Measuring jig for low-frequency underground radar

Abstract

To provide a measuring jig for low-frequency underground radar that can measure a tunnel face efficiently and accurately by holding a long low-frequency underground radar antenna in parallel on a slide rail.SOLUTION: A measurement jig 1 for low-frequency underground radar according to the present invention includes: a guide rail 10 having two rail members 11 arranged in parallel in a height direction; and two slide units 20, which are disposed on a front side of the guide rail 10 and slidably connected along the two rail members 11. The two slide units 20 are configured to hold a transmitting antenna Bs and a receiving antenna Br in parallel.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a measuring jig for a low-frequency ground radar, and particularly to a measuring jig for a low-frequency ground radar capable of efficiently and accurately measuring a face by holding a long low-frequency ground radar antenna in parallel on a slide rail.

Background Art

[0002] In tunnel construction such as mountain tunnels, face collapse accidents occur where the face after excavation collapses toward the construction space side. Face collapse is likely to occur when there is a geological boundary surface parallel to the face in the ground in front of the face, when the ground near the face is soft, or when there are local weak parts in the ground. Therefore, in order to avoid face collapse and perform safe and efficient construction, technologies for accurately grasping the geological characteristics of the ground in front of the face have been developed. As conventional methods for exploring in front of the face, advanced boring, reflection seismic exploration (TSP), resistivity exploration (FDEM), etc. are known. Patent Document 1 discloses a method for exploring in front of the face, in which current electrodes are installed in a plurality of boring holes drilled in front of the face, a filler is filled in the holes, and the potential generated by the current generated from the current electrodes is measured, and the geology of the ground in front of the face is analyzed based on the resistivity distribution.

[0003] On the other hand, the applicant has developed a method for evaluating the ground in front of the face using a low-frequency ground radar as a new technology alternative to these conventional technologies. The low-frequency ground radar is a ground radar with a center frequency of 25 MHz, and includes a long transmitting antenna, a long receiving antenna, and a measuring device communicably connected to the transmitting antenna and the receiving antenna. The transmitting antenna and the receiving antenna are erected vertically, arranged in parallel at a predetermined interval, and while moving these two antennas horizontally close to the face, electromagnetic waves are transmitted from the transmitting antenna into the ground in front of the face, and the reflected waves passing through the ground in front of the face are received by the receiving antenna and measured by a measuring device. Thereby, the depth of the geological interface in the ground in front of the face can be estimated from the concentration position of the reflected waves. Since the measurement time for one cross-section of the low-frequency ground penetrating radar is as short as about 10 minutes and the exploration results can be confirmed on-site, the geological information in front of the face can be grasped quickly.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The measurement using a low-frequency ground penetrating radar has the following problems. <1> Since the length of the antenna is approximately inversely proportional to the frequency of the radar, in the case of a 25 MHz low-frequency radar, the total length of the antenna is about 4 m, and the weight is about 4 kg per antenna. The operation of erecting such a long and heavy antenna in parallel and moving it horizontally while approaching the face is highly difficult, places a large physical burden on the operator, and there is a risk that the measurement accuracy will decrease due to the antenna tilting (Fig. 7). <2> Since the operator enters the front of the face for measurement, it is necessary to spray concrete for preventing collapse on the face surface before measurement. Since it takes nearly 2 hours for the spraying work, although the measurement itself is completed in about 10 minutes, the total working time including the spraying may be prolonged, which may compress the construction cycle.

[0006] An object of the present invention is to provide a measuring jig for a low-frequency ground penetrating radar for solving the problems of the prior art as described above.

Means for Solving the Problem

[0007] The measuring jig for low-frequency ground penetrating radar of the present invention is a measuring jig for low-frequency ground penetrating radar for measuring the ground in front of the face in tunnel construction, using a low-frequency ground penetrating radar equipped with a long transmitting antenna and a long receiving antenna, and is characterized by comprising a guide rail having two rail members arranged in parallel in the height direction, and a slide unit arranged on the front surface side of the guide rail, the slide unit including two slide units slidably connected along the two rail members, and the two slide units being configured to hold the transmitting antenna and the receiving antenna in parallel.

