JP3236478B2 - Underground electromagnetic probe - 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 exploration apparatus, and more particularly to an underground electromagnetic exploration apparatus for determining the structure of a ground or an underground using a frequency domain electromagnetic exploration method.

[0002]

2. Description of the Related Art Conventionally, when excavating a tunnel, it is necessary to accurately grasp the ground conditions in front of the face and around the tunnel for safe and reliable tunnel construction. .

In addition, due to environmental measures, it is necessary to accurately grasp underground pollution conditions, for example, metal pollution, around factories and in other desired environmental pollution control areas.

[0004]

However, with the conventional measurement techniques, there has been no method that allows the user to easily and reliably measure the contamination state in front of the face or underground.

The present invention has been made in view of such a conventional problem, and its object is to provide, for example, a mountain structure around a tunnel, an underground structure in a desired measurement area, and the like.
An object of the present invention is to provide an underground electromagnetic exploration device that can easily and reliably measure.

[0006]

According to the first aspect of the present invention, there is provided a sensor unit which is in contact with a measurement surface;
A control circuit unit connected to the sensor unit, wherein the sensor unit includes a detection loop, a first transmission loop located outside the detection loop, and a second transmission loop located outside the first transmission loop. Wherein the control circuit section supplies an exciting current in a direction opposite to the first and second transmission loops so as to cancel a magnetic field at the detection loop position in a predetermined calibration environment. A current control unit, and a detection unit that detects and measures current data detected from the detection loop, and uses a frequency-domain electromagnetic exploration method from the detected current data to determine whether the sensor unit is in contact with the ground or underground. Is characterized by measuring the resistivity distribution of the sample.

According to a second aspect of the present invention, in the first aspect, the sensor section includes the detection loop and the first and second detection loops.
Of the transmission loop is integrally attached to the housing and fixed.
It is characterized in that a measurer is formed so as to be detachably contactable with the measurement surface.

According to a third aspect of the present invention, in the second aspect, the sensor section includes the detection loop and first and second detection loops.
In the order of the transmission loops.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the control circuit unit outputs to the current control unit an energization command for exciting currents having different frequencies. The current control unit, when an exciting current of a designated frequency is applied to the first and second transmission loops in opposite directions, the magnetic field at the detection loop position in the predetermined calibration environment is canceled. In this manner, the value of the exciting current supplied to each transmission pool is set.

[0010] The invention according to claim 5 includes a sensor unit abutting on a measurement surface, and a control circuit unit connected to the sensor unit, wherein the sensor unit includes a transmission loop and the transmission loop. A control circuit unit including a first reception loop positioned outside a loop and a second reception loop positioned outside the first reception loop, wherein the control circuit unit supplies an excitation current to the transmission loop; An output combining unit that combines currents output from the first and second receiving loops such that current values output from the first and second receiving loops cancel each other in a predetermined calibration environment; and A detection unit for detecting and measuring current data output from the unit, and measuring a specific resistance distribution in the ground or underground at the sensor unit abutting position using an electromagnetic exploration method in the frequency domain from the detected current data. Features That.

According to a sixth aspect of the present invention, in the fifth aspect, the sensor unit includes the transmission loop and the first and second transmission loops.
The receiver loop is attached to the housing and fixed.
It is characterized in that a measurer is formed so as to be detachably contactable with the measurement surface.

According to a seventh aspect of the present invention, in the sixth aspect, the sensor section is formed to have a larger diameter in the order of the transmission loop, the first, and the second reception loop.

According to an eighth aspect of the present invention, in any one of the fifth to seventh aspects, the control circuit unit outputs to the current control unit an energization command for exciting currents having different frequencies. The current control unit is formed so as to supply an exciting current of a designated frequency to the transmission loop, and the output synthesizing unit corresponds to the exciting current of each frequency, and in the predetermined calibration environment, The combination ratio is variably controlled so that the combined outputs of the first and second reception loops are offset.

