Rock bolt structure

Abstract

To provide a rock bolt structure allowing stabilization of the natural ground through exhibiting reinforcement effect by a rock bolt installed in the natural ground of a tunnel, and presence / absence of damage on covering concrete to be confirmed.SOLUTION: A rock bolt structure is configured: to install a steel pipe expansion bolt 1 in an expansion state in a bore hole 101 formed in the natural ground 100 through covering concrete 102 of a tunnel T, of which a hollow male scree part 13 is formed at a base end side; to arrange a plurality of strain gauges 2 arranged apart from each other on an outer surface at an opposite side to a concave part 14 of the steel pipe expansion bolt 1 in a longitudinal direction; to extend a gauge lead wire 21 of each of the strain gauges 2 toward the base end side; and to press a first thrust plate 4, a pressure disk 5, and a second thrust plate 6 consecutively inserted outside the hollow male screw part 13 from a tip side on the covering concrete 102 with a nut 7 screwed on the hollow male screw part 13.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a rock bolt structure capable of confirming both that a rock bolt installed in the rock mass of a tunnel exhibits a reinforcing effect and the rock mass is stabilized, and the presence or absence of damage to the lining concrete formed in the tunnel.

Background Art

[0002] Conventionally, a steel pipe expansion bolt is inserted as a rock bolt into a drilled hole formed in the rock mass through the lining concrete of an existing tunnel, and the steel pipe expansion bolt is brought into an expanded state in the drilled hole, so that the steel pipe expansion bolt is installed from the inner surface of the lining to the surrounding rock mass to stabilize the rock mass (see Patent Document 1). However, in this stabilization of the rock mass, there is a problem that it is difficult to determine whether the deformation of the rock mass is improved and the rock mass is stabilized by the reinforcement by the installation of the expanded steel pipe expansion bolt.

[0003] As a technique capable of confirming the reinforcing effect of such a rock bolt and the stabilization of the rock mass to some extent, there is a method for measuring the fixing force of the rock bolt in Patent Document 2. In this measurement method, an inner thrust plate, an annular load cell corresponding to a pressure disk, and an outer thrust plate are sequentially extrapolated to the protruding portion of the rock bolt fixed to the rock mass, and the load cell is clamped by tightening a nut screwed onto the male thread portion of the protruding portion of the rock bolt, and the display load is read to grasp the fixing force. Using this measurement method, for example, by sequentially extrapolating an inner thrust plate, a pressure disk, and an outer thrust plate to the male thread portion of a steel pipe expansion bolt protruding to the inner peripheral side of the lining concrete of an existing tunnel and tightening the nut, the axial force at the end of the steel pipe expansion bolt is measured to estimate the pushing force of the rock mass, and the reinforcing effect of the rock bolt and the degree of stabilization of the rock mass can be recognized.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] Incidentally, when using the measurement method described in Patent Document 2, as shown by the thick arrow in Figure 7(a), in a state where the surrounding ground 200 of the tunnel T is pushing out and lateral pressure is being applied to the lining concrete 201, the pushing force of the ground 200 can be accurately estimated by measuring the axial force of the protruding portion of the rock bolt of the steel pipe expansion bolt 202 driven into the ground 200. Therefore, the reinforcing effect of the rock bolt and the degree of stabilization of the ground 200 can be accurately recognized.

[0006] However, in a state where the lining concrete 201 has deformed due to ground subsidence, as shown by the thick downward arrow in Figure 7(b), the surrounding ground 200 is no longer pushing against the lining concrete 201. Therefore, even if the axial force is measured at the protruding part of the rock bolt of the steel pipe expansion bolt 202 driven into the ground 200, it becomes impossible to estimate the extruding force of the ground 200 from the measured axial force. In other words, it becomes difficult to recognize the reinforcing effect of the rock bolt or the degree of stabilization of the ground 200. Therefore, a technology is desired that can recognize the reinforcing effect of the rock bolt and the degree of stabilization of the ground 200 regardless of whether or not the lining concrete 201 is damaged. In addition, if the lining concrete 201 is damaged due to ground subsidence or the like, it is also important to recognize that damage has occurred to the lining concrete 201.

