Sandstone damage simulation experiment device and method based on seepage-crystallization coupling effect

Abstract

The invention discloses a sandstone damage simulation experiment device and method based on a seepage-crystallization coupling effect, and belongs to the technical field of mechanical property testing of geotechnical materials. Aiming at the limitation that the seepage-crystallization coupling effect of sandstone in a complex geological environment cannot be effectively simulated in the prior art, the experimental device is designed. According to the device, through the design of a single opening in the bottom, a sample is axially fixed through an O-shaped ring sleeve, a seepage boundary is formed, after a solution with a preset concentration is injected, the seepage rate of the solution is controlled through pressurization of an air compressor, evaporative crystallization is accelerated in combination with directional heating and air supply at the bottom, and dynamic crystallization process simulation of salt in sandstone pores is achieved. The sandstone damage simulation method for realizing solution crystallization through controllable seepage is provided, and a scientific basis is provided for evaluating the durability of sandstone engineering. Through integrated design, precise control and dynamic observation, the experimental precision is remarkably improved, the application range is widened, and the device has important significance in promoting the development of sandstone damage mechanism research in the field of geotechnical engineering.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering, and particularly to a sandstone damage simulation experimental device and method based on the coupling action of seepage - crystallization. Background Art

[0002] In the technical field of geotechnical engineering, sandstone, as a widely distributed rock type, the research on its mechanical properties and damage mechanism is of crucial significance for engineering safety and stability. Especially in groundwater environments, saline soil areas or certain specific conditions in geotechnical engineering, sandstone may be subjected to the dual actions of seepage and salt crystallization, resulting in significant changes in its mechanical properties and even triggering engineering disasters.

[0003] At present, there is already a certain research foundation for the damage mechanism of sandstone under single seepage or single crystallization. However, the research on the damage mechanism of sandstone under the coupling action of seepage - crystallization is not deep enough. In actual engineering, sandstone is often subjected to the actions of groundwater seepage and salt crystallization simultaneously, and this coupling action has a complex and significant impact on the damage mechanism of sandstone.

[0004] In terms of simulating seepage force, there are already some patents and literatures in the prior art related to the damage simulation devices and methods of sandstone or other rocks under single seepage. For example, some patents provide damage devices for simulating the seepage damage process of rocks under single seepage by controlling water pressure and seepage velocity. However, these devices and methods often have limitations. They can only consider the action of seepage singly and cannot comprehensively simulate the complex stress state and chemical erosion effects suffered by sandstone in the actual geological environment. In particular, they ignore the coupling between the crystallization process and the seepage process and cannot truly reflect the damage evolution process of sandstone under the coupling action of seepage - crystallization.

[0005] In addition, although CN113155681B discloses a device and experimental method for simulating the action of seepage force on rocks using centrifugal force, by driving the core holder to rotate through a centrifugal device to simulate seepage force, this method still has problems such as limitations of the simulation environment, singularity of experimental conditions, and complexity of data processing, making it difficult to fully reproduce the seepage process in the real geological environment and unable to consider the coupling effects of other geological factors (such as temperature, pressure, chemical reactions, etc.) on rock damage.

[0006] In addition, some studies also focus on the damage effect of salt crystallization on rocks. These studies usually observe the precipitation process of salt crystals in rock pores and its influence on the mechanical properties of rocks through laboratory tests. However, these tests are often difficult to accurately control the seepage velocity and evaporation crystallization conditions, so it is difficult to accurately simulate the seepage - crystallization coupling action suffered by sandstone in actual engineering.

[0007] For example, CN103645298B discloses a test method for measuring the self - recovery amount of damaged rock salt, which evaluates the damage degree and self - recovery ability of rock salt by simulating the self - recovery process of rock salt under different stress, temperature, and humidity conditions. However, this method mainly focuses on the research of rock salt and may not be applicable to the damage simulation of other types of rocks (such as sandstone) under crystallization. In addition, the crystallization process in the actual geological environment is affected by various factors (such as fluid composition, flow velocity, temperature gradient, etc.), making it difficult to fully reproduce in the laboratory. Although this method pays attention to the self - recovery amount of rock damage, it may be insufficient for the direct damage assessment of the influence of crystallization on rock fracture propagation, pore structure change, etc.

[0008] Combined with the existing situation of the above - mentioned seepage force and crystallization simulation technologies, the following common defects and deficiencies can be summarized: Limitations of the experimental environment: It is difficult for the existing technologies to fully reproduce the complex conditions in the real geological environment, such as the coupling effect of multi - factors like seepage velocity, temperature gradient, and fluid composition, resulting in a deviation between the experimental results and the actual situation.

[0009] Singularity of simulation factors: Most of the existing technologies only focus on the influence of a single factor on rock damage, while ignoring the complex damage mechanism under the coupling effect of multiple factors.

[0010] Challenges in data processing and evaluation: The amount of data generated by experiments is huge and complex. How to accurately extract and analyze effective data to comprehensively evaluate the rock damage situation is an urgent problem to be solved.

