Rock bolt and its manufacturing method

Abstract

To provide a lock bolt that makes it possible to eliminate work of removing a nut and re-tightening in performing a pull-out test and to easily perform the pull-out test.SOLUTION: A lock bolt 1 comprises: a head 13 formed on a rear side in an installation direction of a shaft 11, the head having a diameter larger than that of the shaft 11, the head 13 having a front end surface 16 provided so as to be capable of pressing a bearing plate 2 to be externally inserted to the shaft 11; and a recessed groove 17 provided on the outer circumference of the head 13 in the circumferential direction, the recessed groove being engageable with a protrusion 63 of a pull-out test coupler 6.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a rock bolt used, for example, for supporting a tunnel space, and a manufacturing method thereof. [Background technology]

[0002] In a typical tunnel, as shown in Figures 13 and 14, shotcrete 102 is poured along the tunnel excavation surface 101, and rock bolts 104 are cast radially from the shotcrete 102 into the surrounding natural ground 103. Each rock bolt 104 is fixed to the natural ground 103 with an anchoring material 105, and a nut 108 is fitted onto a male thread 107 at the rear end so that an inserted bearing plate 106 is in close contact with the shotcrete 102. The tunnel space 110 is supported by an arch structure 109 constructed in the natural ground 103 surrounding the tunnel by the rock bolts 104 cast radially.

[0003] The rock bolts 104 driven into and fixed in the natural ground 103 support the arch structure 109 so as not to break by resisting the force F that the natural ground 103 tries to push out with the axial force T in the tensile direction generated in the rock bolts 104. In order for the rock bolts 104 to perform this function, 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 the nuts are tightened on the rock bolts 104 so that the support plate 106 is in close contact with the sprayed concrete 102.

[0004] 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 bearing 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 the plate fixing member presses down on the bearing plate, and the rock bolt is installed in the ground. Therefore, it is possible to omit the work of attaching the bearing 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 bearing plate, since the thickness of the plate fixing member protruding from the bearing plate to the inside of the tunnel is small. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-314993 A Summary of the Invention [Problem to be solved by the invention]

[0006] 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 in which 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, thereby measuring 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.

[0007] Such a pull-out test is usually performed on a sample of rock bolts 104 from all rock bolts 104 driven into the natural ground 103, but even if it is performed on sampled rock bolts 104, it takes a lot of time to remove nuts 108 from the rock bolts 104 and retighten them to return them to their original state. In addition, in a configuration in which male threads 107 at the rear ends of 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 bearing plate 106, there is a risk that the waterproof sheet will be damaged, or it becomes necessary to take separate measures to prevent damage.

[0008] In addition, the rock bolt in Patent Document 1 has a plate fixing member in the form of a simple flat steel plate that holds down the bearing plate and is integrally joined to the rear end, so it is difficult to carry out a pull-out test. Also, if a bent part is formed at the corner of the bearing 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 bearing plate, damaging the waterproof sheet.

[0009] The present invention has been proposed in view of the above problems, and aims to provide a lock 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 lock bolt and a manufacturing method thereof that can prevent damage to the waterproof sheet. [Means for solving the problem]

[0010] The lock bolt of the present invention is made of a steel bar material, and a head portion having a diameter larger than that of the shaft portion is formed integrally with the shaft portion by hot forging on the rear side of the shaft portion in the casting direction, and a forging flow line formed by hot forging that continues from the shaft portion is formed in the head portion, and a front end surface of the head portion is provided so as to be able to press a support plate that is fitted onto the shaft portion. It is a flat surface.At the same time, the head has a recess provided in the circumferential direction on its outer periphery, the recess being engageable with a protrusion formed on the coupler for pull-out tests. 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.

[0011] 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.

[0012] 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, and a shape close to a hemisphere such as a hemisphere or a warhead shape.

[0013] 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.

[0014] The method for manufacturing a lock bolt of the present invention is a method for manufacturing a lock bolt of the present invention, comprising the steps 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 outer circumferential size of the shaft portion; and rotating the steel bar with the head formed thereon. Press the groove cutting tool against a predetermined position on the rotating head, and a second step of forming a 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.

