JP4332643B2 - Installation method of non-polarizable electrode on rock or ground, and electric exploration method or electromagnetic exploration method using the same - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method for installing a non-polarizable electrode on a rock or ground, and an electric exploration method or an electromagnetic exploration method using the same, and in particular, various exploration methods carried out for obtaining electrical properties of a rock or ground. The present invention relates to a method for installing a non-polarizable electrode used as a potential electrode or a current electrode on a rock or ground.

  In electrical resistivity survey, as shown in Fig. 1, the transmitter (DC power supply) of the electrical survey device is connected to a pair of current electrodes installed on the ground, and the receiver (voltmeter) is connected to another pair of potential electrodes. The measurement is performed by measuring the value of the direct current flowing from the current electrode and the potential difference formed between the potential electrodes. When the distance between the current electrode and the potential electrode (electrode distance) is small, the measured data reflects the resistivity of the shallow formation, and as the electrode spacing increases, the influence of the resistivity of the deep formation on the data increases. To be included. Therefore, it is possible to know the specific resistance change in the depth direction of the formation by measuring the electrode interval in various ways. Since resistivity is sensitive to the presence of water, salinity, and clay minerals, and is a parameter affected by temperature changes, resistivity electrical exploration is exploration of resources such as metals and geothermal, groundwater investigation and environmental monitoring, faults, etc. It is used for civil engineering surveys such as rock mass survey.

  In addition, the IP (Induced Polarization) method electric exploration uses a pair of transmission electrodes and a pair of potential electrodes in the same manner as the resistivity electric exploration. However, the measurement methods are different, and there are broadly divided into a time domain measurement method and a frequency domain measurement method. The former causes a current to flow between the current electrodes for a certain period of time to form a potential difference in the ground, measures the change in the attenuation voltage remaining after the current interruption with the potential electrode, and obtains the ratio with the potential difference generated during energization. In the latter, currents of different frequencies are passed, and the difference in potential difference measured by the frequency is measured. IP method electric exploration is a method to measure the electric charging (polarization) effect of the strata, and is used for exploration of strata containing metal minerals and clay minerals that show a large charge rate.

  In the natural potential method, two or more electrodes are installed on the ground, the direct current potential difference between the electrodes is measured with respect to a certain electrode, and the ground potential distribution in the natural state is grasped. In FIG. 1, this corresponds to measurement without using a current electrode.

  In the electromagnetic exploration that measures the electric field like the CSMT (Controlled Source Magneto-Telluric) method, as shown in Fig. 2, the alternating current generated by the current induced by the penetration of artificial electromagnetic waves or natural electromagnetic waves transmitted from far away into the ground The electric field is measured as an AC potential difference generated between one or more pairs of electrodes installed on the ground, and the measured value of the magnetic field measured simultaneously or the strength of electromagnetic waves measured by other methods is used to determine the specific resistance of the ground. Ask.

A metal electrode such as a stainless steel bar or a copper bar is usually used as a potential electrode for electrical resistivity electrical exploration. However, the metal electrode is easily polarized, and even if it is very small, the contact potential difference (electrode potential) with the ground changes when a current flows. Since this change causes noise during potential measurement, if the measured potential is small and high-precision potential measurement is required, the silver-silver chloride, copper-copper sulfate electrode, and lead-lead sulfide electrode can be used instead of the metal electrode. It is necessary to use such a stable non-polarizable electrode.
An example of a typical non-polarizable electrode is shown in FIG. A non-polarizable electrode is generally composed of a combination of a metal electrode and a solution containing a specific salt (ion), and electrical conduction between the ground and the ground is performed by ions moving in the solution. Even when a current flows through the electrode, the ions in the solution suppress the polarization of the surface of the metal electrode and its surroundings, and the electrode potential hardly changes. Non-polarizable electrodes need to immerse the periphery of the metal electrode with the solution, and at the same time maintain the electrical conductivity between the solution and the ground. It is made by a method of making a porous material such as, or a method of hardening a solution with a water retention material such as gypsum or agar. In general, earthenware pottery is used for the copper-copper sulfate electrode (FIG. 3a), and a container with a porous glass filter is used for the silver-silver chloride electrode (FIG. 3b). In addition, in the lead-lead chloride electrode, the periphery of the lead bar covered with lead chloride is covered with gypsum mixed with water, lead chloride powder and sodium chloride (or potassium chloride) (FIG. 3c).

