High-density electrical resistivity electrode apparatus and testing method for large rock samples under true triaxial conditions

Abstract

This invention discloses a high-density electrical resistivity tomography (EDT) electrode device and testing method for large rock samples under true triaxial conditions. The device includes multiple flexible circuit boards closely attached to the surface of the rock sample. Each circuit board includes an insulating plate, multiple electrodes, and multiple cables. The electrodes are evenly spaced on the insulating plate, and each electrode is connected to a cable. Conductive adhesive is applied to the surfaces of the electrodes that contact the rock sample surface. All cables are connected to a multi-core cable connector, which is connected to the corresponding ports of the high-density EDT instrument. This invention is compact and simple in structure, suitable for conducting indoor high-temperature and high-pressure experiments, and allows for rapid and non-destructive setup. It enables high-density EDT measurements of large rock samples under high-temperature and high-pressure environments, obtaining the electrical property changes of rocks in unit-scale stratigraphic environments, thus providing important theoretical basis for the formation mechanism of geotechnical engineering disasters.

Description

Technical Field

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

[0002] High-density resistivity method is an array exploration method. Its basic principle is exactly the same as the traditional resistivity method, based on the difference in conductivity between rock and soil, to study the distribution of underground conduction current under the influence of an artificial stable current field. The difference lies in the high density of measuring points set up during observation. In field exploration, dozens to hundreds of electrodes are deployed at the measuring points, resulting in a measuring point density far exceeding that of the general resistivity method. Due to its numerous advantages, including high efficiency, non-destructive testing, low operating cost, rich data generation, and ease of operation, it is widely used in environmental geology, engineering geology, hydrogeology, ancient tombs and underground structures, and energy and mineral exploration.

[0003] To simulate the real underground environment, conducting indoor high-temperature and high-pressure tests is essential, as indoor testing can effectively control various influencing factors. The electrical properties of rocks are one of their inherent physical properties. Under constant environmental conditions, they are closely related only to the rock's porosity, fracture propagation, and deformation. However, when rocks are subjected to various factors such as loads, environmental changes, and chemical reactions, changes occur in the initiation, propagation, and penetration of internal defects, altering their electrical properties and affecting related electrical parameters. Therefore, conductivity or resistivity can typically be used to represent changes in the electrical properties of rocks, reflecting the development and propagation of internal fractures and quantifying internal rock damage.

[0004] A high-density electrical resistivity tomography (OR tomography) instrument consists of three parts: the main unit, a multiplexer, and the electrode system. Currently, high-density OR tomography instruments are mainly used for large-scale field exploration and surveying. They require the simultaneous deployment of dozens or even hundreds of electrodes connected to the instrument, with large electrode spacing, making them unsuitable for indoor testing. Conventional electrode and cable designs are not suitable for high-temperature and high-pressure devices, and the materials used have limitations such as poor resistance to high temperatures and pressures and poor sealing.

[0005] To address the aforementioned deficiencies and shortcomings, there is an urgent need to propose a high-density electrical resistivity 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 resistivity electrode device and testing method for large rock samples under true triaxial conditions, in order to address the deficiencies in the prior art.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] This invention provides a high-density electrical resistivity tomography (EDT) electrode device suitable for large rock samples under true triaxial conditions. The device includes multiple circuit boards that are closely attached to the surface of the rock sample. Each circuit board includes an insulating plate, multiple electrodes, and multiple cables. The electrodes are evenly spaced on the insulating plate, and each electrode is connected to a cable. Conductive adhesive is applied to the surfaces of the electrodes that contact the rock sample surface. All the cables are connected to a multi-core cable connector, which is connected to the corresponding ports of the high-density EDT instrument.

[0009] Furthermore, the insulating plate of the present invention is also provided with a plurality of copper cores, one end of which is connected to the electrode, the middle part is arranged parallel to the insulating plate, and the other end is connected to the corresponding cable.

[0010] Furthermore, the insulating board of the present invention has the characteristics of high temperature resistance, high insulation and flexibility, and is made of polyimide material.

[0011] Furthermore, the electrode of the present invention is a circular copper sheet electrode, which is embedded in the surface of the insulating plate.

[0012] Furthermore, the conductive adhesive of the present invention is a high-temperature resistant graphite conductive adhesive.

[0013] Furthermore, the length of the insulating plate of the present invention is determined according to the number of electrodes and the electrode spacing.