Next, the operation of the present invention will be described in order from the invention of claim 1 to the invention of claim 4. Note that the invention of claim 5 is the one in which the transmission loop and the reception loop are interchanged from the viewpoint of the mathematical reciprocity theorem, and both are theoretically the same. Therefore, the description of the invention of claim 5 and the inventions dependent thereon are omitted here.

According to the first aspect of the present invention, first, prior to the measurement,
The values of the exciting currents of the first and second transmission loops are determined so that the magnetic field at the position of the detection loop is canceled in a predetermined calibration environment. That is, within a given calibration environment,
An exciting current is applied to the first and second transmission loops in opposite directions, and the value of the exciting current applied to each transmission loop is set so that the magnetic field does not change at the detection loop position.

Next, the sensor unit thus calibrated is brought into contact with a desired measurement surface.

FIG. 1 schematically shows the state at this time. The sensor unit that has been calibrated as described above is
Upon contact with a desired measurement surface, a cancel region 110 having a desired depth and having no change in the magnetic field is generated in front of the detection coil. In addition, at this time, since the detection coil is not affected by the magnetic field from each transmission loop, it is possible to accurately detect a change in the magnetic field in the measurement area 120 in front of the cancel area.

That is, when the sensor section of the present invention is brought into contact with the measurement surface and an excitation current is applied to the first and second transmission loops, the measurement area 12
Zero is generated from the magnetic field. Due to the change in the magnetic field, eddy currents 200 having predetermined values are generated in various places in the measurement area 120 according to the specific resistance of the substance existing in the area.

Therefore, using the detection coil, the measurement area 12
By measuring the generation position and magnitude of this eddy current 200 within zero, the underground structure in the measurement region 120 can be measured as a resistivity distribution.

Such a method for measuring the resistivity distribution has already been established as an underground electromagnetic sounding method in the frequency domain, and a description thereof will be omitted.

A feature of the present invention is that, when conducting an underground electromagnetic survey in such a frequency region, as described above, a cancel region 110 in which the magnetic field does not change is generated in front of the sensor unit, particularly in front of the detection coil. That is.

By adopting such a configuration, for example, even when the sensor portion abuts on a place having an uneven portion such as the ground in a tunnel, the sensor portion is not affected by the unevenness and the underground of the ground is not affected. The structure can be measured accurately.

When the sensor unit of the present invention is brought into contact with the ground or the like in order to measure a change in specific resistance due to, for example, metal contamination of the underground, obstacles on the ground surface, such as grass and pebbles, The underground soil structure can be accurately measured as a resistivity distribution without being affected by irregularities on the ground surface.If the underground contains contaminants such as mercury, Can be measured accurately.

As described above, according to the present invention, when the sensor section is brought into contact with the measurement surface, the measurement portion located at the back of the measurement surface is not affected by irregularities or obstacles near the measurement surface. The ground structure of the region can be accurately measured as a resistivity distribution.

Further, according to the second aspect of the present invention, since the sensor section has an integral structure, a measurer can easily install the sensor section on an arbitrary measurement surface. That is, according to the present invention, since the sensor unit is formed to be portable and freely formed to abut on an arbitrary measurement surface, the measurement can be performed easily as compared with a case where a large measuring device is used. .

In particular, by configuring the sensor section as in the third aspect of the invention, the configuration of the sensor section can be made extremely simple and high-performance.

According to the fourth aspect of the present invention, the exploration depth of the sensor unit can be arbitrarily switched by changing the frequency of the exciting current supplied to the transmission loop. Therefore, it is possible to accurately measure the measurement area in contact with the sensor section from a relatively shallow area to a deep area.

[0028]

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

FIG. 5 shows a preferred example of an underground electromagnetic exploration apparatus according to the present invention. The underground electromagnetic survey device according to the embodiment includes a sensor unit 30 and a control circuit unit 40, and a user 200 operates the sensor unit 30 and the control circuit unit 4.
0 is formed so as to be portable to an arbitrary place.

The embodiment of FIG. 5 specifically shows a case in which a user 200 conducts a forward exploration of a face 100 of a mountain tunnel using the apparatus of the embodiment.