[0007] This invention is proposed in view of the above problems, and aims to provide a rock bolt structure that can confirm both that the rock bolts driven into the ground of the tunnel exert a reinforcing effect and stabilize the ground, and that there is no damage to the lining concrete formed in the tunnel. [Means for solving the problem]

[0008] The rock bolt structure of the present invention is configured such that a steel pipe expansion bolt, having a hollow male threaded portion formed on its base end, is driven in an expanded state into a bore hole formed in the ground through the tunnel lining concrete, and a plurality of strain gauges are provided on the outer surface opposite the recess of the steel pipe expansion bolt, spaced apart in the longitudinal direction of the steel pipe expansion bolt, with the gauge lead wires of each strain gauge extending toward the base end, and a first thrust plate, a pressure disc, and a second thrust plate are fitted onto the hollow male threaded portion in order from the tip side, and are pressed against the lining concrete by nuts that are screwed onto the hollow male threaded portion. The grooved plate is fitted onto the tip side of the first thrust plate of the hollow male thread portion and pressed by the nut, and the gauge lead wire is pulled out to the outside through the groove of the grooved plate. It is characterized by the following. According to this, by drawing the gauge lead wire of the strain gauge through the groove of the grooved plate provided on the tip side of the first thrust plate, it is possible to prevent the gauge lead wire from interfering with the clamping structure of the pressure disc. Furthermore, if the pressure disc is clamped between the grooved plate and the second thrust plate, using the grooved plate as one of the thrust plates, the integrated pressure-receiving area of ​​the groove of the grooved plate will decrease, which may cause a deviation from the calibration value of the pressure disc, or the pressure disc may be deformed by the groove. However, by stacking the grooved plate, the first thrust plate, and the pressure disc, it is possible to prevent deviation from the calibration value of the pressure disc and to prevent deformation of the pressure disc.

[0010] The rock bolt structure of the present invention is characterized in that a counterbore is formed on the inner circumferential surface of the lining concrete, and the hollow male threaded portion, the first thrust plate, the pressure disc, the second thrust plate, and the nut are housed in the counterbore so as not to protrude to the inner circumferential side of the lining concrete. According to this, it is possible to prevent the hollow male threaded portion of the steel pipe expansion bolt, the first thrust plate, the pressure disc, the second thrust plate, and the nut in the rock bolt structure from protruding into the inner circumference of the lining concrete and becoming an obstruction, for example, by preventing these components from entering the internal cross-section of an existing tunnel that is in service.

[0011] The rock bolt structure of the present invention is characterized in that a plug is provided at the end of the first oil supply pipe of the Bourdon tube type pressure disc, and a pressure transducer is provided at the end of the second oil supply pipe of the pressure disc, the first oil supply pipe and the second oil supply pipe are each bent in a U shape, the plug and the pressure transducer are positioned on the base end side of the second thrust plate, and the plug and the pressure transducer are housed in the counterbore so as not to protrude to the inner circumference side of the lining concrete. According to this, it is possible to prevent the closure plugs and pressure transducers of Bourdon tube type pressure discs from protruding into the inner circumference of the lining concrete and becoming an obstruction, for example, by preventing the closure plugs and pressure transducers from entering the internal cross-section of an existing tunnel that is in service. [Effects of the Invention]

[0012] According to the rock bolt structure of the present invention, it is possible to confirm both that the rock bolts driven into the ground of the tunnel exert a reinforcing effect and stabilize the ground, and whether or not there is any damage to the lining concrete formed in the tunnel. [Brief explanation of the drawing]

[0013] [Figure 1] A schematic cross-sectional view of an existing tunnel equipped with a rock bolt structure according to an embodiment of the present invention. [Figure 2] A partially enlarged cross-sectional view of an existing tunnel equipped with the rock bolt structure of the embodiment. [Figure 3] A schematic enlarged cross-sectional view of the area around the counter-excavation section of an existing tunnel equipped with the rock bolt structure of the embodiment. [Figure 4] (a) is an exploded perspective view of the steel pipe expansion bolt, grooved plate, first thrust plate, pressure disc, second thrust plate, and nut in the rock bolt structure of the embodiment, and (b) is a perspective view of the steel pipe expansion bolt, grooved plate, first thrust plate, pressure disc, second thrust plate, and nut assembled as shown in Figure (a). [Figure 5] A perspective view illustrating the steel pipe expansion bolt in the pre-expansion state in the rock bolt structure of the embodiment. [Figure 6] A perspective view illustrating the expanded state of a steel pipe expansion bolt in the rock bolt structure of the embodiment. [Figure 7] (a) is a schematic cross-section of an existing tunnel where the ground is pushing out and lateral pressure is being applied to the lining concrete, and (b) is a schematic cross-section of an existing tunnel where the ground has subsided and the lining concrete has deformed. [Modes for carrying out the invention]

