Strong weathering red layer soft rock dry-wet cycle testing device and method for monitoring quality change

Abstract

The invention provides a strongly-weathered red layer soft rock dry-wet cycle testing device and method for monitoring quality change, and belongs to the field of rock mechanics. The test method comprises the following steps: putting a sample into a saturator, hanging the saturator in a vacuum pot, pumping the vacuum pot to a vacuum state through a suction filtration pump, pressing deionized water into the vacuum pot through atmospheric pressure, continuously performing suction filtration until the vacuum pot reaches a relatively vacuum state, and keeping the state for 12-24 hours, and meanwhile, when the state is reached, the mass sensor is used for testing, and measured data is transmitted to a computer in real time. The experimental device and method are easy and convenient to operate, economical and efficient, and can effectively solve the problem that a mechanical experiment cannot be carried out to obtain related mechanical parameters due to the fact that a sample is damaged after a strongly-weathered red layer soft rock dry-wet cycle experiment; meanwhile, the problem that the permeation water absorption capacity of the sample cannot be specifically quantified in the long-time water absorption process is solved by monitoring the quality of the sample in real time.

Description

Technical Field

[0001] This invention belongs to the field of rock mechanics, specifically relating to a dry-wet cycle testing device and method for monitoring quality changes in strongly weathered red soft rock. Background Technology

[0002] Red bed soft rock is widely distributed in my country and is often used as a load-bearing layer in engineering. However, it is highly susceptible to degradation under wet-dry cycles, exhibiting significant changes in deformation characteristics. Therefore, studying the impact of wet-dry cycles on engineering practice is of great importance. In particular, strongly weathered red bed soft rock suffers from extremely poor cementation due to intense weathering. Its mineral composition is mainly composed of quartz and clay minerals, leading to strong water-rock interaction, high water absorption, and easy disintegration in water, making it impossible to maintain a complete shape. Therefore, studying the effects of wet-dry cycles on strongly weathered red bed soft rock becomes extremely difficult.

[0003] Current research on wet-dry cycles of red bed soft rock mainly focuses on its disintegration properties and mechanisms. For example, Du Zhixiang et al. pointed out in "Disintegration and Strength Weakening Characteristics of Red Bed Soft Rock in Shengzhou-Xinchang Area under Wet-Dry Cycles" that the study of disintegration tests and related mechanisms is of certain significance for the prevention and control of red bed soft rock slopes (Du Zhixiang, Bai Dingwei, Shi Bujiong, et al. Disintegration and Strength Weakening Characteristics of Red Bed Soft Rock in Shengzhou-Xinchang Area under Wet-Dry Cycles [J]. Geological Science and Technology Bulletin, 2024, 43(1): 253-261.). However, there is not much research on the mechanical properties of intact, strongly weathered red bed soft rock samples. The main reason is that it is impossible to ensure the integrity of the strongly weathered red bed soft rock samples during the wet-dry cycle process, which is convenient for subsequent mechanical testing.

[0004] Currently, the main method for wet-dry cycling of rocks with a low degree of weathering is the three-dimensional immersion method. For example, in Dr. Huang Kai's doctoral dissertation at Hefei University of Technology, "Study on the Deterioration Characteristics and Damage Mechanism of Red Bed Soft Rock under Wet-Dry Cycling," the wet-dry cycling method for red bed soft rock with a low degree of weathering is the three-dimensional immersion method (see Huang Kai. Study on the Deterioration Characteristics and Damage Mechanism of Red Bed Soft Rock under Wet-Dry Cycling [D]. Hefei University of Technology, 2022.). This involves placing the intact rock sample on a permeable stone and completely immersing it in water to complete the wet-dry cycle. However, for red bed soft rock with a high degree of weathering, completely immersing the rock sample in water will cause it to disintegrate, losing its intact shape and making subsequent mechanical testing impossible.