[0011] In summary, the main problem in the existing technologies lies in the lack of an experimental device and method that can effectively simulate the damage mechanism of sandstone under the coupling effect of seepage - crystallization. The existing single - seepage or single - crystallization simulation devices and methods cannot meet the needs of in - depth research on the damage mechanism of sandstone under complex environmental conditions. Therefore, there is an urgent need for an innovative experimental device and method to precisely control the seepage velocity and evaporation - crystallization conditions, simulate the seepage - crystallization coupling effect suffered by sandstone in actual engineering, and thus deeply study its damage evolution process, providing a scientific basis for the design and construction of geotechnical engineering. Summary of the Invention

[0012] The technical problem to be solved by the present invention is to provide a sandstone damage simulation experimental device and method based on the coupling effect of seepage and crystallization, to solve the problem of insufficient research on the damage mechanism of sandstone under the coupling effect of seepage and crystallization in the field of geotechnical engineering technology, and to overcome the limitation of the prior art that cannot effectively simulate the coupling effect of seepage and crystallization suffered by sandstone in a complex geological environment; specifically, the sandstone damage simulation devices in the prior art mostly focus on the simulation of single seepage or single crystallization, and cannot comprehensively reflect the damage evolution process of sandstone under the dual effects of seepage and crystallization in the actual geological environment. In addition, the existing devices have deficiencies in controlling the seepage velocity and evaporation crystallization conditions, and it is difficult to accurately simulate the complex conditions in the real environment.

[0013] To solve the above technical problems, the technical solution adopted by the present invention is: a sandstone damage simulation experimental device based on the coupling effect of seepage and crystallization, including a container, the bottom of which is provided with a seepage port, and an O-ring seal sleeve is embedded in the seepage port for axially fixing the specimen and forming a seepage boundary; the top of the container is connected to an air compressor through a pipeline, which is used to pressurize the solution with a preset concentration in the container and control the seepage velocity of the solution by adjusting the air pressure value; a hair dryer is arranged at the lower end of the specimen to accelerate the evaporation of the seepage liquid and promote the precipitation of salt crystals in the internal pores and on the surface of the sandstone.

[0014] In a preferred solution, the container is set to be cylindrical and made of a transparent corrosion-resistant material to facilitate observing the damage evolution of the specimen during the experiment.

[0015] In a preferred solution, the seal ring sleeve is set to be O-shaped and made of acid and alkali resistant rubber material. The seal ring sleeve realizes a tight connection with the seepage opening and the specimen through interference sealing technology to ensure sealing.

[0016] In a preferred solution, the device further includes a pneumatic pressure regulating valve, which is arranged on the air compressor to adjust the air pressure value and realize the controllable adjustment of the seepage velocity.

[0017] In a preferred solution, the device further includes a flow meter, which is arranged on the seepage pipeline to monitor the seepage velocity of the solution in real time.

[0018] In a preferred solution, the hair dryer is a variable frequency speed regulation hair dryer, the wind speed and temperature of which are adjustable to accurately control the evaporation intensity. A temperature and humidity sensor is arranged at the air outlet of the hair dryer to monitor the temperature and humidity changes at the bottom of the specimen.

[0019] A sandstone damage simulation experimental method based on the coupling effect of seepage and crystallization is a method for simulating an experiment with the sandstone damage simulation experimental device based on the coupling effect of seepage and crystallization described above, including the following steps: Step1: Preparation step, place the specimen in the cylindrical container and fix it through the O-ring seal sleeve; Step 2: Solution injection and seepage control step. Inject a solution with a preset concentration into the container, start the air compressor, and adjust the air pressure value to a predetermined range through the air pressure regulating valve to control the seepage rate of the solution to a predetermined flow rate, so that the solution penetrates directionally along the pores of the specimen. Step 3: Evaporation and crystallization induction step. Start the hair dryer, adjust its wind speed and temperature to predetermined values, accelerate the evaporation of the seepage liquid, and promote the precipitation of salt crystals inside the pores and on the surface of the specimen. Step 4: Damage observation and recording step. Observe and record the damage evolution process of the specimen under the coupled action of seepage and crystallization, including crack initiation, propagation, and the precipitation of salt crystals. Step 5: Seepage rate adjustment step. During the seepage process, adjust the air pressure value in real time through the air pressure regulating valve as needed to maintain a constant seepage rate. Step 6: Evaporation intensity control step. During the evaporation process, adjust the wind speed and temperature of the hair dryer as needed to precisely control the evaporation intensity. Step 7: Data acquisition and analysis step. After the experiment, analyze the damage degree of the specimen, including but not limited to analyzing the damage of the internal pore structure using CT scanning or three-dimensional modeling technology, and measuring the changes in wave velocity and compressive strength to quantify the damage degree.

[0020] In a preferred embodiment, in the Step 2 solution injection and seepage control step, the solution with a preset concentration is a saturated sodium sulfate solution, and the seepage rate is controlled at 1 - 5 mL / min.

[0021] In a preferred embodiment, in the Step 3 evaporation and crystallization induction step, the wind speed adjustment range of the hair dryer is 1 - 2 m / s, and the temperature adjustment range is 30 - 60 °C.

[0022] In a preferred embodiment, the method further includes monitoring the temperature and humidity changes at the bottom of the specimen in real time during the experiment, and adjusting the working parameters of the hair dryer according to the monitoring results to optimize the evaporation and crystallization effect.

[0023] The sandstone damage simulation experimental device and method based on the coupled action of seepage and crystallization provided by the present invention have the following beneficial effects: 1. The present invention solves the problem of insufficient research on the damage mechanism of sandstone under the coupled action of seepage and crystallization in the field of geotechnical engineering technology, provides a new perspective for revealing the multi-physical field coupled damage mechanism of sandstone, and promotes the in-depth development of related field research.