[0015] 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.

[0016] 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 extrapolated to the shaft portion being 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.

[0017] 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.

[0018] 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 that engages with the concave portion is formed 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.

[0019] 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 halves divided in the axial direction, 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, 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. Effect of the Invention

[0020] According to the lock bolt of the present invention, there is no need to remove and retighten the nut when conducting a pull-out test, and the pull-out test can be easily performed. [Brief description of the drawings]

[0021] [Figure 1] 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. [Diagram 2] 3A and 3B are perspective explanatory views illustrating the attachment of a pull-out test jig to the rock bolt of the first embodiment. [Diagram 3] 1A is a plan view of a bearing plate that is extrapolated to the rock bolt of the first embodiment, and FIG. [Figure 4] 5(a) to 5(e) are process explanatory views illustrating a manufacturing process of the lock bolt of the first embodiment. [Diagram 5] 4(a) to 4(d) are process explanatory views illustrating the installation process of the rock bolt of the first embodiment. [Figure 6] FIG. 1 is a schematic explanatory diagram of a tunnel constructed with a natural ground reinforcement structure in which rock bolts of the first embodiment are installed. [Figure 7] FIG. 7 is an explanatory diagram illustrating a fixing mechanism of the rock bolt of the first embodiment in the example of the tunnel in FIG. 6. [Figure 8] 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. [Figure 9]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. [Figure 10] 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. [Figure 11] 6(a) to 6(e) are process explanatory views illustrating a manufacturing process of the rock bolt of the second embodiment. [Figure 12] 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. [Figure 13] A schematic diagram of a typical tunnel under construction. [Figure 14] FIG. 2 is an explanatory diagram illustrating a typical fixing mechanism of a rock bolt. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] [Lock bolt of the first embodiment] 1 and 2, a rock bolt 1 according to a first embodiment of the present invention is made of deformed steel bar which is a metal material or a steel bar material, and a substantially conical point 12 is formed at the tip in the driving direction of a shaft 11 which is in the shape of a deformed steel bar. A head 13 having a larger diameter than the shaft 11 is formed on the rear side in the driving direction of the shaft 11, and the head 13 is formed in a substantially cylindrical shape that protrudes outward from the outer periphery of the shaft 11, and a corner 15 on the periphery of a rear end face 14 of the substantially cylindrical head 13 is radius-chamfered.

[0023] The head 13 is provided so that a 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. The front end surface 16 of the head 13 in this embodiment is a flat surface. Also, a recess that can be engaged with a protrusion of a pull-out test coupler 6 (described later) is provided in the circumferential direction on the outer periphery of the head 13, and in this embodiment, a recessed groove 17 is provided around the outer periphery of the head 13 as the recess.

[0024] Furthermore, in the lock bolt 1 of this embodiment, the head 13 and the shaft 11 are integrally formed, and for example, a high-tensile deformed steel bar specified in JIS G3112 is used, and the head 13 is integrally formed by hot forging on the rear side of the shaft 11. That is, 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.

[0025] 3, the support plate 2, which is inserted onto the shaft 11 of the rock bolt 1 and constitutes the rock bolt structure together with the rock bolt 1, is a generally rectangular plate with chamfered corners 22. 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 when viewed from above, 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.

[0026] In the case of manufacturing the rock bolt 1 of this embodiment in which the head 13 is integrally formed by hot forging on the rear side of the shaft 11, a rod-shaped metal material or steel bar material having the outer shape and outer peripheral size of the shaft 11 is used as a 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.

[0027] When processing this deformed steel bar 1m by hot forging, for example, a die 31 and a punch 32 shown in Fig. 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 substantially the same as the outer diameter of the deformed steel bar 1m, and an in-die space 312 formed to communicate with the insertion hole 311 and open on the opposite side to the insertion hole 311. The in-die space 312 has a shape and size that approximately correspond 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 in-die space 312, and can be inserted into the in-die space 312 from the opening side.

