JPH03259782A - Surveying method for underground buried body - Google Patents

Abstract

PURPOSE:To make an excellent survey with high voltage detection sensitivity and a deep-layer survey with a widened electrode interval by specifying the frequency of a sent current which is supplied from a constant current source. CONSTITUTION:An electrode array 14 for resistivity measurement which consists of plural electrodes 12 is fitted on the surface of a sensor main body so that the electrodes 12 are exposed. When one specific adjacent couple of electrodes are used as current transmitting electrodes 12A, an AC power source 18 which supplies the constant sent current of 240 - 1200 Hz in transmission frequency is connected to the electrodes and the current is sent into the ground. When another couple of electrodes whose combination can be changed by a relay box are used as voltage detection electrodes 12B, a signal processor 24 which inputs detection data is connected to them. Then the specific resistivity of the buried body and in its peripheral ground is measured by the electrodes 12B to measure a deep layer part while the reception sensitivity is improved and the supply current value is made large.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an underground conductor exploration method, and more particularly to an underground conductor exploration method suitable for use in metal exploration.

[Conventional technology]

The resistivity method has traditionally been known as a physical exploration method.
For example, a Wenner electrode array is used to search for metal deposits, buried metals, etc. of electrical conductors. This method uses one pair of multiple electrodes as transmitting electrodes to transmit a constant current into the ground, and uses the other pair of electrodes as detection electrodes to measure the underground voltage to determine specific resistance. By the way, the frequency of the transmission current used in conventional physical exploration using the resistivity method was several tens of Hz of direct current. Low frequencies involve polarization phenomena, and skin effects appear when the object to be observed is deep, so a transmission current of 10-odd Hz was normally used. Furthermore, direct current was used for deep exploration.

[Problem to be solved by the invention]

However, according to the conventional exploration method described above, if the observation target is close to a conductor with low resistivity, the electric conductivity is high, so the specific resistance becomes small and the sensitivity of the voltage detection electrode becomes low. There was a problem that made detection extremely difficult. The present invention focuses on the above-mentioned conventional problems, and aims to provide an underground conductor exploration method that can detect conductors such as metal buried underground with high sensitivity. .

[Means and Effects for Solving the Problems] The present inventor focused on the oscillation frequency of the current transmitted from the conventional current transmitting electrode, and determined that the frequency is in the range of 250 to 1200 Hz, especially the alternating current around II (Hz). It has been found that by using it as a transmitting current, it is possible to improve the receiving sensitivity and to increase the supply current value to enable measurement in deep layers.In other words, the exploration of underground conductors according to the present invention The method involves connecting one pair of electrodes in a resistivity measuring electrode array consisting of a plurality of electrodes to a constant current source and transmitting it underground, and connecting a voltage measuring device to the other pair of electrodes to transmit the transmitted current. In the method of exploring a metal conductor buried underground by measuring the underground specific resistance based on
The above object is achieved by transmitting data at a frequency of 1, and measuring the resistivity of the buried conductor and the surrounding underground using voltage detection electrodes to perform discrimination and detection. With this configuration, it has been possible to improve the difficulty in measurement due to a decrease in reception sensitivity due to the high electrical conductivity of metal conductors buried underground. Moreover, the improvement in measurement sensitivity makes it possible to measure deep layers by increasing the electrode spacing.

