Sample preparation, drying-wetting cycle and shearing integrated direct shear test device and method

Abstract

This invention discloses an integrated direct shear testing apparatus and method for sample preparation, wet-dry cycling, and shear testing. The apparatus includes a sample preparation and shearing system, a wet-dry cycling system, and a digital control system, realizing integrated operation of soil and rock sample preparation, humidification and drying, and direct shear testing, avoiding structural disturbance and particle loss caused by multiple sample transfers. The wet-dry cycling system employs ultrasonic-assisted humidification and dynamic power drying, accelerating water penetration through intermittent ultrasonic loading while balancing humidification efficiency and sample structural integrity. Combined with real-time closed-loop control using sensors for mass, temperature, and flow rate, it achieves precise control of moisture content and temperature. This invention significantly reduces experimental errors, improves data repeatability and experimental efficiency, and effectively solves problems such as fragmented functions, uneven humidification, large disturbances, and cumbersome processes in traditional devices. It is suitable for wet-dry cycling direct shear tests on various soil and rock structural surfaces, providing a stable and reliable integrated solution for testing the mechanical properties of geotechnical engineering.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical testing technology, and in particular relates to an integrated direct shear test device and method for sample preparation, wet-dry cycle and shear testing. Background Technology

[0002] Direct shear testing, as a core experimental method in geotechnical testing for exploring the basic mechanical properties of soil and rock structural surfaces, plays an irreplaceable and crucial role in geotechnical engineering due to the irreplaceable importance of its test data in areas such as geotechnical engineering design, disaster early warning, and engineering stability assessment. However, existing direct shear testing technologies and supporting equipment still suffer from numerous technical deficiencies that urgently need to be addressed. For example, the core process of existing direct shear testing (including sample preparation, wet-dry cycle treatment, and shear testing) lacks an integrated design, with each step relying on independent specialized equipment. Some direct shear testing devices even lack dedicated wet-dry cycle modules, failing to meet the wet-dry cycle shear testing requirements of special samples such as rock structural surfaces. Because the equipment in each step lacks a coherent and coordinated design, samples need to be transferred multiple times between different devices. During this process, they are inevitably affected by uncontrollable factors such as mechanical contact, sudden changes in environmental temperature and humidity, and external disturbances, leading to the destruction of the sample's original state. This problem directly leads to a significant increase in the dispersion of test data, making it difficult to guarantee the reliability and repeatability of test results. To offset this error, the number of experimental groups needs to be increased significantly, which not only consumes a lot of manpower and time costs, but also generates additional consumable costs and equipment occupancy costs, resulting in low overall test efficiency.

[0003] Furthermore, existing humidification technologies have significant limitations. Traditional methods often employ direct immersion or spot dripping, both of which have insurmountable technical drawbacks: direct immersion easily leads to localized oversaturation of the sample, causing uneven distribution of internal moisture content; spot dripping cannot achieve uniform coverage of the entire sample, making it difficult to precisely control the degree of humidification; at the same time, the moisture transfer of the above methods relies on natural infiltration, resulting in low humidification efficiency, and the impact of water flow or immersion pressure can cause significant disturbance to the sample; for loose soil or structurally fragile rock samples, this can easily lead to particle shedding and structural damage, thereby destroying the integrity of the original state of the sample and affecting the authenticity of the test data.

[0004] Existing related devices generally suffer from single-function limitations. Compaction, wet-dry cycling, and shear testing equipment operate independently, requiring frequent manual transfer of samples to different containers to complete each stage, making coordinated operation impossible. Even some improved solutions attempting simple assembly of the equipment fail to fully leverage the core advantages of integrated design. The functional modules cannot operate in coordination, and key technical challenges such as sample softening at the ends and uneven moisture content distribution during wet-dry cycling remain unresolved. These issues have become core bottlenecks restricting the improvement of direct shear test accuracy, data reliability, and testing efficiency, urgently requiring effective technical solutions. Summary of the Invention