  Electromagnetic exploration that measures electric fields such as the IP potential electrode and the CSMT method requires a smaller measurement potential than the resistivity resistivity electric exploration and requires precise measurement. In most cases, the potential electrode is a non-polarizable electrode. Is used. Even in the measurement of the natural potential method, a non-polarizable electrode is always used in order to measure a stable potential.

  Since nonpolarizable electrodes use a porous material or a water retaining material on the ground surface, they are weaker in mechanical strength than metal electrodes, and cannot be driven into hard rock or ground like metal electrodes. Therefore, the installation location of the nonpolarizable electrode has been limited to a substantially horizontal surface. On rocks and ground that are greatly inclined, such as walls of tunnels and tunnels, or on the gravest of geological roadheads, it is necessary for a person to hold a non-polarizable electrode during measurement. was there. In such places, high-density measurements that use many non-polarizable electrodes at once and monitoring that requires the installation of non-polarizable electrodes for a long period of time are rarely implemented. .

  In addition, a metal electrode has been used as a current electrode in a resistivity method or IP method electric exploration. This is because the metal electrode can be driven deeply into the ground to reduce the ground resistance, so that a large current is likely to flow. In addition, when a large current is passed using the non-polarizable electrode as a current electrode, there is a problem that the balance of the metal surface is broken and the non-polarized property is destroyed. Therefore, two types of electrodes have always been used in electric exploration using non-polarizable electrodes. However, in the measurement of the normal electrode arrangement such as the two-pole arrangement or the dipole / dipole arrangement, the position of the potential electrode is often the position of the current electrode, and the measurement efficiency increases as the number of switching between the arrangement of the potential electrode and the current electrode increases. Falls. Moreover, since the grounding area and the installation depth of both electrodes are usually different, it is not possible to place the current electrode and the potential electrode at the same position strictly. The difference between the position of the current electrode and the potential electrode directly becomes a measurement error, and this error is not negligible particularly in precision measurement with a purpose of evaluating wall surfaces of tunnels and tunnels, and measurement with a small electrode interval. Will result in a decline.

  Therefore, the present invention solves such problems, and performs high-density measurement of high-precision resistivity method exploration and IP method exploration on rocks or ground with a large slope such as walls and geological roadheads such as tunnels and tunnels. It aims at providing the installation method of the nonpolarizable electrode which enables the monitoring.

  The non-polarizable electrode installation method of the present invention on a rock or ground is used for electric exploration or electromagnetic exploration on the rock or ground. This installation method uses the same salt as the salt used for the non-polarizable electrode, or gypsum mixed with salt that is harmless to the environment, and adheres the non-polarizable electrode to the bedrock or ground. The electric potential is measured while suppressing the polarization reaction and electrochemical reaction that occur in and around the conductive electrode. This non-polarizable electrode is installed by making a hole slightly larger than the outer diameter of the non-polarizable electrode and pouring gypsum into the hole to fix the electrode.

In the electrical exploration method by the specific resistance method or the IP method of the present invention, the nonpolarizable electrode is installed not only as a potential electrode but also as a current electrode.
In addition, the electric exploration method of the present invention performs electric exploration by the natural potential method using the non-polarizable electrodes installed in this way.
In addition, the electromagnetic exploration method of the present invention measures the electric field using the nonpolarizable electrode installed in this way.

  In the present invention, it is possible to perform high-precision measurement and monitoring of the resistivity method and IP method exploration on a highly inclined rock or ground such as a wall such as a tunnel or a tunnel or a geological roadhead. According to the present invention, a stable non-polarizable electrode with little noise can be installed reliably and very easily and inexpensively. Exploration is being applied.

