Device and method for monitoring rock degradation under stress-temperature-seepage coupling

Abstract

The present invention discloses a device and method for monitoring rock degradation over time under stress-temperature-seepage coupling. The device includes a three-dimensional stress loading component, a temperature control component, and a seepage control component. The three-dimensional stress loading component is used to apply axial stress and confining pressure, the temperature control component is used to adjust the heating temperature, and the seepage control component is used to apply seepage pressure. The method includes the following steps: obtaining a correction coefficient; assembling a monitoring device and testing the original porosity and original density of the rock sample; subjecting the rock sample to three-dimensional stress, temperature, and seepage coupling, and calculating the porosity and density of the rock sample at different times using the corrected formula, and finally obtaining the relationship between the porosity, density, and degradation degree of the rock sample over time under three-dimensional stress-temperature-seepage coupling. The present invention simultaneously takes into account the coupling effects of stress, temperature, and seepage fields, and comprehensively reflects the degradation process of rock over time in a complex environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of rock degradation simulation and monitoring, and in particular relates to a device and method for monitoring rock degradation under stress-temperature-seepage coupling. Background Art

[0002] As a key material in various fields, including underground engineering, oil extraction, and geothermal development, rock's long-term stability is affected by multiple environmental factors. In particular, under conditions such as groundwater level fluctuations, temperature fluctuations, and stress loading, rock often experiences multi-field coupling effects, including triaxial stress, temperature, and seepage. These factors interact and jointly influence the rock's mechanical properties and stability. Rock failure is typically caused by the combined effects of multiple factors, such as thermal expansion caused by temperature changes, crack propagation caused by stress changes, and porosity changes caused by seepage pressure. These intertwined factors lead to the propagation of microcracks within the rock and a degradation of its mechanical properties.

[0003] The study of the internal degradation mechanisms of rocks through stress-seepage-temperature coupling is a current hot topic in rock mechanics. Temperature changes can alter the internal stress distribution of rocks through thermal expansion, thereby affecting their mechanical properties. Simultaneously, changes in seepage water pressure can impose additional stress on the rock, altering its crack propagation behavior. This redistribution of internal stress in the rock further influences changes in seepage paths, resulting in a complex three-dimensional stress-seepage-temperature coupling process. This multi-field coupling effect results in highly nonlinear and complex rock degradation, making the prediction of rock degradation processes particularly difficult.

[0004] Traditional rock damage detection methods mostly focus on the effects of a single factor, such as testing rocks under a specific stress or temperature state, and are unable to capture the rock's degradation over time. Existing rock damage detection methods, such as crack growth experiments under stress-temperature field conditions, can reveal the evolution of rock damage under specific field conditions but cannot fully capture the effects of rock degradation over time under the coupling of multiple environmental factors. Alternatively, methods based on strain gauges or stress sensors can typically only monitor the mechanical response of the rock surface, making it difficult to accurately capture the evolution of microscopic pores and degradation within the rock.

[0005] Ultrasonic technology, as a high-precision nondestructive testing method, can detect changes in density and porosity within materials by measuring parameters such as the speed of sound wave propagation and the attenuation coefficient. However, the application of ultrasound in a multi-field coupling environment is still in its early stages of exploration, and there is still a lack of rock degradation monitoring technology that can simultaneously consider the coupled effects of stress, temperature, and seepage. Traditional ultrasonic monitoring methods mostly focus on rock damage detection under a single stress or temperature field, while there is no systematic solution for monitoring rock degradation under multi-field coupling. Therefore, there is an urgent need to develop a rock degradation monitoring device and method under stress-temperature-seepage coupling to accurately monitor the rock degradation process under multi-field coupling in real time, laying the foundation for studying the complex degradation mechanism of rock under multi-field coupling conditions.

[0006] Patent application publication number CN108426782A discloses an ultrasonic monitoring device for rock damage evolution under multi-field coupling. The device comprises a stress loading unit, a water vapor generation unit, and a water vapor circulation unit. The stress loading unit includes an upper pressure head, a lower pressure head, and a hydraulic cylinder. The upper and lower pressure heads are respectively equipped with an ultrasonic transmitting probe and an ultrasonic receiving probe. Hydraulic oil entering the hydraulic cylinder drives the upper and lower pressure heads to apply axial pressure to the rock specimen. The water vapor generation unit includes a solution bottle filled with a chemical solution and a heater at the bottom. The water vapor circulation unit includes an air inlet line and a return line. The air inlet line is connected to the solution bottle at one end and a sealed cover at the other end, while the return line is connected to the solution bottle at one end and a sealed cover at the other end. The water vapor generation unit generates water vapor with a set humidity and temperature. The water vapor circulation unit is used to influence the rock specimen under different humidity and temperature changes, and different chemical solutions can be replaced. The monitoring method includes the following steps: During uniaxial compression, the propagation velocity of the ultrasonic wave in the rock specimen is measured at regular intervals, and the degree of rock damage is defined by the wave velocity. This technical solution has the following defects: (1) Only axial stress is applied to the rock specimen, and confining pressure is lacking, which is inconsistent with the triaxial stress state of underground rock; (2) There is no seepage field, that is, the effect of seepage pressure on rock damage and degradation is not considered. However, in real conditions, seepage is one of the important factors affecting the long-term stability of rock. Seepage pressure will cause changes in rock pores and change the crack propagation behavior of rock. If the effect of the seepage field is not considered, it will not conform to the actual situation and the monitoring results will be inaccurate; (3) During the monitoring process, the degree of rock damage is evaluated only by the propagation velocity of ultrasonic waves in the rock specimen. It is only a macroscopic monitoring and does not consider the microscopic changes such as the pores and internal structure of the rock. The degree of degradation cannot be directly obtained, and the monitoring results are inaccurate. Summary of the Invention

[0007] In order to solve the problems existing in the prior art, the present invention provides a rock aging degradation monitoring device under stress-temperature-seepage coupling. The monitoring device includes a three-dimensional stress loading component, a temperature control component, a seepage control component and a computer control system. The three-dimensional stress loading component is used to apply axial stress to the top and bottom surfaces of the rock sample, respectively, and apply confining pressure to the side of the rock sample. The temperature control component is used to adjust the heating temperature of the rock sample. The seepage control component is used to apply seepage pressure to the rock sample. The computer control system is used to control the axial pressure, confining pressure and heating temperature.