[0014] This invention provides a testing method for a high-density electrical resistivity electrode device for large rock samples under true triaxial conditions, the method comprising the following steps:

[0015] S1, pre-treat the rock sample and mark the electrode installation position;

[0016] S2, apply the conductive adhesive to the electrode, align and attach the circuit board according to the marked positions, and let it stand at room temperature for 24 hours to allow the conductive adhesive to initially cure; during the initial curing process, perform contact resistance testing; then place it in a high-temperature chamber and set the temperature to 80℃ for constant heating for 24 hours to ensure that the electrode is fully coupled with the rock sample;

[0017] S3. After the circuit board is fixed, apply high-temperature and high-pressure resistant insulating adhesive to the surface of the rock sample and let it stand at room temperature for 24 hours to cure.

[0018] S4, fix the prepared rock sample and the electrode in the high-temperature chamber, connect the cable of the circuit board to the multi-core cable connector in the test chamber, and connect the multi-core cable connector to each corresponding port of the high-density electrical resistivity instrument.

[0019] S5, turn on the high-density electrical resistivity meter and set the relevant parameters, including: test mode, electrode device, and test electrode spacing;

[0020] S6, perform self-test on the performance of each electrode and the high-density electrical resistivity meter, and use the high-density electrical resistivity meter to collect data. If each electrode receives a clear signal, it indicates that the electrode and the high-density electrical resistivity meter are working normally.

[0021] S7, begin measuring the rock resistivity under normal temperature conditions;

[0022] 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 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 normal temperature conditions and perform resistivity inversion.

[0023] S9. After the rock sample resistivity measurement at the target temperature T1 is completed, set the target temperature T2, T2>T1, and set the heating time and holding time. After the furnace temperature rises to the target temperature T2 and is held for a certain period of time, the measurement begins. During the heating process, the resistivity data measured under the T1 condition is exported and resistivity inversion is performed.

[0024] S10: Based on the measured rock resistivity, obtain the rock sample resistivity inversion image under true triaxial conditions.

[0025] Furthermore, the pretreatment method of the present invention includes: pretreating the rock sample using a rock cutting and grinding machine to grind the end face of the rock sample smooth and flat; drying all rock samples to remove moisture from the rock sample; and marking and pretreating the electrode installation position according to the experimental design.

[0026] Furthermore, the method for contact resistance detection according to the present invention includes: performing contact resistance detection before the conductive adhesive cures; directly connecting the cable of the circuit board to the high-density electrical resistivity meter, turning on the high-density electrical resistivity meter, using the high-density electrical resistivity meter to perform contact resistance testing, checking whether there are any abnormalities in the contact resistance, and for electrodes with contact resistance greater than a certain threshold, checking whether the cable welding is intact and whether the conductive adhesive is evenly applied; after all the electrodes have no abnormal contact resistance, waiting for the settling process to complete.

[0027] Furthermore, the target temperature T1 of the present invention is 100°C, with a corresponding heating time of 15 min and a holding time of 90 min; the target temperature T2 is 250°C, with a corresponding heating time of 15 min and a holding time of 90 min.

[0028] Further, the method of step S10 of the present invention includes:

[0029] The formula for calculating resistivity is:

[0030]

[0031] in: Apparent resistivity, unit , Geometric factor The measured potential difference, in volts (V). The injected current is expressed in amperes (A).

[0032] The objective function is to minimize the difference between the observed potential difference and the potential difference obtained from the forward modeling through inversion calculation, i.e., to minimize the error between the observed potential difference and the calculated potential difference.

[0033]

[0034] in, It is the first The potential difference measured in this step It is the potential difference calculated based on the resistivity model. It is a regularization term used to smooth the resistivity model. These are regularization parameters that control the weights of the regularization terms;

[0035] By continuously iterating and updating the resistivity model, the objective function value is gradually reduced to obtain a rock failure resistivity contour map, which serves as a resistivity inversion image.

[0036] The beneficial effects of this invention are:

[0037] 1. This invention proposes a high-density electrical resistivity electrode device and testing method for large rock samples under true triaxial conditions. The device uses circular copper sheets as electrodes, arranged at equal intervals and embedded in a flexible plate. Each copper sheet is connected to a wire, which is encased in the flexible plate and separated from each other. A high-temperature, high-pressure resistant cable is connected to one end of the flexible plate. High-density electrical resistivity measurements of large rock samples under high-temperature and high-pressure conditions can reveal the electrical property changes of rocks within a unit-scale stratigraphic environment, thus providing important theoretical basis for the formation mechanism of geotechnical engineering hazards.