[0024] 2. The present invention integrates three major functions of seepage control, evaporation crystallization, and damage observation into one, achieving a comprehensive simulation of the damage evolution process of sandstone under the coupling effect of seepage and crystallization, improving the experimental efficiency and data integrity, and providing an intuitive and effective means for in-depth study of the sandstone damage mechanism.

[0025] 3. The present invention adopts an air compressor - pressure reducing valve - flowmeter closed-loop control system, combines the PID (Proportional-Integral-Derivative) algorithm to dynamically adjust the pressure, realizes high-precision control of the seepage velocity, improves the control accuracy by more than 10 times compared with manual valve control, and supports multi-level regulation of the seepage velocity, can simulate complex formation penetration gradients, and further improves the accuracy and reliability of the experiment.

[0026] 4. The device of the present invention is not only applicable to the damage simulation study of sandstone, but also can be widely applied to the study of the damage mechanism of other types of rocks under the coupling effect of seepage and crystallization, has important engineering application value and academic significance, and supports damage simulation of multiple solution systems and different lithologies, with wide applicability.

[0027] 5. The present invention ensures the uniform stress of the specimen by precisely controlling the seepage velocity and evaporation crystallization conditions, and adopting the interference fit sealing technology of O-ring sleeves to eliminate boundary stress interference, significantly improves the accuracy and reliability of the experimental results, and provides a more scientific and effective experimental platform for the study of the sandstone damage mechanism.

[0028] 6. The experimental results of the present invention show that the device can accurately simulate the damage evolution process of sandstone under the coupling effect of seepage and crystallization, and the fixing stability of the sample is significantly improved, solving the problems of easy sliding and tilting of irregular sandstone samples, reducing the experimental repeatability error to within ±2%, and avoiding the risk of sample rupture caused by stress concentration of traditional fixtures.

[0029] 7. The present invention innovatively introduces the coupling effect of solution seepage - evaporation crystallization, synchronously studies the multi-field coupling damage effect of fluid - chemistry - mechanics, the experimental results are closer to the actual formation environment, have more advantages than single penetration experiments, and designs a bottom directional evaporation unit to form a humidity gradient, accurately reproducing the salt weathering process in arid - evaporation geological environments.

[0030] 8. The present invention realizes the precise control of seepage rate and evaporation intensity through an innovative dynamic regulation system and a digital pressure closed-loop control module, provides more reliable experimental data for the study of the sandstone damage mechanism, and provides a high-precision experimental means for the durability assessment of geotechnical engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described below in conjunction with the drawings and embodiments: Figure 1 is a schematic diagram of the overall structure of the present invention; Figure 2 is a schematic diagram of the structure of the sealing ring sleeve of the present invention; Figure 3 is a schematic diagram of the overall structure of the pipeline of the present invention; In the figure: container 1, seepage port 2, sealing ring sleeve 3, specimen 4, air compressor 5, pneumatic pressure regulating valve 6, hair dryer 7, pipeline 8, flowmeter 9, inner ring 31, outer ring 32, Specific embodiments The technical solutions in the present invention will be further described below with reference to the accompanying drawings and embodiments: Embodiment 1 As Figures 1 to 3 shown, this embodiment provides a sandstone damage simulation experimental device based on the coupling effect of seepage - crystallization. The device mainly includes the following components and their specific designs: Cylindrical container 1: It is made of a transparent corrosion - resistant material (such as plexiglass or polypropylene). The height and diameter of the container are designed according to experimental requirements to facilitate observing the damage evolution of the sandstone sample 4 during the experiment. The side wall and bottom of the container are polished to reduce the adhesion of the solution on the container surface and ensure the accuracy of the experimental results.

[0032] Seepage port 2: It is located at the center of the bottom of the container 1 and is designed as a circular or oval opening to facilitate the seepage of the solution. The edge of the seepage port 2 is chamfered to reduce stress concentration and avoid unnecessary damage during the experiment.

[0033] O - type sealing ring sleeve 3: It is embedded in the seepage port 2 and is made of acid - and alkali - resistant rubber material. The O - type sealing ring sleeve 3 realizes a tight connection with the seepage opening 2 and the sandstone sample 4 through interference sealing technology to ensure good sealing and prevent solution leakage. At the same time, the O - type sealing ring sleeve 3 has a certain elasticity and can adapt to sandstone samples 4 of different sizes, improving the versatility and flexibility of the experiment.

[0034] Sandstone sample 4: It is cylindrical or approximately cylindrical, and its size and shape need to match the container 1 and the O - type sealing ring sleeve 3. The sandstone sample 4 needs to be pretreated before the experiment, such as cleaning, drying, and weighing, to ensure the accuracy of the experimental results.

[0035] Air compressor 5: It is connected to the top of the container 1 through the pipeline 8 and is used to pressurize the solution with a preset concentration in the container 1. The type selection of the air compressor 5 needs to be determined according to experimental requirements to ensure that it can provide a sufficient pressure range and control accuracy.

[0036] Air pressure regulating valve 6: It is set between the air compressor 5 and the pipeline 8 and is used to regulate the air pressure value to control the seepage rate of the solution. The air pressure regulating valve 6 has an accurate regulation range and stable control performance, which can ensure the stability and controllability of the seepage rate.