[0008] Preferably, the three-axis stress loading assembly includes a sealing box, an oil cylinder, a connecting shaft, an upper pressure head base, a lower pressure head base, an upper pressure head, a lower pressure head, an ultrasonic transmitting probe, an ultrasonic receiving probe, a first oil tank, a second oil tank, a first oil pressure pump, a second oil pressure pump, a first oil pressure gauge, a second oil pressure gauge, a first oil pipe, and a second oil pipe.

[0009] In any of the above schemes, it is preferred that the sealing box is cylindrical and made of stainless steel, and the upper pressure head socket and the lower pressure head socket are respectively opened at the center of the top surface and the bottom surface of the sealing box, and the interior of the sealing box is a hydraulic chamber; the oil cylinder is arranged above the top surface of the sealing box, and the connecting shaft socket is opened at the center of the top surface of the oil cylinder.

[0010] In any of the above schemes, it is preferred that the upper pressure head and the lower pressure head are cylindrical with equal diameters and are made of stainless steel; the upper pressure head and the lower pressure head are vertically inserted into the sealing box through the upper pressure head socket and the lower pressure head socket respectively, and the rock sample is placed between the upper pressure head and the lower pressure head; the rock sample is cylindrical, and the diameter of the rock sample is smaller than the diameter of the upper pressure head and the lower pressure head.

[0011] The upper pressure head and the lower pressure head are respectively embedded with the ultrasonic transmitting probe and the ultrasonic receiving probe in the center part near the lower surface thereof and the center part near the upper surface thereof; the first water flow channel and the second water flow channel are respectively provided inside the upper pressure head and the lower pressure head.

[0012] In any of the above schemes, it is preferred that the upper pressure head base and the lower pressure head base are connected to the upper pressure head and the lower pressure head respectively, the upper pressure head base is located in the oil cylinder, one end of the connecting shaft is connected to the upper pressure head, and the other end is connected to the oil cylinder through the connecting shaft socket, and the lower pressure head base is located at the bottom of the sealing box.

[0013] The sealing box, the oil cylinder, the upper pressure head, the lower pressure head, the upper pressure head base, the lower pressure head base, the connecting shaft, and the central axis of the rock sample are located on the same vertical line.

[0014] In any of the above schemes, it is preferred that the first oil tank is connected to the oil cylinder through the first oil pipe, the first oil pressure pump and the first oil pressure gauge are provided on the first oil pipe, and the first oil pressure pump is connected to the computer control system through a line; the second oil tank is connected to the hydraulic chamber through the second oil pipe, the second oil pressure pump and the second oil pressure gauge are provided on the second oil pipe, and the second oil pressure pump is connected to the computer control system through a line.

[0015] In any of the above schemes, it is preferred that the temperature control component includes a heater, a heating tube, and a temperature meter, the heater is connected to the heating tube via a wire, the heating tube is arranged in the hydraulic chamber, the temperature meter is arranged at the output end of the heater, and the heater is connected to the computer control system via a line.

[0016] In any of the above schemes, it is preferred that the seepage control component includes a first water tank, a second water tank, a first water pipe, a second water pipe, a first pressure control valve, and a second pressure control valve. The first water tank is connected to the first water flow channel through the first water pipe, and the first pressure control valve is arranged on the first water pipe. The second water tank is connected to the second water flow channel through the second water pipe, and the second pressure control valve is arranged on the second water pipe.

[0017] The present invention further provides a method for monitoring rock degradation under stress-temperature-seepage coupling, using any of the above-mentioned rock degradation monitoring devices under stress-temperature-seepage coupling, and comprising the following steps in order:

[0018] Step 1: Assemble the various components of the monitoring device and a rock sample according to the designed connection relationship, and inspect the monitoring device to ensure that it has good sealing;

[0019] Step 2: Obtaining the correction coefficient. The specific operation is as follows: first, in a state where no triaxial stress is applied, ultrasonic waves are transmitted to the rock sample through the computer control system, and the time taken from the ultrasonic transmitting probe to the ultrasonic receiving probe to receive the ultrasonic waves is collected, thereby calculating the propagation velocity of the ultrasonic waves in the rock sample; then, the triaxial stress loading component is turned on to apply triaxial stress to the rock sample. After the triaxial stress is stabilized, ultrasonic waves are transmitted to the rock sample through the computer control system, and the time taken from the ultrasonic transmitting probe to the ultrasonic receiving probe to receive the ultrasonic waves is collected, thereby calculating the propagation velocity of the ultrasonic waves in the rock sample; finally, the ratio of the propagation velocity of the ultrasonic waves in the rock sample under the triaxial stress state to the propagation velocity of the ultrasonic waves in the rock sample under the triaxial stress state is used as the correction coefficient; after the operation of obtaining the correction coefficient is completed, the rock sample is removed from the monitoring device;

[0020] Step 3: Assemble the various components of the monitoring device and another rock sample according to the designed connection relationship, and inspect the monitoring device to ensure that it has good sealing performance;

[0021] Step 4: Before subjecting the rock sample to the three-dimensional stress, temperature, and seepage coupling, ultrasonic waves are transmitted to the rock sample through a computer control system. The time taken from the ultrasonic transmitter to the ultrasonic receiver is measured, and the original propagation velocity of the ultrasonic wave in the rock sample is calculated. The original porosity and original density of the rock sample are calculated using the time-averaged formula and the volume-weighted formula, respectively.