[0028] The highly heated deformed steel bar 1m is then 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 projecting from the die space 312 by a predetermined length on the side opposite the insertion hole 311 (see FIG. 4(a)). After that, the punch 32 is slightly inserted into the die space 312 from the projecting 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 roughly 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)).

[0029] Thereafter, the deformed steel bar 1m on which the head 13m1 has been formed is rotated using a lathe or the like, and a 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, an 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 used to form the lock bolt 1 of this embodiment by hot forging may be any suitable method within the scope of the present invention, and may be, for example, free forging hot forging without using a forging die.

[0030] As an example of a rock bolt 1 in which a substantially 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 load strength of 133.5 kN. This exceeds the standard strength (tensile load 122 kN) of an existing nut-tightened lock bolt having a threaded portion made of a 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 having 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 the head 13 are integrally formed by hot forging, making it possible to exhibit high tensile strength.

[0031] 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 bearing 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 bearing plate 2 can be performed in an appropriate manner. For example, it is preferable to hold the bearing plate 2 with a holding mechanism provided near the tip of the guide cell 41 of the rock bolt driving device, hold the rear end of the rock bolt 1 with a push-in type driving machine 42 that slides along the guide cell 41 as described later, and advance the driving machine 42 to insert the shaft 11 of the rock bolt 1 into the insertion hole 21 of the bearing plate 2 held in a predetermined position by the holding mechanism (see Figures 5(a) to (c)). Incidentally, the bearing plate 2 does not have to be moved so as to approach the head 13 of the rock bolt 1, and the bearing plate 2 is positioned in a state of being extrapolated by being positioned near the tip of the shaft portion 11. Also, drill holes 52 are formed in advance in the natural ground 50, or in the natural ground 50 and sprayed concrete 51, and fixing material 53 such as mortar is injected into the drill holes 52 in advance (see FIG. 7).

[0032] Then, as shown by the bold arrow in Fig. 5(c), the rear end of the rock bolt 1 is held by a push-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 from the tip side where the point 12 is formed into the drilled hole 52 into which the fixing material 53 has been injected. 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 ground reinforcement structure constructed in this construction process, the bearing plate 2, which has a chamfered corner 22 and is extrapolated onto the shaft 11, is interposed between the front end face 16 of the approximately cylindrical head 13 and the ground 50 or the surface to be poured of sprayed concrete 51, and the rock bolt 1 is driven into the ground 10 in a state in which the bearing plate 2 can withstand the pushing force when the ground 50 pushes out.

[0033] An example of a tunnel having a natural ground reinforcement structure constructed by the above construction process is shown in Figures 6 and 7. In this example, shotcrete 51 is poured along the excavation surface 54 of the tunnel, and rock bolts 1 are cast radially from the shotcrete 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 face 16 of the approximately cylindrical head 13 is pressed against the bearing plate 2 so that the inserted bearing plate 2 is in close contact with the shotcrete 51. The tunnel space 56 is supported by an arch structure 55 constructed in the natural ground 50 around the tunnel by the rock bolts 1 cast radially.

[0034] Furthermore, in this example, a sheet-like cushioning material 57 such as a nonwoven fabric is laid to cover the generally cylindrical head 13 with rounded chamfered corners 15 on the periphery of the rear end face 14 of the rock bolt 1, which protrudes into the inside of the tunnel, and the support plate 2 with rounded chamfered corners 22, and a waterproof sheet 58 is laid so as to be layered inside the cushioning material 57. In other words, the waterproof sheet 58 is laid so as to indirectly cover the generally cylindrical head 13 with rounded chamfered corners 15 on the periphery of the rear end face 14, and the support plate 2 with rounded chamfered corners 22. The cushioning material 57 and waterproof sheet 58 are laid, for example, by fixing the cushioning material 57 to the shotcrete 51 with fasteners 571 such as anchors or nails and laying it along the inner surface of the shotcrete 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 overlaps the cushioning material 57, is laid along the inner surface of the shotcrete 51. Reference numeral 59 in the figure denotes lining concrete.

