JP3130442B2 - Underground electromagnetic exploration method and apparatus in front of tunnel face - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underground electromagnetic survey method and apparatus, and more particularly, to an underground electromagnetic survey method and apparatus for obtaining a ground structure around a tunnel using a time domain electromagnetic survey technique.

[0002]

2. Description of the Related Art Conventionally, when excavating a tunnel, it is necessary to accurately grasp the conditions in front of the face and around the tunnel, etc. for safe and reliable construction. . In particular, when excavating a mountain tunnel, etc., it is necessary to accurately grasp the tunnel and surrounding conditions, especially the presence of the first layer crush zone, and to take appropriate measures to optimize construction management. Is required for

For this reason, conventionally, a boring survey has been performed at predetermined intervals from the ground surface along a tunnel excavation path,
Or, they performed surveys such as elastic wave exploration, and measured underground structures.

[0004]

However, in such a conventional method, measurement of the underground structure along the tunnel excavation path not only requires enormous time and expense, but also the ground conditions around the tunnel, especially the face face. There was a problem that the situation in front could not always be measured accurately.

For example, when excavating a mountain tunnel, a boring survey cannot always be performed, and even when a boring survey is possible, boring equipment and personnel must be transported deep in the mountain. In addition, there is a problem that the work is extremely difficult, and requires much labor and cost.

Moreover, boring is performed at predetermined intervals,
The underground structure between each sampling point can be estimated and estimated from the stratum at the sampling point. Therefore, there is a problem that, for example, when a crush zone or the like partially exists between the sampling points, it cannot be detected.

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an underground electromagnetic exploration method and apparatus capable of easily and accurately measuring a ground structure around a tunnel. is there.

[0008]

In order to achieve the above object, a method of the present invention comprises a current source for generating smoke ring installed on the ground surface side and a measuring point in a tunnel.
An electromagnetic wave receiving unit installed in the bets, the resistivity distribution in the tunnel face forward with a method of electromagnetic exploration energized transmission current to the smoke ring generator current source, by blocking the transmission current to generate a smoke ring phenomenon that eddy currents propagates the natural ground, the detected underground electromagnetic exploration time storage area attenuation of the eddy currents as a change in the time function of the electromagnetic field with the electromagnetic waves receiver, Inside the tunnel
And measuring the specific resistance distribution of the ground in front of the tunnel face based on the data detected at each measurement point.

Further, the apparatus according to the present invention comprises a current source for generating smoke ring installed on the ground surface side and a current source in a tunnel.
An electromagnetic wave receiving unit installed at a point , energizing means for applying a transmission current to the current source for smoke ring generation, and attenuation of an underground eddy current caused by a smoke ring phenomenon that occurs when the transmission of the transmission current is interrupted, With face in tunnel
For each nearby measurement point, an underground that detects the change in the time function of the electromagnetic field from the output of the electromagnetic wave receiving unit and calculates the resistivity distribution of the ground in front of the tunnel face based on the change in the time function of the obtained electromagnetic field And an underground structure in front of the tunnel face based on the resistivity distribution. With such a configuration,
Passing a transmission current through the smoke ring generation current source,
If this is subsequently cut off, an eddy current propagates underground, causing a smoke ringing phenomenon. This eddy current attenuation
The change is detected as a change in the time function of the magnetic field using the electromagnetic wave receiving unit. Such a detection operation, intends row for each measurement point.

[0010]

In this manner, the geological structure in front of the tunnel face can be accurately grasped by accurately determining the specific resistance structure of the ground around the tunnel.

In particular, by installing the electromagnetic wave receiving unit near the face of the tunnel and obtaining the detection data, the ground structure in front of the face can be accurately grasped.

In this case, the current for generating smoke ring is installed on the ground surface side, and the electromagnetic wave receiving unit is connected to a tunnel.
More it is located Le the side, the electromagnetic wave receiving unit, DOO
It can be easily moved and installed in the channel, and the data at each measurement point can be easily measured.

It is preferable that a transmission loop is used as the current source for generating smoke ring, and a reception loop is used as the electromagnetic wave receiving section.

Thus, the smoke ring phenomenon can be generated with a simple structure, and the detection data can be measured at each measurement point. In particular, with such a configuration, the transmission loop and the reception loop can be easily moved, and data measurement at each measurement point can be easily performed.