[0022] Step 5: Perform three-dimensional stress, temperature, and seepage coupling on the rock sample. The specific operation is to first turn on the seepage control component to apply seepage pressure to the rock sample. After the seepage pressure stabilizes, the three-dimensional stress loading component and the temperature control component are turned on at the same time to apply three-dimensional stress and heat to the rock sample respectively. When the three-dimensional stress, temperature, and seepage pressure all reach the set values ​​and remain stable, the coupling is completed;

[0023] Step 6: While keeping the triaxial stress, temperature, and seepage pressure unchanged, the propagation velocity of the ultrasonic wave in the rock sample is tested once at a certain interval. At the same time, the porosity and density of the rock sample at that time are calculated respectively by the modified time-averaged formula and the volume-weighted formula. The ratio of the porosity at that time to the original porosity is used as the parameter of the degradation degree of the rock sample at that time. Then, the changes of the porosity, density, and degradation degree of the rock sample at a series of different times with time are obtained, and finally the relationship between the porosity, density, and degradation degree of the rock sample with time under the triaxial stress-temperature-seepage coupling is obtained.

[0024] In steps 1 and 3, the rock sample is obtained from underground core drilling, and its surface is intact and undamaged and its internal structure is complete; the diameter of the rock sample shown is 50 mm and the height is 100 mm.

[0025] In step 2, triaxial stress is applied to the rock sample according to the triaxial stress conditions at the site where the rock sample is drilled; the correction coefficient formula is: ,in:

[0026] ——correction factor, dimensionless;

[0027] ——The propagation velocity of ultrasonic waves in rock specimens without triaxial stress, m / s;

[0028] ——The propagation velocity of ultrasonic waves in rock specimens under triaxial stress state, m / s.

[0029] The propagation speed of ultrasonic waves in rock samples is equal to the ratio of the height of the rock sample to the propagation time.

[0030] In step 4, the time average formula is ,in:

[0031] ——the original porosity of the rock sample, dimensionless;

[0032] ——Original propagation velocity of ultrasonic wave in rock sample, m / s;

[0033] ——The propagation speed of ultrasonic waves in skeletal minerals, m / s;

[0034] ——The propagation speed of ultrasonic waves in pore fluids, m / s.

[0035] The propagation speed of ultrasonic waves in rock samples is equal to the ratio of the height of the rock sample to the propagation time.

[0036] The volume weighted formula is ,in:

[0037] ——Original density of rock sample, g / cm 3 ;

[0038] ——Density of framework minerals, g / cm 3 ;

[0039] ——density of pore fluid, g / cm 3 ;

[0040] ——The original porosity of the rock sample, dimensionless.

[0041] In step 6, the corrected time average formula is ,in:

[0042] ——the porosity of the rock sample at different times, dimensionless;

[0043] ——The propagation speed of ultrasonic waves in rock samples at different times, m / s;

[0044] ——The propagation speed of ultrasonic waves in skeletal minerals, m / s;

[0045] ——The propagation speed of ultrasonic waves in pore fluid, m / s;

[0046] ——Correction coefficient, dimensionless.

[0047] The propagation speed of ultrasonic waves in rock samples is equal to the ratio of the height of the rock sample to the propagation time.

[0048] The revised volume weighted formula is: ,in:

[0049] ——Density of rock samples at different times, g / cm 3 ;

[0050] ——Density of framework minerals, g / cm 3 ;

[0051] ——density of pore fluid, g / cm 3 ;

[0052] ——the porosity of the rock sample at different times, dimensionless;

[0053] ——Correction coefficient, dimensionless.

[0054] The degradation degree of the rock sample is ,in:

[0055] ——deterioration degree of rock sample, dimensionless;

[0056] ——the porosity of the rock sample at different times, dimensionless;

[0057] ——The original porosity of the rock sample, dimensionless.

[0058] The porosity, density and degradation of rock samples at different times are shown in the series of changes over time. The porosity is expressed as , the density is expressed as , the degradation degree is expressed as 、 .

[0059] The heater, heating tube, thermometer, fuel tank, fuel pump, fuel pipe, fuel pressure gauge, water tank, water pipe, pressure control valve, and computer control system used in the present invention are all conventional equipment or instruments, with no special requirements for model or structure. The computer control system includes a computer, control panel, switches, interfaces, and other functions, and has data processing and storage capabilities.

[0060] The rock sample can be placed in the sealed box through the upper pressure head socket or the lower pressure head socket. For example, in actual operation, the lower pressure head can be inserted into the sealed box first, and a lower pressure head base is set at the bottom of the lower pressure head. Then the rock sample is inserted into the sealed box from the upper pressure head socket, and the rock sample is made to fall vertically on the top surface of the lower pressure head. Then, the upper pressure head is inserted into the sealed box so that the rock sample is located between the upper pressure head and the lower pressure head.

[0061] After the various components of the monitoring device and the rock samples are assembled together, they need to achieve a good sealing state. The connection parts of the components or the parts with gaps need to be sealed with sealing rings, gaskets or other sealing materials.

[0062] The propagation velocity of ultrasonic waves in skeleton minerals and pore fluids is a fixed value, and the density of skeleton minerals and pore fluids is also a fixed value. These fixed values ​​can be determined according to the type of rock.

[0063] The device and method for monitoring rock degradation over time under stress-temperature-seepage coupling of the present invention have the following beneficial effects: It enables comprehensive monitoring under multi-field coupling, while taking into account the combined effects of multiple factors such as triaxial stress, temperature, and seepage, comprehensively reflecting the degradation process of rock in complex environments and providing more comprehensive data support than traditional single-field monitoring. The high sensitivity and real-time nature of ultrasonic technology enables effective monitoring of rock damage in its early stages, thus providing an accurate basis for project safety assessments. The computer control system can automatically adjust the operating parameters of each unit and issue a warning when damage reaches a preset threshold, ensuring the safety of rock projects.