  A gypsum in which the same salt (ion) and water contained in the non-polarizable electrode are mixed is prepared, and the electrode is bonded to the bedrock / ground by the gypsum as shown in FIG. At this time, if a gypsum-type lead-lead chloride electrode is used as the non-polarizable electrode and the same gypsum used in the electrode is used, the non-polarizable electrode and the gypsum are integrated, and the polarization generated in the electrode and its surroundings. Since no reaction or electrochemical reaction occurs, the most stable potential measurement is possible. However, gypsum itself has only water retention and adhesion, and there is almost no chemical reaction with other salts (ions), so there is almost no problem in principle even if it is used for adhesion to other non-polarizable electrodes. . In addition, when it is judged that the salt contained in a non-polarizable electrode affects the surrounding environment, although a slight fall of stability is anticipated, it is also possible to substitute with harmless salt.

  If you want to securely install a non-polarizable electrode on a surface with a large slope, drill a hole slightly larger than the outer diameter of the electrode about 5 to several tens of millimeters deep, and pour gypsum into it to bond the electrode. Adhesion to salt and rock with gypsum containing salt water also contributes to the reduction of ground resistance, so this electrode can also be used as a current electrode. If the non-polarizable electrode is considered as disposable, the measurement procedure using the non-polarizable electrode installed as a potential electrode after using the non-polarized electrode installed in the dipole method, the tripolar method, and the dipole-dipole arrangement as a current electrode will give a highly accurate ratio. Resistance electrical exploration and IP electrical exploration are possible.

  In order to verify the effect of the present invention, a demonstration experiment was conducted in a tunnel of a clay mine that produces sericite clay. The cross-sectional shape of the tunnel is almost rectangular, with a height of about 2m and a width of about 2.2m. In this experiment, a survey line with a length of 25m was installed along the direction of the tunnel at a height of 1m on the wall surface, and 26 electrodes were installed at 1m intervals. FIG. 5 shows a geological plan view and electrode positions around the mine shaft. There is a sericite clay vein in the center of the survey line, and both sides are covered with andesite. Andesite is dense, but has joints and cracks extending almost parallel to the clay veins, and its surroundings have undergone hydrothermal alteration. Tuff is exposed outside the andesite. Compared to the surrounding andesite, clay veins have a low specific resistance, and the andesite subjected to clay veins and hydrothermal alteration are known to show a high charging rate.

  In this experiment, gypsum-type lead-lead chloride (commercially available) was used for the nonpolarizable electrode. In this electrode, a lead electrode is placed in a vinyl chloride tube having a diameter of 28 mm, and the periphery is covered with gypsum mixed with lead chloride powder, sodium chloride, and water. A lead wire connected to the lead electrode comes out from one side which becomes the upper surface of the electrode, and the periphery thereof is sealed with a leading edge. The gypsum surface on the other side is exposed and is grounded to the bedrock.

  Adhesion of the non-polarizable electrode to the rock mass was performed by drilling a hole with a diameter of 30 mm at a predetermined position with a large hammer drill, about 10 to 20 mm, and pouring gypsum there. The gypsum used at this time was the same as the gypsum used for the non-polarizable electrode. Mix lead chloride powder, sodium chloride, water and gypsum at a predetermined ratio in the field, install non-polarized electrodes on the bedrock with gel-like gypsum, wait about 2 hours until the gypsum hardens, then the resistivity method And the measurement of IP method was started.

The measurement was performed with a dipole / dipole arrangement. The electrode interval a was 1 m, and the electrode separation coefficient n was 1-5. In this measurement, first, a current was passed from a pair of current numbers 1 and 2, and a potential was measured by a pair of 3 and 4 on the right side. Next, the current electrode pair is the same, and the potential electrode pair is moved to the right in order of No. 4 and No. 5, No. 5 and No. 6, No. 6 and No. 7, and No. 7 and No. 8, and the same measurement is performed. Repeated. Then, the current electrode pair is number 2 and number 3, the potential electrode pair is number 4 and number 5, and the same measurement is repeated, and five potential electrode pairs are measured for one current electrode pair. When finished, the current electrode pair was moved to the right by one. If a current is passed through a non-polarizable electrode, the chemical equilibrium state will be broken and the non-polarized property will be lost. By doing so, there is no problem because there is no electrode used as a potential electrode after using as a current electrode.
Measurement is performed in the time domain, and the apparent specific resistance (unit: Ωm) is obtained by measuring the potential difference during current transmission, and the apparent charge rate is obtained by dividing the integral value of the potential difference after current interruption by the potential difference during transmission. (Unit: mV / V) was determined.

