Large rock sample high-density electrical method electrode device suitable for true triaxial condition and testing method

Abstract

The invention discloses a large rock sample high-density electrical method electrode device suitable for a true triaxial condition and a testing method, the device comprises a plurality of flexible circuit boards tightly attached to the surface of a rock sample, and each circuit board comprises an insulating board, a plurality of electrodes and a plurality of cables; the plurality of electrodes are arranged on the insulating plate at equal intervals, and each electrode is connected with one cable; conductive adhesive is arranged on the surface, in contact with the surface of the rock sample, of the electrode; and connecting all the cables to a multi-core cable joint, wherein the multi-core cable joint is connected with each corresponding port of a high-density electrical method instrument. The device is small and simple in structure, is suitable for carrying out indoor high-temperature and high-pressure experiments, and can be rapidly and nondestructively arranged; the large rock sample can be subjected to high-density electrical measurement in a high-temperature and high-pressure environment, and the electrical change characteristics of the rock in a unit scale stratum environment can be obtained, so that an important theoretical basis is provided for a geotechnical engineering disaster inoculation mechanism.

Description

Technical Field

[0001] The invention relates to the field of geotechnical engineering, and in particular to a high-density electrical method electrode device and a testing method for large rock samples under true triaxial conditions. Background Art

[0002] The high-density resistivity method is an array exploration method. Its basic principle is exactly the same as the traditional resistivity method. It uses the difference in conductivity between rock and soil as the physical basis to study the distribution law of underground conductive current under the action of an artificial stable current field. The difference is that a higher density of measuring points is set in the observation. In the field detection, dozens to hundreds of electrodes are arranged at the locations of the measuring points. The density of measuring points far exceeds that of the general resistivity method. Because of its high work efficiency, non-destructive detection, low work cost, rich data information generated, and simple operation, it is widely used in environmental geology, engineering geology, hydrogeology, ancient tombs and underground buildings, energy and mineral exploration.

[0003] In order to simulate the real underground environment, it is necessary to conduct indoor high temperature and high pressure tests. Indoor testing can effectively control a variety of influencing factors. The electrical properties of rock are one of the inherent physical properties of rock. When environmental factors are constant, they are only closely related to the porosity, crack expansion and deformation of the rock. When the rock is subjected to load, environmental changes, chemical reactions and other factors, it will cause changes in the initiation, expansion and penetration of its internal defects, causing changes in its own electrical properties and affecting related electrical parameters. Therefore, conductivity or resistivity can usually be used to represent changes in the electrical properties of rock, which can reflect the changes in the development and expansion of internal cracks and quantify the internal damage of the rock.

[0004] The high-density electrical instrument consists of a host, a multi-channel electrode converter, and an electrode system. At present, the high-density electrical instrument is mainly used for large-scale field exploration and survey. Dozens or even hundreds of electrodes need to be laid out at one time and connected to the instrument at the same time. The electrode spacing is large and it is not suitable for indoor experiments. The general electrode and cable design is not suitable for high-temperature and high-pressure devices. The materials have problems such as not being resistant to high temperature and high pressure and poor sealing.

[0005] In view of the above defects and shortcomings, it is urgent to propose a high-density electrical electrode device and testing method suitable for large rock samples under true triaxial conditions. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a high-density electrical electrode device and a testing method suitable for large rock samples under true triaxial conditions in view of the defects in the prior art.

[0007] The technical solution adopted by the present invention to solve its technical problem is: The present invention provides a high-density electrical method electrode device suitable for large rock samples under true triaxial conditions. The device includes a plurality of circuit boards closely arranged on the surface of the rock sample. The circuit boards include insulating boards, a plurality of electrodes, and a plurality of cable wires. The plurality of electrodes are arranged on the insulating board at equal intervals, and each electrode is connected to one of the cable wires. A conductive adhesive is provided on the surface of the electrode in contact with the rock sample. All the cable wires are connected to a multi-core cable connector, and the multi-core cable connector is connected to the corresponding ports of the high-density electrical method instrument.