[0005] For wet-dry cycles of soils with physical morphology very similar to strongly weathered red bed soft rock, the permeation absorption method is mainly adopted. For example, the experimental method used by Zhou Ziwei in "Intensity Characteristics of Wet-Dry Cycles of Weakly Expansive Soil in Hefei and Deformation Analysis of Deep Foundation Pit Excavation" was used to study the wet-dry cycle of weakly expansive soil in Hefei (see Zhou Ziwei. Intensity Characteristics of Wet-Dry Cycles of Weakly Expansive Soil in Hefei and Deformation Analysis of Deep Foundation Pit Excavation [D]. Xiangtan University, 2024. DOI: 10.27426 / d.cnki.gxtdu.2024.001098.). That is, permeable stone, filter paper and sample are placed in a container in sequence, and water is added to be level with the permeable stone. As the cycle proceeds, water is continuously added to maintain the liquid level, and the wet-dry cycle is completed by the permeation absorption capacity of the sample itself. However, for cylindrical samples of strongly weathered red soft rock, the strong water-rock interaction causes the bottom of the sample to expand violently after water absorption. At the same time, due to the high height of the sample, the long permeation path prevents water from reaching the top, resulting in uneven water distribution between the upper and lower parts, which has a significant impact on the wet-dry cycle effect of the sample.

[0006] The two main wet-dry cycling methods described above cannot guarantee the integrity of the specimen after the wet-dry cycling process, making it impossible to perform relevant mechanical property tests on the specimen. Therefore, a wet-dry cycling method that can guarantee the integrity of the specimen to facilitate subsequent mechanical experiments is needed.

[0007] Meanwhile, during a complete wet-dry cycle, the red bed soft rock will generate seepage channels inside the sample due to the action of water and rock, which will change the water absorption of the sample and further change the mass change pattern of the sample. Therefore, monitoring the mass change of the sample during the wet-dry cycle helps to further reveal the internal change pattern of the red bed soft rock during the wet-dry cycle. Summary of the Invention

[0008] The technical problem this invention aims to solve is one existing problem in the prior art. Specifically, this invention uses a saturator to ensure the stability of the overall morphology of the red bed soft rock sample after wet-dry cycles, with the aim of ensuring the conduct of subsequent related mechanical tests. Simultaneously, a mass sensor connected to the sample monitors the mass change of the sample in real time. The purpose of this is to better understand the deterioration process and changes in the mechanical properties of strongly weathered red bed soft rock under the influence of water by analyzing the mass changes of the sample during wet-dry cycles.

[0009] To achieve the above objectives, the present invention proposes to adopt the following technical solution.

[0010] A wet-dry cycle testing device for monitoring quality changes in strongly weathered red bed soft rock includes an experimental apparatus, a data recording device, and a columnar sample of red bed soft rock. The experimental apparatus includes a filtration pump, a water reservoir, a vacuum pot, and a saturator suspended inside the vacuum pot. The top plate of the vacuum pot is equipped with a water injection valve, an air extraction valve, a mass sensor, and a pressure gauge that communicate with the interior of the vacuum pot. The water injection valve is connected to the water reservoir containing deionized water through a water injection pipe, and the air extraction valve is connected to the filtration pump through an air extraction pipe. The mass sensor suspends the saturator in the vacuum pot through a connecting wire.

[0011] The main body of the saturator is a hollow cylinder. A columnar sample of red soft rock, which is adapted to the internal shape of the hollow cylinder, is installed in the cavity of the hollow cylinder. The upper and lower end faces of the red soft rock columnar sample are flush with the upper and lower end faces of the hollow cylinder. Two permeable stones are fixed on the upper and lower end faces of the hollow cylinder, respectively, and combined with the hollow cylinder to form a closed permeation chamber in the saturator. That is, the deionized water in the saturator can only seep into the red soft rock columnar sample through the permeable stones.

[0012] The data recording device includes a computer, a mass sensor, and a data transmission line; the lower end of the mass sensor is connected to a saturator via a connecting line to monitor the mass of the saturator, and the upper end is connected to the computer via a data transmission line to transmit the mass data recorded by the mass sensor to the computer for recording and storage.