  FIG. 6 shows an apparent specific resistance pseudo sectional view and an apparent charging rate sectional view. The bottom of the figure is the wall, and the top of the figure is the wall. As can be seen from the figure, a low specific resistance was detected corresponding to the clay vein, and a high charging rate was detected corresponding to the andesite that had undergone hydrothermal alteration. This result suggests that the electrical resistivity survey and the IP method electrical survey in the vertical rock can be performed by the measurement according to the present invention.

  Prior to this measurement, a hole having a diameter of 8 mm was formed 10 cm above the non-polarizable electrode and a lead electrode having a diameter of 6 mm was implanted as a current electrode. This is equivalent to using a metal rod for the current electrode as in the prior art. Since the positions of the current electrode and the potential electrode are shifted in the height direction, the above-mentioned results and the quantitative results cannot be compared, but distributions having almost the same tendency were obtained for the apparent specific resistance and the apparent charge rate. In addition, the ground resistance of the nonpolarizable electrode using gypsum is almost equal to the ground resistance of the metal electrode, and it was confirmed that the nonpolarizable electrode can be used as a current electrode.

In addition, after the measurement, installation of non-polarizable electrodes with gypsum in which only sodium chloride and water were mixed without mixing lead chloride powder was performed at two points, but the same results as when lead chloride powder was mixed were obtained. This time, there were no problems with grounding resistance or noise. Although it cannot be determined whether this is applicable in all cases, it is considered possible to replace the salt mixed with gypsum with a harmless one when considering the environment.
The nonpolarizable electrode fixed with gypsum could be easily removed by human power after the measurement. In addition, it is easy to scrape off the gypsum adhering to the bedrock, and a new non-polarizable electrode can be similarly installed at the same position. Is suitable.

  The present invention is an electromagnetic exploration for measuring an electric field such as resistivity electric exploration, IP electric exploration, natural potential electric exploration, and CSMT in a rock or ground inclined greatly like a wall in a mine or a tunnel or a steep geological roadhead. Is possible. Through these surveys, it is possible to determine the resistivity distribution, charge rate distribution, and natural potential distribution within the rock and ground. Electrochemical properties such as specific resistance, charging rate, and natural potential are sensitive parameters to the presence of water and the presence of clay and metal particles, so in the civil engineering field, detection of loose areas and soft layers in tunnels and tunnel walls. It can be used for exploration of metal deposits and clay deposits in disaster prevention and resource fields.

Schematic diagram of measurement method for resistivity method electrical exploration and IP method electrical exploration. Schematic diagram of measurement method of electromagnetic exploration that measures electric field like CSMT method. The schematic diagram of a typical non-polarizable electrode. How to install non-polarizable electrodes on inclined rocks and ground. Geological plan view and survey line position of the mine at the demonstration experiment site. The number in the figure indicates the installation position of the non-polarizable electrode. Results of demonstration experiment. The upper part shows an apparent specific resistance pseudo sectional view, and the lower part shows an apparent charging rate pseudo sectional view. The wall displaying the electrode number is the wall surface.

Claims (5)

In the installation method of non-polarizable electrodes used for electric exploration or electromagnetic exploration for rock or ground,
Using gypsum mixed with the same salt as the salt used for the non-polarizable electrode, the non-polarizable electrode is adhered and installed on the rock or ground,
A method for installing a non-polarizable electrode on a rock or ground, wherein the electric potential is measured while suppressing a polarization reaction or an electrochemical reaction occurring in the non-electrode electrode and its periphery.   The non-polarizable electrode is installed on a rock or ground according to claim 1, wherein a hole larger than the outer diameter of the non-polarizable electrode is drilled and gypsum is poured into the hole to fix the electrode. Method.   3. Electrical exploration by the resistivity method or IP method in which the nonpolarizable electrode is used not only as a potential electrode but also as a current electrode by the method of installing the nonpolarizable electrode on a rock or ground according to claim 1 or 2. Method.   An electric exploration method by a natural potential method in which a non-polarizable electrode is installed by the method for installing the non-polarizable electrode on a rock or ground according to claim 1 or 2. The electromagnetic exploration method which measures an electric field using the installed non-polarizable electrode by the installation method to the bedrock or the ground of the non-polarizable electrode of Claim 1 or 2.

Images