove 17 on the outer periphery of the head 13 that abuts against the bearing plate 2 and screwing the pull-out test coupler 6 onto the tension rod 71, without the need to remove and re-tighten the nut. In addition, after the pull-out test is completed, the rock bolt 1 can be easily restored to its original state by simply removing the pull-out test coupler 6 from the head 13 of the rock bolt 1, making it unnecessary to re-tighten the nut.

In addition, when a configuration is used in a pull-out test in which the pair of halves 60, 60 are mated to engage the convex portion 63 of the pull-out test coupler 6 with the concave groove 17 of the head 13, and the male threaded portion 62 formed by mating the pair of halves 60, 60 is screwed into the female threaded portion 711 formed at the tip of the tension rod 71, the male threaded portion 62 of the pull-out test coupler 6 can be screwed into the female threaded portion 711 of the tension rod 71 to engage the convex strip 63 of the pull-out test coupler 6 with the concave groove 17 of the head 13 of the lock bolt 1, and the lock bolt 1 and tension rod 71 can be connected cheaply and efficiently via the pull-out test coupler 6.

[Lock bolt of the second embodiment]
9 and 10, the lock bolt 1a of the second embodiment according to the present invention is made of a deformed steel bar, which is a metal material or a steel bar material, as in the first embodiment, and has a generally conical sword tip 12a formed at the tip in the driving direction of the shaft 11a, which is in the shape of a deformed steel bar. A head 13a with a larger diameter than the shaft 11a is formed on the rear side in the driving direction of the shaft 11a, and the head 13a is formed in a short, generally bullet-head shape that protrudes outward from the outer periphery of the shaft 11a, and the rear end 14a of the head 13a has a rounded peripheral shape.

The head 13a is arranged so that the front end surface 16a at the tip of the head 13a can press the support plate 2 similar to the first embodiment, which is inserted onto the shaft portion 11a, and the outer diameter of the head 13a is larger than the insertion hole 21 of the shaft portion 11a formed in the support plate 2. The front end surface 16a of the head 13a in the second embodiment is also flat. In addition, a recess is provided in the circumferential direction on the outer periphery of the head 13a that can engage with the protrusion of the pull-out test coupler 6a described later, and in the second embodiment, a recess groove 17a is also provided around the outer periphery of the head 13a as a recess.

Furthermore, in the rock bolt 1a of the second embodiment, the head 13a and the shaft 11a are also integrally formed, and for example, high tensile deformed steel bars as specified in JIS G3112 are used, and the head 13a is integrally formed on the rear side of the shaft 11a by hot forging. That is, in the rock bolt 1a of the second embodiment, the head 13a and the shaft 11a are also integrally formed from the same high tensile metal material. With the rock bolt 1a of the second embodiment, it is basically possible to form a rock bolt structure similar to that of the first embodiment together with the support plate 2, to perform construction in the same construction process as in the first embodiment, and to form a ground reinforcement structure similar to that of the first embodiment.

In the second embodiment of the lock bolt 1a, when manufacturing the lock bolt 1a in which the head 13a is integrally formed on the rear side of the shaft 11a by hot forging, a rod-shaped metal material or bar steel material having the outer shape and outer peripheral size of the shaft 11a is used as the material, for example, the deformed steel bar 1n shown in FIG. 11(a). The deformed steel bar 1n is preferably a high-tensile deformed steel bar, and more preferably a high-tensile deformed steel bar specified in JIS G3112.

When processing this deformed steel bar 1n by hot forging, the deformed steel bar 1n heated to high temperature is inserted through chucks 31a, 32a that can be opened and closed in the radial direction until it hits the stopper 35a, and one end of the deformed steel bar 1n is positioned so that it protrudes a predetermined length L1 on the side opposite the insertion side relative to the chucks 31a, 32a, and is firmly clamped between the chucks 31a, 32a (see Figure 11 (a)). The protruding length L1 of this deformed steel bar 1n is designed to be the same for each processing in order to form the shape of the head 13a from the deformed steel bar 1n by hot forging.