Here, the user 200 operates the sensor unit 3
0, when it comes into contact with an arbitrary position of the face 100, the first and second transmission loops 10 and 12 and the detection loop 20, which will be described later, provided in the sensor unit 30, and the sensor unit 30
Can be accurately measured by using an electromagnetic sounding method in the frequency domain.

In particular, a feature of the present embodiment is that a cancel region 110 in which the magnetic field does not change is generated in front of the sensor unit 30, and a measurement region 120 is provided behind the cancel region 110.
In the configuration. Accordingly, even when the sensor unit 30 is installed on a measurement surface having irregularities such as the ground 100, the ground structure in the measurement area 120 is not affected by the irregularities near the surface of the measurement surface and the obstacle. Can be accurately measured as a specific resistance distribution.

The control circuit section 40 may be integrally formed in the sensor section 30 if necessary.

Hereinafter, a specific configuration of the present invention will be described in detail.

FIG. 1 schematically shows the principle of the present invention. FIG. 2 shows the structure of the sensor unit 30 and the control circuit unit 4.
0 is shown.

In the sensor section 30 of the embodiment, the small-diameter detection loop 20 and the first transmission loop 10 and the second transmission loop 12 located outside the detection loop 20 are arranged substantially concentrically. , 12 are integrally fixed to a housing (not shown). Here, the second
The transmission loop 12 is formed slightly larger in diameter than the first transmission loop 10.

The diameter of each of the loops 20, 10, and 12 can be set to any size as needed. In the present embodiment, the first section is taken into consideration in consideration of the portability of the sensor section 30. The diameter of the transmission loop 10 is formed to be 0.7 m, and the diameter of the second transmission loop 12 is formed to be about 1 m.

The control circuit section 40 includes a current control section 42, a search depth switching section 44, and a detection section 46.

The search depth switching unit 44 controls the current control unit 42 for each of the transmission loops 10 according to the search depth.
12 is output at three different frequencies f1, f2, f3.

The current control unit 42, as shown in FIG.
An exciting current of a designated frequency is formed so as to flow through the first and second transmission loops 10 and 12 in opposite directions. At this time, the first and second transmission loops 10, 1
The values of the excitation currents I ₁₀ and I ₁₂ applied to 2 are set such that the magnetic field at the position of the detection loop 20 becomes 0 in a predetermined calibration environment (in the present embodiment, in the air).

That is, when the frequency of the exciting current is set to f1, the detection loop 20 is set at the frequency of f1.
Each excitation current I ₁₀ , I
Set the value of ₁₂ . Similarly, when the frequencies f2 and f3 are specified, the values of the respective excitation currents are set so that the change in the magnetic field at the position of the detection loop 20 becomes 0 when each transmission loop is driven at the frequency.

In this manner, when the sensor unit 30 that has been calibrated is brought into contact with the surface of the face 100 to be measured as shown in FIGS.
In particular, in front of the detection loop 20, there is a zero cancellation region 110 where the magnetic field hardly changes.

The depth d1 of the cancel area 110 is
It can be set to any value depending on the size, shape, etc. of the transmission loops 10, 12. Since the specific calculation formula is extremely complicated, its description is omitted here. However, as in the embodiment, each loop 10 and 12 has a diameter of 0.7.
m, about 1 m, the cancellation area 11
The depth d1 of 0 is about 10 to 20 cm.

Then, the sensor unit 30 of the embodiment can measure the ground structure of the deep area of the cancel area 110 as a measurement area 120. That is,
When exciting currents I ₁₀ and I ₁₂ are applied to the transmission loops 10 and 12 to change the magnetic field in the measurement area 120,
Due to the change in the magnetic field, an electromagnetic response is generated in the measurement region 120 due to the underground structure. By detecting this electromagnetic response using the detection loop 20 and breaking it using a frequency domain method that treats this electromagnetic response as a function of frequency, the underground structure in the measurement area 120 can be measured as a resistance distribution. it can.

