JP2006003323A - Method of measuring distribution of axial force of lock bolt and the lock bolt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the method of measuring distribution of axial force of a lock bolt capable of surely measuring the axial force with easy management; and to provide the lock bolt. <P>SOLUTION: At the time of execution of the solid lock bolt 10, the ultrasonic measurement is previously performed such that from the input part 11 being an exposed part of the lock bolt 10, the ultrasound is transmitted and received for measuring the receiving time difference between the reference points. Afterward, the ultrasonic measurement is performed again, for calculating the axial force from the change of the received time difference. The lock bolt is provided with reference points between the ultrasound incident part 11 and the end part 12, for reflecting the ultrasound. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lock bolt axial force distribution measuring method for measuring an axial force of a lock bolt used in a ground improvement method such as a natom method, and a lock bolt used therefor.

  As a rock bolt axial force distribution measuring method, for example, the inventions described in Patent Documents 1 and 2 are known. In the invention described in Patent Document 1, a measurement groove is provided in an axial force measuring meter made of a deformed steel bar lock bolt, a strain gauge is attached to the bottom surface, and a lead wire is provided in the measurement groove. In the invention described in Patent Document 2, a strain gauge is affixed to the surface of the steel pipe expansion type lock bolt, and the strain gauge and the input / output cable are protected by a protective pipe, a filler, and the like.

  In any of the prior inventions, the axial force is measured using a strain gauge, and a cable must be arranged up to the measuring section. The handling at the tunnel site is complicated and expensive as a measuring meter. It was.

In addition, although it is a reference example that is completely different from the technical field of the lock bolt, a bolt axial force measurement method using ultrasonic waves is known as described in Patent Document 3. The invention determines the ratio of the propagation time of longitudinal and transverse waves in the axial direction, and is concluded from the relationship between the ratio of propagation time of longitudinal and transverse waves obtained in advance under a known axial force and the tensile stress in the axial direction. The bolt axial force of the entire bolt is obtained. Therefore, there is no suggestion of applying to a rock bolt, and no disclosure about the feasibility at the time of application.
4-38541 JP 2004-37227 A JP-A-5-203513

  In view of such a conventional situation, an object of the present invention is to provide a lock bolt axial force distribution measuring method and a lock bolt that can be easily managed and can reliably measure an axial force.

  In order to achieve the above object, a feature of the lock bolt axial force distribution measuring method according to the present invention is a lock bolt axial force distribution measuring method for measuring an axial force acting on a solid lock bolt, wherein At the time of construction, ultrasonic waves are transmitted and received in advance from the incident part, which is the exposed part of the rock bolt, and the ultrasonic measurement is performed to obtain the reception time difference between the gauge points, and then the ultrasonic measurement is performed again to change the reception time difference. To calculate the axial force.

  According to the same feature, the axial force can be calculated from the change in the reception time difference of the ultrasonic wave at each gauge point without using a strain gauge.

  Moreover, a gage that reflects the ultrasonic wave may be provided between the incident part and the end of the ultrasonic wave in the rock bolt, and each gage may be a notch.

  Furthermore, when the ultrasonic wave is a transverse wave, it is desirable that the incident portion of the lock bolt is inclined with respect to the longitudinal direction of the lock bolt.

  On the other hand, the feature of the lock bolt that can be used in the method for measuring the axial force distribution of the lock bolt is that when the ultrasonic wave is a transverse wave, the ultrasonic wave incident portion is inclined with respect to the longitudinal direction of the lock bolt. There is to be. Further, a plurality of reference points that reflect the ultrasonic waves may be provided between the ultrasonic incident part and the terminal, and the lock bolt may be formed so that the surface is smooth and has a round cross-sectional shape.

  According to the above-described characteristics of the rock bolt axial force distribution measuring method according to the present invention, the use of ultrasonic waves eliminates the need for strain gage wiring and the like, simplifies management, and enables reliable axial force measurement. To provide a rock bolt axial force distribution measuring method and a lock bolt.

  Other objects, configurations, and effects of the present invention will become apparent from the following embodiments of the present invention.

  Next, the present invention will be described in more detail with reference to the accompanying drawings as appropriate. FIG. 1A shows a lock bolt 10 and an axial force distribution measuring device 1 used for measuring an axial force according to the present invention. The axial force distribution measuring apparatus 1 includes a probe 2 that transmits / receives ultrasonic waves to / from the rock bolt 10, a pulsar / receiver 3 that transmits / receives ultrasonic waves, and a PC (that controls and displays received signals). A personal computer 4 and a monitor 5 are provided.