[0038] 2. In the experimental verification process of this invention, copper sheets with a thickness of 0.07 mm and a diameter of 10 mm are used as electrodes. The circuit board is 40 mm wide and 0.4 mm thick, allowing it to be directly attached to the rock surface. The electrode arrangement is simple, requiring no drilling and not damaging the rock structure. The circuit board is manufactured using a mold, and the electrode spacing is fixed, reducing errors from manually arranging the electrodes one by one. Furthermore, the thin circuit board does not affect the loading device's ability to pressurize the rock; on the contrary, as the pressure increases, the contact between the electrodes and the rock becomes better. Applying conductive adhesive between the copper sheet and the rock significantly reduces contact resistance. Compared to ordinary copper rod electrodes, applying conductive adhesive to copper sheets is more convenient and requires less adhesive. Some cables and electrodes are integrated onto a single insulating sheet, eliminating the need for cable management and reducing experimental preparation time. The cables are resistant to high temperature and high pressure, and the insulating board is made of high-temperature and high-pressure resistant polyimide. The conductive adhesive is a high-temperature resistant graphite-containing conductive adhesive, enabling high-density electrical resistivity experiments under high temperature and high pressure conditions.

[0039] 3. Compared with commonly used high-density electrical resistivity electrode devices, the high-density electrical resistivity electrode device for large rock samples under true triaxial conditions is small, simple, suitable for indoor high-temperature and high-pressure experiments, and can be set up quickly and without damage. Attached Figure Description

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0041] Figure 1 This is a schematic diagram showing the material and geometry of the circuit board according to an embodiment of the present invention;

[0042] Figure 2 This is a schematic diagram of the circuit board arrangement on the rock surface according to an embodiment of the present invention;

[0043] Figure 3 This is a schematic diagram of the instrument connection according to an embodiment of the present invention;

[0044] Figure 4 This is a resistivity inversion diagram according to an embodiment of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0046] Example 1

[0047] like Figure 1As shown in the figure, the high-density electrical resistivity electrode device for large rock samples under true triaxial conditions is described in this embodiment of the invention. The device includes multiple circuit boards that are closely attached to the surface of the rock sample. Each circuit board includes an insulating plate, multiple electrodes, and multiple cables. The multiple electrodes are equally spaced on the insulating plate, and each electrode is connected to a cable. Conductive adhesive is provided on the surface of the electrodes that contacts the surface of the rock sample. All the cables 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 resistivity instrument.

[0048] In a preferred embodiment of the present invention, the insulating plate of the present invention is further provided with a plurality of copper cores, one end of the copper cores being connected to the electrode, the middle part being arranged parallel to the insulating plate, and the other end being connected to the corresponding cable.

[0049] In a 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.

[0050] In a preferred embodiment of the present invention, the electrode is a circular copper sheet electrode, which is embedded in the surface of the insulating plate.

[0051] In a preferred embodiment of the present invention, the conductive adhesive is a high-temperature resistant graphite conductive adhesive.

[0052] Example 2

[0053] In this embodiment of the invention, the basic principle of high-density resistivity monitoring is based on the fact that different media have different conductivity (the reciprocal of resistivity). Based on the difference in conductivity of the media, the distribution state of the media in the object 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 anomalies as an example, the equipotential lines of the electric field of a homogeneous geological body are relatively uniformly distributed, while the presence of an anomaly will cause a large distortion in the distribution of the equipotential lines. By measuring the voltage value of the change in electric field distribution caused by the anomaly using measuring electrodes, the distribution of underground resistivity can be deduced, and the location of the anomaly can be found. In the deep simulator prototype, the high-density resistivity imaging unit generates a stable underground current field between different electrode pairs. Based on the distribution law of the current field, the resistivity distribution of the rock is inverted, thereby realizing the location of rock structural surfaces and fractures. The resistivity distribution is measured in real time during rock compression deformation or disturbance. Based on the evolution law of the rock resistivity distribution at different times, the evolution law of micro-fractures inside the rock and the fluid transport law inside the pores are studied. High-density resistivity imaging provides intuitive and effective data for the study of rock and soil structural planes and fracture location and evolution, anisotropy characterization, fluid saturation, seepage and pollutant migration patterns.