[0008] Further, a plurality of copper cores are also provided on the insulating board of the present invention. One end of the copper core is connected to the electrode, the middle part is arranged parallel to the insulating board, and the other end is respectively connected to the corresponding cable wire.

[0009] Further, the insulating board of the present invention has the characteristics of high temperature resistance, high insulation, and flexibility, and is made of polyimide material.

[0010] Further, the electrode of the present invention adopts a circular copper sheet electrode, and the copper sheet electrode is embedded in the surface of the insulating board.

[0011] Further, the conductive adhesive of the present invention adopts a high-temperature resistant graphite conductive adhesive.

[0012] Further, the length of the insulating board of the present invention is determined according to the number of electrodes and the electrode spacing.

[0013] The present invention provides a test method for a high-density electrical method electrode device suitable for large rock samples under true triaxial conditions. The method includes the following steps: S1, preprocess the rock sample and mark the electrode installation positions. S2, apply the conductive adhesive on the electrodes, align and fit the circuit boards according to the marked positions, and let it stand at room temperature for 24 hours to preliminarily cure the conductive adhesive. During the preliminary curing process, detect the contact resistance. Then put it into a high-temperature chamber and set the temperature to 80°C for constant temperature heating for 24 hours to fully couple the electrodes with the rock sample. S3, after the circuit boards are fixed, apply a high-temperature and high-pressure resistant insulating adhesive on the surface of the rock sample, and let it stand at room temperature for 24 hours to cure it. S4, fix the fabricated rock sample and the electrodes in the high-temperature chamber, connect the cable wires of the circuit boards to the multi-core cable connector in the laboratory, and connect the multi-core cable connector to the corresponding ports of the high-density electrical method instrument. S5, turn on the high-density electrical method instrument and set relevant parameters, including: test mode, electrode device, test electrode spacing. S6. Self-check the performance of each of the electrodes and the high-density electrical prospecting instrument, and use the high-density electrical prospecting instrument for acquisition. If obvious signals are received by each of the electrodes, it indicates that the electrodes and the high-density electrical prospecting instrument are working properly. S7. Start measuring the resistivity of the rock under normal temperature conditions. S8. After the resistivity measurement under normal temperature conditions is completed, turn on the high-temperature chamber and set the target temperature T1, the heating time, and the heat preservation time. After the temperature rises to the target temperature T1 and is kept constant for a certain period of time, start the measurement. During the heating process, export the resistivity data measured under normal temperature conditions at the same time and perform resistivity inversion. S9. After the resistivity measurement of the rock sample at the target temperature T1 is completed, set the target temperature T2, where T2 > T1, the heating time, and the heat preservation time. After the furnace temperature rises to the target temperature T2 and continues to be kept warm for a certain period of time, start the measurement. During the heating process, export the resistivity data measured under the condition of T1 at the same time and perform resistivity inversion. S10. Obtain the resistivity inversion image of the rock sample under the true triaxial condition based on the measured resistivity of the rock.

[0014] Further, the preprocessing method of the present invention includes: preprocessing the rock sample using a rock cutting and grinding machine to polish the end face of the rock sample smooth and flat; drying all the rock samples to remove the moisture inside the rock samples; marking and preprocessing the electrode installation positions according to the experimental design.

[0015] Further, the method for detecting the contact resistance of the present invention includes: detecting the contact resistance before the conductive adhesive cures; directly connecting the cable of the circuit board to the high-density electrical prospecting instrument, turning on the high-density electrical prospecting instrument, and using the high-density electrical prospecting instrument to test the contact resistance to check whether there is any abnormality in the contact resistance. For the electrodes with a contact resistance greater than a certain threshold, check whether the cable welding is intact and whether the conductive adhesive is evenly applied; after the contact resistance of all the electrodes is normal, wait for the static state to be completed.

[0016] Further, the target temperature T1 of the present invention is 100 °C, the corresponding heating time is 15 min, and the heat preservation time is 90 min; the target temperature T2 is 250 °C, the corresponding heating time is 15 min, and the heat preservation time is 90 min.