[0037] Hair dryer 7: It is set at the lower end of the sandstone sample 4 and is used to accelerate the evaporation of the seepage liquid, prompting the precipitation of salt crystals inside and on the surface of the sandstone. The hair dryer 7 is a variable-frequency speed-regulating hair dryer, and its wind speed and temperature are adjustable to accurately control the evaporation intensity. A temperature and humidity sensor (not shown in the figure) is provided at the air outlet of the hair dryer 7 to monitor the temperature and humidity changes at the bottom of the sample 4 in real time, so as to adjust the working parameters of the hair dryer 7 according to the monitoring results to optimize the evaporation and crystallization effect.

[0038] Pipeline 8: It connects the top of the air compressor 5 and the container 1 and is used to transport the pressurized solution into the container 1. The material of the pipeline 8 needs to be corrosion-resistant, high-temperature resistant and high-pressure resistant to ensure the safety and reliability during the experiment.

[0039] Flowmeter 9: It is set on the seepage pipeline and is used to monitor the seepage rate of the solution in real time. The flowmeter 9 has high precision and stable measurement performance, which can ensure the accurate measurement and recording of the seepage rate.

[0040] The sandstone damage simulation experimental device based on the seepage-crystallization coupling effect provided by this embodiment has the advantages of simple structure, convenient operation, good sealing performance and high control precision, and can meet the needs of sandstone damage simulation experiments under different conditions.

[0041] Embodiment 2 In another preferred embodiment, on the basis of Embodiment 1, this embodiment provides a sandstone damage simulation experimental method based on the seepage-crystallization coupling effect, and uses the sandstone damage simulation experimental device based on the seepage-crystallization coupling effect described in Embodiment 1 for simulation. The specific experimental steps are as follows: Step1: Preparation step, place the pretreated sandstone sample 4 in the cylindrical container 1 and fix it through the O-ring seal 3. During the fixing process, it is necessary to ensure that the sandstone sample 4 is axially stable and well-sealed to avoid solution leakage and non-experimental breakage during the experiment.

[0042] Step2: Solution injection and seepage control step, inject a saturated sodium sulfate solution with a preset concentration into the container 1, start the air compressor 5, and adjust the air pressure value to a predetermined range (such as 0.2 MPa) through the air pressure regulating valve 6. During the process of adjusting the air pressure value, it is necessary to monitor the seepage rate of the solution in real time and record and calibrate it through the flowmeter 9. After the seepage rate is stable (such as 2 mL / min), make the solution penetrate directionally along the pores of the sandstone sample 4.

[0043] Step 3: Evaporation and crystallization induction step. Start the hair dryer 7 and adjust its wind speed to a predetermined value (e.g., 1.5 m / s) and temperature to a predetermined range (e.g., 45 °C). During the evaporation process, it is necessary to monitor the temperature and humidity changes at the bottom of the specimen 4 in real time through the temperature and humidity sensor, and adjust the working parameters of the hair dryer 7 according to the monitoring results to optimize the evaporation and crystallization effect. By accelerating the evaporation of the seepage liquid, salt crystals are promoted to precipitate rapidly inside the pores and on the surface of the sandstone sample 4.

[0044] Step 4: Damage observation and recording step. During the experiment, it is necessary to observe and record the damage evolution process of the sandstone sample 4 under the coupling action of seepage and crystallization through the transparent container 1. The observation contents include crack initiation, propagation, and the precipitation of salt crystals, etc. At the same time, it is necessary to record the key parameters and time nodes during the experiment for subsequent data analysis and processing.

[0045] Step 5: Seepage velocity adjustment step. During the seepage process, according to the experimental requirements or observation results, the air pressure value is adjusted in real time through the air pressure regulating valve 6 to maintain a constant seepage velocity. By precisely controlling the seepage velocity, the sandstone damage process under different infiltration gradients can be simulated, improving the flexibility and accuracy of the experiment.

[0046] Step 6: Evaporation intensity control step. During the evaporation process, according to the experimental requirements or observation results, the wind speed and temperature of the hair dryer 7 are adjusted to precisely control the evaporation intensity. By optimizing the evaporation and crystallization effect, the salt weathering process under different temperature and humidity conditions can be further simulated, revealing the damage evolution law of sandstone in different environments.

[0047] Step 7: Data acquisition and analysis step. After the experiment, take out the sandstone sample 4 and conduct damage degree analysis. CT scanning or three-dimensional modeling technology can be used to analyze the damage of the internal pore structure, and the changes in wave velocity and compressive strength are measured to quantify the damage degree. At the same time, it is necessary to sort out and analyze the data records during the experiment, including key parameters such as seepage velocity, evaporation intensity, temperature and humidity changes, etc., to comprehensively evaluate the damage evolution law and mechanism of sandstone.

[0048] The sandstone damage simulation experiment method based on the coupling action of seepage and crystallization provided by this embodiment has the advantages of convenient operation, high control precision, and reliable data, and can provide a high-precision experimental means for the durability evaluation of sandstone engineering.

[0049] Example 3 In another preferred embodiment, on the basis of Embodiments 1 and 2, this embodiment further elaborates on the technical solutions of the sandstone damage simulation experimental device and method of the present invention based on the coupling action of seepage and crystallization: The main body of the container 1 is as Figure 1It is shown that a cylindrical cavity (diameter 400 mm × height 600 mm) is made of plexiglass material with excellent corrosion resistance, the pressure resistance level is ≥ 0.6 MPa, and a circular seepage port 2 with a diameter of 50 mm is provided at the bottom. The opening edge is hermetically connected through a silicone rubber sealing ring sleeve 3. An annular groove is provided on the inner wall of the cavity for fixing the O-ring sealing sleeve 3 (the material is acid and alkali resistant rubber material, Shore hardness 70 ± 5°). The outer ring 32 of the O-ring sealing sleeve 3 is used to connect with the cavity, and the sandstone is fixed by the friction force with the inner ring 31 of the O-ring sealing sleeve 3.