[0014] [Lock bolt structure of the embodiment] The rock bolt structure of this embodiment is installed, for example, to be cast from the lining concrete 102 of an existing tunnel into the ground 100, and has a steel pipe expansion bolt 1 as shown in Figures 1 to 6. The steel pipe expansion bolt 1 comprises an expansion pipe 11 whose axial middle section is formed in a roughly C-shape in cross-section and has an axially extending space inside, cylindrical bodies 12 fitted to both ends of the expansion pipe 11 to restrict the expansion of both ends of the expansion pipe 11, and a hollow male threaded portion 13 formed to protrude towards the base end of the expansion pipe 11, with its hollow portion communicating with the internal space of the expansion pipe 11. The cylindrical body 12 fitted to the tip of the expansion pipe 11 is a bottomed cylindrical shape with a closed tip surface, and the cylindrical body 12 fitted to the base end of the expansion pipe 11 is a cylindrical shape that penetrates in the axial direction. Note that "tip side" means the back side of the borehole 101 in the ground 100, and "base side" means the mouth side of the borehole 101. Furthermore, in Figure 1, 1a represents an existing rock bolt that was already installed in the existing tunnel before the rock bolt structure of this embodiment was installed.

[0015] The expansion pipe 11 of the steel pipe expansion bolt 1 expands when a pressurized fluid, such as pressurized water, is injected into its internal space through the hollow portion of the hollow male threaded portion 13 (see Figures 5 and 6). The steel pipe expansion bolt 1 is inserted into a borehole 101 formed in the ground 100 through the lining concrete 102 of the tunnel T, and is then expanded by the injection of pressurized fluid before being driven into the ground 100.

[0016] On the outer surface on the side opposite to the recess 14 of the steel pipe expansion bolt 1, a plurality of strain gauges 2 are provided so as to be spaced apart in the longitudinal direction of the steel pipe expansion bolt 1. The plurality of strain gauges 2 are provided at the positions indicated by the arrows in FIG. 2, and are arranged at substantially the same intervals in the longitudinal direction of the steel pipe expansion bolt 1. The gauge lead wire 21 of each strain gauge 2 extends toward the proximal end side of the steel pipe expansion bolt 1 on the outer surface on the side opposite to the recess 14 of the steel pipe expansion bolt 1. In the present embodiment, a pair of rod-shaped protective materials 22 are extended in the longitudinal direction of the steel pipe expansion bolt 1 on the outer surface on the side opposite to the recess 14 of the steel pipe expansion bolt 1, and the gauge lead wire 21 is provided in the gap between the pair of protective materials 22, and a protective coating material 23 such as synthetic resin is provided so as to cover the gauge lead wire 21 between the pair of protective materials 22 (see FIG. 5).

[0017] Into the hollow male screw portion 13 of the steel pipe expansion bolt 1 driven into the natural ground 100, a grooved plate 3, a first thrust plate 4, a pressure disk 5, and a second thrust plate 6 are inserted in order from the tip side, and are tightened by a nut 7 screwed into the hollow male screw portion 13 on the proximal end side of the second thrust plate 6, so that the grooved plate 3, the first thrust plate 4, the pressure disk 5, and the second thrust plate 6 are provided so as to be pressed against the covering concrete 102. The grooved plate 3, the first thrust plate 4, the pressure disk 5, and the second thrust plate 6 are each formed in a shape having a through hole at the center, and the grooved plate 3 is formed with a groove 31 extending in the radial direction and communicating with the through hole at the center.

[0018] And in the present embodiment, as shown in FIG. 3, a recessed portion 103 is formed on the inner peripheral surface of the covering concrete 102, and the hollow male screw portion 13 of the steel pipe expansion bolt 1, the grooved plate 3, the first thrust plate 4, the pressure disk 5, and the second thrust plate 6 inserted into the hollow male screw portion 13, and the nut 7 screwed into the hollow male screw portion 13 are housed in the recessed portion 103 so as not to protrude to the inner peripheral side of the covering concrete 102, in other words, so as not to protrude into the tunnel space of the tunnel T.