[0017] Further, the method of step S10 of the present invention includes: The formula for calculating the resistivity is:

[0018] Where: is the apparent resistivity, with the unit , is the geometric factor, is the measured potential difference in volts (V), is the injected current in amperes (A); By performing inversion calculations, the observed potential difference is minimized with respect to the potential difference obtained from forward calculations, i.e., the error between the observed potential difference and the calculated potential difference is minimized. The objective function is expressed as:

[0019] where, is the potential difference measured at the -th measurement, is the potential difference calculated based on the resistivity model, is the regularization term used to smooth the resistivity model, is the regularization parameter that controls the weight of the regularization term; By continuously iteratively updating the resistivity model, the value of the objective function is gradually reduced, thereby obtaining a resistivity cloud map of rock failure as the resistivity inversion image.

[0020] The beneficial effects of the present invention are as follows: 1. The present invention proposes a high-density electrical method electrode device and a testing method applicable to large rock samples under true triaxial conditions. The device uses circular copper sheets as electrodes, which are arranged at equal intervals and embedded in a flexible board. Each copper sheet is connected to a wire, and the wires are wrapped by the flexible board and separated from each other. A high-temperature and high-pressure resistant cable is connected to one end of the flexible board. Under high-temperature and high-pressure environments, high-density electrical method measurements can be performed on large rock samples to obtain the characteristics of rock electrical property changes in the unit-scale formation environment, thereby providing an important theoretical basis for the mechanism of geotechnical engineering disasters.

[0021] 2. During the experimental verification process of the present invention, copper sheets with a thickness of 0.07 mm and a diameter of 10 mm are used as electrodes, the circuit board has a width of 40 mm and a thickness of 0.4 mm, which can be directly attached to the rock surface. The electrode arrangement is simple, without the need for drilling, and does not damage the rock structure. The circuit board is fabricated through a mold, and the electrode spacing is fixed, reducing the error caused by manually arranging electrodes one by one. Moreover, the circuit board is thin and does not affect the loading device from applying pressure to the rock. On the contrary, as the pressure increases, the contact between the electrode and the rock becomes better. A conductive adhesive is applied between the copper sheet and the rock, which can significantly reduce the contact resistance. Compared with general copper rod electrodes, it is more convenient to apply the conductive adhesive to the copper sheet and less conductive adhesive is required. The local cable and electrode are integrated on an insulating thin board, eliminating the need for cable line arrangement and reducing the experimental preparation time. The cable can withstand high temperature and high pressure, the material of the insulating board is polyimide that can withstand high temperature and high pressure, and the conductive adhesive is a graphite-containing conductive adhesive that can withstand high temperature, enabling high-density electrical method experiments under high-temperature and high-pressure conditions.

[0022] 3. Compared with the commonly used high-density electrical method electrode device, the high-density electrical method electrode device for large rock samples under true triaxial conditions is small and simple, suitable for carrying out indoor high-temperature and high-pressure experiments, and can be arranged quickly and without damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the drawings and embodiments. In the drawings: Figure 1 is a schematic diagram of the material and geometry of the circuit board in the embodiment of the present invention; Figure 2 is a schematic diagram of the arrangement of the circuit board on the rock surface in the embodiment of the present invention; Figure 3 is a schematic diagram of the instrument connection in the embodiment of the present invention; Figure 4 is the resistivity inversion diagram in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] Embodiment 1 As Figure 1 shown, the high-density electrical method electrode device for large rock samples under true triaxial conditions in the embodiment of the present invention includes a plurality of circuit boards closely arranged on the surface of the rock sample. The circuit board includes an insulating board, a plurality of electrodes and a plurality of cable wires; the plurality of electrodes are arranged on the insulating board at equal intervals, and each electrode is connected with a cable wire; a conductive adhesive is arranged on the surface of the electrode in contact with the rock sample; all the cable wires are connected to a multi-core cable connector, and the multi-core cable connector is connected to the corresponding ports of the high-density electrical method instrument.

[0026] In the preferred embodiment of the present invention, a plurality of copper cores are further arranged on the insulating board of the present invention. One end of the copper core is connected to the electrode, the middle part is arranged parallel to the insulating board, and the other end is respectively connected to the corresponding cable wire.