[Embodiments] Specific embodiments of the underground conductor exploration method according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of a device configuration for carrying out exploration according to an embodiment. As shown, this device includes a sensor body 10 that is placed underground. This is provided on the surface of an insulating plate with a resistivity measuring electrode array 14 in which a plurality of electrodes 12 are arranged 17 at regular intervals to form a dipole electrode array. The resistivity measurement electrode row 14 is attached to the surface of the sensor body 10 with the electrodes 12 exposed, and as shown in FIG. A pair of electrodes placed apart from each other are defined as voltage detection electrodes 12B. The method for detecting specific resistance using this electrode array 14 for measuring specific resistance is as follows. In other words, the electrode spacing is a1 and the number of electrodes is N.
Then, the measurement point is the apex P of a right-angled isosceles triangle whose base is the line segment connecting the midpoints of the current transmitting electrode 12Δ and the voltage detecting electrode 12B. Therefore, the distance from the specific resistance measurement electrode array 14 is determined as h = (N+1)a/2. By changing the position of the voltage detection electrode 12B, this measurement point can be found on the line connecting the measurement point and the midpoint of the current transmission electrode 12A. Therefore, the combination of the current transmission electrode 12A and the voltage detection electrode 12B By appropriately changing , it is possible to create a map in the form of a triangular matrix. This represents the resistivity distribution on the ground surface along the electrode array line in the depth direction of the ground. A relay and box 16 for changing the combination of the current transmitting electrode 12A and the voltage detecting electrode 12B are connected to the resistivity measuring electrode array 14 as described in 1. The combination of the current transmitting electrode 12A and the voltage detecting electrode 12B is changed. Then, an AC power source 18 that supplies a constant current to the current transmitting electrode 12A via the relay box 16 is connected to the voltage detecting electrode 12A.
B has a filter, f filter 20. A signal processing device 24 to which detected data is input is connected via a receiving amplifier 22. The signal processing device 24 outputs a switching signal to the electrode 12,
By inputting a voltage value corresponding to the specific resistance using a built-in voltmeter, a measured specific resistance map is calculated in which data is arranged on a matrix determined by the distance and the spacing a between the electrodes 12. There is. Here, in the embodiment, the transmission frequency of the constant current supplied from the power source 18 is set in the range of 250 to 1200 Hz, and in particular, in the embodiment, it is set to 975 KHz. That is, the power source 18 is composed of an oscillator 28 and an amplifier 30 to oscillate a fixed frequency of 975 kHz, and the oscillator 28 sets the transmission frequency to 975 Hz and supplies it to the transmitting electrode 12A. . The results of checking the frequency characteristics of the underground exploration device configured as described above will be explained next. As shown in FIG. 3, the transmitting electrode 12A and the detecting electrode 12
Using dipole electrodes with a distance of B of 40 cm and an interval of 8 cm between each pair of electrodes, measurements were taken by burying a steel ball (SUS φ14 cm) at a depth of 24 cm underground so that changes in specific resistance would appear. A sine wave of 100 mA is supplied as the transmission current, and the measured voltage when there is a steel ball is v1.The measured voltage when there is no steel ball is V. Then, the sensitivity S was calculated using the following formula. 5=100×(■-V.)/vo ・・・・・・(1)
The following table shows the experimental results of determining the relationship between the transmission frequency of the current supplied from the transmission electrode 12A and its sensitivity using the above device. On the other hand, the following table shows the results of measurements under the same conditions with an insulating ball of the same size buried in place of the steel ball. As is clear from these results, the transmission frequency is set to 25
By supplying the frequency in the range of 0 to 1200 Hz, the reception sensitivity at the detection electrode 12B can be improved. In particular, when the transmission frequency is 975Hz, the reception sensitivity is maximum, so in this embodiment, as described above, the transmission frequency of the constant current supplied from the power supply 18 is set to 975kHz.
It was set to . As described above, according to the present embodiment, the frequency of the current supplied from the transmitting electrode 12A is in the range of 250 to 1200 Hz, particularly in the frequency of 975 Hz, so that the receiving sensitivity is improved and the current is not buried underground. It is possible to reliably detect metal conductors that are Furthermore, the distance between the transmitting electrode 12A and the detecting electrode 12B can be increased, and even buried metal conductors in deep layers can be reliably detected. Effects of the Invention As explained above, according to the present invention, since the frequency of the transmission current supplied from the constant current source is set to 250 to 1200 Hz, the observation target has low resistivity and high electrical conductivity. Even when the specific resistance is small, the voltage detection sensitivity is high, making it possible to conduct a good exploration. At the same time, improved sensitivity allows for deeper exploration by widening the electrode spacing.
This method has the excellent effect of being a suitable method for exploring metal lumps, etc. 8 .

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an underground conductor exploration device for carrying out the method according to the embodiment, FIG. 2 is an explanatory diagram of the exploration method, and FIG. 3 is an explanatory diagram of frequency characteristic experimental equipment. 10...Sensor body, j2A...Transmission electrode, 12B...Detection electrode, 14...
Electrode array for resistivity measurement, 18... AC power supply, 24
...Signal processing device, 28...Transmitter.

Claims (1)

[Claims] 1) Connect one pair of electrodes in a resistivity measuring electrode array consisting of a plurality of electrodes to a constant current source and transmit it underground, and connect a voltage measuring device to the other pair of electrodes to transmit the transmitted current. In the method of detecting a metal conductor buried underground by measuring the underground specific resistance based on the method, the transmitting current supplied from the constant current source is
An underground conductor exploration method characterized by transmitting at a frequency of 0.00Hz, measuring specific resistance between the buried conductor and the surrounding underground using a voltage detection electrode, and performing discrimination detection and exploration.