[0008] In the measuring jig for low-frequency ground penetrating radar of the present invention, the guide rail may have a ladder-shaped structure or a frame-shaped structure formed by connecting two rail members with a plurality of connecting members.

[0009] In the measuring jig for low-frequency ground penetrating radar of the present invention, the rail member includes a rail body and a guide groove extending along the longitudinal direction of the rail body, the slide unit includes a base plate for holding the transmitting antenna or the receiving antenna, and two support blocks provided on the back surface of the base plate, each support block having a block body and a slide roller attached to the block body, and the slide roller may be slidably held in the guide groove.

[0010] In the measuring jig for low-frequency ground penetrating radar of the present invention, the guide groove extends along the back surface of the rail body, and the block body may guide the rail body from the back surface side.

[0011] The measuring jig for low-frequency ground penetrating radar of the present invention may further include a driving device provided on the slide unit for sliding the slide unit along the guide rail.

[0012] In the measuring jig for low-frequency ground penetrating radar of the present invention, the rail member may be made of an aluminum alloy.

[0013] The measuring jig for low-frequency ground penetrating radar of the present invention may have a guide rail composed of a plurality of divided units that can be divided in the longitudinal direction of the rail material.

Effect of the Invention

[0014] The measuring jig for low-frequency ground penetrating radar of the present invention has at least one of the following effects from the above configuration. <1> By holding a long antenna for low-frequency ground penetrating radar parallel on the slide rail, the face can be accurately measured. <2> Since the measurement work can be mechanically performed, labor and personnel savings in the measurement work and construction can be achieved. <3> Since it can be operated at a position away from the face, the safety of the measurement work is high. Also, since the worker does not enter the vicinity of the face, measurement can be performed immediately after the face is opened without waiting for concrete spraying. As a result, the construction cycle can be shortened.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0016] Hereinafter, the measuring jig for a low-frequency ground radar of the present invention will be described in detail with reference to the drawings. In the present invention, terms indicating directions such as "up and down", "left and right", "height", "width", "front surface", and "rear surface" refer to the respective directions in a state where an antenna is attached to the measuring jig for a low-frequency ground radar and the antennas erected in parallel are directed toward the face (that is, the face side is the front surface and the shaft mouth side is the rear surface).

Embodiment

[0017] [Measuring jig for low-frequency ground radar] <1>Overall configuration (Fig. 1) The measuring jig 1 for a low-frequency ground radar (hereinafter referred to as "measuring jig 1") is a jig for measuring the ground in front of the face using a low-frequency ground radar A. The measuring jig 1 includes at least a guide rail 10 and two slide units 20 arranged on the front surface side of the guide rail 10. In this example, it further includes a driving device 30 (not shown) installed on the slide unit 20. As the driving device 30, for example, an electric motor provided with a pinion gear can be adopted. A rack groove is provided along the guide rail 10, and the pinion gear of the driving device 30 is meshed with the rack groove (rack and pinion structure), so that the driving device 30 can slide the slide unit 20. The driving device 30 is remotely operated by a controller connected by wire or wirelessly. One feature of the measuring jig 1 is that the two slide units 20 are configured to be slidable in the horizontal direction along the guide rail 10 while holding the transmitting antenna Bs and the receiving antenna Br in parallel.

[0018] <1.1>Low-frequency ground radar (Fig. 2) The low-frequency ground radar A is a subsurface exploration device for measuring the ground in front of the face in tunnel construction. The low-frequency ground penetrating radar A includes at least a long transmitting antenna Bs, a long receiving antenna Br, and a measuring device A1 communicably connected to the transmitting antenna Bs and the receiving antenna Br (hereinafter also collectively referred to as "antenna B"). In this example, the measuring device A1 is configured as a tablet terminal and is wired-connected to the transmitting antenna Bs and the receiving antenna Br. Each antenna B includes a long antenna body B1 and a processing unit B2 provided on the back side of the antenna body B1. The processing unit B2 has the functions of a transmitter in the transmitting antenna Bs and a receiver in the receiving antenna Br.