[0064] The present invention can simultaneously simulate the multi-field coupling of three-dimensional stress, temperature, and seepage, providing a comprehensive platform for monitoring rock degradation. The combined effects of three-dimensional stress, temperature, and seepage make the rock degradation process more complex. Traditional single-field monitoring methods cannot effectively capture these complex dynamic changes. However, the present invention can accurately monitor the degradation state of rock under multi-field coupling conditions. By accurately measuring the time-dependent degradation of the rock (microscopic monitoring), the present invention can predict the degradation risk of rock under the conditions of three-dimensional stress, temperature, and seepage coupling, allowing appropriate protective measures to be taken in advance. The present invention can adjust the three-dimensional stress, temperature, and seepage conditions in real time during the experiment and simultaneously perform ultrasonic monitoring, providing dynamic rock degradation data over time. This allows researchers to accurately observe the time-dependent degradation process of rock under a multi-field coupling environment, ensuring the reliability and timeliness of the experimental data.

[0065] The present invention introduces a correction coefficient when calculating the porosity and density of rocks. Due to the action of triaxial stress, the pore channels inside the rock are compressed, and the skeleton density and seepage channels of the rock are affected. Therefore, the correction coefficient is introduced to make the monitoring results more accurate and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 Schematic diagram of the overall structure of a monitoring device in a preferred embodiment of a device and method for monitoring rock degradation under stress-temperature-seepage coupling according to the present invention;

[0067] Figure 2 for Figure 1 A schematic structural diagram of a three-dimensional stress loading assembly in the illustrated embodiment;

[0068] Figure 3 for Figure 1 A schematic structural diagram of the temperature control assembly in the illustrated embodiment;

[0069] Figure 4 for Figure 1 A schematic structural diagram of the seepage control assembly in the illustrated embodiment;

[0070] Figure 5 Actual photos of the rock samples used in the examples and comparative examples;

[0071] Figure 6 The porosity of the rock samples in the embodiment and the comparative example varies with time;

[0072] Figure 7 The relationship between the density of the rock samples in the embodiment and the comparative example and the time;

[0073] Figure 8 is the relationship between the degradation degree of the rock samples in the embodiment and the comparative example and the time;

[0074] Figure 9 The internal structure of the rock sample in the embodiment after 24 hours of aging degradation;

[0075] Figure 10 This is the internal structure state of the rock sample of the comparative example after 24 hours of aging degradation.

[0076] Notes in the figure:

[0077] 1- three-axis stress loading assembly, 101 sealing box, 102 oil cylinder, 103- connecting shaft, 104- upper pressure head base, 105- lower pressure head base, 106- upper pressure head, 107- lower pressure head, 108- ultrasonic transmitting probe, 109- ultrasonic receiving probe, 110- first oil tank, 111- second oil tank, 112- first oil pressure pump, 113- second oil pressure pump, 114- first oil pressure gauge, 115- second oil pressure gauge, 116- first oil pipe, 117- second oil pipe, 118- hydraulic chamber, 119- first water flow channel, 120- second water flow channel;

[0078] 2-temperature control assembly, 201-heater, 202-heating tube, 203-temperature gauge;

[0079] 3-seepage control assembly, 301-first water tank, 302-second water tank, 303-first water pipe, 304-second water pipe, 305-first pressure control valve, 306-second pressure control valve;

[0080] 4-Computer control system;

[0081] 5- Rock specimens. DETAILED DESCRIPTION

[0082] In order to further understand the content of the present invention, the present invention will be described in detail below with reference to specific embodiments.

[0083] like Figure 1-4 As shown, according to a preferred embodiment of the rock aging degradation monitoring device under stress-temperature-seepage coupling of the present invention, the monitoring device includes a three-dimensional stress loading component 1, a temperature control component 2, a seepage control component 3 and a computer control system 4. The three-dimensional stress loading component 1 is used to apply axial stress to the top and bottom surfaces of the rock sample 5, respectively, and apply confining pressure to the side of the rock sample 5. The temperature control component 2 is used to adjust the heating temperature of the rock sample 5. The seepage control component 3 is used to apply seepage pressure to the rock sample 5. The computer control system 4 is used to control the axial pressure, confining pressure and heating temperature.

[0084] The three-axis stress loading assembly 1 includes a sealing box 101, an oil cylinder 102, a connecting shaft 103, an upper pressure head base 104, a lower pressure head base 105, an upper pressure head 106, a lower pressure head 107, an ultrasonic transmitting probe 108, an ultrasonic receiving probe 109, a first oil tank 110, a second oil tank 111, a first oil pressure pump 112, a second oil pressure pump 113, a first oil pressure gauge 114, a second oil pressure gauge 115, a first oil pipe 116, and a second oil pipe 117.

[0085] The sealing box 101 is cylindrical and made of stainless steel. The upper pressure head socket and the lower pressure head socket are respectively provided at the center of the top surface and the bottom surface of the sealing box 101. The interior of the sealing box 101 is a hydraulic chamber 118. The oil cylinder 102 is arranged above the top surface of the sealing box 101, and the connecting shaft socket is provided at the center of the top surface of the oil cylinder 102.

[0086] The upper pressure head 106 and the lower pressure head 107 are cylindrical with equal diameters and are made of stainless steel; the upper pressure head 106 and the lower pressure head 107 are vertically inserted into the sealing box 101 through the upper pressure head socket and the lower pressure head socket respectively, and the rock sample 5 is placed between the upper pressure head 106 and the lower pressure head 107; the rock sample 5 is cylindrical, and the diameter of the rock sample 5 is smaller than the diameters of the upper pressure head 106 and the lower pressure head 107.

[0087] The upper pressure head 106 and the lower pressure head 107 are respectively embedded with the ultrasonic transmitting probe 108 and the ultrasonic receiving probe 109 near the center of its lower surface; the first water flow channel 119 and the second water flow channel 120 are respectively provided inside the upper pressure head 106 and the lower pressure head 107.