When the protruding length L1 of the deformed steel bar 1n from the chucks 31a and 32a is thus determined, the stopper 35a is withdrawn laterally from the axis of the deformed steel bar 1n, and then the first die 34a is pressed against the protruding portion of the deformed steel bar 1n so as to abut against the chucks 31a and 32a that are firmly clamping the deformed steel bar 1n, and hot forging is performed to form the first stage head 13n1. Inside the first die 34a, an intermediate shape internal space 33a is formed as a closed space to form the end of the deformed steel bar 1n into the head 13a shape, and the deformed steel bar 1n of the predetermined length L1 is forced into the internal space 33a to form the intermediate shape head 13n1 (see FIG. 11 (b)). After the head 13n1 is formed, the first die 34a is withdrawn.

Next, while the deformed steel bar 1n is firmly clamped between the chucks 31a and 32a, a second die 38a having an internal die space 37a with a shape equivalent to the short warhead-shaped head 13a is placed on the axis of the deformed steel bar 1n, and the second die 38a is pressed into the highly heated head 13n1 of the deformed steel bar 1n until it comes into contact with the chucks 31a and 32a, performing hot forging, and integrally forming a head 13n2 having the same external shape and size as the short warhead-shaped head 13a at the rear of the shaft 11n of the deformed steel bar 1n (see Figures 11(c) and (d)).

After the head 13n2 is formed, the second die 38a is withdrawn and the chucks 31a and 32a are opened to remove the head 13n2. Unnecessary burrs are removed from the deformed steel bar 1n on which the head 13n2 is formed, as necessary. After that, the deformed steel bar 1n on which the head 13n2 is formed is rotated using a lathe or the like, and a groove cutting tool is pressed against a predetermined position of the rotating head 13n2 to form a concave groove 17a on the outer periphery of the head 13n2 (see Figures 11(d) and (e)). Then, a substantially conical tip 12a is separately formed at the tip of the deformed steel bar 1n by hot forging or the like, to obtain the lock bolt 1a of this embodiment. Note that the hot forging when forming the lock bolt 1a of the second embodiment by hot forging is also appropriate within the scope of the spirit of the present invention, and it is also possible to use free forging hot forging without using a forging die, for example.

As an example of a rock bolt 1a in which a roughly short bullet-shaped head 13a is integrally formed by hot forging on the rear side of the shaft 11a, the rock bolt 1a made of deformed steel bar 1n of D22 with a nominal diameter of 22 mm and high tensile strength SD345 specified in JIS G3112 has a tensile strength of 133.5 kN. This exceeds the standard strength (tensile strength 122 kN) of a nut-tightened lock bolt having a threaded portion made of deformed steel bar of D25 with a nominal diameter of 24 mm and high tensile strength SD345 specified in JIS G3112, making it possible to reduce the size. The lock bolt 1a of the second embodiment also does not have a threaded portion, and in addition, the shaft 11a and head 13a are integrally formed by hot forging, making it possible to exhibit high tensile strength.

Next, an example of a pull-out test for the rock bolt 1a of the second embodiment will be described. When a pull-out test is performed on the rock bolt 1a in a state where it is cast in a natural ground reinforcement structure, for example, sprayed concrete 51 is cast along the surface of the natural ground 50, the rock bolt 1a is cast into a drilled hole 52 drilled in the natural ground 50 and the sprayed concrete 51, and the rock bolt 1a is fixed by an anchoring material 53 in the drilled hole 52, and the bearing plate 2 inserted on the shaft 11a is interposed between the front end surface 16a of the head 13a and the surface to which the sprayed concrete 51 is cast. In this ground reinforcement structure, the convex strip 64a corresponding to the convex portion of the pull-out test coupler 6a is engaged with the concave groove 17a corresponding to the concave portion formed on the outer periphery of the head 13a of the cast rock bolt 1a, and the rock bolt 1a and the tension rod 71a are connected via the pull-out test coupler 6a (see Figures 12 and 10).

The coupler 6a for the pull-out test used in this example is composed of a cylindrical body 61a formed by joining a pair of axially divided halves 62a and an outer fitting casing 63a that is fitted onto the pair of joined halves 62a to maintain the shape of the cylindrical body 61a. A convex rib 64a corresponding to a convex portion that engages with a concave groove 17a corresponding to a concave portion of the lock bolt head 13a is formed on the inner circumference of the cylindrical body 61a, and in the illustrated example, a convex rib 64a is formed at the tip of the cylindrical body 61a. A reduced diameter portion 65a is formed on the tension rod 71a side of the cylindrical body 61a, and the shaft portion 711a of the tension rod 71a can be inserted into the reduced diameter portion 65a. The outer fitting casing 63a is formed in a substantially bottomed cylindrical shape, and an insertion hole 631a is provided at the rear end through which the shaft portion 711a of the tension rod 71a can be inserted.