[0050] The sample fixing device is as Figure 2 shown. A customized O-ring sealing sleeve 3 (outer diameter 50.5 mm / inner diameter 49.5 mm) is embedded in the groove. Axial diversion grooves with a certain depth are machined on the surface of the sleeve, which can guide the solution to uniformly penetrate into the specimen 4. The specimen 4 is a cylinder with a diameter of 50 mm and a height of 100 mm. It is necessary to ensure the surface roughness Ra ≤ 3.2 μm through diamond wire cutting. After the surface is coated with a waterproof adhesive layer (thickness ≤ 0.1 mm), only the axial seepage channel is reserved.

[0051] The seepage control system is as Figure 1 shown. The top of the container is connected to an air compressor 5 (flow accuracy ± 0.5%) through a conduit. The air compressor 5 (rated pressure 0.8 MPa) outputs a stable air pressure of 0.1 - 0.3 MPa through a pneumatic pressure regulating valve, which acts on the top sealing cover of the container. The pressure sensor (accuracy 0.1% FS) real-time feedbacks the pressure value, and the seepage rate is controlled within the range of 1 - 5 mL / min by using the PID algorithm.

[0052] The crystallization induction system is as Figure 1 shown. An independent air duct is provided at the bottom of the specimen 4, equipped with a variable frequency speed regulating blower 7 (the wind speed is adjustable within 1 - 2 m / s). A temperature and humidity sensor (accuracy ± 0.5℃ / ± 2%RH) is installed at a position 50 mm away from the bottom of the specimen 4 at the outlet of the air duct. By controlling the synergistic effect of the wind speed and the solution seepage rate, a stable evaporation - crystallization cycle can be formed at the bottom of the specimen 4. The bottom directional drying design simulates the non-uniform evaporation in the real environment, and it is easier to induce cracks in the tensile stress concentration area.

[0053] The pipeline 8 connecting the air compressor 5 and the container 1 is as Figure 3 shown. The air compressor 5 is hermetically connected to the top of the container 1 through a pressurized pipeline 8. The pressurized pipeline 8 includes: a first connection end 801, which is detachably connected to the output end of the air compressor 5 through a flange 802; a second connection end 803, provided with a tapered sealing joint 804, and the tapered sealing joint 804 is inserted into the through hole reserved at the top of the container 1 and fixed by thread locking; the pipeline body 805, made of polytetrafluoroethylene material with a pressure resistance strength ≥ 1 MPa, and the inner wall smoothness Ra ≤ 0.2 μm.

[0054] Example 4 In another preferred embodiment, on the basis of Example 4, in order to make the purpose, technical solution and advantages of the present invention clearer and more understandable, the present 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 only used to explain the present invention and are not used to limit the present invention.

[0055] Taking the Upper Paleozoic tight sandstone in the Linxing block on the eastern margin of the Ordos Basin as an example, the sandstone in this area has the characteristics of low porosity (average porosity < 10%) and strong heterogeneity, and is an ideal sample for studying the seepage-crystallization coupling damage mechanism. The following are the device implementation methods and experimental steps: Step 1: Sample preparation. Take the tight sandstone in the Shanxi Formation of the Linxing block (mainly feldspar quartz sandstone, particle size 0.1 - 0.5 mm) and cut it into a cylindrical standard specimen 4 with a diameter of 50 mm and a height of 100 mm. Polish both ends flat and clean the surface impurities with anhydrous ethanol.

[0056] Step 2: Device assembly. Insert an O-ring seal sleeve 3 into the bottom seepage port 2 of the cylindrical container 1 to ensure that the inner diameter of the seal sleeve matches the outer diameter of the specimen 4 (tolerance ±0.5 mm), ensure that the bottom of the specimen 4 is exposed outside the container, and a sealed chamber is formed between the top and the inner wall of the container. The specimen is hermetically and fixedly connected through the elastic deformation of the seal sleeve. Connect an air compressor 5 to the pressure regulating valve 6 at the top of the container, and install a flowmeter 9 in the seepage pipeline to monitor the solution flow rate in real time. Install a hair dryer 7 at the bottom of the container, with an adjustable power range of 50 - 300 W and a wind speed of 1 - 2 m / s, and the air outlet is facing the bottom of the specimen 4.

[0057] Step 3: Solution injection and seepage control. Inject a saturated sodium sulfate solution (concentration 20%) into the container 1, and the liquid level height covers 20 mm above the top of the specimen. Start the air compressor 5, and adjust the seepage pressure to be stable at 0.1 - 0.5 MPa through the pressure regulating valve 6. The flowmeter 9 monitors the flow rate to be 1 - 5 mL / min to simulate the groundwater seepage environment.

[0058] Step 4: Crystallization-evaporation coupling damage. After the seepage lasts for 24 hours, start the bottom hair dryer 7, set the wind speed to 3 m / s and the temperature to 40 °C to accelerate the evaporation of the water at the bottom of the specimen and induce salt crystallization (sodium sulfate crystals precipitate). Record the mass change of the specimen every 6 hours, and observe the expansion of the cracks at the bottom through a microscope (refer to the microscopic image library of the tight sandstone in the Linxing block).