[0088] The upper pressure head base 104 and the lower pressure head base 105 are connected to the upper pressure head 106 and the lower pressure head 107 respectively. The upper pressure head base 104 is located in the oil cylinder 102. One end of the connecting shaft 103 is connected to the upper pressure head 106, and the other end is connected to the oil cylinder 102 through the connecting shaft socket. The lower pressure head base 105 is located at the bottom of the sealing box 101.

[0089] The sealing box 101 , the oil cylinder 102 , the upper pressure head 106 , the lower pressure head 107 , the upper pressure head base 104 , the lower pressure head base 105 , the connecting shaft 103 , and the central axis of the rock sample 5 are located on the same vertical line.

[0090] The first oil tank 110 is connected to the oil cylinder 102 through the first oil pipe 116, and the first oil pressure pump 112 and the first oil pressure gauge 114 are provided on the first oil pipe 116. The first oil pressure pump 112 is connected to the computer control system 4 through a line; the second oil tank 111 is connected to the hydraulic chamber 118 through the second oil pipe 117, and the second oil pressure pump 113 and the second oil pressure gauge 115 are provided on the second oil pipe 117. The second oil pressure pump 113 is connected to the computer control system 4 through a line.

[0091] The temperature control component 2 includes a heater 201, a heating tube 202, and a temperature gauge 203. The heater 201 is connected to the heating tube 202 via a wire. The heating tube 202 is arranged in the hydraulic chamber 118. The temperature gauge 203 is arranged at the output end of the heater 201. The heater 201 is connected to the computer control system 4 via a line.

[0092] The seepage control component 3 includes a first water tank 301, a second water tank 302, a first water pipe 303, a second water pipe 304, a first pressure control valve 305, and a second pressure control valve 306. The first water tank 301 is connected to the first water flow channel 119 through the first water pipe 303, the first pressure control valve 305 is arranged on the first water pipe 303, the second water tank 302 is connected to the second water flow channel 120 through the second water pipe 304, and the second pressure control valve 306 is arranged on the second water pipe 304.

[0093] This embodiment further provides a method for monitoring rock degradation under stress-temperature-seepage coupling, using the above-mentioned rock degradation monitoring device under stress-temperature-seepage coupling, and including the following steps in order:

[0094] Step 1: Assemble the various components of the monitoring device and a rock sample according to the designed connection relationship, and inspect the monitoring device to ensure that it has good sealing;

[0095] Step 2: Obtaining the correction coefficient. The specific operation is as follows: first, in a state where no triaxial stress is applied, ultrasonic waves are transmitted to the rock sample through the computer control system, and the time taken from the ultrasonic transmitting probe to the ultrasonic receiving probe to receive the ultrasonic waves is collected, thereby calculating the propagation velocity of the ultrasonic waves in the rock sample; then, the triaxial stress loading component is turned on to apply triaxial stress to the rock sample. After the triaxial stress is stabilized, ultrasonic waves are transmitted to the rock sample through the computer control system, and the time taken from the ultrasonic transmitting probe to the ultrasonic receiving probe to receive the ultrasonic waves is collected, thereby calculating the propagation velocity of the ultrasonic waves in the rock sample; finally, the ratio of the propagation velocity of the ultrasonic waves in the rock sample under the triaxial stress state to the propagation velocity of the ultrasonic waves in the rock sample under the triaxial stress state is used as the correction coefficient; after the operation of obtaining the correction coefficient is completed, the rock sample is removed from the monitoring device;

[0096] Step 3: Assemble the various components of the monitoring device and another rock sample according to the designed connection relationship, and inspect the monitoring device to ensure that it has good sealing performance;

[0097] Step 4: Before subjecting the rock sample to the three-dimensional stress, temperature, and seepage coupling, ultrasonic waves are transmitted to the rock sample through a computer control system. The time taken from the ultrasonic transmitter to the ultrasonic receiver is measured, and the original propagation velocity of the ultrasonic wave in the rock sample is calculated. The original porosity and original density of the rock sample are calculated using the time-averaged formula and the volume-weighted formula, respectively.

[0098] Step 5: Perform three-dimensional stress, temperature, and seepage coupling on the rock sample. The specific operation is to first turn on the seepage control component to apply seepage pressure to the rock sample. After the seepage pressure stabilizes, the three-dimensional stress loading component and the temperature control component are turned on at the same time to apply three-dimensional stress and heat to the rock sample respectively. When the three-dimensional stress, temperature, and seepage pressure all reach the set values ​​and remain stable, the coupling is completed;

[0099] Step 6: While keeping the triaxial stress, temperature, and seepage pressure unchanged, the propagation velocity of the ultrasonic wave in the rock sample is tested once at a certain interval. At the same time, the porosity and density of the rock sample at that time are calculated respectively by the modified time-averaged formula and the volume-weighted formula. The ratio of the porosity at that time to the original porosity is used as the parameter of the degradation degree of the rock sample at that time. Then, the changes of the porosity, density, and degradation degree of the rock sample at a series of different times with time are obtained, and finally the relationship between the porosity, density, and degradation degree of the rock sample with time under the triaxial stress-temperature-seepage coupling is obtained.

[0100] In steps 1 and 3, the rock sample is obtained from underground core drilling, and its surface is intact and undamaged and its internal structure is complete; the diameter of the rock sample shown is 50 mm and the height is 100 mm.

[0101] In step 2, triaxial stress is applied to the rock sample according to the triaxial stress conditions at the site where the rock sample is drilled; the correction coefficient formula is: ,in:

[0102] ——correction factor, dimensionless;

[0103] ——The propagation velocity of ultrasonic waves in rock specimens without triaxial stress, m / s;

[0104] ——The propagation velocity of ultrasonic waves in rock specimens under triaxial stress state, m / s.