Then, the pair of halves 62a, 62a are aligned at the position of the head 13a of the rock bolt 1a driven into the natural ground 50 to form the coupler 6a for the pull-out test, and the convex strip 64a is engaged with the concave groove 17a of the head 13a. At the same time, the shaft 711a of the tension rod 71a is inserted into the reduced diameter portion 65a, and the large diameter portion 712a, which is larger than the shaft portion 711a formed at the tip of the tension rod 71a, is fitted into the cylindrical body 61a, and the large diameter portion 712a of the tension rod 71a is engaged in the pull-out direction by the reduced diameter portion 65a. Furthermore, the external fitting casing 63a, which is fitted onto the shaft portion 711a of the tension rod 71a so as to open to the natural ground 50 side, is slid from the tension rod 71a side and externally fitted onto the cylindrical body 61a, and the shape of the cylindrical body 61a formed by the pair of halves 62a, 62a is maintained. This connects the lock bolt 1a and tension rod 71a via the pull-out test coupler 6a, which is composed of a pair of halves 62a/62a or a cylindrical body 61a and an outer fitting casing 63a.

In the example of FIG. 12, a base plate 721 of a roughly cap-shaped pull-out test reaction pedestal 72 is provided so as to be placed on the support plate 2 that is in contact with the sprayed concrete 51 by being pressed by the front end face 16a of the head 13a of the rock bolt 1a, and the head 13a of the rock bolt 1a and the pull-out test coupler 6a are arranged inside the pull-out test reaction pedestal 72. The shaft 711a of the tension rod 71a is inserted into the pull-out test reaction pedestal 72 from a through hole.

As in the first embodiment, a pull-out force is applied to the tension rod 71a via the pull-out test measuring plate 74 and the pull-out test retaining nut 75 by applying pressure in the extension direction of the center hole jack 73, and the pull-out strength of the lock bolt 1a is determined.

According to the second embodiment, the corresponding effect can be obtained from the configuration corresponding to the first embodiment. In addition, by making the periphery of the rear end 14a of the head 13a of the lock bolt 1a round, it is possible to more reliably prevent damage to the waterproof sheet laid so as to directly or indirectly cover the head 13a of the lock bolt 1a. In addition, by simply fitting the external fitting casing 63a to the pair of halves 62a and 62a using the pull-out test coupler 6a, the protruding strip 64a of the pull-out test coupler 6a and the concave groove 17a of the head 13a of the lock bolt 1a can be engaged with each other, and the large diameter portion 712a of the tension rod 71a can be engaged in the pull-out direction, thereby connecting the lock bolt 1a and the tension rod 71a inexpensively and efficiently.

[Scope of the invention disclosed herein]
The inventions disclosed in this specification include, in addition to the inventions and embodiments listed as inventions, those specified by changing partial contents of these to other contents disclosed in this specification, those specified by adding other contents disclosed in this specification to these contents, or those specified by deleting partial contents of these to the extent that partial effects can be obtained, and forming a generic concept. The inventions disclosed in this specification also include the following contents and modifications.

For example, in the rock bolt of the present invention, the recesses that can engage with the protrusions of the pull-out test coupler provided circumferentially on the outer periphery of the head can be other than the grooves 17, 17a of the rock bolts 1, 1a of the above embodiment, and can be, for example, a plurality of recesses dotted circumferentially on the outer periphery of the head of the rock bolt. In this case, the protrusions of the pull-out test coupler can also be formed so as to be dotted circumferentially, and each dotted recess can be configured to engage with the dotted protrusions. It is also possible to configure the dotted protrusions of the pull-out test coupler to engage with the grooves 17, 17a.