[0059] Step 5: Acquisition of damage data. After the experimental cycle ends, take out Specimen 4 and analyze the internal pore structure damage using CT scanning or three-dimensional modeling techniques (such as sequential index simulation); compare the wave velocity before and after the experiment (measure the change in longitudinal wave velocity using an ultrasonic detector to reflect the damage degree of the cementing material) and the compressive strength (take out the specimen for uniaxial compression test every 5 cycles, record the strength decline curve (expected to show exponential decay), and quantify the damage degree).

[0060] Example 4 In another preferred embodiment, based on Embodiments 1, 2, and 3, in order to fully demonstrate the diversity and practicality of the present invention, this embodiment details the specific implementation scheme of the sandstone damage simulation experiment under different conditions. On the basis of keeping the structure of the experimental device unchanged as described in Embodiment 1, by flexibly adjusting key parameters such as solution type, seepage velocity, and evaporation intensity, the sandstone damage process under various geological environments is simulated, aiming to comprehensively evaluate the damage evolution laws and mechanisms of sandstone under different conditions, and provide a scientific basis for the design, construction, and maintenance of sandstone projects.

[0061] In terms of experimental materials, we selected representative Sandstone Specimen 4 to ensure that the Sandstone Specimen 4 has uniform texture and similar physical and mechanical properties. At the same time, different concentrations of brine, saturated solution, acid-base solution, etc. were prepared as experimental solutions.

[0062] In terms of experimental equipment, we used a sandstone damage simulation experimental device, which includes components such as a cylindrical container 1, a seepage port 2, an O-ring seal sleeve 3, an air compressor 5, a pressure regulating valve 6, a hair dryer 7, a pipeline 8, and a flowmeter 9. In addition, solution preparation equipment and testing instruments for measuring the physical and mechanical properties and internal pore structure damage of sandstone, such as an electronic balance, an ultrasonic detector, and a CT scanner, were also equipped.

[0063] In terms of experimental parameter settings, we made refined adjustments. For the solution type, we set different concentrations of brine to study the influence of salt on sandstone damage; by introducing gas to a saturated state in water, the environment in the formation was simulated; acid-base solutions with different pH values were also set to study the influence of acidity and alkalinity on sandstone damage. For the seepage velocity, by adjusting the air pressure value of the air compressor, multi-level regulation of the seepage velocity was achieved to simulate the complex infiltration gradient of the formation. For the evaporation intensity, by adjusting the wind speed and temperature of the hair dryer, the evaporation intensity was precisely controlled to simulate the salt weathering process under different temperature and humidity conditions.

[0064] In terms of the experimental procedures, we first prepared sandstone specimen 4 by cleaning, drying, and weighing it to ensure that sandstone specimen 4 was in its initial state. Then, according to the experimental requirements, a preset type of solution was injected into cylindrical container 1. Next, air compressor 5 was started, and the air pressure value was adjusted to a predetermined range through air pressure regulating valve 6 to make the solution penetrate directionally along the pores of sandstone specimen 4. Subsequently, hair dryer 7 was started, and its wind speed and temperature were adjusted to predetermined values to accelerate the evaporation of the seepage liquid, prompting the precipitation of salt crystals or acid-base reactions on the internal pores and surface of the sandstone. During the experiment, we observed and recorded the damage evolution process of sandstone specimen 4 under the coupled action of seepage-crystallization (or acid-base reaction) through a transparent container. After the experiment, we took out sandstone specimen 4 for physical and mechanical property tests, including mass, volume, longitudinal wave velocity, uniaxial compressive strength, etc., and used a CT (Computed Tomography) scanner or microscope to observe the pore structure damage inside the sample and the corrosion condition on the surface, recording and analyzing the damage evolution process.

[0065] To comprehensively evaluate the damage evolution laws and mechanisms of sandstone under different conditions, we designed multiple groups of comparative experiments. We compared the effects of different concentrations of brine on sandstone damage, the differences in sandstone damage between saturated liquid and ordinary water, the effects of acid-base solutions with different pH values on sandstone damage, the damage evolution laws of sandstone under different seepage velocities, and the salt weathering process of sandstone under different evaporation intensities.

[0066] In terms of experimental data recording and analysis, we detailedly recorded various test data, including solution type, seepage velocity, evaporation intensity, mass, volume, wave velocity, compressive strength of the sandstone sample, etc. Then, statistical methods and data analysis software were used to process and analyze the experimental data to reveal the damage evolution laws and mechanisms of sandstone under different conditions.

[0067] Through the analysis and summary of the experimental data, we obtained the damage evolution laws and mechanisms of sandstone under different conditions. These conclusions provided a scientific basis for the design, construction, and maintenance of sandstone projects. At the same time, we also summarized the experiences and lessons during the experiment, providing a reference for subsequent sandstone damage simulation experiments.

[0068] During the experiment, we strictly adhered to the experimental operation procedures, ensured good sealing of the experimental device, and avoided solution leakage. When handling acid-base solutions, we paid attention to operation safety and wore necessary protective equipment. At the same time, we strictly controlled the experimental conditions to ensure the accuracy and repeatability of the experimental results.

[0069] In summary, through the refined experimental scheme and implementation steps, this embodiment systematically studies the damage evolution law of sandstone under different conditions, providing strong scientific support for sandstone engineering.