  The rock bolt 10 includes an incident portion 11 for allowing ultrasonic waves to enter and the other end portion 12 having a tapered tip. As shown in FIG. 1A, the incident portion 11 serving as an exposed portion is formed by flattening a part of the lock bolt 10 as shown in FIG. The probe 2 is brought into contact with this flat surface, and ultrasonic waves are transmitted and received toward the lock bolt 10. On the other hand, when a transverse wave is incident, as shown in FIG. 3B, the incident portion 11 serving as an exposed portion is formed by obliquely shaving the lock bolt 10 to form a slope. The probe 2 comes into contact with this slope, and ultrasonic waves are transmitted and received toward the lock bolt 10. This inclined surface is inclined approximately 45 degrees with respect to the entire axis of the lock bolt 10, and a transverse wave ultrasonic wave is transmitted from the probe 2. The end portion 12 may be integrally formed with a steel material or the like up to a terminal end 12b with a tapered tip, or a resin cap 12b with a sharp tip may be bonded to the terminal 12a of the lock bolt 10.

  As shown in FIGS. 2 (a) and 2 (b), a plurality of notches N1-5 are formed as reference points at appropriate portions of the lock bolt 10.

  Each of the notches N1-5 is provided in a possible range so as to be cut in the periphery of the lock bolt 10 perpendicularly to the longitudinal direction of the bolt, and is arranged at the same phase at different longitudinal positions. Further, since the end portion 12 is tapered and an appropriate signal is not easily reflected, the notch N5 in the vicinity of the end portion 12 is cut deeper than the other notches N1-4 so that signal reflection is ensured. It is.

  By the way, when a material close to the acoustic impedance of the material of the rock bolt 10 enters each notch N1-5, the reflected signal from each notch N1-5 may be reduced. Therefore, as shown in FIG. 2C, each notch N1-5 has an insert 16 made of a material having a low acoustic wave propagation rate, such as a material having a different acoustic impedance from that of the rock bolt 10 such as a synthetic resin. May be inserted inside each notch N1-5 by filling or the like.

  Each notch N1-4 may be arranged so as to have different phases at different longitudinal positions as shown in FIG. 2 (d). In this case, the ultrasonic waves are those of the notch N1-4 and the end portion 12 at the intermediate portion. It can be detected more reliably. The mark may be a recess or a protrusion other than the notch, but the notch can most clearly detect the reflection of the ultrasonic wave. Further, as shown in FIG. 2 (e), as long as the strength of the lock bolt 10 and the reflection from the subsequent notch are not seriously affected, an entire circumferential groove is formed as a notch N1-5 on the outer periphery of the lock bolt 10. It may be formed.

  At the time of installation, a filler 102 such as cement milk or grout is filled into an insertion hole 101 formed at an appropriate location on the tunnel wall 100. After the filling, the lock bolt 10 is inserted into the insertion hole 101 filled with the filler 102 as shown in FIG. 1A, whereby the fixing of the lock bolt 10 to the insertion hole 101 is completed. After inserting the lock bolt 10 into the insertion hole 101, a filler 102 such as mortar may be filled. A bearing plate is inserted in the vicinity of the incident portion 11 to substantially support the tunnel wall 100.

  In measurement, as shown in FIG. 1A, the probe 2 is brought into contact with the surface of the incident portion 11 via a contact medium, and ultrasonic waves are incident and received. In the case of FIG.3 (b), the probe 2 is made to contact the incident part 11 formed in the slope.

First, the propagation time T _i (i is a section number) is obtained from the difference between the transmission time of the ultrasonic wave and the reception time of the reflected wave reflected from each target point (N1-5) shown in FIG. Next, the section propagation time can be calculated from the difference T _i −T _{i−1 in} the propagation time between adjacent sections. Based on the above procedure, the section propagation times of the respective mark sections SC1 to SC5 are measured as initial values immediately after the rock bolt is placed. Each section propagation time is similarly measured at any time after placement, and a change rate (section propagation time change rate dD) with respect to the initial value is obtained. The axial force of each section can be calculated from the correlation between the axial force obtained in advance and the section propagation time change rate dD.

  According to the experiments by the inventors, it has been found that the axial force F caused by extending the steel specimen and the propagation time change rate dD corresponding to the degree of extension between the gauge points have a certain correlation. In the case of the longitudinal wave, these proportional coefficients dD / F are larger than those in the case of the transverse wave, and in the case of the transverse wave, the axial force F and the propagation time change rate dD are substantially proportional. In the case of the longitudinal wave, in addition to the extension of the test body due to the axial force F, the influence that the propagation speed of the ultrasonic wave decreases due to the axial force F is integrated. And it was confirmed by experiment that the axial force F of the lock bolt 10 can be substantially obtained by using these correlations and the measured propagation time change rate dD. Further, in the case of the longitudinal wave shown in FIG. 1A, the reflected wave detection was better in the frequency region of about 5 MHz, but in the case of the transverse wave shown in FIG. 3B, in the frequency region of about 1 MHz to 2 MHz. It has been found that reflected wave detection is better.