[0005] The purpose of this invention is to provide an integrated direct shear test device and method for sample preparation, wet-dry cycling, and shear testing, so as to achieve integrated and coordinated operation of sample preparation, wet-dry cycling, and shear testing, reduce human disturbance and structural damage during sample transfer, improve the efficiency and uniformity of wet-dry cycling through ultrasonic assistance and precise digital control, reduce test errors, and ensure the reliability and accuracy of test data.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is an integrated direct shear test device for sample preparation, wet-dry cycle and shearing, including a sample preparation and shearing system, a wet-dry cycle system and a digital control system;

[0007] The sample preparation and shearing system includes a soil and rock sample box, a frame, a normal force loading platform, a normal force pressure column, and a tangential force loading device. The soil and rock sample box includes an upper shear box, a lower shear box, and constraint clamps. The soil and rock sample box is mounted on a lower compaction plate. A mass sensor is located at the bottom of the lower compaction plate and is mounted on a base. A water tank is located at the top of the soil and rock sample box. A reaction column is located on one side of the upper shear box. The lower shear box is in contact with the tangential force loading device, which contains a shear stress sensor. An upper compaction plate is located above the soil and rock sample box. A normal stress sensor is located within the upper compaction plate. The upper compaction plate is fixedly connected to the normal force pressure column, which is connected to the normal force loading platform.

[0008] The wet-dry cycle system includes a humidification device and a drying device; the humidification device includes a water tank, water pipes, a water pump, a flow meter, a water tank, and an ultrasonic transducer, with the ultrasonic transducer located on both sides of the soil and rock sample box; the drying device includes a U-shaped electric heating tube surrounding the soil and rock sample box, and a temperature sensor is installed inside the soil and rock sample box.

[0009] The digital control system includes a control platform, a mass sensor, a temperature sensor, a flow meter, a shear stress sensor, and a normal stress sensor, all of which are connected to the control platform via signal transmission.

[0010] Furthermore, the constraint clamp is matched and disposed in the groove of the upper shear box and the lower shear box, and the constraint clamp is provided with a tightening screw.

[0011] Furthermore, the ultrasonic transducer is mounted on both sides of the upper and lower shear boxes via clamps; the ultrasonic transducer includes a transducer housing, a heat sink, a backing block, an insulating rubber ring, a piezoelectric ceramic wafer, a signal connector, a wire, an annular pressure ring, and a matching layer.

[0012] Furthermore, there are four U-shaped heating tubes evenly distributed around the soil and rock sample box, and a preset distance is provided between the U-shaped heating tubes and the soil and rock sample box.

[0013] Furthermore, both the shear stress sensor and the normal stress sensor are equipped with a displacement sensor, which is an LVDT absolute displacement sensor.

[0014] Furthermore, the normal force loading platform can move up and down along the frame, the tangential force loading device can move horizontally along the frame, and the frame is provided with a scale for indicating displacement.

[0015] A direct shear test method integrating sample preparation, wet-dry cycling, and shearing, based on the above-mentioned apparatus, includes the following steps:

[0016] S1: Place the soil and rock sample box on the lower compaction plate and tighten the constraint clamps to fix the upper shear box and the lower shear box;

[0017] S2: The soil sample is placed into the soil and rock sample box in layers, and the normal force pressure column is driven down by the normal force loading platform to compact the layers and obtain the soil and rock sample.

[0018] S3: Start the humidification device. The water pump delivers water from the water tank to the water tank through the water pipe and flow meter and seeps into the soil sample. The mass sensor monitors the weight of the sample in real time. Humidification stops when the preset value is reached. The ultrasonic converter is turned on and intermittent loading mode is used to assist water penetration.

[0019] S4: After the preset resting time is reached, the U-shaped electric heating tube is started to dry the sample. The temperature sensor monitors the temperature in real time and the heating power is dynamically adjusted by the control platform. After the sample weight reaches the set value, heating is stopped and the sample cools naturally, completing one dry-wet cycle.

[0020] S5: Repeat the dry-wet cycle a preset number of times;

[0021] S6: Remove the restraint clamps, apply normal and tangential loads to the soil sample to conduct a direct shear test, and collect shear stress and normal stress data.