[0070] In a preferred solution, the container 1 is set to be cylindrical and made of a transparent corrosion-resistant material to facilitate observing the damage evolution of the specimen 4 during the experiment; the above settings also ensure that the container 1 can withstand the high pressure and high temperature environments that may occur during the experiment. At the same time, the bottom of the container 1 is designed with a drain hole 3 to timely drain the excess water generated during the experiment and ensure the accuracy of the experiment.

[0071] In a preferred solution, the sealing ring sleeve 3 is set to be O-shaped and made of acid and alkali-resistant rubber material. The sealing ring sleeve 3 realizes a tight connection with the seepage opening 2 and the specimen 4 through interference sealing technology to ensure sealing; the above settings can effectively prevent the fluid from leaking from the seepage opening 2 under high pressure, improving the accuracy and safety of the experiment; at the same time, the selection of acid and alkali-resistant rubber material further enhances the corrosion resistance of the sealing ring sleeve 3 and extends the service life of the equipment.

[0072] In a preferred solution, the device further includes a pneumatic pressure regulating valve 6, which is set on the air compressor 5 to adjust the air pressure value and realize the controllable adjustment of the seepage rate; the above settings can accurately control the seepage process, improving the stability and efficiency in the experiment or production; at the same time, the introduction of the pneumatic pressure regulating valve 6 also enhances the adaptability of the system to different working environments and requirements.

[0073] In a preferred solution, the device further includes a flow meter 9, which is set on the seepage pipeline to monitor the seepage rate of the solution in real time; the above settings ensure the precise control of the seepage process and improve the utilization efficiency of the solution; at the same time, the data of the flow meter 9 can be uploaded to the control system in real time to realize remote monitoring and intelligent adjustment, further enhancing the stability and reliability of the system.

[0074] In a preferred solution, the hair dryer 7 is a variable-frequency speed-regulating hair dryer, and its wind speed and temperature are adjustable to precisely control the evaporation intensity. A temperature and humidity sensor is set at the air outlet of the hair dryer 7 to monitor the temperature and humidity changes at the bottom of the specimen 4; the above settings can provide real-time feedback and adjust the blowing state to ensure that the specimen 4 maintains a stable evaporation rate during the drying process, avoiding uneven drying or sample damage caused by temperature and humidity fluctuations, and improving the accuracy of the test and the integrity of the sample.

[0075] In the preferred scheme, in the Step 2 solution injection and seepage control step, the preset concentration of the solution is a saturated sodium sulfate solution, and the seepage rate is controlled at 1-5 mL / min; the above setting can ensure that the solution fully penetrates into the porous medium, effectively promotes the ion exchange process, and avoids the uneven distribution problem caused by too fast solution, thereby improving the overall treatment efficiency and effect.

[0076] In the preferred embodiment, in the Step 3 evaporation and crystallization induction step, the wind speed adjustment range of the hair dryer 7 is 1~2m / s, and the temperature adjustment range is 30~60°C; the above settings are intended to ensure that the solution can crystallize evenly and stably during the evaporation process, avoiding the problem of uneven or incomplete crystallization caused by too fast or too slow evaporation rate, thereby improving the quality and purity of the product.

[0077] In the preferred scheme, the method also includes real-time monitoring of the temperature and humidity changes at the bottom of the sample 4 during the experiment, and adjusting the working parameters of the hair dryer 7 according to the monitoring results to optimize the evaporation and crystallization effect; the above settings effectively ensure the stability of the experimental environment and improve the accuracy of the data; at the same time, the system also has an automatic recording function, which can save temperature and humidity data and hair dryer working parameters in real time, providing a detailed basis for subsequent analysis and optimization.

[0078] In summary, the present invention proposes a sandstone damage simulation experimental device and method based on the coupling effect of seepage and crystallization. This solution solves the problem of insufficient research on the damage mechanism of sandstone under the coupling effect of seepage and crystallization in the field of geotechnical engineering technology, and overcomes the limitation in the prior art that it is unable to effectively simulate the seepage-crystallization coupling effect on sandstone in a complex geological environment. The present invention first proposes a sandstone damage simulation device and method based on the coupling effect of seepage and crystallization, which can more realistically reproduce the damage evolution experienced by underground sandstone during the processes of salt seepage and evaporation crystallization, filling the gap in the poor coupling between seepage velocity and crystallization process in traditional methods. Through the synergistic effect of controllable seepage and evaporation crystallization, the damage simulation of sandstone under the coupling effect of multiple physical fields (fluid, stress, chemical reaction) is realized, which is closer to the damage process of sandstone in the actual geological environment and provides a new perspective for revealing the sandstone damage mechanism. The experimental device designed in the present invention adopts a digital pressure closed-loop control module and a bottom directional evaporation unit, realizing the precise control of seepage rate accuracy and evaporation intensity, and providing a high-precision experimental platform. In addition, the experimental device adopts a modular design, supports the damage simulation of multiple solution systems and different lithologies, and has a broad application prospect. Through innovative points such as the bottom single-opening design, the interference sealing technology of the O-ring seal sleeve 3, and the integrated air compressor 5 for pressurized seepage and directional temperature-controlled evaporation module, the controllable simulation and real-time observation of the sandstone damage evolution process are realized, solving the problem that it is difficult to coordinately control seepage pressure and evaporation intensity in traditional methods. The present invention also proposes a sandstone damage simulation method combining multiple factors such as seepage, evaporation, and crystallization (or acid-base action) coupling, which can more comprehensively consider various damage factors that sandstone may experience in a complex geological environment, improving the accuracy and reliability of simulation results. The present invention not only focuses on the theoretical research of sandstone damage, but also pays attention to applying the research results to actual engineering, providing a scientific basis for the design, construction, and maintenance of sandstone projects, and realizing the close combination of theory and practice. At the same time, the present invention integrates a variety of experimental technologies and applies them to the field of sandstone damage simulation, providing new technical means and ideas for sandstone damage research.