  In the above-described embodiment, the present invention is expressed as a method for measuring the axial force distribution of a rock bolt. However, the present invention can also be expressed as a method for measuring an extension distribution of a lock bolt.

  In the present invention, both a transverse wave and a longitudinal wave can be used, and the lock bolt 10 has an uneven surface as shown in FIG. 3 (a) and an uneven surface as shown in FIG. 1 (a). Both can be used. Therefore, the present invention contemplates a total of four combinations of two types of waves and two types of surface irregularities. However, it is possible to measure the reflected wave even if there is unevenness on the surface, but the one with almost no unevenness on the surface, such as a round bar, as shown in FIGS. 1 (a) and 3 (b). Since the attenuation of the ultrasonic wave is small, it is more suitable for measuring the axial force distribution of the long rock bolt.

  In the above-described embodiment, five notches N1-5 are formed as the reference points on the lock bolt 10. However, the number of reference points is not limited to five, and the strength of the lock bolt 10 is not affected. It can be set arbitrarily within the range.

  INDUSTRIAL APPLICABILITY The present invention can be used as a rock bolt axial force distribution measuring method for measuring the axial force of a lock bolt used in a so-called natom method that is a kind of tunnel construction method. It can also be used in a method for measuring the axial force distribution of rock bolts for ground improvement other than tunnels.

(A) is a fracture view of a lock bolt and a block diagram of an axial force distribution measuring device, (b) is a diagram showing a notch position in the entire length of the lock bolt. (A) is sectional drawing in the plane perpendicular | vertical to the volt | bolt axial direction which shows the relationship between a lock bolt and a notch, (b) is a figure which shows another embodiment of (a), (c) is a lock bolt and a notch. Sectional drawing along the volt | bolt axial direction which shows a relationship, (d) is a figure which shows another embodiment of (a), (e) is a figure which shows another embodiment of (a). (A) and (b) are the crush figure which shows another embodiment of a rock bolt, and the block diagram of an axial force distribution measuring device.

Explanation of symbols

1: axial force measuring device, 2: probe, 3: pulser / receiver, 4: PC, 5: monitor, 10: lock bolt, 11: incident part, 12: end, 12a, 12b: terminal, 16: Insert: 100: Tunnel wall, 101: Insert hole, 102: Filler, N1-5: Mark (notch), SC1-5: Mark section, Da: Propagation time, Db: Section propagation time, dD: Propagation Time change rate

Claims (7)

A lock bolt axial force distribution measuring method for measuring an axial force acting on a solid rock bolt (10), wherein an ultrasonic wave is previously applied from an incident portion (11) which is an exposed portion of the lock bolt when the lock bolt is applied. A rock bolt axial force characterized by performing ultrasonic measurement to obtain a difference in reception time of a reference point by transmitting and receiving, and performing the ultrasonic measurement again afterwards to calculate the axial force by a change in the reception time difference Distribution measurement method. The rock bolt axial force distribution measuring method according to claim 1, wherein a gauge point for reflecting the ultrasonic wave is provided between the incident part (11) and the terminal end (12) of the ultrasonic wave in the rock bolt. The rock bolt axial force distribution measuring method according to claim 1 or 2, wherein the mark includes a notch. The lock bolt axial force according to any one of claims 1 to 3, wherein the ultrasonic wave is a transverse wave, and an incident portion (11) of the lock bolt is inclined with respect to a longitudinal direction of the lock bolt. Distribution measurement method. It is a lock bolt which can be used for the rock bolt axial force distribution measuring method in any one of Claims 1-4, Comprising: The said ultrasonic incident part (11) inclines with respect to the longitudinal direction of a lock bolt. A rock bolt characterized by It is a rock bolt which can be used for the rock bolt axial force distribution measuring method in any one of Claims 1-4, Comprising: An ultrasonic wave is injected between the ultrasonic incident part (11) and termination | terminus (12). A rock bolt characterized by providing a plurality of reflecting marks. It is a lock bolt which can be used for the lock bolt axial force distribution measuring method in any one of Claims 1-4, Comprising: The surface is smooth and has a round cross-sectional shape, The lock bolt characterized by the above-mentioned.

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