[0035] In this natural ground reinforcement structure with waterproof sheet 58 laid, the bearing plate 2 installed on the natural ground 50 protrudes from the surface of the shotcrete 51 by a thickness of, for example, 9 to 12 mm, and furthermore, the substantially cylindrical head 13 protrudes from the surface of the bearing plate 2 inside the tunnel by a height of, for example, about 30 mm, and the buffer material 57 and waterproof sheet 58 are laid to cover these, but since the installation pitch of the rock bolts 1 in the circumferential direction of the tunnel is 1 m or more apart, the actual buffer material 57 and waterproof sheet 58 are laid in a state with less unevenness than in the schematic example of Figure 6. It is also possible to lay the waterproof sheet 58 so as to directly cover the substantially hemispherical head 13 and bearing plate 2 without laying the buffer material 57.

[0036] In this way, in the tunnel ground reinforcement structure equipped with rock bolt 1 driven and fixed into the ground 50 and bearing plate 2, the force F that the ground 50 tries to push out is supported by the bearing plate 2 and is resisted by the axial force T in the tensile direction generated in the rock bolt 1, thereby supporting the arch structure 55 so that it does not break (see Figure 7).

[0037] 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 has been cast in a natural ground reinforcement structure, for example, in a ground reinforcement structure in which shotcrete 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 shotcrete 51 and the natural ground 50, 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 face 16 of the head 13 and the surface to which the shotcrete 51 is cast, a convex strip 63 corresponding to a convex portion of the pull-out test coupler 6 is engaged with a concave groove 17 corresponding to a concave formed on the outer periphery of the head 13 of the rock bolt 1 in the cast state, and the rock bolt 1 and a tension rod 71 are connected via the pull-out test coupler 6 (see Figs. 8 and 2).

[0038] 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 constructed by fitting together a pair of halves 60 / 60 that are split in the axial direction, and the bottomed tubular portion 61, male threaded portion 62, and convex rib 63 are respectively formed when the half-split portions 601, 602, 603 of the pair of halves 60 / 60 are fitted together.

[0039] The pair of halves 60 / 60 are then 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, with the ridge 63 engaging with the groove 17 of the head 13. Furthermore, the male thread 62 of the pull-out test coupler 6 formed by fitting the pair of halves 60 / 60 together is screwed relatively into the female thread 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 / 60 together is stably maintained by the screwing of the male thread 62 and the female thread 711, and the rock bolt 1 and tension rod 71 are connected via the pull-out test coupler 6.

[0040] In the example of Figure 8, a substantially cap-shaped base plate 721 of a pull-out test reaction pedestal 72 is provided so as to be placed on the bearing plate 2 which is in contact with the shotcrete 51 by being pressed by the front end face 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.

[0041] A center hole jack 73 and a pull-out test measuring plate 74 are extrapolated to the part of the tension rod 71 protruding from the pull-out test reaction base 72 on the side opposite the ground 50, and a pull-out test retaining 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.

[0042] 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 retaining 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. By applying a pull-out force to the rock bolt 1 in this way, 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 based on the recognition of 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.

[0043] According to the first embodiment, the pull-out test of the rock bolt 1 can be performed by engaging the convex rib 63 corresponding to the convex portion of the pull-out test coupler 6 with the concave groove 17 corresponding to the concave portion on the outer periphery of the head 13, and the pull-out test of 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 by simply pushing it into the natural 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 so as to directly or indirectly cover the head 13 of the rock bolt 1 can be prevented.

[0044] Furthermore, by forming the recess in the head 13 of the rock bolt 1 into the recessed groove 17, it is not necessary to perform the task of positioning the recess in 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 of the rock bolt 1. Furthermore, by chamfering the corners 15 of the substantially 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. Furthermore, 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.