[0019] The gauge lead wires 21 of each strain gauge 2, which extend to the hollow male threaded portion 13 of the steel pipe expansion bolt 1, are extended toward the outer edge of the groove cutting plate 3, entering into the groove 31 of the groove cutting plate 3, and are drawn out into the tunnel space on the inner side of the lining concrete 102, passing between the peripheral wall of the counterbore section 103 and the first thrust plate 4, pressure disc 5, and second thrust plate 6. In other words, the gauge lead wires 21 are drawn out to the outside of the lining concrete 102 and the counterbore section 103 via the groove 31 of the groove cutting plate 3. A reader (not shown) that converts the strain of the strain gauge 2 into axial force and displays it is provided at the end of the gauge lead wire 21 when measuring and acquiring the axial force, and is removed after measurement.

[0020] Furthermore, in this embodiment, as shown in Figures 3 and 4, a plug 52 is provided at the end of the first oil supply pipe 51 of the Bourdon tube type pressure disk 5, and a pressure transducer 54 that converts hydraulic pressure into an electrical signal such as a voltage signal is provided at the end of the second oil supply pipe 53 of the pressure disk 5, and an electrical cable 55 is connected to the pressure transducer 54. A data logger (not shown) is provided at the end of the electrical cable 55 to read, display, and record the axial force corresponding to the electrical signal applied to the pressure disk 5, and the electrical signal transmitted from the pressure transducer 54 via the electrical cable 55 is captured by the data logger.

[0021] The first oil supply pipe 51 and the second oil supply pipe 53 of the pressure disc 5 are initially in a straight line. After oil is injected into the pressure disc 5 from the first oil supply pipe 51, the first oil supply pipe 51 is closed with a plug 52. Then, both the first oil supply pipe 51 and the second oil supply pipe 53 are bent into a U-shape toward the base end of the second thrust plate 6. That is, with both the first oil supply pipe 51 and the second oil supply pipe 52 bent into a U-shape, the plug 52 and the pressure transducer 54 are positioned toward the base end of the second thrust plate 6. The plug 52 and the pressure transducer 54 positioned toward the base end of the second thrust plate 6 are housed in the counterbore 103 so as not to protrude toward the inner circumference of the lining concrete (see Figures 3 and 4).

[0022] In this embodiment, when acquiring the steel pipe expansion bolt 1 that has been driven into the ground 100 in an expanded state in a rock bolt structure, the axial force is obtained from the strain data of a plurality of strain gauges 2 spaced apart in the longitudinal direction of the steel pipe expansion bolt 1 using a reader, and the axial force of the steel pipe expansion bolt 1 at the installation location of each strain gauge 2 is obtained, thereby approximately obtaining the axial force over the entire length of the steel pipe expansion bolt 1. In addition, the axial force of the base end of the steel pipe expansion bolt 1 near the inner circumference of the lining concrete 102 is acquired by a data logger using a pressure disk 5.

[0023] Furthermore, after measuring and obtaining the axial force at the base end of the steel pipe expansion bolt 1 using the pressure disc 5, the grooved plate 3, the first thrust plate 4, the pressure disc 5, and the second thrust plate 6 are removed, and a standard washer is inserted onto the hollow male threaded portion 13 and tightened with a nut 7. Since the removed pressure disc 5 and other parts are expensive, they are reused in a lock bolt structure at a different location to reduce construction costs.