[0022] Furthermore, the intermittent loading mode is as follows: when the sample side length is ≥100mm or the density is high, a loading of 60s + a gap of 30s is used; when the sample side length is ≤50mm or the porosity is high, a loading of 30s + a gap of 20s is used.

[0023] Furthermore, the operating power of the ultrasonic transducer is set according to the stone content: 15~25W when the stone content is <30%; 20~30W when the stone content is 30%~70%; and 30~40W when the stone content is >70%.

[0024] Furthermore, when the ultrasonic transducer is operating, the rock sample permeability satisfies the following relationship:

[0025] (1)

[0026] In the formula, Permeability of rock sample under ultrasonic treatment; Permeability of rock samples without ultrasonic waves; For sound intensity, ; The correlation coefficient.

[0027] Compared with existing technologies, the beneficial effects of this invention are as follows: This application integrates sample preparation, wet-dry cycling, and shear testing into a single device. By using constraint clamps to position and secure the upper and lower shear boxes, sample preparation and shear testing are integrated, significantly reducing human disturbance caused by sample transfer between multiple devices, effectively reducing test errors, and improving the reliability and repeatability of test results. The wet-dry cycling control method with real-time quality monitoring allows for continuous monitoring and automatic determination of soil sample moisture content, accurately judging whether humidification and drying have met preset requirements, achieving fully automated operation of the test process, improving test accuracy, and reducing system errors. The use of low-power ultrasonic waves to generate micro-disturbances in pore fluids and micro-vibrations in soil particles effectively improves the internal pore connectivity of the soil and significantly accelerates the infiltration and drainage rates of water during the wet-dry cycling process. This invention combines high efficiency with gentle action. Compared with natural wet-dry cycles, it can improve efficiency by 20% to 30%, while avoiding damage to the sample structure caused by high-power ultrasound. It can optimize the uniformity of soil and rock pore distribution, reduce uneven shrinkage and expansion of the sample, preserve the integrity of the original soil and rock structure to the greatest extent, and ensure the authenticity and reliability of test data. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the present invention.

[0030] Figure 2 These are a side view and a cross-sectional view of the soil and rock sample box in the embodiments of the present invention; wherein, (a) is a side view and (b) is a cross-sectional view.

[0031] Figure 3 These are front view and top view schematic diagrams of the ultrasonic loading device in this embodiment of the invention; wherein, (a) is the front view schematic diagram and (b) is the top view schematic diagram.

[0032] Figure 4 This is a schematic diagram of the internal structure of the ultrasonic transducer device in an embodiment of the present invention; wherein, (a) is a top view of the internal structure and (b) is a side view of the internal structure.

[0033] Figure 5 This is a planar distribution diagram of the U-shaped heating element in an embodiment of the present invention.

[0034] In the diagram, 1. Soil and rock sample box; 2. Upper shear box; 3. Lower shear box; 4. Constraint clamp; 5. Tightening screw; 6. Ultrasonic transducer; 601. Transducer housing; 602. Heat sink; 603. Backing block; 604. Insulating rubber ring; 605. Piezoelectric ceramic wafer; 606. Signal connector; 607. Wire; 608. Annular pressure ring; 609. Matching layer; 7. Fixture; 8. Water tank; 9. Lower pressure plate; 10. Mass transfer device. 11. Sensor, 12. Frame, 13. Normal force loading platform, 14. Scale, 15. Tangential force loading device, 16. Shear stress sensor, 17. Normal force pressure column, 18. Upper compaction plate, 19. Normal stress sensor, 20. Reaction column, 21. U-shaped electric heating tube, 22. Water tank, 23. Water pipe, 24. Water pump, 25. Flow meter, 26. Temperature sensor, 27. Soil and rock sample, 28. Control platform, 29. Base. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1,

[0038] An integrated direct shear testing device for sample preparation, wet-dry cycling, and shearing, such as Figure 1 As shown, it includes a sample preparation and shearing system, a wet-dry cycle system, and a digital control system.