[0105] The propagation speed of ultrasonic waves in rock samples is equal to the ratio of the height of the rock sample to the propagation time.

[0106] In step 4, the time average formula is ,in:

[0107] ——the original porosity of the rock sample, dimensionless;

[0108] ——Original propagation velocity of ultrasonic wave in rock sample, m / s;

[0109] ——The propagation speed of ultrasonic waves in skeletal minerals, m / s;

[0110] ——The propagation speed of ultrasonic waves in pore fluids, m / s.

[0111] The propagation speed of ultrasonic waves in rock samples is equal to the ratio of the height of the rock sample to the propagation time.

[0112] The volume weighted formula is ,in:

[0113] ——Original density of rock sample, g / cm 3 ;

[0114] ——Density of framework minerals, g / cm 3 ;

[0115] ——density of pore fluid, g / cm 3;

[0116] ——The original porosity of the rock sample, dimensionless.

[0117] In step 6, the corrected time average formula is ,in:

[0118] ——the porosity of the rock sample at different times, dimensionless;

[0119] ——The propagation speed of ultrasonic waves in rock samples at different times, m / s;

[0120] ——The propagation speed of ultrasonic waves in skeletal minerals, m / s;

[0121] ——The propagation speed of ultrasonic waves in pore fluid, m / s;

[0122] ——Correction coefficient, dimensionless.

[0123] The propagation speed of ultrasonic waves in rock samples is equal to the ratio of the height of the rock sample to the propagation time.

[0124] The revised volume weighted formula is: ,in:

[0125] ——Density of rock samples at different times, g / cm 3 ;

[0126] ——Density of framework minerals, g / cm 3 ;

[0127] ——density of pore fluid, g / cm 3 ;

[0128] ——the porosity of the rock sample at different times, dimensionless;

[0129] ——Correction coefficient, dimensionless.

[0130] The degradation degree of the rock sample is ,in:

[0131] ——deterioration degree of rock sample, dimensionless;

[0132] ——the porosity of the rock sample at different times, dimensionless;

[0133] ——The original porosity of the rock sample, dimensionless.

[0134] The porosity, density and degradation of rock samples at different times are shown in the series of changes over time. The porosity is expressed as , the density is expressed as , the degradation degree is expressed as \ .

[0135] In this embodiment, the heater, heating tube, thermometer, fuel tank, fuel pump, fuel pipe, fuel pressure gauge, water tank, water pipe, pressure control valve, and computer control system used are all conventional equipment or instruments, with no specific requirements for model or structure. The computer control system includes a computer, control panel, switches, and interfaces, and has functions such as data processing and storage.

[0136] The rock sample can be placed into the sealed box through the upper or lower pressure head insertion hole. In actual operation of this embodiment, the lower pressure head is first inserted into the sealed box, and a lower pressure head base is provided at the bottom of the lower pressure head. Then, the rock sample is inserted into the sealed box through the upper pressure head insertion hole, and the rock sample is vertically dropped on the top surface of the lower pressure head. Then, the upper pressure head is inserted into the sealed box so that the rock sample is located between the upper and lower pressure heads.

[0137] After the monitoring device components and rock samples are assembled, they must be well sealed. Sealing rings, gaskets, or other sealing materials are used at joints or gaps between components. The propagation velocity of ultrasound waves in skeletal minerals and pore fluids is fixed, as are the densities of these minerals and pore fluids. These values ​​are determined based on the rock type.

[0138] The device and method for monitoring rock degradation under stress-temperature-seepage coupling of this embodiment have the following beneficial effects: (1) It simultaneously considers the combined effects of multiple factors such as triaxial stress, temperature, and seepage, and comprehensively reflects the degradation process of rock in a complex environment. (2) It can simultaneously simulate the multi-field coupling of triaxial stress, temperature, and seepage, providing a comprehensive degradation monitoring platform for rock. By accurately measuring the degradation conditions inside the rock (microscopic monitoring), it can predict the degradation risk of rock under the conditions of triaxial stress, temperature, and seepage coupling, and take corresponding protective measures in advance. (3) It can adjust the triaxial stress, temperature, and seepage conditions in real time during the experiment, and simultaneously perform ultrasonic monitoring, providing dynamic rock degradation data. (4) A correction coefficient is introduced when calculating the porosity and density of the rock. Due to the effect of triaxial stress, the pore channels inside the rock are compressed, and the skeleton density and seepage channels of the rock are affected. Therefore, the correction coefficient is introduced to make the monitoring results more accurate and reliable.

[0139] In this embodiment, =3268m / s, =3921.6m / s, calculate the correction factor =1.2; =4500m / s, =1501m / s, =3260m / s, the original porosity of the rock sample is calculated =0.181; =2.65g / cm 3 、 =0.191g / cm 3 , the original density of the rock sample is calculated =2.794g / cm 3 .

[0140] In this embodiment, under the combined action of triaxial stress (upper and lower axial pressure, confining pressure), temperature (50°C), and seepage pressure, the propagation velocity of ultrasonic waves in the rock sample is tested every hour within 24 hours. Then, the porosity, density, and degradation degree of the rock sample at the corresponding time are calculated using the modified time-averaged formula and volume-weighted formula, respectively. The temporal relationship of the porosity, density, and degradation degree of the rock sample under the triaxial stress-temperature-seepage coupling is then obtained.

[0141] The following design is a comparative example: the test is carried out using a traditional test device and test method, where only upper and lower axial stresses are applied to the rock sample, without applying confining pressure or seepage pressure; no correction coefficient is introduced, that is, the time-averaged formula and the volume-weighted formula are not corrected, so the porosity, density, degradation degree, etc. of the rock sample calculated are also uncorrected results; the size of the rock sample, the test temperature, the test cycle, the test time interval, etc. are the same as those in the embodiment of the present invention; the parameters such as the propagation velocity of ultrasonic waves in skeleton minerals and pore fluids, the density of skeleton minerals and pore fluids, etc. are the same as those in the embodiment of the present invention; and finally, the relationship between the porosity, density, and degradation degree of the rock sample under axial stress alone and the time is obtained.