[0054] To conduct high-density resistivity monitoring in deep-sea simulation prototypes, a high-density electrical resistivity electrode device suitable for large rock samples under true triaxial conditions was designed. It mainly includes electrodes, cables, and an insulating plate. The insulating plate is made of polyimide, capable of withstanding temperatures above 250℃, and possesses high insulation and a certain degree of flexibility. The insulating plate is 40 mm wide and 0.4 mm thick. The length of the insulating plate is related to the number of electrodes (copper sheets) and the electrode spacing; as the number of electrodes and the electrode spacing increase, the length of the insulating plate increases. Figure 1 The circuit has 5 electrodes (TP1-TP5 in the diagram), an electrode spacing of 80mm, and an insulating plate length of 400mm. The number of electrodes and the electrode spacing can be designed and manufactured as needed. The electrodes are circular copper sheets, 10mm in diameter and 0.07mm thick, embedded in the surface of the insulating plate. When the circuit board is placed tightly against the rock surface, the copper sheets can directly contact the rock. However, due to the roughness of the rock surface, the contact area between the copper sheets and the rock is small, resulting in high contact resistance. To reduce contact resistance, a suitable amount of conductive adhesive is applied between the copper sheets and the rock. Before curing, the conductive adhesive has a certain degree of fluidity, filling uneven areas on the rock surface and increasing the contact area between the copper sheets and the rock. To enable electrical resistivity testing in high-temperature environments, a high-temperature resistant conductive adhesive—graphite-containing conductive adhesive—is used. Each copper sheet is connected to a conductor (copper core). The conductors are separated by an insulating material (polyimide). All conductors converge at one end of the insulating board. At this end, a high-temperature and high-pressure resistant cable is welded to the copper core one by one. The cable diameter is 22AWG, with the copper core being 0.5 mm². The outer shell material is silicone.

[0055] Example 3

[0056] The present invention provides a testing method for a high-density electrical resistivity electrode apparatus for large rock samples under true triaxial conditions, comprising the following steps:

[0057] S1, pre-treat the rock sample and mark the electrode installation position;

[0058] S2, apply the conductive adhesive to the electrode, align and attach the circuit board according to the marked positions, and let it stand at room temperature for 24 hours to allow the conductive adhesive to initially cure; during the initial curing process, perform contact resistance testing; then place it in a high-temperature chamber and set the temperature to 80℃ for constant heating for 24 hours to ensure that the electrode is fully coupled with the rock sample;

[0059] S3. After the circuit board is fixed, apply high-temperature and high-pressure resistant insulating adhesive to the surface of the rock sample and let it stand at room temperature for 24 hours to cure.

[0060] S4, fix the prepared rock sample and the electrode in the high-temperature chamber, connect the cable of the circuit board to the multi-core cable connector in the test chamber, and connect the multi-core cable connector to each corresponding port of the high-density electrical resistivity instrument.

[0061] S5, turn on the high-density electrical resistivity meter and set the relevant parameters, including: test mode, electrode device, and test electrode spacing;

[0062] S6, perform self-test on the performance of each electrode and the high-density electrical resistivity meter, and use the high-density electrical resistivity meter to collect data. If each electrode receives a clear signal, it indicates that the electrode and the high-density electrical resistivity meter are working normally.

[0063] S7, begin measuring the rock resistivity under normal temperature conditions;

[0064] 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 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 normal temperature conditions and perform resistivity inversion.

[0065] S9. After the rock sample resistivity measurement at the target temperature T1 is completed, set the target temperature T2, T2>T1, and set the heating time and holding time. After the furnace temperature rises to the target temperature T2 and is held for a certain period of time, the measurement begins. During the heating process, the resistivity data measured under the T1 condition is exported and resistivity inversion is performed.

[0066] 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, the corresponding heating time is 15 min, and the holding time is 90 min.

[0067] S10. Based on the measured rock resistivity, obtain the rock sample resistivity inversion image under true triaxial conditions. The specific method includes:

[0068] Electrical resistivity measurement calculates the resistivity of rocks by measuring the potential difference and current between electrodes. The specific formula for calculating resistivity depends on the electrode arrangement used. Common arrangements include the Winner method and the Schlumberger method.

[0069] Regardless of the arrangement method, the general formula for calculating resistivity is:

[0070]

[0071] in: apparent resistivity ( ), Geometric factor The measured potential difference (V), The injected current (A).

[0072] The objective function is to minimize the difference between the observed potential difference and the potential difference obtained from the forward modeling through inversion calculation, which is to minimize the error between the observed potential difference and the calculated potential difference.