[0013] Preferably, the diameter of the permeable stone is larger than the outer diameter of the hollow cylinder; the hollow cylinder is composed of three arc plates with a central angle of 120 degrees, and after the three arc plates are combined to form a hollow cylinder, a stainless steel ring hoop is used to fix the outer side of the waist of the hollow cylinder; the saturator also includes two annular cover plates and n tie rods, the diameter of the hollow part of the cover plate is equal to the inner diameter of the hollow cylinder, n internal threaded holes are evenly distributed on the cover plate, and corresponding external threads are opened at both ends of the tie rods;

[0014] During the process, a hollow cylinder is first constructed on the outside of a columnar sample of red soft rock using three arc-shaped pieces and a ring hoop. Then, a permeable stone is placed on the upper and lower ends of the hollow cylinder, with the diameter of the permeable stone being larger than the outer diameter of the hollow cylinder and concentric with it. Two cover plates are placed on the upper and lower parts of the two permeable stones, respectively, and kept concentric. The two permeable stones are then fixed between the cover plates and the hollow cylinder by screwing a tie rod to the cover plates, forming a closed permeation chamber.

[0015] Preferably, filter paper is placed between the permeable stone and the columnar sample of red bed soft rock.

[0016] Preferably, the columnar sample of red bed soft rock is prepared by layering and compacting granular, strongly weathered red bed soft rock soil.

[0017] This invention also provides a method for monitoring quality changes in strongly weathered red bed soft rock through wet-dry cycle testing, comprising the following steps:

[0018] Step 1: Vacuum saturation of columnar samples from red bed soft rock

[0019] The prepared red bed soft rock columnar sample was placed in the hollow cylinder of the saturator, with both ends connected to the outside through filter paper and permeable stone;

[0020] Connect the saturator to the mass sensor using a connecting cable;

[0021] Close the vacuum pot and the water inlet valve; open the air extraction valve and the vacuum pump to extract air, and observe the pressure gauge. When the pressure gauge reaches the specified reading, the vacuum pot is vacuumed.

[0022] After the vacuum pot reaches a vacuum, close the suction valve and open the water injection valve to allow deionized water to enter the vacuum pot under air pressure. After the liquid level has submerged the saturator, close the water injection valve.

[0023] Turn on the vacuum pump and the vacuum valve, and continue to pump air until the pressure gauge reading reaches the range of -100kPa to 0kPa. Confirm that the vacuum pot is in a vacuum saturated state, then turn off the vacuum valve and the vacuum pump to enter the permeation period.

[0024] Step 2: Quality monitoring of red bed soft rock columnar samples during vacuum saturation and permeation periods.

[0025] After the liquid level in step 1 has submerged the saturator, the water injection valve is closed. At the same time, the reading of the mass sensor is zeroed, and its mass reading is transmitted to the computer in real time via the data transmission line. The corresponding real-time mass change curve is automatically generated until the end of the permeation period.

[0026] Step 3: Drying of columnar samples of red bed soft rock

[0027] After the infiltration period ends, the columnar sample of red soft rock is removed from the saturator and its specific dimensions and mass are measured; then it is placed in a desiccator to dry for 12 to 24 hours, and its specific dimensions and mass are measured again to complete one wet-dry cycle.

[0028] Preferably, the infiltration period is 12 to 24 hours.

[0029] Compared with the prior art, the beneficial effects of the present invention include:

[0030] 1. This invention designs a wet-dry cycle device for strongly weathered red bed soft rock, which completes the wet-dry cycle of the strongly weathered red bed soft rock sample by using a saturator, a permeable stone and a filter paper to form a permeation chamber through which only water passes, thus maintaining the morphology of the sample.

[0031] 2. This device uses mass sensors and a computer to automatically monitor the quality of samples during the wet-dry cycle, allowing real-time observation of the saturation level of the sample at different times, resulting in a high degree of automation.

[0032] 3. This device can be adapted to different sizes of samples in strongly weathered rock and soil by adjusting the size of the saturator and permeable stone. The equipment is reusable, easy to operate, and has a wide range of applications. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the overall testing device of the present invention.