[0039] The sample preparation and shearing system includes a soil and rock sample box 1, a frame 11, a normal force loading platform 12, a normal force pressure column 16, and a tangential force loading device 14, used to simulate the natural density formation of soil and rock and the sliding friction process of the soil and rock mass. The soil and rock sample box includes an upper shear box 2 and a lower shear box 3, as shown below. Figure 2 (a) and Figure 2 As shown in (b), the constraint clamp 4 matches the grooves of the upper shear box 2 and the lower shear box 3. The soil sample box 1 is placed on the lower compaction plate 9. The bottom of the lower compaction plate 9 is equipped with a mass sensor 10, and the bottom of the mass sensor is placed on the base 28. A water tank 8 is installed on the top of the soil sample box 1. The right side of the upper shear box 2 is supported by the reaction column 19. The left side of the lower shear box 3 is in contact with the tangential force loading device 14. The tangential force loading device 14 can move left and right on the frame 11. The tangential force loading device 14 is equipped with a shear stress sensor 15. The top of the soil sample box 1 is in contact with the upper compaction plate 17. The upper compaction plate 17 is equipped with a normal stress sensor 18. The upper compaction plate 17 is fixed to the normal force pressure column 16. The middle section of the normal force pressure column 16 is connected to the normal force loading platform 12. The normal force loading platform 12 can move up and down on the frame 11.

[0040] Optionally, displacement sensors are also provided on the shear stress sensor 15 and the normal stress sensor 18, and the displacement sensors are all LVDT high-precision absolute displacement sensors. In the operation steps, when the tangential stress loading device and the normal stress loading device are respectively attached to the shear box, the zeroing adjustment operation of each displacement sensor needs to be performed.

[0041] In some specific embodiments, the humidification device includes a water tank 21, water pipes 22, a water pump 23, a flow meter 24, a water tank 8, and an ultrasonic transducer 6. It is used to simulate the process of increasing the moisture content of soil and rock under rainfall conditions. The water pump 23 is connected to the control platform 27 via a signal transmission line. The water pump 23 draws water from the water tank 21 through the left water pipe 22 and delivers it to the water tank 8 through the right water pipe 22. During the delivery process, the flow rate is monitored by the flow meter 24 to achieve the predetermined moisture content requirement. The water tank 8 is installed on top of the soil and rock sample box 1. Figure 3 (a) and Figure 3 As shown in (b), an ultrasonic transducer 6 is clamped on both sides of the soil and rock sample box 1. Specifically, the ultrasonic transducer 6 is installed on the front and rear sides of the upper shear box 2 and the lower shear box 3 respectively through clamps 7. In this embodiment, the ultrasonic wave can increase the permeability of the rock sample, and the increase in permeability is proportional to the ultrasonic power. However, high-power ultrasonic waves can directly lead to the development of primary cracks in the rock mass. Therefore, this embodiment adopts an intermittent ultrasonic loading method to reduce the influence of ultrasonic waves on rock mass cracks. This loading method can fully utilize the role of ultrasonic waves in accelerating seepage and improving humidification efficiency during the loading stage, and can also reduce the impact of continuous mechanical vibration on the rock mass during the intermittent stage. The disturbance of the soil sample structure balances humidification efficiency and sample structural integrity, effectively ensuring the accuracy and reliability of experimental results. Specifically, when the sample size is large (side length ≥ 100 mm) or the density is high, the loading mode of "loading for 60 s + gap for 30 s" is adopted; when the sample size is small (side length ≤ 50 mm) or the porosity is high, the loading mode of "loading for 30 s + gap for 20 s" is adopted to avoid excessive vibration. Turning on the ultrasonic transducer 6 can make water molecules vibrate rapidly and more efficiently shuttle between the rock and soil gaps, effectively accelerating the water seepage process and thus completing the humidification operation faster. The effects of different loading modes are shown in Table 1.