In addition, the rock bolt of the present invention is preferably configured such that the heads 13, 13a are integrally formed with the shafts 11, 11a by hot forging as in the above embodiment, but it is also suitable to use a rock bolt 1, 1a formed by friction welding the heads 13, 13a of a different material to the rear side of the shafts 11, 11a. In addition, the rock bolt of the present invention also includes those formed by manufacturing methods other than these within the scope of the present invention. For example, it is possible to use a rock bolt configured such that the approximately cylindrical head 13 or the approximately short bullet-shaped head 13a is welded to one end face of a bar steel material having the same shape and size as the shafts 11, 11a, or a rock bolt configured such that the approximately cylindrical head 13 or the approximately short bullet-shaped head 13a is integrally formed with the shafts 11, 11a by cold forging or other means other than hot forging.

In addition, in the installation of the rock bolts 1, 1a in the above embodiment, the rock bolts 1, 1a, which press the bearing plate 2 with the front end faces 16, 16a of the roughly cylindrical head 13 or roughly short bullet-shaped head 13a, are preferably installed by automatically pushing the rock bolts 1, 1a into the installation hole using a driving machine 42 or the like, but it is also possible to manually push the rock bolts 1, 1a into the installation hole and install them.

The present invention can be used, for example, for rock bolts to be installed in tunnels and on slopes.

Reference Signs List 1...Lock bolt 11...Shaft portion 12...Tip portion 13...Head portion 14...Rear end surface 15...Corner portion 16...Front end surface 17...Groove 1a...Lock bolt 11a...Shaft portion 12a...Tip portion 13a...Head portion 14a...Rear end 16a...Front end surface 17a...Groove 1m...Deformed steel bar 11m...Shaft portion 13m1...Head portion 1n...Deformed steel bar 11n...Shaft portion 13n1, 13n2...Head portion 2...Support plate 21...Insertion hole 22...Corner portion 31...Die 311...Insertion hole 312...Space within die 32...Punch 33...Grooving tool 34...R chamfering tool 31a, 32a...Chuck 33a...Space within die 34a...First die 35a...Stopper 37a...space within mold 38a...second mold 41...guide cell 42...casting machine 50...natural ground 51...sprayed concrete 52...drilling 53...anchoring material 54...excavation surface 55...arch structure 56...tunnel space 57...buffer material 571...fastener 58...waterproof sheet 59...lining concrete 6...pull-out test coupler 60...half body 61...bottomed cylindrical portion 62...male threaded portion 63...rib 601, 602, 603...half-split portion 6a...pull-out test coupler 61a...cylindrical body 62a...half body 63a...external fitting casing 631a...insertion hole 64a...rib 65a...reduced diameter portion 71...tension rod 711...female threaded portion 71a...tension rod 711a...shaft portion 712a...large diameter portion 72...Reaction base for pull-out test 721...Base plate 73...Center hole jack 74...Measuring plate for pull-out test 75...Pressing nut for pull-out test BU...Burst L1...Protrusion length T...Axial force F...Force of the ground trying to push out 101...Excavation surface 102...Sprayed concrete 103...Ground 104...Rock bolt 105...Anchor material 106...Support plate 107...Male thread 108...Nut 109...Arch structure 110...Tunnel space

Claims (10)