[0034] Figure 2 This is a schematic diagram of the saturator's structure.

[0035] Figure 3 This is a schematic diagram of the cross-section of the saturator.

[0036] Reference numerals: 1. Filter pump, 2. Computer, 3. Data transmission line, 5. Saturator, 6. Vacuum pot, 7. Columnar sample of red soft rock, 8. Vacuum valve, 9. Mass sensor, 10. Pressure gauge, 11. Deionized water, 12. Water injection valve, 13. Permeable stone, 14. Water reservoir, 15. Cover plate, 16. Tie rod, 17. Annular hoop, 18. Arc plate. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0038] Figure 1 This is a general schematic diagram of the testing device of the present invention. Figure 2 This is a schematic diagram of the saturator's structure. Figure 3 This is a schematic diagram of the cross-section of the saturator. Figures 1-3 As can be seen, the present invention provides a wet-dry cycle testing device for monitoring quality changes in strongly weathered red bed soft rock, including an experimental device, a data recording device, and a columnar sample 7 of red bed soft rock; the experimental device includes a filtration pump 1, a water reservoir 14, a vacuum pot 6, and a saturator 5 suspended inside the vacuum pot 6; the top plate of the vacuum pot 6 is equipped with a water injection valve 12, an air extraction valve 8, a mass sensor 9, and a pressure gauge 10 that communicate with the interior of the vacuum pot 6; the water injection valve 12 is connected to the water reservoir 14 containing deionized water 11 through a water injection pipe; the air extraction valve 8 is connected to the filtration pump 1 through an air extraction pipe; and the mass sensor 9 suspends the saturator 5 in the vacuum pot 6 through a connecting wire.

[0039] The main body of the saturator 5 is a hollow cylinder. A columnar sample 7 of red soft rock, which is adapted to the internal shape of the hollow cylinder, is installed in the cavity of the hollow cylinder. The upper and lower end faces of the columnar sample 7 of red soft rock are flush with the upper and lower end faces of the hollow cylinder. Two permeable stones 13 are fixed on the upper and lower end faces of the hollow cylinder, respectively, and combined with the hollow cylinder to form a closed permeation chamber in the saturator 5. That is, the deionized water in the saturator 5 can only permeate into the columnar sample 7 of red soft rock through the permeable stones 13.

[0040] The data recording device includes a computer 2, a mass sensor 9, and a data transmission line 3. The lower end of the mass sensor 9 is connected to the saturator 5 via a connecting line to monitor the mass of the saturator, and the upper end is connected to the computer 2 via the data transmission line 3 to transmit the mass data recorded by the mass sensor 9 to the computer 2 for recording and storage.

[0041] In this embodiment, the diameter of the permeable stone 13 is larger than the outer diameter of the hollow cylinder; the hollow cylinder is composed of three arc plates 18 with an arc center angle of 120 degrees, and after the three arc plates 18 are combined to form a hollow cylinder, a stainless steel ring hoop 17 is used to fix the outer side of the waist of the hollow cylinder; the saturator 5 also includes two annular cover plates 15 and n pull rods 16. The diameter of the hollow part of the cover plate 15 is equal to the inner diameter of the hollow cylinder, and n internal threaded holes are evenly distributed on the cover plate 15, and corresponding external threads are opened at both ends of the pull rods 16.

[0042] During operation, a hollow cylinder is first constructed by combining three arc-shaped pieces 18 and annular hoops 17 on the outside of the red soft rock columnar sample 7. Then, a permeable stone 13 is placed on the upper and lower end faces of the hollow cylinder, respectively. The diameter of the permeable stone 13 is larger than the outer diameter of the hollow cylinder and is concentric with the hollow cylinder. Two cover plates 15 are placed on the upper and lower parts of the two permeable stones 13, respectively, and kept concentric. Then, the two permeable stones 13 are fixed between the cover plates 15 and the hollow cylinder by screwing the pull rod 16 to the two cover plates 15, forming a closed permeation chamber.

[0043] In this embodiment, the red bed soft rock columnar sample 7 was prepared by layering and compacting granular, strongly weathered red bed soft rock soil.