[0019] <1.2> Low-frequency ground penetrating radar exploration Low-frequency ground penetrating radar (LGPR) exploration is a method of exploring the subsurface structure by emitting low-frequency electromagnetic waves with the radiation surface of the antenna facing the ground and measuring the reflected waves that return after being affected by voids and buried objects in the ground. Here, "low frequency" generally means electromagnetic waves with a frequency of 50 MHz or less, preferably 25 MHz or less. By adopting the 25 MHz frequency band, the exploration depth can be ensured to be approximately 15 m from the face. Also, because the wavelength is long, it becomes easier for the electromagnetic waves to penetrate into the natural ground without being interfered by the unevenness of the face surface. Compared with other exploration methods, low-frequency ground penetrating radar exploration has a relatively short exploration depth. On the other hand, it can obtain the geological distribution in the natural ground in front of the face as surface information, and the exploration accuracy is higher than that of reflection seismic exploration and resistivity exploration. Also, since the exploration results can be obtained simultaneously with the measurement, the investigation time is significantly shorter compared to advanced boring that takes more than one day for the investigation, as well as reflection seismic exploration and resistivity exploration that take more than half a day.

[0020] <2> Guide rail (Figure 3) The guide rail 10 is a member that guides the horizontal sliding of the antenna B. The guide rail 10 includes at least two rail members 11 arranged in parallel in the height direction. In this example, as the guide rail 10, a ladder-shaped structure or a frame-shaped structure formed by connecting two rail members 11 in the height direction with a plurality of connecting members 12 is adopted. The rail member 11 includes a rail body 11a and a guide groove 11b extending along the longitudinal direction of the rail body 11a. In this example, the guide groove 11b is provided along the back surface of the rail body 11a. The materials of the rail member 11 and the connecting member 12 are arbitrary, but an aluminum alloy is particularly suitable because it is lightweight and difficult to interfere with the electromagnetic waves of the antenna B. The guide rail 10 may be configured as a combination of a plurality of divided units 10a and may have a structure that can be disassembled / assembled in the longitudinal direction of the rail member 11. In this case, the length of the guide rail 10 can be extended / shortened according to the width of the face.

[0021] <3> Slide unit (Figure 4) The slide unit 20 is a member that slidably holds the antenna B on the guide rail 10. Two slide units 20 are arranged on the front side of the guide rail 10. In this example, as the slide unit 20, a unit including a base plate 21 that holds the antenna B and two support blocks 22 provided on the back surface of the base plate 21 is adopted. The base plate 21 has a length that can span the front sides of the two rail members 11, and holds the slide unit 20 on the guide rail 10 by sandwiching the two rail members 11 from above and below with the two support blocks 22 provided on the back surface of the base plate 21. The base plate 21 is fixed to the back surface of the antenna B by an appropriate method such as bolt fastening.

[0022] <3.1> Support block (Figure 4) The support block 22 is a member that guides the rail member 11. The support block 22 includes a block body 22a and a slide roller 22b provided on the block body 22a. The block body 22a has a substantially L-shaped cross section including a base portion rising from the back surface of the base plate 21 and an extending portion extending from the base portion to the back side of the rail member 11. The slide roller 22b is rotatably supported on the front side of the extending portion of the block body 22a and housed in the guide groove 11b of the rail member 11. By guiding the rail member 11 from the back side with the block body 22a, the risk of the slide roller 22b coming off the wheel due to the load of the antenna B can be reduced.