The above-mentioned transmission loop and reception loop can be used as the current source for generating the smoke ring and the electromagnetic wave reception unit. However, other current sources and reception units, for example, a line antenna using a ground electrode can be used. May be used as necessary.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the drawings.

FIGS. 4 and 5 show a preferred embodiment of the time domain underground electromagnetic survey according to the present invention.

The apparatus of the embodiment includes a transmission loop 10 and a reception loop 20.

The transmission loop 10 functions as a current source for generating smoke ring, and is configured to be installed at an arbitrary position on the ground surface side. In the example,
It is formed in a loop shape of 100 m in length and 100 to 200 m in width. The transmission current is supplied from the transmission energizing device 30 to the transmission loop 10.

The receiving loop 20 functions as an electromagnetic wave receiving unit, and is configured to be installed in the tunnel 200 premises. The receiving loop 20 is formed to have a small diameter of, for example, about 40 to 50 cm so that the receiving loop 20 can be freely moved and installed in the tunnel 200, and the output thereof is input to the receiving device 50.

When an underground electromagnetic survey around a tunnel is performed by using this device, the installation position of the transmission loop 10 on the ground surface side and the tunnel premises 2
The survey line 300 at 00 is set in advance. Further, a plurality of measurement points P1, P2,... Where the receiving loop 20 is set are set on the survey line 300 in advance. Then, the measurement used in the transmission loop 10 and the reception loop 20 is repeated for each measurement point, and the measurement data is stored in the memory 58 in the reception device 50.

Based on the measurement data obtained at each measurement point, the underground resistivity distribution around the tunnel is calculated, and the underground structure around the tunnel is obtained based on the obtained resistivity distribution.

FIGS. 1 to 3 schematically show the principle of the time domain search method.

At the time of measurement, first, as shown in FIGS. 4 and 5, the transmission loop 10 is installed on the ground surface side so as to be located above the tunnel 200 or the tunnel excavation path 210, and a predetermined measurement in the premises of the tunnel 200 is performed. Point P
The receiving loop 20 is set in the. And the transmission loop 10
, A transmission current is supplied, and this transmission current is rapidly cut off as shown in FIG. As a result, as shown in FIG. 3B, an electromotive force for maintaining the same magnetic field as before the interruption is generated by the law of electromagnetic induction, and an eddy current is generated on the ground surface.
This eddy current is attenuated according to the specific resistance of the ground, but a new eddy current is generated in the ground to prevent the change of the current. This process is repeated, as if the eddy current was 100
However, a phenomenon that propagates from the ground surface to the deep part of the stratum occurs,
This phenomenon is called a smoke ring phenomenon.

FIGS. 2A to 2D show the current density distribution underground at this time in time series. It can be seen that the portion showing the maximum value of the current density permeates deep underground with time.

These eddy currents are attenuated according to the specific resistance of the formation in the propagation path. For this reason, the decay of the eddy current is detected as a change in the time function of the magnetic field as shown in FIG. 6C, using the receiving loop 20 installed in the tunnel yard corresponding to the search position, as shown in FIG. You can know the distribution. For example, when the underground has a high resistivity, the eddy current attenuates rapidly, but when the resistivity is low, it attenuates slowly.

Therefore, the reception loop 20 is moved one after another according to the measurement points of the tunnel premises 200, and the reception data obtained thereby is analyzed.
The specific resistance distribution of the ground around the tunnel 200 can be obtained, and the ground structure can be known based on this specific resistance distribution.

FIG. 6 shows a specific configuration of the transmitting energizing device 30 and the receiving device 50.

The transmission energizing device 30 includes a clock 32
And a transmission current supply unit 34 and a transmission control unit 36.

The transmission current supply section 34 is formed so as to supply the transmission current shown in FIG. 3A in accordance with a command from the transmission control section 36.

The receiving device 50 has a clock 52
, An amplifier 62, an A / D converter 54, and a CPU 56
, A memory 58, and an input / output unit 60. Then, the output of the receiving loop 20 is amplified by the amplifier 62, and is then converted from analog to digital by the A / D converter 54 and input to the CPU 56. The CPU 56
Based on a command from the input / output unit 60, data from the A / D converter 54 is stored in the memory 58.

The transmitting energizing device 30 and the receiving device 50 are configured to operate while being synchronized with each other by clocks 32 and 52. Specifically, since the energizing device 30 and the receiving device 50 are formed separately, the clocks 32 and 52 are adjusted so as to be completely synchronized before the start of measurement. As a result, even if the two devices 32 and 52 are completely separated from each other, the two devices will operate in perfect synchronization with each other.