That is, the electromagnetic survey method as in the embodiment is
It is extremely sensitive to a change in the specific resistance in the measurement region 120, and the distribution of the specific resistance in the measurement region 120 is analyzed using a frequency domain method. For example,
When an alternating current having a predetermined frequency f1 is applied to the transmission loops 10 and 12 as the excitation current as in the present embodiment, a primary magnetic field is generated in the measurement region 120 by the application of the excitation current. This primary magnetic field fluctuates at the same angular frequency as the exciting current and produces an electromotive force according to Faraday's law, which is proportional to the time change of the exciting current. This electromotive force generates a secondary current according to Ohm's law in an underground structure having a conductivity σ. This secondary current is a phase-separated component whose phase is shifted by 90 degrees from the current of the transmission loop, is proportional to the conductivity σ of the underground structure as described above, and is the same as the current flowing in the transmission loop. Secondary magnetic field).

As described above, the sensor unit 30 of this embodiment is
Then, since the detection loop 20 can detect the secondary magnetic field from the measurement region 120 without being affected by the primary magnetic field from the transmission loops 10 and 20, the underground structure of the measurement region 120 can be accurately detected as a resistivity distribution. Can be measured.

[0047] In this case, the detection current I ₂₀ of the detection loop 20 is detected by the detection unit 46 of the control circuit section 40,
It is stored in a memory (not shown). Then, by analyzing the stored detected current data using a well-known underground electromagnetic survey method in the frequency domain, the specific resistance distribution of the measurement area 120 can be accurately obtained.

Further, in the measuring apparatus of this embodiment, the frequency of the exciting current is changed to f1, f2, f
It is configured to be able to switch to three stages of three. In this case, the frequency is set so that its value becomes higher in the order of f1, f2, and f3.
The exploration depth is also 120- in the order of frequencies f1, f2, f3.
As shown by 1, 120-2 and 120-3, the depth gradually increases.

As described above, according to the present embodiment, by changing the frequency of the exciting current supplied to the transmission loop, the exploration depth can be appropriately changed, and the measurement can be performed from a shallow region to a deep region. Becomes

In the embodiment shown in the figure, the detection data is temporarily stored in the memory in the detection section 46, and then the underground structure of the measurement area 120 is analyzed using the electromagnetic exploration technique in the frequency domain. The invention is not limited to this, and the control circuit unit 40
However, the price may be high, but the underground structure of the measurement area 120 may be analyzed in real time using a computer or the like.

The time change of the secondary magnetic field further creates an electric field and a magnetic field in phase with the higher-order transmission current, which is proportional to the square of the electrical conductivity σ of the underground structure. Since the in-phase magnetic field is measured, the resistivity distribution of the underground structure can be obtained more accurately.

FIG. 4 shows computer numerical analysis data of the underground electromagnetic survey device of this embodiment. In the figure, the horizontal axis represents the search depth Z, and the vertical axis represents the magnitude of the magnetic field.

In the same figure, φ ₁₀ represents the magnetic field of the first transmission loop ₁₀ having a diameter of 0.7 m, φ ₁₂ represents the magnetic field of the second transmission loop 12 having a diameter of 1.0 m, and φ represents the excitation. It shows the combined magnetic field of the sensor 30 of the present embodiment in which the currents I ₁₀ and I ₁₂ flow in opposite directions so that the two magnetic fields cancel each other. The transmission loop 10 and 12, when energized one by one, respectively, the surface (Z = 0 m) in a magnetic field H _Z is maximized, but a large current flows in the vicinity of the surface, two transmission loop as in this embodiment When the excitation is performed so that the magnetic fields cancel each other at 10 and 12, the magnetic field near the ground surface becomes 0, and the depth Z =
It was confirmed that the value of the magnetic field became maximum around 0.7 m, and the detection data reflected the specific resistance in the vicinity best. Therefore, it is understood that the use of the sensor unit 30 of this embodiment makes it possible to accurately measure the specific resistance distribution of the measurement region 120 without being affected by cracks near the ground surface, irregularities, plants, and the like. You.

Further, when the underground electromagnetic sounding method in the frequency domain is used as in the present embodiment, as is clear from the reciprocity theorem of mathematics, even if the relation between the transmission loop and the reception loop is exchanged, the same applies. Measurement can be performed.