[0024] According to the rock bolt structure of this embodiment, the axial force of the steel pipe expansion bolt 1 can be obtained from the strain data of a plurality of strain gauges 2 spaced apart in the longitudinal direction of the steel pipe expansion bolt 1. By obtaining the axial force over a range close to the entire length of the steel pipe expansion bolt 1, it is possible to recognize the reinforcing effect of the steel pipe expansion bolt 1, which corresponds to a rock bolt, the degree of ground stabilization, or the deformation of the ground. Furthermore, the axial force of the base end of the steel pipe expansion bolt 1 near the inner circumference of the lining concrete 102 can be obtained with the pressure disk 5, making it possible to foresee the load applied to the lining concrete 102, i.e., the possibility of deformation of the lining concrete 102. Furthermore, by comparing the axial force at the base end of the steel pipe expansion bolt 1, obtained by the pressure disc 5 at the location of the lining concrete 102, with the axial forces of each steel pipe expansion bolt 1 obtained from the strain data of multiple strain gauges 2 spaced apart in the longitudinal direction, it is possible to recognize early on, for example, that if the axial force at the base end is smaller than the axial force detected by the multiple strain gauges 2 spaced apart in the longitudinal direction of the steel pipe expansion bolt 1, there is no damage to the lining concrete 102, or if the axial force at the base end is larger than the multiple strain gauges 2, damage to the lining concrete 102 is foreseeable. In other words, even if axial force is generated in the steel pipe expansion bolt 1 in an expansive ground, if the axial force detected by the pressure disk 5 at the base is smaller than the axial force detected by the strain gauge 2 closest to the lining concrete 102 among the strain gauges 2 spaced apart in the longitudinal direction, it should be evaluated that the force applied from the ground 100 to the lining concrete 102 is sufficiently suppressed by the steel pipe expansion bolt 1. On the other hand, if the axial force at the base becomes greater than the axial force detected by the strain gauge 2 closest to the lining concrete 102, it should be evaluated that the load on the lining concrete 102 is excessive. Therefore, it is possible to confirm both that the rock bolts installed in the ground 100 of the tunnel T are providing a reinforcing effect and stabilizing the ground, and whether or not there is any damage to the lining concrete 102 formed in the tunnel T.

[0025] Furthermore, by drawing out the gauge lead wire 21 of the strain gauge 2 through the groove 31 of the grooved plate 3 provided on the tip side of the first thrust plate 4, it is possible to prevent the gauge lead wire 21 from interfering with the clamping structure of the pressure disk 5. In addition, if the pressure disk 5 is clamped between the grooved plate 3 and the second thrust plate 6 with the grooved plate 3 as one of the thrust plates, the integrated pressure-receiving area of ​​the groove in the grooved plate 3 will decrease, which may cause a deviation from the calibration value of the pressure disk 5, or the pressure disk 5 may be deformed by the groove 31. However, by stacking the grooved plate 3, the first thrust plate 4, and the pressure disk 5, it is possible to prevent deviation from the calibration value of the pressure disk 5 and to prevent deformation of the pressure disk 5.

[0026] Furthermore, by housing the hollow male threaded portion 13, the first thrust plate 4, the pressure disc 5, the second thrust plate 6, and the nut 7 of the steel pipe expansion bolt 1 in the counterbore 103 so as not to protrude on the inner circumference side of the lining concrete 102, it is possible to prevent the hollow male threaded portion 13, the first thrust plate 4, the pressure disc 5, the second thrust plate 6, and the nut 7 from protruding on the inner circumference side of the lining concrete 102 and getting in the way, and for example, it is possible to prevent these components from entering the internal cross-section of an existing tunnel that is in service.

[0027] Furthermore, by bending the first oil supply pipe 51 and the second oil supply pipe 53 of the Bourdon tube type pressure disc 5 into a U-shape and positioning the closure plug 52 and pressure transducer 54 on the base end side of the second thrust plate 6, and by housing the closure plug 53 and pressure transducer 54 in the counter-excavated section 103 so as not to protrude to the inner circumference side of the lining concrete 102, it is possible to prevent the closure plug 52 and pressure transducer 54 of the Bourdon tube type pressure disc 5 from protruding to the inner circumference side of the lining concrete 102 and becoming an obstruction, for example, it is possible to prevent the closure plug 52 and pressure transducer 54 from entering the internal cross-section of an existing tunnel that is in service.

[0028] [Modifications of the embodiments, etc.] The inventions disclosed herein include, in addition to each invention and embodiment, modifications to these partial configurations to the extent applicable, modifications to these partial configurations to the extent applicable, modifications to these partial configurations to the extent applicable, modifications to these partial configurations to the extent applicable, modifications to these partial configurations to the extent applicable, modifications to the extent applicable, modifications to the extent applicable, modifications to these partial configurations to the extent applicable, modifications to the extent applicable, modifications to these partial configurations to the extent applicable, modifications to these partial configurations to the extent applicable, modifications to the extent applicable, modifications to these partial configurations to the extent applicable.