FIG. 7 shows a flowchart of a procedure for performing measurement while moving and installing the receiving loop 20 at each of the measurement points P1, P2... In the tunnel premises.

First, the receiving loop 20 is set at the first measurement point P1 (step S1).

Next, to the transmission loop 10 on the ground surface side, FIG.
The transmission current shown in (A) is supplied, and the current is rapidly cut off (step S2).

When the transmission current is cut off, as shown in FIGS. 1 and 2, a smoke ringing phenomenon in which an eddy current propagates underground occurs. At this time, the attenuation of the eddy current is detected as shown in FIG. 3C as a change in the time function of the electromagnetic wave using the reception loop 20 installed at the measurement point P1.
This detection data is output from the amplifier 54 and converted into a digital signal by the A / D converter 54,
Is written and stored in the memory 58.

A series of search steps including steps S1, S2, and S3 are repeated for all the measurement points P1, P2,... Shown in FIGS.

When the measurement at all the measurement points is completed (step S4), the CPU 56 functions as underground structure calculation means, and based on the measurement data at each measurement point stored in the memory 58, the ground level is calculated. Is calculated to create, for example, an underground structure model shown in FIG. 5 (step S5).

In particular, in the time domain underground electromagnetic survey method as in the embodiment, the underground structure model is estimated and calculated from the measurement data at each measurement point by using the least squares inversion and other methods. Such calculation prescriptions are well known and do not differ from technology.

In this manner, the structural model of the underground can be accurately obtained, and in particular, the ground structure around the tunnel 200, for example, the shatter zone 220 existing on the planned tunnel excavation route 210 can be accurately detected. can do. Experimental Data Using the measuring device of the example, the inventor conducted an experiment for exploring the front face of the face and grasping the state of the mountain, with the already-excavated mountain tunnel being measured.

FIG. 8 schematically shows the ground structure around the tunnel in which the experiment was performed.

Here, FIG. 1A is a schematic plan view thereof, and FIG. 1B is a schematic sectional view thereof.
In FIG. 8B, the vertical axis (Z axis) represents the altitude, and the horizontal axis represents the distance from the tunnel entrance on the horizontal plane as X and Y.
Expressed as an axis component. In order to measure the underground structure around the actual tunnel 200, the position indicated by A on the ground surface and the position B
The experiment was performed by moving the transmission antenna 10 to the position indicated by.

FIGS. 9A, 9B and 9C show data obtained by measuring the transient phenomenon of the magnetic field after the DC current interruption of the transmitting antenna 10A using the receiving antenna 20 installed in the tunnel premises 200. FIG. It is. Here, FIGS. 7A, 7B, and 7C show measurement data of X, Y, and Z components in the tunnel premises at this time.

Similarly, FIGS. 10 (A), (B), (C)
Are measurement data similarly performed using the transmitting antenna 10B.

From the above experimental results, when the time domain measurement method of the present invention is used, a decrease in the eddy current diffusion speed near the low resistivity band around the tunnel is measured, and as a result, the ground around the tunnel is measured. The effectiveness of applying the present invention to mountain and face frontal exploration was confirmed.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention.

For example, in the above-mentioned embodiment, the case where the ground structure near the tunnel face is measured has been described as an example. It is also very suitable for measuring the ground around the tunnel.

In the above-described embodiment, the case where the transmission loop is used as the current source for generating the smoke ring and the reception loop is used as the electromagnetic wave receiving section has been described as an example. However, the present invention is not limited to this. For example, a linear transmission source may be used as a current source for generating smoke ring. In this case, ground both ends of the linear transmission source to the ground,
A transmission current supply source may be provided on the way. Even if a transmission source having such a configuration is used, if the transmission current is interrupted, a smoke ring phenomenon can be generated.

Similarly, as the electromagnetic wave receiving section , for example, a linear receiving section having both ends grounded to the ground may be used to detect the eddy current attenuation as a current change.

[0051]

[0052]

As described above, according to the present invention,
A smoke ring generator current source to the ground surface side and the tunnel, by placing the electromagnetic wave receiving unit, underground structures, tunnel face in front of the underground, in particular can be measured tunnel face in front of the natural ground structure easily and reliably There is an effect that an electromagnetic exploration method and apparatus can be obtained.