[0044] This invention also provides a method for monitoring quality changes in strongly weathered red bed soft rock through wet-dry cycle testing, comprising the following steps:

[0045] Step 1: Vacuum saturation of columnar sample 7 of red bed soft rock

[0046] The prepared red bed soft rock columnar sample 7 is placed in the hollow cylinder of the saturator 5, and both ends are connected to the outside through filter paper 16 and permeable stone 13;

[0047] The saturator 5 is connected to the mass sensor 9 via a connecting cable;

[0048] Close the vacuum pot 6 and the water injection valve 12; open the air extraction valve 8 and the air extraction pump 1 to extract air, and observe the pressure gauge 10. When it reaches the specified reading, the vacuum pot 6 will be in a vacuum.

[0049] After the vacuum pot 6 reaches a vacuum, close the suction valve 8 and open the water injection valve 12 to allow deionized water 11 to enter the vacuum pot 6 under air pressure. After the liquid level has submerged the saturator 5, close the water injection valve 12.

[0050] Turn on the vacuum pump 1 and the vacuum valve 8, and continue to pump air until the reading of the pressure gauge 10 reaches the range of -100kPa to 0kPa. Confirm that the vacuum pot 6 is in a vacuum saturated state, close the vacuum valve 8 and the vacuum pump 1, and enter the permeation period.

[0051] In this embodiment, when the reading of pressure gauge 10 reaches the range of -50 kPa, it is confirmed that the vacuum pot 6 is in a vacuum saturation state.

[0052] Step 2: Quality monitoring of columnar red rock sample 7 during vacuum saturation and permeation periods.

[0053] After the liquid level in step 1 has submerged the saturator 5, the water injection valve 12 is closed. At the same time, the reading of the mass sensor 9 is zeroed, and its mass reading is transmitted to the computer 2 in real time through the data transmission line 3. The corresponding real-time mass change curve is automatically generated until the end of the permeation period.

[0054] Step 3, Drying of columnar sample 7 of red bed soft rock

[0055] After the infiltration period ends, the columnar sample 7 of the red soft rock is taken out from the saturator 5 and its specific size and mass are measured; then it is placed in a desiccator to dry for 12 to 24 hours, and its specific size and mass are measured again to complete one wet-dry cycle.

[0056] The infiltration period is 12 to 24 hours. In practice, the infiltration period is 18 hours.

Claims

1. A wet-dry cycle testing device for monitoring quality changes in strongly weathered red bed soft rock, characterized in that, The experimental setup includes an experimental apparatus, a data recording device, and a columnar sample (7) of red bed soft rock. The experimental apparatus includes a filtration pump (1), a water reservoir (14), a vacuum pot (6), and a saturator (5) suspended inside the vacuum pot (6). The top plate of the vacuum pot (6) is equipped with a water injection valve (12), an air extraction valve (8), a mass sensor (9), and a pressure gauge (10) that are connected to the inside of the vacuum pot (6). The water injection valve (12) is connected to the water reservoir (14) containing deionized water (11) through a water injection pipe. The air extraction valve (8) is connected to the filtration pump (1) through an air extraction pipe. The mass sensor (9) suspends the saturator (5) in the vacuum pot (6) through a connecting wire. The main body of the saturator (5) is a hollow cylinder. A red soft rock columnar sample (7) that matches the internal shape of the hollow cylinder is installed in the cavity of the hollow cylinder. The upper and lower end faces of the red soft rock columnar sample (7) are flush with the upper and lower end faces of the hollow cylinder. Two permeable stones (13) are fixed on the upper and lower end faces of the hollow cylinder respectively and combined with the hollow cylinder to form a closed permeation chamber in the saturator (5). That is, the deionized water in the saturator (5) can only permeate into the red soft rock columnar sample (7) through the permeable stones (13). The data recording device includes a computer (2), a mass sensor (9), and a data transmission line (3); the lower end of the mass sensor (9) is connected to the saturator (5) via a connecting line to monitor the mass of the saturator, and the upper end is connected to the computer (2) via the data transmission line (3) to transmit the mass data recorded by the mass sensor (9) to the computer (2) for recording and storage.