[0027] In the preferred embodiment of the present invention, the insulating board of the present invention has the characteristics of high temperature resistance, high insulation and flexibility, and is made of polyimide material.

[0028] In the preferred embodiment of the present invention, the electrode of the present invention adopts a circular copper sheet electrode, and the copper sheet electrode is embedded in the surface of the insulating board.

[0029] In the preferred embodiment of the present invention, the conductive adhesive of the present invention adopts a high-temperature resistant graphite conductive adhesive.

[0030] Example 2 In the embodiment of the present invention, the basic principle of high-density resistivity monitoring is based on the fact that different media have different conductivities (the reciprocal of resistivity). Based on the conductivity differences of the media, the distribution state of the media in the physical field is obtained by judging the spatial distribution characteristics of the conductivity of the media in an artificially formed electric field. Taking the detection of abnormal bodies as an example, the equipotential lines of the electric field of a homogeneous geological body are relatively uniform, while the presence of abnormal bodies will cause a large distortion in the distribution of the electric field equipotential lines. By measuring the voltage value of the change in the electric field distribution caused by the abnormal body with a measuring electrode, the distribution of the underground resistivity can be deduced inversely, and the position of the abnormal body can be found. In the deep simulator prototype, the high-density resistivity imaging unit generates a stable underground current field between different electrode pairs, and inversely calculates the resistivity distribution of the rock according to the distribution law of the current field, so as to realize the positioning of the rock structural plane and fractures. During the process of rock compression deformation or being disturbed, the resistivity distribution is measured in real time, and according to the evolution law of the rock resistivity distribution at different times, the evolution law of the internal microfractures of the rock and the migration law of the fluid inside the pores are studied. The high-density resistivity imaging method provides intuitive and effective data for the research on the positioning and evolution of the structural plane and fractures of rock and soil masses, anisotropy characterization, fluid saturation, seepage and pollutant migration laws, etc.

[0031] In order to carry out high-density resistivity monitoring in the deep simulation prototype, a high-density electrical method electrode device suitable for large rock samples under true triaxial conditions is designed. It mainly includes electrodes, cable wires, and insulating plates. The insulating plate is made of polyimide material, can withstand high temperatures above 250 °C, has high insulation and a certain degree of flexibility. The width of the insulating plate is 40 mm, and the thickness is 0.4 mm. The length of the insulating plate is related to the number of electrodes (copper sheets) and the electrode spacing. As the number of electrodes increases and the electrode spacing increases, the length of the insulating plate increases ( Figure 1The number of middle electrodes is 5 (i.e., TP1 - TP5 in the figure), the electrode spacing is 80 mm, and the length of the insulating board is 400 mm. The number of electrodes and the electrode spacing can be designed and processed according to requirements. The electrodes are made of circular copper sheets with a diameter of 10 mm and a thickness of 0.07 mm. The copper sheets are embedded in the surface of the insulating board. When the circuit board is closely arranged on the rock surface, the copper sheets can directly contact the rock. However, due to the relatively rough surface of the rock, the contact area between the copper sheets and the rock is small, and the contact resistance is large. To reduce the contact resistance, an appropriate amount of conductive adhesive is applied between the copper sheets and the rock. Before curing, the conductive adhesive has a certain fluidity and can fill the uneven places on the rock surface, increasing the contact area between the copper sheets and the rock. To enable electrical method testing in high-temperature environments, a heat-resistant conductive adhesive - graphite-containing conductive adhesive is used. Each copper sheet is respectively connected to a wire (copper core), and the wires are separated by an insulating material (polyimide). All the wires converge at one end of the insulating board. At this end, a high-temperature and high-pressure cable is welded to the copper core one by one. The diameter of the cable is 22 AWG, with a copper core of 0.5 mm², and the outer shell material is silicone.