[0029] For example, in the above embodiment, the hollow male threaded portion 13, first thrust plate 4, pressure disc 5, second thrust plate 6, and nut 7 of the steel pipe expansion bolt 1 are housed in the counterbore 103 so as not to protrude on the inner circumference side of the lining concrete 102. However, the present invention also includes a rock bolt structure in which the hollow male threaded portion 13, first thrust plate 4, pressure disc 5, second thrust plate 6, and nut 7 of the steel pipe expansion bolt 1 are provided to protrude on the inner circumference side of the lining concrete 102.

[0030] Furthermore, although the pressure disc 5 in the rock bolt structure of the above embodiment was a Bourdon tube type pressure disc 5, the pressure disc in the rock bolt structure of the present invention can be any disc-shaped object capable of detecting pressure, as long as it is appropriate within the scope of the present invention, for example, a sheet-shaped sensor on which piezoelectric elements are arranged. Moreover, the use of the rock bolt structure of the present invention is not limited to application to existing tunnels, but can also be applied when constructing new tunnels. [Industrial applicability]

[0031] This invention can be used when stabilizing the ground in a tunnel by driving rock bolts into the ground. [Explanation of symbols]

[0032] 1...Steel pipe expansion bolt 11...Expansion pipe 12...Cylindrical body 13...Hollow male threaded section 14...Recess 1a...Existing rock bolt 2...Strain gauge 21...Gauge lead wire 22...Protective material 23...Protective coating material 3...Groove cutting plate 31...Groove 4...First thrust plate 5...Pressure disc 51...First oil supply pipe 52...Blocking plug 53...Second oil supply pipe 54...Pressure transducer 55...Electrical cable 6...Second thrust plate 7...Nut 100...Ground 101...Drilling 102...Lining concrete 103...Counter-drilled section T...Tunnel 200...Ground 201...Lining concrete 202...Steel pipe expansion bolt

Claims

1. A steel pipe expansion bolt, with a hollow male threaded portion formed on its base end, is driven into a borehole formed in the ground through the tunnel lining concrete while in an expanded state. Multiple strain gauges are provided on the outer surface of the steel pipe expansion bolt opposite to the recess, spaced apart in the longitudinal direction of the steel pipe expansion bolt. Each of the strain gauges has a gauge lead wire that extends toward the base end. A first thrust plate, a pressure disc, and a second thrust plate are fitted onto the hollow male threaded portion in order from the tip side, and are arranged to be pressed against the lining concrete by nuts that are screwed onto the hollow male threaded portion. A lock bolt structure characterized in that a grooved plate is fitted onto the tip side of the first thrust plate of the hollow male threaded portion and pressed by the nut, and the gauge lead wire is pulled out to the outside through the groove of the grooved plate.

2. A steel pipe expansion bolt, with a hollow male threaded portion formed on its base end, is driven into a borehole formed in the ground through the tunnel lining concrete while in an expanded state. Multiple strain gauges are provided on the outer surface of the steel pipe expansion bolt opposite to the recess, spaced apart in the longitudinal direction of the steel pipe expansion bolt. Each of the strain gauges has a gauge lead wire that extends toward the base end. A first thrust plate, a pressure disc, and a second thrust plate are fitted onto the hollow male threaded portion in order from the tip side, and are arranged to be pressed against the lining concrete by nuts that are screwed onto the hollow male threaded portion. A counter-excavated section is formed on the inner surface of the aforementioned lining concrete. The hollow male threaded portion, the first thrust plate, the pressure disc, the second thrust plate, and the nut are housed in the counterbore so as not to protrude on the inner circumference side of the lining concrete. A plug is provided at the end of the first oil supply pipe of the Bourdon tube type pressure disk, and a pressure transducer is provided at the end of the second oil supply pipe of the pressure disk. The first oil supply pipe and the second oil supply pipe are each bent into a U-shape, and the occluding plug and the pressure transducer are positioned on the base end side of the second thrust plate. A rock bolt structure characterized in that the blockage plug and the pressure transducer are housed in the counter-excavated portion so as not to protrude on the inner circumference side of the lining concrete.

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