[0045] Furthermore, when manufacturing rock bolt 1 by forming head 13, which is larger in diameter than shaft 11, by hot forging at one end of a steel bar having the outer shape and outer circumferential size of shaft 11 of rock bolt 1, head 13 of rock bolt 1 can be formed from the same material as shaft 11. In addition, head 13 has a material structure with homogenous internal structure and high toughness with increased viscosity, in which grain flows are formed by hot forging that continue from shaft 11. Therefore, rock bolt 1 can be obtained that exhibits high strength and high yield strength over its entire length. Furthermore, rock bolt 1 can be manufactured quickly and inexpensively by manufacturing by hot forging. In addition, when a manufacturing process is used in which a deformed steel bar 1m having a head 13m1 formed thereon 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, both the formation of the groove 17 on the outer periphery of the head and the chamfering of the radius of the rear end face of the head can be performed in the process of rotating the deformed steel bar 1m having a head 13m1, thereby making it possible to make the manufacturing process more efficient.

[0046] Furthermore, in the installation method of the rock bolt 1 of this embodiment, there is no need to tighten the nuts until the support plate 2 is in close contact with the ground 50 or sprayed concrete 51, and the rock bolt 1 can be installed simply by moving it in a pushing motion, thereby simplifying the installation work.

[0047] In addition, in a pull-out test of a rock bolt 1 in a natural ground reinforcement structure in which the rock bolt 1 is driven into the natural ground 50 and the bearing plate 2 fitted onto the shaft 11 is interposed between the front end face 16 of the head 13 and the natural ground 50 or the surface to be poured of the shotcrete 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 original state can be easily restored 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.

[0048] Furthermore, when a configuration is used in a pull-out test in which the pair of halves 60·60 are brought together 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 bringing the pair of halves 60·60 together 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.

[0049] [Lock bolt of second embodiment] 9 and 10, a rock bolt 1a according to a second embodiment of the present invention is made of a deformed steel bar, which is a metal material or a steel bar material, in the same manner as in the first embodiment, and a generally conical sword tip 12a is formed at the tip in the driving direction of a 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 peripheral edge of the rear end 14a of the head 13a is rounded.

[0050] The head 13a is provided so that the front end surface 16a at the tip of the head 13a can press the support plate 2 similar to that of the first embodiment, which is fitted 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 a flat surface. In addition, a recess that can be engaged with a protrusion of a pull-out test coupler 6a described later is provided in the circumferential direction on the outer periphery of the head 13a, and in the second embodiment, a recessed groove 17a is also provided around the outer periphery of the head 13a as a recess.

[0051] Furthermore, in the rock bolt 1a of the second embodiment, the head 13a and the shaft 11a are also integrally formed, and for example, a high-tensile deformed steel bar specified in JIS G3112 is 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 such a rock bolt 1a of the second embodiment, it is basically possible to configure a rock bolt structure similar to that of the first embodiment together with the bearing plate 2, to perform construction in the same construction process as in the first embodiment, and to form a natural ground reinforcement structure similar to that of the first embodiment.

[0052] In the case of manufacturing the rock bolt 1a of the second embodiment 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 steel bar material having the outer shape and outer peripheral size of the shaft 11a is used as the raw 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.

[0053] 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 up to a position where it hits a stopper 35a, and one end of the deformed steel bar 1n is positioned in a state where it protrudes by a predetermined length L1 on the side opposite to the insertion side with respect to the chucks 31a, 32a, and is firmly clamped by the chucks 31a, 32a (see FIG. 11(a)). The protruding length L1 of this deformed steel bar 1n is designed to be the same protruding length for each processing in order to form the shape of the head 13a from the deformed steel bar 1n by hot forging.

[0054] When the protruding length L1 of the deformed steel bar 1n from the chucks 31a and 32a is determined in this way, 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 firmly holding 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 inner die space 33a for forming the end of the deformed steel bar 1n into the head 13a shape is formed as a closed space, and the deformed steel bar 1n of the predetermined length L1 is forced into the inner die 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.