[0053] In particular, established a smoke ring generator current source on the ground surface side, by placing the electromagnetic wave receiving unit to the tunnel interior, the movement of the measurement points can be carried out in tunnel side, for example the surrounding mountain tunnel When measuring the ground structure, you are freed from the task of measuring while moving the electromagnetic wave receiving unit for each measurement point set in a steep mountain, and measuring the ground structure in front of the tunnel face. This can be performed easily and reliably.

[0054]

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of the principle of smoke ring generation.

FIGS. 2A to 2D are explanatory views showing a state in which an eddy current spreads over the ground with the passage of time.

FIG. 3 is a timing chart in the case of performing electromagnetic exploration in the time domain.

FIG. 4 is an explanatory diagram showing an example of an underground electromagnetic survey device of the embodiment.

FIG. 5 is a schematic explanatory diagram in the case of measuring a ground structure around a tunnel using the underground electromagnetic survey technique of the present invention.

FIG. 6 is a block diagram showing a preferred example of the underground electromagnetic survey device of the present embodiment.

FIG. 7 is a flowchart of an underground electromagnetic survey method according to the embodiment.

FIG. 8 is an explanatory diagram of an experiment performed using the apparatus of the example.

FIG. 9 is an explanatory diagram of data obtained by the experiment described above.

FIG. 10 is an explanatory diagram of data obtained by the experiment described above.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 transmission loop 20 reception loop 30 transmission energizing device 50 reception device 56 CPU 58 memory 200 tunnel

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiaki Hara 1-7-1 Kyobashi, Chuo-ku, Tokyo Toda Construction Co., Ltd. (72) Inventor Hidehiro Ishikawa 1-23-1 Oi, Shinagawa-ku, Tokyo Mitsui Kinzoku (72) Inventor Kazunari Wada 1-23-1 Oi, Shinagawa-ku, Tokyo Mitsui Metal Resources Development Co., Ltd. (72) Inventor Akira Saito 1-23-1 Oi, Shinagawa-ku, Tokyo Mitsui Inside Metal Resources Development Co., Ltd. (72) Inventor Shun Oya 1-23-1 Oi, Shinagawa-ku, Tokyo Mitsui Metal Resources Development Co., Ltd. (56) References "Illustration Geophysical Exploration" Geophysical Exploration Society, June 1998 Issued daily, pages 65, 75, 78 (58) Fields investigated (Int. Cl. ⁷ , DB name) G01V 3/02 G01N 27/72 G01V 3/10

Claims (4)

(57) [Claims] A method for electromagnetically exploring a resistivity distribution in front of a tunnel face using a current source for generating smoke ring installed on the ground surface side and an electromagnetic wave receiving unit installed at a measurement point in a tunnel. Passing a transmission current through the smoke ring generation current source;
By blocking the transmission current, natural ground to generate a smoke ring phenomenon that eddy currents propagates to be detected and stored attenuation of the eddy currents as a change in the time function of the electromagnetic field with the electromagnetic waves receiver the underground electromagnetic exploration in the time domain, theft
Performed at each measurement point near the face in the tunnel, and based on the detection data at each measurement point, before the tunnel face
Tons characterized by calculating the resistivity distribution of the natural ground of the square
Underground electromagnetic survey method in front of flannel face . 2. The method of claim 1, as a current source for the smoke ring generator, using a transmission loop, wherein the electromagnetic wave receiving unit, tunnel face in front of the underground electromagnetic exploration method characterized by using the receiving loop. 3. A current source for generating smoke ring installed on the ground surface side, an electromagnetic wave receiving unit installed at a measurement point in a tunnel, and an energizing means for applying a transmission current to the current source for generating smoke ring. , the attenuation of the eddy currents underground due to the smoke ring phenomenon occurring during energization of interruption of the transmission current, the working face of the tunnel
At each measurement point in the vicinity, an underground that detects the change in the time function of the electromagnetic field from the output of the electromagnetic wave receiving unit and calculates the resistivity distribution of the ground in front of the tunnel face based on the change in the time function of the obtained electromagnetic field It includes a structure calculating means, and the resistivity distribution tunnel face in front of the earth <br/> under electromagnetic survey apparatus and obtains the tunnel face in front of the earth <br/> under construction on the basis of. 4. The underground electromagnetic survey device in front of a tunnel face according to claim 3, wherein a transmission loop is used as the current source for generating smoke ring, and a reception loop is used as each of the electromagnetic wave receiving units.