[0042] Table 1 Effects of different loading modes

[0043]

[0044] The structure of the ultrasonic transducer 6 is as follows Figure 4 (a) Figure 4As shown in (b), its working principle is as follows: The control platform 27 is connected to the signal terminal 606 on the outside of the ultrasonic converter 6 via a signal transmission line, inputting an electrical signal to it; the signal terminal 606 is connected to the piezoelectric ceramic wafer 605 via a wire 607, converting the input electrical signal into an acoustic signal. An insulating rubber ring 604 is wrapped around the piezoelectric ceramic wafer 605 to ensure that the electrical signal is concentrated on the wafer, ensuring the stability of the wafer's energy conversion process. The two sides of the piezoelectric ceramic wafer 605 are fixedly connected to the backing block 603 and the matching layer 609 respectively by annular pressure rings 608, which can prevent the components from shifting during vibration and ensure the integrity of the structure. The other side of the backing block 603 is tightly fitted to the converter housing 601 to absorb the clutter propagating in the reverse direction of the wafer, prevent the clutter from interfering with the forward sound wave, and ensure the purity and directionality of the ultrasonic wave. The other side of the matching layer 609 is tightly fitted to the upper shear box 2 and the lower shear box 3 to match the acoustic impedance of the air or medium, reduce the reflection loss of ultrasonic waves at the interface between the wafer and the medium, and improve the efficiency of sound wave emission. Heat dissipation slots 602 are provided on both sides of the converter housing 601 to dissipate the heat generated by the wafer during operation in a timely manner and avoid the piezoelectric performance degradation caused by high temperature.

[0045] like Figure 5 The drying device includes four evenly distributed U-shaped heating tubes 20 arranged around the soil and rock sample box 1. The U-shaped heating tubes 20 are spaced 40mm apart from the soil and rock sample box 1 to ensure uniform heat dissipation and avoid local overheating. The U-shaped heating tubes 20 are connected to the control platform 27 via signal transmission lines. The main body of the U-shaped heating tube 20 is a U-shaped tubular structure with a spiral nickel-chromium wire inside. The space between the heating wire and the tube body is densely filled with magnesium oxide powder, and the tube opening is sealed with a sealing material. The power of a single tube is typically 0.5kW-6kW, and multiple tubes can be combined to achieve higher power requirements. Inside the upper shear box 2, between the water tank 8 and the ultrasonic transducer 6, a temperature sensor 25 is installed to monitor the temperature of the soil and rock sample 26 to prevent structural damage caused by excessive temperature.

[0046] The digital control system includes a mass sensor 10, a temperature sensor 25, a flow meter 24, a shear stress sensor 15, a normal stress sensor 18, and a control platform 27. The control platform 27 integrates a data processor, display, and control panel to collect and process data from various sensors. The mass sensor 10 is a high-precision DYHW-108 model with a range of 0-100 kg. It is connected to the control platform 27 via a signal transmission line and is used to display and monitor the sample moisture content in real time, controlling whether the U-shaped heating tube is dried. The temperature sensor 25 is a platinum resistance temperature sensor with a maximum range of 800℃ and an accuracy of ±1℃. It is connected to the control platform 27 via a signal transmission line and is used to monitor the temperature of the soil sample 26, controlling whether the U-shaped heating tube is dried. The flow meter 24 is a high-precision Keyence FD-Q50 model electromagnetic flow meter with a flow rate range of 0.01~100 mL / min and an accuracy of ±0.2%. It is connected to the control platform 27 via a signal transmission line and is used to monitor the required moisture content during humidification and control whether the water pump 23 pumps water for humidification. Both the shear stress sensor 15 and the normal stress sensor 18 are connected to the control platform 27 via signal transmission lines to record test data during the shearing process.

[0047] Example 2,

[0048] A method for using an integrated direct shear testing device for sample preparation, wet-dry cycling, and shear testing is described in the following steps:

[0049] Step S1: Place the soil and rock sample box 1 on the lower compaction plate 9, and then tighten the loosening screw 5 to tighten the constraint clamp 4, which is used to align and fix the upper shear box 2 and the lower shear box 3.

[0050] Step S2: Divide the pre-prepared soil sample into five equal parts, and then place the divided soil samples into the soil and rock sample box 1. Using the control platform 27, drive the normal force loading platform 12 to press down the normal force pressure column 16 to compact the soil sample. Observe the displacement of the normal force loading platform 12 on the scale 13 on the frame 11. After ensuring that the displacement is consistent after each layer is compacted, lift the normal force loading platform 12, and then scrape the soil and rock sample 26 with a scraper. Then add the next soil sample and perform the next compaction in the same way. After layered compaction, the sample is obtained.