[0032] Example 3 The test method of the electrode device for high-density electrical method of large rock samples under true triaxial conditions according to the embodiment of the present invention includes the following steps: S1, preprocess the rock sample and mark the electrode installation positions; S2, apply the conductive adhesive on the electrodes, align and attach the circuit board according to the marked positions, and let it stand at room temperature for 24 hours to preliminarily cure the conductive adhesive; during the preliminary curing process, detect the contact resistance; then place it in a high-temperature chamber and set the temperature to 80 °C for constant-temperature heating for 24 hours to fully couple the electrodes with the rock sample; S3, after the circuit board is fixed, apply a high-temperature and high-pressure insulating adhesive on the rock sample surface and let it stand at room temperature for 24 hours to cure it; S4, fix the made rock sample and the electrodes in the high-temperature chamber, connect the cable of the circuit board to the multi-core cable connector in the laboratory, and connect the multi-core cable connector to the corresponding ports of the high-density electrical method instrument; S5, turn on the high-density electrical method instrument and set relevant parameters, including: test mode, electrode device, test electrode spacing; S6, self-check the performance of each electrode and the high-density electrical method instrument, and use the high-density electrical method instrument for acquisition. If obvious signals are received by each electrode, it indicates that the electrodes and the high-density electrical method instrument are working properly; S7, start measuring the resistivity of the rock under normal temperature conditions; After the resistivity measurement is completed at room temperature, open the high-temperature chamber and set the target temperature T1, the heating time, and the holding time. After the temperature rises to the target temperature T1 and is kept constant for a certain period of time, start the measurement. During the heating process, export the resistivity data measured under room temperature conditions at the same time and perform resistivity inversion. After the resistivity measurement of the rock sample at the target temperature T1 is completed, set the target temperature T2, where T2>T1, the heating time, and the holding time. After the furnace temperature rises to the target temperature T2 and continues to be held for a certain period of time, start the measurement. During the heating process, export the resistivity data measured under the condition of T1 at the same time and perform resistivity inversion. In a preferred embodiment of the present invention, the target temperature T1 is 100 °C, the corresponding heating time is 15 min, and the holding time is 90 min; the target temperature T2 is 250 °C, and the corresponding heating time is 15 min, and the holding time is 90 min.

[0033] S10, according to the measured rock resistivity, obtain the resistivity inversion image of the rock sample under the true triaxial condition. The specific method includes: The electrical method measurement calculates the resistivity of the rock by measuring the potential difference and current between the electrodes. The specific formula for calculating the resistivity depends on the electrode arrangement used. Common arrangements include the Wenner method and the Schlumberger method.

[0034] Regardless of the arrangement used, the general formula for calculating the resistivity is:

[0035] Where: is the apparent resistivity ( ), is the geometric factor, is the measured potential difference (V), is the injected current (A).

[0036] Through the inversion calculation, the observed potential difference is minimized with the potential difference obtained by the forward calculation, that is, the error between the observed potential difference and the calculated potential difference is minimized. The objective function is usually expressed as:

[0037] Where, is the potential difference of the th measurement, is the potential difference calculated according to the resistivity model, is the regularization term used to smooth the resistivity model, is the regularization parameter that controls the weight of the regularization term.

[0038] By continuously iterating and updating the resistivity model, gradually reducing the value of the objective function, a resistivity cloud map of rock failure is obtained as the observed value.

[0039] Example 4 As Figure 1 and Figure 2 shown, the test method of the electrode device for high-density electrical method of large rock samples under true triaxial conditions in the embodiments of the present invention: First, use a rock cutting and grinding machine to preprocess the rock sample, and polish the end face of the rock sample smooth and flat. Before sample preparation, all samples are dried to remove the moisture in the rock samples. According to the experimental design, mark and preprocess the electrode installation positions to facilitate subsequent circuit board fixation and data processing.

[0040] For the flexible circuit board, to reduce the contact resistance, apply an appropriate amount of conductive adhesive evenly on the copper sheet, and then align and attach the flexible circuit board according to the electrode marking positions. Let it stand at room temperature for 24 hours to make it initially cured. During the standing process, a certain pressure can be applied on the circuit board to make the electrodes contact the rock better. At the same time, before the conductive adhesive cures, the contact resistance needs to be detected. Connect the cable of the circuit board directly to the high-density electrical method instrument, turn on the high-density electrical method instrument, use the instrument to test the contact resistance, and check whether there is any abnormality in the contact resistance. For the electrodes with a large contact resistance, it is necessary to check whether the cable welding is intact and whether the conductive adhesive is evenly applied. After the contact resistance of all electrodes is normal, wait for the standing to complete, and finally put it into the high-temperature chamber and set the temperature to 80 °C for constant temperature heating for 24 hours to make the two fully coupled.