[0055] Next, while the deformed steel bar 1n is firmly clamped between the chucks 31a and 32a, a second mold 38a having an internal mold space 37a having a shape corresponding to the approximately short warhead-shaped head 13a is placed on the axis of the deformed steel bar 1n, and the second mold 38a is pressed into the head 13n1 of the deformed steel bar 1n, which has been heated to a high temperature, until it is in contact with the chucks 31a and 32a, thereby performing hot forging, and a head 13n2 having the same external shape and size as the approximately short warhead-shaped head 13a is integrally formed at the rear of the shaft portion 11n of the deformed steel bar 1n (see Figures 11(c) and (d)).

[0056] After the head 13n2 is formed, the second die 38a is withdrawn and the chucks 31a and 32a are opened to remove the deformed steel bar 1n on which the head 13n2 is formed, and unnecessary burrs are removed as necessary from the deformed steel bar 1n on which the head 13n2 is formed. 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 recessed groove 17a on the outer periphery of the head 13n2 (see Figs. 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 present invention, and it is also possible to use free forging hot forging without using a forging die, for example.

[0057] As an example of a rock bolt 1a in which a head 13a of a substantially short bullet-shaped shape is integrally formed by hot forging on the rear side of the shaft 11a, the rock bolt 1a made of a deformed steel bar 1n of D22 with a nominal diameter of 22 mm and made of high-tensile deformed steel bar SD345 specified in JIS G3112 has a tensile strength of 133.5 kN. This exceeds the standard strength (tensile load 122 kN) of a nut-tightened lock bolt having a threaded portion made of a deformed steel bar of D25 with a nominal diameter of 24 mm and made of high-tensile deformed steel bar SD345 specified in JIS G3112, making it possible to reduce the size. The lock bolt 1a of the second embodiment also has no threaded portion, and the shaft 11a and the head 13a are integrally formed by hot forging, making it possible to exhibit high tensile strength.

[0058] 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, in a ground reinforcement structure in which a shotcrete 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 shotcrete 51 and the natural ground 50, 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 shotcrete 51 is cast, a convex strip 64a corresponding to a convex portion of the pull-out test coupler 6a is engaged with a concave groove 17a corresponding to a concave formed on the outer periphery of the head 13a of the rock bolt 1a in the cast state, and the rock bolt 1a and a tension rod 71a are connected via the pull-out test coupler 6a (see Figs. 12 and 10).

[0059] The coupler 6a for 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 joined pair of halves 62a to maintain the shape of the cylindrical body 61a. A convex strip 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, the convex strip 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 to allow the shaft portion 711a of the tension rod 71a to be inserted therethrough.

[0060] Then, the pair of halves 62a are aligned at 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 protruding strip 64a is engaged with the recessed 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 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 locked in the pull-out direction by the reduced diameter portion 65a. Furthermore, the external fitting casing 63a, which is fitted onto the shaft 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 fitted onto the cylindrical body 61a, thereby maintaining the shape of the cylindrical body 61a formed by the pair of halves 62a. As a result, the lock bolt 1a and the tension rod 71a are connected via the pull-out test coupler 6a, which is composed of the pair of halves 62a, 62a or the cylindrical body 61a and the outer fitting casing 63a.

[0061] 12, a substantially cap-shaped base plate 721 of a pull-out test reaction pedestal 72 is provided so as to be placed on the support plate 2 that is in contact with the shotcrete 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 a tension rod 71a is inserted into the pull-out test reaction pedestal 72 from a through hole.

[0062] Then, as in the example of the first embodiment, by applying pressure in the extension direction of the center hole jack 73, 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, and the pull-out strength of the rock bolt 1a is determined.

[0063] According to the second embodiment, the corresponding effects can be obtained from the corresponding configuration to the first embodiment. In addition, by forming a rounded peripheral edge of the rear end 14a of the head 13a of the rock bolt 1a, damage to the waterproof sheet laid so as to directly or indirectly cover the head 13a of the rock bolt 1a can be more reliably prevented. In addition, by simply fitting the outer fitting casing 63a to the pair of halves 62a, the pull-out test coupler 6a can engage the protruding strip 64a of the pull-out test coupler 6a with the recessed groove 17a of the head 13a of the rock bolt 1a and the large diameter portion 712a of the tension rod 71a in the pull-out direction, thereby making it possible to connect the rock bolt 1a and the tension rod 71a inexpensively and efficiently.