[0051] Step S3: After the sample preparation is completed, the normal force loading platform 12 is raised. Then, according to the predetermined moisture content, the corresponding data are set for the flow meter 24, mass sensor 10, and temperature sensor 25. The wet-dry cycle device starts to work. First, the water pump 23 draws water from the water storage tank 21 through the water pipe 22, then flows through the flow meter 24, into the water tank 8, and flows along the side wall of the upper shear box 2 to the soil sample 26. The mass sensor 10 monitors the weight of the soil sample 26 in real time. When the total weight of the soil sample 26 reaches the preset value, the control platform 27 issues a command to turn off the water pump 23 and stop humidification. Then, the ultrasonic converter 6 is turned on to make the water molecules vibrate rapidly. After vibration, the sample is left to stand for a period of time to fully absorb the moisture. The humidification process of the test adopts the natural water absorption method, which can maximize the reproduction of the wet-dry cycle process of soil in actual engineering.

[0052] Step S4: After the set set set set time, the control platform 27 sends a heating command to the U-shaped heating tube 20, which then starts working. The temperature sensor 25 monitors the temperature of the soil and rock sample box 1 in real time and feeds the temperature information back to the control platform 27. Based on the difference between the working temperature and the real-time temperature, the heating power of the U-shaped heating tube 20 is dynamically adjusted. This allows for dynamic monitoring and display of the temperature changes in the upper and lower shear boxes during the wet-dry cycle, and dynamic adjustment of the temperature of the soil and rock sample 26. When the weight of the soil and rock sample 26 reaches the set value, the mass sensor 10 sends a command to the temperature sensor 25, and the U-shaped heating tube 20 stops working. The set set time for the soil and rock sample is then allowed to cool naturally, thus completing the first cycle experiment.

[0053] Step S5: In the fourth stage of loading and drying cycle program on control platform 27, set the number of drying cycles N, and repeat steps S3~S4 to perform drying cycles N times to complete the drying cycle process.

[0054] Step S6: Press the upper pressure plate 17 down until it is in contact with the sample, loosen the tightening screw 5 to remove the constraint clamp 4, and then apply pressure to the normal force device to the preset value. Then, activate the shear stress sensor 15 to control the tangential force plate to move towards the lower shear box at a fixed rate. After the displacement of the shear box reaches the preset value, pause the shear stress sensor 15 to complete the sample shearing. Record the data during the shear failure process through the shear stress sensor 15 and the normal stress sensor 18.

[0055] In this embodiment, during the humidification and drying process of the sample, various sensors monitor relevant data of the soil sample in real time, and the instrument can automatically determine whether the humidification and drying process has met the preset requirements. This embodiment of the invention employs a drying method based on a dynamic power curve, combined with acoustic vibration to accelerate water penetration, significantly improving the wet-dry cycle efficiency of the sample. This enables the instrument to achieve fully automated control of the drying and humidification process, featuring small experimental errors and high working efficiency. The ultrasonic transducer 6, as the core device for generating ultrasonic sound signals, emits sound signals that, when propagating in water, can induce water vibration, forming periodic positive and negative pressure changes: the negative pressure phase causes water to split and form microbubbles, while the positive pressure phase compresses the bubbles until they collapse. Under the intermittent action of sound waves, bubbles generated during water penetration can be effectively removed, thereby accelerating water flow; simultaneously, when the sound signal acts on the solid-liquid interface between soil particles and water, it can weaken the adsorption of water molecules on the surface of soil particles, destroy the water film structure on the particle surface, reduce the apparent viscosity of the water, and reduce water penetration resistance, thus making it easier for water to migrate and move in the soil pores.

[0056] The permeability of rock samples increases under ultrasonic waves, and the increase is proportional to the ultrasonic power.

[0057] Relationship between ultrasonic intensity and rock sample permeability:

[0058] (1)

[0059] In the formula, Permeability of the rock sample under ultrasonic treatment. ; Permeability of rock samples without ultrasonic waves. ; For sound intensity, ; The correlation coefficient.