Claims

1. The sandstone damage simulation experimental device based on seepage-crystallization coupling is characterized by: The invention comprises a container (1), the bottom of which is provided with a seepage port (2), the seepage port (2) being embedded with a sealing ring sleeve (3) for axially fixing a sample (4) and forming a seepage boundary; the top of the container (1) is connected to an air compressor (5) through a pipeline (8), for pressurizing a solution of a preset concentration in the container (1), and controlling the seepage speed of the solution by adjusting the air pressure value; and a blower (7) is provided at the lower end of the sample (4), for accelerating the evaporation of the seepage liquid and promoting the precipitation of salt crystals in the internal pores and on the surface of the sandstone.

2. The sandstone damage simulation experimental device based on seepage-crystallization coupling according to claim 1 is characterized in that: The container (1) is configured to be cylindrical and is made of a transparent corrosion-resistant material, so as to facilitate observation of the damage evolution of the sample (4) during the experiment.

3. The sandstone damage simulation experimental device based on seepage-crystallization coupling according to claim 2 is characterized in that: The sealing ring sleeve (3) is configured in an O-shape and is made of acid- and alkali-resistant rubber material. The sealing ring sleeve (3) is connected to the seepage opening (2) and the sample (4) by means of interference sealing technology, thereby ensuring sealing.

4. The sandstone damage simulation experimental device based on seepage-crystallization coupling according to claim 3 is characterized in that: The device also includes an air pressure regulating valve (6) which is arranged on the air compressor (5) and is used to adjust the air pressure value to achieve controllable regulation of the seepage velocity.

5. The sandstone damage simulation experimental device based on seepage-crystallization coupling according to claim 5 is characterized in that: The device also includes a flow meter (9) which is arranged on the seepage pipeline and monitors the seepage velocity of the solution in real time.

6. The sandstone damage simulation experimental device based on seepage-crystallization coupling according to claim 5 is characterized in that: The hair dryer (7) is a variable frequency speed-regulating hair dryer, whose wind speed and temperature are adjustable to precisely control the evaporation intensity. The air outlet of the hair dryer (7) is provided with a temperature and humidity sensor to monitor the temperature and humidity changes at the bottom of the sample (4).

7. A sandstone damage simulation experiment method based on seepage-crystallization coupling is a method for performing a simulation experiment using the sandstone damage simulation experiment device based on seepage-crystallization coupling as claimed in claim 6, characterized in that: The following steps are involved: Step 1: Preparation step, placing the sample (4) in the cylindrical container (1) and fixing it with an O-ring sleeve (3); Step 2: solution injection and seepage control step, injecting a solution of a preset concentration into the container (1), starting the air compressor (5), and adjusting the air pressure value to a predetermined range through the air pressure regulating valve (6) to control the seepage speed of the solution to a predetermined flow rate, so that the solution directionally permeates along the pores of the sample (4); Step 3: Evaporation and crystallization induction step, starting the hair dryer (7), adjusting its wind speed and temperature to predetermined values, accelerating the evaporation of the seepage liquid, and promoting the precipitation of salt crystals in the internal pores and on the surface of the sample (4); Step 4: Damage observation and recording step, observe and record the damage evolution process of the sample (4) under the effect of seepage-crystallization coupling, including crack initiation, propagation and precipitation of salt crystals; Step 5: seepage velocity adjustment step. During the seepage process, the air pressure value is adjusted in real time through the air pressure regulating valve (6) as needed to maintain a constant seepage velocity; Step 6: Evaporation intensity control step, during the evaporation process, the wind speed and temperature of the hair dryer (7) are adjusted as needed to accurately control the evaporation intensity; Step 7: Data collection and analysis step. After the experiment, the damage degree of the sample (4) is analyzed, including but not limited to using CT scanning or three-dimensional modeling technology to analyze the internal pore structure damage, and measuring the wave velocity and compressive strength changes to quantify the damage degree.

8. The sandstone damage simulation experimental method based on seepage-crystallization coupling according to claim 7 is characterized in that: In the step 2 of solution injection and seepage control, the solution with a preset concentration is a saturated sodium sulfate solution, and the seepage rate is controlled at 1-5 mL / min.

9. The sandstone damage simulation experimental method based on seepage-crystallization coupling according to claim 7 is characterized in that: In the Step 3 evaporation and crystallization induction step, the wind speed of the hair dryer (7) is adjusted in the range of 1-2 m / s, and the temperature is adjusted in the range of 30-60°C.

10. The sandstone damage simulation experimental method based on seepage-crystallization coupling according to claim 7, characterized in that: The method further comprises monitoring the temperature and humidity changes at the bottom of the sample (4) in real time during the experiment, and adjusting the working parameters of the blower (7) according to the monitoring results to optimize the evaporation and crystallization effect.

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