The head is made of a steel bar material having a diameter larger than that of the shaft portion and is integrally formed with the shaft portion by hot forging on the rear side in the casting direction of the shaft portion,
A hot forging process is performed on the head portion to form a continuous grain flow from the shaft portion,
The front end surface of the head portion is a flat surface that is provided so as to be able to press a support plate that is fitted onto the shaft portion,
A lock bolt characterized in that a recess capable of engaging with a protrusion formed on a pull-out test coupler is provided circumferentially on the outer periphery of the head. The lock bolt according to claim 1, characterized in that the recess is a groove formed around the outer periphery of the head. A lock bolt according to claim 1 or 2, characterized in that the periphery of the rear end of the head is formed in a rounded shape. A bearing plate is fitted onto the shaft portion of the rock bolt according to claim 3,
A rock bolt structure characterized in that the corners of the support plate are chamfered with a radius. A method for manufacturing a rock bolt according to claim 2 or 3,
A first step of forming a head having a larger diameter than the shaft portion by hot forging at one end of a steel bar having an outer shape and an outer circumferential size of the shaft portion;
and a second step of rotating the bar steel material on which the head is formed and pressing a groove cutting tool against a predetermined position on the rotating head to form a groove on the outer periphery of the head. A method for installing a rock bolt according to any one of claims 1 to 3,
A first step of inserting a bearing plate from a tip side of the shaft portion of the rock bolt;
A rock bolt installation method comprising a second step of driving the rock bolt into the ground by pressing the front end surface of the head of the support plate against the ground. A ground reinforcement structure in which the rock bolt according to claim 3 is driven,
The rock bolt is driven into the ground with a bearing plate having a rounded corner and fitted onto the shaft portion interposed between the front end surface of the head and the ground or the surface of the sprayed concrete to be poured,
A ground reinforcement structure characterized in that a waterproof sheet is laid so as to directly or indirectly cover the head, the peripheral edge of which at the rear end is formed in a rounded shape. A pull-out test method for a rock bolt in a natural ground reinforcement structure, in which the rock bolt according to any one of claims 1 to 3 is driven into the natural ground, and a bearing plate inserted into the shaft portion is interposed between a front end surface of the head portion and a natural ground or a surface of sprayed concrete to be poured,
A first step of engaging a protrusion of the pull-out test coupler with a recess formed on the outer periphery of the head of the rock bolt in a driven state, and connecting the rock bolt and a tension rod via the pull-out test coupler;
A pull-out test method comprising a second step of applying a force in a pull-out direction to the head via the tension rod and determining the pull-out strength of the rock bolt. A rock bolt is driven into the ground, the head having a larger diameter than the shank is formed on the rear side of the shank in the pouring direction, the front end surface of the head is arranged so as to be able to press a bearing plate inserted into the shank, and the head has a recess formed in the circumferential direction on the outer periphery thereof which is engageable with a protrusion formed on a pull-out test coupler, and the bearing plate inserted into the shank is interposed between the front end surface of the head and the ground or a surface of sprayed concrete to be poured,
A first step of engaging a protrusion of the pull-out test coupler with a recess formed on the outer periphery of the head of the rock bolt in a driven state, and connecting the rock bolt and a tension rod via the pull-out test coupler;
A second step of applying a force in a pull-out direction to the head portion via the tension rod to recognize the pull-out strength of the lock bolt,
the coupler for pull-out test is composed of a bottomed tubular portion arranged on the lock bolt side and a male threaded portion arranged on the tension rod side,
The protrusion that engages with the recess is formed on the inner periphery of the bottomed cylindrical portion,
A pull-out test method characterized in that in the first step, a pair of halves obtained by dividing the pull-out test coupler in the axial direction are brought together to engage the convex portion of the pull-out test coupler with the concave portion of the head, and the male threaded portion formed by bringing the pair of halves together is screwed into a female threaded portion formed at the tip of the tension rod. A rock bolt is driven into the ground, the head having a larger diameter than the shank is formed on the rear side of the shank in the pouring direction, the front end surface of the head is arranged so as to be able to press a bearing plate inserted into the shank, and the head has a recess formed in the circumferential direction on the outer periphery thereof which is engageable with a protrusion formed on a pull-out test coupler, and the bearing plate inserted into the shank is interposed between the front end surface of the head and the ground or a surface of sprayed concrete to be poured,
A first step of engaging a protrusion of the pull-out test coupler with a recess formed on the outer periphery of the head of the rock bolt in a driven state, and connecting the rock bolt and a tension rod via the pull-out test coupler;
A second step of applying a force in a pull-out direction to the head portion via the tension rod to recognize the pull-out strength of the lock bolt,
the coupler for pull-out test is composed of a cylinder formed by joining a pair of halves separated in the axial direction, and an outer fitting casing that is fitted onto the pair of joined halves to maintain the shape of the cylinder,
The convex portion that engages with the concave portion is formed on the inner periphery of the cylindrical body, and a reduced diameter portion is formed on the tension rod side of the cylindrical body,
A pull-out test method characterized in that in the first step, the pair of halves are brought together to engage the convex portion with the concave portion of the head, and the large diameter portion formed at the tip of the tension rod is engaged in the pull-out direction by the reduced diameter portion, and the outer fitting casing is externally fitted from the tension rod side to maintain the shape of the cylindrical body formed by the pair of halves.

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