2. The wet-dry cycle testing device for monitoring quality changes in strongly weathered red bed soft rock according to claim 1, characterized in that, The diameter of the permeable stone (13) is larger than the outer diameter of the hollow cylinder; the hollow cylinder is composed of three arc plates (18) with an arc center angle of 120 degrees, and after the three arc plates (18) are combined into a hollow cylinder, a stainless steel ring hoop (17) is used to fix the outer side of the waist of the hollow cylinder; the saturator (5) also includes two annular cover plates (15) and n pull rods (16). The diameter of the hollow part of the cover plate (15) is equal to the inner diameter of the hollow cylinder. There are n internal threaded holes evenly distributed on the cover plate (15), and corresponding external threads are opened at both ends of the pull rods (16); During operation, a hollow cylinder is first constructed by combining three arc plates (18) and annular hoops (17) on the outside of the red soft rock columnar sample (7). Then, a permeable stone (13) is placed on the upper and lower end faces of the hollow cylinder. The diameter of the permeable stone (13) is larger than the outer diameter of the hollow cylinder and is concentric with the hollow cylinder. Two cover plates (15) are placed on the upper and lower parts of the two permeable stones (13) respectively and kept concentric. Then, the two permeable stones (13) are fixed between the cover plates (15) and the hollow cylinder by screwing the pull rod (16) to the two cover plates (15) to form a closed permeation chamber.

3. The wet-dry cycle testing device for monitoring quality changes in strongly weathered red bed soft rock according to claim 1, characterized in that, The columnar sample (7) of the red bed soft rock was prepared by layering and compacting granular, strongly weathered red bed soft rock soil.

4. A method for monitoring quality changes in strongly weathered red bed soft rock through wet-dry cycle testing, employing the wet-dry cycle testing device for monitoring quality changes in strongly weathered red bed soft rock as described in any one of claims 1-4, characterized in that... Includes the following steps: Step 1, vacuum saturation of the red bed soft rock columnar sample (7) The prepared red bed soft rock columnar sample (7) is placed in the hollow cylinder of the saturator (5), and both ends are connected to the outside through the permeable stone (13); The saturator (5) is connected to the mass sensor (9) by a connecting wire; Close the vacuum pot (6) and the water injection valve (12); open the air extraction valve (8), turn on the vacuum pump (1) to extract air, and observe the pressure gauge (10). When it reaches the specified reading, the vacuum pot (6) will be in a vacuum. After the vacuum pot (6) reaches a vacuum, close the suction valve (8) and open the water injection valve (12) to allow deionized water (11) to enter the vacuum pot (6) under air pressure. After the liquid level has submerged the saturator (5), close the water injection valve (12). Turn on the vacuum pump (1) and the vacuum valve (8) again, and continue to pump air until the reading of the pressure gauge (10) reaches the range of -100kPa to 0kPa. Confirm that the vacuum pot (6) is in a vacuum saturated state, close the vacuum valve (8) and the vacuum pump (1), and enter the permeation period. Step 2, Quality monitoring of columnar samples (7) of red bed soft rock during vacuum saturation and permeation periods. After the liquid level in step 1 has submerged the saturator (5), the water injection valve (12) is closed. At the same time, the reading of the mass sensor (9) is zeroed, and its mass reading is transmitted to the computer (2) in real time through the data transmission line (3). The corresponding real-time mass change curve is automatically generated until the end of the permeation period. Step 3, drying of the red bed soft rock columnar sample (7) After the infiltration period ends, the columnar sample (7) of red soft rock is taken out from the saturator (5) and its specific size and mass are measured; then it is placed in the desiccator to dry for 12 to 24 hours, and its specific size and mass are measured again to complete one wet-dry cycle.

5. A method for monitoring quality changes in strongly weathered red bed soft rock through wet-dry cycle testing according to claim 5, characterized in that, The infiltration period is 12 to 24 hours.

Images