[0073]

[0074] in, It is the first The potential difference measured in this step It is the potential difference calculated based on the resistivity model. It is a regularization term used to smooth the resistivity model. It is a regularization parameter that controls the weight of the regularization term.

[0075] By continuously iterating and updating the resistivity model, the objective function value is gradually reduced to obtain a rock failure resistivity contour map as an observation value.

[0076] Example 4

[0077] like Figure 1 and Figure 2 As shown in the embodiment of the present invention, the testing method of the high-density electrochemical electrode device for large rock samples under true triaxial conditions is as follows: First, the rock sample is pretreated using a rock grinding machine to smooth and flatten the end face of the rock sample. Before sample preparation, all samples are dried to remove moisture from the rock samples. According to the experimental design, the electrode installation positions are marked and pretreated to facilitate subsequent circuit board fixing and data processing.

[0078] For flexible circuit boards, to reduce contact resistance, a suitable amount of conductive adhesive is evenly applied to the copper sheet. Then, the flexible circuit board is aligned and bonded according to the electrode markings. It is left to stand at room temperature for 24 hours to allow for initial curing. During this period, a certain pressure can be applied to the circuit board to improve contact between the electrodes and the rock. Simultaneously, contact resistance testing is required before the conductive adhesive cures. The circuit board's cable is directly connected to a high-density electrical resistivity meter. The meter is turned on, and contact resistance testing is performed to check for any abnormalities. For electrodes with high contact resistance, the cable soldering must be checked for integrity, and the conductive adhesive must be applied evenly. Once all electrodes show no abnormal contact resistance, the standing period is complete. Finally, the circuit board is placed in a high-temperature chamber and heated at 80℃ for 24 hours to ensure full coupling between the two.

[0079] After the circuit board is fixed, in order to separate the rock from the heat-conducting oil and metal pad, a high-temperature and high-pressure resistant insulating adhesive is applied to the surface of the rock and left to stand at room temperature for 24 hours to cure, so that the two are fully coupled.

[0080] (1) Fix the prepared rock sample and electrodes in a high-temperature test chamber, such as Figure 3 As shown, connect the circuit board cable to the multi-core cable connector in the laboratory, and then connect the multi-core cable connector to the corresponding ports of the high-density electrical resistivity meter.

[0081] (2) Turn on the high-density electrical resistivity meter and set the relevant parameters such as test mode, electrode device, and test electrode spacing.

[0082] (3) Perform self-testing, testing and calibration of the performance of each sensor and the acquisition system. Use a high-density electrical resistivity meter to switch each electrode. If each electrode receives a clear signal, it indicates that the electrode and the electrical resistivity meter are working normally.

[0083] (4) Start measuring the rock resistivity under normal temperature conditions.

[0084] (5) After the resistivity measurement is completed under normal temperature conditions, turn on the intelligent heating device and set the target temperature to 100℃, the heating time to 15min, and the holding time to 90min. To ensure that the overall temperature inside and outside the rock sample reaches the set temperature, wait until the temperature rises to 100℃ and is held constant for 60min before starting the measurement. During the heating process, the resistivity data measured under normal temperature conditions can be exported simultaneously for resistivity inversion.

[0085] (6) After the resistivity measurement of the rock sample at 100℃ is completed, set the target temperature to 250℃, the heating time to 15min, and the holding time to 90min. After the furnace temperature reaches 250℃ and is held for 60min, the measurement begins. During the heating process, the resistivity data measured at 100℃ can be exported simultaneously for resistivity inversion.

[0086] Ensure the equipment is connected, communicates, and performs resistivity imaging according to the above heating and holding times, such as... Figure 4 As shown.

[0087] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0088] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A high-density electrical resistivity electrode device suitable for large rock samples under true triaxial conditions, characterized in that, The device includes multiple circuit boards that are closely attached to the surface of a rock sample. After the circuit boards are fixed, a high-temperature and high-pressure resistant insulating adhesive is applied to the surface of the rock sample. Each circuit board includes an insulating plate, multiple electrodes, and multiple cables. The multiple electrodes are equally spaced on the insulating plate, and each electrode is connected to a cable. Conductive adhesive is applied to the surfaces of the electrodes that contact the rock sample surface. All the cables are connected to a multi-core cable connector, which is connected to the corresponding ports of a high-density electrical resistivity meter. The insulating board features high temperature resistance, high insulation, and flexibility, and is made of polyimide material. The electrode is a circular copper sheet electrode, which is embedded in the surface of the insulating plate.