[0142] The actual photos of the rock samples used in the above examples and comparative examples are as follows: Figure 5 As shown; the relationship between the porosity, density and degradation degree of the rock samples in the above embodiment and comparative example over time is shown as follows: Figure 6 、 Figure 7 、 Figure 8 The internal structure of the rock samples of the above embodiment and comparative example after 24h aging degradation is shown as follows: Figure 9 、 Figure 10 shown.

[0143] from Figure 6-Figure 8 The comparison results show that the relationship between the porosity, density and degradation degree of the rock sample measured by the monitoring device and monitoring method of this embodiment is closer to the actual situation, and the test results are more accurate and reliable. Figure 9 and Figure 10 It can be seen that after 24 hours of aging degradation, the rock sample of this embodiment has a compact internal structure and fewer pores, while the rock sample of the comparative example has more pores after 24 hours of aging degradation.

[0144] Special Note: The technical solution of this invention involves numerous parameters, and the synergistic effects between these parameters must be comprehensively considered to achieve the beneficial effects and significant improvements of this invention. Furthermore, the value ranges of each parameter in the technical solution were obtained through extensive testing. The inventors have recorded extensive experimental data for each parameter and their combinations. Due to space limitations, the specific experimental data will not be disclosed here.

[0145] Those skilled in the art will readily appreciate that the stress-temperature-seepage coupled rock degradation monitoring device and method of the present invention encompass any combination of the components described in the Summary and Detailed Description sections of the present invention specification, as well as the components illustrated in the accompanying drawings. Due to space limitations and to maintain clarity, not all of the various solutions resulting from these combinations are described. Any modifications, equivalent substitutions, and improvements within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for monitoring rock degradation under stress-temperature-seepage coupling, characterized in that: The monitoring method comprises the following steps in chronological order: Step 1: Assemble the various components of the monitoring device and a rock sample according to the designed connection relationship, and inspect the monitoring device to ensure that it has good sealing; Step 2: Obtaining the correction coefficient. The specific operation is as follows: first, in a state where no triaxial stress is applied, ultrasonic waves are transmitted to the rock sample through the computer control system, and the time taken from the ultrasonic transmitting probe to the ultrasonic receiving probe to receive the ultrasonic waves is collected, thereby calculating the propagation velocity of the ultrasonic waves in the rock sample; then, the triaxial stress loading component is turned on to apply triaxial stress to the rock sample. After the triaxial stress is stabilized, ultrasonic waves are transmitted to the rock sample through the computer control system, and the time taken from the ultrasonic transmitting probe to the ultrasonic receiving probe to receive the ultrasonic waves is collected, thereby calculating the propagation velocity of the ultrasonic waves in the rock sample; finally, the ratio of the propagation velocity of the ultrasonic waves in the rock sample under the triaxial stress state to the propagation velocity of the ultrasonic waves in the rock sample under the triaxial stress state is used as the correction coefficient; after the operation of obtaining the correction coefficient is completed, the rock sample is removed from the monitoring device; Step 3: Assemble the various components of the monitoring device and another rock sample according to the designed connection relationship, and inspect the monitoring device to ensure that it has good sealing performance; Step 4: Before subjecting the rock sample to the three-dimensional stress, temperature, and seepage coupling, ultrasonic waves are transmitted to the rock sample through a computer control system. The time taken from the ultrasonic transmitter to the ultrasonic receiver is measured, and the original propagation velocity of the ultrasonic wave in the rock sample is calculated. The original porosity and original density of the rock sample are calculated using the time-averaged formula and the volume-weighted formula, respectively. Step 5: Perform three-dimensional stress, temperature, and seepage coupling on the rock sample. The specific operation is to first turn on the seepage control component to apply seepage pressure to the rock sample. After the seepage pressure stabilizes, the three-dimensional stress loading component and the temperature control component are turned on at the same time to apply three-dimensional stress and heat to the rock sample respectively. When the three-dimensional stress, temperature, and seepage pressure all reach the set values ​​and remain stable, the coupling is completed; Step 6: While keeping the triaxial stress, temperature, and seepage pressure constant, the propagation velocity of the ultrasonic wave in the rock sample is tested at regular intervals. At the same time, the porosity and density of the rock sample at that time are calculated using the modified time-averaged formula and the volume-weighted formula, and the ratio of the porosity at that time to the original porosity is used as the parameter of the degradation degree of the rock sample at that time. The changes in the porosity, density, and degradation degree of the rock sample at a series of different times with time are then obtained, and finally the relationship between the porosity, density, and degradation degree of the rock sample with time under the triaxial stress-temperature-seepage coupling is obtained; The corrected time average formula is: in, ——the porosity of the rock sample at different times, dimensionless; ——The propagation speed of ultrasonic waves in rock samples at different times, m / s; ——The propagation speed of ultrasonic waves in skeletal minerals, m / s; ——The propagation speed of ultrasonic waves in pore fluid, m / s; ——correction factor, dimensionless; The revised volume weighted formula is: ,in, ——Density of rock samples at different times, g / cm 3 ; ——Density of framework minerals, g / cm 3 ; ——density of pore fluid, g / cm 3 ; ——the porosity of the rock sample at different times, dimensionless; ——Correction coefficient, dimensionless.