[0041] After the circuit board is fixed, to separate the rock from the heat-conducting oil and metal pads, apply a high-temperature and high-pressure resistant insulating adhesive on the rock surface, and let it stand at room temperature for 24 hours to cure it to make the two fully coupled.

[0042] (1) Fix the prepared rock sample and electrodes in the high-temperature test chamber. As Figure 3 shown, connect the cable of the circuit board to the multi-core cable connector in the test chamber, and then connect the multi-core cable connector to the corresponding ports of the high-density electrical method instrument.

[0043] (2) Turn on the high-density electrical method instrument and set relevant parameters such as the test method, electrode device, and test electrode spacing.

[0044] (3) Self-check, test, and calibrate the performance of each sensor and the acquisition system. Use the high-density electrical method instrument to perform conversions for each electrode. If obvious signals are received by each electrode, it indicates that the electrodes and the electrical method instrument are working normally.

[0045] (4) Start measuring the resistivity of the rock under normal temperature conditions.

[0046] After the resistivity measurement is completed at room temperature, turn on the intelligent heating facility and set the target temperature to 100 °C, the heating time to 15 min, and the holding time to 90 min. To ensure that the overall temperature inside and outside the rock sample reaches the set temperature, after heating to 100 °C and maintaining a constant temperature for 60 min, start the measurement. During the heating process, the resistivity data measured at room temperature can be exported simultaneously for resistivity inversion.

[0047] After the resistivity measurement of the rock sample at 100 °C is completed, set the target temperature to 250 °C, the heating time to 15 min, and the holding time to 90 min. After the furnace temperature rises to 250 °C and continues to hold for 60 min, start the measurement. During the heating process, the resistivity data measured at 100 °C can be exported simultaneously for resistivity inversion.

[0048] According to the above heating and holding times, ensure that the equipment is connected, the communication is normal, and the resistivity imaging is carried out as Figure 4 shown.

[0049] It should be understood that the magnitudes of the sequence numbers of the steps in the above embodiments do not mean the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0050] It should be understood that those of ordinary skill in the art can make improvements or transformations according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A high-density electrical method electrode device for large rock samples under true triaxial conditions, characterized in that The device includes a plurality of circuit boards closely arranged on the surface of the rock sample. The circuit boards include insulating boards, a plurality of electrodes and a plurality of cable wires; the plurality of electrodes are arranged on the insulating board at equal intervals, and each electrode is connected with a cable wire; a conductive adhesive is arranged on the surface of the electrode in contact with the rock sample; all the cable wires are connected to a multi-core cable connector, and the multi-core cable connector is connected to each corresponding port of the high-density electrical method instrument.

2. The high-density electrical method electrode device for large rock samples applicable to the true triaxial condition according to claim 1, characterized in that, A plurality of copper cores are further arranged on the insulating board. One end of each copper core is connected to the electrode, the middle part is arranged parallel to the insulating board, and the other end is respectively connected to the corresponding cable wire.

3. The high-density electrical method electrode device for large rock samples applicable to the true triaxial condition according to claim 1, wherein The insulating board has the characteristics of high temperature resistance, high insulation and flexibility, and is made of polyimide material.

4. The electrode device for high-density electrical method of large rock samples applicable to true triaxial conditions according to claim 1, characterized in that, The electrode adopts a circular copper sheet electrode, and the copper sheet electrode is embedded in the surface of the insulating board.

5. The high-density electrical method electrode device for large rock samples applicable to the true triaxial condition according to claim 1, wherein The conductive adhesive adopts a high-temperature-resistant graphite conductive adhesive.

6. The high-density electrical method electrode device for large rock samples applicable to the true triaxial condition according to claim 1, characterized in that, The length of the insulating board is determined according to the number of electrodes and the electrode spacing.