2. The high-density electrical resistivity electrode device for large rock samples under true triaxial conditions as described in claim 1, characterized in that, The insulating plate is also provided with a plurality of copper cores, one end of which is connected to the electrode, the middle part is arranged parallel to the insulating plate, and the other end is connected to the corresponding cable.

3. The high-density electrical resistivity electrode device for large rock samples under true triaxial conditions as described in claim 1, characterized in that, The conductive adhesive is a high-temperature resistant graphite conductive adhesive.

4. The high-density electrical resistivity electrode device for large rock samples under true triaxial conditions as described in claim 1, characterized in that, The length of the insulating plate is determined according to the number of electrodes and the electrode spacing.

5. A testing method for a high-density electrical resistivity electrode apparatus for large rock samples under true triaxial conditions, comprising the high-density electrical resistivity electrode apparatus for large rock samples under true triaxial conditions as described in any one of claims 1-4, characterized in that, The method includes the following steps: S1, pre-treat the rock sample and mark the electrode installation position; S2, apply the conductive adhesive to the electrodes, align and attach the circuit board according to the marked positions, and let it stand at room temperature for 24 hours to allow the conductive adhesive to initially cure; during the initial curing process, perform contact resistance testing; then place it in a high-temperature chamber and set the temperature to 80℃ for constant heating for 24 hours to ensure full coupling between the electrodes and the rock sample; the method for performing contact resistance testing includes: performing contact resistance testing before the conductive adhesive cures; directly connecting the cable of the circuit board to the high-density electrical resistivity meter, turning on the high-density electrical resistivity meter, and using the high-density electrical resistivity meter to perform contact resistance testing to check for any abnormalities in contact resistance; for electrodes with contact resistance greater than a certain threshold, check whether the cable welding is intact and whether the conductive adhesive is evenly applied; when the contact resistance of all electrodes is normal, wait for the standing period to complete; S3. After the circuit board is fixed, apply high-temperature and high-pressure resistant insulating adhesive to the surface of the rock sample and let it stand at room temperature for 24 hours to cure. S4. Fix the prepared rock sample and the electrode in the high temperature and high pressure true triaxial cavity, connect the cable of the circuit board 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 resistivity instrument. S5, turn on the high-density electrical resistivity meter and set the relevant parameters, including: test mode, electrode device, and test electrode spacing; S6, perform self-test on the performance of each electrode and the high-density electrical resistivity meter, and use the high-density electrical resistivity meter to collect data. If each electrode receives a significant signal, it indicates that the electrode and the high-density electrical resistivity meter are working normally. S7, begin measuring the rock resistivity 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 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 normal temperature conditions and perform resistivity inversion. S9. After the rock sample resistivity measurement at the target temperature T1 is completed, set the target temperature T2, T2>T1, and set the heating time and holding time. After the furnace temperature rises to the target temperature T2 and is held for a certain period of time, the measurement begins. During the heating process, the resistivity data measured under the T1 condition is exported and resistivity inversion is performed. S10: Based on the measured rock resistivity, obtain the rock sample resistivity inversion image under true triaxial conditions.

6. The testing method for the high-density electrical resistivity electrode apparatus for large rock samples under true triaxial conditions as described in claim 5, characterized in that, The pretreatment method includes: pretreating the rock sample using a rock cutting and grinding machine to grind the end face of the rock sample smooth and flat; drying all rock samples to remove moisture from the rock sample; and marking and pretreating the electrode installation positions according to the experimental design.

7. The testing method for the high-density electrical resistivity electrode apparatus for large rock samples under true triaxial conditions as described in claim 5, characterized in that, The method of step S10 includes: The formula for calculating resistivity is: in: Apparent resistivity, unit , Geometric factor The measured potential difference, in volts (V). The injected current is expressed in amperes (A). The objective function is to minimize the difference between the observed potential difference and the potential difference obtained from the forward modeling by performing inversion calculations, i.e., minimizing the error between the observed and calculated potential differences. in, It is the first The potential difference measured in this step It is the potential difference calculated based on the resistivity model. It is a regularization term used to smooth the resistivity model. These are regularization parameters that control the weights of the regularization terms; By continuously iterating and updating the resistivity model, the objective function value is gradually reduced to obtain a rock failure resistivity contour map, which serves as a resistivity inversion image.

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