[0064] [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 specifying them as a higher-level concept. The inventions disclosed in this specification also include the following contents and modifications.

[0065] For example, in the lock 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 may be other than the recess grooves 17, 17a of the lock bolts 1, 1a of the above embodiment, and may be, for example, a plurality of recesses dotted in the circumferential direction on the outer periphery of the head of the lock bolt. In this case, the protrusions of the pull-out test coupler may also be formed so as to be dotted in the circumferential direction, and each dotted recess may engage with the dotted protrusions. It is also possible to configure the dotted protrusions of the pull-out test coupler to engage with the recess grooves 17, 17a.

[0066] In addition, the rock bolt of the present invention is preferably configured such that the heads 13, 13a are integrally formed with the shaft portions 11, 11a by hot forging as in the above embodiment, but it is also suitable to use rock bolts 1, 1a formed by friction welding the heads 13, 13a of a different material to the rear side of the shaft portions 11, 11a. In addition, rock bolts formed by manufacturing methods other than these are also included within the scope of the present invention within the spirit of the present invention, and it is possible to use, for example, a rock bolt configured such that the substantially cylindrical head 13 or the substantially short bullet-shaped head 13a is welded to one end face of a bar steel material having the same shape and size as the shaft portions 11, 11a, or a rock bolt configured such that the substantially cylindrical head 13 or the substantially short bullet-shaped head 13a is integrally formed with the shaft portions 11, 11a by a method other than hot forging, such as cold forging.

[0067] In addition, in installing the rock bolts 1, 1a in the above embodiment, the rock bolts 1, 1a, which press the support plate 2 with the front end faces 16, 16a of the approximately cylindrical head 13 or the approximately short bullet-shaped head 13a, are preferably installed by automatically pushing the rock bolts 1, 1a in with a driving machine 42 or the like, but it is also possible to manually push the rock bolts 1, 1a in and install them. [Industrial Applicability]

[0068] The present invention can be used, for example, for rock bolts to be driven into tunnels, rock bolts to be driven into slopes, etc. [Explanation of symbols]

[0069] DESCRIPTION OF SYMBOLS 1...lock bolt 11...shaft 12...tip 13...head 14...rear end 15...corner 16...front end 17...groove 1a...lock bolt 11a...shaft 12a...tip 13a...head 14a...rear end 16a...front end 17a...groove 1m...deformed steel bar 11m...shaft 13m1...head 1n...deformed steel bar 11n...shaft 13n1, 13n2...head 2...support plate 21...insertion hole 22...corner 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 tubular portion 62...male thread portion 63...rib 601, 602, 603...half portion 6a...pull-out test coupler 61a...tubular body 62a...half body 63a...external fitting casing 631a...insertion hole 64a...rib 65a...reduced diameter portion 71...tension rod 711...female thread 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...Retaining 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

1. 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.

2. 2. The lock bolt according to claim 1, wherein the recess is a groove formed around the outer periphery of the head.

3. 3. The lock bolt according to claim 1, wherein the peripheral edge of the rear end of the head portion is formed in a rounded shape.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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 face of the head is arranged so as to be able to press a support 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 support plate inserted into the shank is interposed between the front end face 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 via the tension rod and recognizing the pull-out strength of the lock bolt, the coupler for pull-out test is composed of a bottomed tubular portion disposed on the lock bolt side and a male threaded portion disposed 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, the pull-out test coupler is divided into a pair of halves in the axial direction, and the convex portion of the pull-out test coupler is engaged with the concave portion of the head so as to mate with the pair of halves, and the male threaded portion formed by mating the pair of halves is screwed into the female threaded portion formed at the tip of the tension rod.

10. 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 face of the head is arranged so as to be able to press a support 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 support plate inserted into the shank is interposed between the front end face 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 via the tension rod and recognizing 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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