7. A test method for a high-density electrical method electrode device for large rock samples under true triaxial conditions, which uses the high-density electrical method electrode device for large rock samples under true triaxial conditions described in any one of claims 1-6, characterized in that, The method includes the following steps: S1, preprocess the rock sample and mark the installation positions of the electrodes; S2, apply the conductive adhesive on the electrodes, align and fit the circuit boards according to the marked positions, and leave them standing at room temperature for 24 hours to preliminarily cure the conductive adhesive; during the preliminary curing process, perform contact resistance detection; then put them into a high-temperature chamber and set the temperature to 80 °C for constant-temperature heating for 24 hours to fully couple the electrodes with the rock sample; S3, after the circuit boards are fixed, apply a high-temperature and high-pressure-resistant insulating adhesive on the surface of the rock sample, and leave it standing at room temperature for 24 hours after application to cure it; S4, fix the made rock sample and the electrodes in a high-temperature and high-pressure true triaxial cavity, connect the cable wires of the circuit boards to the multi-core cable connector in the laboratory, and connect the multi-core cable connector to each corresponding port of the high-density electrical method instrument; S5, turn on the high-density electrical method instrument and set relevant parameters, including: test mode, electrode device, test electrode spacing; S6, self-check the performance of each electrode and the high-density electrical method instrument, and use the high-density electrical method instrument for acquisition. If obvious signals are received by each electrode, it indicates that the electrodes and the high-density electrical method instrument are working normally; S7, start measuring the resistivity of the rock under normal temperature conditions; S8, after the resistivity measurement under normal temperature conditions is completed, turn on the high-temperature chamber, and set the target temperature T1, heating time, and heat preservation time; after the temperature rises to the target temperature T1 and is kept constant for a certain time, start measuring; during the heating process, simultaneously export the resistivity data measured under normal temperature conditions and perform resistivity inversion; S9, after the resistivity measurement of the rock sample at the target temperature T1 is completed, set the target temperature T2, where T2>T1, heating time, and heat preservation time. After the furnace temperature rises to the target temperature T2 and continues to be kept warm for a certain time, start measuring; during the heating process, simultaneously export the resistivity data measured under the condition of T1 and perform resistivity inversion; S10, obtain the resistivity inversion image of the rock sample under the true triaxial condition according to the measured resistivity of the rock.

8. The testing method of the electrode device for high-density electrical method of large rock samples under true triaxial conditions according to claim 7, characterized in that The preprocessing method includes: using a rock cutting and grinding machine to preprocess the rock sample, polishing the end face of the rock sample to be smooth and flat; drying all the rock samples to remove the moisture in the rock samples; marking and preprocessing the electrode installation positions according to the experimental design.

9. The test method for the electrode device of high-density electrical method for large rock samples under true triaxial conditions according to claim 7, characterized in that, The method for detecting the contact resistance includes: detecting the contact resistance before the conductive adhesive cures; directly connecting the cable of the circuit board to the high-density electrical method instrument, turning on the high-density electrical method instrument, using the high-density electrical method instrument to test the contact resistance, checking whether there is any abnormality in the contact resistance, for the electrodes with a contact resistance greater than a certain threshold, checking whether the cable welding is intact and whether the conductive adhesive is evenly applied; after the contact resistance of all the electrodes is normal, waiting for the static state to be completed.

10. The test method for the electrode device of high-density electrical method for large rock samples under true triaxial conditions according to claim 7, characterized in that, The method of step S10 includes: The formula for calculating the resistivity is: Wherein: is the apparent resistivity, with the unit , is the geometric factor, is the measured potential difference, with the unit V, is the injected current, with the unit A; By inversion calculation, the observed potential difference is minimized with the potential difference obtained by forward calculation, that is, the error between the observed potential difference and the calculated potential difference is minimized, and the objective function is expressed as: wherein, is the potential difference of the th measurement, is the potential difference calculated according to the resistivity model, is the regularization term for smoothing the resistivity model, is the regularization parameter that controls the weight of the regularization term; By continuously iteratively updating the resistivity model, the value of the objective function is gradually reduced, so as to obtain the resistivity cloud map of rock failure as the resistivity inversion image.

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