[0060] As shown in equation (1), when the permeability of a rock sample without ultrasonic treatment is constant, the permeability of the rock sample under ultrasonic treatment is determined by the sound intensity. If the sound intensity increases, the permeability of the rock sample under ultrasonic treatment increases. We set the following parameters: axial stress 0 MPa, pore pressure 2.0 and 3.5 MPa, temperature 20℃, and ultrasonic frequency 20 kHz. Taking a carbonaceous mudstone sample with dimensions of 150×150 mm and a compaction degree of 96% as an example, the wettability time of the sample under different ultrasonic power conditions in the actual experiment is shown in Table 2.

[0061] Table 2. Sample wetting time under different ultrasonic powers

[0062]

[0063] From the perspective of sound intensity alone, higher ultrasonic power results in a shorter average wetting time. Based on extensive experimental findings, this implementation method indicates that the ultrasonic power of the ultrasonic transducer 6 is optimally controlled between 20 and 40 W. Specifically, as shown in Table 3, when the stone content of the soil sample is less than 30%, the acoustic power can be selected as 15–25 W; when the stone content is between 30% and 70%, the acoustic power should be set to 20–30 W; and when the stone content is greater than 70%, the acoustic power should be controlled between 30 and 40 W. When the power is below the corresponding range, the permeability efficiency cannot be effectively improved; while when the power exceeds the corresponding range, the mechanical vibration generated by the ultrasonic device will directly damage the original pore structure of the soil sample, thereby altering the physical properties of the soil and ultimately adversely affecting the experimental results.

[0064] Table 3. Effects of different ultrasonic power on humidification

[0065]

[0066] This invention includes functions such as sample preparation, drying, humidification, and shearing. Traditional sample preparation, drying, and humidification are performed in multiple devices, requiring sample transfer to corresponding molds for operation, leading to problems such as sample particle loss. Integration is difficult, as it is hard to coordinate and cooperate the devices with different functions. In addition, traditional drying and humidification methods are inefficient, cause significant sample disturbance, and have high labor costs. For carbonaceous mudstone samples, performing N dry-wet cycles, if simply using immersion humidification and oven drying, requires the experimenter to weigh the sample at regular intervals to determine whether the sample has been dried or humidified, which is time-consuming and labor-intensive. The 2N times of handling and water tank immersion damage the sample structure, and even with careful operation, about 10%-15% of particles are lost. Such samples cannot yield accurate test results.

[0067] Taking a carbonaceous mudstone sample with dimensions of 150×150mm, compaction degree of 96%, and stone content of 70% as an example, we set the following parameters: wet-dry cycle temperature of 20-60℃ and wet-dry cycle number of 6. The mass loss of the soil and rock samples under different test conditions in the actual test is shown in Table 4.

[0068] Table 4. Mass loss of soil and rock samples under different test conditions

[0069]

[0070] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A direct shear test apparatus integrating sample preparation, wet-dry cycling, and shearing, characterized in that, This includes a sample preparation and shearing system, a wet-dry cycle system, and a digital control system; The sample preparation and shearing system includes a soil and rock sample box (1), a frame (11), a normal force loading platform (12), a normal force pressure column (16), and a tangential force loading device (14); the soil and rock sample box (1) includes an upper shear box (2), a lower shear box (3), and a constraint clamp (4); the soil and rock sample box (1) is set on a lower compaction plate (9); a mass sensor (10) is provided at the bottom of the lower compaction plate (9); the mass sensor (10) is set on a base (28); a water tank is provided at the top of the soil and rock sample box (1). 8) A reaction column (19) is provided on one side of the upper shear box (2), the lower shear box (3) is in contact with the tangential force loading device (14), and a shear stress sensor (15) is provided inside the tangential force loading device (14); an upper compaction plate (17) is provided above the soil and rock sample box (1), and a normal stress sensor (18) is provided inside the upper compaction plate (17). The upper compaction plate (17) is fixedly connected to the normal force pressure column (16), and the normal force pressure column (16) is connected to the normal force loading platform (12); The wet-dry cycle system includes a humidification device and a drying device; the humidification device includes a water tank (21), a water pipe (22), a water pump (23), a flow meter (24), a water tank (8), and an ultrasonic transducer (6), the ultrasonic transducer (6) being arranged on both sides of the soil and rock sample box (1); the drying device includes a U-shaped electric heating tube (20) arranged around the soil and rock sample box (1), and a temperature sensor (25) is provided inside the soil and rock sample box (1); The digital control system includes a control platform (27), a mass sensor (10), a temperature sensor (25), a flow meter (24), a shear stress sensor (15), and a normal stress sensor (18), all of which are connected to the control platform (27) via signals.