FIG. 6 shows an example of the sensor unit 30 in which the transmission loop and the reception loop are set in the opposite relation to the embodiment shown in FIG. The members corresponding to those of the above embodiment are denoted by the same reference numerals, and the description thereof is omitted.

The sensor section 30 of this embodiment includes a small-diameter transmission loop 10 located at the center and first and second reception loops 20 and 22 arranged concentrically outside the transmission loop 10. It is integrally fixed to a housing (not shown).

The transmission loop 10 includes a current control unit 42
From the excitation current I ₁₀ is energized energized in the same manner as in Example.

Further, the first and second receiving loops 20,
22 have a diameter of 0.7 m and a diameter of 10 m, respectively.

The first and second receiving loops 2
The outputs of 0 and 22 are combined using an output combining unit 48 such that their values cancel each other out in a predetermined calibration environment, and the combined output is output to the detecting unit 46.

In the embodiment shown in FIG. 6, the excitation current I _{10 is} applied to the transmission coil 10 in a specific calibration environment (in air).
When the current is supplied, the output synthesis is performed so that the synthesized value of the currents I ₂₀ and I ₂₂ for detecting the respective detection loops 20 and ₂₂ becomes zero.

By doing so, when the sensor unit 30 is brought into contact with a predetermined measurement surface and an exciting current is applied,
From the output synthesizing unit 48, a detection current corresponding to the specific resistance distribution of the measurement area 120 can be obtained.

In the embodiment shown in FIG. 6, the output synthesizing unit 48 is configured to cancel the output by connecting the respective receiving loops 20 and 22 in the reverse direction. Not limited to this, for example, the output combining section 48 may be formed as shown in FIG.

That is, the output synthesizing section 48 of the embodiment shown in FIG. 7 includes first and second amplifiers 50 and 52 and a subtractor 54 for subtracting the output of each amplifier. Each of the amplifiers 50 and 52 includes a first and a second detection loops 20, 2
The two detected currents I ₂₀ and I ₂₂ are amplified with desired gains K 1 and K 2, and the amplified outputs are output to the subtractor 54.

The subtractor 54 outputs the output of each of these amplifiers,
The difference operation is performed, and the operation value I _out is output to the detection unit 46.

Here, the causes K1 and K2 of the amplifiers 50 and 52 are caused by the output I _{out of the} subtractor 54 when an exciting current is applied to the transmission loop in a predetermined calibration environment (in air).
Is set to be 0.

The gains 1 and K2 are appropriately switched and set according to the values of the frequencies f1, f2 and f3 of the exciting current to be used, as in the above embodiment. That is, when the respective frequencies f1, f2, and f3 are used, their values are set so that the combined outputs of the first and second reception loops in the predetermined calibration environment are completely canceled for each used frequency. Is set.

In this way, even when the frequency of the exciting current is switched and the search vibration of the measurement area 120 is changed, the respective measurement areas 120-1, 120-2, 120-2,.
It is possible to accurately measure the resistivity distribution of 120-3.

[0068]

As described above, according to the present invention,
It is possible to easily and reliably measure the specific resistance distribution in the ground or underground at the sensor part contact position by using the electromagnetic exploration method in the frequency domain.

[0069]

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of an underground electromagnetic survey device according to an embodiment.

FIG. 2 is a schematic explanatory view of an underground electromagnetic survey device according to the embodiment.

FIG. 3 is a schematic explanatory diagram of a magnetic field generated in a sensor unit.

FIG. 4 is an explanatory diagram of theoretical analysis data of the apparatus of the embodiment.

FIG. 5 is an explanatory diagram of a state of use of the electromagnetic surveying and measuring apparatus of the embodiment.

FIG. 6 is a schematic explanatory view of another embodiment of the present invention.