2. The rock aging degradation monitoring method under stress-temperature-seepage coupling according to claim 1 is characterized in that: In steps 1 and 3, the rock sample is obtained from underground core drilling, and its surface is intact and undamaged and its internal structure is complete; the diameter of the rock sample is 50 mm and the height is 100 mm; In step 2, triaxial stress is applied to the rock sample according to the triaxial stress conditions at the site where the rock sample is drilled; The correction coefficient formula is in, λ——correction coefficient, dimensionless; V0 is the propagation velocity of ultrasonic waves in rock specimens without triaxial stress, m / s; V is the propagation velocity of ultrasonic waves in rock specimens under triaxial stress, m / s; The propagation speed of ultrasonic waves in rock samples is equal to the ratio of the height of the rock sample to the propagation time; In step 4, the time average formula is in, ——the original porosity of the rock sample, dimensionless; ——Original propagation velocity of ultrasonic wave in rock sample, m / s; ——The propagation speed of ultrasonic waves in skeletal minerals, m / s; ——The propagation speed of ultrasonic waves in pore fluid, m / s; The propagation speed of ultrasonic waves in rock samples is equal to the ratio of the height of the rock sample to the propagation time; The volume weighted formula is ,in, ——Original density of rock sample, g / cm 3 ; ——Density of framework minerals, g / cm 3 ; ——density of pore fluid, g / cm 3 ; ——the original porosity of the rock sample, dimensionless; In step 6, the degradation degree of the rock sample is in, D is the degree of degradation of the rock sample, dimensionless; ——the porosity of the rock sample at different times, dimensionless; ——the original porosity of the rock sample, dimensionless; The porosity, density and degradation of rock samples at different times are shown in the series of changes over time. The porosity is expressed as , the density is expressed as , the degradation degree is expressed as 、 .

3. The rock aging degradation monitoring method under stress-temperature-seepage coupling according to claim 2 is characterized in that: A rock aging degradation monitoring device under stress-temperature-seepage coupling was used. The monitoring device included a three-dimensional stress loading component, a temperature control component, a seepage control component, and a computer control system. The three-dimensional stress loading component was used to apply axial stress to the top and bottom surfaces of the rock sample, respectively, and to apply confining pressure to the side surfaces of the rock sample. The temperature control component was used to adjust the heating temperature of the rock sample. The seepage control component was used to apply seepage pressure to the rock sample. The computer control system was used to control the axial pressure, confining pressure, and heating temperature.

4. The rock aging degradation monitoring method under stress-temperature-seepage coupling according to claim 3 is characterized in that: The three-axis stress loading assembly includes a sealing box, an oil cylinder, a connecting shaft, an upper pressure head base, a lower pressure head base, an upper pressure head, a lower pressure head, an ultrasonic transmitting probe, an ultrasonic receiving probe, a first oil tank, a second oil tank, a first oil pressure pump, a second oil pressure pump, a first oil pressure gauge, a second oil pressure gauge, a first oil pipe, and a second oil pipe.

5. The rock aging degradation monitoring method under stress-temperature-seepage coupling according to claim 4 is characterized in that: The sealing box is cylindrical and made of stainless steel. The upper pressure head socket and the lower pressure head socket are respectively provided at the center of the top surface and the bottom surface of the sealing box. The interior of the sealing box is a hydraulic chamber. The oil cylinder is arranged above the top surface of the sealing box, and the connecting shaft socket is provided at the center of the top surface of the oil cylinder.

6. The rock aging degradation monitoring method under stress-temperature-seepage coupling according to claim 5 is characterized in that: The upper pressure head and the lower pressure head are cylindrical with equal diameters and are made of stainless steel; the upper pressure head and the lower pressure head are vertically inserted into the sealing box through the upper pressure head insertion hole and the lower pressure head insertion hole respectively, and the rock sample is placed between the upper pressure head and the lower pressure head; the rock sample is cylindrical, and the diameter of the rock sample is smaller than the diameters of the upper pressure head and the lower pressure head; The upper pressure head and the lower pressure head are respectively embedded with the ultrasonic transmitting probe and the ultrasonic receiving probe in the center part near the lower surface thereof and the center part near the upper surface thereof; the first water flow channel and the second water flow channel are respectively provided inside the upper pressure head and the lower pressure head.

7. The rock aging degradation monitoring method under stress-temperature-seepage coupling according to claim 6 is characterized in that: The upper pressure head base and the lower pressure head base are connected to the upper pressure head and the lower pressure head respectively, the upper pressure head base is located in the oil cylinder, one end of the connecting shaft is connected to the upper pressure head, and the other end is connected to the oil cylinder through the connecting shaft socket, and the lower pressure head base is located at the bottom of the sealing box; The sealing box, the oil cylinder, the upper pressure head, the lower pressure head, the upper pressure head base, the lower pressure head base, the connecting shaft, and the central axis of the rock sample are located on the same vertical line.

8. The rock aging degradation monitoring method under stress-temperature-seepage coupling according to claim 7 is characterized in that: The first oil tank is connected to the oil cylinder through the first oil pipe, the first oil pressure pump and the first oil pressure gauge are provided on the first oil pipe, and the first oil pressure pump is connected to the computer control system through a line; the second oil tank is connected to the hydraulic chamber through the second oil pipe, the second oil pressure pump and the second oil pressure gauge are provided on the second oil pipe, and the second oil pressure pump is connected to the computer control system through a line.

9. The rock aging degradation monitoring method under stress-temperature-seepage coupling according to claim 8 is characterized in that: The temperature control component includes a heater, a heating tube, and a temperature meter. The heater is connected to the heating tube via a wire. The heating tube is arranged in the hydraulic chamber. The temperature meter is arranged at the output end of the heater. The heater is connected to the computer control system via a line.

10. The rock aging degradation monitoring method under stress-temperature-seepage coupling according to claim 9 is characterized in that: The seepage control component includes a first water tank, a second water tank, a first water pipe, a second water pipe, a first pressure control valve, and a second pressure control valve. The first water tank is connected to the first water flow channel through the first water pipe, and the first pressure control valve is arranged on the first water pipe. The second water tank is connected to the second water flow channel through the second water pipe, and the second pressure control valve is arranged on the second water pipe.

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