[0023] <4>Usage method (Figure 5) The measuring jig 1 is used as follows, for example. On the front side of the two slide units 20, a transmitting antenna Bs with its radiation surface standing upright facing the front and a receiving antenna Br are respectively fixed with bolts. Place the measuring jig 1 with the antenna B side facing forward and close to the face of the excavation. In this example, a guide rail 10 is fixed to the tip of the arm of the heavy machine C (drill jumbo), and the heavy machine C is advanced toward the excavation side to set the measuring jig 1 so that the guide rail 10 is parallel to the excavation face. From the above state, drive the driving device 30 with the controller to move the transmitting antenna Bs and the receiving antenna Br attached to the slide unit 20 horizontally along the excavation face. At the same time, transmit electromagnetic waves from the transmitting antenna Bs into the ground in front of the excavation face, and receive the reflected waves passing through the ground in front of the excavation face with the receiving antenna Br and measure them with the measuring device A1. Since the details of the measuring method are not the gist of this application, detailed description is omitted here. Note that the usage method of the measuring jig 1 is not limited to the above, and for example, a stable pedestal may be installed close to the excavation face, and the measuring jig 1 may be fixed to the pedestal for measurement.

[0024] [Embodiment where the guide rail is made of a facing material] In the first embodiment, a ladder-like structure in which two rail members 11 are connected by a plurality of connecting members 12 is adopted as the guide rail 10, but the structure of the guide rail is not limited to the ladder-like structure. The guide rail 10 may have a plate-like structure composed of a guide plate 13 that is long in the width direction and two rail members 11 attached to the upper and lower sides of the guide plate 13 (Fig. 6). As the guide plate 13, for example, a perforated plate made of an aluminum alloy can be adopted. In the case of this example, deformation of the guide rail 10 due to the load of the antenna B can be reduced.

Explanation of Signs

[0025] 1 Measurement jig for low-frequency ground penetrating radar (measurement jig) 10 Guide rail 10a Split unit 11 Rail member 11a Rail body 11b Guide groove 12 Connecting member 13 Guide plate 20 Slide unit 21 Base plate 22 Support block 22a Block body 22b Slide roller 30 Driving device A Low-frequency ground penetrating radar A1 Measuring device B Antenna Bs Transmitting antenna Br Receiving antenna B1 Antenna body B2 Processing unit C Heavy machine

Claims

1. A measuring jig for a low-frequency ground penetrating radar for measuring the ground in front of the face in tunnel construction, using a low-frequency ground penetrating radar equipped with a long transmitting antenna and a long receiving antenna, a guide rail having two rail members arranged in parallel in the height direction, a slide unit arranged on the front side of the guide rail, the slide unit including two slide units slidably connected along the two rail members, characterized in that the two slide units are configured to hold the transmitting antenna and the receiving antenna in parallel. A measuring jig for a low-frequency ground penetrating radar.

2. The guide rail is characterized in that it has a ladder-shaped structure or a frame-shaped structure formed by connecting the two rail members with a plurality of connecting members. The measuring jig for a low-frequency ground penetrating radar according to Claim 1.

3. The rail member includes a rail body and a guide groove extending along the longitudinal direction of the rail body, the slide unit includes a base plate for holding the transmitting antenna or the receiving antenna, and two support blocks provided on the back surface of the base plate, each support block has a block body and a slide roller attached to the block body, characterized in that the slide roller is slidably held in the guide groove. The measuring jig for a low-frequency ground penetrating radar according to Claim 1.

4. The guide groove extends along the back surface of the rail body, the block body is characterized in that it guides the rail body from the back side. The measuring jig for a low-frequency ground penetrating radar according to Claim 3.

5. A driving device provided on the slide unit, further comprising a driving device for sliding the slide unit along the guide rail. The measuring jig for a low-frequency ground penetrating radar according to any one of Claims 1 to 4.

6. The rail member is made of an aluminum alloy. The measuring jig for a low-frequency ground penetrating radar according to any one of Claims 1 to 4.

7. The guide rail is characterized in that it consists of a plurality of divided units that can be divided in the longitudinal direction of the rail member. The measuring jig for a low-frequency ground penetrating radar according to any one of Claims 1 to 4.

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