FIG. 7 is an explanatory view of a modification of the embodiment shown in FIG. 6;

[Explanation of symbols]

 Reference Signs List 10 First transmission loop 12 Second transmission loop 20 Receiving loop 22 Second receiving loop 30 Sensor unit 40 Control circuit unit 42 Current control unit 44 Exploration depth switching unit 46 Detection unit 48 Output synthesis unit 110 Cancel area 120 Measurement area

Continuing on the front page (72) Inventor Toshiaki Hara 1-7-1 Kyobashi, Chuo-ku, Tokyo Toda Construction Co., Ltd. (72) Inventor Akira Saito 1-23-1, Oi, Shinagawa-ku, Tokyo Mitsui Mining & Smelting Resources In-company (72) Inventor Kazunari Wada 1-23-1 Oi, Shinagawa-ku, Tokyo Mitsui Metal Resources Development Co., Ltd. (56) References JP-A-7-110382 (JP, A) JP-A-4-233490 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01V 3/06

Claims (8)

(57) [Claims] 1. A sensor unit that is in contact with a measurement surface; and a control circuit unit that is connected to the sensor unit. The sensor unit includes: a detection loop; A transmission loop, and a second transmission loop located outside the first transmission loop, wherein the control circuit unit is arranged in a direction opposite to the first and second transmission loops and within a predetermined calibration environment. A current control unit that supplies an exciting current such that a magnetic field at the detection loop position is canceled; anda detection unit that detects and measures current data detected from the detection loop, and includes a frequency domain from the detected current data. An underground electromagnetic exploration apparatus characterized in that a specific resistance distribution in the ground or underground at the sensor portion contact position is measured using the electromagnetic exploration method of (1). 2. The sensor section according to claim 1, wherein the sensor section integrally fixes and fixes the detection loop and the first and second transmission loops to a housing, and allows a measurer to detachably contact the measurement surface. An underground electromagnetic exploration device characterized by being formed in. 3. The sensor unit according to claim 2, wherein the sensor unit comprises: a detection loop, a first transmission loop, and a second transmission loop.
An underground electromagnetic exploration device characterized by having a large diameter. 4. The current control unit according to claim 1, wherein the control circuit unit includes a search depth switching unit that outputs an energization command for exciting currents having different frequencies to the current control unit. When the exciting current of the designated frequency is applied to the first and second transmission loops in the opposite directions, the current is applied to each of the transmission pools so that the magnetic field at the detection loop position is offset in the predetermined calibration environment. An underground electromagnetic exploration apparatus formed to set a value of an exciting current to be applied. 5. A sensor unit abutting on a measurement surface, and a control circuit unit connected to the sensor unit, wherein the sensor unit includes: a transmission loop; 1 control loop comprising: a first receiving loop; and a second receiving loop positioned outside the first receiving loop. The control circuit unit includes: a current control unit configured to supply an exciting current to the transmission loop; An output combining unit that combines currents output from the first and second receiving loops so that current values output from the first and second receiving loops cancel each other; and current data output from the output combining unit. And a detection unit for detecting and measuring the transmission loop , wherein the sensor unit integrates the transmission loop and the first and second reception loops.
To the measurement surface.
An underground electromagnetic exploration apparatus which is formed so as to be capable of contacting, and which measures a specific resistance distribution at the ground or underground at the position where the sensor unit abuts from the detected current data by using an electromagnetic exploration method in a frequency domain. 6. The underground electromagnetic exploration apparatus according to claim 5, wherein the sensor section is configured such that the transmission loop and the first and second reception loops are integrally mounted and fixed to a housing. 7. The underground electromagnetic exploration apparatus according to claim 6, wherein the sensor section is formed to have a larger diameter in the order of the transmission loop, the first, and the second reception loop. 8. The current control unit according to claim 5, wherein the control circuit unit includes a search depth switching unit that outputs an energization command for exciting currents having different frequencies to the current control unit. Is formed so as to supply an exciting current of a designated frequency to the transmission loop, and the output synthesizing section, in response to the exciting current of each frequency, a first and a second receiving loop in the predetermined calibration environment. An underground electromagnetic exploration apparatus characterized by variably controlling a combining ratio so that a combined output of the underground electromagnetic waves is canceled.