2. The integrated direct shear test apparatus for sample preparation, wet-dry cycling, and shearing according to claim 1, characterized in that, The constraint clamp (4) is matched and set in the groove of the upper shear box (2) and the lower shear box (3), and the constraint clamp (4) is provided with a tightening screw (5). 3.The device according to claim 1, wherein, The ultrasonic transducer (6) is mounted on both sides of the upper shear box (2) and the lower shear box (3) by a clamp (7); the ultrasonic transducer (6) includes a transducer housing (601), a heat sink (602), a backing block (603), an insulating rubber ring (604), a piezoelectric ceramic wafer (605), a signal connector (606), a wire (607), an annular pressure ring (608), and a matching layer (609).

4. The device according to claim 1, wherein The U-shaped heating tubes (20) are four in number and are evenly distributed around the soil and rock sample box (1). There is a preset distance between the U-shaped heating tubes (20) and the soil and rock sample box (1).

5. The device according to claim 1, wherein Both the shear stress sensor (15) and the normal stress sensor (18) are equipped with displacement sensors, and the displacement sensors are LVDT absolute displacement sensors.

6. The device according to claim 1, wherein The normal force loading platform (12) can move up and down along the frame (11), the tangential force loading device (14) can move horizontally along the frame (11), and the frame (11) is provided with a dial (13) for indicating displacement.

7. A method for sample preparation, drying-wetting cycle and shearing integrated direct shear test, realized based on the device according to any one of claims 1-6, characterized in that, Includes the following steps: S1: Place the soil and rock sample box (1) on the lower compaction plate (9) and tighten the constraint clamp (4) to fix the upper shear box (2) and the lower shear box (3). S2: The soil sample is placed into the soil and rock sample box (1) in layers, and the normal force pressure column (16) is driven down by the normal force loading platform (12) to compact the soil and rock sample (26) in layers. S3: Start the humidification device. The water pump (23) delivers the water in the water tank (21) to the water tank (8) through the water pipe (22) and flow meter (24) and seeps into the soil sample (26). The mass sensor (10) monitors the weight of the sample in real time. After reaching the preset value, the humidification stops. The ultrasonic converter (6) is turned on and the intermittent loading mode is used to assist the water penetration. S4: After the preset resting time is reached, the U-shaped electric heating tube (20) is started to dry. The temperature sensor (25) monitors the temperature in real time and the heating power is dynamically adjusted by the control platform (27). After the sample weight reaches the set value, the heating is stopped and the sample is cooled naturally to complete one dry-wet cycle. S5: Repeat the dry-wet cycle a preset number of times; S6: Remove the constraint clamp (4), apply normal and tangential loads to the soil sample (26) to conduct a direct shear test, and collect shear stress and normal stress data.

8. The method according to claim 7, wherein, The intermittent loading mode is as follows: when the sample side length is ≥100mm or the density is high, the loading is 60s + the gap is 30s; when the sample side length is ≤50mm or the porosity is high, the loading is 30s + the gap is 20s.

9. The method according to claim 7, wherein, The working power of the ultrasonic transducer (6) is set according to the stone content: 15~25W when the stone content is <30%; 20~30W when the stone content is 30%~70%; and 30~40W when the stone content is >70%.

10. The method according to claim 7, wherein, When the ultrasonic transducer (6) is working, the permeability of the rock sample satisfies the following relationship: (1) In the formula, Permeability of rock sample under ultrasonic treatment; Permeability of rock samples without ultrasonic waves; For sound intensity, ; The correlation coefficient.

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